The hypertrophic heart rat: a new normotensive model of genetic cardiac and cardiomyocyte hypertrophy.

We describe a new line of rats with inherited cardiomyocyte and ventricular hypertrophy. From a second-generation cross of spontaneously hypertensive and Fischer 344 rats, we selected for low blood pressure and either high or low echocardiographic left ventricular (LV) mass over four generations to establish the hypertrophic heart rat (HHR) and normal heart rat (NHR) lines, respectively. After 13 generations of inbreeding, HHR had significantly greater (P < 0.0001) LV mass-to-body weight ratio (2.68 g/kg, SE 0.14) than NHR matched for age (1.94 g/kg, SE 0.02) or body weight (2.13 g/kg, SE 0.03). The isolated cardiomyocytes of HHR were significantly (P < 0.0001) longer and wider (161 microm, SE 0.83; 35.6 microm, SE 2.9) than NHR (132 microm, SE 1.2; 29.5 microm, SE 0.35). Telemetric 24-h recordings of mean arterial pressure revealed no significant differences between HHR and NHR. The HHR offers a new model of primary cardiomyocyte hypertrophy with normal blood pressure in which to examine genotypic causes and pathogenetic mechanisms of hypertrophy and its complications.

Regression of cardiac hypertrophy in the SHR by combined renin-angiotensin system blockade and dietary sodium restriction.

Altered operation of the renin-angiotensin-aldosterone system (RAAS) and dietary sodium intake have been identified as independent risk factors for cardiac hypertrophy. The way in which sodium intake and the operation of the renin-angiotensin-aldosterone system interact in the pathogenesis of cardiac hypertrophy is poorly understood. The aims of this study were to investigate the cardiac effects of the renin-angiotensin system (RAS) blockade in the spontaneously hypertensive rat (SHR), using co-treatment with an angiotensin II receptor blocker (ARB) and an angiotensin-converting enzyme (ACE) inhibitor with different sodium intakes. Our experiments with SHR show that, at high levels of sodium intake (4.0%), aggressive RAS blockade treatment with candesartan (3 mg/kg) and perindopril (6 mg/kg) does not result in regression of cardiac hypertrophy. In contrast, RAS blockade coupled with reduced sodium diet (0.2%) significantly regresses cardiac hypertrophy, impairs animal growth and is associated with elevated plasma renin and dramatically suppressed plasma angiotensinogen levels. Histological analyses indicate that the differential effect of reduced sodium on heart growth during RAS blockade is not associated with any change in myocardial interstitial collagen, but reflects modification of cellular geometry. Dimensional measurements of enzymatically-isolated ventricular myocytes show that, in the RAS blocked, reduced sodium group, myocyte length and width were decreased by about 16-19% compared with myocytes from the high sodium treatment group. Our findings highlight the importance of `titrating' sodium intake with combined RAS blockade in the clinical setting to optimise therapeutic benefit.