DIFFERENT ALTERATIONS IN THE INSULIN-STIMULATED GLUCOSE-UPTAKE IN THEATHLETES HEART AND SKELETAL-MUSCLE

Physical training increases skeletal muscle insulin sensitivity. Since training also causes functional and structural changes in the myocard ium, we compared glucose uptake rates in the heart and skeletal muscle s of trained and untrained individuals. Seven male endurance athletes (VO(2)max 72+/-2 ml/kg/min) and seven sedentary subjects matched for c haracteristics other than VO(2)max (43 +/- 2 ml/kg/min) were studied. Whole body glucose uptake was determined with a 2-h euglycemic hyperin sulinemic clamp, and regional glucose uptake in femoral and arm muscle s, and myocardium using F-18-fluoro-2-deoxy-D-glucose and positron emi ssion tomography. Glucose uptake in the athletes was increased by 68% in whole body (P < 0.0001), by 99% in the femoral muscles (P < 0.01), and by 62% in arm muscles (P = 0.06), but it was decreased by 33% in t he heart muscle (P < 0.05) as compared with the sedentary subjects. Th e total glucose uptake rate in the heart was similar in the athletes a nd control subjects. Left ventricular mass in the athletes was 79% gre ater (P < 0.001) and the meridional wall stress smaller (P < 0.001) as estimated by echocardiography. VO(2)max correlated directly with left ventricular mass (r = 0.87, P < 0.001) and inversely with left ventri cular wall stress (r = -0.86, P < 0.001). Myocardial glucose uptake co rrelated directly with the rate-pressure product (r = 0.75, P < 0.02) and inversely with left ventricular mass (r = -0.60, P < 0.05) or with the whole body glucose disposal (r = -0.68, P < 0.01). Thus, in athle tes, (a) insulin-stimulated glucose uptake is enhanced in the whole bo dy and skeletal muscles, (b) whereas myocardial glucose uptake per mus cle mass is reduced possibly due to decreased wall stress and energy r equirements or the use of alternative fuels, or both.