Effect of Hypotensive Agents on the Renin-Angiotensin System in Vascular Walls of Spontaneously Hypertensive Rats

Previous investigations have shown that the renin-angiotensin system (RAS) is activated in vascular walls of spontaneously hypertensive rats (SHR). The present study was undertaken to determine whether antihypertensive drugs attenuate this activation. Two calcium channel blockers, nifedipine and nitrendipine, and the diuretic muzolimine were applied to SHR for 2-4 weeks, and angiotensin (ANG) l-forming angiotensinogenase (AIFA) and ANG I converting enzyme (ACE) activities were determined. The values for both enzymes were elevated in arterial tissues of SHR (P < 0.01), whereas in venous walls AIFA activity was decreased (P < 0.01). All hypotensive drugs reduced arterial ACE activities in SHR (nifedipine and muzolimineP < 0.01; nitrendipineP < 0.05). Angiotensin l-forming angiotensinogenase activity was increased following treatment with nifedipine (P < 0.01) but reduced by nitrendipine (P < 0.05); with muzolimine, no significant alterations were observed. The results obtained indicate that in SHR, stimulation of vascular wall ACE is abolished following treatment with hypotensive agents,and the effect Is independent of their mode of action. It is assumed that the activation of vascular ACE is not caused by, but rather a reaction to, elevated blood pressure.