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

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 = 0.623, p less than 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 less than 0.05) and persistently higher plasma epinephrine (PE) concentrations at rest and during equieffective exercise (p less than 0.05). In patients, PNE was directly related to systolic (r = 0.57, p less than 0.01) and diastolic (r = 0.53, p less than 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, 1.31 +/- 0.30 in eight between 35--49 years, and 1.82 +/- 0.12 microgra/m2 in six above 50 years), which was also more pronounced (p less than 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 micrograms/m2 in eight above 50 years). Thus, 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 result in unopposed alpha-adrenoreceptor-mediated vasoconstriction and thereby contribute to the development of hypertension.