FACTORS AFFECTING THE ABILITY OF THE RENAL MEDULLA TO EXERT AN ANTIHYPERTENSIVE FUNCTION

To examine whether changes in renomedullary osmolality and the activit y of the renin-angiotensin system may influence the ability of the ren al medulla to exert are antihypertensive function, rats were exposed t o several manoeuvers. These affected either the medullary osmolality o r the renin-angiotensin system (salt or saccharose load, salt depletio n, treatment with captopril alone or in combination with salt depletio n). A comparison of the antihypertensive capacity of the renal medulla was studied by transplanting renal medullae from the various groups i nto one-kidney one-clip hypertensive rats. A significant and quantitat ively similar reduction in blood pressure was: observed in hypertensiv e rats that received transplants of the medullae from control, salt or saccharose loaded rats and captopril treated rats. In contrast, medul lae from salt depleted rats did not affect blood pressure when transpl anted into hypertensive animals. The addition of captopril restored th e antihypertensive function of renal medulla in salt depleted rats. Th e 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.