β‐adrenoceptor‐stimulated lipolysis of subcutaneous abdominal adipocytes as a determinant of fat oxidation in obese men

BACKGROUND: To verify whether an impaired lipolytic capacity of subcutaneous adipocytes may contribute to low rate of fat oxidation. DESIGN: Relationships between adipose tissue lipolysis of subcutaneous (subc) abdominal and femoral isolated adipocytes and respiratory quotient (RQ) were investigated in 20 obese men (age: 44 +/- 5 years; means +/- SD) studied in a fasting state. RESULTS: Maximal isoproterenol-induced lipolysis was greater in subcutaneous abdominal than in femoral fat cells even if glycerol release was corrected for variation in cell surface area (P < 0.01). On the other hand, no regional variation was observed in the adipose cell lipolytic responses to postadrenoceptor agents such as dibutyryl-cyclic AMP, forskolin and theophylline. Maximal isoproterenol-induced lipolysis of subc abdominal, but not of femoral adipocytes, was inversely related to RQ (r = - 0.61; P < 0. 01) and positively associated to fat oxidation (r = 0.57; P < 0.01). These relationships were independent of possible confounding factors such as fat mass, fat-free mass, waist girth and subc abdominal adipose tissue accumulation assessed by computed tomography, as maximal isoproterenol-induced lipolysis of subcutaneous abdominal adipocytes was the only variable retained as a significant predictor of RQ levels (38% of variance) and of fat oxidation (30% of variance). CONCLUSION: These results suggest that adipose tissue lipolytic activity of subc abdominal adipocytes acts as a determinant of fat oxidation in obese men.