Which receptor subtype mediates vasodilation and bronchodilation, and is predominantly found in smooth muscle?

Which receptor subtype mediates vasodilation and bronchodilation, and is predominantly found in smooth muscle?

• A. Beta 1 receptors
• B. Beta 2 receptors
• C. Alpha 2 receptors
• D. Dopamine receptors

Answer: (B)

Understanding how beta-adrenergic receptors control smooth muscle helps explain this. Activation of beta-2 receptors, which are abundant in bronchial and vascular smooth muscle, relaxes the muscle. They’re coupled to Gs proteins, so stimulating them raises cyclic AMP inside the cell, promoting smooth muscle relaxation and thus bronchodilation and vasodilation. This is the mechanism behind using beta-2 agonists like albuterol for asthma and other conditions needing airway dilation or improved blood flow to certain tissues. Beta-1 receptors are mainly in the heart, increasing heart rate and contractility, not bronchodilation. Alpha-2 receptors act as autoreceptors that dampen sympathetic output and can influence vascular tone rather than directly causing bronchodilation. Dopamine receptors have broader roles and aren’t the primary mediators of bronchodilation or vasodilation in smooth muscle.

Understanding how beta-adrenergic receptors control smooth muscle helps explain this. Activation of beta-2 receptors, which are abundant in bronchial and vascular smooth muscle, relaxes the muscle. They’re coupled to Gs proteins, so stimulating them raises cyclic AMP inside the cell, promoting smooth muscle relaxation and thus bronchodilation and vasodilation. This is the mechanism behind using beta-2 agonists like albuterol for asthma and other conditions needing airway dilation or improved blood flow to certain tissues. Beta-1 receptors are mainly in the heart, increasing heart rate and contractility, not bronchodilation. Alpha-2 receptors act as autoreceptors that dampen sympathetic output and can influence vascular tone rather than directly causing bronchodilation. Dopamine receptors have broader roles and aren’t the primary mediators of bronchodilation or vasodilation in smooth muscle.