Is 125I iothalamate an ideal marker for glomerular filtration?

Abstract

The triiodinated angiographic contrast medium, iothalamate, has (usually labelled 125I) been used extensively as a marker for glomerular filtration. We have studied the renal handling of 125I iothalamate (IOT) in vivo and in vitro in several species. In renal cortical slices from chicken, rabbit, rat, and monkey, the tissue-to-medium ratio of IOT was twice that of 51Cr-EDTA (EDTA) at 37 degrees C; a difference that was abolished at 0 degree C and markedly reduced by added o-iodohippurate or iodipamide. In five chickens the steady-state renal clearance of IOT (CIOT) was twice (P less than 0.05) that of EDTA (CEDTA) or 3H inulin (C1); a difference that was abolished by administration of 100 mg/kg/hr of novobiocin, an organic anion transport inhibitor. CEDTA was similar to C1 before as well as after transport inhibition. Utilizing the Sperber technique the mean apparent tubular excretion fraction (ATEF) of IOT was 8%, while that of EDTA was 1% (P less than 0.01; N = 10). After novobiocin coinfusion (new steady-state) ATEFIOT was significantly reduced (P less than 0.01) and not different from that of EDTA (-1%). In the same animals the total urinary recovery of IOT was 84 and 57% (P less than 0.01) before and after novobiocin, respectively, while corresponding values for EDTA was unchanged by the inhibitor. In seven rats the renal extraction of IOT was reduced from 29 to 17% (P less than 0.05) by coinfusion of probenecid (5 mg/kg/hr). Corresponding extractions were 82 to 34% (P less than 0.005) and 22% (unchanged) for PAH and EDTA, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular filtration rate measurement and estimation in chronic kidney disease

“…It has been used as 125 I-radiolabeled or without radioactive label, its non-radioactive serum concentration being measured by X-ray fluorescence, high-performance liquid chromatography (HPLC), or by capillary electrophoresis. In a comparison of agents, the plasma clearance of 125 Iiothalamate was 13% higher than that of 51 Cr-EDTA [60]. The difference was reduced by pretreatment of the patients with probenecid, an organic anion secretory inhibitor.…”

“…The difference was reduced by pretreatment of the patients with probenecid, an organic anion secretory inhibitor. Extensive laboratory studies have shown unambiguously that iothalamate is actively secreted by renal proximal tubular cells and may also undergo some tubular reabsorption [60]. The renal clearance of iothalamate significantly exceeds that of inulin in patients with normal renal function The natural logarithm of the iohexol concentration is plotted against the time in minutes.…”

Monitoring renal function: measured and estimated glomerular filtration rates - a review

“…The difference in clearance was reduced by pretreatment of the patients with probenecid, suggesting that tubular secretion of 125 Iiothalamate occurs. Additional studies of the urinary clearances measured during constant infusion showed that the urinary clearance of unlabeled iothalamate substantially exceeded the urinary clearance of inulin in healthy volunteers (8). These data suggest that in humans renal tubular secretion of iothalamate involves an organic anion transport system.…”

How Measuring Glomerular Filtration Rate? Comparison of Reference Methods

“…The absence of tubular secretion and reabsorption was confirmed in a dog model (Griep & Nelp, 1969). However, these reassuring results were not confirmed by Odlind in 1985. This author actually observed in rats a tubular secretion of iothalamate (comparing with 51 Cr-EDTA and using inhibitors of tubular secretion).…”

“…This author actually observed in rats a tubular secretion of iothalamate (comparing with 51 Cr-EDTA and using inhibitors of tubular secretion). In the same view, Odlind described, in 6 healthy subjects, that iothalamate clearance overestimates inulin clearance and that this overestimation is reversible after inhibition of tubular secretion by probenecid (Odlind et al, 1985). In anephric patients, Cangiano described an extra-renal excretion of iothalamate that reached 4 to 8 mL/min.…”