Renal masses

Decreased serum proteins Decreased renal mass, blood flow, and glomerular filtration rate... 

Renal i Glomerular filtration rate i Renal blood flow T Filtration fraction i Tubular secretory function i Renal mass... 

The filtered and secreted marker may irreversibly bind to renal tubule, making their quantification in urine of little value. They are primarily used for static imaging of the kidneys and to obtain information about the functional renal mass. Tc-dimercaptosuccinic acid and Tc-glucoheptonate are good examples of such markers [172 -175]. 

The mechanisms of transfer of molecules and ions across the wall of tubules are more complicated than in the artificial apparatus. In addition to osmosis and simple passive transport viz., ordinary downhill mass transfer due to concentration gradients), renal mass transfer involves active transport viz., uphill mass transport against gradients). The mechanism of active transport, which often occurs in living systems, is beyond the scope of this text. Active transport requires a certain amount of energy, as can be seen from the fact that live kidneys require an efficient oxygen supply. 

Metabolic capacity changes across the life span. Hepatic metabolic capacity rises to a peak around 16 years of age and then declines. In the elderly, hepatic blood flow is reduced by up to 40%. This means that delivery of the drug to the liver is less, leading to reduced metabolism and a longer half-life. Elimination of drug and also drug metabolites is affected. Renal mass may decrease with age, as may... 

R.K. Zalups and M.G. Cherian, Renal metallothionein metabolism after a reduction of renal mass. I Effect of unilateral nephrectomy and compensatory renal growth on basal and metal induced renal metallothionein metabolism. Toxicology 71 83-102, 1992. 

Stockelman et al. (1998) described chronic renal failure in a mouse model of human adenine phospho-ribo-syltransferase deficiency. Hamilton and Cotes (1994) used a partial nephrectomy model in mice with two-thirds of the total renal mass excised to evaluate erythropoiesis and erythropoietin production from extrarenal sources such as the submandibulary salivary gland. Koumegawa et al. (1991) suggested the DBA/2FG-pcy mouse, which develops numerous cysts in kidney cortex and medulla, a progressive anemia and an elevation of blood urea nitrogen, as a useful spontaneous model of progressive renal failure. 

Lariviere R, Lebel M, Kingma T et al. (1998) Effects of losartan and captopril on endothelin-1 production in blood vessels and glomeruli of rats with reduced renal mass. AM J Hypertens 11 989-997... 

Glazer AA, Inman SR, Stowe NT, Novick AC Renal microcirculatory effects of lovastatin in a rat model of reduced renal mass. Urology 50 812-817,1997... 

Zalups, RK Mercer University Macon Macon, GA Mercury nephrotoxicity after a reduction of renal mass. NIEHS... 

Zalups RK, Cherian MG. 1992. Renal metallothionein metabolism after a reduction of renal mass II. Effects of zinc pretreatment on the renal toxicity and intrarenal accumulation of inorganic mercury. Toxicology 71(1-2) 103-117. 

Anderson S, Meyer TW, Rennke HG, Brenner BM. Control of glomerular hypertension limits glomerular injury in rats with reduced renal mass. J Clin Invest 1985 76 612-19. 

Common causes of hypocalcemia are chronic renal failure and hypomagnesemia. In chronic renal failure, hypoproteinemia, hyperphosphatemia, low serum 1,25(0H)2D (reduced synthesis because of inadequate renal mass), and/or skeletal resistance to PTH contribute to hypocalcemia. Magnesium deficiency, as discussed in a later section of this chapter, impairs PTH secretion and causes PTH end-organ resistance. 

Osteitis fibrosa (hyperparathyroid bone disease) is the most common high-turnover bone disease. This disorder is caused by the high concentrations of serum PTH in secondary hyperparathyroidism. Secondary hyperparathyroidism is a consequence of the hypocalcemia associated with hyperphosphatemia and l,25(OH)2D deficiency. Hyperphosphatemia is a result of the kidneys inability to excrete phosphate. l,25(OH)2D deficiency results from the inability of the kidneys to synthesize l,25(OH)2 because of decreased renal mass and suppression of 25(OH)D-la-hydroxylase activity by high concentrations of phosphate. Deficiency of l,25(OH)2D leads to reduced intestinal absorption of calcium and reduced inhibition of PTH secretion by l,25(OH)2D. Skeletal resistance to PTH also contributes to the hypocalcemia and secondary hyperparathyroidism. 

Renal 4 Glomerular filtration rate 4 Renal blood flow t Filtration fraction 4 Tubular secretory function 4 Renal mass... 

The GFR remains the single best index of functioning renal mass. As renal mass declines in the presence of age-related loss of nephrons or coexisting disease states such as hypertension or diabetes, there is aprogressive decline in GFR. The GFR can be used to predict the time to onset of ESKD as well as the risk of complications of chronic kidney disease. Furthermore, accurate assessment of GFR in clinical practice allows proper dosing of drugs excreted renally in order to maximize therapeutic efficacy and avoid potential drug toxicity. 

Pelayo JC, Quan AH, Shanley PE Angiotensin II control of the renal microcirculation in rats with reduced renal mass. Am J... 

An unknown pressor agent has been observed in the blood of animals and man with VE, low renin, hypertension. 3 Suppressed Na, K -ATPase activity in cardiovascular tissues of animals with either one-kidney renal, deoxycorticosterone acetate or reduced renal mass hypertension suggests that this pressor substance is an inhibitor of the Na ,K -ATPase. By inhibiting the Na, K -ATPase of vascular smooth muscle, it is possible that such an agent could contribute to increased vascular resistance or... 

The purpose of a third kind of renal imaging agent is to measure the actual renal mass. To achieve this objective, the metal complex now needs to have different characteristics. Typically, it should have high affinity for the proteins localized in the tubular walls or be thermodynamically weak, allowing transmetalation into renal tubule proteins. Two commercially available Tc complexes fall in this class. The first one is the Tc(V) complex with dimercaptosuccinic acid (dmsa) and the other one is with glucoheptonate. The structure for the first one is quite well known, whereas for the second one a structure is assumed, cf. O Fig. 43.4. 

Indication - known renal mass evaluation. NOT for follow-up of kidney cancer... 

Extrinsic compression on the colon can result from multiple structures such as the iliac vessels, liver, renal masses, and stomach (Macari and Megibow 2001). Compression by one of the iliac arteries is a relatively common finding, and results in a linear extrinsic compression on the sigmoid colon (Fig. 14.21). 

Assessment of renal masses is based upon enhancement and requires an NCCT and contrast-enhanced acquisition to be performed (Szolar et al. 1997 Birnbaum et al. 1996). Currently, noncontrast (NC) CT images are acquired prior to the injection of iodinated contrast agent in order to allow for basehne density measurements of the renal mass and to evaluate for calcification and fat. The most important criterion for the differentiation of benign from malignant masses is the presence of enhancement in a lesion (Israel and Bosniak 2005). 

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