Elevation of Alkaline Phosphatase Activity in the Intestine of the Chick Embryo by Actinomycin D

DURING the development of the mouse, alkaline phosphatase activity in the duodenum rises sharply before birth, falls back slightly, and then increases twenty-fold or more between 15 and 20 days 1 . This second rise is accelerated rather than retarded by inhibitors of RNA and protein synthesis 2,3 . Injection of actinomycin D , an inhibitor of DNA-dependent RNA synthesis 4 , into 9-day-old mice more than doubles their phosphatase activity within a 54 h period 3 , and the enhanced activity shows the normal increased preference for phenylphosphate over beta-glycerophosphate. Because these effects were obtained at a period of development when a considerable amount of phosphatase activity is already present, we thought it would be interesting to investigate the effect of actinomycin at a time when phosphatase activity first appears.