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The Biphasic Stimulatory and Inhibitory Effects of Concanavalin A on Thyroid Activation Induced by Thyrotropin

Department of Medicine, Institute of Adaptation Medicine, Shinshu University School of Medicine Matsumoto 390, Japan

Abstract

Concanavalin A (Con A) was tested for its ability to affect thyroid activation induced by TSH in mouse thyroid lobes. Pretreatment of thyroid lobes with Con A at concentrations from 1.55–400 µg/ml was found to have biphasic stimulatory and inhibitory effects on the TSH-induced accumulation of cAMP and formation of colloid droplets. Low concentrations of Con A potentiated TSH activation of thyroidal formation of cAMP and endocytosis. In contrast, higher concentrations of Con A markedly inhibited these TSH effects. The inhibitory effects observed after preincubation with Con A were abolished by the addition of a-methyl-Dglucoside to the incubation medium. A high concentration of Con A also inhibited cAMP formation induced either by prostaglandin E₂ or the long-acting thyroid stimulator. However, the basal and TSH-stimulated glucose oxidation in mouse thyroid lobes was not depressed by a high concentration of Con A. Uptake of ¹²⁵I-labeled Con A by thyroid tissues increased with time up to 1 h and was directly proportional to tissue weight. These findings suggest that the specific interaction between Con A and its receptors may lead to conformational changes in the structure of the membranes of the thyroid follicular cells which facilitate TSH-induced thyroid hormone secretion via the adenylate cyclasecAMP system. (Endocrinology 102: 1414, 1978)

Footnotes

^* To whom requests for reprints should be addressed.

Received April 5, 1977.