Analysis of cardiovascular responses to major products of angiotensin-converting enzyme and angiotensin-converting enzyme 2
Description
The renin-angiotensin system (RAS) is an important regulator of cardiovascular function. The two major enzymes in this system are angiotensin-converting enzyme (ACE), which generates the potent vasoconstrictor peptide angiotensin II (Ang II), and angiotensin-converting enzyme 2 (ACE2), which generates angiotensin-(1-7) (Ang-(1-7)), a heptapeptide described to counteract Ang II effects. The results of studies examining the in vivo actions of Ang-(1-7) are inconsistent; therefore, we investigated the effects of Ang-(1-7) in the anesthetized rat. While Ang-(1-7) had no direct effects of its own, infusion of the heptapeptide (55 pmol/min iv) selectively potentiated systemic vasodepressor responses to iv injections of BK and BK analogs without altering responses to Ang I or Ang II. The potentiation was mediated through the BK B2 receptor and did not involve ACE inhibition, angiotensin type 1 (AT1) or functional Ang-(1-7) receptors, cyclooxygenase products or nitric oxide (NO). The data suggest that Ang-(1-7)-induced potentiation of BK responses does not represent a major means to counteract the pressor effects of Ang II. Responses to Ang II were blocked by the selective AT1 receptor antagonist losartan. Binding of Ang II to AT1 receptors has been described to activate the Rho-kinase pathway. Rho-kinase (ROCK) elicits vasoconstriction by altering the Ca2+ sensitivity of vascular smooth muscle via the inhibition of myosin phosphatase. However, there is little data on the in vivo responses to ROCK inhibition. We therefore sought to characterize the responses to the ROCK inhibitor fasudil in the anesthetized rat. Fasudil elicited robust and sustained decreases in systemic and pulmonary arterial pressure under baseline conditions; these decreases were augmented when tone was acutely elevated with the thromboxane mimic U-46619 or the NO synthase inhibitor L-NAME. Fasudil also significantly attenuated pulmonary vasoconstrictor responses to Ang II, U-46619, and the Ca2+ channel opener Bay K 8644. The effects of fasudil were similar to those of the L-type Ca 2+ channel blocker isradipine. Immunoblot analysis of lung extracts showed an increase in ROCK activity following vasoconstrictor treatment. These results implicate the ROCK pathway in the normal physiologic regulation of vasoconstrictor tone and suggest that its activity may become up-regulated upon exposure to a pathologic stimulus