1. Patients with mild essential hypertension and elevated plasma renin activity, when compared with normal subjects and hypertensive subjects with normal plasma renin, demonstrated features of sympathetic nervous cardiovascular excitation, accompanied by a raised plasma noradrenaline concentration.

2. An elevated heart rate at rest, shortened cardiac pre-ejection period, and greater heart rate reduction with acute β-adrenoreceptor blockade (intravenous propranolol) in high-renin essential hypertension were indicative of adrenergic cardiac excitation. An elevated total peripheral vascular resistance at rest and a greater fall in peripheral resistance with α-adrenoreceptor blockade (intravenous phentolamine) suggested the existence of a neurogenic increase in arteriolar resistance.

3. Blood pressure was normalized by ‘total’ autonomic blockade (atropine plus propranolol plus phentolamine) in the hypertensive subjects with elevated plasma renin activity.

4. These findings suggest that in mild high-renin essential hypertension increased adrenergic drive to the heart and resistance vessels exists. The elevation of blood pressure is sustained predominantly by neurogenic mechanisms. The high plasma renin activity is seen as an expression of sympathetic nervous system overactivity.

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