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Time-dependent changes of left ventricular contractility in Langendorff perfused hearts from renovascular
R H Kioshi1, I Stefanon, J G Mill
1Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, Brasil.
Insights
Hypertension-induced heart muscle growth (hypertrophy) in rats impairs contractile function over time. Even when normalized for size, hypertrophied ventricles generate less force, indicating reduced capacity.
Area of Science:
- Cardiovascular Physiology
- Renal Hypertension Research
- Cardiac Contractility Studies
Background:
- Renovascular hypertension leads to left ventricular hypertrophy (LVH).
- Understanding the functional consequences of LVH is crucial for cardiovascular health.
- The time course of contractile dysfunction in hypertension requires further investigation.
Purpose of the Study:
- To investigate the contractile activity of hypertrophied myocardium in a rat model of renovascular hypertension.
- To assess the impact of hypertension duration on cardiac function.
- To evaluate the relationship between left ventricular mass and contractile force.
Main Methods:
- Langendorff perfused hearts from one-kidney one-clip (1K1C) hypertensive rats and controls.
- Measurement of mean blood pressure and heart rate.
- Evaluation of left ventricular function curves by isovolumic systolic pressure (ISP) at varying diastolic pressures and extracellular calcium concentrations.
- Determination of left ventricular wet and dry weights.
Main Results:
- 1K1C rats exhibited hypertension and LVH.
- At 30 days post-induction, ISPs were lower in hypertensive rats compared to controls.
- At 60 days, ISPs were higher in hypertensive rats at low calcium, but normalization to LV dry weight revealed reduced pressure generation per unit mass across all time points and calcium levels.
Conclusions:
- Hypertension-induced LVH alters cardiac contractile machinery characteristics.
- Contractile dysfunction progresses with the duration of hypertension.
- Normalized force generation is diminished in hypertrophied ventricles, indicating impaired myocardial capacity.
Abstract:
1. The contractile activity of the hypertrophied myocardium was investigated in Langendorff perfused hearts from one-kidney one-clip (1K1C) renovascular hypertensive rats. 2. Hearts obtained from control and renovascular hypertensive animals were studied 15, 30 and 60 days after sham operation (SO) or renovascular hypertension induction. Rats were anesthetized with ether and mean blood pressure (MBP) and heart rate (HR) were measured. The hearts were then excised and perfused with Krebs solution and bicarbonate buffer, at 31 degrees C, with a perfusion pressure of 75 mmHg, beating spontaneously. The left ventricular function curves were evaluated by measuring the isovolumic systolic pressure (ISP) obtained at diastolic pressures (DP) of 0, 10, 20 and 30 mmHg in 0.62, 1.25 and 2.5 mM extracellular calcium. After the experiments the left ventricle (LV) was dissected, blotted and dried to obtain the dry and wet weights. 3. The 1K1C animals were hypertensive and displayed LV hypertrophy. The LV function curves showed the expected behavior, being similar for all 3 calcium concentrations used for the 15-day groups. However, at 30 days, ISPs were lower than those from the SO control group. Moreover, after 60 days ISPs from 1K1C rat ventricles were higher than controls in 0.62 mM calcium for all DPs. For all other DPs, ISP from 1K1C and control ventricles were similar. Normalization of ISP to LV dry weight showed that the hypertrophied ventricles, at any time and at all calcium concentrations used, developed less pressure by ventricular mass than SO controls. 4. Absolute ISP results suggest changes in the contractile machinery characteristics, not only as a function of the pressure overload but also as a function of the hypertension time course, and that ISP normalization to ventricular mass demonstrated the lower capacity of the hypertrophied muscle to generate force and pressure.