Diminished hepatic L-triiodothyronine nuclear receptor concentration in rats bearing the Walker 256 carcinoma is not due to a generalized decrease in nonhistone protein synthesis.
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.
Starosta
Z
Z
Department of Medicine, Montefiore Medical Center, Bronx, New York 10467.
Gasparini
F
F
Shapiro
L E
LE
Surks
M I
MI
D000818:Animals; D001835:Body Weight; D002279:Carcinoma 256, Walker / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006657:Histones / Q000096:biosynthesis; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008970:Molecular Weight; D009929:Organ Size; D014176:Protein Biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*
D006657:Histones; D011988:Receptors, Thyroid Hormone; D007930:Leucine