Gonadotropic activity of stalk median eminence extracts in hypophysectomized rats.

Abstract

Standard preparations of crude or partially purified porcine LH-RF (prepared by molecular sieving on Sephadex-G25) elicited the same depletion of ovarian ascorbic acid in intact and hypophysectomized rats. At doses of 1/16, 1/4, 1 and 4 stalk median eminence equivalents (SME), crude extracts elicited similar depletions in intact and hypophysectomized rats, which increased with dose. At these same doses, purified extracts evoked a linear dose response in intact rats and nonsignificant responses at the lower 3 doses in hypophysectomized rats. The high dose effected similar responses in both intact and hypophysectomized rats. An assay which depends on release of pituitary LH into the blood stream, under the influence of high doses of LH-RF was not able to distinguish between LH and LH-RF. Both compounds evoked higher activities in the plasma of intact than hypophysectomized rats. The partially purified preparations of LH-RF used in these studies were not contaminated with LH since ultrafiltration of LH through a dialysis membrane removed the LH activity in hypophysectomized assay rats, while filtration of LH-RF did not. The highest doses of the partially purified extracts also contained less than 35 mU of vasopressor activity. This level of vasopressin contamination was too low to affect the depletion of ovarian ascorbic acid. (Endocrinology83: 225, 1968)