[Melatonin in the pineal organ, retina and plasma. Immunologic study in the pigeon].

Circadian variations in melatonin content have been studied in the pineal organ, retina and plasma of adult pigeons using radioimmunoassay. A clear-cut peak of melatonin was observed in the pineal organ at middark; this middark peak was of larger amplitude in July than in November. A nocturnal rise in melatonin concentration was also observed in the retina and plasma. We also used an immunocytochemical technique revealing the positive reactions of a melatonin-like compound in the photoreceptor cell layer (inner segments) of the pigeon's retina. Up to now, no melatonin storage has been visualized in the pineal organ of the pigeon.