1. An inverse relationship was found between plasma noradrenaline and reactivity to exogenous noradrenaline in normotensive subjects.
2. The relationship between plasma noradrenaline and reactivity was disturbed in age-matched patients with essential hypertension.
3. A multiple-regression analysis showed a highly significant correlation between adrenergic activity and reactivity to noradrenaline and the mean arterial blood pressure level (r = 0·91). The results suggest that adrenergic activity and pressor response to noradrenaline combined are important determinants of arterial blood pressure.
4. An inverse relationship could also be demonstrated between plasma renin activity and reactivity to exogenous angiotensin II. No difference was observed between normotensive and hypertensive subjects.