Effects of aging on the hypothalamic-hypophyseal-gonadal axis in female rats
McPherson, J.C.; Costoff, A.; Mahesh, V.B.
Fertility and Sterility 28(12): 1365-1370
1977
ISSN/ISBN: 0015-0282 PMID: 201506 DOI: 10.1016/s0015-0282(16)42986-9Document Number: 439535
The hypothylamic-hypophyseal-gonadal axis in anovulatory retired breeder rats was evaluated to elucidate the changes occurring in aging female rats. Serum gonadotropins were measured and the response to castration and steroid replacement, ovarian responsiveness to exogenous gonadotropin stimulation, and pituitary responsiveness to luteinizing hormone-releasing hormone (LH-RH) determined. Castration and estradiol replacement in 22-month-old rats resulted in a reduced secretion of follicle stimulating hormone but at a lower rate than that seen in younger rats. The responses of serum LH to estradiol followed a similar pattern. Pregnant mare's serum gonadotropin given alone or combined with human chorionic gonadotropin in 22-month-old castrate rats caused a significant ovarian weight increase (p.01) over intact controls with a corresponding increase in uterine weight as well. Aging rats also responded to LH-RH (100 mg) with values of serum LH significantly elevated (p.01). These results suggest that the feedback mechanism of aging rats is less sensitive to stimulation than in younger rats. However, pituitaries are still capable of responding to stimulation. These data are consistent with the hypothesis of altered hypothalamic-hypophyseal function in aged rats.