Which effect is caused by selective Beta 2 receptor stimulation?

• A. Bronchial dilation
• B. Increased heart rate
• C. Peripheral vasoconstriction
• D. Decreased mucus production

Answer: (A)

Selective stimulation of beta-2 receptors mainly targets bronchial smooth muscle. When these receptors are activated, the smooth muscle along the airways relaxes, increasing cAMP inside the cells and causing bronchodilation. That widening of the bronchi and bronchioles improves airflow and relieves bronchospasm, which is why bronchial dilation is the primary and most recognizable effect of beta-2 agonists.

Heart rate is governed largely by beta-1 receptors in the heart, so a true beta-2 selective agent has minimal direct effect there (tachycardia would be more of a side effect at higher doses). Peripheral vasoconstriction is mainly driven by alpha-1 receptors, not beta-2. Decreased mucus production is not the central effect of beta-2 stimulation; the key clinically observed action is opening the airways.