Phosphorylase activity in rat uterus after catecholamine administration

Abstract The effects of epinephrine, norepinephrine, and isoproterenol on uterine phosphorylase were studied in intact, anesthetized rats. All three agents were found to increase uterine phosphorylase a activity when administered in large doses by intraperitoneal injection. Total phosphorylase activity was unaffected. The time course for the effects of epinephrine on uterine phosphorylase activity and glycogen content was also studied. Peak phosphorylase activation occurred within 5 min after injection, and the effect had disappeared within 1 hr. Increase in phosphorylase a activity was accompanied by a decrease in uterine glycogen levels, which were still depressed at a time when phosphorylase a activity had returned to normal. Epinephrine was shown to stimulate phosphorylase a activity in the uteri of ovariectomized and estrogen-primed rats as well as in normal intact animals. Ovariectomized animals treated with estradiol had higher resting phosphorylase a activity than had normal untreated animals. The relative ability of several adrenergic blocking agents to prevent catecholamineinduced increases in uterine phosphorylase a activity was investigated, It was suggested that the catecholamines produced their effects on the uterus both directly, via β-adrenergic stimulation, and indirectly, via ischemia and resultant tissue anoxia induced by activation of a -adrenergic receptors in the uterine vasculature. The ability of epinephrine to activate uterine phosphorylase when administered by intravenous infusion was also demonstrated.