Influence of melatonin on thyroid secretion in pinealectomized rats.

: The influence of a single dose of melatonin administered to pinealectomized and sham operated rats at different times of day on serum T3, T4 concentrations was investigated. It was found that such melatonin influence depends upon a time of day. Both pinealectomy and exogenous melatonin did not influence the thyroid activity in the morning. The most remarkable pineal effect on the thyroid appeared during the night.