Non-Creatinine Chromogen and Creatinine Clearance in the Rat

Abstract

A controversy concerning the significance of renal creatinine clearances in the rat has resulted from conflicting observations. Lipp-man (1) reported that the exogenous creatinine clearance is much greater than the endogenous clearance. Fingl(2) reported that the creati-nine/inulin clearance ratio is depressed toward 1 as the plasma creatinine concentration is raised or after administration of para-amino-hippurate or probenecid. Mattel, Wang, and Gingras(3) have also suggested that creatinine is secreted by the renal tubule of the rat. On the other hand Friedman(4) has reported the identity of creatinine and inulin clearances in the rat. Recently Muntwyler and Griffin(5) performed “true creatinine'1 clearances (utilizing adsorption on Lloyd's reagent) and state that the endogenous and exogenous clearances of “true creatinine” approximate each other in the rat. The earlier reports mentioned above were all based upon total chromogen determinations.

In the experiments reported here endogenous creatinine determinations were performed upon the serum and urine obtained from 6 male and 6 female rats of the Slonaker-Addis strain, taken from stock, where they had received a diet which contained 17% protein. Creatinine determinations were performed upon serum and urine samples both by the total chromogen method of Bonsnes and Taussky(6) and by the method of Miller and Miller(7) which utilizes adsorption on Lloyd's reagent to obtain a value for “true creatinine”. The results are given in Table I.

In spite of the relatively small number of observations. it is clear without statistical analysis that non-creatinine chromogen constitutes about one-third of the total chromogen in rat seruw, while it constitutes not more than one-tenth of the total chromogen in rat urine. These values are similar to. but less striking than. those obtained in plasma and urine by lIuntwyler and Griffin, who used Wistar strain rats. which have a common genetic ancestry with those of the Slonaker-Addis strain.