Decreased Beta-Adrenoreceptor Responsiveness as Related to Age, Blood Pressure, and Plasma Catecholamines in Patients with Essential Hypertension

SUMMARY The role of the sympathetic nervous system as it relates to adreooreceptor-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 = 0.623, p < 0.001) was not found in 56 patients; the latter included some young patients with high values. Sympathetic overactivity in patients (n = 24) as compared with normotensive subjects (n = 20) was suggested by a greater increase in PNE upon standing (242 ± 34 vs 155 ± 25 pg/ml (SEM), p < 0.05) and persistently higher plasma eplnephrine (PE) concentrations at rest and during equieffecrire 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 six below age 34 years, 131 ± 030 in eight between 35-49 years, and1.82 ± 0.12 Mg/m* in six above 50 years), which was also more pronounced (p < 0.05) in hypertensive patients(1.20 ± 1.18 in seven below age 34 years, 2.42 ± 0.30 in nine between 35-49 years, and 6.73 ± 2.44 fig/m in eight above 50 years). Thus, an increase hi the patientsʼ blood pressure and age is associated with a progressive reduction in /3-adrenoreceptor sensitivity and/or reactivity. Defective /3-adrenoreceptor-mediated responses may result in unopposed a-adrenoreceptor-mediated vasoconstriction and thereby contribute to the development of hypertension.