Effects of aging on basal levels of serum gonadotropins, ovarian compensatory hypertrophy, and hypersecretion of gonadotropins after ovariectomy in female rats.

Young adult (four months old) and old (14 months old) female rats were used in a series of experiments to determine the effects of aging on serum gonadotropin levels and on ovarian compensatory hypertrophy. Basal levels of gonadotropins were similar for rats of both ages. On the day after hemiovariectomy, serum FSH levels were elevated in both old and young rats. On that same day, serum LH levels were not elevated and the mean level for old rats was significantly lower than that for young rats. At two weeks and at two months after complete ovariectomy, the serum levels of both LH and FSH were lower in old than in young rats, suggesting imparied hypersecretion of gonadotropins in aged animals. After a suppressive dose of estradiol benzoate, ovariectomized old rats showed lower serum LH levels than did young ovariectomized rats. A comparison of the weights of ovaries removed two weeks after hemiovariectomy with those of the ovaries initially removed suggests that compensatory hypertrophy occurred in both groups of rats. However, ovarian weights, both before and after compensation, were lower in the old than in the young. After hemiovariectomy in old rats, the proportion of ovaries with corpora lutea increased, suggesting activation of some previously inactive ovaries.