Serial Studies on the Metabolism of Human Adipose Tissue. I. Lipogenesis and Free Fatty Acid Uptake and Release in Small Aspirated Samples of Subcutaneous Fat *

Abstract

A simple aspiration method for the serial sampling of human adipose tissue is described. The tissue shreds obtained were studied in vitro to evaluate rates of lipogenesis from glucose and acetate, as well as release and uptake of free fatty acids. These studies lead to the following conclusions In normal human subjects, glucose lipogenesis averages 664.4 [mu]g x 10-4/[mu]Eq of glyceride in 4 hours; acetate lipogenesis, 299.3 [mu]xg x 10-4; and free fatty uptake, 1.68 [mu]Eq/mEq of glyceride in 2 hours, and release, 1.89 [mu]Eq during the same time interval. In obese individuals the average rates are remarkably similar. The activities of different tissue shreds at a given site are nearly as great a source of variability as the different activities found when comparing one subcutaneous site with another. During incubation the adipose diglycerides and triglycerides are highly labeled. Palmitic and other saturated acids contain most of the labeling when acetate is used as precursor. Isocaloric substitution of carbohydrate for fat in the diet produces only a small change in adipose tissue lipogenesis. The effect of insulin on human adipose tissue obtained by this technique is variable and unpredictable. The measurements of tissue N and deoxyribonucleic acid (DNA) reveal that the content of nitrogen or DNA/unit of glyceride varies only slightly in a small series of obese, normal, and very thin individuals.