Learning Objective

By the end of this section, the learner should be able to describe the physiological effects, clinical uses, and receptor selectivity of β-adrenergic agonists and predict their impact on blood pressure and heart rate.

Systemic Effects

• β2 → Vasodilation → ↓ mean BP (↓ diastolic > ↓ systolic)
• β1 → ↑ HR (positive chronotropy), ↑ contractility (positive inotropy)
  → Reflex tachycardia may further increase HR.

Key Drugs and Uses

Isoproterenol (β1 = β2)

• Strong ↑ HR, ↑ contractility (β1)
• Marked vasodilation with ↓ BP (β2)

Dobutamine (β1 > β2)

• ↑ Contractility and cardiac output
• Use: acute heart failure, cardiogenic shock, stress testing

Selective β2 Agonists

• Albuterol, Salmeterol, Terbutaline
• Bronchodilation → Asthma, COPD
• Terbutaline: relaxes the uterus → Premature labor

Selective β3 Agonist

• Mirabegron
• Relaxes detrusor muscle → Overactive bladder

Activity

Activity