Decreased Beta-adrenoreceptor responsiveness as related to age, blood pressure, and plasma catecholamines in patients with essential hypertension.

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Abstract
The role of the sympathetic nervous system as it relates to adrenoreceptor-mediated hemodynamic responses was investigated in patients with essential hypertension and in normal subjects of similar age. An age-related increase in plasma norepinephrine (PNE) concentrations observed in 36 recumbent normal subjects (r [correlation coefficient] = 0.623, P < 0.001) was not found in 56 patients; the latter included some young patients with high values. Sympathetic overactivity in patients (no. = 24) as compared with normotensive subjects (no. = 20) was suggested by a greater increase in PNE upon standing (242 .+-. 34 vs. 155 .+-. 25 pg/ml (SEM [standard error of the mean]), P < 0.05) and persistently higher plasma epinephrine (PE) concentrations at rest and during equieffective exercise (P < 0.05). In patients, PNE was directly related to systolic (r = 0.57, P < 0.01) and diastolic (r = 0.53, P < 0.01) blood pressure. Older age was associated with diminished exercise tachycardia and increased blood pressure responses to exercise, which were both more pronounced in hypertensive patients. This higher pressure/lower heart rate pattern was paralleled by an age-related decrease in isoproterenol sensitivity in normal subjects (0.97 .+-. 0.15 in 6 below 34 yr old, 1.31 .+-. 0.30 in 8 between 35-49 yr and 1.82 .+-. 0.12 .mu.g/m2 in 6 above 50 yr old), which was more pronounced (P < 0.05) in hypertensive patients (1.20 .+-. 1.18 in 7 below 34 yr, 2.42 .+-. 0.30 in 9 between 35-49 yr old and 6.73 .+-. 2.44 .mu.g/m2 in 8 above 50 yr old). An increase in the patients'' blood pressure and age is associated with a progressive reduction in .beta.-adrenoreceptor sensitivity and/or reactivity. Defective .beta.-adrenoreceptor-mediated responses may cause unopposed .alpha.-adrenoreceptor-mediated vasoconstriction and contribute to the development of hypertension.