piperidines and tiotidine

Premedication with a combination of histamine H₁ receptor (H₁R) and H₂ receptor (H₂R) antagonists has been suggested as a prophylactic principle, for instance, in anaesthesia and surgery. Aiming at pharmacological hybrids combining H₁R and H₂R antagonistic activity, a series of cyanoguanidines 14-35 was synthesized by linking mepyramine-type H₁R antagonist substructures with roxatidine-, tiotidine-, or ranitidine-type H₂R antagonist moieties. N-desmethylmepyramine was connected via a poly-methylene spacer to a cyanoguanidine group as the "urea equivalent" of the H₂R antagonist moiety. The title compounds were screened for histamine antagonistic activity at the isolated ileum (H₁R) and the isolated spontaneously beating right atrium (H₂R) of the guinea pig. The results indicate that, depending on the nature of the H₂R antagonist partial structure, the highest H₁R antagonist potency resided in roxatidine-type compounds with spacers of six methylene groups in length (compound 21), and tiotidine-type compounds irrespective of the alkyl chain length (compounds 28, 32, 33), N-cyano-N'-[2-[[(2-guanidino-4-thiazolyl)methyl]thio]ethyl]-N″-[2-[N-[2-[N-(4-methoxybenzyl)-N-(pyridyl)-amino] ethyl]-N-methylamino]ethyl] guanidine (25, pKB values: 8.05 (H₁R, ileum) and 7.73 (H₂R, atrium) and the homologue with the mepyramine moiety connected by a six-membered chain to the tiotidine-like partial structure (compound 32, pKB values: 8.61 (H₁R) and 6.61 (H₂R) were among the most potent hybrid compounds. With respect to the development of a potential pharmacotherapeutic agent, structural optimization seems possible through selection of other H₁R and H₂R pharmacophoric moieties with mutually affinity-enhancing properties.

Topics: Animals; Cimetidine; Guanidines; Guinea Pigs; Histamine H1 Antagonists; Histamine H2 Antagonists; Magnetic Resonance Spectroscopy; Male; Molecular Structure; Piperidines; Pyrilamine

Production of N-alpha-methyl-histamine (NAMH), a histamine H(3) receptor (H3R) agonist, is reportedly promoted in Helicobacter pylori infected human gastric mucosa. NAMH was suggested to act directly on histamine H(2) receptors (H2Rs) in animals to stimulate acid secretion and to be a H2R agonist. As H2Rs and H3Rs play different roles in gastric acid secretion, it is very important to verify that NAMH is a H2R agonist.. To determine whether NAMH is a H2R agonist, as well as a H3R agonist.. We used a Chinese hamster ovary (CHO) cell line expressing human H2Rs (CHO-H2R) and control CHO cells. Expression of human H2Rs was confirmed by tiotidine binding. cAMP production in CHO-H2R and control cells in response to histamine or NAMH was measured. cAMP production in response to 10(-7) M NAMH was also measured in the presence or absence of the H2R antagonist famotidine and the H3R antagonist thioperamide.. NAMH dose dependently stimulated cAMP productions in CHO-H2R cells. This production was inhibited by famotidine but not by thioperamide. Control CHO cells were unresponsive to either histamine or NAMH. In addition, the effect of NAMH, in terms of cAMP production in CHO-H2R cells, was more potent than that of histamine-that is, with a lower EC(50) concentration and higher maximal cAMP production. Both NAMH and histamine, but not R-alpha-methyl-histamine, effectively inhibited [(3)H] tiotidine binding to CHO-H2R cells.. NAMH, which is produced in the gastric mucosa by H pylori, is a potent H2R agonist as well as a H3R agonist.

