Endogenous creatinine clearance in the rat: strain variation.

The clearance of endogenous creatinine was examined in five strains of rats (Wistar, Wistar Kyoto, Spontaneously Hypertensive Rats, Biobreeding/Worcester diabetic prone and diabetic resistant rats). Creatinine clearance was compared with inulin clearance as the standard. Conditions for clearance measurements were also varied (anesthesia with constant infusion, overnight collection of urine, fed vs. unfed state, single-injection technique). The clearance of creatinine adequately reflects the glomerular filtration rate in three strains (Wistar, Wistar-Kyoto and the Spontaneously Hypertensive Rat). In the two strains of the Biobreeding/Worcester rat creatinine clearance is consistently lower than the inulin clearance. When creatinine clearance is measured from an overnight collection of urine with food withheld it is always lower than when food is present. This clearance should always be validated by comparison with inulin clearance measured simultaneously or under comparable conditions. The ease with which endogenous creatinine clearance can be measured makes it a reasonable method when large numbers of repeated determinations of glomerular filtration rate are required.