A. Pruna

Proton Nuclear Magnetic Resonance Spectroscopy of Urine and Plasma in Renal Transplantation Follow-Up

Urine and plasma samples from 39 patients who underwent renal transplantation were analyzed by proton nuclear magnetic resonance (NMR) spectroscopy. The most relevant resonances for evaluating renal function after transplantation were those arising from citrate, trimethylamine-N-oxide (TMAO), alanine, and lactate when compared to creatinine. A resonance at 3.7 ppm was related to cyclosporine toxicity when associated with elevated levels of TMAO. The respective variations in these metabolites in urine could contribute to prognosis and diagnosis of renal function impairment related to cyclosporine toxicity or overdosage, or to rejection. Thus, NMR spectroscopy should improve the follow-up and management of renal transplantation patients.

Renal and Hypertensive Complications of Extracorporeal Shock Wave Lithotripsy: Who Is at Risk?

Extracorporeal shock wave lithotripsy (ESWL) is now used in the treatment of about 90% of renal and ureteral stones. Because of the non-punctual delivery of energy to the stone, a small volume of renal parenchyma is injured giving place to a fibrous scar which can be shown by highly resolutive imaging techniques like magnetic nuclear resonance. Isotopic clearances point to a reduction of 15% in the renal plasma flow on the side of the lithotripsy, but this alteration appears to be transient in nature. In a few cases an abrupt onset of transient hypertension has been reported in clear relation to a compressive perirenal hematoma. The responsibility of ESWL in the late occurrence of permanent hypertension is, however, still uncertain, probably because of the difficulty in showing that this occurrence is not only related to the older age of the patient. The American Food and Drug Administration-sponsored multicentric study begun in 1992 should solve this issue in the future. Recent articles suggest that altered renal function prior to ESWL would predict the late occurrence of hypertension and worsening of renal failure. Furthermore, age and the resistance index of arcuate or interlobar renal arteries (measured by Doppler) could help to screen patients at risk of developing hypertension. In practice in patients over 60 years of age and/or with a plasma creatinine of >to 300 micromol/l, ESWL should be performed with caution, and renal function and blood pressure should be carefully monitored.

Critical Role of Oxalate Restriction in Association with Calcium Restriction to Decrease the Probability of Being a Stone Former: Insufficient Effect in Idiopathic Hypercalciuria

The probability of being a stone former (PSF) was calculated in 3 groups of idiopathic calcium stone formers [with normocalciuria (NC), dietary hypercalciuria (DH) and idiopathic hypercalciuria (IH)] in 4 conditions: while on a free diet; on a calcium- and oxalate-restricted diet during 4 days; after an oxalate load, while on a 1.5-gram calcium diet, and after an oxalate load while on a calcium-restricted diet. Combined calcium and oxalate restriction significantly decreased PSF only in NC and DH whereas the decrease was not significant in IH because of a concomitant significant increase in oxalate excretion. Increase of PSF with the oxalate load was significantly greater during a calcium-restricted diet than during the 1.5-gram calcium diet in all groups of patients (4, 6 and 12 times greater in NC, DH and IH, respectively). These data show the critical role of oxalate restriction when calcium is restricted in order to decrease the PSF. This combined restriction is however not sufficient in idiopathic hypercalciuric patients to decrease their PSF.

Evidence for Magnesium Depletion in Idiopathic Hypercalciuria

Magnesium accounts for about 20% of the total inhibitory activity of urine with respect to calcium stone formation1. Magnesium depletion has been shown to cause calcification in the proximal tubule cells and in the tubular lumen in rats2 and to be responsible for nephrocalcinosis in children. Based on these data, magnesium deficiency has been suspected as a factor in the pathogenesis of calcium stone formation although it has been observed only rarely3. Moreover, the data on magnesium excretion in stone formers are conflicting, and may even be normal4 or increased5. These discrepancies may be explained by the fact that dietary calcium and calcium excretion were not taken into account, despite the fact that in normal individuals magnesium excretion is directly correlated with calcium excretion6. For these reasons it seemed interesting to us to study magnesium metabolism in various groups of idiopathic calcium stone-formers classified according to calcium excretion during a controlled calcium diet.