Endocrinology, Vol 113, 1280-1286, Copyright © 1983 by Endocrine Society
Regulation of a thyroid hormone-dependent protein by growth hormone: the induction of hepatic alpha 2U globulin and its messenger ribonucleic acid in adult male hypothyroid rats
LE Shapiro
Studies in the adult male hypothyroid rat, a known GH-deficient animal,
have shown hepatic alpha 2U-globulin mRNA to be dependent on thyroid
hormones. To study the effects of GH on alpha 2U-globulin synthesis in the
absence of thyroid hormones, adult male rats were rendered hypothyroid
before hormone treatment. The relative effects of bovine GH or T3 were
studied by RIA of alpha 2U-globulin in hepatic cytosol in rats 6 weeks
after thyroid ablation. alpha 2U-Globulin levels in vehicle-treated
controls were 1.3 +/- 0.7 micrograms (+/- SD) alpha 2U- globulin/mg
protein. After 2 days, GH (200 micrograms/100 g X day) resulted in an
increase to 5.7 +/- 1.0 micrograms alpha 2U-globulin/mg (P less than or
equal to 0.05), and T3 50 micrograms/100 g X day) resulted in an increase
to 11.5 +/- 3.6 micrograms/mg (P less than or equal to 0.01). After 7 days,
GH resulted in an increase to 12.4 +/- 4.6 micrograms/mg (P less than or
equal to 0.01), and T3 resulted in an increase to 28.7 +/- 8.7
micrograms/mg (P less than or equal to 0.01). After 4 months of thyroid
ablation, baseline hepatic alpha 2U-globulin levels fell to 4.8 ng alpha
2U-globulin/mg protein. Hepatic alpha 2U- globulin was determined 4 and 8 h
after the injection of GH (200 micrograms/100 g). In these animals with
markedly diminished hepatic alpha 2U-globulin levels, significant (P less
than or equal to 0.01) increases occurred 4 h (25.4 ng/mg) and 8 h (57.2
ng/mg) after GH injection. The effects of treatment with bovine GH (200
micrograms/100 g X day) for 3 days on hepatic alpha 2U-globulin synthesis
in liver slices and alpha 2U-globulin poly (A)+ RNA levels were measured in
rats 10 weeks after thyroid ablation. GH significantly (P less than 0.05)
increased alpha 2U-globulin synthesis as a percentage of total protein
synthesis (from 0.01% to 0.035%) and alpha 2U-globulin mRNA as a percentage
of total mRNA (from 0.03% to 0.24%). The results show that GH rapidly and
specifically stimulates hepatic alpha 2U-globulin and its mRNA activity in
thyroid hormone-deficient rats.