thiourea and clobenpropit

Topics: Corpus Striatum; Histamine; Humans; Imidazoles; Neuroprotective Agents; Parkinson Disease; Receptors, Histamine H4; Thiourea

Histamine is one of the most versatile biogenic amines targeting a variety of cells through extra- and intracellular binding sites and specific receptors, which trigger different signal transduction pathways. It has been associated with cell growth ever since G. Kahlson demonstrated that its synthesis was increased in rapidly growing tissues of plants and animals. He proposed that the newly formed amine, as opposed to its stored counterpart, might play a major role in growth processes. Later on, a number of investigators provided evidence for the contribution of histamine to the expansion of normal and malignant cells, whether of hematopoietic origin or not. These studies have generated conflicting results, revealing growth-promoting as well as inhibitory effects, most likely because the final outcome of exposure to histamine depends on the signaling pathways triggered by distinct receptors and their differential distribution among the target population. The purpose of the present review is to outline our current understanding of the regulatory functions of histamine during growth and differentiation of hematopoietic progenitors, focusing on those mediated through its H4 receptor.

Topics: Animals; Cell Cycle; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cyclin-Dependent Kinase Inhibitor p21; Hematopoiesis; Hematopoietic Stem Cells; Histamine; Humans; Imidazoles; Mice; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Signal Transduction; Thiourea

This review addresses strategies for the generation of ligands for G-protein-coupled receptors outside classical high-throughput screening and literature based approaches. These range from the chemical intuition-based strategies of endogenous ligand elaboration and privileged structure decoration to the in silico approaches of virtual screening and de novo design. Examples are cited where supporting pharmacological data has been presented.

Topics: Combinatorial Chemistry Techniques; Computational Biology; Databases, Factual; Drug Design; Imidazoles; Ligands; Molecular Structure; Piperidines; Receptors, G-Protein-Coupled; Receptors, Histamine H3; Thiourea

Alzheimer's disease (AD) is one of the leading causes for disability and death affecting millions of people worldwide. Thus, novel therapeutic strategies are needed to reduce brain pathology associated with AD. In view of increasing awareness regarding involvement of histaminergic pathways in AD, we explored the role of one H3 receptor inverse agonist BF 2649 and one selective H3 receptor antagonist with partial H4 agonist activity in amyloid beta peptide (AβP) infusion-induced brain pathology in a rat model. AD-like pathology was produced by administering AβP (1-40) intracerebroventricular (i.c.v.) in the left lateral ventricle (250 ng/10 μl, once daily) for 4 weeks. Control rats received saline. In separate group of rats, either BF 2649 (1 mg/kg, i.p.) or clobenpropit (1 mg/kg, i.p.) was administered once daily for 1 week after 3 weeks of AβP administration. After 30 days, blood-brain barrier (BBB) breakdown, edema formation, neuronal, glial injuries, and AβP deposits were examined in the brain. A significant reduction in AβP deposits along with marked reduction in neuronal or glial reactions was seen in the drug-treated group. The BBB breakdown to Evans blue albumin and radioiodine in the cortex, hippocampus, hypothalamus, and cerebellum was also significantly reduced in these drug-treated groups. Clobenpropit showed superior effects than the BF2649 in reducing brain pathology in AD. Taken together, our observations are the first to show that blockade of H3 and stimulation of H4 receptors are beneficial for the treatment of AD pathology, not reported earlier.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Brain; Drug Inverse Agonism; Drug Partial Agonism; Histamine Agonists; Histamine H3 Antagonists; Imidazoles; Male; Rats; Rats, Sprague-Dawley; Receptors, Histamine H4; Thiourea

Leydig-cell tumours (LCTs) are rare endocrine tumours of the testicular interstitium, with recent increased incidence. Symptoms include precocious puberty in children; and erectile dysfunction, infertility and/or gynaecomastia, in adults. So far, scientific evidence points to aromatase (CYP19) overexpression and excessive oestrogen and insulin-like growth factor (IGF) -1 production as responsible for Leydig-cell tumourigenesis. LCTs are usually benign; however, malignant LCTs respond poorly to chemo/radiotherapy, highlighting the need to identify novel targets for treatment. Herein, we investigated the potential role of the histamine receptor H4 (HRH4) as a therapeutic target for LCTs using R2C rat Leydig tumour cells, a well-documented in vitro model for Leydigioma. Also, we studied for the first time the expression of CYP19, IGF-1R, oestrogen receptor (ER) α, ERβ, androgen receptor (AR) and HRH4 in human prepubertal LCTs versus normal prepubertal testes (NPTs). HRH4 agonist treatment inhibited steroidogenesis and proliferation in R2C cells and also negatively affected their pro-angiogenic capacity in vitro and in vivo, as assessed by evaluating the proliferative activity of human umbilical vein endothelial cells and by means of the quail chorioallantoic membrane assay, respectively. Moreover, E2 and IGF-1 inhibited HRH4 mRNA and protein levels. In human prepubertal LCTs, CYP19, IGF-1R, ERα and ERβ were overexpressed compared with NPTs. In contrast, HRH4 staining was weak in LCTs, but moderate/strong and confined to the interstitium in NPTs. Importantly, HRH4 was absent or barely detectable in seminiferous tubules or germ cells. Overall, our results point to HRH4 as a novel therapeutic target in LCTs.

Topics: Age Factors; Angiogenesis Inhibitors; Animals; Antineoplastic Agents; Aromatase; Cell Line, Tumor; Cell Proliferation; Coturnix; Estrogen Receptor alpha; Estrogen Receptor beta; Guanidines; Histamine Agonists; Human Umbilical Vein Endothelial Cells; Humans; Imidazoles; Infant; Leydig Cell Tumor; Male; Molecular Targeted Therapy; Neovascularization, Pathologic; Rats; Receptor, IGF Type 1; Receptors, Androgen; Receptors, Histamine H4; Receptors, Somatomedin; Signal Transduction; Steroid Synthesis Inhibitors; Testicular Neoplasms; Thiourea

Activation of the histamine-3 receptor (H3R) is involved in memory processes and cognitive action, while blocking H3R activation can slow the progression of neurological disorders, such as Alzheimer's disease, schizophrenia and narcolepsy. To date, however, no direct way to examine the activation of H3R has been utilized. Here, we describe a novel biosensor that can visualize the activation of H3R through an intramolecular fluorescence resonance energy transfer (FRET) signal. To achieve this, we constructed an intramolecular H3R FRET sensor with cyan fluorescent protein (CFP) attached at the C terminus and yellow fluorescent protein (YFP) inserted into the third intracellular loop. The sensor was found to internalize normally on agonist treatment. We measured FRET signals between the donor CFP and the acceptor YFP in living cells in real time, the results of which indicated that H3R agonist treatment (imetit or histamine) increases the FRET signal in a time- and concentration-dependent manner with Kon and Koff values consistent with published data and which maybe correlated with decreasing cAMP levels and the promotion of ERK1/2 phosphorylation. The FRET signal was inhibited by H3R antagonists, and the introduction of mutations at F419A, F423A, L426A and L427A, once again, the promotion of ERK1/2 phosphorylation, was diminished. Thus, we have built a H3R biosensor which can visualize the activation of receptor through real-time structure changes and which can obtain pharmacological kinetic data at the same time. The FRET signals may allow the sensor to become a useful tool for screening compounds and optimizing useful ligands.

Topics: Bacterial Proteins; Biosensing Techniques; Cyclic AMP; Fluorescence Resonance Energy Transfer; Gene Expression; Green Fluorescent Proteins; HEK293 Cells; Histamine; Histamine Agonists; Histamine H3 Antagonists; Humans; Imidazoles; Kinetics; Luminescent Proteins; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Phosphorylation; Plasmids; Receptors, Histamine H3; Thiourea; Transfection; Tritium

Hemorrhagic shock has a potential to be life-threatening when it is not treated. The main causes of hemorrhagic shock involve: (1) forces causing injury; and (2) diseases that can cause hemorrhage., Therefore, due to the causes of hemorrhagic shock and the life-threatening potential, the search for new methods of shock treatment is extremely valuable to the modern medicine. The aim of this study was to investigate the influence of clobenpropit in the model of hemorrhagic shock. The experiments were conducted in 110 adult male Wistar rats weighing between 205 and 470g. 1, 2 and 5 μmol/kg of intravenous H3 receptors reverse agonists, clobentropit, and/or 1, 5 and 10 μmol/kg H3 receptor agonist, imetit, were used as general anesthetics. Irreversible hemorrhagic shock was induced by the paused bleeding until the mean arterial pressure (MAP) lowered to the level of 20-25 mmHg. It was proved that, in cases of critical hypotension, clobenpropit triggered a dose-dependent increase of: systolic blood pressure (SBP), diastolic blood pressure (DBP), MPA and heart rate (HR) of rats with critical hypotension. The most significant changes in hemodynamic parameters were achieved by administrating dosages of 2 mmol/kg. This resulted in the survival rate increase to up to 100%. However, imetit did not trigger any hemodynamic changes nor an increase in SBP, DBP, MAP or HR. Furthermore, it was found that the premedication with prazosin, yohimbine, 6-hydroxydopamine and the vasopressin V1a receptor antagonist blocked the effects of clobenpropit. Additionally, premedication with propranolol, captopril and ZD 7155 did not cause any significant changes in the measured hemodynamic parameters. In conclusion, after an intravenous injection clobenpropit, the inverse agonist of H3 histamine receptors/agonist of histamine receptors H4, causes a resuscitating effect on rats in hemorrhagic shock. Moreover, such effect is based on the effector mechanisms of sympathetic nervous system and vasopressin.

Topics: Animals; Blood Pressure; Dose-Response Relationship, Drug; Histamine Agonists; Imidazoles; Male; Rats; Rats, Wistar; Receptors, Histamine H3; Receptors, Histamine H4; Shock, Hemorrhagic; Thiourea

The aim of the study was to explore whether histamine H3 receptor antagonist Clobenpropit could protect propofol-induced neurotoxicity in hippocampal neurons.. Hippocampal neurons were extracted from neonatal rats and induced with propofol. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was performed to detect apoptotic rate of neurons. Western blot was conducted to detect protein levels of cleaved-caspase-3 and Bax/Bcl2. After LY294002 treatment, the PI3K pathway antagonist was applied in neurons, protein levels of cleaved-caspase-3 and Bax/Bcl2 were detected by Western blot as well.. Propofol treatment remarkably induced neuronal apoptosis. Clobenpropit alleviated cell apoptosis induced by propofol. Protein expressions of cleaved-caspase-3 and Bax/Bcl2 were remarkably downregulated in neurons treated with Clobenpropit. LY294002 induction remarkably reverses the protective role of Clobenpropit in neuronal apoptosis, manifesting as downregulated PI3K and p-AKT after LY294002 treatment.. Clobenpropit protects propofol-induced neuronal apoptosis through activating PI3K/AKT pathway.

Topics: Animals; Animals, Newborn; Apoptosis; Dose-Response Relationship, Drug; Hippocampus; Histamine H3 Antagonists; Hypnotics and Sedatives; Imidazoles; Neurons; Phosphatidylinositol 3-Kinases; Propofol; Proto-Oncogene Proteins c-akt; Rats; Signal Transduction; Thiourea

Plasmacytoid dendritic cells (pDC) are specialized in secretion of type I interferon in response to pathogens. Here we show that natural monoamines and synthetic amines inhibit pDC activation by RNA viruses. Furthermore, a synthetic analogue of histamine reduces type I interferon production in a mouse model of influenza infection. We identify CXC chemokine receptor 4 (CXCR4) as a receptor used by amines to inhibit pDC. Our study establishes a functional link between natural amines and the innate immune system and identifies CXCR4 as a potential 'on-off' switch of pDC activity with therapeutic potential.

Topics: Amines; Ammonium Compounds; Animals; Dendritic Cells; Histamine; HIV; Humans; Imidazoles; Interferon Type I; Mice; Orthomyxoviridae; Receptors, CXCR4; Receptors, Histamine; Thiourea; TNF-Related Apoptosis-Inducing Ligand

Animal models based on N-methyl-d-aspartate receptor blockade have been extensively used for schizophrenia. Ketamine and MK-801 produce behaviors related to schizophrenia and exacerbated symptoms in patients with schizophrenia, which led to the use of PCP (phencyclidine)- and MK-801 (dizocilpine)-treated animals as models for schizophrenia.. The study investigated the effect of subchronic dosing (once daily, 7 days) of histamine H3 receptor (H3R) antagonists, ciproxifan (CPX) (3 mg/kg, i.p.), and clobenpropit (CBP) (15 mg/kg, i.p.) on MK-801 (0.2 mg/kg, i.p.)-induced locomotor activity and also measured dopamine and histamine levels in rat's brain homogenates. The study also included clozapine (CLZ) (3.0 mg/kg, i.p.) and chlorpromazine (CPZ) (3.0 mg/kg, i.p.), the atypical and typical antipsychotic, respectively.. Atypical and typical antipsychotic was used to serve as clinically relevant reference agents to compare the effects of the H3R antagonists. MK-801 significantly increased horizontal locomotor activity, which was reduced with CPX and CBP. MK-801-induced locomotor hyperactivity attenuated by CPX and CBP was comparable to CLZ and CPZ. MK-801 raised striatal dopamine level, which was reduced in rats pretreated with CPX and CBP. CPZ also significantly lowered striatal dopamine levels, although the decrease was less robust compared to CLZ, CPX, and CBP. MK-801 increased histamine content although to a lesser degree. Subchronic treatment with CPX and CBP exhibited further increased histamine levels in the hypothalamus compared to MK-801 treatment alone. Histamine H3 receptor agonist, R-α methylhistamine (10 mg/kg, i.p.), counteracted the effect of CPX and CBP.. The present study shows the positive effects of CPX and CBP on MK-801-induced schizophrenia-like behaviors in rodents.

Topics: Animals; Antipsychotic Agents; Behavior, Animal; Disease Models, Animal; Dizocilpine Maleate; Histamine; Histamine H3 Antagonists; Imidazoles; Methylhistamines; Motor Activity; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Schizophrenia; Thiourea

Histamine is a modulatory neurotransmitter regulating neuronal activity. Antidepressant drugs target modulatory neurotransmitters, thus ultimately regulating glutamatergic transmission and plasticity. Histamine H3 receptor (H3R) antagonists have both pro-cognitive and antidepressant effects; however, the mechanism by which they modulate glutamate transmission is not clear. We measured the effects of the H3R antagonist clobenpropit in the Flinders Sensitive Line (FSL), a rat model of depression with impaired memory and altered glutamatergic transmission.. Behavioral tests included the forced swim test, memory tasks (passive avoidance, novel object recognition tests), and anxiety-related paradigms (novelty suppressed feeding, social interaction, light/dark box tests). Hippocampal protein levels were detected by Western blot. Hippocampal plasticity was studied by in slice field recording of CA3-CA1 long-term synaptic potentiation (LTP), and glutamatergic transmission by whole-cell patch clamp recording of excitatory postsynaptic currents (EPSCs) in CA1 pyramidal neurons.. Clobenpropit, administered systemically or directly into the hippocampus, decreased immobility during the forced swim test; systemic injections reversed memory deficits and increased hippocampal GluN2A protein levels. FSL rats displayed anxiety-related behaviors not affected by clobenpropit treatment. Clobenpropit enhanced hippocampal plasticity, but did not affect EPSCs. H1R and H2R antagonists prevented the clobenpropit-induced increase in LTP and, injected locally into the hippocampus, blocked clobenpropit's effect in the forced swim test.. Clobenpropit's antidepressant effects and the enhanced synaptic plasticity require hippocampal H1R and H2R activation, suggesting that clobenpropit acts through disinhibition of histamine release. Clobenpropit reverses memory deficits and increases hippocampal GluN2A expression without modifying anxiety-related phenotypes or EPSCs in CA1 pyramidal neurons.

Topics: Animals; Antidepressive Agents; Anxiety; Behavior, Animal; Depression; Disease Models, Animal; Excitatory Postsynaptic Potentials; Glutamic Acid; Hippocampus; Histamine H3 Antagonists; Imidazoles; Long-Term Potentiation; Male; Memory Disorders; Patch-Clamp Techniques; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Thiourea

High levels of histamine H3 receptors (H3Rs) are found in the globus pallidus (GP), a neuronal nucleus in the basal ganglia involved in the control of motor behavior. By using rat GP isolated nerve terminals (synaptosomes), we studied whether H3R activation modified the previously reported enhancing action of adenosine A2A receptor (A2AR) stimulation on depolarization-evoked [(3)H]-GABA release. At 3 and 10 nM, the A2AR agonist CGS-21680 enhanced [(3)H]-GABA release induced by high K(+) (20 mM) and the effect of 3 nM CGS-21680 was prevented by the A2AR antagonist ZM-241385 (100 nM). The presence of presynaptic H3Rs was confirmed by the specific binding of N-α-[methyl-(3)H]-histamine to membranes from GP synaptosomes (maximum binding, Bmax, 1327 ± 79 fmol/mg protein; dissociation constant, Kd, 0.74 nM), which was inhibited by the H3R ligands immepip, clobenpropit, and A-331440 (inhibition constants, Ki, 0.28, 8.53, and 316 nM, respectively). Perfusion of synaptosomes with the H3R agonist immepip (100 nM) had no effect on K(+)-evoked [(3)H]-GABA release, but inhibited the stimulatory action of A2AR activation. In turn, the effect of immepip was blocked by the H3R antagonist clobenpropit, which had no significant effect of its own on K(+)-induced [(3)H]-GABA release. These data indicate that H3R activation selectively counteracts the facilitatory action of A2AR stimulation on GABA release from striato-pallidal projections.

Topics: Adenosine; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Animals; Biphenyl Compounds; gamma-Aminobutyric Acid; Globus Pallidus; Histamine Agonists; Histamine H3 Antagonists; Imidazoles; Male; Membrane Potentials; Nitriles; Phenethylamines; Piperidines; Potassium; Pyrrolidines; Rats, Wistar; Receptor, Adenosine A2A; Receptors, Histamine H3; Synaptosomes; Thiourea; Triazines; Triazoles; Tritium

To evaluate the anti-tumor effect of clobenpropit, which is a specific H3 antagonist and H4 agonist, in combination with gemcitabine in a pancreatic cancer cell line.. Three kinds of human pancreatic cancer cell lines (Panc-1, MiaPaCa-2, and AsPC-1) were used in this study. Expression of H3 and H4 receptors in pancreatic cancer cells was identified with Western blotting. Effects of clobenpropit on cell proliferation, migration and apoptosis were evaluated. Alteration of epithelial and mesenchymal markers after administration of clobenpropit was analyzed. An in vivo study with a Panc-1 xenograft mouse model was also performed.. H4 receptors were present as 2 subunits in human pancreatic cancer cells, while there was no expression of H3 receptor. Clobenpropit inhibited cell migration and increased apoptosis of pancreatic cancer cells in combination with gemcitabine. Clobenpropit up-regulated E-cadherin, but down-regulated vimentin and matrix metalloproteinase 9 in real-time polymerase chain reaction. Also, clobenpropit inhibited tumor growth (gemcitabine 294 ± 46 mg vs combination 154 ± 54 mg, P = 0.02) and enhanced apoptosis in combination with gemcitabine (control 2.5%, gemcitabine 25.8%, clobenpropit 9.7% and combination 40.9%, P = 0.001) by up-regulation of E-cadherin and down-regulation of Zeb1 in Panc-1 xenograft mouse.. Clobenpropit enhanced the anti-tumor effect of gemcitabine in pancreatic cancer cells through inhibition of the epithelial-mesenchymal transition process.

