EFFECTS OF AMIODARONE ON THYROID IODINE METABOLISM IN VITRO1)

Abstract

Since alterations of thyroid function were reported in patients treated with amiodarone, 2-butyl,3-(4-diethylaminoethoxy-3,5-diiodo, benzoyl) benzofuran, the effects of this drug on the active I transport, organic iodine formation, thryoid peroxidase and the enzymatic iodotyrosine deiodination, were studied. In pig thyroid slices the I-transport was affected by amiodarone at concentrations of 10-4 M and 10-5 M, showing a decrease of T/M (tissue/medium) ratios of 20% and 23%, respectively. Lower concentrations produced no significant differences from controls. Iodotyrosine synthesis was poorly affected by 10-4 M and 10-5 M amiodarine. Inhibition of the DIT [diiodotyrosine] formation was greater than that produced for MIT [monoiodotyrosine]. Thyroid peroxidase activity, as measured by the tyrosine-iodinase assay, showed a 20% decrease at 10-3 M amiodarone. None of the other concentrations affected activity of the enzyme, except for 7% at a concentration of 10-4 M. The iodotyrosine deidination was affected by amiodarone only at a concentration of 10-3 M and 10-4 M. Inhibitions were of 22.5%, and 16.8%, respectively. Under the studied conditions amiodarone did not affect the intrathyroidal I metabolism in concentrations which are usually present in sera of patients treated with this drug. It is not possible to rule out an in vivo direct action if amiodarone is substantially concentrated in the human thyroid gland.