Effects of voluntary exercise on heart function in streptozotocin (STZ) - Induced diabetic rat

Exercise training improves cardiac performance and has been utilized as an effective adjunct to pharmacotherapy in the management of diabetes mellitus. The aims of this study were to characterize voluntary exercise habits in streptozotocin (STZ)-induced diabetic rats and investigate whether attained levels of voluntary, exercise induce effects on diabetic heart function. Diabetes was induced by a single intraperitoneal injection of STZ (60 mg/kg). Animals were divided into 4 groups: Control Sedentary (CS), Diabetic Sedentary (DS), Control Running (CR) and Diabetic Running (DR). DR and CR rats were provided with running wheels. Body weight and blood glucose were measured in running rats at the start and end of the 60-day exercise period. Ventricular action potentials were measured in spontaneously beating heart. Shortening and intracellular Ca²⁺ were measured in electrically stimulated ventricular myocytes. DR rats exercised less than CR rats. At 60 days the mean distance covered by DR rats was 1027 ± 289 m compared to 5975 + 1117 m in CR rats. CR gained whilst DR rats lost weight at the end of the exercise period. Mean blood glucose in CR and DR rats at the start of the exercise period was 71 ± 4 and 426 ± 21 mg/dl, respectively. Glucose levels were not altered in CR rats but were reduced in DR rats at the end of the exercise period. The time to peak shortening and peak Ca²⁺ transient and time to half relaxation of the Ca²⁺ transient were prolonged in myocytes from DS compared to CS rats and were not additionally altered by voluntary exercise. In conclusion, diabetic rats were less inclined to partake in voluntary exercise compared to controls and the levels and duration of exercise were insufficient to significantly alter cardiac performance in either control or diabetic rats.