Topics: Animals; Antimetabolites, Antineoplastic; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Biomarkers, Tumor; Cell Line, Tumor; Cell Movement; Cell Proliferation; Deoxycytidine; Epithelial-Mesenchymal Transition; Gemcitabine; Histamine Agonists; Histamine H3 Antagonists; Humans; Imidazoles; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Pancreatic Neoplasms; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Thiourea; Tumor Burden; Xenograft Model Antitumor Assays

Schizophrenia (SCZ) afflicts around 1% of the world's population with characteristic symptoms such as hallucinations, delusions, and cognitive disorders. Several experimental studies in the past have indicted brain histaminergic neuronal system involvement in the pathogenesis of psychotic disorders including SCZ. Present study investigates anti-schizophrenic activity using two histamine H(3)-receptor (H(3)R)-antagonists/inverse agonists, ciproxifan (3.0 mg/kg, i.p.) and clobenpropit (15 mg/kg, i.p.), on some of the established animal model of schizophrenia, for example, amphetamine (AMPH) and dizocilpine (MK-801)-induced hyperactivity, apomorphine (APO)-induced climbing behavior, scopolamine and MK-801-induced learning and memory deficits and haloperidol-induced catalepsy including determination of acetylcholinesterase (AChE) activity. Results of the present study demonstrate that ciproxifan and clobenpropitwere able to control AMPH and MK-801-induced hyperlocomotor activities demonstrated as reduced horizontal activity and reduced number of movements made by rats. Further, there was overall reduction in APO-induced climbing behavior. Learning and memory deficits, as evaluated on elevated plus maze, followed by estimation of brain AChE activity demonstrated positive results with these protypical imidazole H(3)R-antagonists/inverse agonists.

Topics: Acetylcholinesterase; Animals; Behavior, Animal; Brain; Catalepsy; Female; Histamine Antagonists; Imidazoles; Learning Disabilities; Ligands; Male; Memory Disorders; Mice; Motor Activity; Rats; Rats, Wistar; Receptors, Histamine H3; Schizophrenia; Thiourea

Recently accumulating evidence has highlighted the role of histamine in inflammation and immune reaction by histamine H4-receptor, however the role of histamine via H4-receptor in immunomodulation is still unclear. Therefore, the present study was designed to study the immunomodulatory role of histamine H4-receptor on antibody generation profile in rabbit.. The cohort study comprised of 108 rabbits in six groups. Each group consisted of 18 rabbits. Group I (negative control) remained non-immunized and received vehicle (sterile distilled water, 1 mlkg-1 × b.i.d., s.c. for 10 days (3 days prior to immunization until 7 days after immunization)). Group II (positive control) received vehicle (1 mlkg-1 × b.i.d., s.c. for 10 day), while group III-VI received histamine (100 µgkg-1 × b.i.d., s.c.), H4-agonist (clobenpropit dihydrobromide, 10 µgkg-1 × b.i.d., s.c.), and H4-antagonist (JNJ 7777120, 10 µgkg-1 × b.i.d., i.m.) and DMSO (control group for H4R-antagonist, 1 mlkg-1 × b.i.d., i.m.) respectively for 10 days. Group II-VI were immunized with intravenous injection of sheep red blood cells (SRBC) on day 3. Immunological parameters [immunoglobulins (Ig), immunoglobulin M (IgM), and immunoglobulin G (IgG)] assessed by the whole SRBC-ELISA method and direct hemagglutination assay.. Histamine could influence a detectable antibody response to SRBC as early as day 7 postimmunization (post-I), which lasted until day 58 post-I, whereas H4-receptor by H4R-antagonist treatment showed a similar profile of antibody (Ig, IgM, and IgG) generation as the positive control group. On the other hand, H4R-agonist treatment showed immunostimulant activity as compared to other experimental groups. The results were found statistically significant (p<0.01).. Histamine H4-receptor in biological system modulates immunological function and stimulates antibody production only by exogenously administered agonists not by endogenous histamine (Tab. 1, Fig. 3, Ref. 26).

Topics: Animals; Antibody Formation; Erythrocytes; Female; Hemagglutination Tests; Imidazoles; Immunization; Immunoglobulins; Male; Rabbits; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Sheep; Thiourea

Clobenpropit, an H( 3) receptor antagonist, has been reported to modulate both the release of neurotransmitters and also the activity of histidine decarboxylase (HDC). Therefore, a decarboxylase-positive modulator, namely pyridoxine, was taken for interaction studies with clobenpropit in the electroshock (ES) model of seizures in mice and subsequent changes in brain histamine levels were estimated. A significant inhibition of ES-induced seizures was seen after the simultaneous use of clobenpropit and pyridoxine. No significant effects were evident on the brain histamine levels following this combination. The combination of clobenpropit with pyridoxine appears to exhibit beneficial pharmacodynamic interaction for the prevention of ES-induced seizures, which might not be mediated by the histaminergic mechanisms.

Topics: Animals; Anticonvulsants; Brain; Drug Interactions; Electroshock; Female; Histamine; Histamine H3 Antagonists; Histidine Decarboxylase; Imidazoles; Male; Mice; Pyridoxine; Seizures; Thiourea

The rat mesenteric artery has been shown to be innervated by adrenergic vasoconstrictor nerves and calcitonin gene-related peptide (CGRP)-containing (CGRPergic) vasodilator nerves. The present study was designed to investigate the involvement of histamine H(3) receptors in the neurotransmission of perivascular adrenergic and CGRPergic nerves. The mesenteric vascular beds without an endothelium isolated from male Wistar rats were perfused with Krebs solution and perfusion pressure was measured. In preparations with resting tension, the selective H(3) receptor agonist (R)-α-methylhistamine (α-methylhistamine; 10-100nM) significantly reduced periarterial nerve stimulation (2-8Hz)-induced vasoconstriction and noradrenaline release in the perfusate without an effect on the vasoconstriction induced by exogenously injected noradrenaline (0.5, 1.0nmol). In preparations with active tone produced by methoxamine (2μM) and in the presence of guanethidine (5μM), the periarterial nerve stimulation (1, 2Hz)-induced vasodilator response was inhibited by α-methylhistamine (0.1-1μM) perfusion without affecting vasodilation induced by exogenously injected CGRP (5pmol). Clobenpropit (histamine H(3) receptor antagonist, 1μM) canceled the α-methylhistamine-induced decrease in the periarterial nerve stimulation-induced vasoconstriction and noradrenaline release and periarterial nerve stimulation-induced vasodilation. These results suggest that the stimulation of H(3) receptors located in rat perivascular nerves inhibits presynaptically the neurotransmission of not only adrenergic nerves, but also CGRP nerves, by decreasing neurotransmitters.

Topics: Animals; Calcitonin Gene-Related Peptide; Imidazoles; In Vitro Techniques; Injections; Male; Mesenteric Arteries; Methylhistamines; Norepinephrine; Rats; Rats, Wistar; Receptors, Histamine H3; Synaptic Transmission; Thiourea; Vasoconstriction

Earlier studies have reported the production of histamine in colorectal cancers (CRCs). The effect of histamine is largely determined locally by the histamine receptor expression pattern. Recent evidence suggests that the expression level of histamine receptor H4 (HRH4) is abnormal in colorectal cancer tissues. However, the role of HRH4 in CRC progression and its clinical relevance is not well understood. The aim of this study is to evaluate the clinical and molecular phenotypes of colorectal tumors with abnormal HRH4 expression.. Immunoblotting, real-time PCR, immunofluorescence and immunohistochemistry assays were adopted to examine HRH4 expression in case-matched CRC samples (n = 107) and adjacent normal tissues (ANTs). To assess the functions of HRH4 in CRC cells, we established stable HRH4-transfected colorectal cells and examined cell proliferation, colony formation, cell cycle and apoptosis in these cells.. The protein levels of HRH4 were reduced in most of the human CRC samples regardless of grade or Dukes classification. mRNA levels of HRH4 were also reduced in both early-stage and advanced CRC samples. In vitro studies showed that HRH4 over-expression caused growth arrest and induced expression of cell cycle proteins in CRC cells upon exposure to histamine through a cAMP -dependent pathway. Furthermore, HRH4 stimulation promoted the 5-Fu-induced cell apoptosis in HRH4-positive colorectal cells.. The results from the current study supported previous findings of HRH4 abnormalities in CRCs. Expression levels of HRH4 could influence the histamine-mediated growth regulation in CRC cells. These findings suggested a potential role of abnormal HRH4 expression in the progression of CRCs and provided some new clues for the application of HRH4-specific agonist or antagonist in the molecular therapy of CRCs.

Topics: Antimetabolites, Antineoplastic; Apoptosis; Cell Cycle; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Colorectal Neoplasms; Cyclic AMP-Dependent Protein Kinases; Fluorouracil; Gene Expression; Gene Expression Regulation, Neoplastic; Histamine H3 Antagonists; Humans; Imidazoles; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; RNA, Messenger; Signal Transduction; Thiourea

We have previously reported that histamine at micromolar concentrations reduces the proliferation of melanoma cell lines. It is also known that melanoma cells express histamine H1, H2, and H3 receptors. The aim of this study was to investigate the presence of histamine H4 receptor (H4R) in human melanoma cells and its associated biological processes. To better understand the importance of histamine in tumor development, we explored the expression of H4R in human melanoma tissue biopsies. The expression of H4R in WM35 and M1/15 cells was analyzed by reverse-transcription-PCR, western blot, and immunocytochemistry. To characterize the biological responses we evaluated cell proliferation by clonogenic assay and 5-bromo-2'-deoxyuridine incorporation. In addition, cell senescence and differentiation were determined by β-galactosidase enzyme assay and dopa oxidase activity, respectively. The expression levels of H4R were determined by immunohistochemistry in 19 samples of human malignant lesions. Results indicate that melanoma cells express H4R at the messenger RNA and protein levels. By using histamine agonists, antagonists, and H4R small-interfering RNA we showed that the inhibitory effect of histamine on proliferation was in part mediated through the stimulation of the H4R. The decrease in proliferation was associated with an induction of cell senescence and an increase in melanogenesis, which is a differentiation marker of these cells. Furthermore, H4R was expressed in 42% of human melanoma biopsies. To our knowledge, this is the first report that describes the presence of the H4R in melanoma cells and tissue, suggesting a potential therapeutic application of H4R ligands.

Topics: Cell Differentiation; Cell Growth Processes; Cell Line, Tumor; Guanidines; Histamine; Humans; Imidazoles; Immunohistochemistry; Indoles; Melanoma; Piperazines; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; RNA, Messenger; Skin Neoplasms; Thiourea

Cholangiocarcinoma (CCA) is a biliary cancer arising from damaged bile ducts. Epithelial-mesenchymal transition (EMT) occurs as epithelial cells begin to resemble mesenchymal cells leading to increased invasion potential as the extracellular matrix (ECM) degrades. Histamine exerts its effects by way of four receptors (H1-H4 HRs). Clobenpropit, a potent H4HR agonist, inhibits mammary adenocarcinoma growth. We have shown that (1) cholangiocytes and CCA cells express H1-H4 HRs and (2) the H3HR decreases CCA proliferation. We evaluated the effects of clobenpropit on CCA proliferation, invasion, EMT phenotypes, and ECM degradation. In vitro, we used CCA cell lines to study proliferation, signaling pathways, and the morphological invasive potential. Gene and protein expression of the hepatobiliary epithelial markers CK-7, CK-8, and CK-19, the focal contact protein paxillin, and the mesenchymal markers fibronectin, s100A4, and vimentin were evaluated. Cell invasion across an ECM layer was quantitated and matrix metalloproteinase-1, -2, -3, -9, and -11 gene and protein expression was examined. Evaluation of the specific role of H4HR was performed by genetic knockdown of the H3HR and overexpression of H4HR. Proliferation was evaluated by proliferating cellular nuclear antigen immunoblotting. In vivo, xenograft tumors were treated with either vehicle or clobenpropit for 39 days. Tumor volume was recorded every other day. Clobenpropit significantly decreased CCA proliferation by way of a Ca(2+) -dependent pathway and altered morphological development and invasion. Loss of H3HR expression or overexpression of H4HR significantly decreased CCA proliferation. In vivo, clobenpropit inhibited xenograft tumor growth compared with controls.. Modulation of H4HR by clobenpropit disrupts EMT processes, ECM breakdown, and invasion potential and decreases tumor growth. Interruption of tumorigenesis and invasion by histamine may add to therapeutic advances for CCAs.

Topics: Animals; Apoptosis; Bile Duct Neoplasms; Bile Ducts, Intrahepatic; Biopsy; Cell Division; Cell Line, Tumor; Cholangiocarcinoma; Cyclic AMP; Disease Progression; Epithelial-Mesenchymal Transition; Extracellular Matrix; Histamine H3 Antagonists; Humans; Imidazoles; Inositol 1,4,5-Trisphosphate; Mice; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; RNA, Small Interfering; Signal Transduction; Thiourea; Xenograft Model Antitumor Assays

The histamine H(4) receptor (H(4)R) is a G protein-coupled receptor (GPCR) that plays an important role in inflammation. Similar to the homologous histamine H(3) receptor (H(3)R), two acidic residues in the H(4)R binding pocket, D(3.32) and E(5.46), act as essential hydrogen bond acceptors of positively ionizable hydrogen bond donors in H(4)R ligands. Given the symmetric distribution of these complementary pharmacophore features in H(4)R and its ligands, different alternative ligand binding mode hypotheses have been proposed. The current study focuses on the elucidation of the molecular determinants of H(4)R-ligand binding modes by combining (3D) quantitative structure-activity relationship (QSAR), protein homology modeling, molecular dynamics simulations, and site-directed mutagenesis studies. We have designed and synthesized a series of clobenpropit (N-(4-chlorobenzyl)-S-[3-(4(5)-imidazolyl)propyl]isothiourea) derivatives to investigate H(4)R-ligand interactions and ligand binding orientations. Interestingly, our studies indicate that clobenpropit (2) itself can bind to H(4)R in two distinct binding modes, while the addition of a cyclohexyl group to the clobenpropit isothiourea moiety allows VUF5228 (5) to adopt only one specific binding mode in the H(4)R binding pocket. Our ligand-steered, experimentally supported protein modeling method gives new insights into ligand recognition by H(4)R and can be used as a general approach to elucidate the structure of protein-ligand complexes.

Topics: Cell Line, Tumor; Histamine Antagonists; Humans; Hydrophobic and Hydrophilic Interactions; Imidazoles; Ligands; Models, Molecular; Molecular Conformation; Molecular Dynamics Simulation; Mutagenesis, Site-Directed; Quantitative Structure-Activity Relationship; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H3; Receptors, Histamine H4; Stereoisomerism; Thiourea

G Protein-Coupled Receptors (GPCRs) are integral membrane proteins that play important role in regulating key physiological functions, and are targets of about 50% of all recently launched drugs. High-resolution experimental structures are available only for very few GPCRs. As a result, structure-based drug design efforts for GPCRs continue to rely on in silico modeling, which is considered to be an extremely difficult task especially for these receptors. Here, we describe Gmodel, a novel approach for building 3D atomic models of GPCRs using a normal mode-based refinement of homology models. Gmodel uses a small set of relevant low-frequency vibrational modes derived from Random Elastic Network model to efficiently sample the large-scale receptor conformation changes and generate an ensemble of alternative models. These are used to assemble receptor-ligand complexes by docking a known active into each of the alternative models. Each of these is next filtered using restraints derived from known mutation and binding affinity data and is refined in the presence of the active ligand. In this study, Gmodel was applied to generate models of the antagonist form of histamine 3 (H3) receptor. The validity of this novel modeling approach is demonstrated by performing virtual screening (using the refined models) that consistently produces highly enriched hit lists. The models are further validated by analyzing the available SAR related to classical H3 antagonists, and are found to be in good agreement with the available experimental data, thus providing novel insights into the receptor-ligand interactions.

Topics: Amino Acid Sequence; Drug Discovery; Histamine H3 Antagonists; Humans; Imidazoles; Ligands; Models, Molecular; Molecular Sequence Data; Oximes; Piperidines; Protein Binding; Receptors, G-Protein-Coupled; Receptors, Histamine H3; Sequence Alignment; Thiourea

In the present study, the influence of withdrawal from repeated administration of morphine on intra-ventral hippocampal microinjection of histamine-induced anxiety-like behavior was investigated in male Wistar rats. Three days subcutaneous administration of morphine (5-10 mg/kg) followed by five days free of the drug decreased the percentage open arm time and the percentage open arm entries. Intra-ventral hippocampal administration of histamine (2.5-7.5 microg/rat) decreased percentage open arm time and percentage open arm entries. Intra-ventral hippocampal histamine-induced anxiogenic effect was reversed in animals that had previously received the three days morphine (7.5 mg/kg) followed by five days free of the drug. Intra-ventral hippocampal administration of pyrilamine (5-20 microg/rat) or ranitidine (10-40 microg/rat) decreased percentage open arm time and percentage open arm entries. Pyrilamine- or ranitidine-induced anxiogenic effect was not changed in animals that had previously received the three days morphine (7.5 mg/kg) followed by five days free of the drug. Intra-ventral hippocampal injections of clobenpropit increased percentage open arm time. The percentage open arm time and percentage open arm entries were decreased in the morphine-treated animals compared with non-morphine-treated controls. Percentage open arm entries and locomotor activity was reduced with some doses of clobenpropit. It can be concluded that the histamine system is involved in anxiety-like behavior, and repeated injections of morphine followed by five days free of the drugs interact with histamine receptor mechanism.

Topics: Analysis of Variance; Animals; Anxiety; Behavior, Animal; Hippocampus; Histamine; Histamine Antagonists; Imidazoles; Male; Microinjections; Morphine; Motor Activity; Pyrilamine; Ranitidine; Rats; Rats, Wistar; Substance Withdrawal Syndrome; Thiourea

N-Methyl-D-aspartate (NMDA) receptors are ligand-gated ion channels that mediate a slow, Ca(2+)-permeable component of excitatory synaptic transmission in the central nervous system and play a pivotal role in synaptic plasticity, neuronal development, and several neurological diseases. We describe a fluorescence-based assay that measures NMDA receptor-mediated changes in intracellular calcium in a BHK-21 cell line stably expressing NMDA receptor NR2D with NR1 under the control of a tetracycline-inducible promoter (Tet-On). The assay selectively identifies allosteric modulators by using supramaximal concentrations of glutamate and glycine to minimize detection of competitive antagonists. The assay is validated by successfully identifying known noncompetitive, but not competitive NMDA receptor antagonists among 1800 screened compounds from two small focused libraries, including the commercially available library of pharmacologically active compounds. Hits from the primary screen are validated through a secondary screen that used two-electrode voltage-clamp recordings on recombinant NMDA receptors expressed in Xenopus laevis oocytes. This strategy identified several novel modulators of NMDA receptor function, including the histamine H3 receptor antagonists clobenpropit and iodophenpropit, as well as the vanilloid receptor transient receptor potential cation channel, subfamily V, member 1 (TRPV1) antagonist capsazepine. These compounds are noncompetitive antagonists and the histamine H3 receptor ligand showed submicromolar potency at NR1/NR2B NMDA receptors, which raises the possibility that compounds can be developed that act with high potency on both glutamate and histamine receptor systems simultaneously. Furthermore, it is possible that some actions attributed to histamine H3 receptor inhibition in vivo may also involve NMDA receptor antagonism.

Topics: Aniline Compounds; Animals; Cell Line; Cricetinae; Drug Evaluation, Preclinical; Electrophysiology; Excitatory Amino Acid Antagonists; Fluorescent Dyes; Histamine H3 Antagonists; Humans; Imidazoles; Isothiuronium; Microscopy, Fluorescence; Oocytes; Patch-Clamp Techniques; Piperidines; Radioligand Assay; Receptors, N-Methyl-D-Aspartate; Structure-Activity Relationship; Thiourea; Xanthenes; Xenopus laevis

The present study was designed to investigate the effect of the H3 antagonist clobenpropit on neurotoxicity induced by Abeta42 in differentiated rat PC12 cells. PC12 cells were exposed to Abeta42 (5 microM) for 24h after clobenpropit applied for 18 h. Cell viability, glutamate release or cell surface expression of NMDA receptors were examined. Pretreatment with clobenpropit ameliorated cell impairment induced by Abeta42. In the presence of Abeta42, clobenpropit increased glutamate release, although there were no differences between the Abeta42-treated sample and control. Meanwhile, in the absence of Abeta42, clobenpropit increased the surface expression of NMDA receptors when the total expression of NMDA receptors was not influenced. These results indicate that one of the mechanisms by which clobenpropit attenuates Abeta42-induced neurotoxicity may act through regulation of glutamate release and NMDA receptor trafficking.

