Effects of brain-gut related peptides on cAMP levels in myenteric ganglia of guinea-pig small intestine

This study was designed to test the hypothesis that stimulation of adenylate cyclase and elevation of cAMP is involved in the signal transduction process for substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, cholecystokinin or gastrin releasing peptide in myenteric ganglia. Enzymatically dissociated ganglia from the myenteric plexus of the guinea-pig small intestine were used to study changes in levels of cAMP in response to application of the brain-gut peptides in the presence and absence of forskolin. Application of substance P and calcitonin gene-related peptide were found to increase intraganglionic cAMP in a dose-dependent fashion when a phosphodiesterase inhibitor was present. The ED₅₀ values for substance P and calcitonin gene-related peptide were 5 μM and 0.75 μM, respectively. The presence of forskolin in the incubation medium resulted in significant upward shifts of the dose-response curves for both peptides. Neither vasoactive intestinal peptide. cholecystokinin nor gastrin releasing peptide stimulated increases in intraganglionic cAMP under the same experimental conditions used for substance P and calcitonin gene-related peptide.