Objective   To investigate the relationship of IL-6 expression and proliferation of hepatic cells after 90% portal branch ligation in rats.    Methods   Totally 72 SD rats were randomly divided into Sham operation group and 90% portal vein branches ligation group. Portal vein pressure and the weights of both ligated and non-ligated lobes of liver were measured at postoperative days (POD) 0.5

1

3

5

7 and 14. The morphological changes of the non-ligated liver lobes were observed by light microscopy. The expression of PCNA and IL-6 of the non-ligated liver lobes were detected by immunohistochemical method. The results were analyzed by medical statistical methods.    Results   Portal vein pressure was increased immediately after the operation

it reached the peak point at 0.5 d (P0.01)

and then dropped to normal level at POD7. Hepatic lobe at the ligated side was diminished progressively after 90% portal branch ligation. The ratio of non-ligated lobes weight to the whole liver weight was increased from POD 1 to 5

and came into “a plateau stage” at POD7. The hepatocytes started to proliferate obviously by microscopy

and there were more mitotic-phases existed in the non-ligated lobes at POD 3 to 7

and the hepatocytes were larger than before; PCNA index were increased at POD 0.5 to 5(P0.05)

and then gradually return to normal value. IL-6 expression of the non-ligated liver lobes was increased at POD 0.5 to 5

then slowly returned to the level of Sham operation group from POD 7 to 14. PCNA expressions in non-ligated lobes and portal vein pressure (PVP) had a positive correlation at POD 1

3 and 5

and a negative correlation at POD 14 (P0.05). The expressions of PCNA and IL-6 had a positive correlation at POD 1 and 14.    Conclusion   IL-6 expression may play a pivotal role in liver regeneration after 90% portal branch ligation in rats.