Inhibition by iodine of the release of thyroxine from the thyroid glands of patients with thyrotoxicosis

Abstract

A B S T R A C T A method has been devised which is free of many of the shortcomings of serial epithyroid counting techniques as an index of the rate of thyroid hormone seeretion. By means of this method, the effect of treatment with Lugol's iodine on the rate of thyroidal secretion of thyroxine (T4) has been assessed in eight patients with thyrotoxicosis due to diffuse or multinodular goiter. The technique involves administration of a tracer dose of inorganic 'I followed several days later by an intravenous tracer dose of "'I-labeled T4. Serial observations of serum protein-bound (PB) 'I and 'I are accompanied by frequent measurements of endogenous serum T4 (T4-'I) concentration. Regardless of whether or not its administration was anteceded and accompanied by the administration of large doses of methimazole, iodine induced a rapid decrease in serum T4-RI concentration which could not be explained by an increase in the peripheral turnover of T., as judged from the metabolism of the "I-labeled hormone. Hence, the decreased serum T4 concentration could only have resulted from decreased secretion of the hormone by the gland. Analyses of specific activity relationships between PB'I or T4-1'I and PB1I made possible estimations of the extent to which iodine had decreased the rate of secretion of T4. From such analysis, and in view of other considerations, it is concluded that the rapid decrease in T4 secretion induced by iodine is not the result of an acute, sustained inhibition of T4 synthesis, but rather results from an abrupt decrease in the fractional rate of thyroidal T4 release.

Evaluation of the Efficacy of Potassium Iodide Preparation for Radioactive Iodine Therapy in Graves’ Disease: A Retrospective Chart Review

“…In our study, KI was administered at a median dose of 150 mg in the KI group and hyperthyroidism was considerably treated before RAIT. High doses of iodine suppress RAIU and thyroid hormone secretion [22,23]. Therefore, RAIU before KI discontinuation may have been suppressed by the above administered dose of iodine, and a 4-day discontinuation of KI contributed to improve RAIU to that equivalent of Japanese GD patients without iodine restriction.…”

Empleo del Yopodato Sódico (Biloptin) en el tratamiento agudo de las complicaciones cardiovasculares severas del hipertiroidismo.

“…El uso de los yoduros en dosis farmacológicas bloquea la secreción de las hormonas toroideas por el efecto de Wolff-Chaikoff (31-33), pero este bloqueo es transitorio y el aumento del yodo intratiroideo, así como el fenómeno de escape que puede ocurrir al cabo de pocos días (34), conlleva el riesgo de exacerbar el hipertiroidismo o de desencadenar una tormenta tiroidea. En todo caso su administración aislada o en combinación con tiocarbamidas, si bien constituye un método terapéutico eficaz en el control rápido del hipertiroidismo, no garantiza la desaturación tisular inmediata de T3 (35,36).…”

“…Los betabloqueadores adrenérgicos, como el propanolol, cuyo empleo se ha hecho frecuente en los últimos años, resultan beneficiosos en el control de las manifestaciones cardiovasculares, particularmente de la taquicardia, pero su efecto es casi exclusivamente a través del bloqueo del sistema adrenérgico y sólo inhiben débilmente la conversión periférica de T4 a T3 en dosis altas (37,38), las que a su vez pueden deprimir la fibra miocárdica y desencadenar o empeorar una insuficiencia cardíaca (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39).…”

An Analysis for Aggravation of Thyroid Function After Discontinuing Potassium Iodine in Graves’ Patients Treated With Methimazole and Potassium Iodine

“…KI is often prescribed to patients with severe thyrotoxicosis because it can effectively suppress thyroid hormone release [5,7,11]. However, it is also well known that this effect sometimes becomes ineffective during the treatment.…”

“…Actually, the administration of KI for GD patients has been shown to be one useful therapeutic choice, which can correct thyroid function very rapidly. It is well known that adequate dose of KI suppresses the release and synthesis of thyroid hormone in the thyroid of GD patients [4,5]. In situations that a rapid correction of thyroid function is required, such as severe thyrotoxicosis containing thyroid storm and preparation for urgent thyroidectomy, KI treatment has also been reported to be definitely advantageous [6][7][8][9].…”