Coronary vasodilator reserve, capillarity, and mitochondria in trained hypertensive rats

To test the hypothesis that exercise training can reverse the decrements in coronary reserve, capillary density, and mitochondrial volume density evident during established hypertension, we trained spontaneously hypertensive (SHR) and normotensive (WKY) rats on a treadmill over a 3-mo period. At 7 mo of age we used microspheres to evaluate myocardial perfusion in conscious rats. Exercise training did not alter hypertension or left ventricular hypertrophy but did increase maximal O2 consumption in both SHR and WKY. A decrement in left and right ventricular coronary reserve in SHR, compared with WKY, was indicated by 1) a smaller increment in myocardial perfusion during maximal vasodilation with dipyridamole and 2) a higher minimal coronary vascular resistance per unit mass. Exercise training had no significant effect on any index of myocardial perfusion in SHR or WKY. A 12% decrement in capillary numerical density in the endomyocardium of SHR was not reversed by exercise training. We estimated the volume densities of mitochondria, myofibrils, and sarcoplasm using electron microscopy and point-counting stereology on perfusion-fixed hearts. None of the parameters in either SHR or WKY was changed by exercise training. It is concluded that exercise training does not reverse the decrements in coronary reserve and capillary numerical density associated with hypertension in adult rats. Moreover the previously observed enhancement of mitochondrial volume density due to exercise in young hypertensive rats was not observed in adult SHR.