Ward C.R., Achenbach S.E., Peterson M.E., et al.
OBJECTIVE: To identify within guanosine triphosphate-binding proteins (G proteins) the subset of inhibitory G proteins (G) that have decreased expression in adenomatous thyroid glands obtained from hyperthyroid cats. SAMPLE POPULATION: Adenomatous thyroid glands obtained from 5 hyperthyroid cats and normal thyroid glands obtained from 3 age-matched euthyroid cats. PROCEDURE: Expression of G(i1), G(i2), and G(i3) in enriched membrane preparations from thyroid glands was quantified by use of immunoblotting with G(i) subtype-specific antibodies. RESULTS: Expression of G(i2) was significantly decreased in tissues of hyperthyroid glands, compared with expression in normal thyroid tissue. Expression of G(i1) and G(i3) was not significantly different between normal thyroid tissues and tissues from hyperthyroid glands. CONCLUSIONS AND CLINICAL RELEVANCE: A decrease in G(i2) 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 G(i2) expression may explain excessive growth and function of the thyroid gland in cats with hyperthyroidism.