Cyclic AMP: a mediator of thyroid stimulation by thyrotropin

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Abstract
Theophylline (a cyclic-nucleotide phosphodiesterase inhibitor), cyclic AMP, 5[image]-AMP, ADP, and ATP increased the 125I concentration in the blood of mice whose thyroid iodine was labeled with 125I. Administration of ineffective doses of theophylline with subliminal doses of thyrotropin or cyclic AMP resulted in significant increases in blood-125I. Simultaneous administration of individually ineffective doses of thyrotropin and theophylline caused significant depletion of thyroid radioiodine in rats. Theophylline augmented thyrotropln-induced increases in the ratio of thyroid-to-serum radioiodide in rats and in the thyroid uptake of 131I in mice. It is probable that cyclic AMP mediates the effects of thyrotropin on the major facets of thyroid iodine metabolism.