Response of the urethral smooth muscles to pharmacological agents. I. Cholinergic and adrenergic agonists and antagonists.

We studied the effects of cholinergic and adrenergic agents on the 2 muscle layers of the proximal urethra of the cat. Strips were challenged with bethanechol chloride, phenylephrine and isoproterenol. Bethanechol chloride caused contraction of the longitudinally oriented strips; the circularly oriented strips revealed either minimal or no response to the same doses. The difference between the response of the 2 layers was highly significant (p less than 0.001). Phenylephrine stimulated both layers with a nonsignificant difference. Isoproterenol caused relaxation of both layers with a significant action on the circularly oriented fibers (p less than 0.05). It could be concluded that the cholinergic effect which is predominant on the longitudinal fibers is important for voiding by shortening the proximal urethra. alpha-adrenergic innervation of the bladder neck has a function during ejaculation: closure of the bladder outlet by the circular fibers. beta-adrenergic agonists decrease the urethral pressure probably by relaxing both layers with a dominant effect on the circular layer.