Cofactor Induced Synthesis of D-Glucose-6-phosphate: NADP Oxidoreductase in the Uterus

Abstract

The synthesis of D-glucose-6- phosphate: NADP oxidoreductase (G6PD) in the uterus of the ovariectomized rat has been shown to be controlled by the intracellular concentrations of NADP. A nonsurgical method was used to apply 5.0 μmoles of NADP directly into the lumen of the uterus. This treatment increased the total uterine G6PD activity to the same extent as a single injection (iv) of 5.0 μg of estradiol-17β over a 12 hr period. A dose response curve indicated linear increases in uterine G6PD activity up to the dose of 5.0 μmoles of NADP/ animal. The kinetics of the response to NADP show a 2 hr lag phase followed by increased G6PD activity through the 24th hr. NADPH was equally as effective as NADP in the induction of G6PD synthesis. NAD and NADH promoted increased G6PD activity to a much lesser degree than NADP, and intraluminal application of phenazine methosulfate, histamine and glucose was without effect. A dose responsecurve of the ability of actinomycin D and cycloheximide, applied intraluminally, to inhibit estradiol-17β induced synthesis of G6PD is given. Lower doses of actinomycin D (0.005–0.05 μg) were found to enhance the estrogen induced enzyme synthesis. Actinomycin D (5.0 μg) and cycloheximide (500 μg) applied in this manner are capable of inhibiting the estrogen response to control levels. This dose of cycloheximide also inhibited the NADP induced synthesis of G6PD, but 5.0 μg of actinomycin D was without effect. Collectively, these data suggest that hormonal induction of G6PD synthesis occurs at the level of RNA synthesis and cofactor induction occurs at the level of protein synthesis. The role of intracellular levels of cofactors is discussed in relation to the specificity of protein synthesis during the amplification phase of the uterine response to estradiol. (Endocrinology81: 791, 1967)