Modulation of interrenal cAMP/PKA signalling cascade, PPAR isotypes and hormonal responses in Atlantic salmon by Tributyltin and forskolin

The mechanisms by which TBT produces modulations of the endocrine systems are not fully described. In this study, juvenile salmon were force-fed diet containing TBT (0: solvent control, 0.1, 1 and 10 mg/kg) for 72 hours. Subsequently, fish exposed to solvent control and 10 mg/kg TBT were exposed to waterborne concentrations of the adenyl cyclase stimulator forskolin (200 μg/L) for 2 and 4 hours. Tissue and blood were sampled from individual fish (n=8). Gene expression patterns of steroid acute regulatory (StAR) protein, P450scc, CYP11β, steroidogenic factor-1 (SF-1), glucocortico receptor (GlucR) and peroxisome proliferator activated receptor (PPAR) isoforms were determined by qPCR, and immunochemical methods for protein analysis. Interrenal cyclic AMP (cAMP) and protein kinase A (PKA) levels and plasma estradiol (E2) and testosterone (T) levels were measured by EIA assays. TBT generally decreased mRNA levels of StAR, P450scc, CYP11β and SF-1 compared to the solvent control, whereas GlucR levels were unaffected by TBT treatment. In contrast, StAR and P450scc mRNA expression was upregulated by forskolin, whereas the combined TBT (10 mg/kg) and forskolin exposure eliminated this effect. Interrenal cAMP and PKA levels were increased by TBT and forskolin exposure. Plasma T levels were increased after TBT exposure, whereas only the highest TBT concentration (10 mg/kg) produced an increase in E2 plasma levels. Interestingly, TBT and forskolin produced individual and combined effects on PPAR that is isoform specific and influenced by time of exposure. This study suggests that TBT may exert endocrine disrupting effects through modulation of cAMP/PKA second messenger systems.