Topics: Amyloid beta-Peptides; Animals; Cell Survival; Enzyme-Linked Immunosorbent Assay; Glutamic Acid; Histamine H3 Antagonists; Imidazoles; Neurons; Neurotoxins; PC12 Cells; Peptide Fragments; Rats; Receptors, N-Methyl-D-Aspartate; Thiourea

Effects of the histamine H(4) receptor antagonist JNJ 7777120 (1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methylpiperazine) were tested in two models of allergic contact dermatitis. Dermatitis was induced by 2,4-dinitrochlorobenzene and toluene-2,4-diisocyanate, which differ in their Th1-Th2 profile in that way that 2,4-dinitrochlorobenzene is a classical contact allergen with a pronounced Th1-mediated inflammation, while the respiratory chemical allergen toluene-2,4-diisocyanate induces a Th2-dominated inflammation. JNJ 7777120 (15 mg/kg) administered 2 h and 30 min before and 1 h after challenge did not reduce the hapten-induced ear swelling determined 24 h after challenge. This was confirmed by histological evaluation of the ear skin. A repeated administration of the haptens to the rostral part of the back of sensitized animals resulted in a frequent scratching behaviour. An administration of JNJ 7777120 (15 mg/kg) 30 min before challenge reduced this hapten-induced scratching significantly. The H(1) receptor antagonist cetirizine also reduced the scratching bouts in sensitized mice. A combination of H(1) and H(4) receptor antagonists resulted in the strongest inhibition of scratching behaviour associated with allergic dermatitis. These results indicate that H(4) receptor antagonism fails to reduce the allergic inflammatory response but strongly inhibits allergen-induced itch. Thus, a combination of H(4) and H(1) receptor antagonism might be a new strategy to treat pruritus related to allergic diseases like atopic dermatitis.

Topics: Animals; Dermatitis, Atopic; Dose-Response Relationship, Drug; Female; Haptens; Histamine H1 Antagonists; Imidazoles; Indoles; Inflammation; Mice; Mice, Inbred BALB C; Piperazines; Pruritus; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Th2 Cells; Thiourea; Time Factors

Histamine influences T-cell reactions via histamine receptors 1 and 2. The histamine receptor 4 (H(4)R) is the most recently identified histamine receptor and is also expressed on human CD4(+) T cells; however, its regulation and function are unclear.. To investigate expression, regulation, and function of the H(4)R on human CD4(+) T cells.. Histamine receptor 4 expression was studied by real-time quantitative RT-PCR and by flow cytometry. Effects of H(4)R stimulation on induction of the signal transduction molecules activator protein 1 (AP-1) and nuclear factor-kappaB (NF-kappaB) were determined by electrophoretic mobility shift assay and on cytokine production by RT-PCR and ELISA.. Histamine receptor 4 mRNA and protein were expressed by CD4(+) T cells and upregulated by IL-4. Its expression was higher on T(H)2 cells than T(H)1 cells and naive T-cells. H(4)R agonists (clobenpropit and 4-methylhistamine) induced AP-1 in T(H)2 cells but not in T(H)1 cells. This effect was blocked by the H(4)R antagonist JNJ7777120. H(4)R agonists upregulated IL-31 mRNA in PBMCs and T(H)2 cells, a cytokine that has been associated with T(H)2 cells and the induction of pruritus. IL-31 mRNA induction by H(4)R stimulation was pronounced in PBMCs from patients with atopic dermatitis. Expression of IL-4, IL-5, and IL-13 was not altered by the H(4)R.. Human CD4(+) T cells express a functional H(4)R. The receptor is upregulated under T(H)2 conditions, and its stimulation leads to induction of AP-1 and IL-31.

Topics: Cells, Cultured; Dermatitis, Atopic; Histamine H3 Antagonists; Humans; Imidazoles; Interleukin-4; Interleukins; Methylhistamines; NF-kappa B; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Th1 Cells; Th2 Cells; Thiourea; Transcription Factor AP-1

Siberian hamsters develop hypophagia and increase catabolism of fat reserves in response to short photoperiods resulting in a natural loss of body weight in winter. We previously found that histamine 3 receptor (H3R) mRNA in the posterior hypothalamus is significantly decreased in short photoperiods. We hypothesized that this lower expression of H3R might contribute to the winter hypophagic state, therefore we examined the effects of the H3R agonist imetit and inverse agonists clobenpropit and thioperamide on food intake. We expressed the Siberian hamster H3R receptor in vitro and confirmed that imetit, clobenpropit and thioperamide are bound specifically, thus validating them as tools to investigate the role of H3R in vivo. Intracerebroventricular administration of histamine decreased food intake in hamsters in the fat summer state. Administration of imetit to hamsters in the lean state increased food intake, whereas administration of inverse agonists decreased food intake, though this was associated with decreased locomotor activity. Both H3R inverse agonists prevented the nocturnal rise in body temperature indicating additional effects on energy expenditure. In summary, our results suggest that increased availability of central histamine or the reduction of H3R activity decrease food intake. These effects are similar to those observed in hamsters in short photoperiods.

Topics: Animals; Body Temperature; Cell Line, Transformed; Cricetinae; Disease Models, Animal; Eating; Histamine; Imidazoles; Injections, Intraventricular; Motor Activity; Obesity; Phodopus; Photoperiod; Piperidines; Receptors, Histamine H3; Seasons; Thiourea; Transfection

Nonhibernating seasonal mammals have adapted to temporal changes in food availability through behavioral and physiological mechanisms to store food and energy during times of predictable plenty and conserve energy during predicted shortage. Little is known, however, of the hypothalamic neuronal events that lead to a change in behavior or physiology. Here we show for the first time that a shift from long summer-like to short winter-like photoperiod, which induces physiological adaptation to winter in the Siberian hamster, including a body weight decrease of up to 30%, increases neuronal activity in the dorsomedial region of the arcuate nucleus (dmpARC) assessed by electrophysiological patch-clamping recording. Increased neuronal activity in short days is dependent on a photoperiod-driven down-regulation of H3 receptor expression and can be mimicked in long-day dmpARC neurons by the application of the H3 receptor antagonist, clobenproprit. Short-day activation of dmpARC neurons results in increased c-Fos expression. Tract tracing with the trans-synaptic retrograde tracer, pseudorabies virus, delivered into adipose tissue reveals a multisynaptic neuronal sympathetic outflow from dmpARC to white adipose tissue. These data strongly suggest that increased activity of dmpARC neurons, as a consequence of down-regulation of the histamine H3 receptor, contributes to the physiological adaptation of body weight regulation in seasonal photoperiod.

Topics: Adipose Tissue, White; Animals; Arcuate Nucleus of Hypothalamus; Cricetinae; Electrophysiology; Gene Expression Regulation; Herpesvirus 1, Suid; Histamine H3 Antagonists; Hypothalamus; Imidazoles; Immunohistochemistry; In Situ Hybridization; In Vitro Techniques; Male; Phodopus; Photoperiod; Proto-Oncogene Proteins c-fos; Receptors, Histamine H3; Thiourea

Previous studies have demonstrated that clobenpropit (N-(4-chlorobenzyl)-S-[3-(4(5)-imidazolyl)propyl]isothiourea) binds to both the human histamine H(3) receptor (H(3)R) and H(4) receptor (H(4)R). In this paper, we describe the synthesis and pharmacological characterization of a series of clobenpropit analogs, which vary in the functional group adjacent to the isothiourea moiety in order to study structural requirements for H(3)R and H(4)R ligands. The compounds show moderate to high affinity for both the human H(3)R and H(4)R. Furthermore, the changes in the functional group attached to the isothiourea moiety modulate the intrinsic activity of the ligands at the H(4)R, ranging from neutral antagonism to full agonism. QSAR models have been generated in order to explain the H(3)R and H(4)R affinities.

Topics: Histamine H3 Antagonists; Humans; Imidazoles; Ligands; Male; Molecular Structure; Protein Binding; Quantitative Structure-Activity Relationship; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H3; Receptors, Histamine H4; Thiourea

To investigate the effects of clobenpropit and histidine on reinstatement of morphine-induced conditioned place preference (CPP) in rats.. The persistence, extinction and reinstatement of morphine-induced CPP were established.In clobenpropit group three different doses of clobenpropit (2, 5 and 10 microg/rat, i.c.v.) were administered 15 min after morphine (1 mg/kg, i.p.) was injected. In histidine group histidine (100, 200, 500 mg/kg) was given 1 h prior to morphine treatment (1 mg/kg i.p).. The CPP was reinstated by priming injection of 1 mg/kg morphine. Clobenpropit (5, 10 microg/rat) significantly inhabited the reinstatement by a priming dose of morphine-induced CPP compared with the morphine control group; histidine (100, 200, 500 mg/kg) significantly inhibited the reinstatement in a dose-dependent manner.. Clobenpropit and histidine inhibit the revival of morphine-induced CPP in a dose dependent manner, indicating that endogenous histamine may inhibit relapse of morphine to some extent.

Topics: Animals; Conditioning, Operant; Histidine; Imidazoles; Male; Morphine Dependence; Random Allocation; Rats; Rats, Sprague-Dawley; Receptors, Cell Surface; Substance Withdrawal Syndrome; Thiourea

Histamine is a well known mediator of allergic skin diseases and, with the discovery of the histamine H(4) receptor, the role of histamine is re-evaluated. There are only limited published data elucidating the role of the histamine H(4) receptor in dogs. Twelve beagles intradermally injected with histamine (0.25 micromol and 2.5 micromol/site) reacted with a classical wheal and flare reaction. None of the dogs showed signs of pruritus. The dogs reacted with a wheal and flare reaction after intradermal injection of histamine H(4) receptor agonist/H(3) receptor antagonist clobenpropit (0.1 micromol) and selective histamine H(4) receptor agonist VUF 8430 (1.5 micromol). Again, no scratching occurred in any of the dogs. The highly selective histamine H(4) receptor antagonist JNJ 7777120 reduced the histamine-induced wheal reaction in nine out of 12 dogs. To determine whether canine mast cells are susceptible to histamine H(4) receptor-mediated reactions, effects of clobenpropit and VUF 8430 were tested in canine mastocytoma cells (C2). Incubation with histamine H(4) receptor agonists (up to 10 micromol/L) induced a distinct calcium(2+) influx. C2 cells also responded with enhanced chemotaxis when stimulated with histamine, VUF 8430 and clobenpropit. Neither VUF 8430, nor clobenpropit (up to 10 micromol/L) led to a modulation of histamine concentration in supernatants of canine mastocytoma cells, whereas mastoparan, used as a positive control, enhanced histamine concentration in supernatants. For treatment of allergic skin diseases in dogs, a combination of H(1)R and H(4)R antagonists might be advantageous.

Topics: Animals; Calcium; Cell Line; Dog Diseases; Dogs; Dose-Response Relationship, Drug; Female; Guanidines; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Indoles; Inflammation; Intercellular Signaling Peptides and Proteins; Male; Mastocytoma; Mice; Mice, Inbred BALB C; Peptides; Piperazines; Receptors, G-Protein-Coupled; Receptors, Histamine; Skin Diseases; Thiourea; Wasp Venoms

The aim of this study was to clarify the mechanisms of the inhibitory effect of a histamine H3 receptor agonist, Sch 50971, on nasal signs in an allergic rhinitis model in mice. The severity of allergic rhinitis was assessed by determining the extent of two markers of allergic symptoms (sneezing and nasal rubbing). The topical application of a histamine H3 receptor antagonist, clobenpropit, into the nasal cavities resulted in a dose-dependent increase in sneezing and nasal rubbing, and both Sch 50971 and a tachykinin NK1 receptor antagonist, L-733,060, inhibited these reactions in non-sensitized mice. Sch 50971 caused no inhibition of histamine- and substance P-induced nasal symptoms; however, the reactions induced by capsaicin were significantly decreased by Sch 50971 in non-sensitized mice. Sch 50971 and cetirizine inhibited antigen-induced sneezing and nasal rubbing in sensitized mice. On the other hand, cetirizine inhibited nasal symptoms induced by antigen in capsaicin-pretreated mice, whereas no effect was observed in Sch 50971. From these results, we concluded that Sch 50971 blocked nasal symptoms by the inhibition of substance P release via histamine H3 receptors located on peri]pheral sensory nerve endings.

Topics: Animals; Capsaicin; Cetirizine; Disease Models, Animal; Female; Histamine; Histamine Agonists; Histamine H1 Antagonists, Non-Sedating; Imidazoles; Mice; Mice, Inbred BALB C; Ovalbumin; Piperidines; Pyrrolidines; Receptors, Histamine H3; Rhinitis, Allergic, Perennial; Substance P; Thiourea

The recently cloned histamine H(4) receptor is expressed predominantly in haematopoietic cells and has been found to modulate the function of mast cells, eosinophils, dendritic cells and T lymphocytes. It represents an attractive target for pharmacological interventions against a number of inflammatory and autoimmune disorders. In the present work we used two-electrode voltage-clamp to demonstrate histamine H(4) receptor modulation of G protein-coupled inward rectifier potassium (GIRK) channels heterologously expressed in Xenopus oocytes. In accordance with earlier findings in other effector systems, full agonism by histamine and (R)-alpha-methylhistamine, partial agonism by clobenpropit and inverse agonism by thioperamide were observed. Furthermore, in oocytes injected with low amounts of receptor cRNA, clobenpropit apparently acted as a neutral antagonist. We also used the high temporal resolution afforded by this system to study the differential time courses of response deactivation upon ligand washout for clobenpropit and (R)-alpha-methylhistamine. GIRK channels represent a novel effector system for histamine H(4) receptor modulation, which may be of physiological relevance and prove useful in the development of compounds targeting this receptor.

Topics: Animals; Electrophysiology; G Protein-Coupled Inwardly-Rectifying Potassium Channels; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Methylhistamines; Oocytes; Patch-Clamp Techniques; Piperidines; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Thiourea; Xenopus

Dendritic cells (DC) are the major antigen-presenting cells and play a key role in adaptive immunity as they are able to activate naive T cells. It was recently described, that the histamine H(4) receptor (H4R) is present on human monocyte-derived DC and that chemotaxis and T-helper (Th)1-Th2 polarization is mediated by this receptor. However, the distribution of histamine receptors on murine DC has not been studied yet.. The histamine receptor expression on murine bone marrow (BM)-derived DC and effects of histamine and H4R agonism on DC migration through skin were studied. As it was demonstrated in scratching experiments that NMRI mice are more susceptible to H4R-mediated itch than BALB/c mice, DC function of NMRI and BALB/c mice was compared.. The mRNA of the H1R, H2R and H4R could be detected in murine BM-derived DC, while mRNA of the H3R was found to be low or undetectable. There were no distinct differences in mRNA expression and in H4R protein level (flow cytometry) between NMRI compared with BALB/c mice indicating, that a higher susceptibility is not associated with a generally higher H4R expression in all cell types. Histamine as well as the H4R agonist clobenpropit induced an enhanced chemotaxis in the skin DC migration assay. The enhanced chemotaxis was blocked by the H4R antagonist JNJ7777120. This finding was confirmed by in vitro migration experiments with BM-derived DC.. Referring to DC migration, blocking the H4R on inflammatory cells might be a promising anti-inflammatory, immunomodulatory strategy.

Topics: Animals; Cell Movement; Chemotaxis, Leukocyte; Dendritic Cells; Female; Guinea Pigs; Histamine; Histamine H3 Antagonists; Imidazoles; Immunologic Factors; Injections, Intradermal; Mice; Mice, Inbred BALB C; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H3; Receptors, Histamine H4; Skin; Thiourea

There is increasing evidence that describes a histamine role in normal and cancer cell proliferation. To better understand the importance of histamine in breast cancer development, the expression of histamine H3 (H3R) and H4 (H4R) receptors and their association with proliferating cell nuclear antigen (PCNA), histidine decarboxylase (HDC) and histamine content were explored in mammary biopsies. Additionally, we investigated whether H3R and H4R were implicated in the biological responses triggered by histamine in MDA-MB-231 breast cancer cells. The expression levels of H3R, H4R, PCNA, HDC and histamine content were determined by immunohistochemistry in 40 benign and malignant lesions. MDA-MB-231 cells proliferation (clonogenic assay and BrdU incorporation) and cell cycle distribution (flow cytometry) were evaluated upon treatment with histamine, H3R and H4R agonists and antagonists. Apoptosis was determined by Annexin staining and TUNEL assay. Cell migration was assessed by transwell system. Results indicate that H3R was detected in 67% (10/15) of benign lesions and in almost all carcinomas (24/25), being the level of its expression significantly higher in carcinomas (p = 0.0016). The non-tumoral breast tissue surrounding carcinomas revealed a lower H3R expression compared to the tumor cells. Only 13% (2/15) of the benign lesions expressed H4R compared to 44% (11/25) of the carcinomas. Interestingly, H3R expression was correlated in carcinomas with the expression of HDC and PCNA (p < 0.0001), and also histamine content (p = 0.0229). Accordingly, histamine increased MDA-MB-231 cells proliferation and also migration via H3R. In contrast, activation of H4R inhibited proliferation and this effect was associated with an arrest in the G(0)/G(1) phase of the cell cycle and an induction of apoptosis. Present findings demonstrate the presence of H3R and H4R in human mammary tissue and suggest that H3R may be involved in the regulation of breast cancer growth and progression representing a novel molecular target for new therapeutic approach.

Topics: Adult; Aged; Breast; Breast Neoplasms; Cell Movement; Cell Proliferation; Female; Histamine; Histidine Decarboxylase; Humans; Imidazoles; Middle Aged; Proliferating Cell Nuclear Antigen; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H3; Receptors, Histamine H4; Thiourea

(1) The present study was designed to investigate whether histamine is involved in the protective effect of carnosine on Abeta42-induced impairment in differentiated PC12 cells. (2) PC12 cells were exposed to Abeta42 (5 muM) for 24 h after carnosine (5 mM) applied for 18 h. Histamine receptor antagonists (diphenhydramine, zolantidine, thioperamide, clobenpropit) or histidine decarboxylase inhibitor (alpha-fluoromethylhistidine) were added 15 min before carnosine. Cell viability, glutamate release or cell surface expression of NMDA receptor was examined. (3) Abeta42 caused a concentration-dependent reduction of viability in PC12 cells and pretreatment with carnosine ameliorated this impairment. This amelioration was reversed by the H(3) receptor antagonists thioperamide and clobenpropit, but not by either the H(1) receptor antagonist diphenhydramine or the H(2) receptor antagonist zolantidine. Further, alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, also had no effect. In the presence of Abeta42, carnosine significantly decreased glutamate release and carnosine increased the surface expression of NMDA receptor. (4) These results indicate that the mechanism by which carnosine attenuates Abeta42-induced neurotoxicity is independent of the carnosine-histidine-histamine pathway, but may act through regulation of glutamate release and NMDA receptor trafficking.

Topics: Amyloid beta-Peptides; Animals; Benzothiazoles; Carnosine; Cell Differentiation; Diphenhydramine; Drug Interactions; Glutamic Acid; Histamine H1 Antagonists; Histamine H2 Antagonists; Histamine H3 Antagonists; Imidazoles; Neurons; Neurotoxins; PC12 Cells; Peptide Fragments; Phenoxypropanolamines; Piperidines; Rats; Receptors, N-Methyl-D-Aspartate; Thiourea

Leptin is a key signal linking peripheral adiposity levels to the regulation of energy homeostasis in the brain. The injection of leptin decreases body weight and food intake in lean rodents; however, in a rodent model of high fat diet-induced obesity (DIO), the exogenous leptin cannot improve adiposity. This ineffectiveness is known as leptin resistance, and the factors downstream of leptin signaling have received attention as viable targets in the treatment of obesity. We previously reported that the histaminergic system is one of the targets of leptin. In the present study, the effect of an H(3)-receptor inverse agonist on hypothalamic histamine release and energy intake was investigated in normal and DIO mice. Leptin (1.3 mg/kg, i.p.) significantly increased hypothalamic histamine release and reduced 12 h-energy intake in normal mice, but had no such effects in DIO mice. In contrast, clobenpropit (5 mg/kg, i.p.), an H(3)-inverse agonist, elicited a significant increase in histamine release in both types of mice. Clobenpropit did not reduce 12 h-energy intake; however, it decreased 3 h-energy intake in both types of mice. These results suggest that lack of the activation of the histaminergic system partly contributes to obesity in DIO mice and direct activation of the histaminergic system circumvents leptin resistance.

