Expansion of adipose tissue mass results from increased number and size of adipocyte cells. We hypothesized that subcutaneous abdominal preadipocytes in obese individuals might have an intrinsically higher propensity to differentiate into adipocytes. Thus we investigated the relationship between obesity and the level of in vitro preadipocyte differentiation in Pima Indians. Subcutaneous abdominal stromal vascular fractions containing preadipocytes were cultured from 58 nondiabetic subjects [31 M/27 F, 30 +/- 6 yr, body fat 34 +/- 8% by dual-energy X-ray absorptiometry (means +/- SD)]. The average percentage of preadipocyte differentiation (PDIFF; cell count by microscopy) was 11 +/- 11% (range 0.2-51%). PDIFF correlated negatively with percent body fat (r = -0.35, P = 0.006) and waist circumference (r = -0.45, P = 0.0004). Multiple regression analysis indicated that waist circumference (P = 0.01), sex (P = 0.01), and percent body fat (P = 0.05) were significant determinants of PDIFF. Molecular characterization of predifferentiated cultured cells was performed by real-time PCR measurements of glucocorticoid receptor-alpha (GRalpha), insulin-like growth factor I receptor (IGF-IR), peroxisome proliferator-activated receptor-gamma (PPARgamma), enhancer-binding protein GATA-3, CCAAT/enhancer-binding protein-alpha undifferentiated protein (CUP/AP-2alpha), and endothelial cell-specific marker 2 (ECSM2). The mRNA concentrations of GRalpha correlated with PDIFF (r = 0.29, P = 0.03), but the others did not (IGF-IR, r = 0.003, P = 1.0; PPARgamma, r = -0.1, P = 0.5; GATA-3, r = 0.02, P = 0.9; CUP/AP-2alpha, r = -0.2, P = 0.1; ECSM2, r = 0.04, P = 0.7). Contrary to our hypothesis, the results may indicate a blunted in vitro differentiation potential of preadipocytes in centrally obese individuals. The lower differentiation potential of preadipocytes in the obese subjects might be due, at least partly, to decreased glucocorticoid receptor expression.