Studies on Oxidative Phosphorylation and Steroidogenesis by Ovarian Mitochondria after Gonadotropic Stimulation

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Abstract
No differences in oxidative phosphorylation or in the percentage of [4-14C]cholesterol converted to [4-14C]pregnenolone and [4-14C]progesterone were found in ovarian mitochondria of immature rats after treatment with 20 IU of pregnant mare serum gonadotropin (PMSG) i.v. 30 min before killing. Treatment of immature rats with 20 IU of PMSG s.c. 54 h prior to killing decreased the ADP:O ratio and increased the percentage of [4-14C]-cholesterol conversion. EM studies showed that mitochondria with lamellar cristae were prominent in ovaries of untreated rats, while large pleomorphic mitochondria and mitochondria with tubulovesicular cristae dominated in ovaries of PMSG-treated rats. Ovarian homogenates separated by zonal centrifugation showed 3 peaks of cytochrome oxidase activity which shifted to the heavier end of the gradient after PMSG treatment. PMSG treatment may influence ovarian mitochondria, possibly by stimulating the synthesis of additional functional components and/or the biogenesis of new mitochondria. Aminoglutethimide addition to bovine luteal mitochondria decreased steroidogenesis by 60% when succinate was used as substrate. There was a 16% increase in the ADP:O ratio, apparently due to a decrease in oxygen utilization. When oligomycin was added to luteal mitochondria, there was a 30% decrease in the ADP:O ratio but a 300% increase in [4-14C]cholesterol conversion. Dinitrophenol also decreased mitochondrial steroidogenesis. Energy obtained from succinate oxidation may be diverted from phosphorylation to support steroidogenesis.