IMMUNOLOCALIZATION OF AROMATASE P-450 IN OVARIAN TISSUE FROM PREGNANTAND NONPREGNANT MARES AND IN OVARIAN-TUMORS

Aromatase P-450 (P-450(arom)) is a crucial regulatory enzyme that is n ecessary for conversion of androgens to oestrogens. Corpora lutea and follicles were obtained from the ovaries of cyclic mares and from mare s at day 20 and days 40-70 of pregnancy. The presence of P-450(arom) w ithin specific cell types was investigated by immunostaining to determ ine potential sites of oestrogen synthesis. Immunoreactivity for P-450 (arom) was confined to the granulosa layer of non-atretic follicles > 5 mm in diameter and to corpora lutea at all stages of the oestrous cy cle and during pregnancy. These findings confirm that aromatization of androgens occurs within the granulosa cells of the preovulatory folli cle of the mare and that the corpus luteum of the mare has the capacit y for oestrogen production if adequate androgen substrate is available . Granulosa cells in ovarian tissue from three mares with granulosa ce ll tumours showed little staining for P-450(arom), which suggests that these rumours have little aromatizing capacity.