EXERCISE TRAINING INITIATED AFTER THE ONSET OF DIABETES PRESERVES MYOCARDIAL FUNCTION: EFFECTS ON EX
June 29th, 2008 | by admin |EXERCISE TRAINING INITIATED AFTER THE ONSET OF DIABETES PRESERVES MYOCARDIAL FUNCTION: EFFECTS ON EXPRESSION OF {beta}-ADRENOCEPTORS.
The present study was undertaken to assess cardiac function and characterize beta-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 three weeks 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. beta-adrenoceptors were assessed using Western blots and [(3)H]dihydroalprenolol binding. After seven weeks of diabetes, heart rate decreased by 21%, fractional shortening by 20%, ejection fraction by 9% and basal and isoproterenol induced dP/dt by 35%. beta1- and beta2-adrenoceptor proteins were reduced by 60% and 40%, while beta3-adrenoceptor protein increased by 125%. Ventricular homogenates from diabetic rats bound 52% less [(3)H]dihydroalprenolol, consistent with reductions in beta1- and beta2-adrenoceptors. Three weeks of ExT initiated four weeks after the onset of diabetes minimized cardiac function loss. ExT also blunted loss of beta1-adrenoceptor expression. Interestingly, ExT did not prevent diabetes-induced reduction in beta2-adrenoceptor or the increased of beta3-adrenoceptor expression. ExT also increased [(3)H]dihydroalprenolol binding, consistent with increased beta1-adrenoceptor expression. These findings demonstrate for the first time that ExT initiated after the onset of diabetes blunts primarily beta1-adrenoceptor expression loss, providing mechanistic insights for exercise-induced improvements in cardiac function. Key words: diabetes, rats, heart, -adrenoceptors, exercise training.
Bidasee KR, Zheng H, Shao CH, Parbhu SK, Rozanski GJ, Patel KP.
Department of Pharmacology, DRC Rm 3047, University of Nebraska, Omaha, Nebraska, United States; , United States.