Effects of hydralazine on renal sympathetic nerve activity in normal and congestive heart failure rats

We investigated the effects of hydralazine on renal sympathetic nerve activity in anaesthetized heart failure rats. Sham-operated rats (group 1) received 0.5 mg kg-1 of hydralazine as bolus and were then infused with 0.3-0.5 mg kg-1 h-1 for 3 h intravenously. Heart failure rats received either the same regime (group 2) as group 1, or the same volume of vehicle (group 3). Heart failure rats exhibited lower mean blood pressure (P < 0.05) and elevated renal sympathetic nerve activity (P < 0.01) in the basal state. In group 2, the mean blood pressure decreased 26% after 30 min of hydralazine administration and remained lower for 3 h, with unchanged renal sympathetic nerve activity. In group 1, the mean blood pressure decreased 36%, and the heart rate and renal sympathetic nerve activity were significantly inhibited. Bilateral vagotomy did not alter renal sympathetic nerve response to hydralazine, but resulted in tachycardia. The results indicate that hydralazine, despite its profound hypotensive effect, did not activate renal sympathetic nerve activity in heart failure rats and inhibited renal sympathetic nerve activity in sham-operated rats. This inhibition was not mediated through the vagal nerve.