Differences in Mitochondrial Steroidogenesis Between Follicular and Luteal Tissues of Porcine Ovaries

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Abstract
Mitochondrial preparations from granulosa and theca of large (7-12 mm) follicles of porcine ovaries converted 2-3 times more [4-14C]cholesterol to [4-14C]pregnenolone than did mitochondria from tissues of medium (3-6 mm) follicles. Only small amounts of [4-14C]-progesterone were formed by mitochondria of medium and large follicles. In contrast, mitochondria of corpora lutea converted 4-5 times more [4-14C]cholesterol to [4-14C]progesterone than did follicular mitochondria. Using [3H]pregnenolone as substrate with no exogenous NAD+, follicular mitochondria synthesized less than 1 nmol progesterone/min per mg protein while luteal mitochondria synthesized 7.1 nmol/min per mg protein. As shown by EM, luteal mitochondria resolved further by isopycnic zonal centrifugation contained almost no contamination. While 17-OH progesterone synthesis was observed in luteal mitochondria prepared by differential centrifugation, none was detected in preparations resolved further by zonal centrifugation. Luteal mitochondria purified by zonal centrifugation increased their ability to convert [4-14C]cholesterol to [4-14C]progesterone and [3H]pregnenolone to progesterone. Treatment of luteal mitochondria with Triton X-100 of sonication caused a significant loss of progesterone synthesis activity which could be restored with the addition of exogenous NAD+. Highly purified luteal mitochondria can synthesize progesterone at a high rate. In contrast, mitochondria from follicular tissue can synthesize pregnenolone, but not progesterone.