Cardiac conditioning ameliorates cardiac dysfunction associated with renal hypertension in rats

To explore the effect of physiologic hypertrophy superimposed on pathologic hypertrophy, hearts from female control rats (C), renal hypertensive rats (H), rats conditioned with a 10-12 wk swimming program (Sw), and hypertensive rats trained by the swimming program (H-Sw) were perfused in an isolated working rat-heart apparatus. Systolic blood pressure was approximately 100 mmHg in C and Sw and was 160 mmHg in H and H-Sw. The swimming program had no effect on blood pressure. Compared with C, heart weight was increased by 30% in Sw, 47% in H, and 77% in H-Sw. At high preload and afterload, cardiac output (milliliters per gram dry LV weight) was decreased in H, increased in Sw, and partially restored towards normal in H-Sw. Ejection fraction, percent fractional shortening, and mean velocity of circumferential fiber shortening were enhanced in Sw, depressed in H, and normalized in H-Sw when compared with C. Coronary flow and myocardial oxygen consumption in this series of hearts were depressed in H, with no restoration in H-Sw, but coronary effluent lactate/pyruvate ratios were only elevated in the hearts of H-Sw. Coronary vascular responses were examined in a second series of experiments which used microspheres. In this series, the depressed coronary flow observed in H was partially restored towards normal in H-Sw and the inner/outer myocardial flow ratio was normal when hearts were perfused at 140 cm aortic pressure but was somewhat depressed in both H and H-Sw when the hearts were perfused at 80 cm aortic pressure. These studies demonstrate that hypertrophic hearts from renal hypertensive rats have diminished coronary flow and depressed cardiac function when they are studied in the isolated working heart apparatus, yet there is no evidence of myocardial ischemia. Superimposition of a chronic swimming program results in increased hypertrophy but restoration of cardiac function partially or completely to normal. Thus, pathologic and physiologic hypertrophy are biologically distinct entities. Physiologic hypertrophy may partially ameliorate the defects associated with pathologic hypertrophy.