Role of decreased numbers of follicles on reproductive performance in young and aged rats.

The primary objectives of this study were to: 1) determine if removal of 1.5 ovaries from young rats would mimic reproductive characteristics that normally occur with advancing age and 2) determine if removal of 1.5 ovaries from aged rats would further advance the process of reproductive aging. Removal of 1.5 ovaries increased the number of young (P less than 0.05) and old (P less than 0.01) rats that exhibited abnormal estrous cycles. In addition, concentrations of follicle-stimulating hormone (FSH) were higher at both ages in the groups with half an ovary. The increased concentrations of FSH are consistent with a decrease in the number of growing follicles after removal of 1.5 ovaries. All groups had lower concentrations of estradiol (E2) than young controls. There was a significant increase in the number of abnormal embryos with age and removal of 1.5 ovaries when rats were mated during a 5-day estrous cycle, but there was no effect if they were mated during a 4-day estrous cycle. From the results of this study, we conclude that the reduction in ovarian tissue in young and aged rats mimicked several reproductive characteristics of advancing age. Also, an effect of aging on the hypothalamus was evident in this study.