Centrally-Induced Vasodepressor Responses to Diltiazem, a Calcium Channel Blocker, in Rats

The effects of a calcium channel blocker, diltiazem, on central cardiovascular regulation were investigated by injecting it intracerebroventricularly (i.c.v.) in urethane-anaesthetized rats. The blood pressure decreased immediately after the injection returning to baseline level 20-30 min later. Both heart rate and abdominal sympathetic nerve activity decreased correspondingly. Diltiazem injected intravenously (i.v.) decreased both blood pressure and heart rate without affecting sympathetic nerve firing. Although the central pressor responses to carbachol and prostaglandin E2 were not affected by i.c.v. pretreatment with diltiazem, diltiazem attenuated the pressor responses to angiotensin II. Furthermore, electrical lesioning of the anteroventral third ventricle (AV3V) area significantly attenuated the depressor responses to diltiazem injected i.c.v. These results suggest that diltiazem injected i.c.v. affects the central nervous system to decrease sympathetic outflow, and thereby to attenuate the central vasopressor effects of angiotensin II in the brain AV3V area.