Effect of simultaneously administered iopanoic acid and thyrotropin releasing hormone (TRH) on thyroid hormone metabolism in euthyroid subjects.

The cause of serum T4 elevation after iopanoic acid administration was searched in euthyroid subjects. 3 gr iopanoic acid was given per os to 9 healthy volunteers (group I), in other 5 volunteers a TRH test was performed prior to iopanoic acid administration (group II). In group I TSH, T4, FT4I and rT3 levels increased, in group II T3 and FT3I decreased, but no TSH, T4, FT4I increase was seen, obviously, because of the exhaustion of pituitary TSH content by TRH. On the ground of the findings T4 elevation caused by iopanoic acid is predominantly consequence of TSH release and not that of inhibited T4 conversion rate.