[Initiating and modulating effects of met-enkephalin in the appearance of contractile reactions of the jejunum and ileum].

In acute experiments on cats, an isolated loop of small intestine was vascularly perfused by means of the constant volume pump. The jejunum and ileum contractility was estimated by maximum isometric tension and total contractile activity. Neither N- nor M-cholinoreceptor blockade eliminates the contractile responses of jejunum and ileum to i.a. injection of metenkephalin. I.a. infusion of metenkephalin (10(-8)--10(-6) g/ml/min) potentiated contractile responses to acetylcholine, inhibited those to serotonin, potentiated or inhibited responses to electrical stimulation of vagal efferents. The data suggest metenkephalin to be able to modulate the contractile activity of intestinal smooth muscle, affecting the cholinergic excitatory and noncholinergic, nonadrenergic inhibitory mechanisms.