Topics: Analysis of Variance; Animals; Behavior, Animal; Body Weight; Chromatography, High Pressure Liquid; Electrochemistry; Energy Intake; Fats; Histamine; Histamine H3 Antagonists; Hypothalamus; Imidazoles; Leptin; Male; Mice; Mice, Inbred C57BL; Microdialysis; Obesity; Thiourea; Time Factors

S-Alkyl-N-alkylisothioureas were efficiently synthesized via synthetic approach (A) using 3-phenylpropionyl isothiocyanate (PPI). The utility of the approach was proved by the syntheses of clobenpropit, a potent histamine H(3) antagonist, and its analogues. Alternatively, clobenpropit could be prepared via intramolecular amide cleavage (B) with use of 2-nitrophenylacetyl isothiocyanate (NPAI).

Topics: Alkylation; Histamine H3 Antagonists; Imidazoles; Thiourea

The role of histamine and its receptors in basal ganglia neurocircuitry was assessed in apomorphine-induced turning behavior. Rats with unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta and medial forebrain bundle were administered histaminergic agents, and apomorphine-induced turning behavior was tested on Days 7 and 14 post-lesion. Compared with saline-treated rats, histidine (500 mg/kg, i.p.), a precursor of histamine, increased turning behavior (p<0.05), while alpha-fluoromethylhistidine (alpha-FMH, 25 microg, i.c.v.), an irreversible inhibitor of histidine decarboxylase, decreased turning behavior (p<0.05) but only on Day 14 post-lesion. Both the histamine H(1) receptor antagonist pyrilamine (10 and 50 microg, i.c.v.) and the H(2) receptor antagonist cimetidine (10 and 50 microg, i.c.v.) significantly decreased turning behavior on Days 7 and 14 post-lesion. The histamine H(3) receptor agonist immepip (10 microg, i.c.v.) decreased turning behavior (p<0.05) on Day 14 post-lesion. The present findings indicate the complex interactions of histamine on basal ganglia function.

Topics: Animals; Apomorphine; Basal Ganglia; Enzyme Inhibitors; Histamine Agonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Histidine; Histidine Decarboxylase; Imidazoles; Injections, Intraventricular; Male; Methylhistidines; Narcotic Antagonists; Oxidopamine; Piperidines; Pyrilamine; Rats; Rats, Sprague-Dawley; Stereotyped Behavior; Sympatholytics; Synapses; Thiourea

We have investigated the presence of histamine H(3) receptors (H(3)Rs) on rat thalamic isolated nerve terminals (synaptosomes) and the effect of their activation on glutamate and GABA release. N-alpha-[methyl-(3)H]histamine ([(3)H]-NMHA) bound specifically to synaptosomal membranes with dissociation constant (K(d)) 0.78+/-0.20 nM and maximum binding (B(max)) 141+/-12fmol/mg protein. Inhibition of [(3)H]-NMHA binding by histamine and the H(3)R agonist immepip fit better to a two-site model, whereas for the H(3)R antagonist clobenpropit the best fit was to the one-site model. GTPgammaS (30 microM) decreased [(3)H]-NMHA binding by 55+/-4% and made the histamine inhibition fit better to the one-site model. Immepip (30 nM) induced a modest, but significant increase (113+/-2% of basal) in [(35)S]-GTPgammaS binding to synaptosomal membranes, an effect prevented by clobenpropit (1 microM) and by pre-treatment with pertussis toxin. In thalamus synaptosomes depolarisation-induced, Ca(2+)-dependent glutamate release was inhibited by histamine (1 microM, 25+/-4% inhibition) and immepip (30 nM, 38+/-5% reduction). These effects were reversed by clobenpropit (1microM). Conversely, immepip (up to 1 microM) had no effect on depolarisation-evoked [(3)H]-GABA release. Extracellular synaptic responses were recorded in the thalamus ventrobasal complex by stimulating corticothalamic afferents. H(3)R activation reduced by 38+/-7% the glutamate receptor-mediated field potentials (FPs), but increased the FP2/FP1 ratio (from 0.86+/-0.03 to 1.38+/-0.05) in a paired-pulse paradigm. Taken together, our results confirm the presence of H(3)Rs on thalamic nerve terminals and show that their activation modulates pre-synaptically glutamatergic, but not GABAergic neurotransmission.

Topics: 4-Aminopyridine; Animals; Dose-Response Relationship, Drug; Drug Interactions; Evoked Potentials; gamma-Aminobutyric Acid; Glutamic Acid; Guanosine 5'-O-(3-Thiotriphosphate); Histamine; Histamine Antagonists; Imidazoles; In Vitro Techniques; Male; Methylhistamines; Pertussis Toxin; Presynaptic Terminals; Protein Binding; Rats; Rats, Wistar; Receptors, Histamine H3; Synaptosomes; Thalamus; Thiourea; Tritium

Using the histamine H3 receptor antagonist clobenpropit, the roles of histamine H3 receptors in NMDA-induced necrosis were investigated in rat cultured cortical neurons. Clobenpropit reversed the neurotoxicity in a concentration-dependent manner, and showed peak protection at a concentration of 10(-7) M. This protection was antagonized by the histamine H3 receptor agonist (R)-alpha-methylhistamine, but not by the histamine H1 receptor antagonist pyrilamine or the histamine H2 receptor antagonist cimetidine. In addition, the protection by clobenpropit was inhibited by the GABAA receptor antagonists picrotoxin and bicuculline. Further study demonstrated that the protection by clobenpropit was due to increased GABA release. The inducible GABA release was also inhibited by (R)-alpha-methylhistamine, but not by pyrilamine or cimetidine. Furthermore, both the adenylyl cyclase inhibitor SQ-22536 and the protein kinase A (PKA) inhibitor H-89 reversed the protection and the GABA release by clobenpropit. In addition, clobenpropit reversed the NMDA-induced increase in intracellular calcium level, which was antagonized by (R)-alpha-methylhistamine. These results indicate that clobenpropit enhanced GABA release to protect against NMDA-induced excitotoxicity, which was induced through the cAMP/PKA pathway, and reduction of intracellular calcium level may also be involved.

Topics: Animals; Animals, Newborn; Calcium; Cell Survival; Cells, Cultured; Cerebral Cortex; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cytoprotection; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; GABA Antagonists; gamma-Aminobutyric Acid; Histamine Agonists; Histamine Antagonists; Imidazoles; N-Methylaspartate; Necrosis; Neurons; Neuroprotective Agents; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Thiourea

Agonist apparent affinities (pK(I)') in histamine H(3)-receptor binding assays were higher than expected from apparent affinity values (pK(app)) estimated in bioassay. Here, we investigate whether the degree of pK(I)' overestimation is related to agonist intrinsic efficacy, by studying the effect of buffer composition on the pK(I)' of ligands with varying intrinsic activity.. In the guinea-pig ileum bioassay, intrinsic activity (alpha) was determined from the maximal inhibition of the contraction produced by increasing agonist concentration. pK(app) values were estimated using the method of Furchgott. The pK(L) of [(3)H]clobenpropit in guinea-pig cerebral cortex was estimated by saturation analysis in 20 mM HEPES-NaOH buffer (buffer B(0,0,0)), or buffer B(0,0,0) containing 70 mM CaCl(2), 100 mM NaCl and 100 mM KCl (buffer B(0.07,0.1,0.1)). PK(I) values were determined in competition studies in both buffers.. [(3)H]clobenpropit saturation isotherms had n (H) values of unity in both buffers. In buffer B(0.07,0.1,0.1), agonist pK(I)' values were closer to pK(app) values than in buffer B(0,0,0) but were associated with n (H) values <1. A two-site analysis of agonist data in buffer B(0.07, 0.1, 0.1) provided a better fit than a one-site fit and low affinity values (pK(IL)) were comparable to pK(app). Differences between the pK(I)' in buffer B(0,0,0) and pK(IL) values in buffer B(0.07,0.1,0.1) (DeltapK) were correlated with alpha.. H(3)-receptor binding assays conducted in buffer B(0,0,0) and buffer B(0.07,0.1,0.1) can provide a measure of ligand affinity (pK(app)) and intrinsic efficacy. The assay predicts that some ligands previously classified as H(3)-receptor antagonists may possess residual intrinsic efficacy.

Topics: Animals; Biological Assay; Buffers; Calcium Chloride; Guinea Pigs; Ileum; Imidazoles; Male; Quinolines; Radioligand Assay; Receptors, Histamine H3; Thiourea; Tritium

Studies suggest that measurement of thermodynamic parameters can allow discrimination of agonists and antagonists. Here we investigate whether agonists and antagonists can be thermodynamically discriminated at histamine H(3) receptors.. The pK(L) of the antagonist radioligand, [(3)H]-clobenpropit, in guinea-pig cortex membranes was estimated at 4, 12, 21 and 30 degrees C in 20 mM HEPES-NaOH buffer (buffer A), or buffer A containing 300 mM CaCl(2), (buffer A(Ca)). pK(I)' values for ligands with varying intrinsic activity were determined in buffer A and A(Ca) at 4, 12, 21 and 30 degrees C.. In buffer A, the pK(L) of [(3)H]-clobenpropit increased with decreasing temperature while it did not change in buffer A(Ca). The Bmax was not affected by temperature or buffer and n (H) values were not different from unity. In buffer A, pK(I)' values for agonists remained unchanged or decreased with decreasing temperature, while antagonist pK(I) values increased with decreasing temperature; agonist binding was entropy-driven while antagonist binding was enthalpy and entropy-driven. In buffer A(Ca), temperature had no effect on antagonist and agonist pK(I) values; both agonist and antagonist binding were enthalpy and entropy-driven.. The binding of H(3)-receptor agonists and antagonists can be thermodynamically discriminated under conditions where agonist pK(I)' values are over-estimated (pK(I)' not = pK(app)). However, under conditions when agonist pK(I) approximately pK(app), the thermodynamics underlying the binding of agonists are not different to those of antagonists.

Topics: Animals; Guinea Pigs; Histamine Agonists; Histamine Antagonists; Imidazoles; Male; Models, Biological; Receptors, Histamine H3; Temperature; Thermodynamics; Thiourea

To investigate the effects of histamine on the neurotoxicity induced by beta-amyloid(1-42)(Abeta42) in rat phaeochromocytoma (PC12) cells.. The in vitro model of Alzheimer's disease was constructed with A beta42-treated PC12 cells. Cell morphology and MTT assay were used to evaluate the cell toxicity and histamine effects. The different histamine antagonists were applied to investigate the involvement of receptor subtypes.. The neurotoxicity was induced by A beta42 in a concentration-dependent manner, which was reversed by histamine at concentration of 10(-7), 10(-6) mol/L. The effect was reversed by H(2) antagonist zolantidine and H(3)antagonist clobenpropit, but not by H(1) antagonist diphenhydramine.. Histamine reduces neurotoxicity induced by beta-amyloid(1-42), which may be mediated by H(2) and H(3)receptors.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Benzothiazoles; Diphenhydramine; Dose-Response Relationship, Drug; Histamine; Histamine H2 Antagonists; Histamine H3 Antagonists; Imidazoles; Neuroprotective Agents; PC12 Cells; Phenoxypropanolamines; Piperidines; Rats; Receptors, Histamine H2; Receptors, Histamine H3; Thiourea

The expression of the recently cloned histamine H(4) receptor (H(4)R) by leukocytes suggests a role in immunomodulation.. The expression and function of the H(4)R on human monocytes obtained from peripheral blood was investigated.. H(4)R expression was studied by using flow cytometry. Effects of H(4)R stimulation on Ca(2+) mobilization was determined fluorometrically, CCL2 production was determined by means of ELISA, intracellular CCL2 staining was measured with flow cytometry, and CCL2 mRNA was measured by using real-time quantitative LightCycler PCR. The relevance of CCL2 production was determined in chemotaxis transmigration assays.. H(4)R protein was expressed by monocytes and upregulated by IFN-gamma. H(4)R agonists (clobenpropit and 4-methylhistamine) induce a Ca(2+) mobilization in monocytes, which could be blocked with the selective H(4)R antagonist JNJ7,777,120. Furthermore, H(4)R agonists downregulated CCL2 protein production. This effect could also be blocked by JNJ7,777,120. Supernatants of H(4)R agonist-stimulated monocytes attracted less monocytes in transmigration assays. The downregulation of CCL2 production was regulated at different levels. First, the synthesis of CCL2 mRNA was significantly decreased. Second, intracellular staining suggested an inhibition of CCL2 secretion after stimulation with H(4)R agonists.. Human monocytes express the H(4)R, and its stimulation leads to a Ca(2+) influx and an inhibition of CCL2 production, resulting in a reduction of monocyte recruitment.. The H(4)R could represent an important anti-inflammatory receptor on monocytes and could be an interesting target for drug development.

Topics: Calcium; Cells, Cultured; Chemokine CCL2; Chemotaxis, Leukocyte; Down-Regulation; Histamine; Histamine Agonists; Humans; Imidazoles; Indoles; Interferon-gamma; Matrix Metalloproteinase 1; Matrix Metalloproteinase 3; Matrix Metalloproteinase 8; Methylhistamines; Monocytes; Piperazines; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Thiourea; Up-Regulation

The histamine H(3) receptor mediates inhibitory responses in the nervous system. Here, we demonstrate the coupling of the human histamine H(3) receptor to G protein-coupled inward rectifier potassium (GIRK) channels in Xenopus oocytes, using voltage-clamp. The histamine H(3) receptor agonist (R)-alpha-methylhistamine increased GIRK currents with an EC(50) of 2.5 nM. The response to (R)-alpha-methylhistamine was inhibited by the specific antagonist/inverse agonist clobenpropit. GIRK channels represent a novel effector pathway for the histamine H(3) receptor, also suggesting the use of electrophysiology assays in histamine H(3) receptor drug screening, allowing for the resolution of G protein activation kinetics.

Topics: Animals; Electrophysiology; G Protein-Coupled Inwardly-Rectifying Potassium Channels; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Methylhistamines; Oocytes; Patch-Clamp Techniques; Receptors, Histamine H3; Thiourea; Xenopus

Topics: Animals; Anti-Ulcer Agents; Cytoprotection; Ethanol; Gastric Mucosa; Ghrelin; Histamine; Histamine Antagonists; Imidazoles; Male; Peptide Hormones; Ranitidine; Rats; Rats, Wistar; Regional Blood Flow; Thiourea

The effects of intracerebroventricular (i.c.v.) administration of ultra low doses (ULDs) of histamine, clobenpropit and pyrilamine are studied on morphine state-dependent (STD) memory in mice. Although pre-test administration of different doses of histamine and clobenpropit showed no effect on impairment of memory induced by pre-training morphine, when the above drugs were co-administered with morphine, they inhibited the restoration of memory by morphine. These effects were opposite to microgram doses of the same drugs.

Topics: Analgesics, Opioid; Animals; Avoidance Learning; Behavior, Animal; Dose-Response Relationship, Drug; Drug Interactions; Histamine; Histamine Agents; Imidazoles; Injections, Intraventricular; Male; Memory; Mice; Morphine; Morphine Dependence; Pyrilamine; Reaction Time; Thiourea

The role of histamine in regulating excitability of sympathetic preganglionic neurons (SPNs) and the expression of histamine receptor mRNA in SPNs was investigated using whole-cell patch-clamp electrophysiological recording techniques combined with single-cell reverse transcriptase polymerase chain reaction (RT-PCR) in transverse neonatal rat spinal cord slices. Bath application of histamine (100 microM) or the H1 receptor agonist histamine trifluoromethyl toluidide dimaleate (HTMT; 10 microM) induced membrane depolarization associated with a decrease in membrane conductance in the majority (70%) of SPNs tested, via activation of postsynaptic H1 receptors negatively coupled to one or more unidentified K+ conductances. Histamine and HTMT application also induced or increased the amplitude and/or frequency of membrane potential oscillations in electrotonically coupled SPNs. The H2 receptor agonist dimaprit (10 microM) or the H3 receptor agonist imetit (100 nM) were without significant effect on the membrane properties of SPNs. Histamine responses were sensitive to the H1 receptor antagonist triprolidine (10 microM) and the nonselective potassium channel blocker barium (1 mM) but were unaffected by the H2 receptor antagonist tiotidine (10 microM) and the H3 receptor antagonist, clobenpropit (5 microM). Single cell RT-PCR revealed mRNA expression for H1 receptors in 75% of SPNs tested, with no expression of mRNA for H2, H3, or H4 receptors. These data represent the first demonstration of H1 receptor expression in SPNs and suggest that histamine acts to regulate excitability of these neurons via a direct postsynaptic effect on H1 receptors.

Topics: Action Potentials; Animals; Animals, Newborn; Autonomic Fibers, Preganglionic; Barium; Dimaprit; Female; Ganglia, Sympathetic; Histamine; Histamine Agonists; Histamine H1 Antagonists; Imidazoles; In Vitro Techniques; Male; Membrane Potentials; Neurons; Patch-Clamp Techniques; Potassium; Rats; Rats, Inbred WKY; Receptors, Histamine H1; Receptors, Histamine H2; Receptors, Histamine H3; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Thiourea; Triprolidine

Complications of sickle cell anaemia include vascular occlusion triggered by the adherence of sickle erythrocytes to endothelium in the postcapillary venules. Adherence can be promoted by inflammatory mediators that induce endothelial cell adhesion molecule expression and arrest flowing erythrocytes. The present study characterised the effect of histamine stimulation on the kinetics of sickle cell adherence to large vessel and microvascular endothelium under physiological flow. Increased sickle cell adherence was observed within minutes of endothelial activation by histamine and reached a maximum value within 30 min. At steady state, sickle cell adherence to histamine-stimulated endothelium was 47 +/- 4 adherent cells/mm(2), 2.6-fold higher than sickle cell adherence to unstimulated endothelial cells. Histamine-induced sickle cell adherence occurred rapidly and transiently. Studies using histamine receptor agonists and antagonists suggest that histamine-induced sickle cell adhesion depends on simultaneous stimulation of the H(2) and H(4) histamine receptors and endothelial P-selectin expression. These data show that histamine release may promote sickle cell adherence and vaso-occlusion. In vivo histamine release should be studied to determine its role in sickle complications and whether blocking of specific histamine receptors may prevent clinical complications or adverse effects from histamine release stimulated by opiate analgesic treatment.

Topics: Analysis of Variance; Anemia, Sickle Cell; Cell Adhesion; Cells, Cultured; Endothelial Cells; Endothelium, Vascular; Erythrocytes; Famotidine; Histamine; Histamine Agonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Humans; Imidazoles; Methylhistamines; P-Selectin; Piperidines; Pyrilamine; Stimulation, Chemical; Thiazoles; Thiourea; Venules

The central histaminergic neuron system inhibits epileptic seizures, which is suggested to occur mainly through histamine 1 (H1) and histamine 3 (H3) receptors. However, the importance of histaminergic neurons in seizure-induced cell damage is poorly known. In this study, we used an organotypic coculture system and confocal microscopy to examine whether histaminergic neurons, which were verified by immunohistochemistry, have any protective effect on kainic acid (KA)-induced neuronal damage in the developing hippocampus. Fluoro-Jade B, a specific marker for degenerating neurons, indicated that, after the 12 h KA (5 microM) treatment, neuronal damage was significantly attenuated in the hippocampus cultured together with the posterior hypothalamic slice containing histaminergic neurons [HI plus HY (POST)] when compared with the hippocampus cultured alone (HI) or with the anterior hypothalamus devoid of histaminergic neurons. Moreover, alpha-fluoromethylhistidine, an inhibitor of histamine synthesis, eliminated the neuroprotective effect in KA-treated HI plus HY (POST), and extracellularly applied histamine (1 nM to 100 microM) significantly attenuated neuronal damage only at 1 nM concentration in HI. After the 6 h KA treatment, spontaneous electrical activity registered in the CA1 subregion contained significantly less burst activity in HI plus HY (POST) than in HI. Finally, in KA-treated slices, the H3 receptor antagonist thioperamide enhanced the neuroprotective effect of histaminergic neurons, whereas the H1 receptor antagonists triprolidine and mepyramine dose-dependently decreased the neuroprotection in HI plus HY (POST). Our results suggest that histaminergic neurons protect the developing hippocampus from KA-induced neuronal damage, with regulation of neuronal survival being at least partly mediated through H1 and H3 receptors.

