Comparison of the Effects of Amiodarone and Ipodate on the Rat Heart

Summary

Chronic treatment of rats with amiodarone has been shown to produce hypothyroid-like effects such as a reduction in body and heart weight and increased synthesis of the low ATPase V₃ - cardiac isomyosin (Bagchi, Brown, Schneider and Banerjee 1987). In this report, we have tested the hypothesis that amiodarone causes these effects through the inhibition of intracellular production of triiodothyronine (T₃) from thyroxine (T₄) by comparing the effects of amiodarone with those of ipodate, a potent inhibitor of T₄ to T₃ conversion. Separate groups of rats were given dietary ipodate and amiodarone respectively for six weeks. Both agents increased serum T₄ and T₄/T₃ ratios, a finding consistent with the inhibition of peripheral T₄ to T₃ conversion. However, ipodate failed to produce hypothyroid-like effects on body weight, heart weight and isomyosin transitions similar to those found in the amiodarone group. These data indicate that the hypothyroid-like effects of amiodarone on the rat heart are not due to the inhibition of intracellular generation of T₃ from T₄.

Key-Words

Amiodarone - Ipodate - Myosin Isoenzymes - Thyroid Hormone