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Downregulation of endothelin B receptors in cardiomyopathic hamsters
1Department of Medicine, University of British Columbia, Vancouver Hospital and Health Sciences Centre, Canada.
Insights
Abnormal fluid retention in congestive heart failure (CHF) is linked to the endothelin (ET) hormonal system. ETB receptor downregulation contributes to this fluid imbalance, but enalapril therapy can restore normal function.
Area of Science:
- Nephrology
- Cardiology
- Endocrinology
Background:
- Abnormal fluid retention is a hallmark of congestive heart failure (CHF).
- The precise mechanisms driving salt and water retention in CHF remain incompletely understood.
- Endothelin (ET) is a potential mediator of fluid balance disruption in cardiovascular disease.
Purpose of the Study:
- To investigate the role of endothelin (ET) in mediating salt and water retention in congestive heart failure (CHF).
- To examine ET receptor distribution and density in the kidneys of cardiomyopathic (CM) hamsters.
- To assess the therapeutic effects of enalapril on renal function and ET receptor density in CHF models.
Main Methods:
- Utilized cardiomyopathic (CM) hamsters as a model for moderate heart failure.
- Employed clearance methods to assess renal function (sodium and water excretion) in CM hamsters versus controls.
- Performed radioligand binding studies to quantify ET receptor density in renal tissues, specifically inner medullary collecting ducts.
Main Results:
- CM hamsters showed an attenuated natriuretic and diuretic response to Atrial Natriuretic Factor (ANF) infusion compared to controls.
- A significant decrease in total ET receptor density, particularly ETB receptors, was observed in CM hamsters.
- Enalapril treatment successfully restored the responsiveness to ANF and normalized ET receptor density in diseased hamsters.
Conclusions:
- The renin-angiotensin-aldosterone system and the ET hormonal system interact to promote fluid retention in CHF.
- Downregulation of ETB receptors plays a critical role in the abnormal salt and water retention seen in CHF.
- Enalapril therapy demonstrates potential in reversing these detrimental effects by restoring renal function and ET receptor density.
Abstract:
The mechanisms responsible for abnormal fluid retention in congestive heart failure (CHF) are unclear. Studies were conducted to elucidate how endothelin (ET) may contribute to salt and water retention. Cardiomyopathic (CM) hamsters with moderate heart failure were employed for in vivo and in vitro trials. Clearance methods were used to compare the level of renal function in CM hamsters and control animals. Radioligand binding studies were also performed to determine ET receptor distribution in the inner medullary collecting ducts. CM hamsters exhibited an attenuated response to ANF infusion (FENa: 2.7 +/- 0.5 vs. 5.9 +/- 0.8%, p < 0.01; FEH2O: 1.7 +/- 0.3 vs. 3.2 +/- 0.4%, p < 0.01; UcGMP: 11.2 +/- 2.3 vs. 16.6 +/- 2.0 pmol/min, p < 0.05) and a decrease in total ET receptor density (532 +/- 77 vs. 959 +/- 154 fmol/mg protein, p < 0.005). Particularly ETB receptors were significantly reduced (214 +/- 26 vs. 483 +/- 88 fmol/mg protein, p < 0.003). Enalapril therapy simultaneously restored the natriuretic and diuretic effects of ANF and ET receptor density in the diseased animals. These studies suggest that the renin-angiotensin-aldosterone system and ET hormonal system act together, via ETB receptor downregulation, to promote the abnormal fluid retention observed in CHF.