Absence of plasma melatonin circadian rhythm during the first 72 hours of life in human infants

To assess whether the circadian rhythm of melatonin (MT) described in umbilical cord blood of term babies is due to an active pineal in the newborn, we analyzed 119 normal neonates during the first 72 h of life. Plasma MT was measured by RIA in different neonates at different hours of the day. Statistical analysis consisted of comparison of the means of MT values grouped in two time periods of 12 h each [day period, 0900-2100 h (77 neonates); night period, 2100-0900 h (42 neonates)] and cosinor analyses to determine the existence of a circadian rhythm of MT. Mean MT levels did not vary greatly during the first 72 h of life, and no differences were found between day and night periods. These results suggest that the pineal gland in the neonate actively secretes MT, but not in a rhythmic manner, implying that the circadian rhythm of MT described previously in cord blood is a reflection of the maternal rhythm.

Melatonin concentration in the umbilical artery and vein in human preterm and term neonates and neonates with acute fetal distress

In order to assess the existence of a rhythmic secretion of melatonin (aMT) in newborns and whether this rhythm is affected by neonatal stress, we studied 112 newborns classified in three groups: normal babies delivered at term, preterm infants born before the 38th week, and babies with fetal distress. Melatonin was measured by RIA in the umbilical artery and vein at the time of birth. Melatonin levels in umbilical arterial and venous blood showed a diurnal rhythm in all groups. Melatonin levels in umbilical cord artery and vein were closely related. Nocturnal melatonin levels were increased in newborns with acute fetal distress in comparison with normal term and preterm neonates. These results suggest that (1) a rhythm of aMT secretion exists in newborns, although it cannot be determined whether this rhythm is of maternal or fetal origin and (2) neonatal stress (acute fetal distress) increases aMT production during the night in comparison with normal term and preterm neonates.