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Effects of chronic beta-adrenoceptor antagonism on plasma catecholamines and blood pressure in hypertension
Insights
Beta-adrenoceptor antagonists significantly reduced blood pressure and heart rate in hypertensive patients. However, these drugs do not appear to lower blood pressure via central or peripheral sympatholytic mechanisms.
Area of Science:
- Cardiology
- Pharmacology
- Neuroscience
Background:
- Hypertension management often involves beta-adrenoceptor antagonists.
- The precise mechanism by which these drugs lower blood pressure is still under investigation.
- Sympatholytic effects, involving reduced sympathetic nervous system activity, are a potential mechanism.
Purpose of the Study:
- To investigate the sympatholytic effects of beta-adrenoceptor antagonists in hypertensive patients.
- To determine if chronic beta-adrenoceptor antagonist treatment alters plasma catecholamine levels, an indicator of sympathetic activity.
- To assess the relationship between plasma norepinephrine and cardiovascular parameters during ambulation and exercise.
Main Methods:
- Measurement of plasma catecholamines (norepinephrine and epinephrine) before and after chronic beta-adrenoceptor antagonist treatment.
- Continuous intra-arterial blood pressure and heart rate monitoring during ambulation.
- Assessment of cardiovascular and catecholamine responses during exercise.
- Analysis of the quantitative relationship between plasma norepinephrine and blood pressure/heart rate.
Main Results:
- Chronic beta-adrenoceptor antagonist treatment led to significant reductions in heart rate and blood pressure.
- Plasma norepinephrine remained a quantitative index of sympathetic activity during ambulation post-treatment.
- No significant changes in mean resting plasma norepinephrine or epinephrine levels were observed after chronic treatment.
- During exercise, plasma catecholamine levels were elevated after acute but not chronic treatment.
Conclusions:
- Beta-adrenoceptor antagonists effectively reduce blood pressure and heart rate in hypertensive individuals.
- The findings do not support a sympatholytic mechanism in the central nervous system or at peripheral presynaptic receptors as the primary mode of action.
- Plasma norepinephrine continues to reflect sympathetic activity even under beta-adrenoceptor blockade.
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.