, Volume 14, Issue 6, pp 375-379

The renal paracrine peptide system — possible urologic implications of urodilatin

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Summary

Cardiodilatin/atrial natriuretic peptide (CDD/ANP) is a hormone system of great clinical importance. The prohormone CDD/ANP-1-126 is a peptide synthesized in the heart and cleaved during exocytosis into the circulating form CDD/ANP-99-126. Urodilatin (CDD/ANP-95-126) is a homologue natriuretic peptide that differs from CDD/ANP-99-126 by four amino acids. Whereas CDD/ANP-99-126 circulates in blood plasma and is not excreted into the urine, urodilatin is detected only in urine. Urodilatin exerts its renal effects in a paracrine fashion. After its secretion from cells in the distal tubule, it interacts with luminally located receptors in the collecting duct, resulting in increased diuresis and natriuresis. Results suggest that urodilatin plays an important role in the physiologic regulation of fluid balance and sodium homeostasis. Pharmacology studies reveal significant differences when urodilatin and CDD/ANP-99-126 are given intravenously, showing that stronger diuresis and natriuresis are induced by urodilatin as compared with those induced by CDD/ANP-99-126. Clinical studies indicate the prophylactic and therapeutic effect of urodilatin in patients suffering from acute renal failure following heart and liver transplantation. A significant reduction in requirements for hemodialysis/hemofiltration can be achieved using urodilatin. Postobstructive diuresis and natriuresis is probably due to a defective urinary concentrating mechanism and is usually resistant to treatment with antidiuretic hormone. The distal tubule and collecting duct have often been considered to be the site of altered sodium and water excretion following relief of obstruction. Since circulating CDD/ANP-99-126 levels are markedly elevated during obstruction and decrease upon relief of the obstruction, natriuretic peptides may play an important role in this clinical feature. On the basis of recent findings attributing an important role in sodium homeostasis to urodilatin in contrast to CDD/ANP-99-126, future studies have to clarify whether urodilatin, not CDD/ANP-99-126, might be responsible for the altered renal sodium excretion observed in postobstructive diuresis.