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(Hypertension. 2002;39:e27.)
© 2002 American Heart Association, Inc.

Letters to the Editor

No Net Effect of Angiotensin II on Blood Pressure?

Martin P. Schuijt; Pramod R. Saxena; A.H. Jan Danser

Department of Pharmacology, Erasmus Medical Center, Rotterdam, The Netherlands

To the Editor:

With great interest we read the recent study by Carey et al¹ on angiotensin (Ang) II type 2 receptor (AT₂) receptor–mediated hypotension in anesthetized and conscious rats. These data oppose our findings on the lack of AT₂ receptor–mediated systemic hemodynamic effects in anesthetized rats.² To explain this discrepancy, Carey et al propose that the doses of the Ang II type 1 (AT₁) and AT₂ receptor antagonists used in our study (irbesartan and PD123319, respectively) were insufficient to unmask AT₂ receptor–mediated vasodilation. However, the same doses were high enough to observe AT₂ receptor–mediated vasodilation in the rat coronary vascular bed.³ Furthermore, the dose of irbesartan that we used was high enough to fully block the Ang II–induced vasoconstrictor effects in our study, as well as in studies by others.⁴ Moreover, the PD123319 dose that we used is known to result in micromolar concentrations in blood plasma,⁵ ie, concentrations that are high enough to selectively block AT₂ receptors. Higher doses lead to concentrations that also interfere with AT₁ receptors.⁵

Carey et al mention that AT₂ receptors in the adult rat are present in low copy compared with AT₁ receptors. In agreement with this concept, exogenous Ang II induces vasoconstriction in the absence of AT receptor blockers, and AT₁ receptor blockade with either losartan or valsartan results in vasodilation. Unfortunately, the authors did not study the effect of PD123319 alone. If, indeed, Ang II normally has a net vasoconstrictor effect, based on the much larger density of AT₁ receptors compared with . . . [Full Text of this Article]

Robert M. Carey; Nancy L. Howell; Xiao-Hong Jin; Helmy M. Siragy

University of Virginia School of Medicine, Charlottesville, Virginia