Influence of a single neonatal melatonin treatment on the basal and thyrotropin or melatonin modified blood thyroxine level of adult rats.

Neonatal melatonin treatment caused a significant increase in thyroxine (T4) level at one month of age. Preexposure to melatonin in neonatal age and reexposure after one month accounted for a still greater increase in T4 production. Rats neonatally exposed to melatonin did not respond to TSH at one month of age.