Abstract
Summary
Steroidogenic activity and oxi-dative phosphorylation were measured in ovarian mitochondria of intact mature rats, hypophysectomized mature rats and gonad-otropic-treated, hypophysectomized mature rats to determine the dependence of these parameters on gonadotropic stimulation. Mitochondrial cholesterol oxygenase activity was not detectable in ovarian preparations of hypophysectomized rats, but increased dramatically 54 hr after treatment with 40 IU of pregnant mare serum gonado-tropin (PMSG). In contrast, specific cyto-chrome oxidase activities were similar in mitochondria of all three experimental groups. With both glutamate and succinate as substrates, the ADP:O ratio of ovarian mitochondria of hypophysectomized rats increased significantly over that of mitochondria of intact rats. PMSG treatment of hypophysectomized rats returned the ADP:O ratio to the value observed in intact rats. The succinate oxidation rate of ovarian mitochondria of hypophysectomized rats was significantly greater than those of preparations from intact and from PMSG-treated, hypophysectomized rats. These results indicate that steroidogenic activity in ovarian mitochondria is dependent upon gonadotropic stimulation for its initiation and maintenance, but that cytochrome oxidase activity is not. Also, differences in oxidative phosphorylation between mitochondria of ste-roidogenically active and inactive ovaries may be related to their cholesterol oxygenase activity.
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