Forskolin stimulation of acid and pepsinogen secretion in isolated gastric glands

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Abstract
Forskolin, a specific diterpene activator of adenylate cyclase in intact cells and cellular homogenates, was used to examine the relationship among adenosine 3',5'-cyclic monophosphate (cAMP) metabolism, gastric acid, and pepsinogen secretion in isolated gastric glands. This agent was found to stimulate [14C]aminopyrine (AP) accumulation and respiration, both measurements of which are indexes of parietal cell acid secretory responsiveness and pepsinogen secretion, which is a measure of chief cell activity. Forskolin also increased cAMP content and activated cAMP-dependent protein kinase in the glands. The histamine H2-receptor antagonist, cimetidine, inhibited forskolin-stimulated increases in AP accumulation and respiration when submaximal concentrations of forskolin were used but had not effect on the other response parameters. Forskolin also potentiated the action of the muscarinic agonist, carbachol, in both the presence and absence of cimetidine. Since there was a close kinetic and temporal correlation between the secretory response parameters and cAMP-dependent protein kinase activation, it appears that cAMP plays an important role in the mediation of gastric acid and pepsinogen secretion. The inhibitory action of cimetidine on forskolin-stimulated AP accumulation and respiration suggest that forskolin potentiates the action of endogenous histamine present in the glands. Forskolin potentiation of carbachol in the presence of maximum inhibitory concentrations of cimetidine indicates that previously observed potentiating interactions between carbachol and histamine, secretagogues which appear to act via cAMP-independent and cAMP-dependent mechanisms, respectively, involve intracellular events that occur subsequent to the binding of these agents to their respective receptors and subsequent to an increase in intracellular cAMP content.