EFFECTS OF SUBSTANCE-P ON CARDIOVASCULAR REGULATION IN THE RABBIT

The effect of substance P on blood pressure and aortic reflex was inve stigated in rabbits. Microinjections of substance P and Sar(9), Met(O2 )(11)-SP (a selective NK1-receptor agonist) into the floor of the four th ventricle led to a dose-dependent increase of blood pressure and a sharp enhancement of the baroreflex. These effects were abolished by p retreatment with SR 140333 (a selective NK1-receptor antagonist). Intr aventricular injection of the antagonist alone significantly decreased the amplitude of the aortic reflex. After bivagotomy, the amplitude o f the parasympathetic component of the baroreflex decreased dramatical ly and substance P injections were no longer effective. Our results de monstrate that substance P activation of NK1 receptors plays a major r ole in the modulation of the parasympathetic component of the barocept or reflex.