Non-cholinergic, non-adrenergic inhibitory nerve responses of bladder outlet smooth muscle in vitro

Pig trigone, bladder neck and urethral smooth muscle strips blocked with atropine, phentolamine, propanolol and the prostaglandin synthesis inhibitor ketoprofen were exposed to transmural electric field stimulation in vitro. The strips developed a fast and reproducible relaxation which was sustained during the period of stimulation and ceased slowly after stopping stimulation. The amplitude of the relaxation was proportional to the basal tension. The relaxation was nerve-mediated, since selective nerve blockade with tetrodotoxin abolished the response. Calcium influx inhibition with verapamil did not antagonise the relaxation, while omitting Ca++ from the bath solution caused maximal relaxation. Vasoactive intestinal polypeptide and adenosinetriphosphate evoked submaximal and slowly developing relaxation.