Stability over time of adrenergic sensitivity in isolated human fat cells

The stability over time for lipolysis in isolated human subcutaneous fat cells was investigated in 13 non-obese volunteers who underwent two gluteal fat biopsies under local anaesthesia at random intervals (mean 18 months). Glycerol release to the incubation medium was measured in the absence or the presence of lipolytic or antilipolytic adrenergic agents. The half-maximum effects (ED50) of norepinephrine, the non-selective beta-agonist isoprenaline and the selective alpha 2 agonist clonidine were determined and each had an intraindividual coefficient of variation of 7 per cent. The precision of the lipolysis assay, performed in duplicate, was 10 per cent. The coefficient of variation for lipolysis at the maximum effective concentrations of the agonists was between 20 per cent and 30 per cent. The addition of adenosine deaminase does not reduce the variability. In conclusion, the isolated human fat cell lipolysis assay shows some variability for maximum action of adrenergic agonists on lipolysis. However, there is a small variability in ED50 for such agents which indicates that the assay is well suited for determining drug sensitivity.