The Glomerular Filterability of Inulin and of Different Molecular Weight Preparations of Polyethylene Glycol in the Rabbit

Abstract Jorgensen, K. E., J. V. Møllerand M. I. Sheikh. The glomerular filterability of inulin and of different molecular weight preparations of polyethylene glycol in the rabbit. Acta physiol. scand. 1972. 84. 408–414. It has been claimed on the basis of clearance experiments that inulin is incompletely filterable through the glomerular membrane of the rat kidney (Berglund 1964, 1965). In the present study the renal excretion in the rabbit of inulin and different preparations of polyethylene glycol has been compared during constant infusion of these substances. Identical clearance values were obtained for inulin and polyethylene glycol, having molecular weights of 1500 (PEG–1500) and 4000 (PEG–4000). The ratio of the clearances between polyethylene glycol of a molecular weight of 6000 (PEG–6000) and inulin was smaller than unity (0.89±0.03). Gel filtration analysis of plasma and urine samples indicated unrestricted filtration of inulin through the glomerular membrane of this species. Furthermore, gel filtration and ultrafiltration experiments indicated that the molecular size of inulin and PEG–1500 is similar, while the molecular dimensions of PEG–6000 exceed that of the most high molecular weight fractions of inulin. It is concluded that the clearance of inulin, PEG–1500, and PEG–4000 may be used as a measure of the glomerular filtration rate in the rabbit, whereas the glomerular filtration of PEG–6000 is restricted to some extent. The incomplete filterability of PEG–6000 is attributed to the relatively larger molecular size.