| Abstract: | Plasma catecholamines were measured before and after treatment with beta-adrenoceptor antagonists in 17 hypertensive patients. Chronic treatment with beta-adrenoceptor antagonists caused substantial reductions in heart rate and intra-arterial blood pressure recorded continuously during ambulation. Before treatment, a quantitative relationship was observed between plasma norepinephrine and blood pressure and heart rate during a variety of activities; a similar relationship was also observed after chronic treatment five of six patients, suggesting that plasma norepinephrine remains an index of sympathetic activity despite the influence of beta-adrenoceptor antagonism. After treatment, plasma norepinephrine tended to be higher at any level of blood pressure, although not significantly so. Chronic treatment caused no significant change in mean resting plasma levels of norepinephrine and epinephrine. During exercise, plasma norepinephrine and epinephrine levels were significantly elevated above control after acute but not after chronic treatment. These observations do not support the hypothesis that beta-adrenoceptor antagonist drugs lower blood pressure in hypertensive man through a sympatholytic mechanism in he central nervous system or at peripheral presynaptic receptors. |
