Ribonuclease activity in renal failure. Evidence for toxicity

Ribonuclease isolated from human urine is a glucoprotein of molecular weight 33,000. The purified enzyme inhibits: (1) the stimulation of 3H-thymidine uptake into lymphocytes by phytohemagglutinin, pokeweed, and concanavalin A; (2) the growth of pancreatic fibroblastoid cells in in vitro cell culture, and (3) the growth of colonies in bone marrow cell cultures. Ribonuclease levels in the uremic patient vary from 9,500 to 35,000 U/ml (normal 1,041 +/- 247). Serum ribonuclease levels are unaffected by dialytic procedures. It is suggested that the ribonuclease glycoprotein may represent a large number of nondialyzable high molecular weight uremic 'toxins'.