Ryosai Nakamura

Adrenomedullin Administration Immediately After Myocardial Infarction Ameliorates Progression of Heart Failure in Rats

Background—Adrenomedullin (AM) is expressed in cardiac tissue, and plasma AM levels increase in patients with acute myocardial infarction (MI). This study was performed to determine whether AM administration immediately after acute MI inhibits progression of heart failure in rats. Methods and Results—Rats were infused with 1.0 &mgr;g/h IP AM or saline over 7 days immediately after MI inducted by left coronary ligation and were examined 9 weeks after MI. Compared with the saline infusion, AM infusion significantly improved survival (59% versus 81%; P<0.05) and body weight gain (32%; P<0.01) and reduced heart weight (−28%; P<0.01), lung weight (−26%; P<0.01), left ventricular (LV) end-diastolic pressure (11.4±2.0 versus 4.0±0.6 mm Hg, mean± SEM; P<0.01), collagen volume fraction of noninfarcted LV (−39%; P<0.05), and plasma levels of endogenous rat AM (−38%; P<0.05) without affecting infarct size. To investigate the mechanism of AM actions, another series of MI rats infused with AM were killed on day 7. AM infusion had no effect on organ weights and hemodynamic parameters on day 7 of MI but significantly reduced urinary excretion of isoprostane (−61%; P<0.01) and noninfarcted LV mRNA levels of ACE (−31%; P<0.05) and p22-phox (−30%; P<0.05). Conclusions—AM administration during the early period of MI improved the survival and ameliorated progression of LV remodeling and heart failure. This beneficial effect was accompanied by reductions in oxidative stress and ACE mRNA expression in noninfarcted LV in the AM infusion period.

Beneficial effects of adrenomedullin on left ventricular remodeling after myocardial infarction in rats

Objective: We previously reported that plasma adrenomedullin (AM) levels increase in patients with acute myocardial infarction (MI) and AM inhibits growth of rat cardiac myocytes and fibroblasts. The aim of this study was to examine the effects of long-term administration of AM on left ventricular (LV) remodeling, hemodynamic and hormonal parameters in a rat model of MI. Methods: Rats with MI induced by left coronary ligation were intravenously infused with 1.0 μg/h of recombinant human AM or saline by osmotic mini-pump. After infusion for 4 weeks, hemodynamic and hormonal studies were performed, and the myocyte size and collagen volume in non-infarct LV area were quantified morphometrically. Results: When compared with the MI rats infused with saline, continuous infusion of AM reduced the heart weight/body weight (4.4±0.2 vs. 3.6±0.1 g/kg, P <0.01), myocyte size (922±23 vs. 868±10 μm2, P <0.05) and collagen volume fraction of non-infarct LV area (7.6±0.8 vs. 4.8±0.5%, P <0.05), without affecting the infarct size. The AM infusion had no significant effect on the arterial pressure, but decreased the LV end-diastolic pressure (8.8±1.8 vs. 4.4±0.5 mmHg, P <0.05) in the MI rats. The plasma level of endogenous rat AM in the MI rats infused with human AM was reduced by 27% ( P <0.05), with a slight reduction of plasma atrial natriuretic peptide, compared with the control. Conclusions: Continuous administration of AM had beneficial effects on LV remodeling and hemodynamics in MI rats, suggesting the possibility that this peptide could be a useful therapeutic tool for acute MI.

Beneficial Effects of Adrenomedullin on Left Ventricular Remodeling after Myocardial Infarction in Rats

OBJECTIVE We previously reported that plasma adrenomedullin (AM) levels increase in patients with acute myocardial infarction (MI) and AM inhibits growth of rat cardiac myocytes and fibroblasts. The aim of this study was to examine the effects of long-term administration of AM on left ventricular (LV) remodeling, hemodynamic and hormonal parameters in a rat model of MI. METHODS Rats with MI induced by left coronary ligation were intravenously infused with 1.0 microg/h of recombinant human AM or saline by osmotic mini-pump. After infusion for 4 weeks, hemodynamic and hormonal studies were performed, and the myocyte size and collagen volume in non-infarct LV area were quantified morphometrically. RESULTS When compared with the MI rats infused with saline, continuous infusion of AM reduced the heart weight/body weight (4.4+/-0.2 vs. 3.6+/-0.1 g/kg, P<0.01), myocyte size (922+/-23 vs. 868+/-10 microm(2), P<0.05) and collagen volume fraction of non-infarct LV area (7.6+/-0.8 vs. 4.8+/-0.5%, P<0.05), without affecting the infarct size. The AM infusion had no significant effect on the arterial pressure, but decreased the LV end-diastolic pressure (8.8+/-1.8 vs. 4.4+/-0.5 mmHg, P<0.05) in the MI rats. The plasma level of endogenous rat AM in the MI rats infused with human AM was reduced by 27% (P<0.05), with a slight reduction of plasma atrial natriuretic peptide, compared with the control. CONCLUSIONS Continuous administration of AM had beneficial effects on LV remodeling and hemodynamics in MI rats, suggesting the possibility that this peptide could be a useful therapeutic tool for acute MI.