Role of uroguanylin, a peptide with natriuretic activity, in rats with experimental nephrotic syndrome

Uroguanylin induces natriuresis and diuresis in vivo as well as in vitro and is found mainly in the intestine and the kidney. However, the roles of uroguanylin in nephrotic syndrome, which is associated with sodium and water retention, have not been determined. Therefore, changes in the urine and plasma concentration of immunoreactive uroguanylin (ir-uroguanylin) and its mRNA expression in the kidney and intestine were examined using rats with puromycin aminonucleoside (PAN)-induced nephrosis. Male Sprague-Dawley rats were separated into control and nephrotic groups, and then the urinary excretion of sodium, protein, and ir-uroguanylin was examined over time. The plasma levels and renal and intestinal mRNA expression of uroguanylin at the periods of sodium retention and remarkable natriuresis also were evaluated. The sequential changes of urinary ir-uroguanylin excretion in the nephrotic group were similar to those of urinary sodium excretion. When the urinary excretion of ir-uroguanylin and sodium peaked, the plasma level of ir-uroguanylin also increased compared with that of the control group. Uroguanylin mRNA expression in the kidney increased during the period of sodium retention and then decreased during the period of remarkable natriuresis. Uroguanylin mRNA expression in the small intestines of control and nephrotic rats were identical. However, in a unilateral PAN-induced proteinuria, uroguanylin expression significantly increased in the PAN-perfused kidney compared with that in the opposite kidney. Considering the natriuretic effect of uroguanylin, these results suggested that uroguanylin plays an important role as a natriuretic factor in nephrotic syndrome via both the circulation and the kidney itself.