SELECTIVE AND TIME-RELATED ACTIVATION OF THE CARDIAC RENIN-ANGIOTENSIN SYSTEM AFTER EXPERIMENTAL HEART-FAILURE - RELATION TO VENTRICULAR-FUNCTION AND MORPHOLOGY

Objective: The cardiac renin-angiotensin system is activated in experimental heart failure, but it is unknown at what stage of heart failure it becomes activated, and whether activation is related to ventricular dysfunction and dilatation. Changes in activity of cardiac, renal, and plasma angiotensin converting enzyme (ACE) were therefore examined at different stages of experimental heart failure, with simultaneous measurements of left ventricular pressure, systolic dP/dt, and inner ventricular radius. Methods: Heart failure was induced by experimental infarction in 17 normotensive male Wistar rats; 14 rats were sham operated. Rats were killed 3, 5, or 80 d after infarction. In an isolated heart perfusion, left ventricular pressure and systolic dP/dT were measured. ACE activity was determined in samples of the left and right cardiac ventricle, kidney, and plasma. Radius of the ventricular cavity was planimetrically determined in transverse sections of the left ventricle. Results: At the different stages both left ventricular pressure and systolic dP/dT progressively decreased and inner radius of the left ventricle increased in all heart failure groups. ACE activity in the left ventricle increased significantly in all heart failure groups and correlated inversely with left ventricular pressure (R=-0.81; p<0.001) and dP/dt (R=-0.85; p<0.001). ACE activity in the kidney was only increased 80 d after the induction of heart failure [17(SEM 1) v 11.2(0.5) nM His-Leu generated per min.mg-1, p<0.01], while plasma ACE activity was not increased in any heart failure group. Conclusions: Cardiac ACE is activated in the early stage after induction of heart failure and is related to the amount of dysfunction. ACE in the kidney is activated only in the chronic stage. The cardiac renin-angiotensin system therefore already appears to be an important neurohumoral adjustment in the early stage of heart failure and is thereby a suitable target for early intervention by ACE inhibitors.