Topics: Animals; Cell Death; Cells, Cultured; Coculture Techniques; Convulsants; Hippocampus; Histamine; Histamine Antagonists; Histamine H1 Antagonists; Hypothalamus, Anterior; Hypothalamus, Posterior; Imidazoles; Kainic Acid; Methylhistidines; Microscopy, Confocal; Neurons; Neuroprotective Agents; Organ Culture Techniques; Piperidines; Pyrilamine; Rats; Rats, Sprague-Dawley; Receptors, Histamine H1; Receptors, Histamine H3; Thiourea; Triprolidine

Topics: Cell Line; Glycosylation; Histamine Antagonists; Humans; Imidazoles; Kidney; Protein Processing, Post-Translational; Receptors, Histamine H3; Thiourea

1. A-349821 is a selective histamine H3 receptor antagonist/inverse agonist. Herein, binding of the novel non-imidazole H3 receptor radioligand [3H]A-349821 to membranes expressing native or recombinant H3 receptors from rat or human sources was characterized and compared with the binding of the agonist [3H]N--methylhistamine ([3H]NMH). 2. [3H]A-349821 bound with high affinity and specificity to an apparent single class of saturable sites and recognized human H3 receptors with 10-fold higher affinity compared to rat H3 receptors. [3H]A-349821 detected larger populations of receptors compared to [3H]NMH. 3. Displacement of [3H]A-349821 binding by H3 receptor antagonists/inverse agonists was monophasic, suggesting recognition of a single binding site, while that of H3 receptor agonists was biphasic, suggesting recognition of both high- and low-affinity H3 receptor sites. 4. pKi values of high-affinity binding sites for H3 receptor competitors utilizing [3H]A-349821 were highly correlated with pKi values obtained with [3H]NalphaMH, consistent with labelling of H3 receptors by [3H]A-349821. 5. Unlike assays utilizing [3H]NMH, addition of GDP had no effect on saturation parameters measured with [3H]A-349821, while displacement of [3H]A-349821 binding by the H3 receptor agonist histamine was sensitive to GDP. 6. In conclusion, [3H]A-349821 labels interconvertible high- and low-affinity states of the H3 receptor, and displays improved selectivity over imidazole-containing H3 receptor antagonist radioligands. [3H]A-349821 competition studies showed significant differences in the proportions and potencies of high- and low-affinity sites across species, providing new information about the fundamental pharmacological nature of H3 receptors.

Topics: Animals; Binding, Competitive; Biphenyl Compounds; Cells, Cultured; Guanosine Diphosphate; Histamine; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Methylhistamines; Models, Biological; Protein Binding; Radioligand Assay; Rats; Receptors, Histamine H3; Thiourea

We previously described that agonist-activated histamine H3 autoreceptors inhibit the stimulation of histamine synthesis mediated by calcium/calmodulin- and cAMP-dependent protein kinases (CaMKII and PKA respectively) in histaminergic nerve endings. In the absence of an agonist H3 receptors show partial constitutive activity, so we hypothesized that suppression of constitutive activity by an inverse agonist could stimulate these transduction pathways. We show here that the H3 inverse agonist thioperamide increases histamine synthesis in rat brain cortical slices independently from the amounts of extracellular histamine. Thioperamide effects were mimicked by the inverse agonists clobenpropit and A-331440, but not by the neutral antagonist VUF-5681. In contrast, coincubation with VUF-5681 suppressed thioperamide effects. The effects of thioperamide were completely blocked by the PKA inhibitor peptide myristoyl-PKI14-22, a peptide that did not block depolarization stimulation of histamine synthesis. In addition, thioperamide effects required depolarization and were impaired by blockade of N-type calcium channels (mediating depolarization), but not by CaMKII inhibition. These results indicate that constitutive activity of H3 receptors in rat brain cortex inhibits the adenylate cyclase/PKA pathway, and perhaps also the opening of N-type voltage sensitive calcium channels, but apparently not CaMKII.

Topics: Animals; Biphenyl Compounds; Brain; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; In Vitro Techniques; Male; Models, Biological; Nitriles; Piperidines; Potassium; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Thiourea

There is increasing evidence that histamine as an important mediator of immediate type allergic reactions also effects professional APCs. Recent reports showed effects of histamine on human monocyte-derived dendritic cells (MoDC) mediated primarily via histamine H1 receptors (H1R) and H2R. We show here that MoDC also express H3R and H4R at the mRNA and protein level. mRNA of the H3R is down-regulated and mRNA of the H4R is up-regulated during the differentiation from monocytes to MoDC. H4R or H2R stimulation suppressed IL-12p70 production in MoDC. Induction of cAMP was necessary for IL-12p70 inhibition mediated via the H2R. In contrast, H4R stimulation did not affect cAMP production but induced the transcription factor AP-1, and U0126, an inhibitor of AP-1 transactivation and MEK, rescued H4R mediated IL-12p70 suppression. Moreover, MoDC responded to a H4R agonist (and also to a H2R agonist) with increased F-actin polymerization and migration in modified Boyden chamber assays, suggesting a chemotactic effect of histamine via the H2R and the H4R. Thus, H4R stimulation on MoDC results in immunomodulatory and chemotactic effects. Histamine induces chemotaxis and IL-12p70 suppression via different receptors using different signaling pathways, which might be important for the pathogenesis of and therapeutic interventions in allergic diseases.

Topics: Cell Differentiation; Cells, Cultured; Chemotaxis, Leukocyte; Cyclic AMP; Dendritic Cells; DNA-Binding Proteins; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Interleukin-10; Interleukin-12; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Monocytes; Phosphorylation; Protein Subunits; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H3; Receptors, Histamine H4; Signal Transduction; Thiourea; Transcription Factor AP-1

Using a cyanide model to induce neurotoxic effects in rat brain homogenates, we examined the neuroprotective properties of three H3 antagonists, namely clobenpropit, thioperamide and impentamine, and compared them to aspirin, a known neuroprotective agent. Superoxide anion levels and malondialdehyde concentration were assessed using the nitroblue tetrazolium and lipid peroxidation assays. Clobenpropit and thioperamide significantly reduced superoxide anion generation and lipid peroxidation. Impentamine reduced lipid peroxidation at all concentrations used, but only reduced superoxide anion generation at a concentration of 1 mM. In the lipid peroxidation assay, all the drugs compared favourably to aspirin. This study demonstrates the potential of these agents to be neuroprotective by exerting antioxidant effects.

Topics: Animals; Antioxidants; Aspirin; Brain; Disease Models, Animal; Dose-Response Relationship, Drug; Histamine Agonists; Imidazoles; In Vitro Techniques; Lipid Peroxidation; Male; Malondialdehyde; Neuroprotective Agents; Neurotoxicity Syndromes; Piperidines; Potassium Cyanide; Rats; Rats, Wistar; Receptors, Histamine H3; Superoxides; Thiourea

The main objective of this study was to investigate the ability of histamine receptor antagonists to modulate tryptase release from human colon mast cells induced by histamine. Enzymatically dispersed cells from human colon were challenged with histamine in the absence or presence of the histamine receptor antagonists, and the tryptase release was determined. It was found that histamine induced tryptase release from colon mast cells was inhibited by up to approximately 61.5% and 24% by the H1 histamine receptor antagonist terfenadine and the H2 histamine receptor antagonist cimetidine, respectively, when histamine and its antagonists were added to cells at the same time. The H3 histamine receptor antagonist clobenpropit had no effect on histamine induced tryptase release from colon mast cells at all concentrations tested. Preincubation of terfenadine, cimetidine or clobenpropit with cells for 20 minutes before challenging with histamine did not enhance the ability of these antihistamines to inhibit histamine induced tryptase release. Apart from terfenadine at 100 microg/ml, the antagonists themselves did not stimulate tryptase release from colon mast cells following both 15 minutes and 35 minutes incubation periods. It was concluded that H1 and H2 histamine receptor antagonists were able to inhibit histamine induced tryptase release from colon mast cells. This not only added some new data to our hypothesis of self-amplification mechanisms of mast cell degranulation, but also suggested that combining these two types of antihistamine drugs could be useful for the treatment of inflammatory bowel disease (IBD).

Topics: Calcimycin; Cells, Cultured; Cimetidine; Colon; Histamine; Histamine H1 Antagonists; Histamine H2 Antagonists; Humans; Imidazoles; Ionophores; Mast Cells; Serine Endopeptidases; Serine Proteinase Inhibitors; Terfenadine; Thiourea; Tryptases

Although the effectiveness of histamine-related drugs in the treatment of peripheral and central vestibular disorders may be explained by their action on the vestibular nuclei, it has also been shown that antivertigo effects can take place at the peripheral level. In this work, we examined the actions of H3 histaminergic agonists and antagonists on the afferent neuron electrical discharge in the isolated inner ear of the axolotl. Our results indicate that H3 antagonists such as thioperamide, clobenpropit, and betahistine (BH) decreased the electrical discharge of afferent neurons by interfering with the postsynaptic response to excitatory amino acid agonists. These results lend further support to the idea that the antivertigo action of histamine-related drugs may be caused, at least in part, by a decrease in the sensory input from the vestibular endorgans. The present data show that the inhibitory action of the afferent neurons discharge previously described for BH is not restricted to this molecule but is also shared by other H3 antagonists.

Topics: Afferent Pathways; Ambystoma; Animals; Betahistine; Dose-Response Relationship, Drug; Hair Cells, Auditory; Histamine Agents; Histamine Agonists; Histamine Antagonists; Imidazoles; Neural Inhibition; Piperidines; Receptors, Glutamate; Receptors, Histamine H3; Semicircular Canals; Signal Transduction; Thiourea; Vestibular Nerve; Vestibule, Labyrinth

Methamphetamine administration increases brain levels of histamine and neuronal histamine attenuates several of methamphetamine's behavioral effects. The role of different subtypes of histamine receptors in this negative feedback, however, remains unclear. There is some evidence on possible involvement of histamine H3 receptors in these actions of methamphetamine. The aim of the present study was to evaluate the effects of two histamine H3 receptor antagonists, clobenpropit and thioperamide, on rewarding and neurochemical effects of methamphetamine utilizing three in vivo methodologies, drug self-administration, drug discrimination, and microdialysis in Sprague-Dawley rats. In rats self-administering methamphetamine intravenously under a fixed-ratio schedule, presession treatment with thioperamide (1.0-3.0 mg/kg, subcutaneous, s.c.) or clobenpropit (1.0-3.0 mg/kg, s.c.) potentiated the reinforcing effects of methamphetamine, as indicated by a dose-dependent increase in responding for a low 0.03 mg/kg dose of methamphetamine, that by itself failed to maintain responding above saline substitution levels, and a decrease in responding for a higher 0.06 mg/kg training dose of methamphetamine. In contrast, neither thioperamide nor clobenpropit treatment increased responding during saline substitution. In other rats trained to discriminate intraperitoneal (i.p.) injection of 1.0 mg/kg methamphetamine from i.p. injection of saline, both thioperamide and clobenpropit (0.3-3.0 mg/kg, s.c.) dose dependently increased methamphetamine-appropriate responding when administered with a low 0.3 mg/kg i.p. dose of methamphetamine, which by itself produced predominantly saline-appropriate responding. However, thioperamide and clobenpropit produced only saline-appropriate responding when administered with saline vehicle. Finally, thioperamide and clobenpropit potentiated methamphetamine-induced elevations in extracellular dopamine levels in the shell of the nucleus accumbens, but did not increase brain dopamine levels when given alone. These findings point to histamine H3 receptors as a new and important receptor system modulating the reinforcing, subjective, and neurochemical actions of methamphetamine.

Topics: Adrenergic Uptake Inhibitors; Analysis of Variance; Animals; Behavior, Animal; Dopamine; Dose-Response Relationship, Drug; Drug Synergism; Histamine Antagonists; Imidazoles; Male; Methamphetamine; Microdialysis; Nucleus Accumbens; Piperidines; Rats; Rats, Sprague-Dawley; Self Administration; Thiourea; Time Factors

Data concerning cardiovascular effects of peripherally and centrally located histamine H(3) receptor stimulation are contradictory, and despite excessive studies their role in the control of the cardiovascular function have not been cleared yet. Effect of histamine H(3) receptors activation have been attributed to modulation of sympathetic system activity but exact role of peripherally and centrally located histamine H(3) receptors stimulation in the modulation of vascular tone of the mesentery and intestinal metabolism remains unexplored. Aim of the present study was to evaluate the role of centrally and peripherally located histamine H(3) receptors in the modulation of vascular tone of the mesentery and metabolic activity of intestinal tissue. In anesthetized rats total mesenteric blood flow (MBF), mucosal intestinal blood flow (LDBF), intestinal oxygen uptake (VO(2)) and arterial pressure (AP) were determined. Intestinal arterial conductance (C) was also calculated. Administration of the selective histamine H(3) receptor agonist imetit (10 micromol/kg i.a) evoked marked changes in hemodynamic and metabolic parameters; MBF, LDBF, C and VO(2) were significantly increased, whereas AP was significantly decreased. Pretreatment with histamine H(3) receptor antagonist clobenpropit (4 micromol/kg i.a.) abolished imetit-induced circulatory and oxygen uptake responses. Clobenpropit (4 micromol/kg i.a.) alone failed to affect the MBF, LDBF, AP, C and VO(2) values. Central administration of imetit (0.1 micromol i.c.v.) markedly increased AP and decreased MBF, LDBF, C and VO(2). Pretreatment with histamine H(3) receptor antagonist clobenpropit (0,4 micromol i.c.v.) diminished circulatory and metabolic responses to centrally injected imetit. Central histamine H(3) receptors blockade by clobenpropit evoked no significant changes in the mesenteric arterial and mucosal microcirculatory blood flow, intestinal metabolism and mean arterial pressure. We conclude that, peripheral histamine H(3) receptors when stimulated decreases vasoconstrictory tone of the mesenteric artery and precapillary structures and evokes increase of intestinal oxygen uptake. This might be in part due to inhibition of sympathetic postganglionic fibers vasopressor activity. Central histamine H(3) receptor stimulation activates vasoconstrictory sympathetic adrenergic system with possible involvement of other, presumably non-histaminergic receptors system. At basal conditions neither central nor perip

Topics: Animals; Blood Pressure; Drug Evaluation, Preclinical; Drug Therapy, Combination; Female; Imidazoles; Injections, Intra-Arterial; Injections, Intraventricular; Intestinal Mucosa; Intestines; Male; Microcirculation; Muscle, Smooth, Vascular; Oxygen Consumption; Rats; Rats, Wistar; Receptors, Histamine H3; Splanchnic Circulation; Tachycardia; Thiourea; Time Factors; Vasoconstriction

This study was performed to investigate whether or not the histamine H3-antagonist clobenpropit can ameliorate spatial memory deficits induced by MK-801 (0.3 microg per site) as evaluated by an eight-arm radial maze task of rats. A bilateral intrahippocampal (i.h.) injection of clobenpropit (5, 10 microg per site, dose-dependent) markedly improved the working and reference memory deficits induced by MK-801. Its ameliorating effect was potentiated by histidine, but completely antagonized by immepip (2.5 microg per site), a selective H3-agonist. alpha-Fluoromethylhistidine (FMH, 25 microg per site), a selective histidine decarboxylase inhibitor prevented the ameliorating effect of clobenpropit on the working memory deficits induced by MK-801. In addition, the H(1-antagonist pyrilamine, but not the H2-antagonist cimetidine, also inhibited the procognitive effects of clobenpropit. Both FMH and pyrilamine did not significantly modulate the effect of clobenpropit on reference memory. Therefore, the results of this study suggest that the procognitive effects of clobenpropit in MK-801-induced working memory deficits is mediated by increasing endogenous histamine release. In addition, the ameliorating effect of clobenpropit on reference memory might be due to the increased release of neurotransmitters other than histamine.

Topics: Analysis of Variance; Animals; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Histamine Antagonists; Imidazoles; Male; Maze Learning; Memory Disorders; Piperidines; Rats; Rats, Sprague-Dawley; Spatial Behavior; Thiourea

1. Our study was undertaken to investigate whether bacterial endotoxin/lipopolysaccharide (LPS) affects the neurogenic vasopressor response in rats in vivo by presynaptic mechanisms and, if so, to characterize the type of presynaptic receptor(s) operating in the initial phase of septic shock. 2. In pithed and vagotomized rats treated with pancuronium, electrical stimulation (ES) (1 Hz, 1 ms, 50 V for 10 s) of the preganglionic sympathetic nerve fibers or intravenous bolus injection of noradrenaline (NA) (1-3 nmol x kg(-1)) increased the diastolic blood pressure (DBP) by about 30 mmHg. Administration of LPS (0.4 and 4 mg x kg(-1)) under continuous infusion of vasopressin inhibited the neurogenic vasopressor response by 25 and 50%, respectively. LPS did not affect the increase in DBP induced by exogenous NA. 3. The LPS-induced inhibition of the neurogenic vasopressor response was counteracted by the cannabinoid CB(1) receptor antagonist SR 141716A (0.1 micromol x kg(-1)), but not by the CB(2) receptor antagonist SR 144528 (3 micromol x kg(-1)), the vanilloid VR1 receptor antagonist capsazepine (1 micromol x kg(-1)) or the histamine H(3) receptor antagonist clobenpropit (0.1 micromol x kg(-1)). The four antagonists by themselves did not affect the increase in DBP induced by ES or by injection of NA in rats not exposed to LPS. 4. We conclude that in the initial phase of septic shock, the activation of presynaptic CB(1) receptors by endogenously formed cannabinoids contributes to the inhibition of the neurogenic vasopressor response.

Topics: Animals; Autonomic Fibers, Postganglionic; Autonomic Fibers, Preganglionic; Blood Pressure; Camphanes; Capsaicin; Decerebrate State; Disease Models, Animal; Electric Stimulation; Germany; Imidazoles; Infusions, Intravenous; Lipopolysaccharides; Male; Norepinephrine; Piperidines; Pyrazoles; Rats; Rats, Wistar; Receptor, Cannabinoid, CB1; Receptors, Presynaptic; Rimonabant; Shock, Septic; Solvents; Thiourea; Vagotomy; Vasomotor System; Vasopressins

To investigate the mechanisms of histamine on chronic epilepsy induced by pentylenetetrazole (PTZ).. To induce chemical kindling, a subconvulsive dose (35mg/kg) of PTZ was ip injected every 48 h in rats. Behavior changes were observed for 30 min after every injection of PTZ.. Ip injection of histidine or icv injection of clobenpropit inhibited the development of kindling induced by PTZ, presenting prolonged latency for myoclonic jerks and clonic generalized seizures and depressed seizure stages in a dose-dependent manner. H(3)receptor agonist, immepip, and histidine decarboxylase, alpha-fluoromethylhistidine reversed the ameliorating effect of clobenpropit on seizure development in a dose-dependent manner.. Brain histamine plays an important role in protection against myoclonic jerks and clonic generalized clonic seizures and its action may be via H(3)receptor.

