Subcellular location of corticosteroid-induced alkaline phosphatase in canine hepatocytes

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.