Hypertension in patients on chronic hemodialysis: the role of the renin-angiotensin system.

The effects of volume-loading and removal on mean blood pressure were evaluated in patients with high blood pressure and on chronic hemodialysis. Simultaneous measurements of plasma renin activity, plasma angiotensin II and plasma norepinephrine were made. The patients were divided into two groups according to their levels of plasma renin activity. Group 1 (n = 10) had a basal plasma renin activity below 2.5 ng/ml/hr while the level in group 2 (n = 5) exceeded 2.5 ng/ml/hr. The mean blood pressure of the two groups was 105 +/- 5 mmHg and 107 +/- 4 mmHg, respectively. On the day of hemodialysis, saline loading (0.5 ml/kg/min for 20 min) was followed by routine hemodialysis. The mean blood pressure rose to 113 +/- 6 mmHg in group 1. However, the patients in group 2 did not respond to volume loading and hemodialysis. The plasma renin activity, plasma angiotensin II and plasma norepinephrine were not changed by volume loading in both group 1 and 2. Volume removal by hemodialysis caused a reduction in mean blood pressure in group 2 without alteration of vasoactive hormones. In group 1, the mean blood pressure was not reduced by hemodialysis, accompanied by increases in plasma renin activity, plasma angiotensin II, and plasma norepinephrine. In the high renin group, elevated circulating angiotensin II maintained a high blood pressure and in the low renin group, the renin-angiotensin system influenced the prevention of fall in blood pressure after hemodialysis. These results suggest that the renin-angiotensin system plays an important role in the regulation of blood pressure in relation to volume status regardless of whether the plasma renin activity is high or low.