Compartmentalization of steroidogenesis by the equine corpus luteum

The presence of cytochrome P450(C17) within equine follicles and corpora lu tea (CL) was detected by immunostaining. Two different antibodies were used which had previously been shown by immunoblotting to cross-react with equi ne P450C17. Strong positive immunostaining was present in the theca-derived cells of the CL during the estrous cycle and pregnancy. In the CL from mar es after Day 40 of pregnancy tt;ere were also occasional bands of positivel y stained cells which resembled the polyhedral-shaped theca cells seen in p reovulatory follicles. The pattern of immunostaining suggested compartmenta lization of steroidogenesis within the equine CL with small cells possessin g the potential to produce androgen which could then be aromatized to estro gen by the large luteal cells (C) 2000 by Elsevier Science Inc.