Exercise training normalizes wall-to-lumen ratio of the gracilis muscle arterioles and reduces pressure in spontaneously hypertensive rats

Objective To investigate mechanisms underlying the training-induced blood p ressure-lowering effect we analyzed the hemodynamic responses and morphomet ric changes of the skeletal muscle microcirculation of spontaneously hypert ensive (SHR) and normotensive Wistar-Kyoto (WKY) rats during an exercise tr aining program. Design Training (50-60% VO2 max) was performed on a treadmill for 13 weeks and control groups were kept sedentary over the same period of time. Traine d and sedentary rats were chronically instrumented for hindlimb flow and ar terial pressure (AP) recordings under conscious unrestrained conditions. Gr acilis and myocardial muscle samples were obtained for morphometric analysi s after transcardiac perfusion of fixative. Results SHR, when compared to WKY presented an elevated blood pressure, an increased relative hindlimb vascular resistance, capillary rarefaction in b oth gracilis and myocardium and an increased wall-to-lumen ratio of gracili s arterioles. Training increased significantly both capillary density and c apillary/fiber ratio in the gracilis and myocardium of WKY and SHR groups, causing a complete reversal of capillary rarefaction in trained SHR, In SHR , training also reduced resting blood pressure and caused normalization of both relative hindlimb vascular resistance and gracilis arterioles wall-to- lumen ratio, Regression analysis revealed strong positive correlation betwe en hindlimb vascular resistance and mean AP (MAP) and between arterioles wa ll-to-lumen ratio and MAP. Conclusions The results suggest that low-intensity training can significant ly reduce pressure in SHR while normalizing both the arteriole morphology a nti the resistance of the skeletal muscle microcirculation. J Hypertens 18: 1563-1572 (C) 2000 Lippincott Williams & Wilkins.