Immunolocalization of P450C17 in the mare corpus luteum

Although the mare corpus luteum (CL) is capable of aromatization, the expression of other enzymes involved in estradiol synthesis is not yet clear. This study examined the localization of P450C17 in the mare CL at different stages of its functional development. In ovaries from follicular phase mares P450C17 was localized in the theca cells of ovarian follicles. Following ovulation, no immunostaining for P450C17 was detected in the mature CLs of nonpregnant mares. In pregnant mares, no immunostaining for P450C17 was identified in the corpus luteum prior to secretion of eCG by the feto placental unit at Day 35 of pregnancy. The P450C17 was found to be expressed in CLs retrieved from Day 40 of pregnancy onwards. The changing expression of P450C17 raises the possibility that this may be a regulatory step for estrogen synthesis in the mare ovary.