Evidence for Separate Corticotrophin- and Luteinizing Hormone-Releasing Factors in Hypothalamic Extracts

1. Several fractions obtained after gel filtration of beef (and sheep) stalk-median eminence tissue were active in releasing LH as judged by their ability to evoke OAAD in immature rats pretreated with gonadotropins and to increase plasma LH in ovariectomized, estrogen progesterone-blocked rats. These same fractions failed to release ACTH even when the dose of extract was increased by a factor of five. 2. A fraction from beef stalk-median eminence was active in releasing ACTH as judged by its ability to increase plasma free corticosteroids in both Nembutal-morphine and Dexamethasone-blocked rats. The fraction also evoked AAAD in rats with effective hypothalamic lesions. This extract had little or no LHreleasing activity in immature rats pretreated with gonado,trophins. 3. Since equivalent doses of crude hypothalamic extracts are equally active in releasing ACTH and LH, whereas the purified fractions tested here gave selective release of either LH or ACTH, it is concluded that the LH-RF and CRF are distinct entities.