RESUMO
The fact that calcium ions regulate the secretion of thyroid hormones could be extended to explore how the mechanisms of anuran metamorphosis is controlled by thyroid hormones. In the present study, an attempt was made to investigate the effects of both calcium channel blocker, Diltiazem (DT) and calmodulin inhibitor, Trifluoperazine (TFP) on metamorphosis and various developmental stages of the anuran tadpole, Rana tigerina. Both DT (25 microM) and TFP (2 microM) treatments caused total inhibition of the development and metamorphosis of the tadpole at premetamorphic stages. The metamorphosis was delayed by DT and totally inhibited by TFP when tadpoles were exposed at prometamorphic stages. Both drugs could not affect the tadpoles at climax stage. The findings suggest an active involvement of thyroid hormone in premetamorphic tadpoles. Calcium channel blockage with DT could not prevent the progression of tadpoles through prometamorphic stages which suggest that the change in calcium pool is not a determining factor mediating thyroid hormone release mechanism. The study suggests that in tadpole growth thyroid hormone secretion is modulated by calmodulin bound intracellular calcium.