Studies on the source of cyclic AMP in canine gastric juice

Cyclic AMP and gastric secretion in man. An in vivo study in healthy volunteers, duodenal ulcer patients, and pernicious anaemia patients

The metabolism of cyclic AMP and HCl secretion has been studied in eight healthy volunteers, in eight duodenal ulcer (DU) patients, and in four pernicious anaemia patients. Pentagastrin showed a tendency to increase adenylate cyclase and cyclic nucleotide phosphodiesterase activities in the fundal mucosa and caused a significant increase in cyclic AMP output into the gastric juice in healthy volunteers and in DU patients. Cimetidine inhibited all these events but had no effect on basal cyclic AMP output. Vagotomy significantly inhibited basal cyclic AMP output. We conclude that cyclic AMP is involved both in basal and in pentagastrin-stimulated gastric secretion in man. Basal secretion is mainly controlled by vagal tone. The main pathway for this stimulus at the parietal cell may be via other than H2-receptors, probably through acetylcholinergic receptors. However, a significant part of the pentagastrin stimulation of the human parietal cell is via H2-receptors.

Cyclic AMP in gastric juice does not reflect histamine H2 receptor activity in Heidenhain pouch dog

It is strongly believed that cAMP mediates histamine H2 receptor activity, but does not mediate gastrin and acetylcholine stimulation of gastric acid secretion. Therefore, cAMP production could be a marker of H2 receptor activity. Whether endogenous histamine mediates gastrin and/or acetylcholine stimulation, at least partially, remains to be elucidated. If cAMP in the gastric juice reflects H2 receptor activity, we can investigate whether endogenous histamine mediates gastrin and/or acetylcholine stimulation in vivo. In this study, we investigated whether cAMP in the gastric juice reflected histamine H2 receptor activity in the Heidenhain pouch dog in vivo using different kinds of inhibitors of gastric secretion. Our hypothesis was as follows: Upon betazole stimulation, cimetidine, an H2 receptor antagonist, should decrease cAMP output into the gastric juice, but omeprazole, an H+, K+-ATPase blocker, should not, because it blocks at a site more peripheral than the H2 receptor and the production of cAMP. Sixty minutes after betazole administration, 4.0 mumol/kg of cimetidine and 0.18 mumol/kg omeprazole were administered intravenously and they inhibited gastric juice volume to a similar degree, that is, 49.6% and 52.1%, respectively. However, omeprazole caused a greater decrease in cAMP output than cimetidine. Inhibition with 4 mumol/kg/h of cimetidine or 0.2 mumol/kg of omeprazole from the beginning of betazole stimulation also caused similar decreases in gastric juice volume, 66.6% and 60.6%, respectively. Both inhibitors decreased cAMP output into the gastric juice in a similar fashion in the first two 30 minute periods. These results do not agree with our hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)