Abstract
We investigated the changes in thyroid hormones by furosemide-induced acute diuresis in healthy subjects. After overnight controlled conditions, 19-or 20-year-old five males were orally administered 40 mg furosemide, and blood was drawn before and 1, 2, 3, 4 and 6 hours after drug administration for the determination of serum total protein (TP) by Biuret method, total T3 (TT3), total T4 (TT4), free T3 (FT3), free T4 (FT4), TSH and TBG by radioimmunoassay (RIA), and T3-U by Triosorb-S kit. FT3 and FT4 assays were performed by RIA kit employing 125I-labelled T4 analogue as tracer. Urine output increased with a peak between 1 and 2 hours, the cumulative amount for 6 hours was 2488±166 ml (mean±SE), resulting in hemoconcentrated TP increase from 7.03±0.14 to 8.01±0.11 g/dl in maximum at 2 hours. The concentration of TT3 at 2 hours, TT4 at 2, 3 and 4 hours, FT3 and FT4 at 2, 3, 4 and 6 hours, and TBG at 3 and 6 hours significantly increased as compared with each value before the drug administration. TSH, T3-U and TT3/TT4 values, and TT3, TT4 and TBG divided by TP to correct hemoconcentration, remained unchanged. These results indicated that the TT3, TT4 and TBG increase seemed to be due to only hemoconcentration without interference with pituitary-thyroid axis.
Because albumin has been known to be a factor in the apparently higher FT3 and FT4 values in such an analogue method, the same correction to FT3 and FT4 by TP instead of albumin was done, and consequently, both the FT3 and FT4 corrected were still significant at 2 hours. As far FT4, however, the changes of free thyroxine index by several fomulas were controversial. Thus, the changes of the free hormone, especially FT4, appeared not to be determined, and should be confirmed by other methods such as equilibrium dialysis. If the significance of the free hormone increase truly occurred in spite of these conflicting results, one of the mechanisms of this possible free hormone elevation might be due in part to furosemide itself, which has been reported to possess the inhibiting effect of T4 on TBG binding.
