Thyroid Function in a Goiter Endemic: I. Impairment of Hormone Synthesis and Secretion in the Goitrous Gland

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Abstract
Further investigations of the metabolism of hormonal iodine were carried out in 12 untreated and iodine-treated goitrous patients from the Uele endemic in Central Africa. Evaluation of stable and radioactive iodine kinetics in the thyroid gland and in the plasma brought to light 2 different types of behavior of the thyroid metabolism. In the first type, the following findings were obtained in the glands: low iodine concentration, normal or increased iodine content, and a high MIT*/DIT* ratio with only traces of T4* in the pancreatic hydrolysate2; on the other hand, evidence was given of the presence in the gland of a single homogeneous iodine pool with a low organic I131 output. Such results imply a definite retardation of the hormonogenesis and secretion mechanisms. So far as the synthesis of DIT* from MIT* is concerned, this retardation is inversely related to the iodine concentration of the gland. In the second type, the I131 turnover rate of the gland is increased, as shown by the high PBI131 levels and the fast release of the organic I131 from the gland. In comparison with the first type, much larger amounts of radiothyroxine were observed in these glands; on the other hand, their iodine content was much lower. This type of dynamics differs from the first type only because of the presence of a hyperactive small iodine pool in the gland. It is concluded that the adaptation mechanism to iodine-deficient conditions is associated with a modification of the normal pattern of the organic iodine metabolism within the gland. The retardation of hormonogenesis is related to the decrease of the iodine concentration of the thyroid tissue.