IMMUNOREACTIVE CYTOCHROME-P-450 17-ALPHA IN RAT AND GUINEA-PIG GONADS, ADRENAL-GLANDS AND BRAIN

The cytochrome P-450(17-alpha)-hydroxylase, 17 --> 20 lyase (P-450(17-alpha)) is the key enzyme responsible for the biosynthesis of androgens in steroidogenic organs. Its cellular localization has been examined with an immunohistochemical technique. In immature rat ovary, P-450(17-alpha) was first detected in sparse interstitial cells on postnatal Day 8. The number of immunoreactive interstitial cells increased thereafter and the intensity of P-450(17-alpha) staining in these cells was highest at 3 weeks of age. The intensity of staining then started to decline and was very faint at Day 35. From 6 weeks on, the distribution of immunoreactive P-450(17-alpha) was of the adult type: it was detected exclusively in the thecal cells of the large antral, preovulatory, follicles. P-450(17-alpha) was not detectable during pregnancy except on the day of parturition, when thecal cells were transiently immunoreactive. The staining had vanished 24 h after delivery. Human chorionic gonadotrophin (hCG), injected into immature females on Days 24 to 26, induced P-450(17-alpha) prematurely in thecal cells. When injected on Days 12 to 14 of pregnancy, hCG also induced P-450(17-alpha) in the thecal cells surrounding the largest follicles, whereas the interstitial and luteal cells were not immunostained. The anti-progestin RU486, injected on Day 16 of pregnancy, reinstated P-450(17-alpha) (and P-450scc) immunoreactivity in the thecal cells. Oestradiol selectively suppressed P-450(17-alpha) expression in the thecal cells of RU486-treated females. In immature guinea-pig ovary, P-450(17-alpha) was immunostained in thecal cells, not in interstitial cells, although the interstitial cells expressed the DELTA-5-3-beta-hydroxysteroid dehydrogenase. P-450(17-alpha) was also immunolocalized in the Leydig cells of rat and guinea-pig testes, and in the guinea-pig adrenal cort" (zonae fasciculata and reticularis), but not in the rat adrenal cortex. P-450(17-alpha) was not detectable in the brain of either rat or guinea-pig.