Effect of Histamine and Serotonin in Stimulating Phosphorylase Activity in the Rat Uterus

Abstract

Determinations of uterine phosphorylase activity were made in spayed rats which received repeated intra peritoneal injections of histamine at 30-min intervals for 6 hr. Phosphorylase a (active) was unchanged, phosphorylase t (total) was decreased and a/t ratios were increased when results were expressed as activity per unit weight of tissue. Calculation of phosphorylase activities per total uterine weight showed that a increased and t was unchanged. Histamine also increased uterine weight and glycogen levels. Estradiol injected subcutaneously produced essentially the same results within 6 hr. Uterine phosphorylase measurements in spayed rats which received intra-uterine (luminal) injections of histamine (controls received 1.8% saline) were the same as in the controls. “Sham” intra-uterine injections into spayed rats (controls not injected) produced effects on phosphorylase activity within 6 hr, relatively similar to those produced by estradiol or by intraperitoneal injections of histamine. Serotonin had no effect on phosphorylase when substituted for histamine in similar experiments. Spayed rats were injected with estradiol and immediately given either the antihistamine chlorpheniramine (Chlor-Trimeton) or 1.8% saline (controls) via the uterine lumen. Enzyme activity determined 6 hr later showed a marked decrease in phosphorylase a, t and the a/t ratios expressed per unit weight of uterus and per uterus in the experimental rats. There was no significant difference in uterine weights in the treated and control rats. The data support, in part, the hypothesis proposed by Spaziani and Szego that endogenous uterine histamine, released by estradiol, mediates some of the early effects of estrogen.