Regulation of forearm lipolysis in different types of obesity: In Vivo evidence for adipocyte heterogeneity

Forearm and systemic adipose tissue free fatty acid (FFA) release was measured in eight nonobese, six lower-body obese, and eight upper-body obese women under basal, hyperinsulinemic, and hypoinsulinemic conditions to determine whether forearm fat is regulated in a similar manner as whole body fat. Results: Adipose tissue palmitate release was greater from forearm than whole body (5.97±0.75 vs. 3.84±0.34 μmol·kg fat^-1·min^-1, respectively, P < 0.005, n = 22 subjects). Systemic palmitate release, relative to fat mass, was significantly (P < 0.01) greater in nonobese than upper-body obese, and upper-body obese than lower-body obese women, and forearm adipose tissue palmitate release followed the same pattern. Hyperinsulinemia suppressed systemic and forearm lipolysis to similar degrees, however, hypoinsulinemia consistently increased systemic palmitate flux without increasing forearm palmitate release. These results confirm the heterogeneity of adipose tissue in an in vivo model and emphasize the need to consider which adipose tissue depots are responsible for the differences in systemic FFA flux in obese and nonobese humans.