ABSTRACT. Plasma concentrations of peptide YY ( P W ) were measured in cord blood and at 6, 12, and 18 days of postnatal life in 24 healthy preterm neonates, from cord blood of eight full-term neonates, and from peripheral blood of 13 infants 9 months old. Concentrations were high in cord blood (73 f 9 pmol/liter versus adult fasting 10.4 f 1.3, p < 0.001) and rose postnatally in the premature infants to 399 f 48 pmol/liter at 6 days, 489 f 42 at 12 days, and fell to 414 f 43 at 18 days. Plasma PYY concentrations were much lower in infants 9 months old (32 f 3 pmol/liter), suggesting that the postnatal surge of plasma PYY is a feature of early adaptation to extrauterine life. Gel permeation chromatograms revealed that the major circulating form of PYY in the neonate eluted in a position identical to that of the pure 36 amino acid peptide. There was, however, evidence of two larger molecular forms that may be precursor molecules. Because P W is a peptide that exhibits potent effects on gastrointestinal secretion and motility in humans, these observations suggest that this candidate gut hormone may be important in the adaptation to enteral nutrition in the neonate. (Pediatr Res 20: 1225-1227 Abbreviation PYY, peptide tyrosine tyrosine or peptide W PYY is a recently discovered candidate gut hormone that has a broad spectrum of biological actions (1-5). PYY is produced by endocrine cells in the distal bowel, and plasma concentrations rise in response to the ingestion of food (3, 6, 7). Infusion studies in adult humans, at doses producing increments of plasma PYY concentrations within the physiological range, have revealed potent inhibitory effects on gastric secretion and emptying and also a delay of mouth-cecum transit (8,9). Recently we observed that circulating PYY concentrations in young healthy pigs were greater than those of adult humans and rats (6, 10). Although this difference may have been due to species it raised the possibility that PYY plays a particular role in the developing animal (7). The aim of the present study was to measure plasma PYY concentrations at birth and in early life to evaluate whether this peptide could be important in the adaptation of the human neonate to extrauterine life.
PATIENTS AND METHODSHealthy infants born before 34 wk gestation entered the study, which was approved by the hospital ethics committee. Informed parental consent was also obtained; 24 infants were studied. The mothers of 15 of these (birth weight 1620 _+ 67 g, gestation 32 _+ 1 wk, mean _+ SE) wanted to establish lactation, and their infants were fed only with regular boluses of breast milk by nasogastric feeding tube. The nine infants of mothers not wishing to breastfeed (birth weight 1564 _+ 1 17 g, gestation 3 1 _+ 1 wk, mean _+ SE) were given regular boluses of an adapted milk formula (Nenatal, Nutricia International BV) in daily volumes as recommended by the manufacturer. Both groups of infants tolerated their feeds well and gained weight as expected. None developed diarrhea or any other complication, and ...