Thomopoulos P
Clinique des maladies endocriniennes et métaboliques, Hôpital Cochin, Paris.
Rev Prat. 1998 Nov 15;48(18):1987-91.
Thyroid gland fulfills two functions. On one hand, it synthesizes and builds up stocks of thyroid hormones in thyroglobulin molecules of the colloid in its follicles, such as they can maintain the hormonal secretion during several days and even weeks. To do this, it captures and concentrates plasma iodide through a specific membrane transporter and it oxidizes iodide through the action of thyroperoxidase and H2O2. This makes it able to bind to tyrosine residus of thyroglobulin. Then, the iodotyrosines can form the thyroid hormones (T4 and T3) by a coupling reaction. On the other hand, thyroid secretes the hormones after internalization and proteolysis of thyroglobulin. All the steps of synthesis and secretion are regulated by pituitary TSH, through a negative feed-back action of T4 and T3. Thus, any increase or decrease of circulating thyroid hormones induces the opposite modification of TSH. In addition, an important fraction of plasma and tissue T3 is produced through the extrathyroidal monodeiodination of T4 by enzymes (5' deiodases) which are regulated by the nutritional status and by thyroid hormones.
甲状腺具有两种功能。一方面，它在其滤泡胶体的甲状腺球蛋白分子中合成并储存甲状腺激素，以便在数天甚至数周内维持激素分泌。为此，它通过一种特定的膜转运蛋白捕获并浓缩血浆碘化物，并通过甲状腺过氧化物酶和过氧化氢的作用将碘化物氧化。这使其能够与甲状腺球蛋白的酪氨酸残基结合。然后，碘酪氨酸可通过偶联反应形成甲状腺激素（T4和T3）。另一方面，甲状腺在甲状腺球蛋白内化和蛋白水解后分泌激素。合成和分泌的所有步骤都由垂体促甲状腺激素（TSH）通过T4和T3的负反馈作用进行调节。因此，循环甲状腺激素的任何增加或减少都会引起TSH的相反变化。此外，血浆和组织中很大一部分T3是通过酶（5'脱碘酶）对T4进行甲状腺外单脱碘作用产生的，这些酶受营养状况和甲状腺激素的调节。
