The Renin-Angiotensin System and Hypertension

In renal hypertension the activity of the renin-angiotensin system may be increased, normal, or depressed. By the clamping of one renal artery, leaving the contralateral kidney untouched, the renin system is stimulated, whereas the activity is normal when the contralateral kidney is removed. In the latter condition, however, the normal renin activity corresponds to a relative increase, since after unilateral nephrectomy plasma renin activity and renal renin decrease. Reduction of renal mass by 70% is followed by suppressed renin activity and hypertension, which in the initial phase is caused by increased cardiac output. In unilaterally nephrectomized normotensive patients plasma renin activity was low, and its response to furosemide was suppressed, confirming the observation in rats that after reduction of renal mass the response of the renin system is blunted. In renal hypertensive rats negative sodium balance develops when blood pressure exceeds 180 mm Hg, resulting in high renin activity, which is the consequence and not the cause of hypertension.