Lead nitrate induced changes in the thyroid physiology of the catfish Clarias batrachus (L)

Chronic exposure of Clarias batrachus to sublethal dose of 5 ppm lead nitrate for a period of 150 days impaired thyroid function. Histological observations revealed hypertrophy, increased cell height, vacuolation, and reduction of colloid. The thyrotrophs of the pituitary also exhibited hypertrophy. But radioiodine (131I) uptake was significantly lowered. Fish exposed to 5, 10, and 25 ppm of lead nitrate for 7 days also exhibited significant reduction in 131I uptake which was dose dependent. These findings suggest that lead nitrate impairs thyroid function involving the hypothalamohypophysiothyroid axis.