Topics: Animals; Brain; Chronic Disease; Dose-Response Relationship, Drug; Epilepsy; Histamine; Histidine; Imidazoles; Male; Pentylenetetrazole; Piperidines; Rats; Rats, Sprague-Dawley; Thiourea

The effects of histamine H3 antagonists on amygdaloid kindled and maximal electroshock seizures in rats were studied to determine their potential as new antiepileptic drugs. Under pentobarbital anesthesia, rats were fixed to a stereotaxic apparatus and a stainless steel guide cannula for drug administration was implanted into the lateral ventricle. In amygdaloid kindled seizures, electrodes were implanted into the right amygdala and electroencephalogram was recorded bipolarly; stimulation was applied bipolarly every day by a constant current stimulator and continued until a generalized convulsion was obtained. In the maximal electroshock (MES) seizure test, electroconvulsion was induced by stimulating animals through ear-clip electrodes, and the durations of tonic and clonic seizures were measured. Thioperamide, clobenpropit, iodophenpropit, VUF5514, VUF5515 and VUF4929 caused a dose-dependent inhibition of both seizure stage and afterdischarge (AD) duration of amygdaloid kindled seizures. The duration of tonic seizure induced by MES was also inhibited by H3 antagonists, but the duration of clonic seizures were unchanged. Among the H3 antagonists tested, clobenpropit and iodophenpropit were somewhat more potent than the other drugs on amygdaloid kindled seizures and MES seizures, respectively. These results indicate that some H3 antagonists may be useful as antiepileptic drugs, especially for secondary generalized seizures and/or tonic-clonic seizures in humans.

Topics: Amygdala; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Electroencephalography; Electroshock; Epilepsy, Tonic-Clonic; Histamine Agonists; Histamine Antagonists; Imidazoles; Injections, Intraventricular; Isothiuronium; Kindling, Neurologic; Lateral Ventricles; Male; Methylhistamines; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Seizures; Thiourea

Reactive hyperemia (RH) is an abrupt blood flow increase following release from mechanical occlusion of an artery, with restoration of intra-arterial pressure. The mechanism of this postocclusion increase in blood flow in the gut is multifactorial. Relaxation of intestinal resistance vessels, observed during RH, may involve myogenic, metabolic, hormonal and neurogenic factors. Evidence exists that histamine is an important endogenous mediator of various functions of the gut, including blood flow. The vascular effects of histamine in the intestinal circulation are due its agonistic action on histamine H1, H2 and H3 receptors. In the present study the hypothesis was tested that peripheral histamine H3 receptors are involved in the mediation of RH in the intestinal circulation. In anesthetized rats, anterior mesenteric artery blood flow (MBF) was determined with ultrasonic Doppler flowmeter, and arterial pressure (AP) was determined with a transducer. The increase in the volume of blood accumulating during RH (RH-volume), the peak increase of arterial blood flow (RH-peak response) and the duration of the hyperemia (RH-duration) were used to quantify RH after occluding the anterior mesenteric artery for 30, 60 and 120 s. Hyperemia parameters were determined before and after administration of the selective histamine H3 receptor antagonist clobenpropit. Pretreatment with clobenpropit was without any effect on control MBF and AP but significantly reduced most of RH responses. These findings support the hypothesis that histamine H3 receptors do not play any role in the control of intestinal vasculature at basal conditions but these receptors participate in the intestinal hyperemic reaction in response to complete temporal intestinal ischemia.

Topics: Animals; Blood Pressure; Female; Histamine Agonists; Histamine Antagonists; Hyperemia; Imidazoles; Infusions, Intra-Arterial; Intestinal Mucosa; Intestines; Male; Mesenteric Arteries; Mesenteric Vascular Occlusion; Rats; Rats, Wistar; Receptors, Histamine H3; Regional Blood Flow; Thiourea

Human, guinea pig and rat histamine H(3) receptors have been investigated at both pharmacological and molecular levels in recent years. Here we report the cloning, molecular, and pharmacological characterization of the mouse histamine H(3) receptor. The amino acid sequence of the mouse histamine H(3) receptor exhibits high homology to rat, guinea pig and human histamine H(3) receptors with 98%, 95%, 94% identities, respectively. The distribution of the mRNA encoding the mouse histamine H(3) receptor was predominant in the brain as detected by Reverse Transcription-Polymerase Chain Reaction (RT-PCR) and RNase protection assay. Although several splice forms have been reported for human, guinea pig and rat histamine H(3) receptor mRNAs, we did not detect equivalent isoforms in the mouse in several tissues by either RNase protection assay or robust Polymerase Chain Reaction (PCR) amplifications. Human embryonic kidney (HEK)-293 cells transiently transfected with mouse histamine H(3) receptor cDNA and Gq(i5) exhibited increases of intracellular Ca(2+) in response to histamine and several histamine H(3) receptor agonists. COS-7 (African green monkey kidney) cells transfected with mouse histamine H(3) receptor cDNA showed high affinity binding for histamine H(3) receptor ligands in competition binding assays. The pharmacological comparison of human, guinea pig, rat and mouse histamine H(3) receptors indicated that, as expected, the mouse histamine H(3) receptor exhibited a more similar pharmacological profile to the rat histamine H(3) receptor than to either the human or the guinea pig histamine H(3) receptor. Taken together, these findings allow a further appreciation of the histamine H(3) receptor at the molecular level and provide an additional species to assist in the pharmacological assessment of histamine H(3) receptor function.

Topics: Alternative Splicing; Amino Acid Sequence; Animals; Brain; Calcium; Cells, Cultured; Chlorocebus aethiops; Cloning, Molecular; Guinea Pigs; Histamine; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Mice; Molecular Sequence Data; Rats; Receptors, Histamine H3; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sequence Homology; Thiourea

This study was performed to investigate whether or not endogenous histamine can protect seizure development of pentylenetetrazole (PTZ)-induced kindling in rats. An intracerebroventricular (i.c.v.) injection with clobenpropit (5 and 10 microg), a representative H(3)-antagonist, significantly prolonged the onset of kindling and inhibited the seizure stages in a dose-dependent manner. Its action was significantly reversed by both immepip (2 microg, i.c.v.), an H(3)-agonist, and alpha-fluoromethylhistidine (alpha-FMH, 10 microg, i.c.v.), a selective histidine decarboxylase inhibitor. alpha-FMH (20 microg, i.c.v.) and pyrilamine (1 and 5 mg/kg i.p.), a classical H(1)-antagonist, markedly augmented the severity of seizure development of PTZ-induced kindling. Therefore, these results indicate that brain endogenous histamine plays a certain protective role on seizure development of PTZ-induced kindling in rats, and that its protective roles are mediated by H(1)-receptors.

Topics: Animals; Dose-Response Relationship, Drug; Drug Synergism; Histamine; Histamine Release; Histidine; Imidazoles; Injections, Intraventricular; Kindling, Neurologic; Male; Methylhistidines; Pentylenetetrazole; Piperidines; Pyrilamine; Rats; Rats, Sprague-Dawley; Seizures; Thiourea

1. Histamine (0.004-2 microm) induced a concentration-dependent shape change of human eosinophils, but not of neutrophils or basophils, detected as an increase in forward scatter (FSC) in the gated autofluorescence/forward scatter (GAFS) assay. 2. The histamine-induced eosinophil shape change was completely abolished by thioperamide (10 microm), an H3/H4 receptor antagonist, but was not inhibited by pyrilamine or cimetidine (10 microm), H1 and H2 receptor antagonists, respectively. The H4 receptor agonists, clobenpropit and clozapine (0.004-2 microm), which are also H3 receptor antagonists, both induced eosinophil shape change, which was inhibited by thioperamide (10 microm). The H3/H4 receptor agonists, imetit, R-alpha-methyl histamine and N-alpha-methyl histamine (0.004-2 microm) also induced eosinophil shape change. 3. Histamine induced actin polymerisation (0.015-10 microm), intracellular calcium mobilisation (10-100 microm) and a significant upregulation of expression of the cell adhesion molecule CD11b (0.004-10 microm) in eosinophils, all of which were inhibited by thioperamide (10-100 microm). In addition, the H4 receptor agonist/H3 receptor antagonist clozapine (20 microm) stimulated a rise in intracellular calcium in eosinophils. 4. Activation of H4 receptors by histamine (1 microm) primed eosinophils for increased chemotactic responses to eotaxin, but histamine (0.1-10 microm) did not directly induce chemotaxis of eosinophils. 5. Pertussis toxin (1 microg ml-1) inhibited shape change and actin polymerisation responses induced by histamine showing that these effects are mediated by coupling to a Galphai/o G-protein. 6. This study demonstrates that human eosinophils express functional H4 receptors and may provide a novel target for allergic disease therapy.

Topics: Actins; Calcium; CD11b Antigen; Cell Size; Chemokine CCL11; Chemokines, CC; Chemotaxis; Clozapine; Cytoskeleton; Dose-Response Relationship, Drug; Eosinophils; Histamine; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Pertussis Toxin; Piperidines; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Thiourea; Up-Regulation

The participation of histamine H(3) receptors in the regulation of skin vascular permeability changes in mast cell-deficient mice was studied. Although intradermal injection of histamine H(3) antagonists, iodophenpropit and clobenpropit, at a dose of 100 nmol/site caused significant increases in skin vascular permeability in both mast cell-deficient (WBB6F1 W/W(v)) and wild-type (WBB6F1 +/+) mice, this response was significantly lower in mast cell-deficient mice than in the wild-type controls. Histamine also caused dose-related increases in skin vascular permeability in both wild-type and mast cell-deficient mice. Significant effects were observed at doses of 10 and 100 nmol/site, and no significant difference in skin vascular permeability was observed between mast cell-deficient and wild-type mice. However, histamine contents of dorsal skin in mast cell-deficient mice were significantly lower than in wild-type mice. In addition, the H(1) antagonists diphenhydramine and chlorpheniramine and the NK(1) antagonists, L-732,138 and L-733,060, were able to antagonize H(3) antagonist-induced skin vascular permeability. These results indicated that blockade of H(3) receptors by H(3) antagonists induce skin vascular permeability through mast cell-dependent mechanisms. In addition, histamine and, to a lesser extent substance P are involved in the reaction.

Topics: Animals; Capillary Permeability; Chlorpheniramine; Diphenhydramine; Evans Blue; Female; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Injections, Intradermal; Injections, Intravenous; Isothiuronium; Mast Cells; Mice; Mice, Mutant Strains; Piperidines; Receptors, Histamine H3; Skin; Thiourea; Tryptophan

The purpose of this study was to investigate whether or not clobenpropit, a selective and potent histamine H(3) receptor antagonist, can protect from pentylenetetrazole (35 mg/kg)-kindled seizures in rats. I.c.v. injection with clobenpropit (10 and 20 microg) significantly delayed the seizure stage and prolonged the latency to the onset of myoclonic jerks and the latency to the clonic generalized seizure in a dose-dependent manner. The protection by clobenpropit (20 microg) was completely antagonized by both immepip (5 and 10 microg, i.c.v.), a selective potent histamine H(3) receptor agonist, and alpha-fluoromethylhistidine (alpha-FMH, 50 microg, i.c.v.), a selective histidine decarboxylase inhibitor. In addition, clobenpropit markedly potentiated the histidine (100 and 200 mg/kg)-induced inhibition of pentylenetetrazole-kindled seizures. Pyrilamine (2 and 5 microg, i.c.v.) reversed the inhibition of pentylenetetrazole-kindled seizures induced by clobenpropit, whereas cimetidine had no effect even at a high dose of 5 microg. These results indicate that clobenpropit protects against pentylenetetrazole-kindled seizures in rats, and that its action is mainly due to the activation of endogenous histamine by blocking autoinhibitory presynaptic histamine H(3) receptors.

Topics: Animals; Dose-Response Relationship, Drug; Imidazoles; Male; Pentylenetetrazole; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Seizures; Thiourea

1. The extraneuronal monoamine transporter from rat (EMTr) was heterologously expressed by stable transfection in human embryonic kidney 293 cells and characterized in radiotracer experiments. 2. EMTr-mediated uptake of 1-methyl-4-phenylpyridinium (MPP(+)) was saturable, with a K(m) of 151 micro mol l(-1) and V(max) of 7.5 nmol min(-1) mg protein(-1). 3. Compared to the human orthologue EMTh (gene symbol SLC22A3), EMTr was about two orders of magnitude more resistant to most inhibitors, including disprocynium24 and corticosterone. 4. Strikingly, inhibitors and substrates at low concentration stimulated EMTr-mediated transport above control level with MPP(+) and noradrenaline as substrate, but not with cimetidine. Results were confirmed with EMT from mouse. 5. With different IC(50)-values for different substrates, the standard method to calculate K(i)-values is not applicable. 6. Our experiments suggest that activation is not caused by changes in membrane potential or trans-stimulation. Since the extent of activation depends markedly on the chemical structure of the monitored substrate, involvement of a receptor-mediated signalling pathway or recruitment of transporter reserve are implausible. 7. To explain activation, we present a kinetic model which assumes two binding sites for substrate or inhibitor per transporter entity, possibly resulting from the assembly of homodimers. 8. Activation explains previous reports about inhibitor-insensitive catecholamine transport in rat brain. 9. We speculate that activation may serve to keep the transporter working for specific substrates in the face of inhibitors.

Topics: 1-Methyl-4-phenylpyridinium; Animals; Biological Transport; Cell Line; Cimetidine; Cloning, Molecular; Corticosterone; Dose-Response Relationship, Drug; Gene Expression; Genetic Vectors; Humans; Imidazoles; Kinetics; Mice; Norepinephrine; Organic Cation Transport Proteins; Papaverine; Piperidines; Quinolines; Rats; Thiourea; Transfection; Tritium

Histamine H3 receptors modulate histamine synthesis, although little is known about the transduction mechanisms involved. To investigate this issue, we have used a preparation of rat brain cortical miniprisms in which histamine synthesis can be modulated by depolarization and by H3 receptor ligands. When the miniprisms were incubated in presence of forskolin, dibutyryl-cAMP, or 3-isobutyl-1-methylxanthine (IBMX), histamine synthesis was stimulated in 34, 29, and 47%, respectively. These stimulations could be prevented by the selective cAMP protein kinase blocker Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPs). Preincubation with the H3 receptor agonist imetit prevented IBMX- (100% blockade) and forskolin- (70% blockade) induced stimulation of histamine synthesis. The H3 inverse agonist thioperamide enhanced histamine synthesis in the presence of 1 mM IBMX or 30 mM potassium (+47 and +45%, respectively). Similarly, the H3 antagonist clobenpropit enhanced histamine synthesis in the presence of 30 mM potassium (+ 59%). The cAMP-dependent protein kinase blockers Rp-cAMPs and PKI14-22 could impair the effects of thioperamide and clobenpropit, respectively. These results indicate that the adenylate cyclase-protein kinase A pathway is involved in the modulation of histamine synthesis by H3 autoreceptors present in histaminergic nerve terminals.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Brain; Bucladesine; Colforsin; Cyclic AMP; Drug Interactions; Histamine; Imidazoles; In Vitro Techniques; Male; Piperidines; Potassium; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Thionucleotides; Thiourea

1. A study was made of the regulation of [(3)H]-gamma-aminobutyric acid ([(3)H]-GABA) release from slices of rat striatum by endogenous dopamine and exogenous histamine and a histamine H(3)-agonist. Depolarization-induced release of [(3)H]-GABA was Ca(2+)-dependent and was increased in the presence of the dopamine D(2) receptor family antagonist, sulpiride (10 microM). The sulpiride-potentiated release of [(3)H]-GABA was strongly inhibited by the dopamine D(1) receptor family antagonist, SCH 23390 (1 microM). Neither antagonist altered basal release. 2. The 15 mM K(+)-induced release of [(3)H]-GABA in the presence of sulpiride was inhibited by 100 microM histamine (mean inhibition 78+/-3%) and by the histamine H(3) receptor-selective agonist, immepip, 1 microM (mean inhibition 81+/-5%). The IC(50) values for histamine and immepip were 1.3+/-0.2 microM and 16+/-2 nM, respectively. The inhibitory effects of histamine and immepip were reversed by the H(3) receptor antagonist, thioperamide, 1 microM. 3. The inhibition of 15 mM K(+)-induced [(3)H]-GABA release by immepip was reversed by the H(3) receptor antagonist, clobenpropit, K(d) 0.11+/-0.04 nM. Clobenpropit alone had no effect on basal or stimulated release of [(3)H]-GABA. 4. Elevated K(+) caused little release of [(3)H]-GABA from striatal slices from reserpinized rats, unless the D(1) partial agonist, R(+)-SKF 38393, 1 microM, was also present. The stimulated release in the presence of SKF 38393 was reduced by 1 microM immepip to the level obtained in the absence of SKF 38393. 5. These observations demonstrate that histamine H(3) receptor activation strongly inhibits the dopamine D(1) receptor-dependent release of [(3)H]-GABA from rat striatum; primarily through an interaction at the terminals of GABA neurones.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Calcium; Dopamine; Dopamine D2 Receptor Antagonists; gamma-Aminobutyric Acid; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; In Vitro Techniques; Male; Membrane Potentials; Neostriatum; Piperidines; Potassium; Rats; Rats, Wistar; Receptors, Dopamine D1; Receptors, Dopamine D2; Receptors, Histamine H3; Reserpine; Sulpiride; Thiourea

This study was designed to determine if the histamine H3 receptor agonist R-alpha-methylhistamine would play a role in modulation of sympathetically evoked mydriasis in anesthetized rats, and if so, to ascertain the specific receptor subtype(s) involved. Reproducible frequency-response curves of pupillary dilation were generated by stimulation of the cervical preganglionic sympathetic nerve (1-32 Hz). Systemic administration of R-alpha-methylhistamine (0.3-3.0 mg kg(-1)) produced a dose-related inhibition of the evoked mydriasis. The greatest inhibition was seen at lower frequency levels, with about 43% depression observed at 2 Hz. The specific histamine H3 receptor antagonist, clobenpropit (3.0 mg kg(-1), i.v.), blocked the inhibitory effect of R-alpha-methylhistamine, whereas neither the histamine H2 receptor antagonist, cimetidine (5.0 mg kg(-1), i.v.), nor the histamine H1 receptor antagonist, chlorpheniramine (0.5 mg kg(-1), i.v.), was effective. The histamine H2 receptor agonist, dimaprit (10 mg kg(-1), i.v.), was also without effect on the evoked mydriasis. R-alpha-methylhistamine (3.0 mg kg(-1)) did not inhibit phenylephrine-induced mydriasis. These results support the conclusion that R-alpha-methylhistamine produces inhibition of sympathetically evoked mydriasis via histamine H3 receptor stimulation, presumably by an action on presynaptic histamine H3 receptors.

Topics: Animals; Chlorpheniramine; Cimetidine; Dimaprit; Dose-Response Relationship, Drug; Electric Stimulation; Histamine Agonists; Histamine Antagonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Imidazoles; Male; Methylhistamines; Mydriasis; Pupil; Rats; Rats, Sprague-Dawley; Sympathetic Nervous System; Thiourea

Thioperamide, the prototypical histamine H(3) receptor antagonist, acts at the brain histamine H(3) autoreceptor to promote the release and metabolism of neuronal histamine, resulting in higher brain levels of the metabolite tele-methylhistamine. However, unlike thioperamide, several new histamine H(3) receptor antagonists enter the central nervous system (CNS), block brain histamine H(3) receptors and increase histamine release without increasing brain tele-methylhistamine levels. Experiments were performed presently in an attempt to understand these results. Consistent with previous findings, thioperamide significantly increased the content and synthesis rate of tele-methylhistamine in mouse and rat brain. In contrast, the histamine H(3) receptor antagonists GT-2227 (4-(6-cyclohexylhex-cis-3-enyl)imidazole) and clobenpropit did not affect tele-methylhistamine synthesis rate in mouse whole brain. The histamine H(3) receptor ligand GT-2016 (5-cyclohexyl-1-(4-imidazol-4-ylpiperidyl)pentan-1-one) had no effect on tele-methylhistamine levels in any rat brain region and decreased tele-methylhistamine synthesis rates in the mouse whole brain. To examine the possibility that these histamine H(3) receptor antagonists might prevent the methylation of newly released histamine, they were co-administered with thioperamide to determine their effects on the thioperamide-induced stimulation of tele-methylhistamine synthesis. GT-2016 significantly reduced the thioperamide-induced activation of tele-methylhistamine synthesis in mouse whole brain and in several regions of rat brain. Although further clarification is needed, these results suggest that some histamine H(3) receptor antagonists may promote the release of neuronal histamine, but also act to reduce histamine methylation in vivo by an unknown mechanism.

