To estimate the glomerular filtration rate (GFR) in horses, an optimum dose of the nonionic contrast medium iodixanol as a tracer was assessed with blood-sample times. Iodixanol was administered intravenously at 10-40 mg I/kg to geldings and mares, and blood was collected 30, 60, 90, 120, 150, and 180 min later. Serum iodixanol concentration was determined by high-performance liquid chromatography (HPLC), and serum urea nitrogen (UN) and creatinine concentrations were also measured. The combination of 20 mg I/kg iodixanol and sampling times of 60, 90, and 120 min after injection was considered to be appropriate for practical use. In clinically healthy horses, the reference values were determined to be 1.90 ± 0.03 ml/min/kg (150.8 ± 2.94 ml/min/m2), consistent with historical data using different tracers. The result suggests that serum clearance of iodixanol is a ready-to-use tool for a screening of alterations in the equine GFR, although it is necessary to perform a more longitudinal study using horses with a variety of renal functions.

To estimate the glomerular filtration rate (GFR) sequentially in conscious rats, we validated a single-blood-sample method using a bolus injection of the nonionic contrast medium iodixanol as a tracer. First, to clarify basal age-related GFR profiles, iodixanol was intravenously administered once weekly at 1500 mg kg(-1) I to clinically healthy male F344 rats from 6 to 15 weeks of age. The blood sample was collected 120 min later, and serum iodixanol concentration was measured by HPLC. GFR values decreased gradually by 9 weeks, presumably due to rapidly increased body weights, and then remained constant from 10 weeks onward. When converting the GFR from body weight to body surface area, the reference range (40-60 ml min(-1) m(-2) ) in the latter was much more stable than that (6-11 ml min(-1) kg(-1) ) in the former. For nephropathy rats induced by cisplatin (3.75-7.5 mg kg(-1) , i.v., single dose), bromoethylamine hydrobromide (BEA, 250-500 mg kg(-1) , i.v., single dose) or puromycin aminonucleoside (PAN, 15 mg kg(-1) day(-1) , s.c., 10 days), GFR decreased or tended to decrease before increasing in serum urea nitrogen (UN) and creatinine concentrations. Accordingly, serum UN and creatinine concentrations became elevated when the GFR decreased to 50-60% of the basal value. This method without urine collection contributes to the reduction of animal numbers because of repeated application to the same animals.