Table 2.
Comparative Receptor Pharmacology and Physiologic Effects of Stimulation of β‐ and α1‐Adrenergic Receptors
| β–adrenergic receptor | α1–adrenergic receptor | |
|---|---|---|
| Pharmacology | ||
| Agonists | Isoproterenol> dobutamine> epinephrine> norepinephrine> dopamine (relative receptor affinity) | Norepinephrine> epinephrine> dobutamine> dopamine (relative receptor affinity) |
| Antagonists | Propranolol (nonselective β1‐AR and β2‐AR), metoprolol (selective β1‐AR) | Prazosin |
| Mechanism of action | ||
| Receptor | GPCR | GPCR |
| Signaling system | ↑ cAMP and protein kinase A | ↑ Inositol 1, 4, 5‐triphosphate (IP3) and diacylglycerol (DAG) |
| Myocardial metabolism | +++ Oxygen consumption through β1‐AR stimulation | +/− Oxygen consumption |
| Cardiac effects | ||
| Electrophysiology | ++ Positive chronotropy (via β1‐AR stimulation) | +/− |
| Myocardial mechanics | ++ Contractility, lusitropy, stroke volume, and cardiac output (via β1‐AR stimulation) | +/− |
| Vascular smooth muscle | ||
| Coronary and peripheral arterioles | Dilatation (via β2‐AR stimulation) | Constriction |
GCPR indicates G‐protein coupled receptor; β1‐AR, beta 1 adrenergic receptor; β2‐AR, beta 2 adrenergic receptor; and cAMP, cyclic adenosine monophosphate.