Induction by estradiol-17 beta of polycystic ovaries in the guinea pig

In the present study we wished to develop a model for polycystic ovarian syndrome (PCOS) using the guinea pig, because this animal's cycle, compared to other rodent models, more closely emulates that of humans. Four silastic capsules, either empty or containing cholesterol or estradiol-17 beta, were placed subcutaneously for 48 h on Day 10 or 12 of the cycle. Vaginal smears were taken daily. Cardiac blood was drawn at various intervals. At necropsy, trunk blood was collected and ovaries were excised and analyzed histologically. Cycle length was extended over that in controls in animals treated with estradiol-17 beta (E2) on Day 12 of the cycle. Treatment with E2 resulted in an increase in serum estrogen 2 h after capsule insertion. No changes were evident in progesterone or androstenedione concentrations with treatment. Animals treated with E2 and killed late (54 days after capsule removal) showed cysts grossly (group A), while occult cysts were present in E2-treated animals killed early (17 days; group B); no cysts were observed in control groups. Ovarian weight and size were increased in group A over controls. There was an increase in the fraction of atretic:total follicles < 500 mm in size in group A compared to group B as well as compared to controls. Since these results are similar to those seen in human PCOS, we conclude that the guinea pig may serve as an exceptional and unique model for the study of PCOS and may be applicable to humans.