Evidence for the excitatory cholinergic innervation in the rabbit portal vein.

We examined the possible existence of excitatory cholinergic innervation in isolated rabbit portal vein. Longitudinal strips of the vein in the presence of both phenoxybenzamine, an alpha-adrenoceptor antagonist, and NG-nitro-L-arginine, an inhibitor of nitric oxide synthase, exhibited a small contraction in response to transmural electrical stimulation (ES). The contractile response to ES was augmented by physostigmine, an anticholinesterase agent, and inhibited by atropine. These findings indicate the existence of an excitatory cholinergic innervation in addition to the known adrenergic and non-adrenergic, non-cholinergic innervations in the rabbit portal vein.