Arteriolar reactivity and capillarization in chronically stimulated rat limb skeletal muscle post-MI

The purpose of this study was to assess whether electrical stimulation-indu ced increases in muscular activity could improve capillary supply and corre ct previously documented abnormal vasodilator and vasoconstrictor responses of arterioles in limb skeletal muscle post-myocardial infarction (MI). Ext ensor digitorum longus (EDL) muscle from rats with surgically induced MI (s imilar to 30% of the left ventricle) was chronically stimulated (Stim) 8 h/ day for 6 +/- 1 days, at 11 wk post-MI. Third- (3A) and fourth-order (4A) a rterioles in EDL from nine MI rats and four MI + Stim rats were compared wi th those of 11 controls (Con). Compared with Con rats, MI alone caused a re duction in the resting diameter of 3A and 4A arterioles, which was complete ly reversed by MI + Stim. However, Stim did not correct the attenuated vaso dilator response to 10(-4) M adenosine seen in 4A arterioles from MI rats c ompared with Con. The constrictor response of both 3A and 4A vessels in MI rats to low doses of acetylcholine (10(-9) M, 10(-8) M) and norepinephrine (10(-9) M) was accentuated in MI + Stim. The proportion of oxidative fibers in EDL was unaffected by MI or MI + Stim combination. However, Stim signif icantly increased (P < 0.05) the capillary-to-fiber ratio in this muscle co mpared with Con. Thus, although the increase in muscle activity induced by chronic electrical stimulation normalized the reduction in resting vessel d iameter seen after MI, it failed to correct the abnormalities in vasoreacti vity of these same vessels.