Exploring the Glucocorticoid Actions of 1α-Hydroxycorticosterone (1α-OH-B) in the Elasmobranch Fishes

The corticosteroid 1α-hydroxycorticosterone (1α-OH-B) is unique to the elasmobranch fishes. It is thought that 1α-OH-B acts as both the primary glucocorticoid (GC) and mineralocorticoid (MC) in these fishes, a dual role analogous to that of cortisol in the teleost fishes. The MC characteristics of 1α-OH-B are well supported, but data supporting its GC functions are lacking. In this study, the putative GC actions of 1α-OH-B were examined. The first experiment characterized the physiological stress response of the Atlantic stingray (Dasyatis sabina) to air exposure, with particular regards to the roles of corticosteroids and metabolic fuels. Results demonstrate that corticosteroids increase in a corresponding manner to glucose, supporting a GC role for 1α-OH-B. Also, to determine the ability of 1α-OH-B to regulate the transcription of genes classically regulated by GCs, I isolated and sequenced the mRNA encoding serum- and glucocorticoid- inducible kinase 1 (SGK1). SGK1 mRNA abundance was upregulated in red blood cells incubated with 1α-OH-B. The results of these studies support the putative GC actions of 1α-OH-B, including the correlation of 1α-OH-B with basal glucose in vivo and the first report of direct mRNA regulation by this unique corticosteroid. Future studies should focus on the characterization of transcriptional regulation by 1α-OH-B, including the identification of GC response elements in the promoter of SGK1 and other genes, and also the development of a specific antibody for the quantification of 1α-OH-B