Control of thyroid hormone secretion in normal subjects receiving iodides

Area of Science:

• Endocrinology
• Thyroid Physiology
• Pharmacology

Background:

• Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are crucial for metabolic regulation.
• Iodide is an essential component for thyroid hormone synthesis.

Purpose of the Study:

• To investigate the effects of exogenous iodides on thyroid hormone levels and TSH in euthyroid individuals.
• To understand the regulatory mechanisms involved in thyroid hormone homeostasis under iodide load.

Main Methods:

• Administration of saturated solution of potassium iodide (SSKI) to normal male volunteers in controlled phases.
• Measurement of serum concentrations of T4, T3, and TSH at baseline, during SSKI administration, and after withdrawal.

Main Results:

• Exogenous iodides (SSKI) significantly decreased serum T4 and T3 levels.
• A significant increase in serum TSH was observed during SSKI administration.
• Hormone levels returned to baseline after SSKI withdrawal, with changes remaining within normal physiological limits.

Conclusions:

• In euthyroid individuals, iodides appear to inhibit thyroid hormone release.
• The resulting decrease in T4 and T3 stimulates TSH secretion, which counteracts iodide's inhibitory effect.
• A new equilibrium is established, maintaining the euthyroid state despite exogenous iodide administration.