Mechanism of elevation of serum alkaline phosphatase activity in biliary obstruction: an experimental study.

Bile duct ligation in rats increased alkaline phosphatase activity in serum and liver. In the serum, the activity reached a peak 24 h after bile duct ligation, earlier than in the liver. This finding indicates that the elevation of serum alkaline phosphatase activity is not due to simple overspill of this enzyme from the liver into the circulation. An electrophoretic study, employing polyacrylamide gel with Triton X-100, and a gel filtration study disclosed that 24 h after bile duct ligation the serum contained a high molecular weight form of alkaline phosphatase in addition to the hepatic and intestinal isoenzymes. The high molecular weight form was also found in bile, indicating that regurgitation of bile contributed to the increase in alkaline phosphatase activity in the serum. The absence of the high molecular weight alkaline phosphatase in the sera of rats with intrahepatic cholestasis induced by alpha-naphthylisothiocyanate suggests that, in this type of cholestasis, regurgitation of bile alkaline phosphatase does not play an important role in the elevation of serum alkaline phosphatase activity. These findings indicate that the high molecular weight alkaline phosphatase in serum is a useful diagnostic marker of biliary obstruction.