The Renal Clearance of Alkali-Stable Inulin

Commercial inulin available at present is not a homogeneous product (1). It consists of two major fractions the proportions of which vary: (a) a portion of relatively large molecular weight resistant to heating in alkali; and (b) a portion of smaller molecular weight susceptible to destruc-tion with alkali. In addition, most samples con-tain a small percentage of fructose, which also yields color in the analytical methods for inulin unless removed by treatment with yeast or hot alkali. Two recent reports (2, 3) indicate that the clearance of the alkali-stable and alkali-labile frac-tions of inulin may not be equal. Since some com-mercial preparations of inulin (such as the one used in this study) may contain as much as 50 per cent of the alkali-labile material, considerable errors in estimation of glomerular filtration rate would occur if a difference in clearance of the two fractions exists. The present report indicates that the clearance of the two fractions is identical, within the limits of error of analysis, in confirmation of the prelimi-nary report by Cotlove (1).