Topics: Analysis of Variance; Animals; Binding Sites; Brain; Histamine; Histamine Antagonists; Imidazoles; Male; Methylhistamines; Mice; Pargyline; Piperidines; Rats; Receptors, Histamine H3; Thiourea

The effect of clobenpropit on regional cerebral blood flow (rCBF) was investigated in the rat hippocampus.. rCBF was determined in the hippocampus by the hydrogen clearance method. The blood pressure was measured by a tail-cuff plethysmograph.. Intracerebroventricular (icv) injection of clobenpropit (20, 50 microg), a representative H3-antagonist, dose-dependently and significantly increased rCBF in the hippocampus. The increase of rCBF induced by clobenpropit was enhanced by metoprine (1, 2 mg/kg), a selective histamine N-methyltransferase inhibitor; however, was antagonized by an H3-agonist, (R)-alpha-methylhistamine (5 microg), an H(1)-antagonist, mepyramine (5-10 mg/kg), and an H2-antagonist, zolantidine (10 mg/kg). Clobenpropit caused no apparent effects on blood pressure even at a high dose of 50 microg.. These results suggest that brain endogenous histamine may contribute to increase rCBF in the rat hippocampus via both the post-synaptic H1-, H2-receptors and the pre-synaptic H3-receptor.

Topics: Animals; Cerebrovascular Circulation; Dose-Response Relationship, Drug; Hippocampus; Histamine Agonists; Histamine Antagonists; Imidazoles; Injections, Intraventricular; Male; Methylhistamines; Pyrimethamine; Rats; Rats, Wistar; Thiourea

The effects of pertussis toxin (PT) and the role of histaminergic H(1), H(2) and H(3) receptor blockade on the actions of histamine on blood pressure, heart rate, blood gas values, and mortality were studied in anaesthetized rats. Four days after treatment with PT, histamine dose-dependently decreased mean arterial blood pressure (MAP) and PT enhanced the histamine-induced decrease in MAP. In the PT but not in the inactivated PT (IPT) or saline treated group three out of six animals died after the highest dose of histamine (300 mg kg(-1), i.v.) In order to determine the type of histamine receptor that mediates HS, 4 days after PT the selective antagonists mepyramine (H(1)), cimetidine (H(2)) and clobenpropit (H(3)) were administered 20 min before the challenge with histamine. Mepyramine completely inhibited both the enhanced histamine-induced decrease in MAP and mortality brought about by PT. Cimetidine and clobenpropit had no protective effects, but rather enhanced the histamine-induced mortality elicited by PT. The present study shows that PT caused HS in rats which is primarily mediated via H(1) and secondarily via H(2) and H(3) receptors. These results are considered to be a first step in the elucidation of the mechanism(s) of the HS test used in the quality control of acellular pertussis vaccine.

Topics: Animals; Blood Gas Analysis; Blood Pressure; Cimetidine; Drug Interactions; Histamine; Histamine Antagonists; Imidazoles; Male; Pertussis Toxin; Pyrilamine; Rats; Rats, Wistar; Receptors, Histamine; Thiourea; Virulence Factors, Bordetella

The effects of GABAmimetic drugs on inhibition of amygdaloid kindled seizures induced by clobenpropit were investigated to clarify the relationship between histaminergic and GABAergic systems in seizures. I.p. injection of clobenpropit caused dose-dependent inhibition of amygdaloid kindled seizures. GABAmimetic drugs such as diazepam, sodium valproate and muscimol also inhibited amygdaloid kindled seizures in a dose-dependent manner. Diazepam at doses of 0.2 and 0.5 mg/kg, which showed no significant effect on amygdaloid kindled seizures when used separately, significantly potentiated the effect of clobenpropit. Similar findings were observed with sodium valproate and muscimol at doses of 100 mg/kg and 5 ng, respectively, although neither showed any significant effects when administered separately. Bicuculline caused significant antagonism of the inhibition of amygdaloid kindled seizures induced by clobenpropit, while the effect of diazepam was not antagonized by diphenhydramine. These results suggested that inhibition of amygdaloid kindled seizures induced by histamine is closely associated with the actions of GABA.

Topics: Amygdala; Animals; Bicuculline; Diazepam; gamma-Aminobutyric Acid; Histamine; Imidazoles; Kindling, Neurologic; Male; Muscimol; Rats; Rats, Wistar; Seizures; Thiourea; Valproic Acid

The distribution of histaminergic fibers in the zebrafish brain was recently shown to resemble that in mammals. Expression of L-histidine decarboxylase (HDC) mRNA was shown only in the area corresponding to that expressing HDC in mammals. This indicates that the zebrafish could be a useful model for studies on the function of the brain histaminergic system. In this study an H(3)-like receptor is identified in zebrafish brain. With binding studies using N-alpha-[(3)H]methylhistamine on zebrafish brain sections, signals were observed in several regions. Highest densities were detected in optic tectum and hypothalamus. The autoradiographic signal was abolished completely by the H(3)-specific antagonist clobenpropit and significantly reduced by another H(3) antagonist, thioperamide. Histamine and immepip induced an increase of guanosine 5'-(gamma-[(35)S]thio)triphosphate binding in several areas of the zebrafish brain. The activation was blocked with clobenpropit but not with cimetidine or mepyramine. These results indicate that the zebrafish has a histamine H(3)-like receptor that functionally interacts with the inhibitory, G(i)/G(o), class of G proteins. No previous evidence for a histamine receptor in zebrafish exists. The receptor described here is apparently similar to the mammalian H(3) receptor, making this the first description of a histamine H(3)-like receptor in a lower vertebrate.

Topics: Animals; Autoradiography; Brain; Cimetidine; Female; Guanosine 5'-O-(3-Thiotriphosphate); Histamine Agonists; Histamine Antagonists; Imidazoles; Kinetics; Male; Methylhistamines; Piperidines; Pyrilamine; Radioligand Assay; Receptors, Histamine H3; Sulfur Radioisotopes; Thiourea; Tritium; Zebrafish

The effect of histamine H3-receptor antagonist, clobenpropit (VUF9153) on spatial memory deficits induced by scopolamine was investigated in rats.. Eight-Arm radial maze performance was used to measure spatial memory in rats, and the brain regions were subsequently dissected and histamine contents were determined by HPLC.. Intracerebroventricular (icv) injection of clobenpropit (50 micrograms) ameliorated memory impairment induced by scopolamine in both parameters of radial maze performance. The amelioration induced by clobenpropit was antagonized by an H3-agonist, (R)-alpha-methylhistamine (5-10 micrograms). alpha-Fluoromethylhistidine (10, 20 micrograms), a histidine decarboxylase inhibitor, also effectively reversed clobenpropit-induced ameliorating effects.. The brain histamine H3-receptor antagonists are highly related to the spatial memory, and this action may be due to cholinergic neurons.

Topics: Animals; Brain; Histamine; Histamine Antagonists; Imidazoles; Injections, Intraventricular; Male; Maze Learning; Memory Disorders; Rats; Rats, Wistar; Scopolamine; Thiourea

Stimulation-evoked 3H-noradrenaline release in human cerebrocortical slices was inhibited by histamine (in a manner sensitive to clobenpropit) and by imetit, suggesting H3 receptor-mediated inhibition of noradrenaline release in human brain.

Topics: Animals; Brain; Cerebral Cortex; Dimethindene; Electric Stimulation; Hippocampus; Histamine; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; Male; Mice; Mice, Inbred Strains; Norepinephrine; Piperidines; Ranitidine; Receptors, Histamine H3; Thiourea; Tritium

Studies were performed to assess the functional activity of histamine H3 receptors on neurogenic sympathetic end organ responses in cryopreserved human saphenous vein. (R)-alpha-methylhistamine inhibited electrical field stimulation-evoked contractile responses in a dose dependent manner (pD2 = 8.20). Prazosin (1 microM) and tetrodotoxin (1 microM) blocked the electrical field stimulation-evoked contractile responses in human saphenous vein indicating a sympathetic neural origin of these contractions. The histamine H3 antagonists thioperamide (pA2 = 8.41) and clobenpropit (pA2 = 10.10) produced parallel rightward shifts in the concentration response curve to (R)-alpha-methylhistamine in human saphenous vein and guinea pig ileum (pA2 = 8.59 and 9.83, respectively). Pretreatment with (R)-alpha-methylhistamine (1 microM) did not alter contractions to exogenous norepinephrine in human saphenous vein. In addition, clonidine (pD2 = 10.28) inhibited electrical field stimulation-evoked contractile responses in human saphenous vein which were blocked by yohimbine (30 nM, pA2 = 9.92) but did not alter the (R)-alpha-methylhistamine dose response curve. These results demonstrate the presence of functional presynaptic histamine H3 heteroreceptors on cryopreserved human saphenous vein sympathetic nerves that, upon activation, attenuate electrical field stimulation-evoked contractile responses in this vessel.

Topics: Adrenergic alpha-Antagonists; Aged; Animals; Dose-Response Relationship, Drug; Electric Stimulation; Female; Guinea Pigs; Histamine Agonists; Histamine Antagonists; Humans; Ileum; Imidazoles; In Vitro Techniques; Male; Methylhistamines; Middle Aged; Muscle Contraction; Piperidines; Prazosin; Receptors, Histamine H3; Saphenous Vein; Tetrodotoxin; Thiourea; Yohimbine

Histamine H3 receptor ligands have been proposed to be of potential therapeutic interest for the treatment of different central nervous system disorders; however, the psychopharmacological properties of these drugs have not been studied extensively. In this work, we investigated the possible involvement of histamine H3 receptor function in experimental models of anxiety (elevated plus-maze) and depression (forced swimming test). Male Sprague-Dawley rats were treated i.p. with the histamine H3 receptor agonist R-alpha-methylhistamine (10 mg/kg) or the histamine H3 receptor antagonist thioperamide (0.2, 2 and 10 mg/kg) and 30 min afterwards the time spent in the open arms of an elevated plus-maze was registered for 5 min. The immobility time of male OF1 mice in the forced swimming test was recorded for 6 min, 1 h after the i.p. administration of R-alpha-methylhistamine (10 and 20 mg/kg), thioperamide (0.2, 2, 10 and 20 mg/kg) or another histamine H3 receptor antagonist, clobenpropit (5 mg/kg). The locomotor activity of mice was checked in parallel by means of an activity meter. Both saline controls and active drug controls were used in all the paradigms. Neither thioperamide nor R-alpha-methylhistamine significantly changed animal behaviour in the elevated plus-maze. R-alpha-methylhistamine and the higher dose of thioperamide assayed (20 mg/kg) were also inactive in the forced swimming test. By contrast, thioperamide (0.2-10 mg/kg) dose-dependently decreased immobility, the effect being significant at 10 mg/kg (33% reduction of immobility); clobenpropit produced an effect qualitatively similar (24% reduction of immobility). None of these histamine H3 receptor antagonists affected locomotor activity. These preliminary results suggest that the histamine H3 receptor blockade could be devoid of anxiolytic potential but have antidepressant effects. Besides, the stimulation of these receptors does not seem to be followed by changes in the behavioural parameters studied.

Topics: Analysis of Variance; Animals; Anxiety; Depression; Disease Models, Animal; Histamine Agonists; Histamine Antagonists; Imidazoles; Ligands; Male; Maze Learning; Methylhistamines; Mice; Motor Activity; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Swimming; Thiourea

1 We have investigated the binding of a novel histamine H3-receptor antagonist radioligand, [3H]- clobenpropit ([3H]-VUF9153), to guinea-pig cerebral cortex membranes. 2 Saturation isotherms for [3H]-clobenpropit appeared biphasic. Scatchard plots were curvilinear and Hill plot slopes were significantly less than unity (0.63+/-0.03; n = 12+/-s.e.mean). The radioligand appeared to label two sites in guinea-pig cerebral cortex membranes with apparent affinities (pKD') of 10.91+/-0.12 (Bmax = 5.34+/-0.85 fmol mg(-1) original wet weight) and 9.17+/-0.16 (Bmax = 23.20+/-6.70 fmol mg(-1)). 3 In the presence of metyrapone (3 mM) or sodium chloride (100 mM), [3H]-clobenpropit appeared to label a homogeneous receptor population (Bmax=3.41+/-0.46 fmol mg-1 and 3.49+/-0.44 fmol mg(-1), pKD' = 10.59+/-0.17 and 10.77+/-0.02, respectively). Scatchard plots were linear and Hill slopes were not significantly different from unity (0.91+/-0.04 and 0.99+/-0.02, respectively). Granisetron (1 microM), rilmenidine (3 microM), idazoxan (0.3 microM), pentazocine (3 microM) and 1,3-di-(2-tolyl)guanidine (0.3 microM) had no effect on the binding of [3H]-clobenpropit. 4 The specific binding of [3H]-clobenpropit appeared to reach equilibrium after 25 min at 21+/-3 degrees C and remained constant for >180 min. The estimated pKD' (10.27+/-0.27; n = 3+/-s.e.mean) was not significantly different from that estimated by saturation analysis in the presence of metyrapone. 5 A series of histamine H3-receptor ligands expressed affinity values for sites labelled with [3H]-clobenpropit which were not significantly different from those estimated when [3H]-R-alpha-MH was used to label histamine H3-receptors in guinea-pig cerebral cortex membranes.

Topics: Animals; Binding, Competitive; Cerebral Cortex; Guinea Pigs; Histamine Antagonists; Imidazoles; In Vitro Techniques; Kinetics; Metyrapone; Piperidines; Radioligand Assay; Receptors, Histamine H3; Thiourea; Tritium

In previous research we found that pre-training administration of histamine H3 receptor agonists such as (R)-alpha-methylhistamine and imetit impaired rat performance in object recognition and a passive avoidance response at the same doses at which they inhibited the release of cortical acetylcholine in vivo. Conversely, in the present study we report that the post-training administration of (R)-alpha-methylhistamine and imetit failed to affect rat performance in object recognition and a passive avoidance response, suggesting that H3 receptor influences the acquisition and not the recall processes. We also investigated the effects of two H3 receptor antagonists, thioperamide and clobenpropit, in the same behavioral tasks. Pre-training administration of thioperamide and clobenpropit failed to exhibit any procognitive effects in normal animals but prevented scopolamine-induced amnesia. However, also post-training administration of thioperamide prevented scopolamine-induced amnesia. Hence, the ameliorating effects of scopolamine-induced amnesia by H3 receptor antagonism are not only mediated by relieving the inhibitory action of cortical H3 receptors, but other mechanisms are also involved. Nevertheless, H3 receptor antagonists may have implications for the treatment of degenerative disorders associated with impaired cholinergic function.

Topics: Amnesia; Analysis of Variance; Animals; Avoidance Learning; Behavior, Animal; Cognition; Histamine Agonists; Histamine Antagonists; Imidazoles; Injections, Intraperitoneal; Injections, Subcutaneous; Male; Methylhistamines; Pattern Recognition, Visual; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Scopolamine; Thiourea

Topics: Acetylcholine; Animals; Cerebral Cortex; Cimetidine; Electroencephalography; Histamine; Histamine H1 Antagonists; Histamine H2 Antagonists; Imidazoles; Male; Neurons; Rats; Rats, Wistar; Substantia Innominata; Telencephalon; Thiourea; Triprolidine

We investigated the effects of histamine H3-receptor ligands on hippocampal synaptic transmission by using anesthetized rats in vivo. The medial perforant path was stimulated, and the population excitatory postsynaptic potential (pEPSP) and population spike were recorded from the granule cell layer of the dentate gyrus. Intracerebroventricular injection of the H3-receptor agonist (R)-alpha-methylhistamine decreased both the pEPSP and population spike, while H3-receptor antagonists, clobenpropit and thioperamide, increased both the pEPSP and population spike. These results suggest that the histaminergic system plays a role in inhibition of hippocampal synaptic excitation via the H3 receptor.

Topics: Animals; Dentate Gyrus; Excitatory Postsynaptic Potentials; Histamine Antagonists; Imidazoles; Injections, Intraventricular; Male; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Synaptic Transmission; Thiourea

The effects of histamine H3-receptor antagonists, thioperamide, and clobenpropit on amygdaloid kindled seizures were investigated in rats. Both intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) injections of H3-antagonists resulted in a dose-related inhibition of amygdaloid kindled seizures. An inhibition induced by thioperamide was antagonized by an H3-agonist [(R)-alpha-methylhistamine] and H1-antagonists (diphenhydramine and chlorpheniramine). On the other hand, an H2-antagonist (cimetidine and ranitidine) caused no antagonistic effect. Metoprine, an inhibitor of N-methyltransferase was also effective in inhibiting amygdaloid kindled seizure, and this effect was augmented by thioperamide treatment.

Topics: Amygdala; Animals; Brain Chemistry; Enzyme Inhibitors; Histamine Antagonists; Histamine N-Methyltransferase; Imidazoles; Injections, Intraventricular; Kindling, Neurologic; Male; Piperidines; Pyrimethamine; Rats; Rats, Wistar; Receptors, Histamine H3; Seizures; Thiourea

IL-12 is essential for T helper 1 (Th1) development and inhibits the induction of Th2 responses. Atopic diseases, which are characterized by Th2 responses, are associated with the overproduction of histamine. Here we present evidence that histamine, at physiological concentrations, strongly inhibits human IL-12 p40 and p70 mRNA and protein production by human monocytes. The use of specific histamine receptor antagonists reveals that this inhibition is mediated via the H2 receptor and induction of intracellular cAMP. The inhibition of IL-12 production is independent of IL-10 and IFN-gamma. The observation that histamine strongly reduces the production of the Th1-inducing cytokine IL-12 implies a positive feedback mechanism for the development of Th2 responses in atopic patients.

Topics: Dinoprostone; Histamine; Histamine Agonists; Histamine Antagonists; Histamine H2 Antagonists; Humans; Imidazoles; Interleukin-12; Interleukins; Monocytes; Ranitidine; Receptors, Histamine H2; RNA, Messenger; Thiourea; Triprolidine

The anticonvulsant activity of clobenpropit, an isothiourea derivative of histamine and potent H3-receptor antagonist, was investigated in two representative seizure models in mice. In the maximal electroshock seizure threshold test, clobenpropit dose-dependently raised the electroconvulsive threshold for tonic (hindlimb extension) seizures, but a significant increase of about 15% was determined only at the high dose of 40 mg/kg i.p. The protective action of this drug was reduced by immepip and (R)-alpha-methylhistamine, selective H3-receptor agonists. In co-medication with two standard antiepileptics, clobenpropit (20 and 40 mg/kg) significantly increased the anticonvulsant effectiveness of carbamazepine and tended to increase the effectiveness of valproate. Additional studies indicated that the high dose of clobenpropit also significantly enhanced the plasma carbamazepine concentration. One the other hand, in the s.c. PTZ seizure threshold test clobenpropit revealed no protective effects. In the rotarod ataxia test, impaired motor function was observed at 80 mg/kg clobenpropit. In conclusion, the present findings indicated no pronounced anticonvulsant effects of clobenpropit against generalized tonic as well as clonic seizures.

