Meeting Abstract

P1.74  Thursday, Jan. 3  Pharmacological characterization of avian corticosteroid binding globulins (CBG) in desert songbirds: Phylogenetic comparisons reveal conserved binding properties. FOKIDIS, H.B*; ORCHINIK, M.; DEVICHE, P.; Arizona State University; Arizona State University; Arizona State University bfokidis@asu.edu

Plasma corticosteroid binding globulins (CBG) are proteins that can affect the transport, solubility, availability, and activity of circulating glucocorticoids. Therefore, these plasma proteins are integral components of the stress response that may shape cellular responses to glucocorticoids. The properties and roles of CBG are well characterized in rodents and humans, but much less so in other vertebrates. We determined the affinity, abundance and hormone binding specificity of CBG in five Sonoran Desert species (Abert�s and Canyon Towhees, Northern Mockingbird, Curve-Billed Thrasher, and House Sparrow) using radioligand binding assays of 3H-corticosterone (CORT) and rapid vacuum filtration. Estimates of the affinity of CBG for CORT did not differ between species. CBG binding specificity, determined from competition studies between radiolabeled CORT and unlabelled steroids, revealed that progesterone, testosterone, and dihydrotestosterone, but not estradiol, bound to CBG with high affinity. Progesterone consistently bound to CBG with the highest affinity, but the relative affinities of other steroids for CBG varied between species. The implications of these results will be discussed, particularly with emphasis on the development of standardized methods for examining the binding characteristics of CBG.