Determination of the plasma concentrations of beta-thromboglobulin (BTG), thromboxane B2 (TxB2) and platelet factor 4 (PF4) were made at the time of birth in 18 newborns and their respective mothers. Both groups show significant elevation of all these molecular markers, suggesting marked platelet activation. The elevated TxB2 levels in the newborn group, 25 +/- 8 pg/ml, are compatible with a normally functioning and activated platelet prostaglandin pathway. Mode of delivery, vaginal or caesarean section, does not significantly influence the degree of activation in either group. Ultrastructural platelet examination did not reveal any morphologic differences between maternal and newborn platelets. There appears to be marked activation of the newborn and maternal platelet systems at the time of birth, and we postulate that this may explain in part the transient platelet dysfunction observed in newborns.

Kinetics of three amino acids with different sites and characteristics of metabolic regulation were studied in low-birth-weight infants during enteral and parenteral feeding regimens typical of clinical practice. Primed constant infusions of [15N]glycine, L-[1-13C]leucine, and L-[1-13C]phenylalanine were administered simultaneously by the same route as the feeding, with isotope enrichment measured in urine over 12 h. The effect of feeding regimen was specific to each amino acid (mean +/- SD): glycine flux was lower during parenteral feeding (470 +/- 15 vs 561 +/- 69 mumol.kg-1.h-1, P less than 0.05), leucine flux was unaffected (360 +/- 77 vs 388 +/- 78 mumol.kg-1.h-1), and phenylalanine flux was higher (106 +/- 29 vs 56 +/- 6 mumol.kg-1.h-1, P less than 0.01). Kinetics were influenced by the interaction of several factors, including amino acid intake and routes of feeding and tracer administration. Glycine was most affected by route of feeding and phenylalanine was most affected by intake whereas leucine was little affected. Estimates of whole-body protein turnover calculated from leucine and phenylalanine were different; thus calculations of protein turnover from kinetics of a single amino acid should be interpreted with caution.

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