Effect of postnatal hypoxia on the energy homeostasis of the newborn rat during the early neonatal period

Normal serum alanine concentration differentiates transient neonatal lactic acidemia from an inborn error of energy metabolism

BACKGROUND

Elevated blood lactate levels are common in the critically ill neonate; however, sometimes they are difficult to interpret. Persistent or recurrent lactic acidemia might point to an inborn error of metabolism, like disturbances of the oxidative phosphorylation. Chronic lactic acidemia results in increased serum alanine levels. Serum alanine levels in newborns with transient lactic acidemia have not yet been studied.

OBJECTIVE

We designed a pilot study to evaluate the use of serum alanine levels as an additional metabolic marker to differentiate the transient effect of circulatory failure from a possible mitochondrial dysfunction.

METHODS

We prospectively evaluated 10 newborns with transient lactic acidemia after mild dysoxia, and 10 newborns with recurrent lactic acidemia consecutively diagnosed with a disorder in oxidative phosphorylation.

RESULTS

No significant serum alanine level elevation was found in transient lactic acidemia. Increased serum alanine was a sensitive marker in mitochondrial dysfunction.

CONCLUSIONS

We propose to measure the serum alanine level in hypotonic newborns with lactic acidemia to facilitate the decision making in further diagnostics and management.

Ammonia metabolism during the suckling period in the rat

1. The time-courses of blood glutamine, glutamate, alanine, ammonia, urea and allantoin concentrations during the first 15 days of extrauterine life were studied. 2. Glutamine and glutamate concentrations followed the same pattern and correlated positively, suggesting that both amino acids are utilized or released synchronously. 3. Alanine concentrations decreased during the first 3 days, reaching levels close to those of adults which persisted up to the end of the observation period. 4. A highly significant correlation was found between ammonia and urea concentrations, suggesting that during the suckling period urea synthesis may be limited by blood ammonia availability. 5. The time-course of allantoin concentrations suggests that the synthesis of purines was enhanced during the first day, decreasing sharply during the 2nd to steeply increase to the end of the suckling period.

Regulation of hepatic gluconeogenesis in newborn rabbit: controlling factors in presuckling period

We have previously shown (Comp. Biochem. Physiol. 77B: 35-39, 1984) that a rapid postnatal increase in hepatic mitochondrial adenine nucleotide content activates pyruvate carboxylation and gluconeogenesis in the newborn rabbit. This study investigated factors limiting flux through the gluconeogenic pathway and examined the physiological stimuli responsible for the activation phenomenon. There is a 2.3-fold increase in total mitochondrial adenine nucleotides, along with a threefold increase in the matrix ATP/ADP ratio, by 2 h after birth, resulting overall in a sixfold increase in the amount of ATP/mg mitochondrial protein. Analysis of gluconeogenic intermediates, measured in freeze-clamped livers between birth and 4 h postnatal, suggests that pyruvate carboxylase controls gluconeogenic flux during this period. Newborn rabbits reared in an hypoxic environment (5% O2) exhibited decreased mitochondrial adenine nucleotide content, decreased rates of pyruvate carboxylation, and depressed blood glucose levels compared with littermates reared in room air or 95% O2. Manipulation of the insulin-to-glucagon ratio in vivo by injecting insulin at birth significantly delayed postnatal increases in the mitochondrial adenine nucleotide content and the rate of pyruvate carboxylation. Conversely, glucagon injection produced a supranormal increase in both mitochondrial adenine nucleotide content and pyruvate carboxylation. In addition, insulin injection prevented, whereas glucagon enhanced, the normal postnatal increase in tissue ATP/ADP. These results suggest that tissue oxygenation and a decreased insulin-to-glucagon ratio promote the rapid influx of adenine nucleotides from the liver cytosol into the mitochondrial matrix, thereby activating pyruvate carboxylation and gluconeogenesis during the presuckling period.