1. Fat cells were isolated from massively obese patients at or before gastric bypass, from other patients after normalization of body weight after gastric bypass or gastroplasty (post-bypass patients) and from control subjects of a stable normal body weight.
2. The inhibition of isoprenaline-stimulated lipolysis by N6-(phenylisopropyl)adenosine in the presence of adenosine deaminase was much attenuated in cells from the massively obese patients as compared with those from normal-weight control subjects, but was normal in cells from post-bypass patients.
3. Isolated fat cells of the massively obese patients were larger (913 ± 197 pl, mean ± sem) than those of the normal-weight group (437 ± 95 pl). The volume of cells from the post-bypass patients was only 125 ± 49 pl, although the body mass index of this group was almost exactly the same as that of the normal-weight control subjects.
4. Although epidemiological studies have suggested that genetic factors are important in the development and maintenance of obesity, these results demonstrate that the changes observed in the inhibitory regulation of lipolysis in obesity are secondary.