Cholinergic modulation of the release of serotonin in the gastric interstitial fluid. An in vivo study in rabbits.

Dialysis fibers chronically implanted into the gastric submucosa of rabbits allowed us to simultaneously (a) collect an interstitial fluid dialysate in which 5-hydroxytryptamine concentrations were measured, and (b) locally perfuse drugs such as acetylcholine, neostigmine, and atropine, which stimulated the release of 5-hydroxytryptamine. The effect of acetylcholine was not blocked by atropine but was blocked by hexamethonium. Furthermore, 5-hydroxytryptamine concentrations in the interstitial fluid were lower when acetylcholine and hexamethonium were injected together than when hexamethonium was injected alone. We conclude that acetylcholine stimulates the release of 5-hydroxytryptamine into the gastric interstitial fluid by acting on nicotinic receptors, and has inhibitory effects by stimulating the muscarinic receptors.