Sympathetic control of substance P releasing enteric neurones in the guinea pig ileum.

The contractile response of the isolated guinea-pig ileum to cholecystokinin octapeptide (CCK-8) that remained in the presence of atropine was greatly inhibited by the substance P antagonist D-Pro2,D-Trp7,9-substance P. This indicates that the atropine-resistant contraction to CCK-8 is mediated by the release of substance P from enteric neurones. Activation of alpha-adrenergic receptors by noradrenaline, clonidine or mesenteric sympathetic nerve stimulation inhibited the atropine-resistant contraction to CCK-8 but did not affect the contractile effect of substance P. It is concluded that alpha-adrenergic receptors exert an inhibitory influence on the release of substance P from enteric neurones.