Adrenergic responsiveness in prehypertensive subjects.

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Abstract
To determine if alterations in adrenergic activity precede hypertension, we evaluated the pressor effect of an alpha agonist (phenylephrine) and the chronotropic effect of a beta agonist (isoproterenol) in prehypertensive young men. The subjects were selected from a 5-year follow-up of individuals in the upper ("high") and lower ("low") deciles of the blood pressure distribution in a high school population. At follow-up, the blood pressure differences between groups were maintained. The baroreflex slopes of the high (n = 13) and low (n = 10) blood pressure groups did not differ. The dose of phenylephrine required to increase systolic blood pressure by 20 mm Hg (PD20) was greater in the high blood pressure group than in the low blood pressure group (250 +/- 38 micrograms vs 167 +/- 35 micrograms, p less than 0.05). The dose of isoproterenol required to increase the heart rate by 25 beats/min (CD25) was also greater in the high than in the low blood pressure group (1.9 +/- 0.5 micrograms vs 0.9 +/- 0.2 micrograms, p less than 0.05). The increase in plasma renin activity in response to treadmill exercise was less in the high than in the low blood pressure group (1.8 +/- 0.6 ng/ml/hr vs 3.4 +/- 0.7 ng/ml/hr, p less than 0.03). Overall, systolic blood pressure correlated with PD20 (r = 0.52, p less than 0.01) and CD25 (r = 0.62, p less than 0.001). Plasma norepinephrine correlated with systolic blood pressure (r = 0.44, p less than 0.04) and with PD20 (r = 0.63, p less than 0.001). We conclude that baroreflex sensitivity is not altered in young men with relatively high blood pressure. Insensitivity to alpha and beta agonists may be related to the positive correlation of systolic blood pressure with plasma norepinephrine concentration.