The effect of insulin on lipolysis, in vivo. In black (B) and white (W) obese women: Relationship to visceral fat and insulin sensitivity of glucose uptake

We studied 10 B and 10 W premenopausal (age, mean±SEM, 37±2 and 35±2), obese (BMI 35±1 and 33±1, %fat by DEXA , 45±1 and 45±1) non-diabetic women with a wide range of visceral adiposity (VAT, 33-153 and 25-211 cm , respectively). Insulin sensitivity of glucose uptake was measured by the minimal model (sensitivity index, Si) and was not different between groups (3.3±0.8 and 3.0±0.8, range 0.3-8.4 and 0.6-8.6, respectively). Lipolysis (LIPO) was measured, in vivo, as glycerol (RaGlyc) and palmitate (RaPalm) turnover rates in the basal state, and during a pancreatic euglycemic clamp at lower (mean±SD, 7±3 uU/ml) and then higher (19±5 uU/ml) insulin (I) levels. The degrees of suppression of LIPO by I varied widely (56-72% and 14-69% suppression of RaGlyc, and, 28-55% and 19-64% suppression of RaPalm, for B and W groups, respectively) and were related to both VAT and Si. The slopes of these relationships were not significantly different between the 2 groups, however, RaGlyc was suppressed to greater degree in B than in W women (below*, p<0.05) while the effect of I on RaPalm was not different between groups, umole/mm RaGlyc (low I) RaGlyc (high I) RaPalm (low I) RaPalm (high I) B(mean±SEM) 312±38 122±17*173±21 99±13 W 303±26 173±30 151±16 93±17 These could represent differences in lipolysis and fatty acids re-esterification rates at the subcutaneous and/or visceral adipose tissue (AT) level, or differences in glycerol metabolism, outside of AT.