Pyelonephritis and acute renal failure.

Bacterial invasion of the renal parenchyma, pyelonephritis, is rarely considered as a primary cause of acute renal failure, particularly in adults. We report two cases of acute renal failure occurring in absence of hypotension, urinary tract obstruction, or nephrotoxic medications that are likely the direct consequence of pyelonephritis. The first case involved a 48-year-old HIV-positive woman who presented with 3 days of nonspecific symptoms and was noted to have acute renal failure. Due to unremitting renal dysfunction, a renal biopsy was performed confirming the diagnosis of bacterial pyelonephritis. The second case, a 33-year-old man with HIV disease, presented with fever and was found to have pyelonephritis by urine culture and ultrasonography. These cases represented initial diagnostic dilemmas for the admitting physicians and demonstrate the varied clinical presentations of acute renal failure as a direct consequence of bacterial infiltration of the renal parenchyma.

NHERF-1 is required for renal adaptation to a low-phosphate diet.

The sodium-dependent renal phosphate transporter (Npt2, Na-Pi IIa) is the major regulated phosphate transporter in the renal proximal convoluted tubule. Npt2 associates with a number of PDZ-containing proteins including Na+H+ exchanger regulatory factor-1 (NHERF-1). To determine whether NHERF-1 is involved in the acute regulation of phosphate transport, wild-type and NHERF-1 (-/-) mice were stabilized on a high-phosphate diet and then acutely changed to a low-phosphate diet. At 24 h after the change to a low-phosphate diet, there was a significant decrease in the urinary excretion of phosphate in both groups but the urinary excretion of phosphate in NHERF-1 (-/-) mice was significantly higher than in wild-type animals (1,097 +/- 356 vs. 255 +/- 54 ng/min, P < 0.05). Renal mRNA levels and total cellular Npt2 protein did not differ between the animal groups or in response to the changes in diet. Renal brush-border membrane (BBM) expression of Npt2 protein, however, was lower in NHERF-1 (-/-) mice compared with wild-type. In addition, with both the high- and low-phosphate diets, there was increased detection of Npt2 in submicrovillar domains that were particularly prominent in NHERF-1 (-/-) mice compared with wild-type animals. On the other hand, a change from a low-phosphate diet to a high-phosphate diet was associated with a similar increase in the urinary excretion of phosphate in wild-type and NHERF-1 (-/-) animals. These experiments demonstrate that full renal adaptation to a low-phosphate diet requires NHERF-1, which serves to increase BBM expression of Npt2.

Expression of NHERF-1, NHERF-2, PDGFR-alpha, and PDGFR-beta in normal human kidneys and in renal transplant rejection.

Sodium-hydrogen exchanger regulatory factor-1 and -2 (NHERF-1 and NHERF-2) are adaptor proteins that regulate renal electrolyte transport and interact with the platelet-derived growth factor receptors (PDGFR). The distribution of the NHERF proteins and PDGFR was studied in normal human kidneys and in renal transplant rejection using immunocytochemistry. In normal kidneys, NHERF-1 was detected in proximal tubules. NHERF-2 was detected in glomeruli, peritubular capillaries, and collecting duct principal cells. NHERF-2 was also weakly detected in the proximal tubule. PDGFR-beta was detected in glomeruli but not in tubules while PDGFR-alpha was detected in renal tubules and minimally in glomeruli. Acute and chronic transplant rejection was associated with increased expression of PDGFR-alpha in tubules and expression in the glomeruli. PDGFR-beta expression in the glomeruli was increased in transplant rejection and became detectable in tubules. Expression of NHERF-1 and NHERF-2 was not different in the patient groups. These results indicate that in contrast to the rat, both NHERF isoforms are detected in the human proximal tubule. In renal transplant rejection, there is increased expression of both PDGFR subtypes consistent with a role for PDGF in injury or repair.