Summarydata obtained in the stressed low birth weight human neonate.The energy-rich substrates available to the fasting stressed baboon neonate ~n d infant are quantitatively similar to the metabolic fuels presented to the stressed low birth weight human newborn. Within a few hours after birth, fasting arterial plasma glucose levels in the baboon neonate approximate those of 4-6-week-old baboon infants after a 20-hr fast. Lactate levels are high and comparable for both age groups. In contrast, /3-hydroxybotymte is quite low in the immediate neonatal period, but rises to significantly higher levels (P < 0.001) after a fast at 4-6 weeks. In addition, glycerol levels are higher (P < 0.02) in the fasted older infant compared with the fasting neonate.Computation of mean cerebral blood arteriovenous differences and oxygen equivalents for animals studied in the first 50 hr of life demonstrates that glucose uptake can account for 50% or less of cerebral oxygen consumption in the newborn period. In confirmation, the respiratory quotient in these animals is 0.52 * 0.06.Cerebral oxygen consumption in the immediate neonate is greater than can be explained by utilization of glucose and the small quantities of acetoacetate and &hydroxybutyrate available at this time. At birth, cerebral uptake of lactate is noted, but this phenomenon is not observed at 6 and 12 weeks of age.
SpeculationThe baboon model for dynamic studies of neonatal energy metabolism may permit investigations of greater clinical relevance than those in lower mammalian model systems. It is suggested that lactate may be a significant cerebral energy source in the immediate neonatal period.Physiologic adaptation of the newly born infant to extrauterine life has been the subject of intensive investigation. Homeostatic adjustments in energy metabolism which occur postnatally have been of particular concern because of the clinical significance of disordered energy metabolism in the human neonate. Studies of these neonatal adaptations have been carried out in a number of mammalian species including the rat, lamb, and pig (4,12,29,32). Conclusions drawn from these studies have on occasion been applied to the human newborn.In an attempt to develop a clinically relevant model for investigation of metabolic alterations in the neonate, we have turned to a subhuman primate, the baboon. This animal has a gestational period of 184 2 10 days. At birth, it resembles the smallfor-gestational age human infant in terms of responses to fasting and diminished body fat. We have examined fasting arterial plasma levels of energy substrates and have compared these with Further, as an initial step in defining the usefulness of this preparation, studies of cerebral uptake of energy substrates have been carried out.
METHODSTwenty baboon infants were studied. Infants were the products of timed matings. Fourteen baboon neonates were delivered by cesarean section at term after a gestation of 172 k 1 days, and six were delivered spontaneously after a gestation of 175 * 4 days. The mean birth...