Effects of actinomycin D on rat liver alkaline phosphatase.

Abstract

Bile duct ligation in the rat causes a 5- to 10-fold increase in the activity of hepatic alkaline phosphatase and a lesser increase in the serum alkaline phosphatase (1, 2). The latter is due to leakage of the hepatic enzyme into the blood stream (3). The increase in hepatic alkaline phosphatase is dependent upon de novo protein synthesis and does not occur if protein synthesis is inhibited (2-4). This report examines the role of RNA synthesis in the changes in hepatic alkaline phosphatase induced by bile duct ligation. The data confirm a previous report (4) that the increase in this enzyme, both in liver and serum, is dependent upon intact RNA synthesis. In addition, actinomycin D has no paradoxical stimulatory effect on alkaline phosphatase induction (5, 6). Methods. Animal experiments. Male Charles River CDr rats, weighing approximately 100 g, were maintained on standard chow and tap water. On the day of an experiment they were anesthetized lightly with ether and the abdomen was opened through a midline incision. The common bile duct was isolated and then doubly ligated close to the liver to avoid damage to the pancreatic ducts (7). Control animals were sham operated. Groups of rats were sacrificed at varying times after operation, and the abdomen was reopened. Blood was withdrawn from the vena cava into a heparinized syringe and the livers were perfused with 20 ml of cold 0.25 M sucrose through a portal vein cannula. The livers were then excised, blotted dry, weighed, and minced with scissors. All animals had been fasted for 18 hr prior to sacrifice. In experiments involving inhibition of RNA synthesis, the above procedures were repeated, but actinomycin D (Lyovac-Cosmogen, Merck, Sharp and Dohme, West Point, Pa.), 50 μg/100 g of body weight, was given intramuscularly either 1 hr before surgery or at 1, 3, or 8 hr after surgery.