Renal Clearances of Labelled Inulin (Inulin‐Carboxyl‐¹⁴C, Inulin‐Methoxy‐³H) and a Polyethylene Glycol (PEG 1000) in the Rat

Abstract

Abstract The simultaneous renal clearances of 14 C‐inulin, 3 H‐inulin and PEG 1000 were measured in 10 unanesthetized male Sprague‐Dawley rats by a constant infusion technique. Both the 3 H‐inulin/PEG 1000 and the 3 H‐inulin/ 14 G‐inuiin clearance ratios were significantly below unity. There was a negative correlation between 3 H‐inulin/PEG 1000 or 14 C‐inuIin/PEG 1000 clearance ratios and the clearance of PEG 1000, indicating more efficient “sieving” at increased filtration rates. Inulin (unlabelled, as well as labelled derivatives) is considered unsuitable for the accurate measurement of glomerular filtration rate in the rat.