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Induction of stein‐leventhal‐like polycystic ovaries (PCO) in the rat: A new model for cystic ovarian disease

An injection of estradiol valerate (EV) in the rat produces an anovulatory polycystic ovarian (PCO) condition. Chronic estrogen exposure, produced by subcutaneously implanted, estradiol (E2)‐containing chronic release capsules, results in acyclicity and in hypothalamic changes similar to those seen in the EV‐injected rat. We, therefore, examined the ovarian histology and plasma gonadotropin patterns in the E2‐implanted rat and found that this model exhibits a poiycystic ovarian condition and a plasma gonadotropin pattern very different from those in the EV‐treated model. The plasma patterns of LH and FSH are bimodal consisting of small frequent pulses as well as less frequent large episodes of long duration. The ovaries contain multiple small cysts, characterized by an extensively hypertrophied theca interna, and vast chords of hypertrophied secondary interstitial cells. In contrast, cystic follicles in EV‐treated rats are fewer in number, but much larger than those in the E2‐implanted animals. The cystic theca and the secondary interstitial cell clusters are also far less extensive in the EV‐induced poiycystic ovary. These and other differences between the two types of PCO indicate that they are produced by fundamentally different morphogenic mechanisms. The cystic ovary produced by the E2 implants is similar in appearance to that seen in the human Stein‐Leventhal condition, and thus provides a new model for the study of cystic ovarian disease.