Beta adrenoceptor antagonism and pressor response to phenylephrine

Area of Science:

• Pharmacology
• Cardiovascular Medicine
• Hypertension Management

Background:

• Beta-blockers are commonly prescribed for hypertension.
• Topical alpha-adrenoceptor agonists like phenylephrine can cause blood pressure increases.
• A theoretical risk exists of enhanced pressor response due to unopposed alpha-adrenoceptor activity in patients on beta-blockers.

Purpose of the Study:

• To investigate whether beta-blockade enhances pressor responsiveness to phenylephrine in patients with hypertension.
• To determine if the presumed mechanism of unopposed alpha-adrenoceptor activity is significant.

Main Methods:

• A randomized, double-blind, crossover study.
• 12 hypertensive patients received propranolol, metoprolol, or placebo for 2 weeks.
• Increasing intravenous doses of phenylephrine were infused to assess blood pressure response.

Main Results:

• No significant difference in the phenylephrine dose required to increase systolic blood pressure by 25 mm Hg was observed between beta-blocker and placebo groups.
• Baroreceptor-mediated heart rate decreases were similar across all treatment conditions.
• Beta-blockade did not significantly enhance alpha-adrenoceptor activity.

Conclusions:

• Beta-blockade does not appear to induce appreciable enhancement of alpha-adrenoceptor activity in hypertensive patients.
• Patients with hypertension receiving beta-blockers likely do not have an enhanced pressor response to phenylephrine.