The Intramedullary Connections of the Area Postrema Involved in the Central Cardiovascular Response to Angiotensin II

Abstract

1. The intramedullary connections of the area postrema involved in the central cardiovascular response to angiotensin were studied in the chloralose-anaesthetized greyhound. 2. In the intact animal the response to vertebral arterial infusions of angiotensin (32 ng/min for 5 min) was decreased by unilateral ablation of the area postrema suggesting that both areas postrema contribute to this response. 3. In the animal in which both vagi were blocked by cooling, the residual sympathetically mediated pressor response was unmodified by unilateral ablation of the area postrema suggesting that each area postrema can mediate the central sympathetic component of the response to angiotensin. 4. In the animal in which one vagus only had been blocked, unilateral ablation of the area postrema, irrespective of side, did not abolish the central cardiovascular response to angiotensin demonstrating that each area postrema can influence both vagi. 5. Midcollicular transection of the midbrain did not significantly alter the response to vertebral arterial infusions of angiotensin. This demonstrated that the central cardiovascular response to angiotensin is not dependent on connections with centres above the midbrain. 6. These results are consistent with the concept that the angiotensin-area postrema system is a neuro-humoral vasomotor centre afferent pathway.