Neuroendocrine Control of Thyrotropin Secretion

THE GLYCOPROTEIN hormone TSH is the major regulator of the secretion of thyroid hormones (T4 and T3) from the thyroid gland. As the regulator of thyroid hormone release it plays an important, albeit indirect, role in the control of a variety of metabolic processes including protein synthesis, carbohydrate metabolism, thermogenesis, and cell growth. Historically, the concept of pituitary control of the thyroid gland stretches back to the observations of Niépce (1) in 1851 that cretins had markedly enlarged pituitary glands and of Rogowitsch (2) in 1889, who observed hypertrophy of the anterior pituitary after thyroidectomy in the rabbit. This concept was firmly established by the studies of Smith (3, 4) between 1916 and 1922, when he showed that ablation of the tadpole adenohypophysis resulted in thyroid attrition and prevented metamorphosis and that the atrophied thyroid gland could be made to hypertrophy by injections of beef anterior pituitary extracts.