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

Abstract

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 β-adrenergic responsiveness and on the β-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° 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 β-adrenergic stimulation. It did not blunt the diabetes-induced decrease of β1-adrenoceptors protein expression, displayed a significant decrease in the β2-adrenoceptors protein expression and normalized the β3-adrenoceptors protein expression.

Conclusions: Intense exercise training accentuated the decrease in the myocardial responsiveness to β-adrenergic stimulation induced by diabetes. This defect stems principally from the β2-adrenoceptors protein expression reduction. Thus, these results demonstrate that intense exercise training induces specific effects on the β-adrenergic system in diabetes.

Figure 1

Effect of intense exercise training on myocardial basal function and responsiveness to isoproterenol stimulation. Isoproterenol was infused to isolated hearts of sedentary control (n = 13), trained control (n = 7), sedentary diabetic (n = 11) and trained diabetic (n = 7) rats in ascending concentrations ranging from 1.10^-8 to 1.10^-5 M. In trained control rats, 1.10^-6 and 1.10^-5 M isoproterenol doses were not tested for technical reason. Data are presented as mean ± SEM. *= significantly different from sedentary controls (p <0.05), † = significantly different from trained controls (p <0.05), ‡ = significantly different from sedentary diabetics (p <0.05).

Figure 2

Effect of intense exercise training on β-adrenoceptors expression. Representative Western blots show steady state levels of β1-, β2- and β3-adrenoceptors in left ventricular muscles from sedentary control (n = 8), trained control (n = 8), sedentary diabetic (n = 7) and trained diabetic (n = 9) rat hearts. Data are presented as mean ± SEM. *= significantly different from sedentary controls (p <0.05), ‡ = significantly different from sedentary diabetics (p <0.05).