Carbachol and sodium fluoride, but not TSH, stimulate the generation of inositol phosphates in the dog thyroid

In dog thyroid slices prelabeled with myo-[2- 3H]inositol, carbachol (10 −710 −4M) and NaF (10-20 mM) stimulated IP 1, IP 2and IP 3generation. These effects did not require the presence of extracellular calcium. Atropine and PDBu inhibited the action of the cholinergic agonist. No effect of TSH (1–100 mUml) could be detected on PIP 2hydrolysis and IP production. These results suggest that (i) IP 3could play a role in the metabolic actions of carbachol in the thyroid; (ii) a G-protein coupling the hormone-receptor binding to phospholipase C activation exists in the thyroid membrane; (iii) the well known TSH-induced increased PI turnover does not result in IP 3accumulation.