M4 PM Endocrine Disruption in Fish (Part 2)
Monday, 14 November 2005: 1:50 PM - 5:30 PM in Ballroom 4

(VIJ-1117-701228) Ah receptor activation impairs the rate limiting steps in steroidogenesis in rainbow trout.

Aluru, N¹, Vijayan, M¹, ¹ University of Waterloo, Waterloo, Ontario, Canada

ABSTRACT- Anthropogenic stressors activating aryl hydrocarbon (Ah) receptor signaling, including polychlorinated biphenyls, impair the adaptive corticosteroid response to stress, but the mechanisms involved are far from clear. Using Ah receptor agonist (beta-naphthoflavone; BNF) and antagonist (resveratrol; RVT), we tested the hypothesis that steroidogenic pathway is a target for endocrine disruption by xenobiotics activating Ah receptor signaling. Trout (Oncorhynchus mykiss) were fed BNF (10 mg/kg/day), RVT (20 mg/kg/day) or a combination of both (RBNF) for 5 days, and subjected to a handling stress. BNF induced cytochrome P4501A1 (CYP1A1) expression in the interrenal tissue and liver, while this response was abolished by RVT, confirming Ah receptor activation. In control fish, handling stress transiently elevated plasma cortisol and glucose levels and transcript levels of interrenal steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side chain cleavage (P450scc) and 11 beta-hydroxylase over a 24 h period. BNF treatment attenuated this stress-induced plasma and interrenal responses; these BNF-mediated responses were reverted back to the control levels in the presence of RVT. We further examined whether these in vivo impact of BNF on steroidogenesis can be mimicked in vitro using interrenal tissue preparations. BNF depressed ACTH-mediated cortisol production and this decrease corresponded with lower StAR and P450scc, but not 11 beta-hydroxylase mRNA abundance. RVT eliminated this BNF-mediated depression of interrenal corticosteroidogenesis in vitro. Altogether, xenobiotics activating Ah receptor signaling are corticosteroid disruptors, and the mode of action includes inhibition of StAR and P450scc, the rate limiting steps in steroidogenesis.

Key words: StAR, P450scc, Stress, Cortisol