Abstract. Dogs received either 4 mg/kg of prednisone or sterile saline daily for 32 days. Serum samples were assayed every 4 days for total alkaline phosphatase (ALP) and corticosteroid-induced ALP isoenzyme (CIALP) activity. The initial and major increase of serum ALP was attributed to the liver isoenzyme of ALP (LALP), however, CIALP began to increase by day 8 and was significantly increased by day 24. Prior to treatment and on day 32, sections of liver from control and prednisone-treated dogs were stained for ALP activity after blocking the staining activity of LALP with levamisole. The staining activity of CIALP was compared to the staining activity of LALP in liver sections from control dogs and from dogs in which the bile duct was ligated. It was determined that CIALP was located in that area of the hepatocyte membranes which comprise the bile canaliculi.Corticosteroid-induced alkaline phosphatase is an isoenzyme normally not detected in dog serum by routine isoenzyme electrophoresis. This isoenzyme appears in canine serum after the prolonged influence of either endogenous or exogenous cortico~teroids.~ The tissue of origin of corticosteroid-induced alkaline phosphatase (CIALP) was shown to be the liver,8 but its exact subcellular location was not demonstrated. Characterization studies of CIALP using L-phenylalanine inhibition of enzymatic activity, heat inactivation, and immunochemical studies with polyclonal antibody produced in the rabbit, indicated that it was not related to the liver isoenzyme of alkaline phosphatase (LALP)8 but was similar to intestinal alkaline phosphatase isoenzyme (IALP).** It differs from IALP in net negative ~h a r g e ,~ and intravascular half life, which is about 3 days for CIALP as opposed to 6 minutes for IALP.I0 Treatment with neuraminidase eliminates these differences suggesting that these isoenzymes may differ only in their sialic acid content.Associated with the appearance of CIALP in the serum are hepatocellular lesions which include severe vacuolation and cell ~welling.~ The relationship of CIALP to these lesions and the significance of the enzyme's appearance have not been determined.Staining activity for LALP in canine liver is in the area of the hepatocyte membrane comprising the bile canaliculi, primarily in the periportal zone of the hepatic There have been no attempts to determine the histochemical location of CIALP staining activity in the canine liver.Since both CIALP and LALP are found in the liver, specific staining of CIALP requires a differential staining step. In the dog, levamisole is a potent inhibitor of LALP but does not inhibit IALP.*' Levamisole inhibition of canine LALP activity can approach 100% and will likely block all staining activity of LALP in liver sections. The minimal effect of levamisole on canine IALP activity and the similarity of IALP and CIALP with regard to their inhibition by L-phenylalanineZ2 suggest levamisole may be an excellent aid in the histologic localization of CIALP in the liver. However, the possible inhibitory effect of l...
A sensitive assay for the corticosteroid-induced alkaline phosphatase isoenzyme (CAP), adaptable to most clinical chemistry autoanalyzers, is described and validated. This assay is based on the greater than 98% inhibition of liver alkaline phosphatase isoenzyme (LAP) activity with 4.2 mM levamisole, as compared to the 42% inhibition of CAP activity. Analysis of serum with total alkaline phosphatase (AP) activity within the reference range, resulted in a reference range of 0 to 19 U/L for CAP activity. Analysis of serum from 160 clinical patients with AP activity above the reference range, revealed 73% with increased CAP activity ranging from 20 to 7,000 U/L. The diagnostic significance of this increased CAP activity is discussed.
Feline alkaline phosphatase and alkaline phosphatase isoenzymes have been studied in tissue and serum. Alkaline phosphatase from various organs was quantitated and then subjected to cellulose acetate electrophoresis. The effects of bile duct ligation, prednisolone treatment and phenobarbital treatment on serum alkaline phosphatase was measured. The diagnostic importance of feline serum alkaline phosphatase levels is discussed in light of the results of this and other studies.
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