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 (10⁻⁷10⁻⁴ M) and NaF (10-20 mM) stimulated IP₁, IP₂ and IP₃ generation. 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 ) could be detected on PIP₂ hydrolysis and IP production. These results suggest that (i) IP₃ could 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 IP₃ accumulation.