Vasodepressor mechanisms in experimental hypertension: studies using chemical medullectomy

There is evidence that neither activation of the renin-angiotensin system nor changes in sodium balance can fully explain the maintenance of blood pressure in Goldblatt hypertension. Thus, in Goldblatt two-kidney, one clip hypertension in the rat sodium balance is negative and in hypertension of a few months' duration plasma renin initially elevated has returned to normal. When hypertension is reversed by removal of the constricting clip from the renal artery, blood pressure falls within a matter of hours even when hypertension has been present for many months, suggesting that the effect of structural changes in vascular resistance vessels has been overcome. In addition, blockade of the renin-angiotensin system during renal artery declipping does not influence the pattern of the blood pressure fall. We investigated the role of the renomedullary vasodepressor system by inducing medullary necrosis with 2-bromo-ethylamine hydrobromide. This causes a moderate blood pressure increase in normal rats, and partly inhibits the fall of blood pressure in Goldblatt two-kidney, one clip hypertension when the renal clip is removed. Chemical medullectomy is associated with a slightly negative sodium balance, plasma volume contraction, a reduction in plasma renin activity and urinary PGE2, and a minimal elevation in plasma vasopressin. Blood pressure elevation appears to be attributable to inhibition of a vasodepressor system based on the renal medulla. Chemical medullectomy offers a valuable tool for investigating the role of this medullary vasodepressor system.