Topics: Animals; CHO Cells; Cimetidine; Cricetinae; Cyclic AMP; Famotidine; Female; Histamine Agonists; Histamine Antagonists; Histamine H2 Antagonists; Methylhistamines; Ovary; Piperidines; Receptors, Histamine H2; Receptors, Histamine H3

It is unknown why the potencies and efficacies of long-chained guanidine-type histamine H2-receptor (H2R) agonists are lower at the H2R of human neutrophils than at the H2R of the guinea pig atrium. To elucidate these differences, we analyzed fusion proteins of the human H2R (hH2R) and guinea pig H2R (gpH2R), respectively, and the short splice variant of Gsalpha (GsalphaS) expressed in Sf9 cells. The potencies and efficacies of small H2R agonists in the GTPase assay and the potencies of antagonists at inhibiting histamine-stimulated GTP hydrolysis by hH2R-GsalphaS and gpH2R-GsalphaS were similar. In contrast, the potencies and efficacies of guanidines were lower at hH2R-GsalphaS than at gpH2R-G(salphaS). Guanidines bound to hH2R-GsalphaS with lower affinity than to gpH2R-GsalphaS, and high-affinity binding of guanidines at gpH2R-GsalphaS was more resistant to disruption by GTPgammaS than binding at hH2R-GsalphaS. Molecular modeling suggested that the nonconserved Asp-271 in transmembrane domain 7 of gpH2R (Ala-271 in hH2R) confers high potency to guanidines. This hypothesis was confirmed by Ala-271-->Asp-271 mutation in hH2R-GsalphaS. Intriguingly, the efficacies of guanidines at the Ala-271-->Asp-271 mutant and at hH2R/gpH2R chimeras were lower than at gpH2R. Our model suggests that a Tyr-17/Asp-271 H-bond, present only in gpH2R-GsalphaS but not the other constructs studied, stabilizes the active guanidine-H2R state. Collectively, our data show 1) distinct interaction of H2R species isoforms with guanidines, 2) that a single amino acid in transmembrane domain 7 critically determines guanidine potency, and 3) that an interaction between transmembrane domains 1 and 7 is important for guanidine efficacy.

Topics: Alternative Splicing; Amino Acid Sequence; Animals; Binding Sites; Cell Membrane; Cells, Cultured; Cimetidine; GTP-Binding Protein alpha Subunits, Gs; Guanidine; Guanidines; Guanosine 5'-O-(3-Thiotriphosphate); Guinea Pigs; Histamine Agonists; Humans; Insecta; Models, Molecular; Molecular Sequence Data; Piperidines; Protein Conformation; Protein Isoforms; Ranitidine; Receptors, Histamine H2; Sequence Homology, Amino Acid; Species Specificity; Structure-Activity Relationship; Sulfur Radioisotopes; Tritium

Based on animal models, lafutidine, a novel histamine H(2) receptor (H(2)R) antagonist, is reported to show potent and long-lasting antagonisms of histamine H(2)R-mediated effects. However, no reports have been published concerning its direct interaction with the human H(2)R. This study aims at characterizing its interaction with human H(2)R.. Chinese hamster ovary cell lines stably expressing human H(2)Rs were obtained. The dose-dependent effects of lafutidine and famotidine on [(3)H]tiotidine binding and histamine-stimulated cAMP production were analyzed. The effects of preincubation with 2.78 x 10(-7) M of lafutidine or famotidine for 30 min on histamine-dependent cAMP production and [(3)H]tiotidine binding were also examined after 0, 1, 2, 4, and 12 h. This concentration is below the C(max) of lafutidine (10 mg p.o.) and above the C(max) of famotidine (20 mg p.o.).. Lafutidine inhibited [(3)H]tiotidine binding and histamine-stimulated cAMP production as or more potently than famotidine. At higher concentrations lafutidine was more potent than famotidine. In addition, preincubation with 2.78 x 10(-7) M lafutidine, but not with 10(-5) M famotidine, had marked inhibitory effects which persisted as long as after extensive washing.. Lafutidine shows a potent and long-lasting antagonism on the human H(2)R.

Topics: Acetamides; Animals; CHO Cells; Cimetidine; Cricetinae; Cyclic AMP; Dose-Response Relationship, Drug; Famotidine; Histamine H2 Antagonists; Humans; Piperidines; Pyridines; Receptors, Histamine H2; Transfection

