Comparison of cimetidine with new H2-antagonists in rabbit and guinea pig gastric cells

'In vitro' action of histamine and cimetidine on amylase secretion in the rat pancreas

We report here the effect of histamine on amylase secretion in isolated lobules from the rat pancreas. Different concentrations of histamine increased amylase secretion, while the stimulatory effect was reduced by cimetidine although not by chlorpheniramine. These findings suggest that pancreatic lobules have H2 receptors. On the other hand, bethanechol induced a stimulatory effect on pancreatic lobules that was inhibited by cimetidine. Vibrio cholerae toxin stimulated amylase secretion, but this effect was not reduced by cimetidine. Cimetidine may thus block the stimulated amylase secretion interfering with the Ca2+ messenger system.

Gizzard ulceration in chicks fed cysteamine alone or in combination with a histamine H2-receptor antagonist

A study was carried out to evaluate the effect of cysteamine-HCl administration on gizzard ulceration and growth performance in broiler chicks. The effectiveness of the histamine H2-receptor antagonist, SKF 93479, in preventing gizzard ulcerations when given in combination with cysteamine-HCl was also examined. In the initial experiment cysteamine-HCl at the level of 2400 mg/kg of the diet caused severe gizzard ulceration and mortality and decreased feed intake and growth in chicks. The effect was not seen when cysteamine-HCl was administered at 600 or 1200 mg/kg of the diet. In Experiment 2 broiler chicks administered cysteamine-HCl at 1800 mg/kg of the diet had an increased incidence of gizzard ulceration and decreased growth performance. The severity of gizzard lesions and the depression of growth performance were not as great as in the group in Experiment 1 which received the 2400 mg/kg level of cysteamine-HCl. Addition of the H2 antagonist SKF 93479 at 54 mg/kg of the diet had no effect on improving gizzard ulcer score or growth performance in chicks which received cysteamine-HCl at the 1800 mg/kg of the diet level. From these data it appears that the administration of ulcerogenic levels of cysteamine-HCl in the chicken may involve a more complex pathogenesis in which factors other than acid hypersecretion are involved.

Pharmacological studies of 2-(3-(3-(1-piperidinylmethyl)-phenoxy)propylamino)-4 (3H)-quinazolinone (NO-794), a new histamine H2-receptor antagonist

The pharmacological profile of a new histamine H2-receptor antagonist, 2-(3-(3-(1-piperidinylmethyl)phenoxy)propylamino)-4 (3H)-quinazolinone (NO-794), was studied. NO-794 was a potent and selective histamine H2-receptor antagonist in the guinea-pig atria and gastric mucosal cells. NO-794 (1 X 10(-5) M) did not interact with H1-, muscarinic and beta 1-receptors. In guinea-pig atria, antagonism of NO-794 was unsurmountable. The onset of action of NO-794 was slow, and this antagonism was apparently irreversible not only on the guinea-pig atria but also on the gastric mucosal cells. In addition, NO-794 inhibited gastric acid secretion in pylorus ligated rats when administered intraduodenally. These results indicate that NO-794 is a powerful and unique histamine H2-receptor antagonist and may be useful in the treatment of peptic ulcer.

Pharmacological analysis of the pentagastrin-tiotidine interaction in the mouse isolated stomach

The pentagastrin-tiotidine interaction has been analysed, using improved techniques, in the mouse isolated, lumen-perfused, stomach assay. For comparison and quantification of the H2-receptor blocking activity of tiotidine, histamine-tiotidine interactions have also been analysed in the mouse stomach and guinea-pig isolated right atrial preparation. Tiotidine behaved as a competitive antagonist of histamine both in the guinea-pig right atrium (pKB 7.57) and mouse stomach (pKB 6.96). The difference in pKB was attributed to the loss of tiotidine into the gastric secretion. On the stomach assay, pentagastrin concentration-effect curves were significantly flatter with lower maximal responses than those obtained to histamine. In addition the profile of inhibition observed with tiotidine was different in that the pentagastrin curve maxima were depressed with only a small concomitant dextrad shift. A mathematical model has been developed which accounts for the differences in agonist concentration-effect curves and describes in a quantitative manner the expectations for the competitive antagonism of endogenous histamine assumed to be released by pentagastrin. Fitting of the pentagastrin-tiotidine data to this model provided a reasonable goodness-of-fit. The results are discussed in terms of the role of endogenous histamine in gastrin-stimulated acid secretion. We conclude that the results are consistent with the hypothesis that pentagastrin stimulates acid secretion via the release of endogenous histamine under the present experimental conditions.