thiourea and imetit

A suitable inflammatory signal influences extracellular matrix accumulation and determines the quality of the myocardial infarction scar. The aim of the present study was to determine the influence of mast cell sonicates or histamine on collagen accumulation in heart myofibroblast culture and on the deposition of collagen in the myocardial infarction scar. The histamine receptor involved in the process was investigated. Myocardial infarction was induced by ligation of the left coronary artery. Myofibroblasts were isolated from the scar of myocardial infarction. The effects of mast cell sonicates, histamine and its receptor antagonists, i.e. ketotifen (H

Topics: Animals; Cells, Cultured; Cicatrix; Collagen; Heart; Histamine; Imidazoles; Male; Mast Cells; Myocardial Infarction; Myofibroblasts; Rats; Rats, Wistar; Receptors, Histamine; 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

Myocardial infarction is an alarming health issue, needs great attention. The present study investigated the role of histamine-H3 receptor (H3R) agonist imetit in relationship to sympathetic and renin angiotensin system in Wistar rats.. Subcutaneous injection of isoproterenol (85 mg/kg) on last 2 consecutive days in per se group and 7 days treatment of different groups at 24 h interval induced myocardial infarction in Wistar rats. H3R agonist imetit (10 mg/kg), H3R antagonist thioperamide (5 mg/kg), losartan (10 mg/kg) were administered orally to evaluate imetit's cardioprotective potential effect by measuring plasma cardiac antioxidant markers, angiotensin II, norepinephrine levels and histopathological analysis.. Isoproterenol significantly elevated the angiotensin II and norepinephrine levels in rat plasma. This study revealed that pre-treatment with imetit similar to losartan attenuated norepinephrine and angiotensin II levels whereas thioperamide showed its antagonistic effect by diminishing imetit's effects. Furthermore, its protective effect was confirmed by restoration of cardiac antioxidant markers and histopathological improvement of myocardium integrity.. This study confirm imetit's cardioprotective potential and also reveals renin angiotensin system, sympathetic system and H3R correlation in isoproterenol induced toxicity in rats. However, molecular studies must be warranted to prove the role of H3R in myocardial infarction.

Topics: Angiotensin II; Animals; Antioxidants; Cardiotonic Agents; Histamine Agonists; Histamine H3 Antagonists; Imidazoles; Isoproterenol; Losartan; Male; Myocardial Infarction; Myocardium; Norepinephrine; Piperidines; Rats; Renin-Angiotensin System; Sympathetic Nervous System; Thiourea

The cardioprotective role of histamine H3 receptor (H3R) agonist imetit (IMT) in isoproterenol (ISO)-induced alterations of hemodynamic and oxidative stress was investigated in Wistar rats. In this study, rats were treated with IMT (5 and 10 mg/kg, per orally [p.o.]), carvedilol (10 mg/kg, p.o.) and ISO control group (normal saline) for 7 d, with concurrent subcutaneous administration of ISO (85 mg/kg) at 24 h interval on last two consecutive days whereas control group was administered with vehicle only. ISO significantly attenuated cardiac antioxidant enzymes superoxide dismutase, catalase and increased plasma cardiac injury biomarkers creatine kinase-MB, alanine transaminase and aspartate transaminase. ISO also altered cardiac activity as evidenced by decrease in blood pressure (34.60%) and increase in heart rate (11.40%). The damage due to oxidative stress was revealed by histopathology alterations such as myocyte necrosis, myofibrillar degeneration and pyknotic nucleus. However, pre-treatment with IMT demonstrated restoration of hemodynamic alterations along with significant preservation of antioxidants and myocyte injury-specific marker enzymes. Furthermore, protective effect of IMT was reconfirmed by the histopathological salvage of myocardium. Results of the present study demonstrated the cardioprotective potential of IMT, as evidenced by favorable improvement in ISO-induced hemodynamic, plasma cardiac biomarkers and tissue antioxidant status along with maintenance of integrity of myocardium.

Topics: Adrenergic beta-Agonists; Animals; Antioxidants; Biomarkers; Blood Pressure; Body Height; Body Weight; Carbazoles; Cardiotonic Agents; Carvedilol; Heart Diseases; Heart Rate; Hemodynamics; Histamine Agonists; Humans; Imidazoles; Isoproterenol; Male; Myocardium; Oxidative Stress; Propanolamines; Rats; Rats, Wistar; Thiourea

Recently we reported that cultured rat cortical astrocytes express histamine H3 receptor that is functionally coupled to Gi/o proteins and participates to the stimulatory effect of histamine. Due to the lack of data on the distribution of histamine H3 receptors on glial cells we further investigated their presence in cultured astrocytes from different brain regions. Real-time PCR was performed to examine the expression of native histamine H3 receptor in cultured rat astrocytes from cortex,cerebellum, hippocampus and striatum.Double-antigen immunofluorescence staining and[3H]N-α-methylhistamine([3H]NαMH) binding studies were utilized to specifically identify and characterize receptor binding sites in astrocytes. Histamine H3 receptor mRNA was detected in rat astrocytes from all the regions under investigation with the highest levels in striatal astrocytes followed by hippocampal astrocytes and approximately equal levels in cerebellar and cortical astrocytes.Double-antigen immunofluorescence confirmed the presence of histamine H3 receptors on the membrane of all examined astroglial populations.[3H]NαMH bound with high affinity and specificity to an apparently single class of saturable sites on cortical astrocytic membranes(KD¼4.5570.46 nM; Bmax¼5.6370.21 fmol/mg protein)and competition assays with selective agonists and antagonists were consistent with labeling of histamine H3 receptor(range of pKi values 7.50–8.87). Our study confirmed the ability of cultured astrocytes from different rat brain regions to express histamine H3 receptors.The observed diverse distribution of the receptors within various astrocytic populations possibly mirrors their heterogeneity in the brain and indicates their active involvement in histamine-mediated effects.

Topics: Animals; Animals, Newborn; Astrocytes; Binding, Competitive; Brain; Cells, Cultured; Ciprofloxacin; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Methylhistamines; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; RNA, Messenger; Thiourea

Recent studies suggest that the brain histaminergic system and especially the H3 receptors are involved in the regulation of alcohol consumption and alcohol-induced behaviors. Part of this effect might be due to a modulation of ethanol-induced sedation by central histamine. The aim of the present study was to investigate the effects of several histaminergic drugs on ethanol-induced sedation using the loss of righting reflex experimental protocol in female Swiss mice. A pretreatment with L-histidine, the histamine precursor, significantly reduced ethanol-induced sedation, suggesting that brain histamine protects against the sedative effects of ethanol. In a second set of experiments, several H3 receptor agonists (immepip or imetit) and inverse agonists/antagonists (thioperamide, A331440, or BF2.649) were tested. Surprisingly, both H3 receptor agonists and antagonists potentiated the sedative effects of ethanol. This paradoxical effect might be due to the subtle regulatory actions related to the H3 heteroreceptor function.

Topics: Animals; Biphenyl Compounds; Brain; Ethanol; Female; Histidine; Hypnotics and Sedatives; Imidazoles; Mice; Nitriles; Piperidines; Pyrrolidines; Receptors, Histamine H3; Reflex, Righting; Thiourea

Centrally acting histamine H(3) receptor ligands are proposed as potential treatments for obesity, although the value of inverse agonists at these receptors is still debated. Functional inhibition of H(3) autoreceptors activates neurones in a hypothalamic 'satiety' centre. The H(3) receptor antagonist, proxyfan was used as a tool to assess the action of histaminergic compounds in this model.. We compared the actions of histamine on feeding with those of an H(3) receptor agonist (imetit) and inverse agonist (thioperamide) in rats and mice. Sites of action were identified by immunohistochemistry and the hypothalamic ventromedial nucleus (VMN) was investigated using electrophysiological techniques.. Central histamine or thioperamide decreased fast-induced feeding, whereas imetit increased feeding. Systemic thioperamide entered the brain to activate hypothalamic feeding centres and to reduce feeding without causing any adverse behaviours. Thioperamide activated neurones in the VMN through an action on histamine autoreceptors, whilst imetit had the opposite effect. Proxyfan administered alone did not affect either feeding or electrical activity. However, it blocked the actions of both thioperamide and imetit, acting as a neutral antagonist in this system.. The H(3) receptor inverse agonist, thioperamide, potently reduced appetite without adverse behavioural effects. This action was blocked by proxyfan, acting as a neutral antagonist in this model and, therefore, this compound is useful in determining the selectivity of H(3) receptor-directed drugs. A major action of thioperamide is through presynaptic autoreceptors, inducing stimulation by endogenous histamine of postsynaptic H(1 ) receptors on anorectic hypothalamic neurones.

