Metabolism of subcutaneous adipose tissue in the immediate postnatal period of human newborns. 1. Developmental changes in lipolysis and glycogen content.

Abstract

Extract: 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 glyc-erol/100 μUg 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. Speculation: These 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 extra-uterine life.