Different Effects of L/N-Type and L-Type Calcium Channel Blockers on the Renin-Angiotensin-Aldosterone System in SHR/Izm

Background: The L/N-type calcium channel blocker (CCB) cilnidipine has been demonstrated to suppress sympathetic nerve activity. In the present study, we investigated the effects of cilnidipine on the renin-angiotensin-aldosterone system (RAAS) in SHR/Izm rats to confirm differences from the effects of L-type CCB. Methods: Male SHR/Izm rats received vehicle, cilnidipine (0.3, 3 mg/kg) or amlodipine (0.3, 3 mg/kg) by gavage for systolic blood pressure (SBP) measurement. For biochemical analyses, the experiments were performed under anesthesia. Results: Low doses of cilnidipine or amlodipine had no effect on SBP or RAAS parameters. A high dose of either drug produced similar effects on SBP levels. Although cilnidipine had no effect on plasma renin activity or the plasma angiotensin II level, amlodipine significantly increased these parameters as compared to levels in the vehicle group. The cilnidipine group had a significantly lower plasma aldosterone level and renal cortical tissue norepinephrine level than the vehicle group. Conclusions: Cilnidipine had effects different from those of L-type CCB on the RAAS in SHR/Izm rats. Our results indicate that suppression of RAAS hyperactivity by cilnidipine can be partly explained by its sympatholytic action.