ELECTROPHYSIOLOGICAL AND MECHANICAL INVESTIGATIONS ON THE DUAL ACTION OF PROSTAGLANDIN E₁ IN THE PREGNANT RAT MYOMETRIUM IN VITRO

Abstract

Effects of prostaglindin E₁ (PGE₁) on the myometrial activity of the pregnant rat were investigated by recording the contractile response and intracellular electrical activity. PGE₁ (10^-9-10^-6g/ml) caused a depression of the contractile activity in the fresh preparations of either longitudinal or circular muscle strip (within 2-5hr after exposure to the artificial saline media). However neither membrane potential nor action potential was significantly affected by the treatment with the agents. By contrast, in the aged preparations (bathed in the saline media longer than 2-5hr), an increase in the contractile response dose-dependently was caused. The generation of action potential was facilitated without depolarization of the membrane. The inhibitory response induced by PGE₁ in the fresh preparation was converted to an excitatory response when treated with bretylium. The discussion covers the inhibitory effect of PGE₁ which is mediated through intrauterine adrenergic system, and is perhaps due to the focal hyperpolarization block of the conduction of excitation. The excitatory effect is very likely caused by a direct action on myometrial cell membrane.