Endothelin is an important determinant of renal function in a rat model of acute liver and renal failure

Abstract

Background and aims: Renal failure occurs in approximately 55% of patients with acute liver failure. We have previously shown that plasma endothelin 1 concentrations are elevated in patients with acute liver failure and the hepatorenal syndrome. There are few reported satisfactory animal models of liver failure together with functional renal failure. In this study, a rat model of acute liver failure induced by galactosamine that also develops renal failure was first characterised. This model was used to investigate the hypothesis that endothelin 1 is an important mediator involved in the pathogenesis of renal impairment that occurs in acute liver failure.

Methods: Acute liver failure was induced in male Sprague-Dawley rats by intraperitoneal injection of galactosamine together with treatment with the endothelin receptor antagonist Bosentan. Twenty four hour urine collections were made using a metabolic cage. Renal blood flow was measured in anaesthetised animals.

Results: This model developed renal failure and liver failure in the absence of any significant renal pathology, and with an accompanying fall in renal blood flow. Plasma concentrations of endothelin 1 were increased twofold following the onset of liver and renal failure (p<0.05), and there was significant upregulation of the endothelin receptor A (ET(A)) in the renal cortex (p<0.05). Administration of Bosentan prevented the development of renal failure when given before or 24 hours after the onset of liver injury (p<0.05) but had no effect on liver injury itself, or on renal blood flow.

Conclusions: This study demonstrates that this animal model has many of the features needed to be regarded as a model of renal failure that occurs in acute liver failure. The observation that plasma levels of endothelin 1 and ET(A) receptors are increased and upregulated, and that renal failure is prevented by an endothelin antagonist supports the hypothesis originally put forward that ET(A) is important in the pathogenesis of renal failure that occurs in patients with acute liver failure.

Figure 1

Morphological changes in the kidney. Light micrograph (original magnification ×25) of kidney from (A) sham rats and (B) 1.1 g/kg galactosamine (GalN) injected rats at 48 hours. Kidney sections were fixed in formalin, paraffin embedded, and stained with haematoxylin and eosin. The kidneys showed no abnormality of the renal cortex or medulla in the GalN animals; n=6 in both groups. Electron micrograph (original magnification ×7500) of (C) kidney from sham rats and (D) kidney from 1.1 g/kg GalN injected rats at 48 hours. Kidney sections were fixed in glutaraldehyde and stained with uracyl acetate and Reynold's lead citrate. In GalN animals, the glomeruli were normal. However, in the proximal tubules, the vacuolar system was slightly more prominent, with larger apical vacuoles as well as more prominent vacuoles with flocculent proteinaceous material towards the base of the epithelial cells; n=6 in both groups.

Figure 2

Effect of acute liver failure on endothelin 1 (ET-1) receptor expression in the kidney. Specific binding (total−non specific binding) of endothelin receptor A and B (ET_A and ET_B) selective radioligands [¹²⁵I]-PD151242 (A–D) and [¹²⁵I]-BQ3020 (E–H), respectively, in the different sections of the kidney in saline (Con) and galactosamine (GalN) injected rats. Densitometric analysis of ET_A and ET_B receptor binding demonstrated that there was a 20% increase in expression of ET_A receptor in the renal cortex of those animals injected with GalN (p<0.05); n=5 in both groups. Values are mean (SEM). CXT, cortex; CMJ, corticomedullary junction; MED, medulla; PEL, pelvis. Autoradiographs depicting total and non-specific binding of [¹²⁵I]-PD151242 and [¹²⁵I]-BQ3020 in control and GalN rats.

Figure 3

Effect of Bosentan on creatinine clearance. Creatinine clearance decreased significantly in rats with acute liver failure (galactosamine (GalN)) compared with controls (Con) (**p<0.001). Treatment with Bosentan, either before (pre-GalN) of after (post-Galn), prevented the development of renal failure (p<0.05). Groups: Con (n=12), GalN (n=12), saline+Bosentan (Bos) (n=4), Bosentan given 24 hours prior to GalN injection (pre-GalN) (n=8), or Bosentan given 24 hours after GalN injection (n=12) (post-GalN). Values are mean (SEM).