Determination of simultaneous effective renal plasma flow and glomerular filtration rate with 131-I-ortho-iodohippurate and 125-I-allyl inulin.

Abstract

Abstract This investigation was initiated to study the cause of the difference between the renal clearance of PAH and O 131 IH in dogs and also to demonstrate the feasibility of measuring the simultaneous glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) by the use of 125 I-allyl inulin and O 131 IH. Measurements of the GFR and the ERPF were made with the radioactive materials mixed with inulin and sodium paraaminohippurate. Clearance values as determined by radioactive measurements were compared with the clearance values as obtained by chemical methods. This was done by calculating the analysis of variance for regression and the coefficient of correlation. The measurements of the average GFR using 125 I-allyl inulin agreed with the chemical determinations to within 2.5 per cent. The best agreement between the radioactive and the chemical determinations of the average ERPF was 96 per cent. This good agreement was obtained only with the removal of free 131 I from the infusing solutions, prior infusion of nonradioactive OIH, and also infusion of carrier OIH. Our data would seem to indicate that the difference between the clearance of O 131 IH and PAH is to a large extent due to the binding of a small fraction of the O 131 H to plasma proteins. We were able to achieve rapid and accurate determinations of the GFR and the ERPF using 125 I-allyl inulin and O 131 H. The use of these radioactive materials and the methods described would allow the measurement of these sensitive parameters of renal function to become standard in any institution with a suitable gamma ray detection apparatus.