Chemically induced hypothyroidism produces elevated amounts of the α subunit of the inhibitory guanine nucleotide binding protein (G(i)) and the β subunit common to all G-proteins

Adiopocytes of hypothyroid rats display an increased responsiveness to agents which function by inhibiting the production of cyclic AMP. Anti-peptide antisera which selectively recognise the α subunit of the inhibitory guanine nucleotide binding protein (G(i)) detected a 40 kDa polypeptide in adipocyte plasma membranes of both euthyroid and hypothyroid rats. Amounts of the α subunit of G(i) were elevated some 2-fold in the hypothyroid preparations in comparison with the euthyroid controls, when equal amounts of membrane protein of the two treatments were examined. As cells from the hypothyroid animals contained 2.7 times as much membrane protein as those from the control animals, the amounts of α subunit of G(i) are elevated some 5.6-fold per cell in adipocytes of the hypothyroid animals compared with the euthyroid controls. Amounts of the 36 kDa β subunit of G-proteins were also elevated in plasma membranes of adipocytes of hypothyroid animals, in this case by some 50% when compared on a protein basis. These results provide direct evidence for alterations in the amounts of the subunits of G(i) caused by the hypothyroid state.