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Control of Tyrosine--Ketoglutarate Transaminase Synthesis in Rat Liver: Studies of superinduction in force-fed rats¹

Department of Physiological Sciences, School of Veterinary Medicine, University of California, Davis, California

Actinomycin D and cycloheximide caused an increase in tyrosine--ketoglutarate transaminase activity in rats depleted of dietary protein and force-fed with casein hydrolysate. In rats fed a high protein diet and then force-fed with glucose, the antibiotics did not have this effect. Insulin did not abolish the antibiotic-mediated increase of tyrosine--ketoglutarate transaminase activity in rats force-fed with casein hydrolysate. In the rats force-fed with glucose, tyrosine--ketoglutarate transaminase activity was decreased by two doses (100 µg/dose) of glucagon; and in these animals actinomycin D and cycloheximide caused a 10- and 5-fold increase, respectively, in tyrosine--ketoglutarate transaminase activity. In the animals force-fed with glucose, hydrocortisone acetate (5 mg) did not alter the activity of tyrosine--ketoglutarate transaminase; and in the glucocorticoid-treated animals, actinomycin D caused a two-fold increase in enzyme activity, whereas the effect of cycloheximide was negligible. The data were interpreted as an indication that increased glucagon release is necessary for the superinduction to occur, but that superinduction cannot be explained by assuming that the antibiotics stimulate glucagon release.

Manuscript received 6 September 1968.