Topics: Animals; Eating; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Male; Mice; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Thiourea; Ventromedial Hypothalamic Nucleus

The role of histamine neurons in schizophrenia and psychostimulant abuse remains unclear. Behavioural sensitization to psychostimulants is a cardinal feature of these disorders. Here, we have explored the ability of imetit and ciproxifan (CPX), a reference H₃-receptor agonist and inverse agonist, respectively, to modulate locomotor sensitization induced in mice by methamphetamine (MET). Mice received saline, CPX (3 mg/kg) or imetit (3 mg/kg) 2 h before MET (2 mg/kg), once daily for 12 days, and were killed after a 2-day wash out. Imetit had no effect, but CPX induced a decrease of MET-induced locomotor activity, which became significant at Day 5, and even more at Day 10. Quantitative polymerase chain reaction was used in the sensitized mice to quantify brain-derived neurotrophic factor (BDNF) and N-methyl-D-aspartate (NMDA)-receptor subunit 1 (NR1) mRNAs, two factors that are altered in both schizophrenia and drug abuse. Imetit and CPX used alone had no effect on any marker. Sensitization by MET decreased BDNF mRNAs by 40% in the hippocampus. This decrease was reversed by CPX. Sensitization by MET also induced strong decreases of NR1 mRNAs in the cerebral cortex, hippocampus and striatum, but not hypothalamus. These decreases were also reversed by CPX. The strong modulator effect of CPX in mice sensitized to MET may result from its modulator effect on NR1 mRNAs in the cerebral cortex and striatum. The reversal by CPX of BDNF and NR1 mRNAs in the hippocampus of sensitized animals further strengthens the interest of H₃-receptor inverse agonists for the long-term treatment of cognitive deficits of patients with schizophrenia.

Topics: Animals; Behavior, Animal; Brain; Brain-Derived Neurotrophic Factor; Central Nervous System Stimulants; Histamine Agonists; Histamine H3 Antagonists; Humans; Imidazoles; Male; Methamphetamine; Mice; Motor Activity; Receptors, N-Methyl-D-Aspartate; Schizophrenia; Thiourea

The effects of the histamine H(3) receptor agonists (R)-α-methylhistamine, imetit and immepip on methamphetamine (METH)-induced stereotypical behavior were examined in mice. The administration of METH (10 mg/kg, i.p.) to male ddY mice induced behaviors including persistent locomotion and stereotypical behaviors, which were classified into four categories: stereotypical head-bobbing (1.9%), circling (1.7%), sniffing (14.3%), and biting (82.1%). Pretreatment with (R)-α-methylhistamine (3 and 10 mg/kg, i.p.) significantly decreased stereotypical sniffing, but increased stereotypical biting induced by METH, in a dose-dependent manner. This effect of (R)-α-methylhistamine on behavior was mimicked by imetit or immepip (brain-penetrating selective histamine H(3) receptor agonists; 10 mg/kg, i.p. for each drug). Hypothalamic histamine levels 1 h after METH challenge were significantly increased in mice pretreated with saline. These increases in histamine levels were significantly decreased by pretreatment with histamine H(3) receptor agonists, effects which would appear to underlie the shift from METH-induced stereotypical sniffing to biting.

Topics: Animals; Behavior, Animal; Central Nervous System Stimulants; Histamine; Histamine Agonists; Hypothalamus; Imidazoles; Male; Methamphetamine; Methylhistamines; Mice; Motor Activity; Piperidines; Random Allocation; Stereotyped Behavior; Thiourea

To discuss the treatment of H3R agonist, IMETIT, on the allergic rhinitis(AR) ,and the influence to mRNA of Substance P(SP) and Substance P Receptor (SP-R) in AR model of guinea pigs.. The severity of AR was assessed by allergic symptoms (sneezing, nasal rubbing and nose blocking). The changes in the nasal mucosa were studied by pathological methods. The expression of SP positive cell was detected by immunohistochemistry, and the expression of SP-R mRNA was detected by reverse transcriptive polymerase chain reaction (RT-PCR).. Histamine H3R agonists, IMETIT can effectively improve the AR symptoms, sneezing, nasal itching, nasal congestion, reduce the pathological changes in the nasal mucosa, cut down the SP secretion and SP-R mRNA expression.. Histamine H3R agonist, IMETIT can effectively relieve the symptoms of AR in guinea pigs, which is related to reducing SP secretion and SP-R mRNA expression.

Topics: Animals; Female; Guinea Pigs; Imidazoles; Male; Receptors, Histamine H3; Receptors, Neurokinin-1; Rhinitis, Allergic, Perennial; Substance P; Thiourea

To explore the influence of histamine H3 receptor agonist, IMETIT and simultaneous use of IMETIT and H1-receptor antagonist, Loratadine, on the symptoms of allergic rhinitis (AR) and substance P(SP) secretion and expression of SP receptor (SP-R) mRNA in AR model in guinea pigs.. Guinea pigs were divided randomly into 4 groups: AR group (group A), IMETIT group (group B), Loratadine group (group C) and IMETIT+Loratadine group (group D). The severity of AR was assessed by determining the extent of three markers of allergic symptoms (sneezing, nasal rubbing and nose blocking). The changes in the nasal mucosa were studied by pathological methods. The expression of positive cell of SP was detected by immunohistochemistry. SP-R mRNA expression in nasal mucosa was used to do reverse transcriptive-polymerase chain reaction (RT-PCR). Statistical analysis was performed using a SPSS 13.0 software.. In Group B, the mean (x ± s) number of sneeze [(15.0 ± 1.3) times], scratching nose [(16.5 ± 2.3) times] and respiratory frequency [(76.3 ± 4.1) times/min] were significantly improved than those in group A [(23.5 ± 2.6) times, (26.1 ± 4.1) times and (66.5 ± 5.8) times/min, respectively), P value were 0.000, 0.000 and 0.001, respectively]. The numbers of SP-positive cells [(11.6 ± 3.6)/HP] and SP-R mRNA expression (0.64 ± 0.04) in group B were reduced significantly compared to group A [(27.1 ± 9.7)/HP, (0.83 ± 0.03), P value were 0.000, 0.000, respectively]. Sneeze [(10.0 ± 2.3) times], scratching nose [(11.8 ± 1.7) times] and respiration [(90.0 ± 5.0) times/min] in Group D were improved significantly than those in group B (P value were 0.000, 0.002 and 0.000, respectively). SP-positive cells [(2.0 ± 1.7)/HP] and SP-R mRNA expression (0.52 ± 0.06) in Group D compared with group B were also significantly reduced (P value were 0.012 and 0.000, respectively). Pathological changes in guinea pig nasal mucosa in group B, group D were alleviated than those in group A. The combination of IMETIT and Loratadine had a synergistic effect on these effects (F value were 11.59, 8.28, 5.61, 5.48, 6.50, respectively, P value were 0.002, 0.008, 0.025, 0.027, 0.017).. IMETIT and the combination of IMETIT with Loratadine can effectively relieve the symptoms of AR in guinea pigs, its mechanism may be relevant to reduce SP secretion and the expression of SP-R mRNA, and the two has a synergistic effect. It may be useful as a novel therapeutic approach in nasal allergy.

Topics: Animals; Female; Guinea Pigs; Histamine Agonists; Imidazoles; Loratadine; Male; Nasal Mucosa; Receptors, Neurokinin-1; Rhinitis, Allergic, Perennial; RNA, Messenger; Substance P; Thiourea

Cocaine and methamphetamine (METH) are two commonly abused drugs that have behavioral-stimulant properties. These stimulant effects are partially mediated by the dopaminergic system. Recent evidence has suggested that the histamine H(3) receptor (H(3)R) may modulate the release of dopamine induced by METH. The aim of the present study was to examine the role of H(3)R in the behavioral-stimulant effects of cocaine and METH in mice and monkeys.. Nonhabituated, experimentally naïve mice (n = 5-6) were pretreated with the H(3)R agonist imetit 30 min before METH or cocaine, and activity was measured for 90 min. The behavioral-stimulant effects of METH and cocaine were also studied in squirrel monkeys (n = 3) under a fixed-interval schedule of stimulus termination. Monkeys were pretreated with imetit 30 min before the peak behavioral-stimulant doses of METH or cocaine derived from individual subjects.. Pretreatment with imetit did not affect basal activity in mice. Imetit significantly attenuated the behavioral-stimulant effects of METH, but not cocaine. In monkeys, no dose of imetit tested significantly altered the behavioral-stimulant effects of METH or cocaine.. These results suggest a role of H(3)R in the behavioral-stimulant effects of METH, but not cocaine, in mice and no role in monkeys.

