The role of renal proximal tubule transport in the regulation of blood pressure

The electrogenic sodium/bicarbonate cotransporter 1 (NBCe1) on the basolateral side of the renal proximal tubule plays a pivotal role in systemic acid-base homeostasis. Mutations in the gene encoding NBCe1 cause severe proximal renal tubular acidosis accompanied by other extrarenal symptoms. The proximal tubule reabsorbs most of the sodium filtered in the glomerulus, contributing to the regulation of plasma volume and blood pressure. NBCe1 and other sodium transporters in the proximal tubule are regulated by hormones, such as angiotensin II and insulin. Angiotensin II is probably the most important stimulator of sodium reabsorption. Proximal tubule AT(1A) receptor is crucial for the systemic pressor effect of angiotensin II. In rodents and rabbits, the effect on proximal tubule NBCe1 is biphasic; at low concentration, angiotensin II stimulates NBCe1 via PKC/cAMP/ERK, whereas at high concentration, it inhibits NBCe1 via NO/cGMP/cGKII. In contrast, in human proximal tubule, angiotensin II has a dose-dependent monophasic stimulatory effect via NO/cGMP/ERK. Insulin stimulates the proximal tubule sodium transport, which is IRS2-dependent. We found that in insulin resistance and overt diabetic nephropathy, stimulatory effect of insulin on proximal tubule transport was preserved. Our results suggest that the preserved stimulation of the proximal tubule enhances sodium reabsorption, contributing to the pathogenesis of hypertension with metabolic syndrome. We describe recent findings regarding the role of proximal tubule transport in the regulation of blood pressure, focusing on the effects of angiotensin II and insulin.

Reversible Proximal Renal Tubular Dysfunction after One-Time Ifosfamide Exposure / Journal of the Korean Cancer Association, 대한암학회지

The alkylating agent ifosfamide is an anti-neoplastic used to treat various pediatric and adult malignancies. Its potential urologic toxicities include glomerulopathy, tubulopathy and hemorrhagic cystitis. This report describes a case of proximal renal tubular dysfunction and hemorrhagic cystitis in a 67-year-old male given ifosfamide for epitheloid sarcoma. He was also receiving an oral hypoglycemic agent for type 2 diabetes mellitus and had a baseline glomerular filtration rate of 51.5 mL/min/1.73 m2. Despite mesna prophylaxis, the patient experienced dysuria and gross hematuria after a single course of ifosfamide plus adriamycin. The abrupt renal impairment and serum/urine electrolyte imbalances that ensued were consistent with Fanconi's syndrome. However, normal renal function and electrolyte status were restored within 14 days, simply through supportive measures. A score of 8 by Naranjo adverse drug reaction probability scale indicated these complications were most likely treatment-related, although they developed without known predisposing factors. The currently undefined role of diabetic nephropathy in adult ifosfamide nephrotoxicity merits future investigation.