A new procedure for evaluation of renal function without urine collection in rat

Background A new procedure to improve the accuracy of inulin assessment and renal glomerular filtration rate (GFR) avoiding urine sampling was compared and validated versus the reference procedure (with urine sampling and Anthrone reaction) in conscious unrestrained male Wistar rats. Methods. The hemodynamic study consisted of a priming dose of inulin (16 mg/kg) and para-aminohippurate (PAH: 8 mg/kg) followed by an infusion of inulin (36 mg/mL) and PAH (5.8 mg/mL) at a rate of 0.055 mL/min until steady-state conditions were reached (105 min). Inulin concentrations from samples were determined by a new enzymatic assay and Anthrone reaction. PAH concentrations were determined according to the standard method described by Smith et al. Results. A high correlation was found between GFR and renal blood flow (RBF) values calculated using the alternative (without urine sampling) and the reference (with urine sampling) clearance techniques (r = 0.98, P < 0.001, and r = 0.97, P < 0.001, respectively). Moreover, a significant and positive correlation between the values obtained from enzymatic and Anthrone inulin assessments was found (r = 0.99, P < 0.001). Likewise, the values of the 95% confidence interval (mean +/- 2 SD) for the enzymatic inulin assay showed a good agreement with those achieved with Anthrone (1.14 +/- 0.21 and 1.14 +/- 0.19 mL.min(-1).100 g(-1) rat body weight, respectively). Conclusions. This new approach has methodological and experimental advantages with respect to traditional procedures, making it a useful tool, not only for research purposes but also in the clinical setting.