Adrenal and sympathetic nervous activity in subjects with "low' and "high' normal blood pressure

Possible adrenal and autonomic mechanisms contributing to the onset of essential hypertension were studied in 18 men selected from the upper and lower extremes of blood pressure distribution within a larger population. In eight of the nine pairs of subjects, who were matched for age and obesity, those with higher pressure had significantly higher resting levels of both free adrenaline and noradrenaline sulphate in plasma than their lower pressure counterparts. The higher pressure group showed a positive correlation between diastolic blood pressure and both free and total noradrenaline levels (r = 0.77, P less than 0.05, and r = 0.81, P less than 0.01, respectively). In those with lower pressure, systolic blood pressure correlated closely with plasma adrenaline (r = 0.92, P less than 0.001). Increased adrenal medullary activity and altered autonomic tone appear to be features of the higher range of normal blood pressure and may precede the onset of essential hypertension.