Training-Induced, Pressure-Lowering Effect in SHR

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Abstract
We showed that the training-induced, pressure-lowering effect correlates with decreased arteriole wall/lumen ratio and venule growth in the gracilis muscle. To investigate whether these beneficial changes are tissue-specific or occur in other muscles and tissues, we analyzed the effects of hypertension and training on microcirculatory profile of locomotor/nonlocomotor muscles and another nonmuscular tissue. Spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats were submitted to low-intensity training (50% to 60% maximal exercise capacity, 13 weeks); age-matched control rats were kept sedentary. Trained and sedentary rats were instrumented for pressure and heart rate measurements at rest. Morphometric analyses (arterioles, capillaries, venules) were performed in all tissues. Training attenuated pressure and heart rate only in SHR. Arterioles (inner diameter <30 μm) were markedly hypertrophied in sedentary SHR, but wall/lumen ratio was equally reduced (≈30%) and normalized by training in locomotor (soleus, gastrocnemius, gracilis) and nonlocomotor skeletal muscles (temporalis) in the myocardium and diaphragm, without changes in the renal cortex. Training also increased venule density (≈2-fold) only in locomotor and nonlocomotor muscles of SHR. Capillary density was similarly increased in all exercised muscles of both groups, with no change in temporalis and kidneys. Data suggest that growth/proliferation of small venules and regression of hypertrophied arteriole wall/lumen ratio are generalized tissue-specific (skeletal muscle) and group-specific (SHR) adjustments to training to reduce local resistance and augment physical capacity of circulation, thus contributing to training-induced pressure-lowering effect. They are accompanied by remodeling of myocardium (cardiac output) and diaphragm arterioles (ventilatory adjustments), stressing the importance of training as a nonpharmacological therapy to control pressure levels in hypertension.