Circadian and Estrous Rhythms in Pineal Melatonin and 5-Hydroxy Indole-3-Acetic Acid.

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Abstract
Differential extractions and fluorometry of pineal 5-hydroxy indole-3-ace-tic acid and melatonin in adult rats demonstrate circadian rhythms correlated with periods of light and darkness and possibly influenced to a lesser degree by the estrous cycle. Pineal 5-hydroxy indole acetic acid in females rises from a nocturnal basal level of 4 ng/pineal to an early afternoon maximum of 18 ng/pineal and falls sharply at the start of darkness. Pineal melatonin rises at the start of darkness from 1 to 3 ng/ pineal; 5-methoxy indole acetic acid, averaging 0.98 ng/pineal, shows no circadian change. The specificity of the measurements and their implications for pineal indole metabolism and function are discussed.