Based on animal models, IT-066, a histamine H2-receptor antagonist, is reported to possess potent and long-lasting antagonisms on histamine H2 receptor (H2R) -mediated effects. However, no reports have been published concerning its interaction with the human H2R. The aim of this study is to characterize its interaction with human H2R. Chinese hamster ovary cell lines stably expressing human H2Rs were obtained. The effects of IT-066, famotidine, and ranitidine on tiotidine binding and histamine-stimulated cAMP production were analyzed. IT-066 inhibited [3H]tiotidine binding and histamine-stimulated cAMP production more potently than famotidine or ranitidine. In addition, preincubation with 10(-5) M IT-066, but not with 10(-5) M famotidine or 10(-4) M ranitidine, had marked inhibitory effects long after extensive washing. Paraformaldehyde fixation of the cells blunted inhibition of [3H]tiotidine binding induced by preincubation with IT-066, but not that by preincubation with famotidine or ranitidine. IT-066 has potent and long-lasting antagonisms on human H2R. At least one of the IT-066 binding sites is not shared by famotidine, ranitidine, or tiotidine and is affected by paraformaldehyde fixation.

Topics: Animals; Anti-Ulcer Agents; CHO Cells; Cimetidine; Cricetinae; Cyclic AMP; Famotidine; Fixatives; Formaldehyde; Histamine H2 Antagonists; Piperidines; Polymers; Protein Binding; Pyridines; Ranitidine; Receptors, Histamine H2

1. Rat histamine H2 receptors were epitope-tagged with six histidine residues at the C-terminus to allow immunological detection of the receptor. Recombinant baculoviruses containing the epitope-tagged H2 receptor were prepared and were used to infect insect Sf9 cells. 2. The His-tagged H2 receptors expressed in insect Sf9 cells showed typical H2 receptor characteristics as determined with [125I]-aminopotentidine (APT) binding studies. 3. In Sf9 cells expressing the His-tagged H2 receptor histamine was able to stimulate cyclic AMP production 9 fold (EC50=2.1+/-0.1 microM) by use of the endogenous signalling pathway. The classical antagonists cimetidine, ranitidine and tiotidine inhibited histamine induced cyclic AMP production with Ki values of 0.60+/-0.43 microM, 0.25+/-0.15 microM and 28+/-7 nM, respectively (mean+/-s.e.mean, n=3). 4. The expression of the His-tagged H2 receptors in infected Sf9 cells reached functional levels of 6.6+/-0.6 pmol mg(-1) protein (mean+/-s.e.mean, n=3) after 3 days of infection. This represents about 2 x 10(6) copies of receptor/cell. Preincubation of the cells with 0.03 mM cholesterol-beta-cyclodextrin complex resulted in an increase of [125I]-APT binding up to 169+/-5% (mean+/-s.e.mean, n=3). 5. The addition of 0.03 mM cholesterol-beta-cyclodextrin complex did not affect histamine-induced cyclic AMP production. The EC50 value of histamine was 3.1+/-1.7 microM in the absence of cholesterol-beta-cyclodextrin complex and 11.1+/-5.5 microM in the presence of cholesterol-beta-cyclodextrin complex (mean+/-s.e.mean, n=3). Also, the amount of cyclic AMP produced in the presence of 100 microM histamine was identical, 85+/-18 pmol/10(6) cells in the absence and 81+/-11 pmol/10(6) cells in the presence of 0.03 mM cholesterol-beta-cyclodextrin complex (mean+/-s.e.mean, n=3). 6. Immunofluorescence studies with an antibody against the His-tag revealed that the majority of the His-tagged H2 receptors was localized inside the insect Sf9 cells, although plasma membrane labelling could be identified as well. 7. These experiments demonstrate the successful expression of His-tagged histamine H2 receptors in insect Sf9 cells. The H2 receptors couple functionally to the insect cell adenylate cyclase. However, our studies with cholesterol complementation and with immunofluorescent detection of the His-tag reveal that only a limited amount of H2 receptor protein is functional. These functional receptors are targeted to the plasma membrane.

