Abstract
The locus of gonadotropin-induced acute stimulation of pregnenolone production by cholesterol side-chain cleavage (CSCC) enzyme containing cytochrome P450 (cytP450scc) was examined in rat corpus luteum. Mitochondria were isolated from pseudopregnant rat ovaries after treatment with different doses of human CG (hCG) (25-200 IU) for 30 min; Electron Paramagnetic Resonance (EPR) spectra of high spin cholesterol complex of cyt P450scc (type I high spin EPR signal) and the cyt P450scc activity were determined. hCG treatment increased the formation of type I EPR spectra compared to that obtained with saline-treated controls, and pretreatment with cycloheximide (30 mg/kg BW) before hCG abolished this increase. The magnitude of type I EPR signal diminished with increasing pH over the range of 6.2-7.3. The type I EPR signal increased with doses of hCG and correlated well with the pregnenolone production. Aminoglutethimide treatment (competitive inhibitor of CSCC) before hCG injection led to an increased accumulation of cholesterol in inner mitochondrial membranes with a corresponding decrease in the outer membrane cholesterol, and cycloheximide treatment inhibited this accumulation. This suggests that the transport of cholesterol to inner mitochondrial membranes from outer membranes is regulated by hCG. In addition, gonadotropin also regulates the redistribution of cholesterol within the inner mitochondrial membranes.
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