Topics: Animals; Behavior, Animal; Central Nervous System Stimulants; Cocaine; Conditioning, Operant; Dose-Response Relationship, Drug; Drug Interactions; Histamine Agonists; Imidazoles; Male; Methamphetamine; Mice; Motor Activity; Receptors, Histamine H3; Reinforcement Schedule; Saimiri; Thiourea

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

Histamine 3 (H(3)) receptors are distributed throughout the brain and regulate histamine as well as the activity of other neurotransmitters including acetylcholine (ACh). Impaired ACh neurotransmission is associated with deficits of cognitive-related functioning in many species including humans. The goal of these studies was to evaluate the behavioral and neurochemical effects of JNJ-10181457, a selective non-imidazole histamine H(3) receptor antagonist, in rats. The pharmacokinetic profile and receptor occupancy of JNJ-10181457 were tested. The efficacy of JNJ-10181457 was evaluated, acutely, in the imetit-induced water licking model, delayed non-matching to position (DNMTP) task and microdialysis studies. In addition, the effects of repeated administration of JNJ-10181457 were evaluated in the reversal learning task. A single administration of JNJ-10181457 (10 mg/kg, i.p.) resulted in significant plasma and brain exposure and maximal H(3) receptor occupancy. In addition, JNJ-10181457 reversed imetit-induced water licking, similarly to thioperamide (10 mg/kg, i.p.). In the DNMTP task, scopolamine (0.06 mg/kg, i.p.) significantly decreased percentage correct responding. These effects were significantly reversed by JNJ-10181457 (10 mg/kg, i.p.) and also by donepezil (1 mg/kg, i.p.), an acetylcholinesterase inhibitor, and were associated with normalization of ACh neurotransmission in the cortex. Repeated administration of JNJ-10181457 (10 mg/kg, i.p.) significantly increased percentage correct responding in the reversal learning task. Treatment discontinuation was not associated with rebound effects on cognition. These results indicate that selective blockade of histamine H(3) receptors might have therapeutic utility for the treatment of working memory deficits and learning disorders, especially those in which ACh neurotransmission is compromised.

Topics: Acetylcholine; Animals; Anticonvulsants; Brain; Cholinesterase Inhibitors; Cognition; Conditioning, Operant; Donepezil; Drinking Behavior; Drug Evaluation, Preclinical; Histamine Agonists; Histamine Antagonists; Imidazoles; Indans; Learning; Microdialysis; Morpholines; Muscarinic Antagonists; Nootropic Agents; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Scopolamine; Synaptic Transmission; Thiourea

In the present study, we investigated the effect of imetit, a selective histamine H(3) agonist, on the improvement of NMDA receptor agonists in H(1) antagonist-induced working memory deficit and the decrease of hippocampal theta activity in rats. Pyrilamine (35 mg/kg, i.p.) impaired spatial memory and decreased hippocampal theta activity during the radial maze task. In addition, intrahippocampal injection of D-cycloserine (1 microg/side) and spermidine (10 microg/side) improved the pyrilamine-induced working memory deficit and the decrease of hippocampal theta activity. The improvement effects of D-cycloserine and spermidine were antagonized by intrahippocampal injection of imetit (10 microg/side). These results indicate that, the facilitation of neurotransmitter release from the presynaptic terminals besides direct stimulation of postsynaptic NMDA receptors take part in the improvements of NMDA receptor agonists on pyrilamine-induced spatial memory deficit and the decrease of hippocampal theta activity.

Topics: Animals; Cycloserine; Excitatory Amino Acid Agonists; Hippocampus; Histamine Agonists; Histamine H1 Antagonists; Imidazoles; Male; Maze Learning; Memory; Memory Disorders; Pyrilamine; Random Allocation; Rats; Receptors, N-Methyl-D-Aspartate; Space Perception; Spermidine; Theta Rhythm; Thiourea

We examined whether cannabinoid CB(1) and histamine H(3) receptors resemble alpha(2)-adrenoceptors in that their presynaptically mediated cardiovascular effects are less marked in urethane- than in pentobarbitone-anaesthetized pithed rats.. Effects of the cannabinoid agonist CP-55,940 and the H(3) receptor agonist imetit on electrically induced tachycardic and vasopressor responses, respectively, was compared in pithed rats anaesthetized with urethane or pentobarbitone. The affinity of urethane for the three receptors was measured by radioligand binding studies in rat brain cortex membranes and its potency assessed in superfused mouse tissues preincubated with (3)H-noradrenaline.. The neurogenic tachycardic response was less markedly inhibited by CP-55,940 in urethane- than in pentobarbitone-anaesthetized pithed rats. Imetit inhibited the neurogenic vasopressor response after pentobarbitone but not after urethane. The catecholamine-induced tachycardic and vasopressor response did not differ between rats anaesthetized with either compound. Urethane 10 mM (plasma concentration reached under anaesthesia) did not affect binding to CB(1) or H(3) receptors and alpha(2) adrenoceptors, nor did it alter the inhibitory effect of agonists at the three receptors on electrically evoked (3)H-noradrenaline release.. Urethane, but not pentobarbitone, abolished the H(3) receptor-mediated vascular response in pithed rats and attenuated the CB(1) receptor-mediated cardiac response much more than pentobarbitone. The weaker effects of CB(1), H(3) and alpha(2) receptor agonists cannot be explained by antagonism by urethane at the three receptors in vitro. Pentobarbitone, but not urethane, is suitable as an anaesthetic for investigations of inhibitory presynaptic receptor function in pithed and anaesthetized rats.

Topics: Adrenergic alpha-2 Receptor Agonists; Anesthetics; Animals; Cardiovascular System; Cerebral Cortex; Cyclohexanols; Decerebrate State; Electric Stimulation; Histamine Agonists; Imidazoles; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Pentobarbital; Radioligand Assay; Rats; Rats, Wistar; Receptor, Cannabinoid, CB1; Receptors, Presynaptic; Thiourea; Urethane; Vasoconstrictor Agents

The present study was performed to study the participation of histamine H(3) receptors in nasal symptoms using Sch 50971, a potent and selective agonist of the H(3) receptor. Repeated topical application of antigen caused an increase in sneezing and nasal rubbing in sensitized mice. Oral administration of Sch 50971 and imetit, specific H(3)-receptor agonists, resulted in an inhibition of nasal symptoms induced by an antigen similar to an H(1)-receptor antagonist, cetirizine. Furthermore, simultaneous use of H(3)-receptor agonists, Sch 50971 or imetit, and an H(1)-receptor antagonist, cetirizine, caused a significant inhibitory effect on nasal symptoms at doses that showed no effect when used separately. The number of eosinophils in the nasal mucosa of mice sensitized with antigen was significantly decreased by cetirizine; however, Sch 50971 and imetit had no effect on eosinophil infiltration. These results clearly indicate that H(3) receptors are involved in the etiology of nasal allergy, and the stimulation of H(3) receptors may be useful as a novel therapeutic approach in nasal allergy.

