Effects of ageing and exercise training on endothelium-dependent vasodilatation and structure of rat skeletal muscle arterioles

Abstract

Ageing reduces endothelium-dependent vasodilatation in humans and animals, and in humans, exercise training reverses the ageing-associated reduction in endothelium-dependent vasodilatation. The purpose of this study was to determine the mechanism(s) by which 10-12 weeks of treadmill exercise enhances endothelium-dependent vasodilatation in muscles of differing fibre composition from young and old rats. Three- and 22-month-old male Fischer 344 rats were assigned to young sedentary, young exercise-trained, old sedentary, or old exercise-trained groups. Arterioles were isolated from the soleus and gastrocnemius muscles; luminal diameter changes were determined in response to the endothelium-dependent vasodilator acetylcholine (ACh, 10(-9)-10(-4) mol l(-1)) alone and in the presence of the nitric oxide synthase (NOS) inhibitor l-NAME (10(-5) mol l(-1)) or the combination of l-NAME and the cyclooxygenase inhibitor indomethacin (10(-5) mol l(-1)). Training ameliorated the ageing-induced reduction in endothelium-dependent vasodilatation in soleus muscle arterioles. Treatment with l-NAME alone and in combination with indomethacin abolished differences in ACh vasodilatation occurring with ageing and training. Expression of endothelial NOS (eNOS) mRNA in soleus arterioles was unaltered by ageing, whereas eNOS protein was increased with age; training elevated both eNOS mRNA and protein. In gastrocnemius muscle arterioles, ageing did not alter maximal vasodilatation, but ageing and training increased maximal arteriolar diameter. These results demonstrate that ageing-induced reductions and training-induced enhancement of endothelial vasodilatation both occur through the nitric oxide signalling mechanism in highly oxidative skeletal muscle, but ageing and training do not appear to act on the same portion of the signalling cascade.

Figure 1. Maximal diameter of arterioles from the soleus (young SED, n = 22; old SED, n = 23; young ET, n = 20; old ET, n = 25) and gastrocnemius (young SED, n = 23; old SED, n = 31; young ET, n = 25; old ET, n = 26) muscles

Values are means ±s.e.m.*Indicates significant difference from young SED group (P = 0.05). †Indicates significant difference from old SED group (P = 0.05). All soleus muscle arteriolar maximal diameters are significantly less than that of gastrocnemius muscle arterioles (P = 0.05).

Figure 2. Concentration–response relation of soleus muscle arterioles from young and old, SED and ET rats to acetylcholine (ACh)

A, age significantly reduced vasodilator responses to ACh in soleus muscle arterioles. Exercise training restored vasodilator responses to ACh in soleus muscle arterioles from old rats and enhanced vasodilator responses to ACh in soleus muscle arterioles from young rats. B, l-NAME inhibited the vasodilator response to ACh in arterioles from all groups, and abolished the ageing and training-induced differences in ACh vasodilatation. C, combination of l-NAME and indomethacin inhibited the vasodilator response to ACh in arterioles from all groups, and eliminated the ageing and training-induced differences in ACh vasodilatation. Values are means ±s.e.m.*Indicates young significantly different from old (P = 0.05). #Indicates ET rats significantly different from respective SED rats (P = 0.05).

Figure 3. Concentration–response relation of gastrocnemius muscle arterioles from young and old SED and ET rats to acetylcholine (ACh)

A, vasodilator responses to ACh in gastrocnemius muscles were not affected by age. Exercise training enhanced vasodilatation to ACh in gastrocnemius muscle arterioles from young rats but not old rats. B, l-NAME did not inhibit maximal vasodilator responsiveness to ACh in any group, but reduced sensitivity (IC₅₀) to ACh in the old SED rats and in the young and old ET rats. C, combination of l-NAME and indomethacin reduced maximal vasodilatation to ACh in young ET rats, while sensitivity (IC₅₀) to ACh was reduced in all groups. Values are means ±s.e.m.#Indicates young ET significantly different from young SED (P = 0.05).

Figure 4. eNOS mRNA (A) and protein (B) expression in soleus muscle 1A arterioles of young and old, SED and ET rats

Values are means ±s.e.m.*Indicates significant difference from young SED group (P = 0.05). †Indicates significant difference from old SED group (P = 0.05).

Figure 5. eNOS mRNA (A) and protein (B) expression in 1A arterioles from gastrocnemius muscle of young and old, SED and ET rats

Values are means ±s.e.m.*Indicates significant difference from young SED group (P = 0.05). †Indicates significant difference from old SED group (P = 0.05).

Figure 6

Sample immunoblot showing eNOS and GAPDH proteins from cultured coronary venular endothelial cells (CVEC, an internal control sample) and soleus muscle arterioles of young sedentary (YS), old sedentary (OS), young exercise trained (YET), and old exercise trained (OET) rats