SUMMARY Urinary excretion patterns of creatinine (Cr) and inulin (In) under free-flow and stop-flow conditions were compared in female and male dogs before and after reduction of renal mass. The mean free-flow and mean stop-flow Cr u/p⫽In u/p ratios (where u = urine and p = plasma) in males were 1.03 and 2.05, respectively, before reduced renal mass and 1.25 and 2.94, respectively, after reduced renal mass. In females, these ratios were 1.02 and 1.48 before reduced renal mass and 1.02 and 1.58 after reduced renal mass. The results indicate a weak secretory mechanism for Cr in the proximal tubule which was enhanced after reduction of renal mass in male dogs. Evidence for a secretory mechanism was found in female dogs before and after reduced renal mass, but was less evident than that in male dogs. It is concluded that Cr clearance remains a valid method for measurement of glomerular filtration rate (gfr) in normal dogs and in female dogs with reduced renal mass, but overestimates filtration rate during reduced renal mass in male dogs.
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Robinson et al. (1974) studied this question.