Topics: Animals; Anti-Allergic Agents; Cetirizine; Chemotaxis, Leukocyte; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Eosinophils; Female; Histamine Agonists; Histamine H1 Antagonists, Non-Sedating; Imidazoles; Mice; Mice, Inbred BALB C; Nasal Mucosa; Ovalbumin; Pruritus; Pyrrolidines; Receptors, Histamine H3; Rhinitis, Allergic, Perennial; Sneezing; Thiourea; Time Factors

Despite the well-established role of histamine as an anorexigenic neurotransmitter, the role of histamine H(3) receptors in feeding behavior is controversial. Herein we investigated the role of histamine H(3) receptor on several orexigenic agents in mice. Thioperamide (histamine H(3) receptor inverse agonist) inhibited neuropeptide Y- and nociceptin-induced hyperphagia but had no effect on U-50488 (opioid kappa-receptor agonist)-induced hyperphagia. In contrast, imetit (histamine H(3) receptor agonist) inhibited U-50488-induced hyperphagia but augmented neuropeptide Y-induced hyperphagia while it did not alter nociceptin-induced hyperphagia. These results indicate distinctive roles of histamine H(3) receptors in various orexigenic pathways.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Appetite; Histamine Agonists; Histamine H3 Antagonists; Hyperphagia; Imidazoles; Male; Mice; Mice, Inbred C57BL; Neuropeptide Y; Nociceptin; Opioid Peptides; Piperidines; Receptors, Histamine H3; 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

Histamine H3 receptors (H3Rs) are located on the presynaptic membranes and cell soma of histamine neurons, where they negatively regulate the synthesis and release of histamine. In addition, H3Rs are also located on nonhistaminergic neurons, acting as heteroreceptors to regulate the releases of other amines such as dopamine, serotonin, and norepinephrine. The present study investigated the effects of H3R ligands on appetite and body-weight regulation by using WT and H3R-deficient mice (H3RKO), because brain histamine plays a pivotal role in energy homeostasis. The results showed that thioperamide, an H3R inverse agonist, increases, whereas imetit, an H3R agonist, decreases appetite and body weight in diet-induced obese (DiO) WT mice. Moreover, in DiO WT mice, but not in DiO H3RKO mice, imetit reduced fat mass, plasma concentrations of leptin and insulin, and hepatic triglyceride content. The anorexigenic effects of imetit were associated with a reduction in histamine release, but a comparable reduction in histamine release with alpha-fluoromethylhistidine, an inhibitor of histamine synthesis, increased appetite. Moreover, the anorexigenic effects of imetit were independent of the melanocortin system, because imetit comparably reduced appetite in melanocortin 3 and 4 receptor-deficient mice. The results provide roles of H3Rs in energy homeostasis and suggest a therapeutic potential for H3R agonists in the treatment of obesity and diabetes mellitus.

Topics: Animals; Appetite; Body Weight; Diabetes Mellitus; Histamine Agonists; Imidazoles; Insulin; Leptin; Mice; Mice, Knockout; Obesity; Piperidines; Receptors, Histamine H3; Thiourea

In rats lesioned neonatally with 6-hydroxydopamine (6-OHDA), repeated treatment with SKF 38393 (1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol), a dopamine D(1)/D(5) receptor agonist, produces robust stereotyped and locomotor activities. The gradual induction of dopamine D(1) receptor supersensitivity is known as a priming phenomenon, and this process is thought to underlie not only the appearance of vacuous chewing movements in humans with tardive dyskinesia, but also the onset of motor dyskinesias in L-dihydroxyphenylalanine (L-DOPA)-treated Parkinson's disease patients. The object of the present study was to determine the possible influence of the histaminergic system on dopamine D(1) agonist-induced activities. We found that neither imetit (5.0 mg/kg i.p.), a histamine H(3) receptor agonist, nor thioperamide (5.0 mg/kg i.p.), a histamine H(3) receptor antagonist/inverse agonist, altered the numbers of vacuous chewing movements in non-primed-lesioned rats. However, in dopamine D(1) agonist-primed rats, thioperamide alone produced a vacuous chewing movements response (i.e., P < 0.05 vs SKF 38393, 1.0 mg/kg i.p.), but did not modify the SKF 38393 effect. Notably, both imetit and thioperamide-induced catalepsy in both non-primed and primed 6-OHDA-lesioned rats, comparable in magnitude to the effect of the dopamine D(1)/D(5) receptor antagonist SCH 23390 (7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine; 0.5 mg/kg i.p.). Furthermore, in primed animals both imetit and thioperamide intensified SCH 23390-evoked catalepsy. In vivo microdialysis established that neither imetit nor thioperamide altered extraneuronal levels of dopamine and its metabolites in the striatum of 6-OHDA-lesioned rats. On the basis of the present study, we believe that histaminergic systems may augment dyskinesias induced by dopamine receptor agonists, independent of direct actions on dopaminergic neurons.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Animals, Newborn; Benzazepines; Catalepsy; Corpus Striatum; Dialysis Solutions; Dopamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Male; Mastication; Microdialysis; Motor Activity; Oxidopamine; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Stereotyped Behavior; Thiourea

H(3) autoreceptors provide feedback control of neurotransmitter synthesis in histaminergic neurons, but the transduction pathways involved are poorly understood. In rat brain cortical slices, histamine synthesis can be stimulated by depolarization and inhibited by H(3) agonists. We show that histamine synthesis stimulation by depolarization with 30 mM K(+) requires extracellular calcium entry, mostly through N-type channels, and subsequent activation of calcium/calmodulin-dependent protein kinase type II. In vitro, this kinase phosphorylated and activated histidine decarboxylase, the histamine-synthesizing enzyme. Inhibition of depolarization-stimulated histamine synthesis by the histamine H(3) receptor agonist imetit was impaired by preincubation with pertussis toxin and by the presence of a myristoylated peptide (myristoyl-N-QEHAQEPERQYMHIGTMVE-FAYALVGK) blocking the actions of G-protein betagamma subunits. The stimulation of another G(i/o)-coupled receptor, adenosine A(1), also decreased depolarization-stimulated histamine synthesis. In contrast, protein kinase A activation, which is also repressed by H(3) receptors, elicited a depolarization- and calcium/calmodulin-independent stimulation of histamine synthesis. Protein kinase A was able also to phosphorylate and activate histidine decarboxylase in vitro. These results show how depolarization activates histamine synthesis in nerve endings and demonstrate that both pathways modulating neurotransmitter synthesis are controlled by H(3) autoreceptors.

Topics: Amino Acid Sequence; Animals; Brain; Calcium Channel Blockers; Calcium-Calmodulin-Dependent Protein Kinases; Cyclic AMP-Dependent Protein Kinase Type II; Cyclic AMP-Dependent Protein Kinases; Histamine; Histamine Agonists; Histidine Decarboxylase; Imidazoles; In Vitro Techniques; Male; Molecular Sequence Data; Peptide Fragments; Pertussis Toxin; Phosphorylation; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Recombinant Proteins; Thiourea

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

The existence of mouse H3-receptor isoforms was investigated by PCR analysis and cDNA cloning. Splicing mechanisms previously reported in various species are conserved in the mouse. The retention/deletion of a fragment in the third intracellular loop of the mouse receptor leads to the existence of three isoforms designated mH(3(445)), mH(3(413)) and mH(3(397)) according to the length of their deduced amino acid sequence. PCR analysis showed that mouse H3-receptor isoforms display different expression patterns in the brain. Following expression in Cos-1 cells, [125I]iodoproxyfan binding indicated similar pharmacological profiles of the mH(3(445)), mH(3(413)) and mH(3(397)) isoforms. The pharmacological profile of the mouse H3 receptor is more similar to the rat receptor than to the human receptor, although some differences were also observed between the mouse and rat receptors. For example, the potency of thioperamide and ciproxifan is slightly higher at the mouse receptor than at the rat receptor but 40-100-fold higher than at the human receptor. In situ hybridization histochemistry showed that the distribution of H3-receptor mRNAs in the mouse brain is rather similar to that previously reported in the rat brain. However, the autoradiographic and cellular expression patterns observed in several brain areas such as the thalamus or hippocampus reveal important differences between the two species.

