Objective—To identify within guanosine triphosphate–binding proteins (G proteins) the subset of
inhibitory G proteins (Gi) that have decreased expression
in adenomatous thyroid glands obtained from
Sample Population—Adenomatous thyroid glands
obtained from 5 hyperthyroid cats and normal thyroid
glands obtained from 3 age-matched euthyroid cats.
Procedure—Expression of Gi1, Gi2, and Gi3 in
enriched membrane preparations from thyroid glands
was quantified by use of immunoblotting with Gi subtype-specific antibodies.
Results—Expression of Gi2 was significantly
decreased in tissues of hyperthyroid glands, compared
with expression in normal thyroid tissue.
Expression of Gi1 and Gi3 was not significantly different
between normal thyroid tissues and tissues from
Conclusions and Clinical Relevance—A decrease in
Gi2 expression decreases inhibition of adenylyl
cyclase and allows a relative increase in stimulatory G
protein expression. This results in increased amounts
of cAMP and subsequent unregulated mitogenesis
and hormone production in hyperthyroid cells.
Decreased Gi2 expression may explain excessive
growth and function of the thyroid gland in cats with
hyperthyroidism. (Am J Vet Res 2005;66:1478–1482)