Increased ratio between changes in blood pressure and plasma norepinephrine in essential hypertension. 
The pathogenic role of the sympathetic system in essential hypertension was evaluated by combined analysis of plasma catecholamine levels and the pressor sensitivity to endogenous norepinephrine.  The latter was estimated indirectly by the ratio between changes in blood pressure and those in plasma norepinephrine after adrenergic neuronal blockage with debrisoquine (given orally for 6 weeks).  Normal subjects and patients with borderline or established essential hypertension had comparable pretreatment levels of plasma norepinephrine and epinephrine.  Debrisoquine lowered plasma norepinephrine by a similar degree (almost 50%) in these three groups; in contrast, blood pressure decreased only slightly in normal or borderline hypertensive subjects [-3.4 +/- 3.2% and -5.4 +/- 1.6% (SE), respectively] but fell significantly more (P less than 0.005) in patients with established essential hypertension (-20.7 +/- 3.9%).  The ratio between percentile changes in blood pressure and those in endogenous norepinephrine levels was comparable in normal and borderline hypertensive subjects (0.03 +/- 0.08 and 0.17 +/- 0.04, respectively), but increased (P less than 0.001) in established essential hypertension (0.62 +/- 0.11).  This suggests that essential hypertension may be maintained, at least partly, by the inappropriate association of normal plasma norepinephrine levels with increased norepinephrine pressor sensitivity.