To examine the mechanism of the α1-adrenoceptor-mediated inhibition of the release of thyroid hormones in the mouse thyroid, the effect of noradrenaline on the production of inositol phosphates was investigated using thyroids preloaded with [3H]inositol. Noradrenaline increased [3H]inositol accumulation into inositol phosphates in the mouse thyroid during a 30-min incubation whereas TSH (10 mU/ml) was without effect. The effect of noradrenaline was mimicked by phenylephrine, but not by clonidine or isoprenaline. Prazosin antagonized the effect of noradrenaline, while yohimbine had no effect. These results suggest that noradrenaline-induced production of inositol phosphates is mediated by α1-adrenoceptors. The inhibition of release of thyroid hormones elicited by α1-adrenergic agonists in the mouse thyroid is possibly mediated through the hydrolysis of membrane phosphoinositides followed by the generation of second messengers such as inositol phosphates and diacylglycerol.
J. Endocr. (1987) 115, 289–293