Nutritional and hormonal regulation of liver deoxycytidine kinase activity

Administration of CdR (50 mg/100 g every 12 h) elevated hepatic CdR kinase (EC 2.7.1.74) activity in normal or adrenalectomized rats over the control values 2- to 2.7-fold. Actinomycin (5 micrograms/100 g) or cycloheximide (50 micrograms/100 g) blocked the increase in enzyme activity. In starved rats, liver CdR kinase decreased to 64% compared to fed controls; refeeding restored enzyme activity to normal range. Steroid treatment (triamcinolone 1 mg/100 g/day) elevated liver CdR kinase activity to 138%, 169% and 193% of controls in 1, 2 and 3 days, respectively. Actinomycin or cycloheximide prevented this rise. These data suggest that the substrate and steroid induction of hepatic CdR kinase activity may be due to increased mRNA production and enhanced protein biosynthesis.