Molecular inhomogeneity as a source of error in inulin clearance studies

In recent years there has been disagreement among workers in different parts of the world as to whether the straight-line relationship between plasma level and inulin excretion holds, whatever the concentration of the polysaccharide in the blood. The published results, e.g. those of Ferguson, Olbrich, Robson & Stewart (1950) and of Kennedy & Kleh (1953) are not always strictly comparable, on account of differences in the technique employed. Barnard, Bassir & Hough (1955) observed in a number of individuals a marked fall in the renal clearance of inulin with the passage of time, especially 24-48 hr after a single intravenous injection. After considering a few other possibilities, these authors postulated molecular inhomogeneity of the inulin they used as a feasible explanation of their results. In the present paper evidence is presented on some of the physical properties of six different brands of inulin, as well as the fractional excretion of one of these after a single intravenous injection.