Arterial wall renin-like activity and blood pressure regulation in the rat.

In this study the Importance of the generation of angiotensin II within the blood vessel wall in determining the pressor response to injected renin was investigated. An injection of renin, given to rats after bilateral nephrectomy, produced a pressor response. The level of circulating renin, although initially elevated, returned to the normal range within three hours. However, the level of renin present in the aortic wall remained significantly elevated for six hours after the injection, as did the pressor response. Infusions of the angiotensin II antagonist saralasin at three and six hours after the renin injection confirmed that the pressor response was maintained by the renin-angiotensin system. An injection of renin into normal rats produced the same initial pressor response as was observed in the nephrectomised rats. However, the blood pressure subsequently returned to the pre-injection level after one hour. In the normal rats the pressor response was not related to the level of renin present within the aortic wall. It was concluded that the activity of the renin present within the blood vessel wall was more relevant to the control of blood pressure than the circulating level. However, when the kidneys were present this local action of the renin-angiotensin system was overriden by renal anti-hypertensive systems. This was not dependent on the presence of the renal medulla since the pressor response after chemical renal medullectomy was the same as that observed in the normal rats. The increase in the level of renin within the aortic wall after the injection of exogenous renin confirmed that renin can enter the walls of blood vessels from the circulation. It was concluded that this occurred by a process of passive diffusion.