[Excitatory beta-adrenoreceptors on cholinergic interneurons of the myenteric plexus]

Contractile responses of small intestine segments to isopropylnoradrenaline (INA) disappeared after the blockade of M- and N-cholinoreceptors, beta-adrenoreceptors and increased after the blockade of alpha-adrenoreceptors. Infusion of acetylcholine in subthreshold doses enhanced the small intestine contractile responses to the INA. The blockade of beta-adrenoreceptors with propranolol reduced contractile responses to exogenous (i. a. administration) and endogenous (electrical stimulation of the n. vagus' efferent fibers) acetylcholine, histamine and bradykinin. Stimulation of beta-adrenoreceptors with the INA enhanced contractile responses to exogenous acetylcholine and histamine and reduced the responses to bradykinin. The data obtained suggest the existence of activating beta-adrenoreceptors, apart from alpha- and beta-inhibitory adrenoreceptors, in the small intestine. Activating beta-adrenoreceptors are situated on cholinergic interneurons of the myenteric plexus and mediate the activating effect of endogenous catecholamines upon cholinergic neurons of small intestine.