Influence of Luteinizing Hormone on Corpus Luteum Metabolism and Progesterone Biosynthesis Throughout the Bovine Estrous Cycle11

Abstract

Progesterone biosynthesis in vitro by slices of bovine corpora lutea obtained surgically throughout the estrous cycles has been measured. Synthetic activity per gram of tissue was greatest in youngest corpora lutea, gradually decreasing until about 18 days post-estrum, after which time it fell to undetectable levels. LH [luteinizing hormone] added to the incubation medium always increased progesterone synthesis in "active" corpora lutea (obtained prior to 19 days post-estrum), whereas it failed to do so in "inactive" corpora lutea (obtained at 19 days or later). NADP + glucose-6-phosphate added to the incubation medium caused minimal stimulation of progesterone synthesis in the youngest corpora, becoming progressively more effective as the cycle progressed. Progesterone synthesis in "inactive" corpora lutea could be restored by the addition of NADP + glucose-6-phosphate. Glucose uptake and lactic acid production in "active" corpora, but not in "inactive" corpora were increased by the in vitro addition of LH to the incubation medium. Metabolism of glucose via the pentose phosphate pathway appeared somewhat greater in "active" than in "inactive" corpora lutea. "Inactive" corpora contained approximately normal concentrations of sterols and retained the ability to produce progesterone from exogenous pregnenolone. Therefore, the defect in corpora lutea obtained near the end of the estrous cycle would appear to be in their inability to form pregnenolone. Possible explanations for this defect are discussed.