Pharmacological and chemical properties of astressin, antisauvagine-30 and α-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 protein-coupled receptors. Two CRF receptor subtypes, CRF1 and CRF2, have been identified. Since the physicochemical properties of CRF receptor antagonists might influence their biological potency, the peptidic antagonists astressin, alpha -helical CRF9-41 (alpha -helCRF) and antisauvagine-30 (aSvg-30) have 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 the 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 analysis of the CRF receptor-dependent cAMP production of transfected HEK cells, aSvg-30 exhibited a competitive antagonism and displayed a 340 fold selectivity for mCRF(2 beta) receptor. For astressin, however, the pharmacodynamic profile could not be explained by a simple competitive mechanism as indicated by Schild slopes > 1 for rCRF(1) or mCRF(2 beta) receptor. Behavioral experiments demonstrated that after i.c.v. injection, alpha -helCRF reduced oCRF-induced anxiety-like behavior tn the elevated plus-maze, whereas astressin, despite its higher in vitro potency, did not. These findings could be explained by different physicochemical properties of the antagonists employed. (C) 2001 Elsevier Science Ltd. All rights reserved.