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BASIC SCIENCE

Angiotensin receptor blockade improves myocardial beta-adrenergic receptor signaling in postinfarction left ventricular remodeling

A possible link between beta-adrenergic receptor kinase-1 and protein kinase C epsilon isoform

Toshiyuki Takahashi, MD^*, Toshihisa Anzai, MD^*,*, Tsutomu Yoshikawa, MD^*, Yuichiro Maekawa, MD^*, Keitaro Mahara, MD^*, Michikado Iwata, MD^*, H. Kirk Hammond, MD and Satoshi Ogawa, MD^*

^* Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine, Tokyo, Japan
Departments of Medicine, Veterans Affairs Medical Center of San Diego and University of California, San Diego, California, USA

Manuscript received February 13, 2003; revised manuscript received July 2, 2003, accepted July 31, 2003.

^* Reprint requests and correspondence: Dr. Toshihisa Anzai, Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
anzai{at}cpnet.med.keio.ac.jp

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.

Abbreviations and Acronyms   ARB = angiotensin II type 1 receptor blocker   AR = adrenergic receptor   ARK1 = adrenergic receptor kinase-1   cAMP = 3',5'-cyclic adenosine monophosphate   dP/dt = rate of rise in left ventricular pressure   GRK = G-protein–coupled receptor kinase   HF = heart failure   ICYP = (125I)-iodocyanopindolol   ISO = isoproterenol   LV = left ventricle/ventricular   MI = myocardial infarction   PKC = protein kinase C   Vcf = circumferential fiber shortening velocity

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