LIPID AND CARBOHYDRATE-METABOLISM IN IDDM DURING MODERATE AND INTENSEEXERCISE

Insulin-dependent-diabetes mellitus (IDDM) is characterized by a metab olic and hormonal disarray that may be more evident during exercise. H owever, the metabolic response to exercise of different intensities ha s not been evaluated in IDDM. We therefore used stable isotope techniq ues and indirect calorimetry to quantify substrate kinetics and oxidat ion during 30 min of exercise at 45 and 75% of maximal oxygen uptake ( Vo(2max)) in seven men with IDDM (D group) infused with insulin at a c onstant basal rate. Normal control subjects (C group) matched for age, weight, and Vo(2max), were also studied. During moderate exercise, gl ucose uptake (R(d)) was lower in the D than in the C group (15.3 +/- 1 .0 vs. 20.8 +/- 1.6 mu mol . min(-1). kg(-1); P < 0.05). Carbohydrate oxidation also tended to be lower in the D group (71.0 +/- 7.2 vs. 87. 5 +/- 10.6 mu mol . min(-1). kg(-1); P = 0.08). The D group relied on fat oxidation to a greater extent than did the C group (16.9 +/- 1.1 v s. 10.4 +/- 1.6 mu mol . min(-1). kg(-1) P < 0.05). The enhanced fat o xidation was not due tb increased lipolysis because no differences occ urred in glycerol release (R(a)) or in plasma free fatty acid R(a) or concentration, and the source of the extra lipid appeared to be intram uscular fat stores. These differences in substrate metabolism were not evident during exercise at 75% of Vo(2max). The lower glucose uptake and oxidation in the diabetic subjects during moderate, but not intens e, exercise suggest that glucose metabolism is regulated differently d epending on exercise intensity. During moderate exercise, glucose upta ke into muscle seems to be limiting, and the higher intramuscular trig lyceride oxidation observed in IDDM might be a compensatory adaptation needed to maintain energy supply.