[Role of alpha- and beta-adrenoreceptors of the jejunum and ileum in displays of their contractile reactions].

Acute experiments were performed on isolated segments of the cat small intestine vessels. The contractile activity of the jejunum and ileum was estimated by the maximal isometric tension. Blocking of the alpha-adrenoreceptors with phentolamine induced a reinforcement of the contractile reactions, whereas blocking of the beta-adrenoreceptors with propranolol led to inhibition of both jejunum and ileum contractile responses either to exogenous acetylcholine or electrical stimulation of vagal efferent fibers. The subthreshold activation of alpha-adrenoreceptors with noradrenaline induced mostly inhibition, whereas activation of beta-adrenoreceptors with isopropylnoradrenaline caused a potentiation of the contractile response to exogenous acetylcholine. The data obtained suggest existence of excitatory beta-adrenoreceptors with a presynaptic localization in the jejunum and ileum.