Utilization of Dietary Amino Acids for Energy Production in Neonatal Rat Liver

Abstract

Suneroxide dismutase activitv was determined in blood and lung ;issue from adults and varibus infant groups. Enzyme activity in human fetuses and infants was significantly lower than in adults. Similarly, S O D activity was related to age in rats and rabbits with much lower activity found in late fetal animals cornpared with the adult animals. No significant differences in enzyme activity, however, were seen between (I) infants with I R D S / H M D and their premature peers without I R D S / H M D and between (2) premature infants and full term infants.Experiments in which animal lung tissue was exposed either to 80-85% oxygen in vivo or 100% oxygen in vitro demonstrated an enhancement of pulmonary S O D activity in response to this hyperoxic challenge. In the rat, the ability to increase pulmonary S O D activity under hyperoxic conditions was age related, with the maximum effects occurring during the first 18 days of life.These data suggest that S O D is an enzyme for which increasing activity associated with maturation may be obligatory to newborn lung for the provision of protection against the relative hyperoxia of extrauterine life. Pediat. Res. 10: 158-164 (1976) Amino acid metabolism metabolic development glycogen phosphoenolpyruvate carboxykinase activity gluconeogenesis starvation liver Utilization of Dietary Amino Acids for EnergyProduction in Neonatal Rat Liver Departmenl of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, U S AExtract increased from 3 days to 19 days of age, with a decrease to adult levels. Liver glycogen concentration increased from 3 days to 19 The 3-day-old rat has a high basal level of phosphoenolpyruvate days of age, with no additional increase observed at 3 months. There carboxykinase (PEPCK), the activity of which is not increased upon was a decrease with age in the specific activity of liver glycogen starvation. The lower basal activity of the enzyme in 19-day-old rat (from [14C]alanine and [14C]leucine). In fed rats given [14C]alanine, liver can, however, be stimulated by starvation. Serum glucose levels 14C02 expiration tended to decrease with age. The 14C02 produc-

Effects of 24-hour starvation period on metabolic parameters of 20-day-old rats

“…Starvation induced a sharp increase in gluconeogenic ability on day 19 after birth in rats (WHITE & MILLER, 1976), this activation being, however, lower than in adults (SNELL & WALKER, 1973). This increase lowered lactate levels, not affecting those of glycerol, despite the increase found in adults with fasting (PALOU et al, 1981) because of enhanced lipolysis (KNOPP et d., 1970).…”

Early Postnatal Metabolism of Amino Acids in Rat

“…In a recent study about hepatic amino acid utilization, White and Miller (21) concluded that 14C0, expiration tended to decline with age for alanine and leucine. However, their kinetics showed that I4CO, production was higher in 19-day-old animals than in 3-day-old newborns when measured during the first hour following injection.…”

Variations in Free Amino Acids in Tissues of Rats from Birth to Puberty

“…This is surprising since the solid diet provides more nitrogen than maternal milk [22] and there is a parallel increase in the efficiency of the rat intestine to absorb amino acids [23,24], However, the fall in concentration of essential amino acids could be related to the increase in protein concen tration in these tissues, associated with the high protein synthesis rates reported during the weaning period [10], when concentra tions of essential amino acids in plasma are also reduced [14], The low concentrations of other amino acids may be related to a further increase in the ureogenic capabilities, since weaning results in an increased daily urinary nitrogen excretion [25]. Alanine depletion occurs both in kidney and liver, at a time when alanine aminotransferase activity in these tissues reaches adult values [6].…”

“…The variations in the hormonal environ ment during the weaning period are in accor dance with the changes in the ratio of fat/carbohydrate in the diet, since glucagon de creases and plasma insulin increases be tween 20 and 30 days after birth [3,28], with parallel maturation of the pituitary-thyroid axis during this period [29], All these endo crine events could be related to the changes in concentration of amino acids in the tis sues while, at the same time, the abundance of amino acids with a lower biological value than milk proteins [30] in the solid diet could be used mainly for energetic purposes [25].…”