The renin–angiotensin system in a rat model of hepatic fibrosis: Evidence for a protective role of Angiotensin-(1–7)

doi:10.1016/j.jhep.2006.10.018

Journal of Hepatology

Volume 46, Issue 4, April 2007, Pages 674-681

https://doi.org/10.1016/j.jhep.2006.10.018 Get rights and content

Background/Aims

The circulating renin–angiotensin system (RAS) [plasma renin activity (PRA), Angiotensin (Ang) I, Ang II and Ang-(1–7)] was evaluated in a model of hepatic fibrosis in rats. To investigate the pathophysiological involvement of Ang-(1–7), animals were treated with the Ang-(1–7) Mas receptor antagonist, A-779.

Methods

RAS components, liver function and histology were examined in male Wistar rats (220–300 g). Animals were submitted to sham-surgery or ligature of the bile duct and evaluated 1, 2, 4 and 6 weeks later. Blood samples were obtained to determine biochemical parameters and RAS components. A second group was treated with A-779 or vehicle to measure liver hydroxyproline and total transforming growth factor β-1 (TGFβ₁).

Results

PRA and Ang I were significantly elevated in rats at 4 and 6 weeks compared to sham-operated animals. Ang II and Ang-(1–7) progressively increased over the 6 weeks. Changes in RAS profile correlated with histological signs of fibrosis and deterioration in liver function. Pharmacological blockade of the Ang-(1–7) receptor aggravated liver fibrosis with a significant elevation in hydroxyproline and total TGFβ₁.

Conclusions

Hepatic fibrosis was associated with RAS activation in our model. Our data also suggested that Ang-(1–7) played a protective role in hepatic fibrosis.

Introduction

It is well established that the renin–angiotensin system (RAS) is involved in a number of fibrogenic processes [1], [2], [3], [4] and angiotensin (Ang) II acting on its Type 1 receptors (AT₁) may have profibrotic and mitogenic effects [1], [4], [5]. Moreover, inhibition of the RAS was associated with reduced collagen expression and tissue fibrosis in models of kidney [2] and heart injury [3].

Recent studies also indicate that the RAS may be involved in hepatic fibrosis [6], [7], [8], [9], [10], [11]. Thus activation of AT₁ receptors by Ang II induces contraction and proliferation of hepatic stellate cells [11], [12], [13], [14] and increases the expression of collagen I and of the pro-fibrogenic cytokine transforming growth factor β-1 (TGFβ₁) [8], [10]. The role of other angiotensins has not been evaluated in any detail in models of hepatic fibrosis. Among the putative mediators of RAS, Ang-(1–7) is particularly interesting. Ang-(1–7) can be formed directly from Ang I by neutral-endopeptidase 24.11 or prolyl-endopeptidase or from Ang II via prolyl-endopeptidase, prolyl-carboxypeptidase [15], [16] or the newly discovered enzyme ACE2 [17]. Experimental evidence has shown that Ang-(1–7) plays a counter-regulatory role in the RAS [15], [18] by opposing the vascular and proliferative effects of Ang II [15], [18], [19]. Therefore it is possible that Ang-(1–7) may also play a role in modulating the pro-fibrogenic effects of Ang II in hepatic fibrosis.

Ang-(1–7) is an endogenous ligand for the G-protein-coupled receptor Mas and the latter receptor appears to mediate most of the biological actions of Ang-(1–7) [20]. The physiological relevance of Ang-(1–7) can be evaluated by using the Mas receptor antagonist, A-779 [21], [22], [23]. The aims of the present study were to detect the plasma levels of components of the RAS in a rat model of bile duct ligation (BDL) and to evaluate the effect of Mas receptor antagonism on the early stages of hepatic fibrosis.

Section snippets

Animals and experimental design

Male Wistar rats (220–300 g) were housed in a controlled environment in our animal facility. To induce hepatic fibrosis, animals were anesthetized intraperitoneally with 2.5% tribromoethanol. Then, a 1.5 cm midline abdominal incision was made, the common bile duct located, double ligated with 4–0 silk and sectioned, as described elsewhere [24]. The study was approved by the Ethics Committee of our Institution.

General measurements

Because there did not appear to be any difference in the many variables studied in the sham group at 1, 2, 4 and 6 weeks after sham operation, results from all the sham-operated groups were pooled for ease of presentation at Table 1. All rats had a similar body weight at the beginning of the experimental protocol and no differences were observed in water and food intake (Table 1). The 24-h urinary volume of animals at 1 and 2 weeks after BDL did not differ from sham-operated rats. However,

Discussion

The present study supports the concept that the RAS contributes to organ damage in the liver and in other tissues [2], [3], [4]. Our data show that the progression of liver dysfunction in BDL rats is characterized by marked changes in Ang II and Ang-(1–7) levels and that the overall activation of circulating RAS was associated in time with the progression of hepatic fibrosis. Furthermore, the pharmacological blockade of endogenous Ang-(1–7) accelerated liver fibrosis as demonstrated

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The renin–angiotensin system in a rat model of hepatic fibrosis: Evidence for a protective role of Angiotensin-(1–7)

Background/Aims

Methods

Results

Conclusions

Introduction

Section snippets

Animals and experimental design

General measurements

Discussion

Regul Pept

Curr Opin Pharmacol

Gastroenterology

J Hepatol

Gastroenterology

Hepatology

Gastroenterology

Gastroenterology

Hepatology

Curr Biol

Int J Biochem Cell Biol

Brain Res Bull

Regul Pept

Peptides

J Hepatol

Pharmacol Ther

Life Sci

Kidney Int

The role of the Renin Angiotensin System in the development of cardiovascular disease

Am J Cardiol

Molecular and cellular mechanisms of Angiotensin II-mediated cardiovascular and renal diseases

Pharmacol Rev

Angiotensin II receptors

J Am Soc Nephrol