The relationship of liver regeneration to immunoactivity was examined after ursodesoxycholic acid (UDCA) administration to partially (about 66%) hepatectomized rats. The UDCA was given orally. Liver regeneration was evaluated by the hepatocyte mitotic index (MI) and immunoactivity by natural killer cell (NK) activity in the blood. When UDCA 12.5 mg/kg/day was administered, a significant increase in the MI was observed 2 and 3 days after hepatectomy, and the MI response 2 days after hepatectomy tended to be dose-dependent in the range of 0–25 mg/kg/day. NK activity was decreased 2 days after hepatectomy when UDCA was given, and a significant correlation between MI and NK activity was obtained. The increase in MI and decrease in NK activity was blocked completely or partially (respectively) by interleukin-2 administration. It was also noted that UDCA did not affect serum parameters indicating liver and kidney function. These findings suggest that liver regeneration can be modified by orally administered UDCA through a change in immunoactivity.
