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.