Diminished hepatic L-triiodothyronine nuclear receptor concentration in rats bearing the Walker 256 carcinoma is not...

To determine whether the decrease in hepatic T3 nuclear receptors in rats bearing the Walker 256 carcinoma (T rats) is a consequence of nonthyroidal disease or related to a generalized decrease in hepatic protein synthesis, we measured hepatic T3 nuclear receptors and [3H]leucine incorporation into protein in control and T rats. Mean protein contents of liver homogenate, purified nuclei, 0.4 M NaCl extracts of nuclei, and nonhistone protein fractions were similar in control and T rats. In pooled data from three experiments, [3H]leucine incorporation into protein in these liver fractions was significantly increased (55-73%) in T rats. Since the precursor nonradioactive leucine pool, measured by a novel HPLC method, was similar in control and T rats, the increased incorporation of [3H]leucine in all liver fractions suggests an increase in protein synthesis in T rats. Additional measurements in the same rats (two experiments) indicated that hepatic nuclear receptors were decreased to 50% of the control value in T rats (P less than 0.001). Our findings suggest that in the Walker tumor model of nonthyroidal disease, decreased hepatic nuclear T3 receptors appears relatively specific and is not associated with a generalized decrease in hepatic protein synthesis.