Improved myocardial efficiency in the working perfused heart of the spontaneously hypertensive rat

We assessed the relationship between determinants of myocardial oxygen demand--wall stress, peak rate of change of pressure and heart rate--and measured myocardial oxygen consumption over a range of loading conditions in the perfused, working heart of 6-month-old spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY). Two isolated heart preparations, an aortic-ejecting heart and an isovolumically contracting preparation with and without isoproterenol (10(-7)M) added, were employed. Under a constant perfusion pressure of 110 mm Hg, the heart rate, developed wall stress, and peak rate of change of pressure were not different between the two groups, but coronary flow and myocardial oxygen consumption were significantly lower in the SHR. Systolic values of myocardial high energy phosphate compounds (adenosine 5'-triphosphate, phosphocreatine) and myocardial lactate in the two preparations were not significantly different between SHR and WKY. Following adenosine infusion at maximum developed pressure (isovolumic preparation), both SHR and WKY demonstrated preservation of coronary reserve. These results indicate that cardiac hypertrophy represents a compensatory adaptation with improved mechanical efficiency in the 6-month-old SHR when maximally stressed and may be related to the shift from V1 to V2 and V3 isomyosin phenotypes that was observed in the hypertensive animals.