Whole Body and Tissue Inulin and Sucrose Spaces in the Rat

¹ From the Department of Physiology, Washington University School of Medicine, Saint Louis, Missouri

Whole body inulin space in nephrectomized rats, calculated as found inulin/concentration in plasma water, rises exponentially with time, equalling water extractable Na space at about 15 hours, total body water at about 48 hours, and exceeding body volume at 68 hours. The rise is due to inulin stored in cells, cell entry proceeding at high complex rates in liver and spleen and at lower exponential rates in skin and skeletal muscle. Inulin space is initially lower than sucrose space, but rises faster. It overtakes sucrose at 9 hours and progressively exceeds it thereafter. The only meaningful expression of space in nephrectomized animals is obtained by taking plasma water level extrapolated to zero time. Nephrectomy 24 hours prior to inulin injection does not influence the results, indicating that cell permeability to inulin is not significantly changed after nephrectomy. The continuous infusion (with postinfusion recovery) method probably gives correct values in intact subjects because the intracellular inulin is not recovered during collection.