The correlation between spontaneous contractions and postjunctional supersensitivity of the smooth muscle of the rat vas deferens.

Chronic postganglionic denervation of the rate vas deferens produces an increase in the sensitivity of the in vitro smooth muscle to norepinephrine, methoxamine, acetylcholine, potassium and electrical stimulation. The maximal contractile response to norepinephrine and acetylcholine is increased but the maximal response to potassium or electrical stimulation is not affected. In addition, the vas deferens becomes spontaneously active after denervation. The spontaneous contractions are not prevented by tetrodotoxin, phentolamine or atropine. The appearance and magnitude of the spontaneous contractions are temporally correlated with the development of postjunctional supersensitivity. At a given time after denervation there is a significant correlation between the magnitude of the spontaneous contractions and the sensitivity to norepinephrine, i.e., the sensitivity to norepinephrine being greatest in those tissues with the largest spontaneous contractions. There is an inverse relationship between the magnitude of the spontaneous contractions and the endogenous norepinephrine concentration. Pretreatment of rats with reserpine (1. 0 mg/kg/day for 5-7 days) results in supersensitivity of the vas deferens ,o norepinephrine and acetylcholine. Those tissues obtained from reserpine-pretreated rats which are supersensitive are also spontaneously active. It is concluded that the -ppearance of spontaneous contractions in the rat vas deferens is an index of postjunctional supersensitivity.