BSCI450: Smooth/Cardiac Muscle - Adrenergic Receptors

α1 Receptor Location

Smooth muscle of most blood vessels, iris radial muscle, bladder sphincter, prostate.

α1 Receptor Effect

Smooth muscle contraction causing vasoconstriction, pupil dilation (mydriasis), and sphincter contraction.

Clinical Use of α1 Agonists

Increase blood pressure during hypotension or shock.

Clinical Use of α1 Antagonists

Treat hypertension and benign prostatic hyperplasia (BPH).

α2 Receptor Location

Presynaptic sympathetic nerve terminals.

Function of α2 Receptors

Negative feedback that decreases norepinephrine release.

Effect of α2 Agonists

Reduce sympathetic activity and lower blood pressure.

Example of an α2 Agonist

Clonidine.

Additional Use of α2 Agonists

Reduce aqueous humor production in glaucoma.

β1 Receptor Location

SA node, AV node, and cardiac muscle.

β1 Receptor Effects

Increase heart rate, contractility, and cardiac output.

Positive Chronotropic Effect

Increased heart rate.

Positive Inotropic Effect

Increased force of cardiac contraction.

Clinical Use of β1 Blockers

Treat hypertension and arrhythmias by lowering heart rate and contractility.

β2 Receptor Location

Bronchioles, uterus, liver, and skeletal muscle blood vessels.

β2 Receptor Effects

Bronchodilation, uterine relaxation, vasodilation, glycogenolysis, and gluconeogenesis.

Clinical Use of β2 Agonists

Treat asthma by causing bronchodilation.

Example of a β2 Agonist

Albuterol

Additional Clinical Use of β2 Agonists

Relax the uterus to delay premature labor.

β3 Receptor Location

Adipose tissue

β3 Receptor Effect

Lipolysis (breakdown of triglycerides into glycerol and fatty acids).

Why Aren't β3 Agonists Used for Weight Loss?

They are not selective and may stimulate β1 receptors, causing hypertension and cardiovascular complications.

α1 Agonists

Increase blood pressure through vasoconstriction.

α1 Antagonists

Lower blood pressure through vasodilation.

α2 Agonists

Decrease norepinephrine release and reduce blood pressure.

β1 Agonists

Increase heart rate and contractility.

β1 Antagonists

Decrease heart rate, contractility, and blood pressure.

β2 Agonists

Cause bronchodilation and uterine relaxation.

β3 Agonists

Stimulate lipolysis.