Handling of iodothyronines by the liver and kidney in patients with chronic liver disease

Abstract

Abstract. Possible arterio-venous gradients of T4, T3, rT3 and 3,3'-diiodothyronine (3,3'-T2) across the liver and the kidneys were measured in 9 patients with varying degrees of liver failure undergoing diagnostic catheterization. Plasma iodothyronine levels were measured in peripheral, hepatic and renal veins before and at 10-min intervals until 60 min after iv injection of 400 μg of TRH. In 2 patients estimated hepatic plasma flow and effective renal plasma flow were determined as well. In these 2 patients, no significant differences between iodothyronine levels in arterial and peripheral venous plasma were found. T4 and T3 levels were not significantly different between peripheral, renal and hepatic veins. Hepatic vein rT3 and 3,3'-T2 concentrations were 10.7 ± 8.3% (mean ± sd, P < 0.005) and 36 ± 18% (P < 0.001) lower than those in the peripheral vein (N = 9). Renal vein rT3 was just (6.2 ± 7.5%, P < 0.05) lower than rT3 in peripheral vein, whereas 3,3'-T2 was not different between the two veins. Estimates of hepatic and renal plasma flow were in agreement with values from the literature. On the basis of these data approximate hepatic clearance rates of 110 and 380 1/day for rT3 and 3,3'-T2 and a renal clearance rate of about 35 1/day for rT3 were calculated. Sixty min after TRH, plasma T3 was increased to 147 ± 56% (P < 0.05) and 3,3'-T2 in peripheral plasma was increased to 142 ± 36% (P < 0.025), whereas plasma T4 and rT3 did not change. These data suggest that the liver is the major site of plasma rT3 and 3,3'-T2 clearance in patients with mild liver disease and probably also in healthy humans. The kidneys may account for roughly 25% of plasma rT3 clearance. The increase in plasma 3,3'-T2 after TRH may be secondary to the rise in precursor T3, but thyroidal secretion of 3,3'-T2 is not excluded.