Effects of prazosin on reflex changes in heart rate evoked by vasopressor and vasodepressor stimuli in conscious rabbits.

In conscious rabbits prepared for continuous arterial pressure measurements by means of a catheter placed into the main ear artery, intravenous administration of prazosin (5.0 micrograms/kg, i.v. over 20 min) produced a significant decrease in arterial pressure and cardioacceleration. This dose of prazosin inhibited by approximately 70% the pressor effects of phenylephrine. However, prazosin failed to produce significant functional modifications of either the bradycardia or the tachycardia which accompanied the changes in arterial pressure evoked, respectively, by intravenous bolus injections of angiotensin II or acetylcholine. It is concluded that prazosin in the dose studied does not appear to interfere with reflex heart rate responses to vasodepressor or vasopressor stimuli in conscious rabbits.