Tubular function

Aminophenol is a selective nephrotoxic agent and intermpts proximal tubular function (121,122). Disagreement exists concerning the nephrotoxity of the other isomers although they are not as potent as 4-aminophenol (123,124). Respiration, oxidative phosphorylation, and ATPase activity are inhibited in rat kidney mitochondria (125). The aminophenols and their derivatives are inhibitors of 5-Hpoxygenase (126) and prostaglandin synthetase... 

The Assessment of the Tubular Function of the Kidneys Bertil Josephson and Jan Ek... 

Natiuretic response to diuretics including fruse-mide and bumetanide is reduced as a result of decreased renal tubular secretion of diuretic Thus, age-related changes in renal tubular function may influence not only pharmacokinetics but also drug action on the kidney (pharmacodynamics). 

Fux CA, Christen A, Zgraggen S, Mohaupt MG, Furrer H. Effect of tenofovir on renal glomerular and tubular function. AIDS 2007 21(ll) 1483-5. 

The loop diuretics are usually required in treating chronic renal failure, since drugs with lesser intrinsic activity are not sufficiently effective when tubular function has been compromised greatly. Larger than normal amounts of furosemide are frequently employed, and thus it is especially important to monitor the patient for... 

Many glomerular diseases, such as those associated with diabetes mellitus or systemic lupus erythematosus, exhibit renal retention of salt and water. The cause of this sodium retention is not precisely known, but it probably involves disordered regulation of the renal microcirculation and tubular function through release of vasoconstrictors, prostaglandins, cytokines, and other mediators. When edema or hypertension develops in these patients, diuretic therapy can be very effective. If heart failure is also present, see the warnings mentioned above. 

A form of salt loss in infancy was long considered to be due to renal tubules that were refractory to aldosterone. Recent studies have described variant roots of the condition, either mutations in the mineralocorticoid receptor, the genes coding the epithelial sodium channel (ENaC), or other causes [6]. Many infant patients recover spontaneously, probably due to maturation of proximal tubular function. 

Aminophenol is a selective nephrotoxic agent and interrupts proximal tubular function. 

Colchicine is cleared by a different CYP450 isozyme than fluvastatin and pravastatin are, but another possible mechanism is synergistic myotoxicity, since colchicine causes myopathy by disrupting tubular function with subsequent vacuolization. Patients taking colchicine should be informed about possible muscular and gastrointestinal adverse effects and advised to stop. 

The filtration-reabsorption theory of renal function indicates that the two main factors which come into play are the amino acid blood levels and the tubular function (both reabsorption or eventually secretion). For early references to studies of filtration and tubular reabsorption of amino acids in the kidney, see S17. 

It is only when the renal tubular function becomes disturbed that hyperamino aciduria appears, in comparison to normal subjects, under the influence of protein overloading in the diet (S34). Dubois et al. attribute also to the same renal tubular deficiency the temporary rise in amino aciduria observed in the first days of high-protein dietary treatment of kwashiorkor cases (D25, D26), a situation which has also been seen by others (C9, M4). It has been attributed both to hepatic and renal deficiencies (C3). 

According to Jonxis and Huisman (J6, J9, J12), hyperamino aciduria may be observed among the other members of the family of a patient with common rachitis and may sometimes (but not always) be corrected by vitamin D administration. There are presumably different grades of hereditary vitamin sensitiveness of the renal tubular function to vitamin D. The regulation does not take place through the mediation of the parathyroid hormone. 

Duarte CG, Chomety F, Giebisch G (1971) Effect of amiloride, ouabain and furosemide on distal tubular function in the rat. Am J Physiol 221 632-640... 

The most useful way to utilize urine electrolyte information is to calculate the fractional excretion (FE), which is the proportion of the filtered load that is excreted from the plasma. If both tubular function and plasma electrolyte values are normal, increases in electrolyte FE values clearly reflect a decrement in GFR. With tubular malfunction, the direction of the change in FE values depends on the net direction of electrolyte transport (i.e., FE will increase for electrolytes that are primarily reabsorbed and will decrease for secreted electrolytes) (Finco 1997 Stockham and Scott 2002). 

Although FE of sodium is most commonly used to assess tubular function, FE of magnesium has been shown to be the most sensitive index in detecting low-level tubular injury in humans (Futrakul et al. 1999 Kang et al. 2000 Oladipo et al. 2003). Increases in FE of magnesium and/or calcium have also been shown to serve as sensitive indices of effects on renal function unrelated to overt renal injury (Lam and Adelstein 1986 Barton et al. 1987 Tuso and Nortman 1992 Eliott et al. 2000). 

Emeigh Hart SG, Kinter LP (2005) Assessing Renal Effects of Toxicants in vivo. In Tarloff JB, Lash LH (eds) Toxicology of the Kidney, 3rd edn. CRC Press, Boca Raton, pp 81-147 Finco DR (1997) Kidney function. In Kaneko JJ, Harvey JW, Bruss ML (eds) Clinical Biochemistry of Domestic Animals, 6th edn. Academic Press, San Diego, pp 441—485 Futrakul P, Yenrudi S, Futrakul N et al. (1999) Tubular function and tubulointerstitial disease. Am J Kidney Dis 33 886-891... 

Due to size limitations, most enzymes present in plasma are not filtered into the urine but there are some exceptions (e.g., lysozyme) these will be increased in the urine if tubular function (and uptake of filtered protein) is decreased. In addition, if glomerular injury accompanies tubular injury leakage of larger molecular weight proteins may occur and plasma source enzymes that ordinarily would not be filtered may appear in urine. AST, LDH and IALP may thus appear in urine. 

An increase in the level of calcium delivered to the kidneys leads to hypercalciuria and kidney stones. Proximal tubular functions of the... 

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