Angiotensin II receptor blockade in Syrian hamster (T0-2) cardiomyopathy does not affect microscopic cardiac material properties: implications for mechanisms of tissue remodeling

Enalapril and Losartan Are More Effective Than Carvedilol in Preventing Dilated Cardiomyopathy in the Syrian Cardiomyopathic Hamster

To assess the role of the renin—angiotensin (RAS) and adrenergic systems in the development and progression of dilated cardiomyopathy in the Syrian cardiomyopathic hamster (SCH), echocardiographic parameters were evaluated in 6-month-old animals after 5 months of treatment with enalapril (25 mg/kg/day) plus losartan (10 mg/kg/day), or with carvedilol (1 mg/kg/day). Cardiac output indexes (COI) increased by 53% after RAS blockade and by 20% after β-blockade in SCH. Moreover, LVEDV and LVESV decreased 30% and 62%, respectively ( P < .05) during RAS blockade, whereas ejection fraction (EF) increased by 48%. By contrast, carvedilol reduced LVESV by only 28% ( P < .05) and increased EF by only 15% ( P < .05). These results suggest that RAS activation plays a critical role in the development of cardiac dysfunction in SCH and that suppression of RAS may be more effective than β-blockade in retarding the development of cardiomyopathy in SCH. Owing to timing (pre—heart failure stage) and to the single dose protocol, the implications of this study for human subjects remain to be clarified.

Effects of losartan on the collagen degradative enzymes in hypertrophic and congestive types of cardiomyopathic hamsters

The present study was undertaken to determine the effects of AT1 receptor blockade which occurred in response to losartan, on the extracellular matrix (ECM) degradation process in the Bio 14.6 (n = 12) and Bio 53.58 (n = 12) strains which are referred as models of hypertrophic and dilated cardiomyopathy, respectively. The administration of losartan (30 mg/kg/day) in hamsters from 10-20 weeks of age reduced the accumulation of the left ventricular collagen matrix in both of the Bio 14.6 and the Bio 53.58 strains. According to the RT-PCR, the levels of mRNA for matrix metalloproteinase (MMP) and the tissue inhibitor of MMP (TIMP) were examined. MMP-1, -2, -3, and -9 were more enhanced in both myopathic strains than in the control F1beta, strains. With losartan, the levels of MMP-1, -2, -9, TIMP-1 and -2 decreased in the both strains but those for MMP-3 did not in Bio 14.6 strains. TIMP-3 and -4 mRNA levels did not change in any of the experimental hamsters, whether treated or untreated with losartan. The Western blots also showed similar observations in the both strains as seen in mRNA expressions although MMP-2 in the Bio 53.58 strains did not differ between treated and untreated with losartan. Although losartan has an inhibitory effect on collagen accumulation in the development of cardiomyopathy, MMPs (-1, -2, -9) and TIMPs (-1, -2) seem to be susceptible to responding to losartan in Bio cardiomyopathic hamsters.

Hemodynamic and histomorphometric characteristics of dilated cardiomyopathy of Syrian hamsters (Bio TO-2 strain)

The natural history of the disease of the dilated strain Bio TO-2 of cardiomyopathic hamsters (CMH) is not totally characterized. We investigated its hemodynamic and histomorphometric characteristics at 140, 180, 220, 260, and 300 days of age. Forty CMH and 40 controls were investigated (8 at each stage). Mean arterial pressure (MAP, carotid artery catheter) and cardiac output and femoral blood flow (CO, FBF, transit time method) were measured in anesthetized animals. Systemic (SVR) and femoral (FVR) vascular resistances were calculated. Atria, left and right ventricles (LV, RV), lungs, and liver were weighed. LV cavity area, LV and RV wall thicknesses and collagen densities were determined (computer-assisted image analyzer). Pulmonary and hepatic congestion were assessed (arbitrary scales). Compared with controls, MAP, CO and FBF were significantly lower in CMH throughout the study (on average: –22%, –34%, –33%, respectively), FVR was significantly increased (+15%), but SVR was not significantly modified. Concerning histomorphometric characteristics, differences between groups significantly increased with age for most variables: at 300 days, atria (+292%), RV (+13%), lungs (+44%), and liver (+23%) weights, LV cavity area (+130%), LV (+364%) and RV (+181%) collagen densities were significantly increased in CMH vs controls, whereas LV (–40%) and RV (–23%) wall thicknesses were significantly decreased. At 260 and 300 days, CMH showed significant pulmonary congestion without hepatic alteration. Bio TO-2 CMH progressively develop an alteration of cardiac function leading to decreased MAP and musculo-cutaneous blood flow associated with cardiac remodeling including atria hypertrophy and LV dilation, wall thinning and a rise in collagen density.Key words: cardiomyopathy, heart failure, regional blood flow, remodeling.

Downregulation of cardiac AT1-receptor expression and angiotensin II concentrations after long-term blockade of the renin-angiotensin system in cardiomyopathic hamsters

We monitored cardiac angiotensin II concentration and AT1-receptor density after long-term blockade of the renin-angiotensin system in inbred control hamsters treated with placebo or losartan (100 mg/kg/day) and cardiomyopathic hamsters treated with placebo, low-(30 mg/kg/day), or high-dose (100 mg/kg/day) losartan or quinapril (100 mg/kg/day). All treatments were started at age 50 days. Angiotensin II-receptor density and affinity were measured by radioligand-binding assays, and ventricular angiotensin II concentration was determined by radioimmunoassay. After 125 and 275 days of treatment, both doses of losartan significantly reduced AT1-receptor density, whereas quinapril had no effect. The administration of both drugs resulted in significant reductions in ventricular angiotensin II concentration. The prolonged administration of losartan was associated with an increase in cardiac hypertrophy, suggesting that angiotensin II signaling is not directly involved or at least does not play a major role in the remodeling process observed in cardiomyopathic hamsters.

In vitro characterization of a novel, tissue-targeted ultrasonic contrast system with acoustic microscopy

Targeted ultrasonic contrast systems are designed to enhance the reflectivity of selected tissues in vivo [Lanza et al., Circulation 94, 3334 (1996)]. In particular, these agents hold promise for the minimally invasive diagnosis and treatment of a wide array of pathologies, most notably tumors, thromboses, and inflamed tissues. In the present study, acoustic microscopy was used to assess the efficacy of a novel, perfluorocarbon based contrast agent to enhance the inherent acoustic reflectivity of biological and synthetic substrates. Data from these experiments were used to postulate a simple model describing the observed enhancements. Frequency averaged reflectivity (30-55 MHz) was shown to increase 7.0 +/- 1.1 dB for nitrocellulose membranes with targeted contrast. Enhancements of 36.0 +/- 2.3 dB and 8.5 +/- 0.9 dB for plasma and whole blood clots, respectively, were measured between 20 and 35 MHz. A proposed acoustic transmission line model predicted the targeted contrast system would increase the acoustic reflectivity of the nitrocellulose membrane, whole blood clot, and fibrin plasma clot by 2.6, 8.0, and 31.8 dB, respectively. These predictions were in reasonable agreement with the experimental results of this paper. In conclusion, acoustic microscopy provides a rapid and sensitive approach for in vitro chracterization, development, and testing of mathematical models of targeted contrast systems. Given the current demand for targeted contrast systems for medical diagnostic and therapeutic use, the use of acoustic microscopy may provide a useful tool in the development of these agents.