Progesterone Biosynthesis in Rabbit Ovarian Interstitial Tissue Mitochondria

Mitochondria isolated from rabbit ovarian interstitial tissue metabolize both endogenous and exogenous cholesterol to progesterone in the presence of NADPH. Normally, little pregnenolone accumulated during a standard 60 min incubation, indicating an active mitochondrial 3β-hydroxysteroid dehydrogenase. Luteinizing hormone (LH) failed to stimulate this conversion under the mitochondrial incubation conditions employed, whether incubated directly with mitochondria, or preincubated with ovarian slices prior to isolation of mitochondria. In addition, addition, progesterone synthesis in mitochondria prepared from ovaries of rabbits administered LH in vivo did not differ from that of control values. Adenosine-3′,5′-monophosphate (cyclic AMP) failed to stimulate progestin synthesis when added directly to mitochondria, under the experimental conditions employed. These results suggest, but do not prove conclusively, that LH and cyclic AMP may stimulate progestin synthesis in the rabbit ovary by mechanisms other tha...