Intense exercise training induces adaptation in expression and responsiveness of cardiac β-adrenoceptors in diabetic rats

Background: Informations about the effects of intense exercise training on diabetes-induced myocardial dysfunctions are lacking. We have examined the effects of intense exercise training on the cardiac function of diabetic rats, especially focusing on the Langendorff beta-adrenergic responsiveness and on the beta-adrenoceptors protein expression. Methods: Control or Streptozotocin induced-diabetic male Wistar rats were randomly assigned to sedentary or trained groups. The training program consisted of 8 weeks running on a treadmill (10 degrees incline, up to 25 m/min, 60 min/day) and was considered to be intense for diabetic rats. Results: This intense exercise training amplified the in vivo diabetes-induced bradycardia. It had no effect on Langendorff basal cardiac contraction and relaxation performances in control and diabetic rats. In diabetic rats, it accentuated the Langendorff reduced responsiveness to beta-adrenergic stimulation. It did not blunt the diabetes-induced decrease of beta 1-adrenoceptors protein expression, displayed a significant decrease in the beta 2-adrenoceptors protein expression and normalized the beta 3-adrenoceptors protein expression. Conclusions: Intense exercise training accentuated the decrease in the myocardial responsiveness to beta-adrenergic stimulation induced by diabetes. This defect stems principally from the beta 2-adrenoceptors protein expression reduction. Thus, these results demonstrate that intense exercise training induces specific effects on the beta-adrenergic system in diabetes.