Cyclic adenosine monophosphate and human gastric acid secretion

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)

Cyclic nucleotide response to acid-secreting stimuli in guinea pig gastric mucosa in vitro

To investigate the mechanism of intracellular transmission of three representative stimuli for gastric acid secretion, the dose-response relations of cyclic nucleotides accompanied by acid secretion stimulated by histamine, pentagastrin and bethanechol were comparatively studied using an in vitro preparation of guinea pig gastric mucosa surviving with a constant potential difference and acid secretion sensitive to amytal. The following results were obtained. (1) Both histamine- and pentagastrin-stimulated acid secretion accompanied a significant increase in cyclic AMP contents in the gastric mucosa and in the serosal solution without any increase in cyclic GMP. However, the ratio of the increase in acid secretion to that in cAMP content was significantly greater with pentagastrin than with histamine, indicating that pentagastrin exerts its acid-secreting stimulus with less increase in cyclic AMP. (2) Stimulation with bethanechol resulted in a significant increase in the mucosal cyclic GMP content without any change in cyclic AMP. From these findings, it has been concluded that the above three stimuli were transmitted differently in the target cells, presenting evidence against the common final mediator theory of histamine for gastric acid secretion.

Studies on the source of cyclic AMP in canine gastric juice

The possibility that cyclic AMP in gastric juice is derived from plasma by simple clearance was evaluated. The effect of exogenous cyclic AMP administration (1 mg/min) on radioimmunoassayable cyclic AMP in plasma and gastric juice was studied in dog stomach during histamine (8--16 micrograms/kg/hr) infusion. Experiments were performed in vagally denervated fundic (Heidenhain) and in innervated gastric pouches. During infusion of cyclic AMP with histamine, plasma cyclic AMP concentration rapidly increased 500-fold. Simultaneously, gastric juice cyclic AMP levels decreased almost 50%. In contrast, dibutyryl cyclic AMP infusion increased gastric juice cAMP concentration 5-fold, suggesting that the gastric mucosa is more permeable to dibutyryl cyclic AMP. In Heidenhain pouch experiments the clearance of dibutyryl cyclic AMP into gastric juice was only 1.5% of the clearance of aminopyrine. It appears that plasma clearance of cyclic AMP fails to account for most of the cyclic AMP present in gastric juice.