Abstract
Stimulated by reports that Concanavalin A (Con A), a plant protein and lectin from jack bean, has an inhibitory effect on thyroid activation induced by thyrotropin, we set out to test whether Con A inhibits thyroid action on hormone-sensitive target tissues in amphibians. We noted that premetamorphic tadpoles injected with 0.15 ml of thyroxin (T 4 0.24 μ M) responded by accelerating metamorphic change as indicated by precocious disappearance of the tail, and appreciable growth of the hind limbs and changes in mouth-part morphology. Tadpoles given an injection of thyroxin immediately followed by an injection of Con A (9.6 μ M) showed no such metamorphic changes. In the second series of experiments tail fin discs obtained from premetamorphic tadpoles when placed in cultures supplemented with T 4 (0.24 μ M) had completely shrunk within 96 hr. Tail fin discs that were raised in vitro in medium containing Con A as well as thyroxin failed to regress. In the third series of experiments tail discs were initially cultured in medium containing thyroxin and transferred within 48 hr to medium containing Con A. When Con A was added after this 48-hr exposure to thyroxin it was no longer effective in preventing tail fin disc resorption. We conclude tentatively (1) that Con A is a peripheral inhibitor of thyroxin and (2) this it somehow binds to the tissue or interacts with thyroxin rendering it ineffective before the hormone has a chance to act. The significance of finding a peripherally active inhibitor of thyroid hormone for studies of mechanism of action of this hormone on development and differentiation of hormone-sensitive target structures is obvious.
Published Version
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