Muscarinic control of phase III contractions and motilin release in dogs.

The role of muscarinic receptor subtype(s) in the control of gastric phase III contractions and motilin release was determined in dogs. Pirenzepine (226 nmol/kg/h) shortened the phase III cycle, causing an early increase in plasma motilin concentrations. Both AF-DX116BS and 4-DAMP inhibited the occurrence of spontaneous and motilin-induced phase III contractions, and 4-DAMP also inhibited the spontaneous increase in plasma motilin concentration. Only 4-DAMP inhibited carbachol-induced motilin release in perifused duodenal mucosal cells. In conclusion, M1 receptors are involved in the indirect inhibition of motilin release. Motilin-induced contractions are mediated mainly by M3 receptors and partly by M2 receptors, and M3 receptors are present in motilin-producing cells.