The sympathetic nervous system and the renin-angiotensin system in borderline hypertension.

1. Plasma catecholamine levels as well as plasma renin activity and plasma renin concentration were compared in normotensive volunteers and in subjects with borderline hypertension. All subjects were studied at rest and during bicycle ergometry. 2. The two groups of volunteer subjects did not differ in the plasma concentrations of noradrenaline and adrenaline, both at rest and during physical activity. The same was true for plasma renin activity and plasma renin concentration. Furthermore, urinary excretion of noradrenaline, adrenaline and 4-hydroxy-3-methoxymandelic acid was similar in both groups. 3. The results do not support the assumption that there is increased sympathetic activity in subjects with borderline hypertension.