Serial measurement of renal plasma flow.

Effective renal plasma flow was measured two or three times in 1 h in 12 healthy volunteers. Radiohippuran (ortho-iodohippurate) was injected intravenously, and blood samples were obtained 8, 13 and 18 min post-administration. The problem of interference in succeeding measurements by activity from preceding injections was overcome by the use of three different radiolabels. These were, in order of use, 125I, 123I and 131I. The principal energies of gamma- and/or X-ray emission were 30, 160 and 365 KeV, respectively, allowing completely independent assay. A close correlation was observed between the results obtained for the three radionuclides over a wide range of renal plasma flow. The technique is relatively non-invasive and is presented as a suitable method for the important task of measuring renal plasma flow under the influence of drugs, especially of anaesthetics.