[Role of adrenergic mechanisms in manifesting the contractile effects of the smooth musculature of the ileum induced by serotonin].

In acute experiments on cats, an isolated portion of the ileum was vascularly perfused with constant blood volume. Contractile activity of the ileum was estimated by isometric tension. The subthreshold dose of acetylcholine (6.10(-10)-6.10(-9) mol/ml/min) potentiated or inhibited the contractile responses of the ileum induced by i. a. administration of serotonin (2.5 X X 10(-8)-1.10(-7) mol). Blockade of beta-adrenergic receptors with propranolol (0.2 mg/kg) diminished, and blockade of alpha-adrenergic receptors with phentolamine (1 mg/kg) increased the serotonin-induced contractile responses. After beta-adrenergic blockade acetylcholine potentiated these responses in all experiments. After alpha-adrenergic blockade acetylcholine mostly inhibited serotonin-induced contractile responses. The facilitating effect of acetylcholine on the serotonin-induced contractile responses of the ileum seems to stem from the changed balance between inhibiting adrenergic and activating cholinergic mechanisms, the latter being predominant.