title: A method for accurate measurement of GFR in conscious, spontaneously voiding rats.
abstract: Renal function measurement by clearance methods relies on accurately timed urine collection. In small experimental animals, renal function measurement is usually performed under anesthesia and/or with the application of bladder catheters to ensure accurate urine collection. To avoid both anesthesia and the need for bladder catheters we developed a method to measure glomerular filtration rate (GFR) in spontaneously voiding conscious rats. GFR was measured as the urinary clearance of constantly infused 125I-iothalamate. To correct for incomplete bladder emptying urinary clearance of 125I-iothalamate was multiplied by the ratio of plasma and urinary clearance of simultaneously infused 131I-hippuran, a correction method that has been previously validated in humans. Reproducibility of the technique was evaluated by analysis of the results of four consecutive clearance periods during the day (intra-assay variation) in a group of 17 rats and of two consecutive clearance periods on two or three separate days in a group of 20 rats (inter-assay variation), all with normal renal function. Application of the correction method reduced the intra-assay coefficient of variation (mean +/- SD) from 37.4 +/- 14.3 to 5.4 +/- 2.3% (P < 0.05). The mean inter-assay coefficient of variation fell slightly from 23.4 +/- 10.3 to 11.0 +/- 7.2% (P < 0.10). In rats with moderately impaired renal function (N = 8) the intra-assay variation fell from 27.9 +/- 20.7 to 2.7 +/- 1.6% (P < 0.05). Our data show that this correction method is a useful technique to assess renal function in conscious, spontaneously voiding rats.
authors.affiliation: Groningen Institute for Drug studies (GIDS), Department of Internal Medicine, State University Hospital, The Netherlands.
authors.forename: P A
authors.initials: PA
authors.lastname: Marcel de Vries
authors.forename: G
authors.initials: G
authors.lastname: Navis
authors.forename: E
authors.initials: E
authors.lastname: de Boer
authors.forename: P E
authors.initials: PE
authors.lastname: de Jong
authors.forename: D
authors.initials: D
authors.lastname: de Zeeuw
mesh_terms: D000818:Animals; D005919:Glomerular Filtration Rate; D007457:Iodine Radioisotopes; D007465:Iodohippuric Acid; D007483:Iothalamic Acid; D008297:Male; D008433:Mathematics; D009401:Nephrosis / Q000139:chemically induced / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results
chemical_list: D007457:Iodine Radioisotopes; D007465:Iodohippuric Acid; D007483:Iothalamic Acid