Aging blunts the dynamics of vasodilation in isolated skeletal muscle resistance vessels

Abstract

Aging is associated with an altered ability to match oxygen delivery (QO2) to consumption ((.)VO2) in skeletal muscle and differences in the temporal profile of vasodilation may provide a mechanistic basis for the QO2-to-(.)VO2 mismatching during the rest-to-exercise transition. Therefore, we tested the hypothesis that the speed of vasodilation will be blunted in skeletal muscle first-order arterioles from old vs. young rats. Arterioles from the soleus and the red portion of the gastrocnemius (Gast(Red)) muscles were isolated from young (Y, 6 mo; n = 9) and old (O, 24 mo; n = 9) Fischer 344 rats and studied in vitro. Vessels were exposed to acetylcholine (ACh; 10(-6) M), sodium nitroprusside (SNP; 10(-4) M), and increased intraluminal flow, and the subsequent vasodilation was recorded at 30 frames/s. The data were fit to a monoexponential model and the dynamics of vasodilation [i.e., time delay, time constant (tau), and rate of change (delta/tau)] were calculated. With old age, the rate of vasodilation was significantly blunted in resistance vessels from the soleus to ACh (Y, 27.9 +/- 3.6; O, 8.8 +/- 2.6 microm/s) and flow (Y, 12.8 +/- 2.1; O, 3.1 +/- 0.9 microm/s). In the Gast(Red) the old age-associated impairment of endothelium-dependent vasodilator dynamics was even greater than that of the soleus. With SNP neither the magnitude nor time constant of vasodilation was affected by age in either muscle. The results indicate that aging impairs the dynamics of vasodilation in resistance vessels from the soleus and Gast(Red) muscles mediated, in part, through the endothelium. Thus the old age-associated slower rate and magnitude of vasodilation could inhibit the delivery of O2 during the critical transition from rest to exercise in moderate to highly oxidative skeletal muscle.

Fig. 1.

Vasodilator dynamics of arterioles from the soleus muscle of young and old rats to flow (A), ACh (B), and sodium nitroprusside (SNP; C). Exposure to a given condition began at time 0. Dashed lines represent the 95% confidence intervals. *P < 0.05.

Fig. 2.

Vasodilator dynamics of arterioles from the red portion of the gastrocnemius muscle (Gast_Red) of young and old rats to flow (A), ACh (B), and SNP (C). Exposure to a given condition began at time 0. Dashed lines represent the 95% confidence intervals. *P < 0.05.

Fig. 3.

Vasodilator dynamics of arterioles from the low oxidative white portion of the gastrocnemius muscle (Gast_White) of young and old rats to the endothelium-dependent vasodilator ACh. No age-related differences in the dynamics of vasodilation or the percent relaxation were observed.

Fig. 4.

Time course of vasodilation to endothelium-dependent stimuli increased intraluminal flow (A) and ACh (B) in arterioles from the soleus and Gast_Red of young and old rats. Data are plotted as a function of the delta (i.e., change in diameter between pre- and postintervention) to normalize the percent vasodilation between the means of the two groups.

Fig. 5.

Time course of vasodilation to endothelium-independent vasodilator SNP in arterioles from the soleus and Gast_Red of young and old rats. Data are plotted as a function of the delta (i.e., change in diameter between pre- and postintervention) to normalize the percent vasodilation between the means of the two groups.