TWENTY-FOUR-HOUR CYCLE OF A MELATONIN-LIKE SUBSTANCE IN THE PLASMA OF HUMAN MALES

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Abstract
Plasma samples obtained during darkness from 5 male volunteers contained a substance with melanin aggregating and chromatographic properties similar to those of melatonin. Peak levels were apparently inversely related to pineal calcification and/or age. Neither this substance nor an inhibitor against its biologic activity was detected in daytime samples.