ROLE OF ENDOGENOUS 5-HYDROXYTRYPTAMINE IN THE REGULATION OF GASTRIC CONTRACTIONS BY MOTILIN IN DOGS

Role of endogenous 5-hydroxytryptamine in the regulation of gastric co ntractions by motilin in dogs. Am. J. Physiol. 270 (Gastrointest. Live r Physiol. 33): G20-G28, 1996.-It has been suggested that 5-hydroxytry ptamine(3) (5-HT3) receptors are involved in the control of phase III contractions in the stomach. We examined the effect of depletion of en dogenous 5-HT by p-chlorophenylalanine (pCPA) on spontaneously and mot ilin-induced phase III contractions in conscious dogs, and the effect of 5,6-dihydroxytryptamine (5,6-DHT) in an isolated perfused dog stoma ch. Three-day treatment with pCPA significantly reduced plasma 5-HT co ncentration and 5-HT content in the stomach, and strongly suppressed t he spontaneous and motilin-induced phase III contractions in the stoma ch. When spontaneous phase III contractions recovered in the stomach a fter a 3-day treatment, exogenous motilin induced typical phase III-li ke contractions, and the 5-HT content in the muscle layer was recovere d to the normal pretreatment level. In the perfused stomach, 5,6-DHT d ecreased 5-HT content in the muscle layer alone and abolished motilin- induced contractions. In conclusion, endogenous 5-HT, probably in 5-HT neurons, plays an important role in the control of interdigestive pha se III activity by motilin in the stomach.