Topics: Animals; Blotting, Northern; Brain; Chlorocebus aethiops; Cloning, Molecular; Competitive Bidding; COS Cells; Gene Expression; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; In Situ Hybridization; Iodine Radioisotopes; Isoenzymes; Mice; Piperidines; Radioligand Assay; Rats; Receptors, Histamine H3; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Thiourea; Transfection

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

Neurons which discharge selectively during waking (waking selective) have been found in the tuberomamillary nucleus (TM) and adjacent areas of the posterior hypothalamus. Although they share some electrophysiological properties with aminergic neurons, there is no direct evidence that they are histaminergic. We have recorded from posterior hypothalamic neurons during the sleep-wake cycle in freely moving cats, and investigated the effects on waking selective neurons of specific ligands of histaminergic H3-receptors, which autoregulate the activity of histaminergic neurons. Two types of neurons were seen. Waking selective neurons, termed "waking-on (W-on)," were located exclusively within the TM and adjacent areas, and discharged at a low regular rate during waking (1.71-2.97 Hz), decreased firing during light slow wave sleep (SWS), became silent during deep SWS and paradoxical sleep (PS) and resumed their activity on, or a few seconds before, awakening. "Waking-related" neurons, located in an area dorsal to the TM, displayed a similar, although less regular, low rate of firing (1.74-5.41 Hz) and a similar discharge profile during the sleep-wake cycle; however, unlike "W-on" neurons, they did not completely stop firing during deep SWS and PS. Intramuscular (i.m.) injection of ciproxifan (an H3-receptor antagonist, 1mg/kg), significantly increased the discharge rate of W-on neurons and induced c-fos expression in histamine-immunoreactive neurons, whereas i.m. injection of imetit (an H3-receptor agonist, 1mg/kg) or microinjection of alpha-methylhistamine (another H3-receptor agonist, 0.025-0.1 microg/0.2 microl) in the vicinity of these cells significantly decreased their discharge rate. Moreover, the effect of the antagonist was reversed by the agonists and vice versa. In contrast, "waking-related" neurons were unaffected by these H3-receptor ligands. These data provide evidence for the histaminergic nature of "W-on" neurons and their role in cortical desynchronization during waking, and highlight the heterogeneity of posterior hypothalamic neuronal populations, which might serve different functions during the wakefulness.

Topics: Action Potentials; Animals; Cats; Drug Administration Schedule; Electroencephalography; Electromyography; Electrooculography; Electrophysiology; Female; Geniculate Bodies; Hippocampus; Histamine; Histamine Agonists; Histamine Antagonists; Hypothalamus, Posterior; Imidazoles; Immunohistochemistry; Male; Methylhistamines; Neurons; Thiourea; Time Factors; Wakefulness

Despite histamine being a potent endogenous vasoactive agent released in increasing amounts postburn, its role in postburn oedema formation has been controversial and its effect on burn circulation poorly investigated. The present study investigated the involvement of H(1), H(2) and H(3) receptors in postburn edema in rats exposed to skin and muscle burns and their influence on skin circulation postburn. We used the selective antagonists clemastine (H(1)), ranitidine (H(2)), thioperamide (H(3)) and the selective H(3) receptor agonist, imetit. Results showed that none of the antagonists or the H(3) agonist had significant effect on postburn edema measured by quantitative spectrophotometric analysis of extravasated Evans blue-albumin in the full-thickness burned skin or muscle. Clemastine and thioperamide failed to induce significant effect on blood flow in the partial- or full-thickness skin burn injury as measured by laser Doppler flowmetry, while ranitidine significantly (P<0.01) reduced blood flow in the full-thickness burn. In contrast, the H(3) receptor agonist, imetit, significantly increased blood flow, both in the partial-thickness burn injury (P<0.05) and in the full-thickness burn (P<0.01). Moreover, imetit significantly (P<0.01) increased mean arterial pressure while thioperamide significantly (P<0.01) reduced systemic pressure. In conclusion, H(1), H(2) and H(3) receptors are not important actors in the regulation of vascular patency permeability, whereas H(3) receptors play an important role by increasing skin circulation postburn, presumably by relaxation of vascular smooth muscle and/or by interacting with other inflammatory neurotransmitters. Data also suggest that H(2) receptor blockers may not be best choice for stress ulcer prophylaxis in burn patients.

Topics: Animals; Burns; Clemastine; Edema; Histamine Agonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Imidazoles; Male; Piperidines; Ranitidine; Rats; Rats, Sprague-Dawley; Receptors, Histamine; Receptors, Histamine H3; Regional Blood Flow; Skin; Statistics, Nonparametric; Thiourea

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

Activation of presynatic histamine H(3) receptors (H(3)R) down-regulates norepinephrine exocytosis from cardiac sympathetic nerve terminals, in both normal and ischemic conditions. Analogous to the effects of alpha(2)-adrenoceptors, which also act prejunctionally to inhibit norepinephrine release, H(3)R-mediated antiexocytotic effects could result from a decreased Ca(2+) influx into nerve endings. We tested this hypothesis in sympathetic nerve terminals isolated from guinea pig heart (cardiac synaptosomes) and in a model human neuronal cell line (SH-SY5Y), which we stably transfected with human H(3)R cDNA (SH-SY5Y-H(3)). We found that reducing Ca(2+) influx in response to membrane depolarization by inhibiting N-type Ca(2+) channels with omega-conotoxin (omega-CTX) greatly attenuated the exocytosis of [(3)H]norepinephrine from both SH-SY5Y and SH-SY5Y-H(3) cells, as well as the exocytosis of endogenous norepinephrine from cardiac synaptosomes. Similar to omega-CTX, activation of H(3)R with the selective H(3)R-agonist imetit also reduced both the rise in intracellular Ca(2+) concentration (Ca(i)) and norepinephrine exocytosis in response to membrane depolarization. The selective H(3)R antagonist thioperamide prevented this effect of imetit. In the parent SH-SY5Y cells lacking H(3)R, imetit affected neither the rise in Ca(i) nor [(3)H]norepinephrine exocytosis, demonstrating that the presence of H(3)R is a prerequisite for a decrease in Ca(i) in response to imetit and that H(3)R activation modulates norepinephrine exocytosis by limiting the magnitude of the increase in Ca(i). Inasmuch as excessive norepinephrine exocytosis is a leading cause of cardiac dysfunction and arrhythmias during acute myocardial ischemia, attenuation of norepinephrine release by H(3)R agonists may offer a novel therapeutic approach to this condition.

Topics: Animals; Calcium; Calcium Channel Blockers; Cell Line; Dose-Response Relationship, Drug; Exocytosis; Guinea Pigs; Histamine Agonists; Humans; Imidazoles; Male; Myocardial Ischemia; Myocardium; Neuroblastoma; Neurons; Norepinephrine; omega-Conotoxins; Potassium; Receptors, Histamine H3; Thiourea; Time Factors; Transfection; Tumor Cells, Cultured

Histamine exerts its numerous physiological functions through interaction with G protein-coupled receptors. Three such receptors have been defined at both the pharmacological and molecular level, while pharmacological evidence hints at the existence of further subtypes. We report here the cloning and characterization of a fourth histamine receptor subtype. Initially discovered in an expressed-sequence tag database, the full coding sequence (SP9144) was subsequently identified in chromosome 18 genomic sequence. This virtual coding sequence exhibited highest homology to the H(3) histamine receptor and was used to generate a full-length clone by polymerase chain reaction (PCR). The distribution of mRNA encoding SP9144 was restricted to cells of the immune system as determined by quantitative PCR. HEK-293 cells transiently transfected with SP9144 and a chimeric G protein alpha-subunit (Galpha(q/i1,2)) exhibited increases in intracellular [Ca(2+)] in response to histamine but not other biogenic amines. SP9144-transfected cells exhibited saturable, specific, high-affinity binding of [(3)H]histamine, which was potently inhibited by H(3) receptor-selective compounds. The rank order and potency of these compounds at SP9144 differed from the rank order at the H(3) receptor. Although SP9144 apparently coupled to Galpha(i), HEK-293 cells stably transfected with SP9144 did not exhibit histamine-mediated inhibition of forskolin-stimulated cAMP levels. However, both [(35)S]GTPgammaS binding and phosphorylation of mitogen-activated protein kinase were stimulated by histamine via SP9144 activation. In both of these assays, SP9144 exhibited evidence of constitutive activation. Taken together, these data demonstrate that SP9144 is a unique, fourth histamine receptor subtype.

