Objectives: We tested the hypothesis that angiotensin II type 1 receptor blocker (ARB) may improve beta-adrenergic receptor (AR) coupling in heart failure (HF) after myocardial infarction (MI).
Background: Beta-AR desensitization is one of the mechanisms underlying the transition from compensated to decompensated HF. Beta-adrenergic receptor kinase-1 (ARK1), which can be induced by protein kinase C (PKC) in vitro, is activated in the failing myocardium, resulting in beta-AR uncoupling.
Methods: Models of MI in rats were produced by ligation of left coronary artery. Four weeks after surgery, they were randomized to vehicle (MI/control [C]) or candesartan (10 mg/kg/day) treatment (MI/ARB). Sham-operated rats, or shams, served as controls.
Results: After two weeks of treatment, echocardiography and hemodynamics showed that the left ventricular (LV) dimension increased and that the percent of fractional shortening and maximum rate of rise in left ventricular pressure (dP/dt) decreased in MI rats compared with shams. There were no differences in these indexes between MI/C and MI/ARB. An increase in maximum dP/dt under isoproterenol (ISO) stimulation was attenuated in MI/C but improved in MI/ARB. Reductions in the percentage of high-affinity sites of beta-AR and ISO-stimulated cyclic adenosine monophosphate production in noninfarcted myocardium were also improved by ARB treatment. Up-regulation of beta-ARK1 and PKC-epsilon isoform protein levels and activation of PKC in noninfarcted myocardium from MI/C were both inhibited by ARB treatment.
Conclusions: Treatment with ARB during the chronic phase of MI improved beta-AR coupling in noninfarcted myocardium without affecting basal LV function. Cross-talk between beta-AR and angiotensin signaling through beta-ARK1 and PKC-epsilon may be responsible for the phenomenon.