Exercise training initiated after the onset of diabetes preserves myocardial function: effects on expression of  -adrenoceptors (original) (raw)

2008, Journal of Applied Physiology

The present study was undertaken to assess cardiac function and characterize ␤-adrenoceptor subtypes in hearts of diabetic rats that underwent exercise training (ExT) after the onset of diabetes. Type 1 diabetes was induced in male Sprague-Dawley rats using streptozotocin. Four weeks after induction, rats were randomly divided into two groups. One group was exercised trained for 3 wk while the other group remained sedentary. At the end of the protocol, cardiac parameters were assessed using M-mode echocardiography. A Millar catheter was also used to assess left ventricular hemodynamics with and without isoproterenol stimulation. ␤-Adrenoceptors were assessed using Western blots and [ 3 H]dihydroalprenolol binding. After 7 wk of diabetes, heart rate decreased by 21%, fractional shortening by 20%, ejection fraction by 9%, and basal and isoproterenol-induced dP/dt by 35%. ␤1and ␤2-adrenoceptor proteins were reduced by 60% and 40%, respectively, while ␤ 3-adrenoceptor protein increased by 125%. Ventricular homogenates from diabetic rats bound 52% less [ 3 H]dihydroalprenolol, consistent with reductions in ␤ 1-and ␤2-adrenoceptors. Three weeks of ExT initiated 4 wk after the onset of diabetes minimized cardiac function loss. ExT also blunted loss of ␤1-adrenoceptor expression. Interestingly, ExT did not prevent diabetes-induced reduction in ␤2-adrenoceptor or the increase of ␤3-adrenoceptor expression. ExT also increased [ 3 H]dihydroalprenolol binding, consistent with increased ␤ 1-adrenoceptor expression. These findings demonstrate for the first time that ExT initiated after the onset of diabetes blunts primarily ␤1-adrenoceptor expression loss, providing mechanistic insights for exercise-induced improvements in cardiac function.