Control of progesterone biosynthesis in the bovine corpus luteum: effects of luteinizing hormone and of reduced nicotinamide–adenine dinucleotide phosphate in vitro
The effects of luteinizing hormone (LH) and of reduced nicotinamide–adenine dinucleotide phosphate (NADPH) upon in vitro progesterone synthesis by bovine corpus luteum slices incubated for varying periods of time have been examined. The increased net synthesis of progesterone caused by LH was accompanied by markedly increased incorporation of acetate-1-14C into progesterone and decreased incorporation of acetate-1-14C into cholesterol. In most experiments, especially at longer incubation times, exogenous NADPH decreased incorporation of acetate-1-14C into progesterone. The effect of NADPH on incorporation of acetate-1-14C into cholesterol was variable, increasing cholesterol specific activity in some experiments and decreasing it in others. At all time intervals in all experiments, the specific activity of progesterone synthesized was greater than that of the cholesterol remaining in the tissue at the end of the interval. With increasing duration of incubations, specific activity of the progesterone synthesized became increasingly greater than that of cholesterol remaining at the end of the incubation period. These findings suggest that newly synthesized cholesterol is utilized for progesterone formation without coming into equilibrium with a large portion of the intracellular cholesterol pool. Experiments with radioactive cholesterol in vitro indicated that a significant amount of conversion of this precursor occurred in the incubation medium by enzymes which had leaked out of the tissue, and this conversion was strikingly stimulated by exogenous NADPH but not by LH. Rates of progesterone synthesis were greatest in shortest incubations, declining as incubation periods were extended. Highly significant correlations were observed between the increments, caused by LH, in net synthesis (mass) of progesterone, incorporation of acetate-1-14C into progesterone, and lactic acid production. Inhibition by puromycin of the stimulatory action of LH upon progesterone synthesis failed to prevent the stimulatory action of this gonadotropin upon glycolysis. These findings indicate that the stimulation of glycolysis is not a consequence of stimulated progesterone synthesis but may be related to the stimulatory action of LH upon 3′,5′-AMP production.