Simplified Method to Measure Glomerular Filtration Rate by Iohexol Plasma Clearance in Conscious Rats

Abstract

Background/Aims: Glomerular filtration rate (GFR) is the best index for evaluating renal function. We aimed to develop a simplified iohexol plasma clearance procedure for GFR measurement in rats without urine collection, animal catheterization or anesthesia, with limited sampling and requiring blood instead of plasma, to further reduce the sample volume and improve animal welfare. Methods: After iohexol injection (129.4 mg), samples were drawn according to 2-compartment kinetics and analyzed by high performance liquid chromatography. Healthy male Lewis rats were used to find a correction factor (CF) to obtain the ‘reference clearance' from the simplified 1-comparment model. This approach was validated using male or female (Lewis, Sprague-Dawley) rats and animals with renal mass reduction (RMR). In additional rats, different simplified approaches were evaluated. Results: Iohexol concentrations in blood and plasma strongly correlated (r = 0.9784, p < 0.0001). A CF of 0.90 enabled the calculation of the reference GFR. Validation results in male Lewis rats were 0.99 ± 0.27 for the reference GFR and 1.03 ± 0.29 ml/min/100 g for the simplified approach. Results in female Sprague-Dawley rats confirmed the suitability of the proposed method. In RMR rats, GFR was 0.14 ± 0.05 and 0.14 ± 0.04 ml/min/100 g for the reference and simplified model, respectively. Conclusion: The procedure we set up to measure GFR in conscious rats was proven to be reliable, required a small volume of blood at only 4 selected time points, without the need to collect urine or catheterize the animals, was applicable to rats from different strains and sexes, both healthy and with renal function impairment. Moreover, the procedure enables the monitoring of GFR changes over time in the same animal, thereby reducing the number of animals to be used.

Revisiting Experimental Models of Diabetic Nephropathy

“…Iohexol is an iodinated, non-ionic radiographic contrast agent that has been proposed as an alternative exogenous marker for GFR evaluation [77]. Recent studies in rats from Carrera et al [81] showed an easy iohexol clearance measurement method, which prevents urine sampling, anesthesia, and animal catheterization. This procedure is similar to the non-steady state inulin clearance method.…”

“…Next, an iohexol bolus is injected to the animal and blood samples are drawn at fixed times after the administration for plasma clearance evaluation. Plasma iohexol concentrations are then measured by HPLC [81]. The tracer concentration decay is finally analyzed according to a two-compartment kinetic model.…”

Impact of Metabolic Surgery on Renal Injury in Pre-Clinical Models of Diabetic Kidney Disease

“…Zhiqing et al [20] also measured serum cystatin C at 8 weeks after DJB, finding that it was elevated relative to values in sham-operated rats. To date, no studies have directly measured glomerular filtration rate using available methodologies including plasma clearance of iohexol and transcutaneous measurement of FITC-sinistrin clearance [27,28].…”

Complications during pregnancy and fetal development: implications for the occurrence of chronic kidney disease

“…Transcutaneous measurement of GFR can detect the clearance rate of a fluorescent inulin-like substance which can be injected through a venous catheter or via tail vein to avoid catheterization thus allowing serial measurements (52, 53). In a study by Carrara et al, injection of non-radiolabeled ioxhexol into conscious restrained rats followed by four small blood draws from a tail vein was sufficient to calculate GFR (54). This procedure, which requires analysis of iohexol by HPLC, was validated for male and female rats under healthy conditions or following renal injury (54).…”

“…In a study by Carrara et al, injection of non-radiolabeled ioxhexol into conscious restrained rats followed by four small blood draws from a tail vein was sufficient to calculate GFR (54). This procedure, which requires analysis of iohexol by HPLC, was validated for male and female rats under healthy conditions or following renal injury (54). MRI with measurement of clearance by a contrast agent can also be used for estimation of GFR (55).…”