Effects of cilnidipine on sympathetic outflow and sympathetic arterial pressure and heart rate regulations in rats

Aims Cilnidipine is a unique Ca2⁺ channel blocker that inhibits both L-type and N-type Ca2⁺ channels. The present study aimed to assess the effects of intravenous cilnidipine on sympathetic outflow and sympathetic arterial pressure (AP) and heart rate (HR) regulations. Main methods Carotid sinus baroreceptor regions were isolated from the systemic circulation in anesthetized and vagotomized Wistar Kyoto rats. Changes in efferent sympathetic nerve activity (SNA), AP and HR in response to a stepwise input of carotid sinus pressure were examined before and during intravenous cilnidipine administration (30 μg/kg bolus + 100 μg kg^{- 1} h^{- 1} infusion, n = 6). Key findings Cilnidipine significantly reduced the AP response range (from 68.0 ± 10.2 to 34.6 ± 4.1 mmHg, P = 0.007) but did not affect the SNA response range (from 90.4 ± 10.3 to 84.7 ± 9.5%, P = 0.297) or the HR response range (from 50.4 ± 10.1 to 48.1 ± 6.2 beats/min, P = 0.719). Significance Cilnidipine, at a depressor dose used in the present study, does not acutely suppress sympathetic outflow from the central nervous system. Also, it spared the sympathetic HR response, suggesting that N-type Ca2⁺ channel blocking action at the cardiac sympathetic nerve endings may be a modest one.