Relevance of Blockade of Cardiac and Circulatory Angiotensin-Converting Enzyme for the Prevention of Volume Overload–Induced Cardiac Hypertrophy

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Abstract
Background Angiotensin-converting enzyme (ACE) inhibitors show major differences in their affinity for cardiac and other tissue ACEs, and their effects on tissue ACE range from minimal to nearly complete blockade. Angiotensin II taken up from the circulation or generated in the heart may mediate the cardiac hypertrophic response to increased cardiac load. Thus, differences between the ACE inhibitors regarding their effects on cardiac ACE may determine their effects on prevention or regression of cardiac hypertrophy. Methods and Results In the present study, we assessed the effects of ACE inhibitors with low (enalapril) and high (quinapril) affinity for cardiac tissue ACE on prevention of volume overload–induced cardiac hypertrophy in relation to their hemodynamic effects. Both blockers were equipotent for circulatory ACE as assessed from the pressure response curve to angiotensin I. Both blockers partially (and similarly) prevented the increase in left ventricular end-diastolic pressure by aortocaval shunt. However, only quinapril prevented or attenuated the development of right ventricular hypertrophy and left ventricular hypertrophy and dilation. Conclusions The present findings further stress the involvement of the renin-angiotensin system as a trophic stimulus in the development of cardiac hypertrophy in this model. Moreover, the low affinity of enalapril for cardiac ACE appears to lead to continuous angiotensin II generation in the heart and can thus explain the failure of enalapril to attenuate hypertrophic response of the heart induced by shunt despite decreasing cardiac volume overload.

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