Effect of pressor agents on blood pressure, plasma renin activity and plasma aldosterone concentration in essential hypertension

Abstract

The responses of blood pressure, plasma renin activity (PRA) and plasma aldosterone concentration (PAC) to infusion of either angiotensin II (10 ng/Kg/min) or norepinephrine (100 ng/Kg/min) were observed in 25 patients with essential hypertension. The difference in modes of response between low renin essential hypertension and normal or high renin essential hypertension was analyzed. For comparison, 5 patients with Conn's syndrome, 4 with renovascular hypertension, and 5 normotensive subjects were also studied. Following infusion of angiotensin II the changes in diastolic blood pressure (DBP) were +24±3.0 mmHg in low renin essential hypertension and +25±3.1 mmHg in normal or high renin essential hypertension, in PRA -0.28±0.06 ng/ml/h in low renin essential hypertension and -0.69±0.02 mg/ml/h in another and in PAC +3.7±1.4 and +7.6±1.8ng/100ml respectively. There was a significant difference in magnitude of response in PRA between the 2 groups of essential hypertension (p <0.05). Norepinephrine induced rise in DBP with decreases both in PRA and PAC. The mean changes in DBP were +6±1.4mmHg in low renin essential hypertension and +16±2.2 mmHg in another and the pressor response in the later was significantly greater (p <0.01). The changes in PRA were -0.14±0.07 ng/ml/h in low renin essential hypertension and -0.67±0.26 ng/ml/h in normal or high renin essential hypertension, and in PAC -4.9±1.3 and -3.3±1.9 ng/100ml respectively. The greater fall in PRA in normal or high renin essential hypertension was observed but the difference between the 2 groups of essential hypertension was not significant. The changes in PAC did not parallel the changes in PRA. Angiotensin II induced essentially similar effects on blood pressure in both groups but the greater feedback inhibition of PRA was produced by this peptide in normal or high renin essential hypertension than in low renin essential hypertension. Norepinephrine induced significantly greater pressor effect in normal or high renin essential hypertension. The adopted dose of norepinephrine suppressed both PRA and PAC and atendency to the greater fall in PRA was observed in normal or high renin essential hypertension. There was no difference in responses of PAC to both agents between the 2 groups of essential hypertension. © 1975, International Heart Journal Association. All rights reserved.