Abstract
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 microgram, 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, glycerideglycerol, and CO2. Glucose conversion to total lipid or CO2 was unaffected by the presence of purified porcine insulin (0, 10, 100, 1000, and 100,000 microM/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 microgram adipocytes than for 63--102 or 102--153 microgram 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 was less than observed for glyceride fatty acid synthesis.
Highlights
Adipose tissue slices were prepared from middle subcutaneous or perirenal adipose tissue excised from pigs of different ages and incubated with [U14C]glucose.After incubation, the slices were fixed with osmium tetroxide and separated into diameter ranges of 20-63, 63- 102, and 102- 153 p m, respectively
Prolific accretion of subcutaneous adipose tissue occurred in both experiments (Table I). This rapid development of adipose tissue was paralleled by an increase in average adipocyte size (Fig. 1)
O'Hea and Leveille [19] noted that the rate o f glucose oxidation and fatty acid synthesis in subcutaneous adipose tissue from 40-60 kg pigs was not enhanced by the presence of insulin (0.1 IU/ml)
Summary
Adipose tissue slices were prepared from middle subcutaneous or perirenal adipose tissue excised from pigs of different ages (and obesity) and incubated with [U14C]glucose.After incubation, the slices were fixed with osmium tetroxide and separated into diameter ranges of 20-63, 63- 102, and 102- 153 p m , respectively. Effects of cell size and animal age on glucose metabolism in pig adipose tissue. Enzymatic ( 1) o r radiolabeled glucose experiments [2] have shown that conversion of glucose carbon to total lipid o r C 0 2 reaches a maximum at 4-5 months of age and thereafter declines These data were expressed on a tissue weight basis. T h e ability of insulin to stimulate glucose oxidation and fatty acid synthesis in larger adipocytes from older, more obese rats is markedly impaired when comparisons are made with adipocytes from younger, leaner animals [3,4,5,6]. I n one report [7], increasing adipocyte size was associated with unchanged rates of glucose oxidation, but was associated with an enhanced incorporation of glucose into
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