Precocious Vaginal Opening and Cornification in Rats Following Injections of Extracts of Steer Median Eminence and Pars Tuberalis1

Experiments were carried out to determine whether stored gonadotropin in the pituitary of immature female rats could be released by injections of hypothalamic extracts. The extracts were prepared from pars tuberalis and median eminence tissue of steers and were injected for 8 days, beginning on the 21st day of age. Significant acceleration of the vaginal opening time resulted from injections of extracts of pars tuberalis and the combination of pars tuberalis and median eminence. Extracts of median eminence alone had no observable effect. None of the extracts caused vaginal opening in hypophysectomized rats. The pars tuberalis and median eminence extracts both contained LH and the pars tuberalis extract contained a small amount of FSH. However, injections of the amount of LH found in the combined extracts plus a larger amount of FSH in immature rats did not accelerate vaginal opening time or cornification. The results suggest that the extracts contained an FSH-releasing factor which caused FSH to be released from the pituitaries of the immature animals. (Endocrinology75: 861, 1964)