FITC-Inulin Measurement of Glomerular Filtration Rate

Assessment of GFR in conscious, ambulatory rats was performed using a modified version of a protocol described by Dr. Timo Rieg (27). Briefly, animals (Wistar and T2DN, male and female, >48 (aged)-wk-old rats, n ≥ 4 per group) are sedated and then receive a tail vein injection of 2% FITC-Inulin (TdB Consultancy AB, Uppsala, Sweden). The decay in the fluorescence of freely filtered FITC-Inulin is then tracked using a NanoDrop 3300 Fluorospectrometer (Thermo Fisher Scientific). GFR was calculated from the observed decrease in FITC fluorescence and corresponding inulin clearance from the blood. The decrease in FITC fluorescence was a product of the initial fast decay representing the redistribution of FITC-inulin from the intravascular compartment to the extracellular fluid, and the slower phase reflecting clearance from the blood. The differential rate law was used to evaluate changes in FITC concentration. GFR was estimated from the rate constant of the second-order reaction of FITC fluorescence changes.