The distribution of cytochrome P-450 (C-P450), an essential component of the oxidative enzyme system involved in the hydroxylation of steroids, was measured by quantitative cytochemistry in cryostat sections of preovulatory follicles obtained from rats in proestrous. The sections were reacted with medium saturated with carbon monoxide with or without the addition of sodium dithionite. The absorbance spectrum was measured from 400 to 500 nm and a difference spectrum calculated by subtracting the extinction obtained from incubations without sodium dithionite from that obtained in the presence of sodium dithionite. A distinct peak at 450nm was recorded in cells of the peripheral portion of the membrana granulosa (MG) but not in those of the cumulus, providing evidence for the presence and differential distribution of C-P450 in the MG of the preovulatory follicle.
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