Generation of nitrate during dialysis as a measure of nitric oxide synthesis

Nitric oxide (NO) is a recently identified messenger, which influences the local regulation of blood flow and platelets as well as neuronal and inflammatory pathways. Disturbed NO information might be involved in the uremic syndrome and might also cause hypotension during dialysis. To clarify these issues, we analyzed plasma and dialysis fluid concentrations of nitrate, the stable NO metabolite, in 9 patients during hemodialysis. Plasma nitrate was raised at the onset of dialysis as compared with healthy subjects (83 +/- 9 versus 26 +/- 2 mumol/L). The plasma concentration decreased to 20 +/- 2 mumol/L (p < 0.01) during the dialysis. The relative decrease was more pronounced than the relative reduction in creatinine, phosphate, and urea concentrations. A parallel decrease in nitrate was seen in effluent dialysis fluid (32 +/- 4 to 14 +/- 1 mumol/L; p < 0.01). Calculations of the amount of nitrate coming to and from the dialyzer were performed in 7 of the 9 patients, and in 5 of the 7 patients, generation of nitrate within the dialyzer could be postulated. This might explain the paradoxical venodilation noted during hemodialysis.