Plasma norepinephrine response to tilting in essential hypertension.

A significant increase in the plasma concentration of norepinephrine on tilting 19 normal st:bjects from the horizontal to 600 upright is described. Evidence that this represents an increased neuj-oadrenergic activity to maintain cerebral circulation despite the periph-e-pooling of blood has previously been reported. When 9 subjects with severe essen-LI il hypertension were similarly tilted, the rise in plasma norepinephrine concentration m as insignificant. This may indicate a diminished neuroadrenergic activity in essential hypertension due to compensatory reflexes from the baroreceptor regions. rji ERE is sufficient evidence to indicate l hpat essential hypertension is not due to in(1-(used neuroadrenergic activity.1-3 The deiii .:istration of elevated levels of urine nor-epiiid,)irine excretion in only 16.4 per cent of 500 hypertensive patients is additional evidence .4 Conversely, there is suggestive evi-denl j of a diminished neuroadrenergic activ-tly in essential hypertension. Gellhorn, in his monograph "Autonomic Imbalance and the Hypothalamus" cites the classical investigation of earlier workers to support the general thesis that a "fall of the blood pressure leads to increased sympathetic and adrenal discharges , and that a rise of blood pressure causes increased parasympathetic discharges. "5 Sun-din demonstrated a 3-to 4-fold increase in urine norepinephrine excretion on tilting normal subjects from the horizontal to an upright position.6 In hypertensive subjects the rise was only about 60 per cent. He suggested that the chronically elevated pressure in the baroreceptor areas in essential hyper-tension leads to a state of diminished endog-enous norepinephrine production. A previous report from this laboratory described the measurement of a significant increase in the concentration of plasma nor-epinephrine within minutes of tilting normal subjects from the horizontal to 600 upright. A failure to detect a significant rise in subjects with postural hypotension was also described. In order to investigate further the thesis of a diminished neuroadrenergic activity in essential hypertension, this method was extended to hypertensive subjects. METHOD Nineteen normotensive subjects (resting dias-tolic pressure below 90 mm. Hg), with a mean age of 59 years (range 29 to 80), served as a control group. These were compared with 9 subjects with essential hypertension (resting diastolic pressure above 100 mm. Hg), with a mean age of 60 years (range 43 to 73). Thirteen subjects formed an "intermediate" group (resting diastolic pressure 90 to 100 mm. Hg). All were ambulatory and none was on medication. The usual clinical and laboratory methods were used to eliminate patients with an identifiable cause for their …