IMMUNOHISTOCHEMICAL LOCALIZATION OF CYTOCHROME-P450 AROMATASE IN EQUINE GONADS

Estrogens are the major steroids produced by equine gonads. To identif y the cells responsible for estrogen synthesis, an antiserum against p urified equine testicular cytochrome P450 aromatase was produced in ra bbits. The reactivity and specificity of the antiserum were assessed b y ELISA, immunoblot analysis, and immunoneutralization studies, Immuno fluorescence microscopy demonstrated that in the male gonad, cytochrom e P450 aromatase (P450(arom)) was localized in the interstitial tissue , whereas, under the experimental conditions used, the Sertoli and ger m cells did not show any specific staining. In the ovary, the granulos a cells of small follicles exhibited faint immunofluorescent staining for P450(arom) and the granulosa cells of large, viable mare follicles showed a high degree of immunoreactivity. In the corpus luteum, all t he luteinized cells showed immunoreactivity. No immunoreactivity was d etected in other cells of small and large viable follicles. Immunoloca lization of P450(arom) in the equine testicular Leydig cells and in ov arian granulosa and luteinized cells indicates that these cells have t he ability to metabolize androgens to estrogens and possibly to catech ol estrogens.