Topics: Adenylyl Cyclases; Animals; Baculoviridae; beta-Cyclodextrins; Blotting, Western; Cell Line, Transformed; Cholesterol; Cimetidine; Cyclic AMP; Cyclodextrins; Epitopes; Fluorescent Antibody Technique; Guanidines; Histamine H2 Antagonists; Histidine; Insecta; Microscopy, Confocal; Oligonucleotides; Piperidines; Ranitidine; Rats; Receptors, Histamine H2; Transfection

1. The effect of central H3 histamine receptor activation on gastric acid and pepsin production has been investigated in pylorus-ligated rats. 2. Intracerebroventricular injections (i.c.v.) of the selective H3 agonist, R-alpha-methylhistamine (0.5-50 nmol per rat) caused a dose-dependent inhibition of gastric acid secretion while intravenous administration (5-500 nmol per rat) was completely ineffective. 3. I.c.v. microinjections of mepyramine, tiotidine and thioperamide (51 nmol per rat), selective antagonists at H1-, H2- and H3-sites respectively, failed to modify the acid secretory response to pylorus ligation. 4. The antisecretory effect of R-alpha-methylhistamine (5 nmol per rat, i.c.v.) was selectively prevented by the H3-blocker, thioperamide (51 nmol per rat, i.c.v.), mepyramine and tiotidine pretreatment being completely inactive. 5. Unlike acid secretion, pepsin production was not significantly affected by all the tested compounds. 6. These findings provide the first pharmacological evidence that the activation of central H3 histamine receptors exerts a negative control in the regulation of gastric acid secretion in conscious pylorus-ligated rats.

Topics: Animals; Cimetidine; Female; Gastric Acid; Gastric Mucosa; Histamine Agonists; Histamine Antagonists; Injections, Intraventricular; Methylhistamines; Piperidines; Pylorus; Pyrilamine; Rats; Rats, Wistar; Receptors, Histamine H3

The present study was conducted to investigate the histamine H2-receptor antagonistic property of FRG-8813 by using isolated guinea pig right atria, gastric cells and cerebral cortex preparations. FRG-8813 inhibited the histamine-induced positive chronotropic response of the right atria and shifted the concentration-response curve of histamine to the right with suppression of the maximal response. Although the inhibitory effect of FRG-8813 was enhanced in a time-dependent manner and long-lasting, the antagonism was reversible. The potency of FRG-8813 was 2 times and 50 times greater than those of famotidine and cimetidine, respectively. FRG-8813 decreased the histamine-induced [14C]aminopyrine accumulation in gastric cells. Schild plot analysis showed that the slopes of FRG-8813, famotidine and cimetidine were 1.56, 1.40 and 1.07, respectively, suggesting that the mode of the antagonism of FRG-8813 is also unsurmountable in gastric cells. The lack of effect on dbcAMP- and bethanechol-induced [14C]aminopyrine accumulations indicated the selectivity of FRG-8813 for histamine H2-receptor. As in the right atria, the potency of H2-antagonism was 1.5 times and 40 times greater than those of famotidine and cimetidine, respectively. In the [3H]tiotidine binding study of the cerebral cortex preparation, the Ki values showed that the affinity of FRG-8813 was 2 times and 80 times more potent than those of famotidine and cimetidine, respectively. In conclusion, FRG-8813 is an unsurmountable and selective histamine H2-receptor antagonist with 2 times greater potency than famotidine. The antagonistic activity is reversible in spite of the time-dependent increase of the antagonism.

Topics: Acetamides; Aminopyrine; Animals; Cerebral Cortex; Cimetidine; Dose-Response Relationship, Drug; Gastric Mucosa; Guinea Pigs; Histamine H2 Antagonists; In Vitro Techniques; Male; Myocardial Contraction; Piperidines; Pyridines; Stimulation, Chemical; Time Factors

The histamine H2-receptor antagonistic activity and antisecretory effects of KU-1257 (N-ethyl-N'-[3-[3-(piperidinomethyl) phenoxy]propyl]urea, CAS 120958-90-9) were studied. The Ki values of KU-1257, roxatidine acetate, famotidine and cimetidine for the inhibition of [3H]-tiotidine binding to guinea-pig cerebral cortex were 0.040, 0.13, 0.016 and 0.40 mumol/l, respectively. The KB values of KU-1257, roxatidine acetate, famotidine and cimetidine for the antagonism against histamine-induced positive chronotropic response of isolated guinea-pig right atrium were 0.041, 0.14, 0.031 and 0.51 mumol/l, respectively. In pylorus-ligated rats, KU-1257, roxatidine acetate and famotidine inhibited gastric acid secretion with respective intraduodenal ID50 values of 12.3, 18.5 and 0.45 mg/kg. In dogs with Heidenhain pouch, the ID50 values of KU-1257 for the inhibition of acid output stimulated by histamine, tetragastrin and meat meal were 0.08, 0.39 and 0.15 mg/kg p.o., respectively. KU-1257 was 2-3 times more potent than roxatidine acetate regardless of secretagogues and twice less than famotidine in meat meal stimulation. These results indicate that KU-1257 is a potent and competitive histamine H2-receptor antagonist.

