Correlation Between the Activities of Enzymes Involved in Glucose Oxidation in Corpus Luteum and the Concentration of Sex Steroids in Systemic Plasma During the Reproductive Cycle of the Guinea Pig

The activities of six enzymes (hexokinase, phosphofructokinase, lactic dehy-drogenase, glucose-6-phosphate dehydrogenase, iso-citric dehydrogenase, and malic dehydrogenase) i n the glycolytic pathway, pentose-shunt, and tricarboxylic acid (TCA) cycle were assayed with Lowry's quantitative histochemistry method in the luteal cells of the guinea pig corpus luteum during the reproductive cycle. The concentrations of progesterone and estradiol in circulating blood plasma at ovariectomy were also measured by radioim-munoassay. Progesterone reached its highest level of concentration (3.28 to 4.82 ng/ml) between days 5 and 10 after ovulation. The concentration of estradiol fluctuated between 12 and 23 pg/ml throughout the various stages of the reproductive cycle. The activities of glucose-6-phosphate dehydrogenase, isocitric dehydrogenase, and malic dehydrogenase were positively correlated with plasma proges-terone concentration (p < 0.02), whereas the activities of hexokinase, phosphofructokinase, and lactic dehydrogenase were unrelated to the concentration of progesterone during the cycle. These data suggest that sequential changes in the activities of the endogenous enzymes, glucose-6-phosphate dehydrogenase of the pentose-shunt and isocitric dehydrogenase and malic dehydrogenase of the TCA cycle, are important during steroid biosynthesis in the luteal cells of the guinea pig ovary. (Endocrinology95: 1213, 1974)