The metabolism in vitro of subcutaneous adipose tissue from human newborns of different ages was investigated and comparisons were made with material taken from healthy adult volunteers. In the first hours of life, glycerol release (micromoles glycerol/100 ixg DNA/90 min) by suspensions of isolated adipocytes was increased (P < 0.001), but the response to the addition of norepinephrine was minimal. The release of free fatty acids (FFA) in relation to glycerol by suspensions of free adipocytes was considerably lower in neonates than in adults. Glycogen content of the adipose tissue between 0 and 4 hr of age was significantly greater than in older neonates and adults (P < 0.01). In infants less than 4 hr of age, glycogen content of the adipose tissue was inversely correlated with the length of labor (P < 0.05). Elevated reesterification of FFA seems to be related to the higher glycogen content and breakdown in subcutaneous adipose tissue immediately after birth. SpeculationThese investigations of the subcutaneous adipose tissue from human neonates show that the two basic energy substrates (carbohydrates and lipids) are closely and reciprocally related in the first hours and days of life. The findings are compatible with a transition from predominantly carbohydrate catabolism in the first hours of life to preferential utilization lipids in older neonates. Age-dependent changes in the in vitro metabolism of the adipose tissue parallel the relative importance of carbohydrates and lipids as substrates and energy sources in the total metabolism of the newborn infant. Thus, the subcutaneous adipose tissue may serve as an easily obtainable model for the study of the metabolic adaptation of the human newborn infant to extrauterine life. Introductiontrients from the mother. He must now supply not only The metabolic situation of the human newborn his basal metabolic requirements but also must find changes abruptly when the interruption of the fetoplaadditional energy sources for respiration, digestion, cental circulation cuts off the constant supply of nuand the maintenance of body temperature, and he is

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Carnitineacetyltransferase (CAT) and carnitinepalmitoyltransferase (CPT) and the carnitine content of white adipose tissue from human newborns and adult volunteers were estimated. The activity of CAT/mg mitochondrial protein did not change with age, while that of CPT was decreased in the adult. Carnitine content of newborn white adipose tissue was about 26 nmol/g wet weight, much lower than in other organs from human fetuses. Isolated white adipose tissue cells from newborn babies reacted to deoxycarnitine addition by a decrease in respiration; no such effect was observed in adult cells. In addition, the enhancing effect of norepinephrine on oxygen consumption of newborn cells could be further elevated by adding l-carnitine and again this was not observed in adult adipocytes.

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