The Inhibitory Effect of Acute Administration of Excess Iodide on the Formation of Adenosine 3′,5′-Monophosphate Induced by Thyrotropin in Mouse Thyroid Lobes

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Abstract
An inhibitory action of excess I- on thyrotropin-induced thyroid hormone secretion occurs at a site subsequent to the generation of cyclic[c]AMP. Thyroidal cAMP formation induced by thyrotropin in vitro was markedly inhibited by the acute administration of excess I- to mice fed a low I diet. In contrast, excess I- failed to produce inhibition in animals fed a regular diet. In vitro stimulation by long-acting thryoid stimulator (LATS), prostaglandin E2 and 4-methylhistamine of cAMP formation in mouse thyroid lobes were significantly inhibited by the acute in vivo administration of excess I-. The inhibition was completely relieved by the administration of methimaxole prior to excess I-. Thyroid adenylate cyclase activity induced by thyrotropin was markedly depressed by excess I- under similar experimental conditions. One of the inhibitory actions of excess I- may be on the adenylate cyclase-cAMP system, and iodide can elicit its inhibitory action after its conversion to some form of organic I.