Final answer:
Norepinephrine (NE) and epinephrine (E) are agonists that activate alpha adrenergic receptors and produce effects similar to the body's own ligands by binding to these receptors.
Step-by-step explanation:
Norepinephrine (NE) and epinephrine (E) both activate alpha adrenergic receptors. NE and E are agonists. An agonist is any exogenous substance that binds to a receptor and produces a similar effect to the endogenous ligand. Epinephrine and norepinephrine are part of the catecholamines, and they both bind to alpha (a)-adrenergic receptors, which come in three subtypes: α1, α2, and α3. Unlike antagonists, which produce an opposing effect to the endogenous ligand, agonists like NE and E mimic the actions of the endogenous ligands by binding to the same receptors and triggering a biological response.