Effect of isoproterenol on the isolated pregnant rat myometrium

In pregnant rat myometrium, isoproterenol (10(-8) M) inhibited spontaneous contractions without causing hyperpolarization. Isoproterenol (10(-6) M) relaxed the depolarized muscle without affecting the membrane potential. The presence of 80 mM Na+ did not affect the degree of high-K+ depolarization. It was also without any influence on the effects of isoproterenol on the depolarized uterus. The results are consistent with the concept that hyperpolarization is not a prerequisite for beta-adrenoceptor induced relaxation of uterine smooth muscle.