Liver protein synthesis and catabolism in mirex-pretreated rats with enlarging livers

Incorporation and retention of [14C]amino acids in protein were studied in rats with enlarging livers. Rats were injected (i.v.) with 20 mg of mirex per kg b. wt. to stimulate liver enlargement with a concomitant and proportional increase in liver total protein. Eighteen hours later, mirex-pretreated and control rats received an i.p. dose of a L-[14C]amino acid mixture and were killed at predetermination intervals up to 48 hr. Mirex-pretreated rats incorporated [14C]amino acids into liver protein at the same rate as controls, but retained more of the radiolabeled amino acids in liver protein for a longer time. In a second experiment, (14C]bicarbonate was substituted for the amino acid mixture to determine whether differences in [14C]amino acid retention were due to reutilization or mobilization. The change in protein metabolism, which leads to an almost 2-fold increase in liver total protein within 66 hr, appears to be due to a decrease in the quantity of protein catabolized per unit time rather than an increase in the rate of protein synthesized.