Effects of chronic nitric oxide activation or inhibition on early hepatic fibrosis in rats with bile duct ligation

Hepatic fibrosis or increased liver collagen contents drive functional abno rmalities that, when extensive, may be life threatening. The purpose of thi s study was to assess the effects of the chronic stimulation or inhibition of nitric oxide synthesis in rats with hepatic fibrosis induced by permanen t common bile duct ligation (3 weeks) and the role of expression of the dif ferent nitric oxide synthase isoforms. Bile duct ligation led to an importa nt accumulation of collagen in the hepatic parenchyma, as shown both histol ogically and by the hydroxyproline contents of livers. Bilirubin and serum enzyme activities (measured as markers of cholestasis) increased several-fo ld after bile duct ligation. The area of fibrotic tissue, liver hydroxyprol ine content and serum markers of cholestasis were clearly related in obstru cted rats. The absence of modifications in haemodynamic parameters excludes circulatory changes from being responsible for the development of liver al terations. In animals treated with N-G-nitro-L-arginine methyl ester (L-NAM E) the area of fibrosis was similar to that of untreated animals, the signs of cholestasis and cellular injury being more evident. In rats treated wit h L-arginine the area of fibrosis was almost three times larger than that f ound in bile duct ligated rats and in L-NAME-treated bile duct ligated rats , although the observed biochemical changes were similar to those seen in r ats treated with L-NAME. Our results with inducible nitric oxide synthase, obtained by Western blots and immunohistochemistry, indicate a greater expr ession of the inducible enzyme in bile duct ligated and L-arginine-treated animals and a lower expression in the L-NAME and control groups. Constituti ve nitric oxide synthase expression, obtained by Western blots, was very si milar in all groups, except for the L-arginine-treated rats in which it was lower. These results suggest that nitric oxide production may be a key fac tor in the development of fibrosis in bile duct ligated rats. They also sup port the hypothesis of a dual role for nitric oxide; one beneficial, mediat ed by its circulatory effects, and the second negative, through its local t oxic effects.