Topics: Amino Acid Sequence; Cells, Cultured; Cloning, Molecular; Histamine; Histamine Agonists; Humans; Imidazoles; Molecular Sequence Data; Radioligand Assay; Receptors, Histamine; Receptors, Histamine H3; RNA, Messenger; Sequence Homology, Amino Acid; Thiourea; Tissue Distribution; Transfection

Following a previous report by our research group on discriminative properties of a series of aliphatic histamine homologues, we now studied immepip, imetit and its lower and higher sidechain homologues as ligands for the histamine H(3) receptor in a [(125)I]-iodophenpropit binding assay using rat cerebral cortex membranes, and two functional H(3) receptor models (inhibition of the neurogenic contraction of the guinea pig jejunum and inhibition of [(3)H]-noradrenaline release in rat cerebral cortex slices). The immepip homologues behaved as competitive H(3)-receptor antagonists in both functional systems. The potencies (pA(2) values) observed at the guinea pig jejunum were 8.4 and 6.2 for the immepip homologues VUF 4929 and VUF 4735, respectively, whereas on the electrically evoked release of [(3)H]-noradrenaline from cortical slices the pA(2) values were 7.1 and 5.5 for VUF 4929 and VUF 4735, respectively. Moreover, immepip, but not the (R)-alpha-methylhistamine, showed almost a tenfold higher agonistic potency in the rat cerebral cortex than in the guinea pig jejunum. For imetit and its homologues important discrepancies in the potencies in the two functional assays were noticed as well. VUF 8328 acts as a potent (pD(2)=8.0) partial agonist in the brain, but as a very active (pA(2)=9.4) competitive antagonist in the guinea pig jejunum. The partial agonistic activity of VUF 8328 in the brain was confirmed by GTP gamma S-sensitive, biphasic displacement of [(125)I]-iodophenpropit binding to rat cerebral cortex membranes. The differences in potencies shown by the various ligands are discussed in relation to H(3) receptor heterogeneity.

Topics: Animals; Cerebral Cortex; Guinea Pigs; Histamine Agonists; Imidazoles; Jejunum; Male; Piperidines; Radioligand Assay; Rats; Receptors, Histamine H3; Structure-Activity Relationship; Thiourea

Agonist-independent activity of G-protein-coupled receptor, also referred to as constitutive activity, is a well-documented phenomenon and has been reported recently for both the histamine H(1) and H(2) receptors. Using SK-N-MC cell lines stably expressing the human and rat H(3) receptors at physiological receptor densities (500-600 fmol/mg of protein), we show that both the rat and human H(3) receptors show a high degree of constitutive activity. The forskolin-mediated cAMP production in SK-N-MC cells is inhibited strongly upon expression of the G(i)-coupled H(3) receptor. The cAMP production can be further inhibited upon agonist stimulation of the H(3) receptor and can be enhanced by a variety of H(3) antagonists acting as inverse agonists at the H(3) receptor. Thioperamide, clobenpropit, and iodophenpropit raise the cAMP levels in SK-N-MC cells with potencies that match their receptor binding affinities. Surprisingly, impentamine and burimamide act as effective H(3) agonists. Modification of the amine group of impentamine dramatically affected the pharmacological activity of the ligand. Receptor affinity was reduced slightly for most impentamine analogs, but the functional activity of the ligands varied from agonist to neutral antagonist and inverse agonist, indicating that subtle changes in the chemical structures of impentamine analogs have major impact on the (de)activation steps of the H(3) receptor. In conclusion, upon stable expression of the rat and human H(3) receptor in SK-N-MC cells constitutive receptor activity is detected. In this experimental system, H(3) receptors ligands, previously identified as H(3) antagonists, cover the whole spectrum of pharmacological activities, ranging from full inverse agonists to agonists.

Topics: Animals; Burimamide; Cyclic AMP; Histamine Antagonists; Humans; Imidazoles; Male; Rats; Rats, Wistar; Receptors, Histamine H3; Recombinant Proteins; Thiourea; Tumor Cells, Cultured

We studied the effects of histamine H(3) receptor ligands on the release of endogenous acetylcholine from the isolated, vascularly perfused rat stomach. The stomach was perfused via the celiac artery with modified Krebs-Ringer solution containing physostigmine. Released acetylcholine from the portal vein was electrochemically measured using high-performance liquid chromatography and an enzyme system. Vagus nerves were electrically stimulated twice for 2 min (0.5 or 2.5 Hz). Acetylcholine release evoked at 2.5 Hz was slightly inhibited by histamine and effectively potentiated by thioperamide, a histamine H(3) receptor antagonist. Acetylcholine release evoked at 0.5 Hz in the presence of atropine was not influenced by thioperamide, but effectively inhibited by histamine, R-alpha-methylhistamine or imetit, histamine H(3) receptor agonists. These inhibitory effects were abolished by thioperamide or pertussis toxin. These results suggest that histamine attenuates acetylcholine release from vagus nerves through histamine H(3) receptor-mediated and pertussis toxin-sensitive mechanisms in the rat stomach.

Topics: Acetylcholine; Animals; Atropine; Gastric Mucosa; GTP-Binding Proteins; Histamine; Imidazoles; Male; Methylhistamines; Perfusion; Pertussis Toxin; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H3; Thiourea; Vagus Nerve; Virulence Factors, Bordetella

The effects of different histamine receptor agonists and antagonists on apomorphine-induced licking behavior in rats were investigated. Subcutaneous (s.c.) injection of various doses of apomorphine (0. 125-1.25 mg/kg) induced licking. The licking response was counted by direct observation and recorded for a 75-min period. Intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of the histamine H(1) or H(2) receptor agonist, HTMT (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl) heptanecarboxamide) (50 and 100 microg per rat), or dimaprit (10 and 15 mg/kg, i.p.), respectively, potentiated apomorphine-induced licking, while the histamine H(3) receptor agonist, imetit (5 and 10 mg/kg, i.p.), reduced the licking response induced by apomorphine. Pretreatment with various histamine receptor antagonists, dexchlorpheniramine (30 and 40 mg/kg, i.p.), diphenhydramine (20, 30 and 40 mg/kg, i.p.), famotidine (30 and 40 mg/kg, s.c.) and ranitidine (20, 30 and 40 mg/kg), reduced apomorphine-induced licking, while thioperamide (5 and 10 mg/kg, i.p.) potentiated the apomorphine effect. The effects of HTMT and dimaprit were blocked by dexchlorpheniramine (20 mg/kg, i.p.) and famotidine (20 mg/kg, s.c.), respectively. The inhibitory effect elicited by imetit on apomorphine-induced licking behavior was also abolished in animals treated with thioperamide (2.5 mg/kg, i.p.). The results suggest that histaminergic mechanisms may be involved in the modulation of apomorphine-induced licking behavior.

Topics: Animals; Apomorphine; Chlorpheniramine; Dimaprit; Diphenhydramine; Dopamine Agonists; Drug Interactions; Famotidine; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Male; Piperidines; Ranitidine; Rats; Rats, Sprague-Dawley; Stereotyped Behavior; Thiourea; Toluidines

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

The pharmacological mechanisms involved in the interactions between C-fibers, cholinergic fibers and mast cells were investigated in tracheally perfused rabbit lungs by measuring the simultaneous release of substance P and histamine in lung effluents. The amounts of substance P and histamine released in lung superfusates were measured by radioimmunoassay (RIA) after administration of capsaicin and carbachol. Capsaicin (10(-4) M) induced a simultaneous increase in substance P (273 +/- 56% of baseline) and histamine (460 +/- 138%) release. Similarly, carbachol (10(-4) M) caused an increase in the release of both substance P (367 +/- 111%) and histamine (1379 +/- 351%). The effect of capsaicin was prevented by pretreating the lungs with the tachykinin NK1 receptor antagonist SR 140333 (10(-7) M), and atropine (10(-6) M). SR 140333 prevented the carbachol-induced release of substance P but not of histamine. Exogenous substance P induced an increase in histamine release (136 +/- 7%) which was significantly greater in lungs perfused with the neutral endopeptidase inhibitor, thiorphan (10(-5) M) (272 +/- 35%). This effect was prevented by atropine (10(-6) M). Pretreatment of lungs with imetit (5 x 10(-8) M), a selective H3 receptor agonist, prevented the capsaicin-induced release of both mediators. Imetit also blocked the carbachol-induced release of substance P but not of histamine. Exogenous substance P-evoked histamine release was inhibited by imetit. Therefore, it can be concluded that substance P released through the action of capsaicin can activate cholinergic fibers, leading to cholinoceptor stimulation with subsequent activation of C-fibers and mast cells. While the presence of presynaptic H3 receptors modulating substance P-induced acetylcholine release was only surmised, the existence of modulating histamine H3 receptors on C-fibers was confirmed.

