Kidneys using inulin

Most contrast agents elicit nephrotoxicity because they are primarily excreted by the kidneys. However, when administered in small doses, they constitute a rich source of GFR markers. The two major classes of contrast agents that are finding clinical utility as GFR markers are iodinated aromatic compounds and metal complexes. lodinated aromatics such as iohexol and iothalamate (Fig. 13) are commonly used as contrast agents for computed tomography (GT). They also have pharmacokinetics similar to inulin and hence are useful indicators of renal status [215]. The iodinated molecules used for GFR measurements consist of a triiodo-benzene core and hydrophilic groups to enhance solubility in aqueous medium. 

Inulin is used in an important test for renal failure called the inulin clearance method (Gretz et al., 1993 Chiu, 1994). As inulin is neither secreted nor reabsorbed in the kidney, it can be administered by injection to measure glomerular filtration rate. The relative amounts of inulin in the plasma and urine give an indication of renal function. 

INULIN Inulin is a polymer of D-fructose molecules (fructofuranose), which are linked to each other in fi-2.1 bonds. There is a terminal glucose molecule. Inulin occurs as a reserve food instead of starch in plants, mainly within the family Asteraceae for example Inula helenium L., Asteraceae. In the form of a 10% aqueous solution inulin is used in tests of kidney function (like mannitol). Inulin is not absorbed or metabolised. Since there is no reabsorption in the tubules, the rate of excretion is a measure of the function of the glomerulus (inulin clearance). 

The microinjection technique described by Gottschalk, Morel and Mylle (5) was applied with some minor modifications. Known volumes (10 to 25 nl) of a colored solution of buffered saline containing tritiated inulin and urate labeled with 14c were injected with a calibrated pipette into proximal or distal surface convolutions. Inulin was used as the reference substance (6) and was totally recovered in the urine of the punctured kidney after technically satisfactory microinjections. It was assumed that the injected inulin remained solely within the lumen of the tubule, i.e. the liaihinal membrane was impeinneable to inulin. It was further assumed that labeling of urate did not impair its physiological properties and that excreted 14c represented urate. 

The first section of Table II represents the transepithelial parameters. The fluid/plasma K activity ratio of 1.9 0.2 is significantly greater than unity (P < 0.01) but is not significantly different from an inulin ratio of 1.5 0.2 in the latter part of the proximal tubule of the Necturus kidney. The potassium equilibrium potential (Ej ) calculated from the Nernst equation using the K" " activity ratio yield a value of 16.4 1.0 mV. This is not significantly different from the mean transepithelial PD of 14.5 A 1.5 mV. Thus K ion is in electro-chemical equilibrium distribution across the proximal tubular epithelium of Necturus. 

F. may be used as low-cost sources of rather pure fructose. Their viscosity makes them useful as thickeners, binders and as protective encapsulating agent for flavors, colors and pharmaceuticals. Inulin is used for the production of dietary food. Inulin is not degraded by the enzymes of the mucosa and can be used in diagnostics to determine the filtration rate of the kidney. 

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