Effect of reduced ovarian tissue on cyclicity, basal hormonal levels and follicular development in old rats.

Reduction of the number of growing follicles was proposed to contribute to the decline in reproductive performance with aging (Butcher and Page, 1981). To investigate the effects of a reduced number of follicles, rats which maintained regular estrous cycles at greater than 1 yr of age had either unilateral ovariectomy (ULO) or control surgery. Irregular estrous cycles and periods of constant estrus were more frequent during a period of 90 days after ULO than in controls. Follicle-stimulating hormone (FSH) concentration in plasma collected at 0900-1100 h of the metestrus nearest to 20, 50, and 90 days after surgery was increased by ULO; in both treatment groups, FSH increased between 20 and 90 days. Compensation in ovarian weight and number of corpora lutea had occurred by 90 days after ULO. Estradiol, estrone and luteinizing hormone (LH) concentrations did not change with time or treatment. Numbers of small, medium and large antral follicles per ovary at metestrus were increased by ULO, while the number of follicles per rat was decreased. It was concluded that the reduction in ovarian tissue (which decreased the number of growing follicles) resulted in an elevation of basal FSH followed by irregularity in estrous cycles.