A Delayed Antagonistic Effect of Progesterone on Estradiol-Induced Increases in Uterine Glucose-6-Phosphate Dehydrogenase

Abstract

Estradiol (5μg) given daily to ovariectomized mature rats causes an 8-fold increase in the levels of uterine glucose-6-phosphate dehydrogenase, G6PD, (D-glucose-6-phosphate: NADP+ oxidoreductase, E. C. 1.1.1.49) after 3 days. Simultaneous administration of progesterone (2mg/ day) had no effect on the early increase in this enzyme; but after 36 hr, progesterone blocked further increases in uterine G6PD activity at a level which was 50% of the level ultimately reached when estradiol was given in the absence of exogenous progesterone. Administration of progesterone (with estradiol) after the enzyme levels had been maximally elevated by estradiol caused the enzyme levels to decline at a rate nearly equivalent to that observed after estrogen withdrawal. Progesterone did not enhance the rate of loss of uterine G6PD after estrogen withdrawal. These data suggest that the uterine progestational response is dependent on the prior action of estradiol on the uterus. (Endocrinology92: 636, 1973)