Turnover of thyrotropin-releasing hormone in patients with chronic renal failure and chronic alcoholic liver disease

Homogenates of liver and kidney tissues are efficient in degrading TRH, but the liver contains only membrane-bound pyroglutamyl aminopeptidase, active in degrading TRH at the extracellular side of cell membranes. In the present study the effect of liver and kidney failure on the degradation of infused TRH was investigated in man. In 7 uremic patients (group I) and 7 patients with chronic alcoholic liver disease (group II) plasma clearance rate, half-time of disappearance (t1/2) and half time of disappearance of TRH in serum in vitro (t1/2p) was determined. The plasma clearance rate, t1/2 and t1/2p were, respectively, 19.8 +/- 6.2 ml.kg-1.min-1, 6.6 +/- 1.5 min and 16.4 +/- 6.2 min in group I versus 28.2 +/- 4.8 ml.kg-1.min-1, 9.3 +/- 2.6 min and 25.3 +/- 15 min (mean +/- SD) in group II. The volume of distribution of TRH was 19.3% of the body weight in group I and 36.5% in group II. The calculated half-time in the extravascular tissue compartment (t1/2) was 5.4 +/- 1.4 min in group I and 9.2 +/- 2.7 min in group II patients (mean +/- SD). TRH metabolism in the uremic patients was almost identical to that previously reported in normal subjects. In the patients with chronic liver disease plasma clearance rate was significantly greater than in normal subjects, indicating an increased TRH-degrading enzyme activity in the tissue compartment. However, owing to the very large expansion of this compartment, the t1/2 and t1/2t were significantly prolonged. Hence, half-time determination of TRH is no reliable indicator of overall TRH degradation in patients with liver disease.