Coincidence of counter-antigonadal and counter-antithyroid action of melatonin administration via the drinking water in male golden hamsters

Abstract

Administration of melatonin via the drinking water prevented the gonadal involution and the thyroid hormone depletion normally observed in blinded hamsters. Ten weeks after blinding male hamsters had plasma thyroxin levels that were 57% of controls and testis weights that were 8% of controls. Administration of melatonin (80 μg melatonin/ml drinking water) to blinded hamsters restored thyroxin levels to 86% of controls and testis weights to 93% of controls. Dose response data showed that as little as 1.25 μg (approximately 10 μg/hamster/day) produced a significant effect on testis weight, whereas the lowest dose required to produce a significant increase in thyroxin levels was 10 μg/ml. The coincidence of counter-antigonadal and counter-antithyroid actions of melatonin suggests a single site of action.