|ISSN No. 1606-7754 Vol.15 No.2 August 2007|
Effects of voluntary exercise on heart function in streptozotocin (STZ) – induced diabetic rat
FC Howarth, S Al-Ali, S Al-Sheryani, H Al-Dhaheri, S Al-Junaibi S, FA Almugaddum, MA Qureshi, M Ljubisavijevic
Department of Physiology, Faculty of Medicine & Health Sciences, United Arab Emirates University, Al Ain, UAE
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. (Int J Diabetes Metab 15: 32-37, 2007).
Key words: Diabetes mellitus, streptozotocin, voluntary exercise, heart muscle, ventricular myocytes
It has been frequently demonstrated that chronic, dynamic exercise has beneficial effects on several structural and functional properties of both healthy and diabetic heart muscle. Hallmark adaptations include a training induced resting bradycardia, an increase in end-diastolic dimension and in maximal stroke volume and general improvement in ventricular performance and in contractile function. Exercise training has long since been utilized as an effective adjunct to pharmacotherapy in the management of diabetes mellitus and physical activity influences several aspects of diabetes mellitus including blood glucose metabolism, insulin action and cardiovascular risk factors.1,2 Previous studies have demonstrated the beneficial effects of exercise on cardiac performance in diabetes mellitus. For example exercise training has been shown to reverse bradycardia and hypotension in diabetic rats.3 Training also prevents the decreased end-diastolic volume and attenuates increased end-systolic volume that accompanies sedentary diabetes.1 Reductions in left ventricular end-diastolic chamber and myocardial wall compliance, due to diabetes-induced changes in collagen, are also improved with exercise training.4 Most of the studies carried out to date have utilised enforced exercise regimes. 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.