Immunolocalization of aromatase P-450 in ovarian tissue from pregnant and nonpregnant mares and in ovarian tumours

Abstract

Aromatase P-450 (P-450(arom)) is a crucial regulatory enzyme that is necessary for conversion of androgens to oestrogens. Corpora lutea and follicles were obtained from the ovaries of cyclic mares and from mares at day 20 and days 40-70 of pregnancy. The presence of P-450(arom) within specific cell types was investigated by immunostaining to determine 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 cycle and during pregnancy. These findings confirm that aromatization of androgens occurs within the granulosa cells of the preovulatory follicle of the mare and that the corpus luteum of the mare has the capacity for oestrogen production if adequate androgen substrate is available. Granulosa cells in ovarian tissue from three mares with granulosa cell tumours showed little staining for P-450(arom), which suggests that these tumours have little aromatizing capacity.