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Potentiation by prostaglandins e1, e2, and f2alpha of the contraction response to transmural stimulation in the bovine iris sphincter muscle.

The contraction response to transmural stimulation in the bovine iris sphincter muscle was abolished by atropine but was left virtually unchanged by hexamethonium, and by adrenergic neuron and receptor blockers, indicating activation of postganglionic cholinergic nerve fibres. Low doses of prostaglandins e1, e2 and F2alpha (0.1-5.3 ng/ml) consistently and apparently in a dose-dependent manner enhanced the contraction response to transmural stimulation. Prostaglandins E1 and E2 were equipotent while F2alpha was at least 10 times less active. Within the same dose range the prostaglandins also enhanced the contraction response to exogenous acetylcholine, indicating that part of the enhancing effect of the prostaglandins on neuromuscular transmission was due to a postjunctional action. A spontaneous increase in tone of the preparation commonly occurred about 1 h after the beginning of the experiment. SC 19220, a potent antagonist of prostaglandin action, reduced the tone and the contraction responses as well as the enhancing effect of the prostaglandins. It is concluded that prostaglandins might serve the function of controlling neuroeffector transmission and muscular tone in the sphincter muscle of the bovine iris.