Effects. of cell size and animal age on glucose metabolism in pig adipose tissue

Adipose tissue slices were prepared from middle subcutaneous or perirenal adipose tissue excised from pigs of different ages (and obesity) and incubated with [U-¹⁴C]glucose. After incubation, the slices were fixed with osmium tetroxide and separated into diameter ranges of 20-63, 63-102, and 102-153 μm, respectively. Following determination of cell size and number, the fixed adipocytes were decolorized with H₂O₂ prior to quantification of glucose conversion to total lipid, glyceride fatty acids, glyceride-glycerol, and CO₂. Glucose conversion to total lipid or CO₂ was unaffected by the presence of purified porcine insulin (0, 10, 100, 1000, and 100000 μU/ml). Within animals, adipocytes of different sizes were not different with regard to insulin sensitivity. Within a weight (age) group, conversion of glucose to total lipid (insulin present) or to glyceride fatty acids and glyceride-glycerol (insulin absent) per cell was significantly greater in large adipocytes compared to small adipocytes, regardless of the group examined. With increasing weight or age, there was a markedly decreased conversion of glucose to total lipid and glyceride fatty acids among adipocytes of similar size within a cell-size fraction. The diminution in glucose metabolism was greater (as a percentage) in 20-63 μm adipocytes than for 63-102 or 102-153 μm adipocytes. However, for all cell-size fractions there was a marked decrease in glucose conversion to fatty acids. Glyceride-glycerol synthesis was impaired in adipocytes from older pigs, but the decrease wasx less than observed for glyceride fatty acid synthesis.