AT₂-antagonist sensitive potentiation of angiotensin II-induced vasoconstrictions by blockade of nitric oxide synthesis in rat renal vasculature

Abstract

1. Although the actions of angiotensin II (Ang II) on renal haemodynamics appear to be mediated by activation of the AT₁ receptor subtype, AT₂ binding sites have also been evidenced in the adult kidney vasculature. As NO is known to mask part of the renal effects of vasoconstrictor drugs, we queried whether the Ang II-induced vasoconstrictions could occur via multiple receptor subtypes during inhibition of NO synthesis. We explored the effect of AT₁ and AT₂ receptor (AT-R) antagonists on Ang II-induced pressure increases during NO synthase or soluble guanylyl cyclase inhibition in rat isolated kidneys perfused in the presence of indomethacin at constant flow in a single-pass circuit.

2. In the absence of NO blockade, the AT₁-R antagonist L-158809 (500 nM) antagonized the Ang II-induced vasoconstrictions, while the AT₂-R antagonist PD-123319 (500 nM) had no effect.

3. Perfusing kidneys in the presence of either NO synthase inhibitors, L-NAME (100 μM) or L-NOARG (1 mM), or soluble guanylyl cyclase inhibitor, LY-83583 (10 μM), significantly increased both molar pD₂ (from 9.40±0.25 to 10.36±0.11) and E_max values (from 24.9±3.1 to 79.9±4.9 mmHg) of the concentration–response curve for Ang II-induced vasoconstriction.

4. In the presence of L-NAME, 500 nM L158809 abolished the Ang II-induced vasoconstrictions whatever the concentration tested. On the other hand, 500 nM PD-123319 reversed the left shift of the concentration–response curve for Ang II (molar pD₂ value 9.72±0.13) leaving E_max value unaffected (91.3±7.6 mmHg).

5. In the presence of L-NAME, the potentiated vasoconstriction induced by 0.1 nM and the augmented vasoconstriction induced by 10 nM Ang II were fully inhibited in a concentration-dependent manner by L-158809 (0.05–500 nM). By contrast, PD-123319 (0.5–500 nM) did not affect the 10 nM Ang II-induced vasoconstriction and concentration-dependently decreased the 0.1 nM Ang II-induced vasoconstriction plateauing at 65% inhibition above 5 nM antagonist.

6. Similar to PD-123319, during NO blockade the AT₂-R antagonist CGP-42112A at 5 nM decreased by 50% the 0.1 nM Ang II-induced vasoconstriction and at 500 nM had no effect on 10 nM Ang II-induced vasoconstriction.

7. In conclusion, the renal Ang II-induced vasoconstriction, which is antagonized only by AT₁-R antagonist in the presence of endogenous NO, becomes sensitive to both AT₁- and AT₂-R antagonists during NO synthesis inhibition. While AT₁-R antagonist inhibited both L-NAME-potentiated and-augmented components of Ang II-induced vasoconstriction, AT₂-R antagonists inhibited only the L-NAME-potentiated component.

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