Localization of central pressor action of bradykinin in medulla oblongata

The intracerebroventricular injection of bradykinin produces an increase in arterial blood pressure. The site of action for this effect has been reported to be in the lateral septal area, in the hypothalamus, or in the ventral portion of the third ventricle. Bradykinin injected into the fourth cerebral ventricle of unanesthetized rats produced a pressor effect with a shorter latency and a larger maximal effect than when injected in the third or lateral ventricles. Bradykinin in the fourth ventricle was also 10 times more potent than in the third ventricle and 100 times more potent than in the lateral ventricle. No changes in blood pressure were observed when bradykinin was injected into the cerebellum or in the subarachnoid space of the ventral surface of the brain or of the medulla. Microinjections in the medulla oblongata showed that the pressor responses were obtained when bradykinin was injected in the nucleus tractus solitarius or in the dorsal spinal trigeminal tract. No effect was observed after injections were given into the ventral, ventral lateral medulla, or other medullary regions. The data suggest that bradykinin may play a regulatory role in the central control of blood pressure by stimulating sites that are near the dorsal and dorsal lateral surfaces of the medulla and accessible to kinins in cerebrospinal fluid and in the cerebral arterial circulation.