Pineal melatonin synthesis following neutralization of circulating N-acetylindolealkylamines

In order to determine whether pineal products may influence pineal activity in mammals, day and night pineal melatonin levels were measured following injection of melatonin, the melatonin precursor, N-acetylserotonin (NAS), the pineal peptide arginien vasotocin (AVT) or immunization against circulatin melatonin and/or NAS. Darkness significantly enhanced pineal melatonin content. Pineal melatonin levels were not significantly altered by injection of either melatonin, NAS, or AVT, or by passive immunization against circulating melatonin. However, active immunization against circulating melatonin caused a further elevation of night pineal melatonin levels over and above that seen in controls, but did not affect day levels of melatonin.The significant increase in night pineal melatonin levels following neutralization of circulating melatonin suggests that this indoleamine may modulate its own biosynthesis at night via a negative feedback system. However, it is also possible that the observed enhancement of pineal melatonin levels was due to a reduction in the rate of melatonin secretion or some other factor.