Abstract
ABSTRACT In guinea pig thyroid tissue incubated at 25°C for forty hours the binding (organification) of iodide appears to be the step most sensitive to TSH. Binding is independent of uptake in this system and physiological doses of TSH can stimulate binding while uptake is partially inhibited. At a suitably low concentration of PTU, the addition of TSH can counteract the effect of this drug. At less than maximal concentrations, the effects of TSH and theophylline (a phosphodiesterase inhibitor) are additive, which supports the hypothesis that TSH acts by stimulating the production of cyclic 3′,5′-AMP. The effect of TSH appears to be exerted equally on any iodide present in the thyroid at the beginning of, or taken up during, incubation in vitro. In this system deiodination has been excluded as a major complicating factor.
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