Topics: Animals; Cerebral Cortex; Cimetidine; Dogs; Famotidine; Food; Gastric Acid; Guinea Pigs; Heart Atria; Heart Rate; Histamine H2 Antagonists; In Vitro Techniques; Kinetics; Male; Phenylurea Compounds; Piperidines; Pylorus; Rats; Rats, Wistar; Tetragastrin

The actions of zolantidine dimaleate and five other histamine H2 receptor antagonists, given into the lateral ventricle of rats, were assessed on nociceptive responses in the presence and absence of systemically administered morphine. On the tail flick response, zolantidine induced a time- and dose-dependent inhibition of morphine antinociception, with no effect on responses in the absence of morphine. Zolantidine and another H2 receptor antagonist, tiotidine, also inhibited morphine responses in the hot plate test. Four other H2 receptor antagonists of varying structure, brain-penetrating ability, and H2 potency also induced dose-related inhibition of morphine tail flick responses. Over three orders of magnitude, the potency of these compounds as inhibitors of morphine antinociception was highly correlated with H2 receptor antagonist potency (r = 0.98, P less than 0.005, n = 5). Taken with previous studies showing the selectivity of these compounds for histamine H2 receptors, and the antinociceptive properties of histamine, these results strongly suggest a role for brain histamine H2 receptors in the expression of morphine antinociception.

Topics: Animals; Benzothiazoles; Brain; Cimetidine; Histamine H2 Antagonists; Injections, Intraventricular; Male; Morphine; Nociceptors; Phenoxypropanolamines; Piperidines; Rats; Rats, Inbred Strains; Receptors, Histamine H2; Thiazoles

The histamine H2 receptor-blocking activity of ranitidine and lamtidine analogues has been investigated to gain information on the structure of the receptor area adjacent to the site fitted by the polar group. The introduction of differently shaped alkyl moieties on the polar group is always accompanied by maintenance or by an increase of H2 receptor antagonism with respect to the starting lead compound (KB on guinea-pig isolated atria ranging from 49 nM to 1.5 nM). The results seem to indicate the presence in the histamine H2 receptor of an area of a predominantly hydrophobic nature located at the boundary of the site fitted by the polar group.

Topics: Animals; Binding Sites; Cerebral Cortex; Cimetidine; Guinea Pigs; Heart Atria; Histamine H2 Antagonists; Ileum; Male; Piperidines; Ranitidine; Receptors, Histamine H2; Structure-Activity Relationship; Triazoles

1. The novel benzthiazole derivative zolantidine (SK&F 95282) is a potent antagonist of histamine at H2-receptors in guinea-pig atrium and rat uterus. Only apparent pA2 values of 7.46 and 7.26 respectively could be calculated since the slopes of the Schild plots were significantly less than unity. 2. Zolantidine is equally potent as an antagonist at histamine H2-receptors in guinea-pig brain. The compound inhibited histamine stimulated adenylate cyclase (pKi 7.3) and dimaprit stimulated adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation (approx pA2 7.63), and competed with [3H]-tiotidine binding (pKi 7.17). 3. Zolantidine is at least 30 fold more potent at H2-receptors than at other peripheral and central receptors investigated. 4. Infusion of zolantidine into rats produces a brain concentration greater than the plateau blood concentration (brain/blood ratio 1.45). 5. Zolantidine is thus characterized as a potent selective brain-penetrating H2-receptor antagonist, and will be a valuable pharmacological tool for investigating possible physiological and pathological roles for histamine in the central nervous system.

Topics: Animals; Benzothiazoles; Binding, Competitive; Brain Chemistry; Cimetidine; Cyclic AMP; Female; Guinea Pigs; Hippocampus; Histamine H2 Antagonists; In Vitro Techniques; Male; Phenoxypropanolamines; Piperidines; Rats; Thiazoles; Uterus