Lecture 15 — Adrenergic Effects and Receptors
Bronchodilation
Epinephrine and isoproterenol relax bronchial smooth muscle through beta-2 receptors. The slides describe norepinephrine as a relatively weak bronchodilator.
Pupil and CNS
Epinephrine and norepinephrine cause mydriasis by contracting the radial iris dilator muscle. Catecholamines cross the blood-brain barrier poorly; epinephrine can nevertheless produce peripheral anxiety-like symptoms.
Catecholamines and noncatecholamines
Natural catecholamines listed: epinephrine, norepinephrine and dopamine. Noncatecholamine examples include ephedrine, amphetamine, methylphenidate, pseudoephedrine, phenylpropanolamine and oxymetazoline.
Alpha-1 receptor signaling
Alpha-1 couples to Gq: phospholipase C generates IP3 and DAG; IP3 raises intracellular calcium and DAG activates PKC, supporting smooth-muscle contraction.
Alpha-2 receptor signaling
Alpha-2 couples to Gi, inhibiting adenylyl cyclase and decreasing cAMP. The slides connect this with reduced norepinephrine release.
Beta receptor signaling
Beta receptors couple to Gs, stimulating adenylyl cyclase, increasing cAMP and activating protein kinase A.
Clinical comparison
The response to epinephrine, norepinephrine and isoproterenol differs according to receptor preference and the receptor distribution in each vascular bed.
