Effects of GFR and renal plasma flow on urine osmolarity

¹ Department of Physiology, University of Michigan School of Medicine, Ann Arbor, Michigan

The effects on total urine osmolarity of renal plasma flow rate (RPF) and glomerular filtration rate (GFR) were determined in dogs during mannitol diuresis. While one kidney served as a control, RPF and GFR in the other kidney were varied by one of the following methods; A—Partial occlusion of the ureter. This decreased GFR with negligible decrease in RPF. B—Partial occlusion of the renal artery. This decreased both GFR and RPF simultaneously. C—A combination of partial ureteral occlusion and partial occlusion of the renal artery to obtain reductions in GFR and RPF other than those attained by methods A or B. GFR was determined by creatinine clearance and RPF by the Fick principle using the renal A-V difference for PAH. Graphical correlations were obtained relating urine osmolarity to GFR and RPF. The data show that the RPF has an important independent effect on urine osmolarity in addition to its indirect action through its effect on GFR.