Topics: Animals; Capsaicin; Carbachol; Cholinergic Fibers; Drug Interactions; Female; Histamine Agonists; Histamine Release; Imidazoles; In Vitro Techniques; Lung; Male; Mast Cells; Rabbits; Radioimmunoassay; Receptors, Histamine H3; Substance P; Thiourea

Activation of histaminergic and noradrenergic/adrenergic neurons in the brain stimulates the release of the neurohypophysial hormones arginine vasopressin (AVP) and oxytocin (OT) and are involved the mediation of the hormone responses to physiological stimuli such as dehydration and suckling. We therefore investigated whether the two neuronal systems interact in their regulation of AVP and OT secretion in conscious male rats. When administered intracerebroventricularly (i.c.v.), histamine (HA) as well as the H1 receptor agonist 2-thiazolylethylamine or the H2 receptor agonist 4-methylHA stimulated AVP and OT secretion. Prior i.c.v. infusion of antagonists specific to alpha or beta adrenergic receptors or their subtypes did not significantly affect the hormone response to HA or the histaminergic agonists. Infused i.c.v. norepinephrine (NE) or epinephrine (E) increased AVP and OT secretion. Prior i.c.v. infusion of the H1 receptor antagonist mepyramine or the H2 receptor antagonist cimetidine significantly inhibited the AVP and OT responses to NE and the AVP response to E, whereas only cimetidine inhibited the OT response to E significantly. Systemic pretreatment with imetit, which by activation of presynaptic H3 receptors inhibits neuronal synthesis and release of HA, decreased the AVP and OT responses to NE and E significantly. In the doses used, HA and E had no significant effect on mean arterial blood pressure. NE increased mean arterial blood pressure 10% at 1 and 2.5 min, whereafter the blood pressure returned to basal level within 10 min. The results indicate that noradrenergic and adrenergic neurons stimulate AVP and OT secretion via an involvement of histaminergic neurons, which may occur at magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus. The stimulatory effect of the amines on neurohypophysial hormone secretion seems to be independent of a central action on blood pressure. In contrast, a functionally intact noradrenergic and adrenergic neuronal system seems not to be a prerequisite for a HA-induced release of AVP and OT. The present findings further substantiate the role of histaminergic neurons in the central regulation of neurohypophysial hormone secretion.

Topics: Animals; Arginine Vasopressin; Blood Pressure; Cerebral Ventricles; Cimetidine; Epinephrine; Histamine; Histamine Agonists; Hypothalamus; Imidazoles; Infusions, Parenteral; Male; Methylhistamines; Norepinephrine; Oxytocin; Pituitary Gland, Posterior; Pyrilamine; Rats; Rats, Wistar; Receptors, Histamine H2; Thiazoles; Thiourea

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

The ability of histamine H3 receptor ligands to interact with 5-HT3 receptors in NG108-15 cells was studied using the whole cell patch clamp recording technique. Imetit, a histamine H3 receptor agonist, generated inward currents and exhibited weak partial agonist activity at the 5-HT3 receptor (EC50 = 11.8 microM). Imetit-induced currents were slow to desensitize and at a high concentration reduced in size. The histamine H3 receptor antagonists iodophenpropit and thioperamide did not generate inward currents but were able to inhibit 5-hydroxytryptamine (5-HT) responses with an IC50 of 1.57+/-0.3 microM and 13.7+/-3.5 microM, respectively. Thioperamide is probably a non-competitive antagonist which may have more than one binding site on the receptor.

Topics: Animals; Cells, Cultured; Dose-Response Relationship, Drug; Histamine Agonists; Histamine Antagonists; Hybrid Cells; Imidazoles; Ion Channels; Isothiuronium; Membrane Potentials; Mice; Piperidines; Rats; Receptors, Histamine H3; Receptors, Serotonin; Receptors, Serotonin, 5-HT3; Serotonin Antagonists; Serotonin Receptor Agonists; Thiourea

We compared the effects of modulating the postsynaptic histamine receptor subtype 2 (H2) and inhibitory presynaptic autoreceptor subtype 3 (H3) on memory processing in the septum. Mice were partially trained on footshock avoidance in a T-maze. Immediately after training, saline or a drug solution was infused into the septum. One week later, retention was tested by continuing training until the mice made five avoidance responses in six consecutive trials. The results indicate that dimaprit, an H2 agonist, facilitated retention (25 and 50 pg) with a U-shaped dose-response curve typical of drugs acting at postsynaptic receptors. Cimetidine, an H2 antagonist, impaired retention (15-50 ng). The H3 agonist. imetit, impaired retention (25-200 ng), while the H3 antagonist, thioperamide, facilitated retention (10-400 ng). An unusual feature of the dose-response curve for thioperamide was that it did not appeal to yield a U-shaped curve as occurs with drugs acting postsynaptically, but facilitated retention to approximately the same degree from 50 to 400 ng. As histamine neurons project to various limbic system structures involved in memory processing, it may play an important role in regulating the activity of structures such as the septum, hippocampus and amygdala.

Topics: Animals; Cimetidine; Dimaprit; Histamine Agonists; Histamine Antagonists; Imidazoles; Limbic System; Male; Memory; Mice; Piperidines; 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; Dimaprit; Histamine Agonists; Histamine Antagonists; Histamine Release; Imidazoles; Impromidine; Male; Mast Cells; Peritoneal Cavity; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Thiourea

We studied whether interactions between the presynaptic histamine H3 and prostaglandin EP3 receptors on the noradrenergic neurons of the mouse brain cortex occur. Cerebral cortex slices from the mouse (and, in few experiments, from the rat) were preincubated with [3H]noradrenaline and then superfused with a physiological salt solution. Tritium overflow was evoked electrically, either at 0.3 or 3 Hz (2 min) (standard stimulation protocol) or at 100 Hz (eight pulses) (stimulation protocol under which almost no activation of the presynaptic alpha2-adrenoceptors by endogenous noradrenaline occurs). In another set of experiments, Ca2+ ions were introduced into Ca2+-free K+-rich medium containing tetrodotoxin to evoke tritium overflow. The electrically-evoked tritium overflow (0.3 Hz) was inhibited by histamine or the H3 receptor agonist imetit, acting via H3 receptors. and by prostaglandin E2 or the EP3 receptor agonist sulprostone, acting via EP3 receptors. When histamine or imetit was given first (at concentrations causing the maximum effect at H3 receptors), the effect of prostaglandin E2 on the evoked tritium overflow was attenuated by 5-10%. When prostaglandin E2 or sulprostone was given first (at concentrations causing the maximum effect at EP3 receptors), the effect of histamine or imetit on the evoked overflow was attenuated by almost 50%. The previous administration of prostaglandin E2 also blunted the effect of histamine on the evoked tritium overflow evoked at 3 Hz; the degree of attenuation was identical when the current strength was 25 mA or was increased to 100 or 200 mA in order to partially compensate for the inhibitory effect of prostaglandin E2 on the evoked overflow. In addition, prostaglandin E2 attenuated the effect of histamine when tritium overflow was evoked (i) by 100 Hz, eight pulses or (ii) by Ca2+ ions or (iii) when rat (instead of mouse) brain cortex slices were used. An interaction of prostaglandin E2 or sulprostone with the H3 receptor recognition site could be excluded since both prostanoids did not affect the specific binding of the H3 agonist radioligand [3H]N(alpha)-methylhistamine to rat brain cortex membranes. In conclusion, mutual interactions occur between the presynaptic H3 and EP3 receptors involved in the inhibition of noradrenaline release in the mouse brain cortex. Pre-activation of the H3 receptor slightly attenuates the EP3 receptor-mediated effect whereas pre-activation of the EP3 receptor more markedly attenuates

Topics: Animals; Brain; Calcium; Cerebral Cortex; Dinoprostone; Electric Stimulation; Histamine; Histamine Agonists; Imidazoles; In Vitro Techniques; Male; Mice; Mice, Inbred Strains; Nerve Endings; Norepinephrine; Radioisotope Dilution Technique; Rats; Receptors, Adrenergic, alpha-2; Receptors, Histamine H3; Receptors, Prostaglandin E; Receptors, Prostaglandin E, EP3 Subtype; Thiourea; Tritium

We examined the possible existence of prejunctional histamine H3 receptors on sympathetic nerve fibers innervating rat tail artery. The stimulation-evoked tritium outflow from isolated vessels preincubated with [3H]-noradrenaline and perfused/superfused in the presence of the alpha2-adrenoceptor antagonist rauwolscine, 3 microM, was inhibited by histamine 10 microM (by 8%) and the H3 agonists R-(-)-alpha-methylhistamine, 10 microM (by 18%), and imetit, 0.1-10 microM (by < or =20%). The inhibitory effect of imetit, which did not occur in the absence of rauwolscine, was counteracted by thioperamide, 1 microM. In the presence of rauwolscine, 3 microM, the inhibitory effect of imetit also occurred when the current strength or the Ca2+ concentration in the medium was reduced to compensate for the increase in tritium overflow elicited by rauwolscine, indicating that the inhibitory action of imetit is not associated with the increase in noradrenaline release produced by rauwolscine. In spontaneously hypertensive rats (SHRs), imetit also inhibited the overflow of tritium. This inhibitory effect was comparable to that observed in Wistar-Kyoto (WKY) rats and indicates that the sympathetic nerves of the rat tail artery in SHRs, like those in normotensive rats, are endowed with prejunctional histamine H3 receptors.

