Effect of intragastric amino acids on lower esophageal sphincter pressure and serum gastrin in man.

The effects of the intragastically administered individual L-amino acids, phenylalanine, tryptophan, glycine, aspartic acid, and leucine on lower esophageal sphincter (LES) pressure and serum gastrin concentration were studied in normal subjects. On separate days and in random, double-blind fashion, 13 adult male subjects received isotonic 0.1 M concentration of amino acids and saline, at pH 5.5 in a volume of 600 ml by rapid intragastric instillation over 5 min. LES pressure and serum gastrin concentration were monitored basally and then at frequent intervals for 90 min. Only tryptophan had a significant effect on LES pressure when compared with saline, decreasing LES pressure from 20 to 60 min after administration (p less than 0.01). Only phenylalanine and tryptophan produced significant stimulation of serum gastrin levels with peak increases above basal occurring 30 min after administration (p less than 0.05). It is concluded that: aspartic acid, leucine and glycine produced no significant changes in LES pressure or serum gastrin level; tryptophan and phenylalanine significantly increased serum gastrin concentration; tryptophan significantly decreased LES pressure whereas phenylalanine had no effect; the mechanism of inhibition of LES pressure by tryptophan is not defined and may be mediated by neural or hormonal pathways possibly involving a duodenal receptor.

MK-208, a novel histamine H2-receptor inhibitor with prolonged antisecretory effect.

MK-208 is a guanidinothiazole derivative reported to be a potent H2 blocker devoid of antiandrogenic activity. Its potency and duration of action, in inhibiting pentagastrin-stimulated gastric secretion in man, was evaluated in this double-blind, five-way cross-over trial. Ten healthy male volunteers received single oral doses of placebo, cimetidine 300 mg, and MK-208 5, 10, and 20 mg. A continuous intravenous infusion of pentagastrin (1 microgram/kg/hr) was given 2-4 and 5-7 hr after each oral dose. Gastric contents were continuously aspirated and volumes and acid content determined every 30 min. Plasma levels for MK-208 and cimetidine were monitored over the 7 hr of the study. Cimetidine and all doses of MK-208 significantly inhibited gastric acid secretion in the initial 2-4 hr; however, 10- and 20-mg doses of MK-208 were significantly more potent than cimetidine. In the 5- to 7-hr period, cimetidine 300 mg was not different from placebo, while MK-208 in all doses studied continued to significantly suppress gastric secretion. Plasma levels for MK-208 showed dose-related increments. The results suggest that: (1) MK-208 is a potent inhibitor of gastric secretion in man, in a dose-related fashion at the doses tested; (2) under the study conditions, 5 mg MK-208 was equipotent to 300 mg cimetidine but with greater duration of action, extending at least 7 hr; and (3) these data suggest a future role for this new agent in therapy for acid-peptic disease in man.

Effects of ranitidine and of cimetidine on pentagastrin-stimulated gastric acid secretion.

We compared the effect of oral and intravenous ranitidine, a new H2-receptor antagonist, with that of cimetidine on pentagastrin-stimulated gastric acid secretion in normal subjects. Ranitidine in intravenous doses of 20, 60, and 100 mg and oral doses of 100, 150, and 200 mg inhibited acid secretion. Only the 100 mg iv ranitidine dose was substantially more effective than cimetidine. Comparable dose-related decreases in gastric secretory volume were observed. Acid inhibition correlated strongly (r = 0.90) with plasma ranitidine concentration, with the estimated plasma concentration producing 50% inhibition (IC50) being 95 ng/ml. Maximal acid inhibition achieved was 87.3%. We conclude that ranitidine is a potent inhibitor of gastric acid secretion and should be a valuable addition to the medical treatment of acid-peptic disease.