Topics: Animals; Anticonvulsants; Behavior, Animal; Carbamazepine; Differential Threshold; Electroshock; Histamine Antagonists; Imidazoles; Male; Mice; Motor Activity; Pentylenetetrazole; Seizures; Thiourea; Valproic Acid

Acute inflammation of the intestine is associated with motility changes. We investigated the acute effect of inflammatory mediators such as interleukin-1beta, interleukin-2 and tumor necrosis factor-alpha (TNF-alpha) on electrically stimulated ascending and descending reflex responses of the rat small intestine. Exogenous application of interleukin-1beta caused a concentration-dependent inhibition of the oral contraction (0.1 ng/ml: -22.9+/-3.8%, 10 ng/ml: -57.0+/-7.4%, P < 0.05, n=10) but had no effect on anal relaxation. The interleukin-1 receptor antagonist alone had no significant effect on the reflex response, but prevented the inhibitory effect of interleukin-1beta (10 ng/ml: -3.9+/-11.4%, n=8). Interleukin-2 and TNF-alpha had no significant effect on the oral contractile and the anal inhibitory response (n.s., n=10). Using reverse transcriptase polymerase chain reaction (RT-PCR) the presence of mRNA of the interleukin-1 receptor was demonstrated in the rat small intestine. Preincubation of the preparation with indomethacin (10(-6) M), the histamine H1 receptor antagonist, pyrilamine (10(-8) M), and the histamine H3 receptor antagonist, clobenpropit (10(-8) M), decreased the oral contraction by 60.1+/-7.7%, 42.8+/-6.9% and 44.4+/-14.2% as well as the anal relaxation. These data suggest that acute administration of interleukin-1beta inhibits the ascending and descending contractile reflex pathway and this effect seems not to be mediated by prostaglandins or histamine receptors.

Topics: Animals; Cyclooxygenase Inhibitors; Electric Stimulation; Histamine Antagonists; Imidazoles; In Vitro Techniques; Indomethacin; Interleukin-1; Interleukin-2; Intestine, Small; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Muscles; Pyrilamine; Ranitidine; Rats; Rats, Wistar; Receptors, Histamine H1; Receptors, Histamine H2; Receptors, Histamine H3; Receptors, Interleukin-1; Reflex; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Thiourea; Tumor Necrosis Factor-alpha

We investigated the effect of the new potent and selective histamine H3 receptor agonist, immepip, and the histamine H3 receptor antagonist, clobenpropit, on in vivo neuronal histamine release from the anterior hypothalamic area of urethane-anesthetized rats, using microdialysis. Intrahypothalamic perfusion with immepip at concentrations of 1 and 10 nM reduced histamine release to 75% and 35% of its basal level, respectively. Peripheral injection of immepip (5 mg/kg) caused a sustained decrease in histamine release of 50%. Clobenpropit potently increased histamine release after intrahypothalamic perfusion. The maximal increase in histamine release was 2-fold, observed at a concentration of 10 nM clobenpropit. Peripheral injection of clobenpropit (5-15 mg/kg) increased histamine release to about 150% of the basal value. A more marked increase in histamine release was found after injection of the histamine H3 receptor antagonist, thioperamide (5 mg/kg). In conclusion, intrahypothalamic perfusion of the histamine H3 receptor agonist, immepip and the histamine H3 receptor antagonist, clobenpropit, potently and oppositely modulated in vivo histamine release from the anterior hypothalamic area. The decreased histamine release after peripheral injection of immepip indicates that this novel agonist readily crosses the blood-brain barrier, making it a potential candidate for in vivo histamine H3 receptor studies. The differential increase in histamine release after peripheral injection of clobenpropit and thioperamide is discussed.

Topics: Animals; Histamine Agonists; Histamine Antagonists; Histamine Release; Hypothalamus; Imidazoles; Injections, Subcutaneous; Male; Microdialysis; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Thiourea

Our previous results demonstrate the occurrence of presynaptic inhibitory histamine H3 receptors on sympathetic neurons innervating resistance vessels of the pithed rat. The present study, in which new H3 receptor ligands with increased potency and selectivity (imetit, clobenpropit) were used, was designed to further explore the role of H3 receptors in the regulation of the rat cardiovascular system. In particular we were interested whether these receptors may be activated by endogenous histamine and whether they are detectable in an experimental model of hypertension. All experiments were performed on pithed and vagotomized rats treated with rauwolscine 1 mumol/kg. In normotensive Wistar rats the electrical (1 Hz, 1 ms, 50 V for 20 s) stimulation of the preganglionic sympathetic nerve fibres increased diastolic blood pressure by about 35 mmHg. Two H3 receptor agonists, R-(-)-alpha-methylhistamine and imetit, inhibited the electrically induced increase in diastolic blood pressure in a dose-dependent manner. The maximal effect (about 25%) was obtained for R-(-)-alpha-methylhistamine at about 10 mumol/kg and for imetit at about 1 mumol/kg. Two H3 receptor antagonists, thioperamide 1 mumol/kg and clobenpropit 0.1 mumol/kg, attenuated the inhibitory effect of imetit. The neurogenic vasopressor response was increased by about 15% by thioperamide 1 mumol/kg and clobenpropit 0.1 mumol/kg and decreased by 25% by the histamine methyltransferase inhibitor metoprine 37 mumol/kg. R-(-)-alpha-Methylhistamine, imetit, thioperamide, clobenpropit and metoprine did not affect the vasopressor response to exogenously added noradrenaline 0.01 mumol/kg (which increased diastolic blood pressure by about 40 mmHg). Metoprine had only a very low affinity for H3 binding sites (labelled by 3H-N alpha-methylhistamine; pKi 4.46). In pithed Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats, electrical (1 Hz, 1 ms, 50 V for 10 s) stimulation increased diastolic blood pressure by 28 and 37 mmHg, respectively. Imetit inhibited the neurogenic vasopressor response to about the same extent in WKY and SHR rats (maximal effect of about 30%). The inhibitory influence of imetit was diminished by thioperamide 1 mumol/kg to about the same degree in rats of either strain. The present study confirms the occurrence of presynaptic H3 receptors on sympathetic nerve fibres involved in the inhibition of the neurogenic vasopressor response. Moreover, it demonstrates that these H3 receptors are

Topics: Adrenergic Fibers; Animals; Blood Pressure; Decerebrate State; Electric Stimulation; Histamine; Histamine Agonists; Histamine Antagonists; Hypertension; Imidazoles; Male; Methylhistamines; Piperidines; Pyrimethamine; Rats; Rats, Wistar; Receptors, Histamine H3; Thiourea; Vagotomy; Vascular Resistance

Topics: Animals; Guinea Pigs; Histamine Agonists; Histamine Antagonists; Imidazoles; Intestine, Small; Male; Methylhistamines; Muscle Contraction; Peristalsis; Piperidines; Receptors, Histamine H3; Thiourea

The effects of clobenpropit (VUF-9153), a potent histamine H3-receptor antagonist, on a scopolamine-induced learning deficit in the step-through passive avoidance test was studied in mice. Clobenpropit (10 and 20 mg/kg) alone showed a tendency to ameliorate the scopolamine-induced learning deficit, and clobenpropit (10 mg/kg) in combination with zolantidine (20 mg/kg), a histamine H2-receptor antagonist, ameliorated the scopolamine-induced effect. This ameliorating effect was antagonized by (R)-alpha-methylhistamine (20 mg/kg), a histamine H3-receptor agonist and pyrilamine (20 mg/kg), a histamine H1-receptor antagonist, suggesting that clobenpropit in combination with zolantidine showed the ameliorating effect via histamine H3 receptors and/or histamine H1 receptors. We also studied the effects of clobenpropit on cholinergic and monoaminergic systems. Clobenpropit did not show any significant effect on these neuronal systems except the activation of noradrenergic system. The present results suggest that the effect of clobenpropit might be partially involved with the activation of noradrenergic system, and the histaminergic system may play certain important roles in learning and memory.

Topics: Acetylcholine; Animals; Avoidance Learning; Benzothiazoles; Biogenic Monoamines; Brain; Drug Interactions; Histamine Antagonists; Histamine H2 Antagonists; Imidazoles; Male; Memory; Methylhistamines; Mice; Mice, Inbred ICR; Phenoxypropanolamines; Piperidines; Pyrilamine; Receptors, Histamine H1; Receptors, Histamine H3; Scopolamine; Thiazoles; Thiourea

Using a microdialysis method and a new high performance liquid chromatography (HPLC)-fluorometric method for the detection of gamma-aminobutyric acid (GABA), we investigated the effect of thioperamide, an H3 receptor antagonist, on the GABA content in the dialysate from the anterior hypothalamic area of rats anesthetized with urethane. The addition of thioperamide to the perfusion fluid increased the release of GABA and histamine. Depleting neuronal histamine with alpha-fluoromethylhistidine, a specific inhibitor of histidine decarboxylase, and the administration of immepip, an H3 agonist, had no effect on basal- and thioperamide-induced GABA release. In addition, an infusion of clobenpropit, the most specific H3 receptor antagonist available, did not alter the basal release of GABA. On the other hand, histamine release was decreased by immepip and increased by thioperamide and clobenpropit. Removing Ca2+ from the perfusion fluid did not alter the effect of thioperamide on the GABA release, whereas that on histamine release was abrogated. These results suggest that the effect of thioperamide on GABA release is not mediated by histamine H3 receptors and that thioperamide acts on the transporter to cause an efflux of GABA from neurons and/or glia. Thioperamide is a popular H3 receptor antagonist which has been used applied to many studies. However, results using this compound should be interpreted in consideration of its effects on GABA release.

Topics: Animals; Calcium; Enzyme Inhibitors; gamma-Aminobutyric Acid; Histamine Agonists; Histamine Antagonists; Histidine Decarboxylase; Hypothalamus; Imidazoles; Male; Methylhistidines; Microdialysis; Neurons; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Thiourea

Recent studies have shown that cimetidine, burimamide and improgan (also known as SKF92374, a cimetidine congener lacking H2 antagonist activity) induce antinociception after intracerebroventricular administration in rodents. Because these substances closely resemble the structure of histamine (a known mediator of some endogenous analgesic responses), yet no role for known histamine receptors has been found in the analgesic actions of these agents, the structure-activity relationships for the antinociceptive effects of 21 compounds chemically related to H2 and H3 antagonists were investigated in this study. Antinociceptive activity was assessed on the hot-plate and tail-flick tests after intracerebroventricular administration in rats. Eleven compounds induced time-dependent (10-min peak) and dose-dependent antinociceptive activity with no observable behavioral impairment. ED50 values, estimated by nonlinear regression, were highly correlated across nociceptive assays (r2 = 0.98, n = 11). Antinociceptive potencies varied more than 6-fold (80-464 nmol), but were not correlated with activity on H1, H2 or H3 receptors. Although highly potent H3 antagonists such as thioperamide lacked antinociceptive activity, homologs of burimamide and thioperamide containing N-aromatic substituents retained H3 antagonist activity and also showed potent, effective analgesia. A literature review of the pharmacology of these agents did not find a basis for their antinociceptive effects. Taken with previous findings, the present results suggest: 1) these compounds act on the brain to activate powerful analgesic responses that are independent of known histamine receptors, 2) the structure-activity profile of these agents is novel and 3) brain-penetrating derivatives of these compounds could be clinically useful analgesics.

Topics: Analgesics, Non-Narcotic; Animals; Burimamide; Dose-Response Relationship, Drug; Histamine Antagonists; Histamine H2 Antagonists; Imidazoles; Male; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Structure-Activity Relationship; Thiourea

The effects of histamine and N(alpha)-methylhistamine, two components of gastric juice, on vagal and transmural stimulation of the guinea-pig isolated oesophagus were compared with their effects on cholinergic and on non-adrenergic-non-cholinergic (NANC) neuronal responses in the isolated ileum, both tissues having been pretreated with mepyramine (1 microM). Histamine (< or = 10 microM) and N(alpha)-methylhistamine (< or = 1 microM) had no significant effect on either vagal or transmural stimulation in the oesophagus. Substance P, which produces a contraction by activation of cholinergic nerves in the oesophagus also was unaffected by histamine. In contrast, the agonists inhibited contractions produced by cholinergic nerve stimulation in the ileum; the inhibition produced by histamine (10 microM) was up to 73 +/- 5%, that by N(alpha)-methylhistamine (1 microM), 48 +/- 5%. Histamine also inhibited responses to stimulation of NANC neurons by up to 37 +/- 14%. The effects of histamine and N(alpha)-methylhistamine in the ileum were inhibited by clobenpropit (0.1 microM). These findings suggest that histamine and N(alpha)-methylhistamine have no role in the modulation of neuronal function in the oesophagus, in contrast with their effect in the ileum.

Topics: Acetylcholine; Animals; Atropine; Dose-Response Relationship, Drug; Electric Stimulation; Esophagus; Guinea Pigs; Histamine; Histamine Antagonists; Ileum; Imidazoles; In Vitro Techniques; Methylhistamines; Muscle, Skeletal; Muscle, Smooth; Neurons; Neurons, Afferent; Pyrilamine; Receptors, Cholinergic; Receptors, Neurokinin-1; Receptors, Neurokinin-3; Substance P; Tetrodotoxin; Thiourea; Vagus Nerve

We investigated the brain penetration of the histamine H3 receptor antagonists thioperamide and clobenpropit using ex vivo [125I]iodophenpropit binding. Homogenates of the rat cortex, striatum and mouse whole brain were prepared 1 h after subcutaneous injection of the H3 antagonists and incubated with [125I]iodophenpropit, a radiolabeled H3 receptor antagonist, to determine the H3 receptor occupancy. Specific [125I]iodophenpropit binding to the rat cortex and striatum was inhibited by thioperamide with IC30 values of 1.0 and 1.5 mg/kg, respectively. Clobenpropit also inhibited [125I]iodophenpropit binding, but was less potent (IC30: 18 and 19 mg/kg in the rat cortex and striatum, respectively) than thioperamide. Similar results were obtained in experiments with mouse whole brain (3.5 and 13 mg/kg for thioperamide and clobenpropit), indicating that there is no important species differences in the brain penetration of these drugs between rats and mice. These findings suggest that after peripheral injection both in rat and mouse thioperamide penetrates the blood-brain barrier more efficiently compared to clobenpropit.

Topics: Animals; Brain; Cerebral Cortex; Corpus Striatum; Histamine Antagonists; Imidazoles; Iodine Radioisotopes; Isothiuronium; Male; Mice; Mice, Inbred BALB C; Piperidines; Radioligand Assay; Rats; Rats, Wistar; Thiourea

The effect of the histamine H3 receptor agonist (R) alpha-methylhistamine on duodenal bicarbonate secretion was investigated in the anaesthetized rat. (R) alpha-methylhistamine (3-30 mumol/kg i.v.) caused a dose-dependent increase in alkaline secretion which was completely blocked by the H3 receptor antagonist clobenpropit (3 mumol/kg i.v.). This antagonist caused a slight reduction (19%) of the secretory response to PGE2 50 micrograms/kg i.v. These data indicate that the alkaline response to (R) alpha-methylhistamine is related to the activation of histamine H3 receptors and suggest that this could be an additional mechanism involved in the previously observed gastroprotective effect of this compound.

Topics: Anesthesia; Animals; Bicarbonates; Dinoprostone; Dose-Response Relationship, Drug; Duodenum; Histamine Agonists; Histamine Antagonists; Imidazoles; Infusions, Intravenous; Male; Methylhistamines; Oxytocics; Rats; Rats, Wistar; Stimulation, Chemical; Thiourea

1. Conflicting reports in the literature over heterogeneity (West et al., 1990) or homogeneity (Arrange et al., 1990) of histamine H3-receptor binding sites may be attributed to the use of different incubation conditions. In the present study we have investigated the extent to which the binding of H3-receptor ligands to rat cerebral cortical membranes can be modified by both sodium ions and guanine nucleotides. 2. The H3-selective antagonist, thioperamide, discriminated between two specific binding sites for [3H]-N alpha-methylhistamine (IC50 1 = 2.75 +/- 0.87 nM, IC50 2 101.6 +/- 12.0 nM, % site 1 = 24 +/- 2%) in 50 mM Tris HCl buffer, but showed homogeneity of binding in 50 mM Na/K phosphate buffer. 3. Sodium ions markedly altered the binding characteristics of thioperamide (i.e. heterogeneity was lost and IC50 value shifted towards the high affinity site). The competition curves for a second H3-antagonist, clobenpropit and the H3-agonist N alpha-methylhistamine however, were unaltered in the presence of sodium ions. 4. Guanylnucleotides displaced only 60% of specific [3H]-N alpha- methylhistamine binding and modulated thioperamide binding in the same way as sodium ions. 5. These data suggest that the H3-receptor can exist in different conformations for which thioperamide, but not N alpha-methylhistamine and clobenpropit, show differential affinity. 6. The potential nature of these sites, and the implications of this apparent receptor heterogeneity for H3-receptor antagonism by thioperamide, are discussed.

Topics: Animals; Cerebral Cortex; Guanine Nucleotides; Histamine Agonists; Histamine Antagonists; Imidazoles; In Vitro Techniques; Male; Membranes; Methylhistamines; Piperidines; Rats; Receptors, Histamine H3; Sodium; Thiourea

The effect of clobenpropit (VUF-9153), a new histamine H3 receptor antagonist, on electrically induced convulsions was studied in mice. Clobenpropit significantly and dose dependently decreased the duration of each convulsive phase. Its anticonvulsant effects were prevented by pretreatment with (R)-alpha-methylhistamine and imetit (VUF-8325), histamine H3 receptor agonists. These findings suggest that the effect of clobenpropit on electrically induced convulsions is due to an increase in endogenous histamine release in the brain, which is consistent with biochemical results that clobenpropit increased brain histidine decarboxylase activity dose dependently. The anticonvulsive effect of clobenpropit was antagonized by mepyramine, a histamine H1 receptor antagonist, but not by zolantidine, a histamine H2 receptor antagonist, indicating that histamine released by the anticonvulsant effect of clobenpropit interacts with histamine H1 receptors of postsynaptic neurons. The present findings of the effect of clobenpropit on electrically induced convulsions are fully consistent with those of thioperamide as described previously (Yokoyama et al., 1993, Eur. J. Pharmacol. 234, 129), supporting the hypothesis that the central histaminergic neuron system is involved in the inhibition of seizures.

Topics: Animals; Anticonvulsants; Brain; Brain Chemistry; Electroshock; Histamine Agonists; Histamine Antagonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Histidine Decarboxylase; Imidazoles; Male; Mice; Mice, Inbred Strains; Seizures; Thiourea

The pharmacological activity of the histamine H3 receptor antagonist VUF 9153 (S-[3-(4(5)-imidazolyl)]propyl-N-(4-chlorobenzyl)isothiourea) has been investigated in vitro and in vivo. VUF 9153 displaced [3H]N alpha-methylhistamine binding to rat cortex/hippocampal membranes (pKi = 9.77 +/- 0.03) and antagonised the inhibitory responses to (R)-alpha-methylhistamine against electrical field stimulation in the isolated longitudinal smooth muscle preparation of guinea-pig ileum (pKB = 9.95 +/- 0.07). In these assays, VUF 9153 was 10-50-fold more potent than the prototype H3 receptor antagonist thioperamide. VUF 9153 showed no or very weak activity in in vitro functional assays for histamine H1 or H2 receptors. Systemic administration of VUF 9153 (s.c. or p.o.) dose-dependently inhibited the ex vivo binding of [3H]N alpha-methylhistamine to rat cortex/hippocampal membranes and dipsogenic responses induced by (R)-alpha-methylhistamine. Calculation of ED50 values, at the 1 h pretreatment time used, revealed that VUF 9153 administered s.c. or p.o., was approximately 2-fold weaker than thioperamide. These data indicate that, like thioperamide, VUF 9153 is a potent and selective antagonist for histamine H3 receptors in vitro, possesses the ability to penetrate the blood-brain barrier to access central H3 receptors and can inhibit H3 receptor-mediated functional responses in vivo.

Topics: Animals; Cerebral Cortex; Dose-Response Relationship, Drug; Drinking; Electric Stimulation; Guinea Pigs; Hippocampus; Histamine Agonists; Histamine Antagonists; Ileum; Imidazoles; In Vitro Techniques; Male; Methylhistamines; Muscle, Smooth; Piperidines; Rats; Receptors, Histamine H1; Receptors, Histamine H2; Thiourea