PT  - JOURNAL ARTICLE
AU  - Marilyn H. Perrin
AU  - Steve W. Sutton
AU  - Laura A. Cervini
AU  - Jean E. Rivier
AU  - Wylie W. Vale
TI  - Comparison of an Agonist, Urocortin, and an Antagonist, Astressin, as Radioligands for Characterization of Corticotropin-Releasing Factor Receptors
DP  - 1999 Feb 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 729--734
VI  - 288
IP  - 2
4099  - http://jpet.aspetjournals.org/content/288/2/729.short
4100  - http://jpet.aspetjournals.org/content/288/2/729.full
SO  - J Pharmacol Exp Ther1999 Feb 01; 288
AB  - The characteristics of a high-affinity antagonist radioligand are compared with those a high-affinity agonist in binding to the cloned corticotropin-releasing factor receptor type 1 (CRF-R1) and type 2 (CRF-R2) and to the native receptors that exist in rat cerebellum and brain stem. The relative potencies of CRF antagonists and agonists to the two types of cloned CRF receptors overexpressed stably in Chinese hamster ovary cells are determined using the antagonist radioligand 125I- [DTyr1]astressin (Ast*), and the agonist radioligand, 125I -[Tyr0]rat urocortin (Ucn*). The inhibitory binding constants (Ki) of astressin and urocortin are 1 to 2 nM for all receptors and are independent of which radioligand is employed. Astressin binds with high affinity to the native cerebellar/brain stem receptor and relative potencies of selected CRF analogs determined with Ast* on the native receptor are similar to those obtained for the cloned CRF-R1. The specific binding of Ast* to endogenous brain receptors is greater than that of Ucn*, resulting in more sites being detected by the antagonist than by the agonist. In contrast to another CRF agonist, the binding of Ucn* to the cloned receptors is relatively insensitive to guanyl nucleotides at both 20°C and 37°C; however, its binding to the native receptor is displaced by guanyl nucleotides at 37°C and, to a lesser degree, at 20°C. As expected, the binding of the antagonist Ast* is not affected by guanyl nucleotides. Because it is a high-affinity, specific CRF antagonist, astressin is eminently suitable as a ligand for detection and characterization of both endogenous and cloned CRF receptors. The American Society for Pharmacology and Experimental Therapeutics