Differential Blocking Action of Dihydropyridine Ca2+ Antagonists on a T-Type Ca2+ Channel (α1G) Expressed in Xenopus Oocytes

Effects of a New Calcium Channel Blocker, Azelnidipine, on Systemic Hemodynamics and Renal Sympathetic Nerve Activity in Spontaneously Hypertensive Rats

Antihypertensive treatment with dihydropyridine calcium channel blockers elicits sympathetic nerve activation, which may contribute to cardiovascular events. However, recent clinical studies showed that treatment with azelnidipine, a new dihydropyridine calcium channel blocker, significantly reduced blood pressure in hypertensive patients while either maintaining or actually decreasing heart rate (HR). In this study, we examined the effects of azelnidipine and amlodipine on systemic hemodynamics and renal sympathetic nerve activity (RSNA) in anesthetized spontaneously hypertensive rats (SHR). We also examined the effects of these agents on baroreflex functions by infusing phenylephrine (30 microg/kg/min, i.v.) and sodium nitroprusside (10 microg/kg/min, i.v.) into azelnidipine- or amlodipine-treated SHR. Fifty min after administration of azelnidipine (10 microg/kg/min for 10 min, i.v.), mean arterial pressure (MAP) significantly decreased from 153+/-5 to 122+/-5 mmHg; however, HR and integrated RSNA did not change significantly (from 352+/-9 to 353+/-10 beats/ min and 115+/-5% of baseline, respectively). Infusion of amlodipine (50 microg/kg/min for 10 min) elicited similar effects on MAP (from 152+/-5 to 120+/-4 mmHg). However, amlodipine significantly increased HR (from 351+/-9 to 375+/-11 beats/min) and integrated RSNA (165+/-5% of baseline). Analyses of baroreflex function curves revealed that azelnidipine-treated rats showed a smaller baroreflex function than amlodipine-treated rats (p<0.05). These data suggest that azelnidipine possesses sympathoinhibitory effects, which may be one reason why it had less pronounced effects on HR in hypertensive patients.