BREUNER, C.W.*; WADA, H.; SHYU, J.; LOVE, O.P.; University of Texas at Austin; University of Texas at Austin; University of Texas at Austin; Simon Fraser University: Corticosteroid Binding Globulin Capacity Responds to Chronic Hormone Treatment but not Acute Stressors

There is increasing evidence that corticosteroid binding globulins (CBG) regulate glucocorticoid action in surprising and unpredictable directions. However, many basic questions of CBG regulation and action remain unanswered. Here, we examine the possible change in CBG capacity in response to acute and chronic changes in stress and glucocorticoids. 1) In the acute capture and handling protocol, a number of labs have obtained preliminary data that indicate a possible change in CBG capacity within 30-60 minutes of capture. We have CBG measures from baseline and stress-induced blood samples from house sparrows (Passer domesticus), starlings (Sturnus vulgaris), and white-crowned sparrows (Zonotrichia leucophrys). In each species there is no detectable change in capacity during the capture and handling protocol, relieving the need to sample CBG at every time point during the stress series. 2) Over longer time periods, CBG capacity appears to be controlled by glucocorticoid levels in both mammalian and reptilian species, but in opposite directions. In house sparrows, we demonstrate that CBG capacity increases with corticosterone implants and decreases with mitotane treatment (which reduces endogenous levels of corticosterone). The change in CBG capacity is robust enough so that there is no difference in estimated free hormone levels between the three treatments. Taken together, these studies will help determine the best strategy for incorporating CBG measures into free-living and captive studies of stress physiology.