A Method for the Determination of Extracellular Space with 3H Inutin

A method for the extraction and quantitation of 3H inulin from tissues is described. This method does not require either combustion technics or time-consuming acid extraction procedures. Inulin is as soluble in the liquid scintillation medium as it is in water. Therefore, hot-water tissue extracts without further treatment were employed to quantitate l1 inulin. Nearly 100 % recovery was obtained when different 3H inulin internal standards were added either to water or to tissue homogenates. The values obtained with this method for the extracellular space of different tissues of the rat agree with those reported in the literature. THE EXTIIACELLULAI1 sic of tissues has been determined by maimy different methods. One of time commonly used methods is 1)ased on distribution of inulin. However, the colorimetric determination of inulii.i is not accurate due to the presemice of otimer keto acids in the tissue which may contribute an unkmuowmmamnoummtof color (1). A method based on time ineasumrememit of radioactive inulimu would obviate this limumitation. (111 time other hamud, l)ecause of techmmical difficulties (2), conml)ustion o