Recovery of intravenously infused chromium EDTA and lithium sulphate in the urine of cattle and their use as markers to measure urine volume.
The renal plasma clearance of the 51Chromium labelled complex with ethylenediaminetetraacetic acid ([51Cr]EDTA) underestimates that of inulin by 5-15%. Interaction of the anionic CrEDTA with polyanions in the glomerular filter and tubular reabsorption may add to the difference. A re-examination of the protein binding of CrEDTA showed that the protein binding is not negligible, because following ultrafiltration in vitro, the molality of CrEDTA was 5% lower in the ultrafiltrates than in the retentates. With a correction for the distribution of small ions this indicates at least 10% binding to human albumin. pKA = 7.36 was found for the equilibrium CrEDTA(H2O)- in equilibrium with CrEDTA(OH)2- + H+. One CrEDTA molecule carries one or two negative charges at near physiological pH. Renal plasma clearance of [51Cr]EDTA may be corrected to glomerular filtration rate (GFR) by multiplication with 1.10.