Nitrite-induced alterations in sex steroids and thyroid hormones of Labeo rohita juveniles: effects of dietary vitamin E and L-tryptophan

An experiment was conducted to study the effect of sub-lethal nitrite exposure on sex steroids (testosterone and estradiol), cortisol and thyroid hormones (T₃ and T₄) of Labeo rohita juveniles. Fishes previously fed with normal or elevated levels of vitamin E (VE) and tryptophan for 60 days were exposed to sub-lethal nitrite for another 45 days with same feeding regime. There were nine treatment groups, viz. VE₀TRP₀−N, VE₀TRP₀+N, VE₁₀₀TRP₀−N, VE₁₀₀TRP₀+N, VE₁₀₀TRP₀.₇₅+N, VE₁₀₀TRP₁.₅+N, VE₁₅₀TRP₀+N, VE₃₀₀TRP₀+N and VE₂₀₀TRP₁+N. Except the groups VE₀TRP₀−N and VE₁₀₀TRP₀−N, all other groups were exposed to nitrite. At the end of the 45 days of nitrite exposure, serum samples were assayed for sex steroids, cortisol and thyroid hormones. The serum T₃ and T₄ levels decreased to the extent of 84.5 and 94.06 %, respectively, upon nitrite exposure. Dietary supplementation with additional amounts of VE and tryptophan appears to reduce the decline of the production of T₄. The serum testosterone and estradiol decreased 97.31 and 92.86 %, respectively, upon nitrite exposure. Supplementation with additional amounts of VE was found to reverse nitrite-induced inhibition of testosterone and estradiol production. Serum cortisol increased upon nitrite exposure and unexposed (VE₁₀₀−N) group showed lower levels, which were comparable to groups fed with elevated levels of VE. The overall results of the present study revealed that environmental nitrites have a negative impact on steroidogenesis, which can be overcome by dietary supplementation of elevated amounts of VE (minimum of 150 mg VE Kg diet⁻¹) and to a lesser extent by tryptophan (only at the level of 1.5 % of the diet).