Amiodarone inhibits T4 and T3 secretion but does not affect T4 deiodination to T3 in perfused dog thyroid lobes.

Amiodarone interferes with thyroid hormone homeostasis in several ways. In the present study we assessed if amiodarone has direct effects on thyroid secretion of T4 and T3 and on intrathyroid T4 deiodination to T3 as studied in perfused dog thyroid lobes. 10(-4) mol/l amiodarone inhibited the TSH stimulated T4 secretion to 73.0 +/- 8.3 per cent of control (mean +/- SE, n = 4, p less than 0.05) and T3 secretion to 68.3 +/- 6.2 per cent of control (p less than 0.05). Amiodarone did not alter intrathyroidal T4 deiodination to T3 since the T4/T3 ratio in thyroid effluent was not affected. The mechanism behind the amiodarone effect on the thyroid is unknown but probably different from that responsible for the effect of certain other iodine containing aromatic compounds (e.g. ipodate).