A new method of measuring renal function in conscious rats without the use of radioisotopes.

The purpose of the current experiment was to develop fast and accurate assays for measuring glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). An enzymatic method was developed for the determination of inulin, and a colorimetric method was developed for determination of p-aminohippurate (PAH) in the plasma and urine of rats. These assays are easily automated and do not require the use of radioisotopes or corrosive chemicals. Glomerular filtration rate was measured by the clearance of inulin, and effective renal plasma flow was measured by the clearance of PAH. Blood pressure, heart rate, and renal function (urine volume, electrolytes, GFR, and ERPF) were measured in conscious rats for 1.5 h prior to drug treatment and for 3 h after treatment. Baseline renal function was compared to historical data. Acute changes in GFR and ERPF following administration of the vasoconstrictor peptide endothelin-1 (ET-1) were accurately measured with results similar to those obtained with older methodologies. These new methods offer many advantages over previously described methods by eliminating the use of radioisotopes and harsh chemicals. In addition, these methods can be used with an automated instrument with high accuracy and precision. Therefore, these new methods can be used to accurately determine GFR and ERPF and are sensitive enough to detect acute changes in GFR and ERPF in conscious animals.