Changes in pineal indoleamine metabolism in vitamin A deficient rats.

Weanling, male rats were fed a vitamin A deficient (VAD) diet from 20 to 77 days of age. The circadian rhythms of the precursors and metabolites of pineal melatonin were measured along with the activity of N-acetyltransferase (NAT). Significant decreases in peak melatonin levels (0100 hours) and in nightime NAT activity (0100 and 0300 hours) were found in the pineals of the VAD rats. In contrast, the contents of serotonin, 5-hydroxytryptophan and 5-hydroxyindole acetic acid were only moderately affected by the deficiency. Daily administration of 25 micrograms melatonin from 20 to 74 days of age markedly reduced NAT activity in control and VAD rats. These data suggest that NAT activity is more sensitive to chronic VAD than any other parameters of melatonin metabolism.