Abstract
A quantitative and histochemical study of phosphorylase has been made in the human, rat and rabbit placentae. The placental enzyme was found to have the same optimal pH as liver phosphorylase. Since cyclic 3',5'-AMP, glucagon or adrenaline had no influence on enzyme activity, phosphorylase probably exists only in the active form in the placenta. The activity of phosphorylase was localized histochemically in the decidua basalis, the cytotrophoblast of the spongy zone of the chorioallantoic placenta and in the visceral layer of the inverted yolk sac of the rat. It was present mainly in the decidua basalis of placenta of the rabbit although a few cytotrophoblastic cells of the trophoblastic tubules also showed weak activity. In the human placenta the enzyme was active in the cytotrophoblast and the mesodermal core of the villi. It was present occasionally in the syncytiotrophoblast. The quantity of the enzyme fluctuates during gestation in both the human and rat fetal placentae. These fluctuations do not appear to bear relation to either placental glycogen level or to fetal liver phosphorylase activity. Nor is there any obvious correlation between placental phosphorylase and the activity of glucagon-like substance of the fetal pancreas.