ALURU, N*; VIJAYAN, M.M.; Univ. of Waterloo, Waterloo,ON: β-Naphthoflavone impacts interrenal corticosteroidogenesis in rainbow trout.

The objective of the study was to investigate the impact of aryl hydrocarbon receptor (AhR) on interrenal steroidogenesis in rainbow trout (Oncorhynchus mykiss). We used β-napthoflavone (BNF) and α-napthoflavone (ANF) as agonist and antagonist of AhR, respectively. Fish were given a single intraperitoneal implant of either oil alone or oil containing ANF, BNF and a combination of both (ANF/BNF) and sampled at 2 and 6 day post-implantation. Higher CYP1A protein expression in the liver and mRNA abundance in head kidney revealed significant AhR activation with BNF. In vitro stimulation of interrenal cells with either ACTH or 8-br-cAMP showed a lower capacity for cortisol production in fish treated with BNF suggesting that AhR activation lowers interrenal capacity for cortisol production in trout. ANF had no significant impact on interrenal steroidogenesis nor blocked the effect mediated by BNF. However, ANF abolished the higher plasma cortisol levels seen with BNF in trout. Furthermore, no significant changes in the mRNA abundance of key steroidogenic enzymes (StAR protein, P450 side chain cleavage and 11β-hydroxylase) were observed. Taken together, these results imply that AhR activation may not offset the genomic integrity of the steroidogenic pathway, but affects acute interrenal responsiveness to ACTH stimulation in rainbow trout.