The extrathyroidal conversion of 3,5,3'-triiodothyronine to 3,5-diiodothyronine in patients with liver cirrhosis.

Simultaneous kinetic studies of 3,5-diiodothyronine (3,5-T2) and T3 were performed in 8 patients with biopsy proven cirrhosis and in 15 healthy subjects using the single injection, noncompartmental approach. The following T3 kinetic data were obtained in patients with cirrhosis and normal subjects (mean +/- SD): serum T3 (nmol/liter) 1.27 +/- 0.30 vs. 1.79 +/- 0.28 (P less than 0.001); MCR [liters X day-1 X (70 kg)-1] 22.9 +/- 5.3 vs. 26.7 +/- 4.4 (P less than 0.10); production rate [nmol X day-1 X (70 kg)-1] 29.0 +/- 9.6 vs. 47.7 +/- 9.0 (P less than 0.001). In patients with cirrhosis serum 3,5-T2 levels were reduced to 58 +/- 38% of those found in normal subjects (P less than 0.02). The MCR was unaffected, 125 +/- 85%, whereas the production rate was reduced to 57 +/- 26% (P less than 0.005). The conversion rate from T3 to 3,5-T2 was unaltered, 96 +/- 34% of that found in normals. It is concluded that reduced serum levels of 3,5-T2 in cirrhosis are due to a diminished amount of substrate, T3, and not to decreased 3'-deiodination of T3 or to an increase clearance of 3,5-T2.