DECREASING MELATONIN AND 6-HYDROXYMELATONIN SULFATE EXCRETION WITH ADVANCING GESTATIONAL-AGE IN PRETERM AND TERM NEWBORN MALE INFANTS

We investigated the ontogeny of melatonin synthesis during fetal matur ation by measuring the melatonin (MLT) and 6-hydroxymelatonin sulfate (MLTS) excretion in the urine of male infants aged 2-7 days and gestat ional age 26-42 weeks. We found a negative correlation between advanci ng gestational age and the MLT and MLTS excretion expressed as total 2 4-h amount, ratio of 24-h amount to creatinine and ratio of 24-h amoun t to body surface area, The ratio of MLT to MLTS was found to be about ten times higher in the study group than in prepubertal children, whi ch might reflect the immaturity of hepatic sulfation capacities. The t otal amount of excreted MLT and MLTS was only one-tenth the prepuberta l values. No day/night differences in MLT and MLTS excretion could be detected. We conclude that the fetal pineal gland is capable of a limi ted melatonin synthesis from the 26th week of gestation onwards, with decreasing values reaching its nadir around term. This indicates that the amount of fetal MLT excretion is not determined by synthesizing ca pacities of the pineal gland but by the development of neural connecti ons to the pineal gland.