Alkaline phosphatase activity and isoenzymes in experimental fractures

Serum alkaline phosphatase activity and isoenzymes were studied after experimental fractures of the rat tibia. The enzyme activity was measured as the light absorption of p-nitrophenol, produced after hydrolysis of p-nitrophenyl phosphate. Enzyme separation was performed with a disc electrophoresis technique using polyacrylamide gel as supporting medium. From 4 h after the fracture serum enzyme activity rose to reach a peak value after 24 h and then decreased again to normal values after 14 days. It is suggested that the serum enzyme increase is mainly a result of the early cell proliferation in the fracture area. In the fracture callus the enzyme activity was significantly increased with a maximum value 14 days after fracture. Three enzyme fractions were found in serum from control rats. A similar serum enzyme pattern was seen in experimental animals. Also in fracture callus and control cortical bone of the tibia three enzyme bands were seen with a broad fast migrating zone. This fast moving zone, however, was more active in fracture callus.