The metabolism of subcutaneous adipose tissue in the immediate postnatal period of human newborns. 2. Developmental changes in the metabolism of 14 C-(U)-D-glucose and in enzyme activities of phosphofructokinase (PFK; EC. 2.7.1.11) and -hydroxyacyl-CoA dehydrogenase (HAD; EC. 1.1.1.35).

Abstract

Extract: Changes in the in vitro metabolism of subcutaneous adipose tissue have been compared in normal human newborns from 2 hr to 2 weeks of age. A group of healthy adult volunteers was also included. Samples were obtained by using a needle biopsy technique. More of the isotope from 14C-(U)-D-glucose was incorporated into triglycerides (P < 0.05) and also oxidized by suspensions of adipose cells from infants 2–3 hr of age than in older infants (P < 0.01). The ratio of radioactivity in carbon dioxide to radioactivity in triglyceride was also significantly greater in 2− to 3-hr-old infants than in older neonates (P < 0.05). Thin layer chromatography of the total lipid extract showed the greatest amount of radioactivity in the triglycerides, a small amount in 1,3-diglycerides and 1,2-diglycerides, and a trace in fatty acids and monogiycerides. These findings were compared with the developmental changes in two key enzymes: phosphofructokinase (PFK), which represents the glycolytic pathway, and β-hydroxyacyl-coenzyme A (CoA) dehydrogenase (HAD), which is involved in the β oxidation of fatty acids. The activity ratio of these enzymes decreased with age. In a preparation of isolated mitochondria, HAD activity increased with age (P < 0.001). These changes in substrate utilization and enzyme activity are consistent with an active metabolism of glucose in the subcutaneous adipose tissue in the first hours of life and relatively greater catabolism of fatty acids in older newborns. Speculation: Subcutaneous adipose tissue of human newborns is in many respects more active metabolically than the same tissue in adults. For example, lipolysis and reesterification seem to be more active, at least shortly after birth, and oxygen consumption is increased. This tissue is easily and safely accessible for examination, It responds sensitively to the metabolic situation of the newborn and could be effectively used as a source of information regarding peculiarities of newborns in whom fetal development was abnormal, such as premature delivery, intrauterine growth retardation, and maternal diabetes. Such studies might provide important information for the management of high risk infants.