Effects of irradiation and starvation on the regulation of rat liver enzymes.

Abstract

The elevation of liver enzymes by the administration of various substances was studied in adrenalectomized rats after whole-body X irradiation. Because irradiation alone almost eliminates food intake, irradiated rats were starved and compared to fed and starved adrenalectomized controls. Starvation greatly enhanced (2.5- to 3.5-fold) the response of tyrosine transaminase to hydrocortisone and increased its response to [alpha]-methyltryptophan and pyridoxine. Starvation did not enhance the response of tryptophan pyrrolase to any regulators. Irradiation did not diminish the response of either enzyme to hydrocortisone, but decreased the response of both enzymes to substrate-type compounds. The increase of tryptophan pyrrolase by its substrate analogue was abolished after irradiation with 1600 r. The increase of tyrosine transaminase by [alpha]-methyltryptophan and pyridoxine was significantly inhibited by 800 r. These effects are different from that of puromycin, which inhibits both types of elevation of these enzymes, and different from actinomycin, which inhibits only the hormonal type of elevation. Irradiation, by inhibiting the substrate-type but not the hormone-type of elevation of these 2 enzymes, has an effect opposite to that of actinomycin.