Effects of angiotensin II on the renal excretion of urodilatin in the isolated rat kidney

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Background

The kidney-derived peptide urodilatin has been suggested to be important in the regulation of natriuresis and diuresis. This hormone has been used clinically as a drug for the treatment of incipient renal failure in cardiac surgery patients and is known to be increased in these patients if renal function is preserved [1]. However, the mechanisms involved in the regulation of the production of urodilatin are far from being clear. This study was designed to determine, if Angiotensin II may influence the renal excretion of urodilatin (V_UROU).

Materials and methods

Isolated kidneys from Sprague-Dawley rats were perfused for 180 min with a pressure of 100 mmHg in a recirculating perfusion system. After an equilibration time of 90 min (baseline-period), the following drugs were added to the perfusion medium: Angiotensin II (AII: n=5); Losartan (LOSA: n=5), and both drugs combined (LOSA-AII: n=5) and the kidneys were perfused for another 90 min (intervention-period). Five kidneys served as controls (CON). Measurements were performed every 30 min. Data of both observation periods were averaged (baseline: 0-90 min; intervention: 91-180 min); baseline data were normalized to 100%. Statistical analyses were performed with ANOVA and Fisher's PLSD.

Results

Data for the intervention period are given in percent of average baseline values (Table 1). RVR: renal vascular resistance; VU: urine flow; V_NaU: urinary excretion of sodium; GFR: glomerular filtration rate; V_UROU urinary excretion of urodilatin.

Conclusions

These observations suggest that V_UROU is affected - directly or indirectly - by vasoconstrictory concentrations of Angiotensin II and may help to explain recent findings on the regulation of the renal excretion of urodilatin; especially the positive relationships of V_UROU with plasma sodium [2] and renal perfusion pressure [3].

Table 1