The isoelectric focusing properties of serum alkaline phosphatase in disease and following prednisolone and phenylbutazone administration in the horse.

This study was undertaken to ascertain if the isoelectric focusing pattern of serum alkaline phosphatase (AP) from sick horses with high activity is useful for determining its tissue origin. The effect of oral prednisolone and phenylbutazone therapy on this enzyme in healthy horses was also investigated. The sick horses were divided into three groups: hepatic, intestinal and miscellaneous. All sera had approximately thirteen bands of AP activity when focused on agarose gels with a pH gradient of 3.5 to 9.5. All the horses in the liver disease group had greater than 65% of enzyme activity in bands 3 to 7 (counted from the anode) whereas the other two groups had at least 30% and up to 80% of activity in bands 8 to 13. This was true even in the several cases of primary intestinal disease that had additional biochemical evidence of liver damage. All bands were heat sensitive indicating that little if any AP was of small intestinal or renal origin. Oral prednisolone and phenylbutazone for 20 and 12 days respectively had no affect on serum AP activity or isoelectric pattern. We concluded that the AP in bands 3 to 7 is of liver origin but the origin of bands 8 to 13 remains undetermined although small intestinal or renal origin is unlikely. Isoelectric focusing of serum AP shows promise in differentiating cases of primary from secondary liver disease but further studies are required correlating serum patterns and tissue patterns in animals with diseases.