Thyroxine-binding globulin and thyroxine-binding prealbumin in hypothyroid and hyperthyroid developing rats.
We present evidence based on equilibrium and non-equilibrium binding studies, as well as on immunological techniques, that of the two rat specific thyroid-hormone-binding proteins, i.e., thyroxine-binding globulin (TBG) and thyroxine-binding prealbumin (TBPA), TBG but not TBPA is regulated by the thyroid hormones (TH). Hypothyroidism, induced from the day of birth by daily treatment with propylthiouracil (PTU-rats), leads to dramatic and sustained increases of the TH-binding abilities of the sera measured at equilibrium, whereas hyperthyroidism, induced by treatment with thyroxine (T4-rats), leads to the decrease of these abilities. Polyacrylamide gel electrophoresis and isoelectrofocalisation of radioiodinated T4-labelled sera, together with immunoassay of TBPA, demonstrate that both effects are due to TBG, the levels of which rise in PTU-rats and decline in T4-rats, while TBPA levels do not respond to either depletion or excess of the thyroid hormones. TBG rather than TBPA appears as the key thyroid-hormone-binding protein of the rat, inasmuch as it alone expresses a regulatory function of the thyroid hormones at protein synthesis level.
Savu
L
L
Unité 224, INSERM affiliée au CNRS, Paris, France.
Vranckx
R
R
Maya
M
M
Gripois
D
D
Blouquit
M F
MF
Nunez
E A
EA
D000375:Aging; D000818:Animals; D006980:Hyperthyroidism / Q000097:blood*; D007037:Hypothyroidism / Q000097:blood*; D007700:Kinetics; D011441:Propylthiouracil / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000097:blood; D013975:Thyroxine-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D014284:Triiodothyronine / Q000097:blood
D013975:Thyroxine-Binding Proteins; D014284:Triiodothyronine; D011441:Propylthiouracil; D013974:Thyroxine