Topics: Adrenergic alpha-2 Receptor Antagonists; Animals; Arteries; Electric Stimulation; Histamine; Histamine Agonists; Imidazoles; Male; Norepinephrine; Piperidines; Rats; Rats, Inbred SHR; Rats, Wistar; Receptors, Histamine H3; Sympathetic Fibers, Postganglionic; Thiourea; Yohimbine

The modulatory role of histamine H3 receptors in pulmonary oedema induced by acetylcholine, capsaicin and by exogenous substance P was investigated in isolated, ventilated rabbit lungs. Endothelial permeability was evaluated by measuring the capillary filtration coefficient (Kf,c). Acetylcholine (10(-8) to 10(-4) M), substance P (10(-10) to 10(-6) M), capsaicin (10(-4) M) and 5-hydroxytryptamine (5-HT) (10(-4) M) induced an increase in the Kf,c. Carboperamide, a novel histamine H3 receptor antagonist, induced a significant leftward shift of the concentration-response curve to acetylcholine and also enhanced the effect of capsaicin on the Kf,c, while it had no significant effect on the response to substance P and 5-HT. Imetit, a new histamine H3 receptor agonist, strongly inhibited the effects of acetylcholine and capsaicin. Imetit also strongly protected the lung against substance P effects but did not prevent the 5-HT-induced increase in the Kf,c. Carboperamide completely blocked the inhibitory effect of Imetit on the acetylcholine response. (R)-alpha-Methylhistamine, an other histamine H3 receptor agonist, had the same protective effect against acetylcholine response as Imetit. We conclude that histamine H3 receptors could protect the lung against acetylcholine- and capsaicin-induced oedema via a prejunctional modulatory effect on the C-fibres. However, since the response to exogenous substance P was also inhibited by histamine H3 receptor stimulation, the presence of such receptors at a postsynaptic level, probably on mast cells, was also suggested.

Topics: Acetylcholine; Animals; Capillary Permeability; Capsaicin; Dose-Response Relationship, Drug; Drug Interactions; Endothelium; Female; Histamine Agonists; Histamine Antagonists; Imidazoles; In Vitro Techniques; Lung; Male; Nerve Fibers; Piperidines; Pulmonary Edema; Rabbits; Receptors, Histamine H3; Serotonin; Substance P; Thiourea

Norepinephrine release contributes to ischemic cardiac dysfunction and arrhythmias. Because activation of histamine H3-receptors inhibits norepinephrine release, we searched for the presence of H3-receptors directly in sympathetic nerve endings (cardiac synaptosomes) isolated from surgical specimens of human atria. Norepinephrine was released by depolarization with K+. The presence of H3-receptors was ascertained because the selective H3-receptor agonists (R) alpha-methylhistamine and imetit reduced norepinephrine release, and the specific H3-receptor antagonist thioperamide blocked this effect. Norepinephrine release was exocytotic, since it was inhibited by the N-type Ca(2+)-channel blocker omega-conotoxin and the protein kinase C inhibitor Ro31-8220. Functional relevance of these H3-receptors was obtained by showing that transmural electrical stimulation of sympathetic nerve endings in human atrial tissue increased contractility, an effect blocked by propranolol and attenuated in a concentration-dependent manner by (R) alpha-methylhistamine. Also, thioperamide antagonized the effect of (R) alpha-methylhistamine. Our findings are the first demonstration that H3-receptors are present in sympathetic nerve endings in the human heart, where they modulate adrenergic responses by inhibiting norepinephrine release. Since myocardial ischemia causes intracardiac histamine release, H3-receptor-induced attenuation of sympathetic neurotransmission may be clinically relevant.

Topics: Cell Separation; Electric Stimulation; Exocytosis; Heart; Histamine Agonists; Histamine Antagonists; Humans; Imidazoles; In Vitro Techniques; Indoles; Methylhistamines; Myocardial Ischemia; Myocardium; Norepinephrine; Piperidines; Protein Kinase C; Receptors, Histamine H3; Synaptosomes; Thiourea

Bombesin (BN) and its mammalian homologue, gastrin-releasing peptide (GRP), are potent satiety agents and have been implicated in the physiological regulation of food intake. The mechanism(s) of action of this effect remains unclear. There is a functional and anatomic overlap between histamine and BN in relationship to feeding, which led us to hypothesize that BN may mediate its satiety effects through activation of the histaminergic system. To assess this contention, we examined the effects of R-alpha-methylhistamine (alpha-MH) and Imetit, selective H3-receptor agonists that inhibit the release and synthesis of histamine, on BN- or cholecystokinin (CCK)-induced satiety. In this report we present the first evidence for the role of histamine H3 receptors in the mediation of BN-elicited satiety. During the first hour of the 4-h daily feeding session, BN reduced food intake by > 50% relative to the control condition; this suppression was blocked by prior treatment with the H3-receptor agonist, alpha-MH. This blockade of BN-induced satiety was dose related and selective to BN as alpha-MH failed to attenuate sulfated CCK-8-induced satiety. When alpha-MH was administered alone, it failed to significantly affect food intake. The specificity of this effect was further supported by the demonstration that another H3 agonist, Imetit, was also able to block the feeding-suppressant effects of BN. Furthermore, thioperamide, an H3-receptor antagonist, blocked these effects of Imetit.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Behavior, Animal; Bombesin; Eating; Gastrin-Releasing Peptide; Histamine; Histamine Agonists; Histamine Antagonists; Imidazoles; Male; Methylhistamines; Motor Activity; Peptides; Piperidines; Rats; Rats, Sprague-Dawley; Satiation; Sincalide; Thiourea

The effects of a new agonist of histamine (HA) H3 receptors, Imetit (S-[2-(4-(imidazolyl)ethyl]isothiourea) were investigated in vitro and in vivo and compared to those of (R)-alpha-methylhistamine [(R)-alpha-MeHA], a prototypic drug. Imetit inhibited the binding of [3H](R-alpha-MeHA to rat brain membranes with a Ki value of 0.1 +/- 0.01 nM. The release of endogenously synthesized [3H]HA induced by K(+)-depolarization from rat brain slices and synaptosomes was inhibited by Imetit with EC50 values of 1.0 +/- 0.3 and 2.8 +/- 0.7 nM, respectively. Imetit behaved as a full agonist and was about 4 times more potent than (R)-alpha-MeHA and 60 times more potent than HA. Thioperamide, a selective H3 receptor antagonist, elicited a parallel rightward shift of the concentration-response curve for Imetit with an apparent Ki value of 5.6 +/- 1.4 nM. Imetit potencies relative to HA were less than 0.1% and only 0.6% at HA H1 and H2 receptor reference systems, respectively. Imetit was found not to be a substrate or an inhibitor of HMT. After p.o. administration to mice or rats, Imetit decreased (by approximately 50%) the tele-MeHA level in the cerebral cortex with ED50 values of 1.0 +/- 0.3 and 1.6 +/- 0.3 mg/kg, respectively. This effect was still maximal after 6 hr. The in vivo potency and duration of action of Imetit were in the same range as those of (R)-alpha-MeHA. It is therefore concluded that Imetit represents a new potent and selective HA H3 receptor agonist.

Topics: Animals; Cerebral Cortex; Guinea Pigs; Histamine Agonists; Histamine N-Methyltransferase; Histamine Release; Imidazoles; Methylhistamines; Mice; Rats; Receptors, Histamine; Receptors, Histamine H3; Thiourea; Urea