In vitro inhibition of protein synthesis by dialysates of plasma from uraemic patients

Abstract

An in vitro technique was devised to test the effects on protein synthesis of plasma dialysate from control and uraemic subjects. Each plasma was dialysed for 24 h to extract the molecules having molecular weight less than 12,000 and the dialysate was lyophilized. Protein synthesis was studied in vitro, using a cell-free system form mouse Krebs II ascites cells. The cells were lysed, and the 30,000 g supernatant ("S-30 lysate") was used to test the protein-synthesizing activity of dialysates of control and uraemic plasma. The rate of protein synthesis was monitored by measuring the incorporation of [14C]leucine into tri-chloracetic acid-precipitable material in the presence of various amounts of plasma dialysate. The presence of normal plasma dialysate increased the [14C]leucine incorporation rate which went through a maximum for 20-22 microliters of added plasma dialysate. In contrast, in the presence of uraemic plasma dialysate, the incorporation rate of the radiolabel decreased as the amount of uraemic dialysate was raised. The ratio of incorporation in the presence of these two kinds of plasma dialysates significantly differed (P less than 0.01) in the range of 15-25 microliters of added plasma dialysate. Heating the uraemic plasma dialysate at 100 degrees C for 1 h prior to incubation almost restored the ratio of [14C]leucine incorporation to control values. Therefore it is concluded that: (1) uraemic plasma inhibits protein synthesis, (2) a significant part of this inhibitory effect is related to thermosensitive molecules, (3) the total inhibition appears to be the results of combined effects of ionic and organic compounds accumulated in uraemic plasma.