Stimulus secretion coupling: role of cyclic GMP and calcium in the regulation of secretion from rat exocrine pancreas.

In rat pancreatic fragments, stimulation of amylase and labeled protein release by carbachol, caerulein, and ionophore A 23187 results within minutes in a short rise in cyclic GMP levels. Cyclic AMP levels do not change significantly. The secretory response elicited by each secretagogue is not modified when combined in pairs. Under intracellular calcium depleting conditions, both the cyclic GMP and the secretory responses to secretagogues are inhibited in parallel, suggesting a good correlation between both processes. Furthermore, 8-Bromocyclic GMP induces pancreatic secretion, but to a lesser extent, and fails to alter the increase in secretion caused by the various secretagogues. However, other agents such as imidazole, ascorbic acid, phenylhydrazine, and sodium azide also increase cyclic GMP levels but fail to stimulate pancreatic secretion. On the other hand, dibutyryl cyclic AMP also stimulates amylase and labeled protein discharge and potentiates the increase caused by cabachol, caerulein, and ionophore A 23187. These results do not permit conclusions regarding a cause and effect relationship between cyclic GMP and secretion. A role for calcium seems to be the most likely.