[Contractile reactions of the small intestine induced by stimulation of beta-adrenoreceptors].

Isopropylnoradrenaline (1-2 micrograms/ml-1) induced contractile responses of the jejunum and ileum. The contractions could occur practically simultaneously with the onset of responses of arterial vessels or their latency period (reaching up to 33 sec). Blockade of M-cholinoreceptors with atropine (0.2-0.4 mg/kg) prevented both response types whereas blockade of alpha-adrenoreceptors with phentolamine (1 mg/kg) augmented them. Preliminary infusion of acetylcholine in subthreshold concentration (10(-5)-10(-6) g/ml; 1 ml/min) into the small intestine vascular bed considerably augmented the responses to isopropylnoradrenaline. The data obtained corroborate existence of presynaptic activating beta-adrenoreceptors localized on a cholinergic neuron, in the small intestine.