Mechanism of Action of Albuterol

Albuterol works by relaxing bronchial smooth muscle through stimulation of beta-2 adrenergic receptors, which is option A. 1

Primary Mechanism

Albuterol is a selective beta-2 adrenergic receptor agonist that stimulates adenyl cyclase, the enzyme catalyzing the formation of cyclic-3',5'-adenosine monophosphate (cyclic AMP) from adenosine triphosphate (ATP) 1
The increased cyclic AMP mediates bronchial smooth muscle relaxation, resulting in bronchodilation 1
Beta-2 adrenergic receptors are widely distributed throughout the human bronchial tree, with the highest density in alveolar regions 2

Albuterol demonstrates preferential effects on beta-2 adrenergic receptors compared to non-selective agents like isoproterenol 1
This selectivity allows albuterol to provide effective bronchodilation with fewer cardiovascular side effects than non-selective beta-agonists 1, 3
While beta-2 receptors predominate in bronchial smooth muscle, approximately 10-50% of beta-receptors in the human heart may also be beta-2 receptors 1

Short-acting beta-agonists like albuterol provide rapid, dose-dependent bronchodilation with minimal side effects 2
Onset of action occurs within 5 minutes, with peak effect at approximately 30-60 minutes and duration of 4-6 hours 2, 1
Albuterol has a longer duration of action than isoproterenol because it is not a substrate for cellular uptake processes for catecholamines or for catechol-O-methyl transferase 1, 3

Albuterol does NOT inhibit acetylcholine at muscarinic receptors (option B) - this is the mechanism of anticholinergic agents like ipratropium 2
Albuterol does NOT inhibit IgE binding to receptors on mast cells (option C) - this mechanism is associated with certain anti-allergic medications 2
Albuterol does NOT block acetylcholine in bronchial smooth muscle (option D) - again, this describes anticholinergic agents 2

The beta-2 selective action explains why albuterol is effective for rapid reversal of airflow obstruction and prompt relief of asthmatic symptoms 2
This mechanism also explains potential side effects like tremor, anxiety, tachycardia, and metabolic effects (decreased potassium, increased glucose) which are dose-dependent 2, 4
Regular use of beta-2 agonists can lead to tolerance through receptor downregulation, particularly affecting bronchoprotection rather than bronchodilation 2

Albuterol's mechanism of action is most effectively utilized through inhalation, which delivers the medication directly to airway beta-2 receptors 2
Systemic side effects are minimized with inhaled administration compared to oral or parenteral routes 4
The dose delivered depends on the patient's lung volume and inspiratory flow rate 2