Fasting Plasma Levels of Glucose, Acetoacetate, D-β-Hydroxybutyrate, Glycerol, and Lactate in the Baboon Infant: Correlation with Cerebral Uptake of Substrates and Oxygen

Abstract

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...

The in Vivo Effect of Bilirubin and Sulfisoxazole on Cerebral Oxygen, Glucose, and Lactate Metabolism in Newborn Piglets

“…Measurements of the cerebral consumption of oxygen, glucose, and lactate have been performed in vivo in fetal sheep (26), infant baboons (27), and newborn piglets (28). The cerebral blood flow and rates of consumption of oxygen and glucose in newborn piglets have been previously demonstrated to be similar to those of human infants (13,28).…”

Substrate Utilization and Brain Development

“…Cerebral energy metabolism in fasting-stressed neonatal and infant baboons was studied by Levitsky et al (1977). In the newborn animals, the mean plasma glucose concentration was 2.9 mM, and uptake of glucose by brain accounted for only 50% or less of the cerebral oxygen consumption.…”

Cerebral Metabolic Intermediate Response following Severe Canine Intrauterine Growth Retardation

“…Lactate may function as cerebral cortical fuel in many newborn species, including man (14)(15)(16). Other studies among newborn beagles by our group (1 8) and Gregoire et al (17) have demonstrated release of lactate from the brain.…”

“…Both fuels pobably have little effect on cerebral energy metabolism. Glycerol in particular has not been demonstrated to be taken up by the newborn brain in mice, subhuman primates, or man (3,16,24).…”