The development of rhythmic melatonin secretion in full-term neonates seems to occur at about 12 weeks of age, but activity of the pineal gland from 1 to 12 weeks of age is not well documented. To determine whether the pineal gland actively secretes melatonin and reacts to photoperiodic information during this period, we analyzed 45 full-term infants exposed to continuous artificial light during 24, 48 and 72 h after birth for treatment of hyperbilirubinemia. During this light treatment, the eyes of the neonates were completely covered to avoid damage, thus the infants were under continuous light deprivation. Phototherapy significantly decreased plasma bilirubin during treatment. With regard to pineal gland activity, the shortest period of light deprivation tested, 24 h, significantly increased plasma melatonin levels from 152.66±11.57 to 244.86±19.49 ng/l (mean±sem; p<0.001). The other periods tested, 48 and 72 h of light deprivation, led to similar percentages of melatonin stimulation. These results suggest that the pineal gland of neonates, before displaying rhythmic metabolic activity, is sensitive to changes in environmental illumination, indicating maturity of some features of suprachiasmatic nuclei function.
F Jaldo-Alba, A Muñóz-Hoyos, A Molina-Carballo, JA Molina-Font and D Acuña-Castroviejo
A Munoz-Hoyos, A Molina-Carballo, M Macias, T Rodriguez-Cabezas, E Martin-Medina, E Narbona-Lopez, A Valenzuela-Ruiz and D Acuna-Castroviejo
OBJECTIVE: To analyze the kynurenine and methoxyindole metabolic pathways of tryptophan in order to identify changes in premature neonates and in neonates suffering from fetal distress. METHODS: One hundred and twelve neonates were assigned to three groups: normal neonates (control group), preterm neonates (neonates born before the 37th gestational week) and neonates suffering from fetal distress. Each of these groups was then divided in two subgroups according to the time of birth corresponding with the time of blood sampling: a diurnal subgroup, comprising neonates whose blood was sampled between 0900 and 2100 h, and a nocturnal subgroup, comprising neonates whose blood was sampled between 2100 and 0900 h. Blood samples from the umbilical artery and vein were taken in the delivery room at birth from each neonate for measurement of melatonin, the main methoxyindole pathway metabolite. Urine samples were collected from 0900 to 2100 h (diurnal groups) and from 2100 to 0900 h (nocturnal groups), and the presence of kynurenic acid, xanturenic acid, 3-hydroxyantranilic acid, L-kynurenine and 3-hydroxykynurenine determined. RESULTS: The results show the existence of diurnal/nocturnal differences in the concentration of melatonin in cord blood and in the urinary excretion of kynurenines. In normal neonates, the production of methoxyindoles (determined as melatonin) is decreased during the day and increases at night, whereas production of kynurenines is high during the day, decreasing at night. In the fetal distress group, a significant increase in the umbilical artery concentration of melatonin was found. This group also showed a reduction in L-kynurenine concentrations in the diurnal and nocturnal groups, and an increase in xanturenic acid and 3-hydroxyantranilic acid during the day. Correlation and regression studies confirmed that the differences in the day/night pattern of the tryptophan metabolic pathways were greater in normal neonates than in the preterm and fetal distress groups. CONCLUSIONS: The results indicate the existence of an imbalance in tryptophan metabolites in preterm infants and those with fetal distress, blunting the normal diurnal/nocturnal rhythm of both melatonin and kynurenines.