Effects of norepinephrine, theophylline and dibutyryl cyclic AMP on in vitro lipolysis of human adipose tissue in obesity.

Abstract

Lipolysis (release of glycerol and free fatty acids) of subcutaneous human adipose tissuein vitro has been investigated in relation to relative body weight and fat cell size. Studying 86 persons, there was a highly significant logarithmic relation between relative body weight, fat cell size and lipid content of subcutaneous adipose tissue obtained from the abdominal region. Even in extreme obesity a mean fat cell diameter of 135 μ was generally not exceeded. In these cases overweight is due to hypertrophy as well as hyperplasia of adipose tissue. — The basal FFA and glycerol release, calculated on the basis of the lipid content, did not significantly differ in normal and overweight persons. The lipolysis of the individual cell increased, however, with increasing cell diameter. The quotient of resterification (FFA release: glycerol release) was significantly lower in obesity. — When lipolysis was stimulated with norepinephrine, theophylline or dibutyryl-cyclic AMP, the dose response relations were similar in obesity and normal weight. — The stimulation of lipolysis, expressed as % of baseline, was diminished in obesity. Stimulation with dibutyryl-cyclic-AMP was negatively correlated to the cell diameter. — The absolute release of metabolites per fat cell after stimulation with norepinephrine, theophylline or dibutyryl-cyclic AMP was positively correlated with the fat cell diameter. — Addition of glucose resulted in an increment in glycerol release and an inhibition of FFA release. However, the correlation of lipolysis with fat cell diameter was not affected. — The observations suggest that large fat cells are provided with additional total lipase. Under basal conditions the relation of inactive pro lipase to active lipase seemed to change in favour of the active enzyme.