[Effect of acetylcholine on contractile reactions of the cat ileum induced by serotonin before and after cholinoreceptor blockade].

In acute experiments on cats, an isolated portion of the ileum was vascularly perfused. Contractile activity of the ileum was estimated by isometric tension. The subthreshold dose of acetylcholine (6.10(-10) mol/ml, 1 ml/min) facilitated the contractile responses of the ileum induced by i.a. administration of serotonin (2.5 . 10(-8) or 5 . 10(-8) mol). Blockade of nicotinic receptors with benzohexonium (10 mg/kg) diminished the serotonin-induced contractile responses but did not affect the facilitating effect of acetylcholine. Blockade of muscarinic receptors with atropine (0.2 ml/kg) abolished the serotonin-induced responses. The facilitating effect of acetylcholine on the serotonin-induced contractile responses of the ileum seems to be actualized at postganglionic level of the intramural nervous plexus with the participation of muscarinic cholinoreceptors.