Suppression of whole body and regional lipolysis by insulin: Effects of obesity and exercise

The aim of this study was to evaluate in premenopausal women (six endurance -trained nonobese, six sedentary nonobese, and five sedentary obese) the su ppression of whole body and regional lipolysis by insulin. Lipolysis was de termined using H-2(5)-glycerol infusion and microdialysis of sc adipose tis sue (AT) during a two-stage [6-10 (low; LO) and 12-20 (moderate; MOD) mU/m. min] hyperinsulinemic-euglycemic clamp. Microdialysis probes were positione d in abdominal and femoral sc AT to monitor interstitial glycerol and nutri tive blood flow. Basal plasma glycerol was 102 +/- 9, 52 +/- 6, and 143 +/- 30 mu mol/L in endurance-trained nonobese, sedentary nonobese, and sedenta ry obese, respectively (P < 0.05, sedentary nonobese < endurance-trained no nobese, sedentary obese). The plasma glycerol concentration was decreased ( P < 0.05) to a greater extent in endurance-trained nonobese and sedentary n onobese [both to similar to 50% (LO) and similar to 45% (MOD) of basal] tha n in sedentary obese [to 72% (LO) and 63% (MOD) of basal]. The rate of appe arance of glycerol was suppressed to 36 +/- 7%, 44 +/- 10%, and 62 +/- 7% o f basal during LO in endurance-trained nonobese, sedentary nonobese, and se dentary obese, respectively (P < 0.05, endurance-trained nonobese < sedenta ry obese), and to 34 +/- 3%, 36 +/- 5%, and 53 +/- 8% of basal during MOD, respectively (P < 0.05, endurance-trained nonobese < sedentary obese). Ther e were no between-group differences in the suppression of lipolysis in abdo minal sc AT, as evidenced by similar reductions in dialysate glycerol level s [all to similar to 65% (LO) and similar to 55% (MOD) of basal]. Femoral d ialysate glycerol was reduced (P < 0.05) more in sedentary nonobese and end urance-trained nonobese (to similar to 75% of basal) than in sedentary obes e (to 90% of basal) during LO, but to a similar extent (to similar to 60% o f basal) in all groups during MOD. The results indicate that the sedentary obese women had whole body resistance to the suppression of lipolysis by in sulin. Intraabdominal AT may be the site of resistance, as resistance was n ot evident in abdominal or femoral sc AT.