Effects on renal tubular protein reabsorption of the infusion of free haemoglobin

Abstract. Hydroxy-ethyl-starch cryopreserved blood with a mean free haemoglobin content of 260 μmol/l (SD 57 μmol/l) was infused into five normal volunteers. The renal clearance of six proteins of differing molecular weight was measured together with an analysis of the qualitative changes in protein excretion during the infusion and over the following 48 h. Other aspects of renal tubular function were assessed by the measurement of urinary N -acetyl-β- D -glucosaminidase, phosphate and amino acids. Increased clearance of low molecular weight proteins and N -acetyl-β- D -glucosaminidase occurred during the 12 h following infusion. β₂ microglobulin clearance × 10³ creatinine clearance rose from a mean of 0·4 (SD 0·1) to a mean of 74·5 (SD 32·3) and N -acetyl-β- D -glucosaminidase from 54·2 units/mmol creatinine (SD 18·0) to 1525 units/mmol creatinine (SD 2318). Increased amounts of low molecular weight proteins were detected in the urine by crossed immunoelectrophoresis. Creatinine clearance remained unaltered. It is argued that these changes may be caused by the competitive inhibition of low molecular weight protein reabsorption in the renal tubule by filtered haemoglobin.