Angiotensin II-induced hypertension in bradykinin B2 receptor knockout mice

The present study was performed to examine the role of endogenous bradykinin (BK) in the development of angiotensin II (Ang II)-induced hypertension in mice. BK B-2 receptor knockout (B2R-/-) and wild-type (B2R+/+) mice (22 to 26 g) were infused with either saline (SAL) or Ang II (40 ng/min) via an osmotic minipump implanted intraperitoneally. On day 12 after implantation, there was no difference in systolic blood pressure (SBP, tail-cuff plethysmography) between SAL/B2R+/+ and SAL/B2R-/- mice (128+/-5 versus 133+/-6 mm Hg, n=24/oroup). In contrast, SEP was higher on day 12 of infusion in Ang II/B2R-/- than in Ang II/B2R+/+ mice (173+/-6 versus 156+/-5 mm Hg; P<0.05, n=27 and 28). Mean arterial pressure (MAP) was also higher in anesthetized Ang II/B2R+/+ mice than in Ang II/B2R+/+ mice (139+/-3 versus 124+/-3 mm Hg; P<0.05, n=16 and 14), Unlike Ang II, long-term norepinephrine (NE) infusion via an osmotic minipump (45 ng/min) caused equivalent increases in SEP in B2R+/+ and B2R-/- mice measured on day 12 after implantation (151+/-4 versus 149+/-5 mm Hg, n=9 and 8). MAP also did not differ on day 13 after implantation between NE/B2R+/+ and NE/B2R-/- mice (120+/-6 versus 122+/-4 mm Hg, n=9 and 8). There were no differences in glomerular filtration rate and urinary sodium excretion among the groups. However, renal plasma flow (RPF) was lower in Ang II/B2R-/- mice than in Ang II/B2R+/+ mice (2.34+/-0.06 versus 4.33+/-0.19 mL.min(-1).g(-1); P<0.05), Acute inhibition of NO synthase (NOS) with nitro-L-arginine- methyl ester (0.5 g.g(-1).min(-1)) in SAL/B-2(+/+) and SAL/B-2(-/-) mice caused equal increases in MAP (142+/-1 versus 145 +/- 1 mm Hg) and decreases in RPF (2.06+/-0.06 versus 2.12 +/- 0.15 mL.min(-1).g(-1)). However, short-term NOS inhibition caused a greater increase in MAP of Ang II/B2R+/+ mice than of Ang II/B2R-/- mice, such that MAP after NOS inhibition in Ang II/B2R+/+ approached that of Ang II/B2R-/- mice (156+/-2 versus 159+/-2 mm Hg). These changes were associated with a decrease in RPF in Ang II/B2R+/+ mice to values similar to those of Ang II/B2R-/- mice before NOS inhibition (2.12+/-0.09 versus 2.34+/-0.06 mL.min(-1).g(-1)). These results demonstrate that the kallikrein-kinin system selectively buffers the vasoconstrictor activity of Ang II. Furthermore, the enhanced susceptibility of B2R-/- mice to Ang II-induced hypertension and renal vasoconstriction is likely due to an impaired ability to release NO by endogenous kinins.