Effects of Castration and Gonadal Hormones on Hypothalamic Content of Luteinizing Hormone Releasing Factor (LRF)12

The effects of castration, estradiol benzoate, testosterone propionate, progesterone and combined estrogen-progesterone treatment were determined on hypothalamic LRF content in mature male and female rats. LRF activity was tested by incubating hypothalamic extract from the differently treated rats with pituitaries of male rats for 1 hr. The medium was later assayed for LH by the OAAD method of Parlow. The results indicate that castration for 21 days in male rats elicited a 2.5-fold increase in hypothalamic LRF content, whereas daily subcutaneous injections of 1 mg of testosterone propionate prevented the elevation in hypothalamic LRF content in castrate rats. In female rats, castration for 21 days resulted in a significant reduction in hypothalamic LRF content, to only 30% of that present in intact rats. Subcutaneous injections of 0.8 μg of estradiol benzoate daily for 21 days significantly depressed hypothalamic LRF content in ovariectomized rats. The pituitaries of ovariectomized rats showed a out a 4-fold increase in LH concentration, whereas estrogen injections largely prevented this increase. Subcutaneous injections of 4 mg of progesterone daily for 21 days into ovariectomized rats had no effect on hypothalamic LRF content, whereas injections of 4 mg of progesterone together with 0.8 μg estradiol benzoate prevented the latter from depressing LRF content. When pituitary tissue was incubated for 1 hr in the presence of estradiol, a significant increase in LH release into the medium was observed. These results suggest that ovariectomy stimulates release more than synthesis of hypothalamic LRF; that systemic injections of estrogen can inhibit both release and synthesis of LRF; and that estrogen can act directly on the pituitary to stimulate LH release. (Endocrinology79: 432, 1966)