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Action of gonadotrophic hormones on cholesterol side-chain cleavage and cholesterol ester hydrolase in the ovary of the immature rat

Summary. Immature rats were injected with PMSG (Day 0) and hCG (Day 3). PMSG caused an increase in cholesterol side-chain cleavage activity and the concentration of its terminal oxidase, cytochrome P-450, and an increase in cholesterol ester hydrolase activity in ovarian homogenates; the activity of both enzymes was further increased after hCG injection. Cholesterol ester hydrolase activity/mg ovarian wet weight was unchanged between Days 0 and 13, but the concentration of cytochrome P-450/mg wet weight increased 3-fold between Days 5 and 6. Cholesterol side-chain cleavage activity, measured in terms of pregnenolone production/mg wet weight, showed its largest increase (10-fold) between Days 6 and 7. Addition of exogenous cholesterol maintained the rate of pregnenolone production in incubated ovarian homogenates on Days 7–9.