Enhanced endothelium-dependent vasodilatation in human skin vasculature induced by physical conditioning

Functional alterations to the endothelial cells of the vascular system may contribute to the improved circulatory performance induced by physical cond itioning. We evaluated microvascular reactivity to iontophoretic applicatio n of acetylcholine (ACh) and sodium nitroprusside (SNP) through the skin an d blood perfusion measurements in the same area using laser Doppler flowmet ry. Whereas ACh acts on smooth muscle cells of the vascular system via the production of vasodilator substances from the endothelium, SNP is an endoth elium-independent vasodilator acting on vascular smooth muscle cells direct ly. The study was performed using two groups of subjects with different lev els of aerobic endurance, long distance runners competing at national level (n = 9) and controls (n = 9). The subjects were tested for 40 min on a tre admill before and after an exercise test at 80% of their maximal oxygen upt ake. During stimulation by ACh cutaneous perfusion increased to a higher le vel in the athletes than in the controls (overall P < 0.05), whereas an acu te period of exercise abolished this difference (overall P > 0.6). There wa s no significant difference between the athletes and the controls with resp ect to the SNP-induced increase in cutaneous perfusion either before (P > 0 .9) or after(P > 0.9) exercise. The higher cutaneous perfusion responses to stimulation with ACh in the athletes than in the controls may support the hypothesis that regular exercise modifies the responsiveness of the cutaneo us endothelium. The difference in ACh-induced perfusion and in unstimulated forearm perfusion between the two groups was present only at rest. This fi nding indicated that mechanisms were introduced during exercise, which comp ensated for the lower endothelial sensitivity to stimulation in the control s at rest.