Sympathetic cardiovascular reflex initiated by bradykinin-induced stimulation of cardiac pain receptors in the dog.

1. Bradykinin (0.02-5 microgram) applied to the epicardium of the left ventricle in the open-chest, anaesthetized dog, elicits dose-related reflex pressor effects and acceleration of the heart rate. 2. Bradykinin-induced reflex tachycardia was suppressed after the blockade of beta-adrenoceptors with propranolol, whereas reflex pressor responses were prevented by blocking the alpha-adrenoceptor sites with phenoxybenzamine. 3. Vagotomy and atropine treatment did not affect reflex hypertension and tachycardia to epicardial bradykinin. 4. After spinal section at C1, the pressor responses to epicardial bradykinin were significantly reduced, but still present in all but one experiment. A small acceleration of the heart occurred in two out of five spinal dogs with intact vagi and was absent in three vagotomized spinal dogs. 5. The results indicate the reflex activation of the sympathetic outflow to the heart and blood vessels, mediated mainly at a supraspinal level as a predominant mechanism for the cardiovascular response initiated by bradykinin-induced stimulation of cardiac pain receptors.