Involvement of alpha 1-adrenergic receptors in stimulation of phosphatidylinositol metabolism by catecholamines in mouse thyroids

The effects of alpha-adrenergic agonists and thyroid stimulating hormone on the incorporation of radioactive phosphate into phosphatidylinositol were investigated in mouse thyroids in vitro. The incorporation of 32P orthophosphate into phosphatidylinositol was stimulated by thyroid stimulating hormone, norepinephrine (a mixed alpha 1- and alpha 2-adrenergic agonist), methoxamine and phenylephrine (alpha 1-agonists) and slightly by clonidine and oxymetazoline (alpha 2-agonists) but not by isoproterenol (beta-agonist). Prazosin (alpha 1-antagonist) inhibited the stimulation by norepinephrine of 32P incorporation into phosphatidylinositol, but yohimbine (alpha 2-antagonist) was less effective. Although norepinephrine inhibits the thyroid stimulating hormone-induced release by activating alpha-, especially alpha 1-adrenoceptors in mouse thyroids [M. L. Maayan et al., Metabolism 26, 473 (1977); M. L. Maayan et al., Endocrinology 101, 284 (1977); T. Muraki et al., Endocrinology 110, 51 (1982)] alpha 1-agonists did not decrease the stimulation of turnover elicited by thyroid stimulating hormone and did not have additive action with it. These results suggest that (1) the stimulation of phosphatidylinositol turnover of mouse thyroids elicited by adrenergic agonists is mediated by activation of alpha 1-adrenoceptors and (2) the inhibitory effect of norepinephrine on the thyroid stimulating hormone-induced release of thyroxine is not mediated by norepinephrine-inhibition of phosphatidylinositol-turnover stimulated by thyroid stimulating hormone.