Selective and nonselective beta-blockade of the peripheral circulation.

Area of Science:

• Cardiovascular Pharmacology
• Adrenergic Receptor Physiology

Background:

• The impact of selective beta-1 versus nonselective beta-adrenergic blocking drugs on peripheral circulation remains under-investigated.
• Beta-adrenergic receptors play a crucial role in regulating heart rate, blood pressure, and vascular resistance.

Purpose of the Study:

• To compare the effects of selective beta-1 (metoprolol) and nonselective beta (propranolol) adrenergic blocking drugs on peripheral circulation in healthy subjects.
• To assess the impact of these drugs on blood pressure, calf blood flow, and vascular resistance during rest, exercise, and isoproterenol infusion.

Main Methods:

• A double-blind, crossover study involving ten healthy subjects.
• Administration of placebo, metoprolol, and propranolol in increasing doses over several weeks.
• Measurements included calf blood flow, mean blood pressure, calf vascular resistance, and responses to exercise and isoproterenol infusion.

Main Results:

• Both metoprolol and propranolol demonstrated equivalent reductions in exercise heart rate at the studied doses.
• Metoprolol exhibited a greater effect on lowering resting and exercise mean blood pressure compared to propranolol.
• Neither drug adversely affected resting or exercise calf blood flow or vascular resistance.
• Isoproterenol infusion revealed distinct vascular beta-2 adrenergic-blocking effects, with metoprolol showing greater beta-2 receptor sparing.

Conclusions:

• In normotensive individuals, metoprolol is more effective than propranolol in reducing exercise-induced mean arterial pressure when doses are equated for exercise heart rate reduction.
• Both metoprolol and propranolol do not deleteriously affect peripheral calf blood flow or vascular resistance.
• Metoprolol demonstrates a greater selectivity for beta-1 adrenergic receptors, sparing vascular beta-2 adrenergic receptors, as evidenced by isoproterenol challenge.