Comparison between tryptophan methoxyindole and kynurenine metabolic pathways in normal and preterm neonates and in neonates with acute fetal distress.

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.

Relationships between methoxyindole and kynurenine pathway metabolites in plasma and urine in children suffering from febrile and epileptic seizures.

OBJECTIVE: The methoxyindole pathway metabolite, melatonin (aMT), and the kynurenine pathway metabolites, kynurenic acid (KYNA), xanturenic acid (XA) and 3-hydroxyantranilic acid (3HANA) are anticonvulsants, whereas the kynurenine pathway metabolites, L-kynurenine (KYN) and 3-hydroxykynurenine (3HK), are proconvulsants. It is thought that alterations in the concentrations of these compounds may be responsible for the excitotoxic aspect of human seizures. The aim of this study was to determine whether alterations in tryptophan metabolism might be related to the occurrence and type (febrile or non-febrile) of seizures in children. DESIGN: One hundred and eighteen children from the University of Granada Hospital were studied. They were divided into two main groups (febrile or epileptic convulsive) depending upon their clinical diagnosis. An age-, weight- and gender-matched control group was also studied. Each group was then divided into two subgroups of patients sampled between 0900 h and 2100 h (diurnal groups) and patients sampled between 2100 h and 0900 h (nocturnal groups). MEASUREMENTS: Plasma melatonin was measured in samples obtained from both the diurnal and nocturnal groups. Urinary excretion of melatonin and kynurenine metabolities were measured in an aliquot of 12-h urine samples collected from both the diurnal and nocturnal groups. RESULTS: Besides the typical circadian rhythm of melatonin we also found diurnal/nocturnal differences in the concentrations of all the kynurenines, which reached significantly higher levels during the day. In normal humans the production of methoxyindoles is lower during the day and rises at night, whereas the production of kynurenines is higher during the day and decreases at night. In patients suffering from febrile and epileptic convulsions, however, there was a significant increase in the nocturnal production of KYN, 3HK, KYNA and XA. Thus we found the circadian rhythm of kynurenines to be altered in convulsive patients. Furthermore, while the various kynurenine metabolites increased by the same amount during the night in febrile convulsive children, in epileptic children the increase in KYN and 3HK was significantly lower than the increase in KYNA and XA. During the day the proconvulsant KYN decreased significantly and the anticonvulsant XA increased in both convulsive groups. Moreover, plasma aMT increased during the day in febrile convulsive group and also during the night in both febrile and epileptic groups although showing no significant change in their urinary excretion levels. CONCLUSIONS: Our results point to the existence of an imbalance in the tryptophan metabolite pathways during convulsions, blunting the normal diurnal-nocturnal rhythm of kynurenines. They also support the idea of a difference in the production of tryptophan metabolites between febrile and epileptic patients, suggesting that the tryptophan pathways follow different routes depending upon the type and duration of the convulsion.

5-Methoxytryptophol and melatonin in children: differences due to age and sex.

It seems clear that the pineal hormone, melatonin (N-acetyl-5-methoxytryptamine), is involved in the reproductive behavior of several animal species including humans. Moreover, several data also support a role for 5-methoxytryptophol (ML), another pineal hormone, in the control of sexual processes. To test the role of ML in human reproductive axis, 128 healthy children, 68 boys and 60 girls, were studied. Each of these groups was divided in three age subgroups of 6, 11, and 14 years. A single blood sample (0900 hours) was obtained from each subject to determine melatonin, ML, FSH, LH, estradiol (girls), and testoterone (boys) by RIA. Statistical analysis of the data included ANOVA-II (factor I: age, factor II: sex) and an analysis of covariance with age as covariate. A similar plasma melatonin concentration, with a significant decrease between 6 and 11 years, was found in boys and girls. Melatonin concentrations correlate well with initiation of the pubertal development in these children, although no sex differences were found. Concentrations of ML are approximately 50% of those of melatonin. In contrast to melatonin, ML levels show significant age and sex differences. Plasma ML concentration significantly increased in boys (P < 0.001) and decreased in girls (P < 0.001) after 8 years of age. These results support the hypothesis that, besides melatonin, other pineal compounds such as ML may be involved in the maturation process in humans. The pineal indole ML may also be used as a marker of the different chronobiology in the pubertal development in boys and girls.

Day-night variations in melatonin secretion by the pineal gland during febrile and epileptic convulsions in children.

The pineal gland is a complex neuroendocrine organ with pronounced effects on central nervous system activity. Because previous studies in animals and humans have suggested an anticonvulsant role for the pineal hormone melatonin, we studied the day-night variations in plasma melatonin in normal children and children with febrile or epileptic convulsions. We found significant changes in day-night melatonin levels during convulsions, consistent with the hypothesis that melatonin has an inhibitory function on central nervous system activity.

Effects of febrile and epileptic convulsions on daily variations in plasma melatonin concentration in children.

Plasma melatonin was measured in 118 infants and children (39 controls, 28 with epileptic convulsions, and 51 with febrile convulsions). The control group displayed a typical circadian rhythm, with melatonin peaking between 0200 and 0400. This normal daily variation significantly changed in the epileptic group, which showed a characteristic phase-advance, with the nocturnal melatonin peak appearing between 2400 and 0200. Febrile convulsions were associated with the disappearance of the normal circadian rhythm of melatonin, which was replaced by melatonin bursts throughout the light:dark cycle. In both febrile and epileptic children, melatonin levels were significantly increased in comparison with normal children.

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.