[Features of the response of the rat thyroid gland to melatonin in pinealectomized rats]

The thyroid status of pinealectomized Wistar male rats was studied under basal conditions and after melatonin (M) administration to elucidate the role of the epiphysis in promoting antithyroid exogenous M influence. Activation of the hypophyseothyroid complex of pinealectomized rats with parallel development of adaptive changes in the system of peripheral transport and metabolism of thyroid hormones was established. The inhibiting effect of M with relation to thyroid function of rats with the intact epiphysis and its absence was revealed. The system of peripheral deiodination of thyroid hormones was found to become more sensitive to M action against a background of pinealectomy. It was shown that the inhibiting character of exogenous M action on thyroid function of rats was not mediated by their own epiphysis.