Effects of Angiotensin II Type 1 Receptor Blockade and Angiotensin-Converting Enzyme Inhibition on Cardiac β-Adrenergic Signal Transduction

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Abstract
Abstract —Inhibition of the renin-angiotensin system has been shown to improve symptoms and prognosis in heart failure. We compared the effects of inhibition of angiotensin-converting enzyme or blockade of angiotensin II type 1 (AT 1 ) receptors in a model with renin-induced hypertension that is known to exhibit similar changes in sympathetic activation and β-adrenergic desensitization, as observed in heart failure. Treatment with captopril (100 mg/kg of feed) or the AT 1 -antagonist Bay 10–6734 (100 mg/kg of feed) was performed in transgenic rats harboring the mouse renin 2 d gene [TG(m REN 2)27]. Neuropeptide Y and angiotensin II levels, adenylyl cyclase activity, β-adrenergic receptors, G sα , and G iα were investigated. TG(m REN 2)27 showed a depletion of myocardial neuropeptide Y stores and an increase in myocardial angiotensin II concentrations. Isoprenaline- and guanylylimidodiphosphate-stimulated adenylyl cyclase activities and β-adrenergic receptor density were reduced, whereas the catalyst and G sα -function were unchanged. G iα protein and mRNA concentrations were increased. All alterations were normalized by both treatments. Systolic left ventricular pressures, plasma atrial natriuretic peptide, and myocardial steady state atrial natriuretic peptide mRNA concentrations and heart weights were similarly reduced by both treatments. Sympathetic neuroeffector defects are similarly reversed by angiotensin-converting enzyme inhibition or AT 1 antagonism. The data support the concept that pharmacological interventions in the myocardial renin-angiotensin system significantly reverse local sympathetic neuroeffector defects. This could be important for the beneficial effects of these agents.