P-31 MAGNETIC-RESONANCE SPECTROSCOPY OF PRESSURE OVERLOAD HYPERTROPHY IN RATS - EFFECT OF REDUCED PERFUSION-PRESSURE

Study objective - The purpose of the study was to confirm the presence of abnormalities in the coronary vessels of hypertensive hearts, and to examine the effects of reduced coronary perfusion pressure.Design - Rats were made hypertensive by aortic banding, after which coronary flow and myocardial energy metabolites were studied in isolated hearts at physiological (140 cm H2O) and reduced (80 cm H2O) coronary perfusion pressures and compared with normotensive controls.Subjects - Wistar-Kyoto rats between 250 and 300 g were used. Left ventricular hypertrophy was generated by aortic banding in 29 rats; 8 were studied one week after banding, and 21 three weeks after banding. There were 45 controls.Measurements and results - Energy metabolites were assessed using 31P magnetic resonance spectroscopy, standardised by high performance liquid chromatography of rapidly freeze clamped tissue. Left ventricular wall thickness was determined using two dimensional echocardiography. Coronary flow (normalised for heart weight) was reduced significantly after one and three weeks of left ventricular hypertrophy, and at either physiological or below physiological pressures. Hearts from aortic banded animals developed higher intraventricular pressure with reduced oxygen consumption when perfused at a physiological pressure, indicating increased thermodynamic efficiency. When perfused at reduced pressure, the developed pressure declined significantly in both the one week and the three week banded groups compared to normal hearts. The phosphorylation potential and intracellular pH (pHi) were not significantly lower after one week and three weeks of left ventricular hypertrophy when perfused at physiological pressure. When perfused at reduced pressure, phosphorylation potential declined significantly in both groups of hypertrophied hearts, whereas pH, declined significantly only in the three week hypertrophy group.Conclusions - There is improved thermodynamic efficiency of the hypertrophied myocardium when perfused at a physiological pressure, but when perfused at a reduced pressure, ventricular function, phosphorylation potential and pHi decline in rat hearts after three weeks of aortic constriction, indicating an impairment of coronary reserve.