Plasma free fatty acid concentration during hyperglycemic glucose clamp with and without somatostatin infusion in obese subjects with normal glucose tolerance.

In the present study we evaluated the regulation of plasma free fatty acid (FFA) concentration by glucose and insulin in human obesity. To this purpose we measured plasma FFA concentration in normoglycemic, normoinsulinemic obese (n = 8) and nonobese (n = 8) healthy subjects during 240 min of exogenous hyperglycemia (hyperglycemic glucose clamp) in presence of both glucose-stimulated (0-120 min and 180-240 min) and somatostatin-inhibited (120-180 min) insulin secretion. We found that plasma FFA curves were roughly parallel in the 0-120 min period and FFA values of obese subjects were constantly higher throughout the experimental period. Moreover, the difference between the two groups was significant when individual data were expressed as a percent of fasting FFA value (P less than 0.0001 from 0 to 120 min). Plasma insulin levels were similar in the two groups during the entire study. The amount of glucose metabolized during the 80-120 min period was significantly lower in obese than in nonobese subjects (172 +/- 7 v. 341 +/- 11 mg/m2.min, P less than 0.01; means +/- s.e.). During the somatostatin period (120-180 min) plasma insulin was lowered close to basal values in both groups (116 +/- 15 and 109 +/- 11 pmol/l) and plasma FFA concentrations rose in a linear fashion. Our data suggest that suppression of plasma FFA concentrations by glucose and insulin is qualitatively similar in healthy nonobese and obese subjects, the latter having higher FFA values. Insulin action on FFA metabolism isn ot grossly impaired in obese subjects who are clearly insulin resistant as far as glucose metabolism is concerned.