Sodium load combined with low doses of exogenous angiotensin II upregulate intrarenal angiotensin II

The present study was designed to evaluate the effects of a salt load combined with exogenous low nonhypertensive angiotensin II (Ang II) doses on Ang II intrarenal regulation.

Sprague-Dawley rats were infused with Ang II nonhypertensive doses (0.1 microg.kg(-1).h(-1) and 5 microg.kg(-1).h(-1)) and saline overload (Na 0.5 M, Na 1.0 M and Na 1.5 M) for 2 h (0.04 ml.min(-1)). Sodium tubular reabsorption, sodium urinary excretion and mean arterial pressure (MAP) were measured. Ang II was evaluated in the kidneys by immunohistochemistry.

Ang II levels in glomeruli and vessels were exacerbated when sodium load and Ang II were given simultaneously, independently of MAP elevation. In tubules, Ang II staining in the presence of sodium overload was greater in the Ang 0.1 groups than in the Ang 5 groups. Compared with the controls, sodium tubular reabsorption rose in the Ang 0.1-Na 0.5 and Ang 0.1-Na 1 groups and sodium urinary excretion decreased in the Ang 5-Na 0.5 and Ang 5-Na 1 groups. MAP increased in the Ang 5-Na 1 and Ang 5-Na 1.5 groups.

We conclude that local renal Ang II levels were upregulated when acute sodium overload and nonhypertensive Ang II doses were administered simultaneously in normal rats, independently from blood pressure and glomerular function changes.