INHIBITORY EFFECT OF ADRENOCORTICOTROPIN ON CORTICOTROPIN-RELEASING FACTOR RELEASE FROM RAT HYPOTHALAMUS IN VITRO

Effects of ACTH and ACTH fragments on immunoreactive corticotropin-releasing factor (I-CRF) release were examined by utilizing rat hypothalamic perifusion system and a rat CRF RIA. ACTH-(l–39) had a dose-related inhibitory effect on I-CRF release. Mean percent inhibition of I-CRF release was 52, 55, 49, 30 and less than 5% by ACTH-(l–39), ACTH-(1–24), α-MSH and ACTH-(18–39) at 2.2 nM concentrations, respectively. These results suggest the presence of a negative short-loop feedback mechanism, and also that the active core is contained within the ACTH-(1–17) structure.