Magnetic Resonance Spectroscopy

Abstract

During hyperinsulinemia, exercise strongly stimulates glycogen synthesis in skeletal muscle of healthy subjects. However, little is known about the additional effect of exercise in obesity upon insulin stimulated glucose uptake. Ten obese subjects underwent a euglycemic hyperinsulinemic clamp for 150 min, with simultaneous measurement of glycogen in skeletal muscle. A short exercise increased the rate of glycogen synthesis rate ~165% compared to ~317% in healthy subjects. Blood flow had no relation with these increases. The glycogen synthesis rate after exercise under hyperinsulinemic condition is reduced in obesity, independent of age. These results indicate that in humans, insulin and exercise mediated glucose uptake are interrelated. synthesis rate was 0.22 ± 0.05 A.U./min in old obese subjects and 0.30 ± 0.05 A.U./min. (significantly higher, p<0.05) in young obese subjects. Exercise increased the rate of glycogen synthesis substantially to 0.35 ± 0.05 in the old obese group (p<0.05) and to 0.53 ± 0.02 A.U./ min (p<0.05) in the young obese group, both an increase of ~165%, compared to 317% in young healthy subjects (figure 1). A strong correlation (r = 0.77; p= 0.0006) was found between the whole body glucose uptake or M- value of all subjects and the increase in glycogen synthesis due to exercise (figure 2). After exercise, calf blood flow in the exercised leg of three old obese increased from 2.21 ± 1.08 to 12.43 ± 4.34 (p< 0.001) mL/dL/min, but blood flow returned to 2.6 ± 0.70 within 30 minutes and further decreased afterwards, while the increase in glycogen synthesis was stable and still ongoing. Discussion: These results indicate that in humans, a short bout of exercise has an acute effect on the glycogen synthesis rate under hyperinsulinemic conditions. The glycogen synthesis rate after exercise under hyperinsulinemic condition is reduced in obesity, independent of age. Although exercise was a strong stimuli for vasodilatation, the lack of a temporal relationship between the increase and subsequent decrease in blood flow and the linear increase in glycogen synthesis rate argue against a direct causal effect. The similarity of the reduced effects of exercise in obesitas, suggests that the insulin and exercise mediated glucose uptake share a common pathway. Since in healthy humans glucose transport is the rate limiting step in glycogen synthesis, the reduced glucose uptake enhancing effect of exercise under hyperinsulinemia in obesity suggests an reduced additional translocation of GLUT4 to the cell membrane in obesitas.