Studies on the Induction and Repression of Enzymes in Rat Liver

The effects of cortisone on the dietary induction and repression of serine dehydrase, ornithine transaminase, and tyrosine transaminase were studied. In rats pretreated with cortisone dietary induction was affected relatively little, but carbohydrate repression was largely eliminated. The effects of cortisone and phenobarbital on the dietary induction of serine dehydrase and ornithine transaminase were studied. Pretreatment with phenobarbital had little effect on the induction of serine dehydrase and ornithine transaminase, but pretreatment with cortisone and phenobarbital together caused an enhanced response of these enzymes to casein hydrolysate feeding, with respect to both total amount of enzyme produced and activity per g of liver protein. Neither cortisone nor phenobarbital acted as an inducing agent when administered alone or in combination; their effects were manifested only in the presence of dietary inducer.