Factors affecting the ability of the renal medulla to exert an antihypertensive function.

To examine whether changes in renomedullary osmolality and the activity of the renin-angiotensin system may influence the ability of the renal medulla to exert an antihypertensive function, rats were exposed to several manoeuvers. These affected either the medullary osmolality or the renin-angiotensin system (salt or saccharose load, salt depletion, treatment with captopril alone or in combination with salt depletion). A comparison of the antihypertensive capacity of the renal medulla was studied by transplanting renal medullae from the various groups into one-kidney one-clip hypertensive rats. A significant and quantitatively similar reduction in blood pressure was observed in hypertensive rats that received transplants of the medullae from control, salt or saccharose loaded rats and captopril treated rats. In contrast, medullae from salt depleted rats did not affect blood pressure when transplanted into hypertensive animals. The addition of captopril restored the antihypertensive function of renal medulla in salt depleted rats. The results do not support the view that osmolality of the renal medulla regulates its antihypertensive capacity, and suggest that angiotensin II may restrain renomedullary antihypertensive function.