Diurnal variations of melatonin and N-acetylserotonin in the tissues of quails (Coturnix sp.), pigeons (Columba livia), and chickens (Gallus domesticus).

The levels of melatonin and N-acetylserotonin in the pineal, serum, retina, and brain of quails (Coturnix sp.), pigeons (Columba livia), and chickens (Gallus domesticus) were studied. The birds were kept under a photoperiod of 12 hr light and 12 hr dark for a minimum of 5 days before they were decapitated at midlight or middark under a 25 W red light. Melatonin and N-acetylserotonin in the pineal, serum, retina, and brain samples were extracted and determined by radioimmunoassay. It was found that the levels of melatonin in all the tissues collected in the dark period were significantly higher (P less than 0.05) than the melatonin levels of the tissues obtained in the light period. Similarly, N-acetylserotonin levels in the pineal and retinal of birds collected in the dark period were significantly higher (P less than 0.05) than those collected in the light period. But the levels of N-acetylserotonin in the serum and brain samples collected in the daytime were not significantly different from those collected in the nighttime. The results suggest that in quails, pigeons, and chickens, diurnal rhythms of melatonin are present in the pineal, serum, retina, and brain, but diurnal rhythms of N-acetylserotonin may only be present in the pineal and retina.