Kidney inulin clearance

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. 

The clearances of other compounds can be compared with inulin clearances to determine how the kidney functions in the elimination of the test compound. A clearance ratio is constructed by dividing the renal clearance of the test compound (X) by the renal clearance of inulin ... 

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). 

O Donnel P, Burne M, Nemoto T, Keane WF, RabbH Direct measurement of renal function in mice with ischemia-reperfusion injury comparison of inulin clearance with serum creatinine, (abstract) J Am Soc Nephrol 11 606A, 2001 Chiao H, Kohda Y, McLeroy P, Craig L, Linas S, Star RA A-melanocyte-stimulating hormone inhibits renal injury in the absence of neutrophils. Kidney Int 54 765-774, 1998... 

However, although cystine clearance in some cystinurics equals that of inulin, clearance of lysine, ornithine, and arginine is markedly below that of inulin. These discrepancies between the reabsorption of cystine and that of the dibasic monocarboxylic acid are explained by the fact that the kidney possesses only one transport system for cystine, but it possesses two for lysine [171]. 

The determination of renal function in anesthetized animals provides specific information on the effects of chemicals on glomerular filtration rate and renal blood flow. In addition, the ability of the kidney to reabsorb or secrete electrolytes may be determined by fractional clearance of Na+, K+, HCO3, Cl, and so on. Fractional clearance involves comparison of electrolyte clearance to the clearance of a substance such as inulin, which is removed from plasma by glomerular filtration. Thus, fractional clearance takes glomerular filtration rate into account, allowing comparisons of electrolyte transport between treated and control animals even if renal hemodynamics have changed. Nephron function may be assessed by free water clearance, representing the ability of the kidney to remove almost all Na+ from urine. 

While the interspecies variability in metabolism precludes the possibility of a simple allometric relationship for the plasma kinetics of ARA-C, the non-metabolic clearance by the kidney does exhibit a power-law relationship with body weight. Figure 30.7 shows the kidney clearance of ARA-C and its deami-nated product ARA-U on a log-log plot as a function of body weight for mice, monkeys, dogs, and humans. The slope is 0.80, which is essentially the same as the value of 0.77 for inulin (1). 

Figure 24-8 The relationship between serum creatinine concentration and GFR, measured as the clearance of inulin, in 171 patients with glomerular disease.The hypothetical relationship between GFR and serum creatinine is shown as a continuous line, assuming that only filtration of creatinine takes place.The dashed horizontat tine represents the upper limit of a normal serum creatinine (1.4mg/dL). Because of creatinine secretion and/or a creatinine deficit through gut excretion, the serum creatinine consistently overestimates the GFR. (From Sfiemesfi O, Golbetz H, Kriss JP, /Myers BD. Limitations of creatinine os a filtration marker in glomerulopathic patients. Kidney Int I98S 28 830.)...

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