Stop-flow analysis of creatinine excretion in the dog

¹ Department of Physiology, University of Minnesota, Minneapolis, Minnesota

Urinary excretion patterns of creatinine and inulin under stop-flow conditions in male mongrel dogs were compared. Evidence for a weak creatinine secretory mechanism at the proximal tubule level include the following: 1) Exogenous creatinine in the stop-flow samples appears prior to inulin when both are injected midway during a 10-min ureteral clamping period. 2) The ratio of creatinine/inulin U/P values (creatinine clearance ratio) shows a peak and a distribution coextensive with PAH/inulin clearance ratios. 3) Self-depression of the peak stop-flow creatinine clearance ratio was obtained at high plasma creatinine concentrations. 4) High plasma p-aminohippuric acid levels depressed the free-flow and peak stop-flow creatinine clearance ratios and, conversely, high plasma creatinine concentration depressed free-flow and peak stop-flow PAH clearance ratios (competitive inhibition). 5) Probenecid reduced free-flow and peak stop-flow creatinine clearance ratios (creatinine secretory mechanism blocked). The mean free-flow creatinine/inulin clearance ratios in 44 clearance periods was 1.2±0.1 (sd), compared to the peak stop-flow ratio of 1.8±0.4 (sd) (N = 20) at plasma creatinine concentrations less than 20 mg/100 ml.