Pharmacological and chemical properties of astressin, antisauvagine-30 andalpha-helCRF: significance for behavioral experiments

Corticotropin releasing factor (CRF) represents an early chemical signal in the stress response and modulates various brain functions through G protei n-coupled receptors. Two CRF receptor subtypes, CRF1 and CRF2, have been id entified. Since the physicochemical properties of CRF receptor antagonists might influence their biological potency, the peptidic antagonists astressi n, alpha -helical CRF9-41 (alpha -helCRF) and antisauvagine-30 (aSvg-30) ha ve been analyzed. The rank order of solubility of these compounds in artificial cerebrospinal fluid (aCSF, pH 7.4) was aSvg-30 > alpha -helCRF > > astressin, whereas th e rank order of relative lipophilicity as determined with RP-HPLC was alpha -helCRF > astressin > aSvg-30. The calculated isoelectric points were 4.1 (alpha -helCRF), 7.4 (astressin) and 10.0 (aSvg-30). According to Schild an alysis of the CRF receptor-dependent cAMP production of transfected HEK cel ls, aSvg-30 exhibited a competitive antagonism and displayed a 340 fold sel ectivity for mCRF(2 beta) receptor. For astressin, however, the pharmacodyn amic profile could not be explained by a simple competitive mechanism as in dicated by Schild slopes > 1 for rCRF(1) or mCRF(2 beta) receptor. Behavior al experiments demonstrated that after i.c.v. injection, alpha -helCRF redu ced oCRF-induced anxiety-like behavior tn the elevated plus-maze, whereas a stressin, despite its higher in vitro potency, did not. These findings coul d be explained by different physicochemical properties of the antagonists e mployed. (C) 2001 Elsevier Science Ltd. All rights reserved.