Reduced amount and disrupted temporal pattern of spontaneous exercise in diabetic rats.

Introduction/purpose: The beneficial effects of exercise for subjects with diabetes or prediabetic states are well established. However, the converse, that is, the effect of diabetes on spontaneous exercise performance, is not as well defined. Mice with mdx muscular dystrophy not only reduce total spontaneous running distance, but also decrease the duration of periods during which they are active, suggesting a defect in endurance. Studies tested the hypothesis that Type I diabetes causes similar changes in spontaneous exercise performance.

Methods: Wistar rats received streptozotocin to produce a model of Type I diabetes or buffer alone, and had access to running wheels for the next 8 wk.

Results: Diabetic rats had elevated serum glucose levels (689 +/- 85 vs 270 +/- 21 mg x dL(-1), P = 0.0003) but normal serum bicarbonate levels. After 8 wk, diabetic rats were running for considerably lower distances than normal animals (daily distance 182 +/- 58 vs 4981 +/- 1373 m, P = 0.006). Furthermore, the average consecutive running time was much shorter in diabetic than normal rats (16 +/- 1 vs 40 +/- 6 min, P = 0.004). Differences in running behavior between diabetic and normal mice were absent early after injection of streptozotocin, but were fully established by week 4 for both total distance and consecutive running times.

Conclusion: Severe untreated Type I diabetes in rats reduces spontaneous exercise in a manner similar to that seen in mdx mouse muscular dystrophy, with reduced running distance and consecutive running times.