Physiological agonism describes the action of a substance which ultimately produces the same effects in the body as another substance—as if they were both agonists at the same

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

—without actually binding to the same receptor. Physiological antagonism describes the behavior of a substance that produces effects counteracting those of another substance (a result similar to that produced by an

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...

blocking the action of an agonist at the same receptor) using a mechanism that does not involve binding to the same receptor.

Examples

Physiological agonists

Epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...

induces platelet aggregation, and so does hepatocyte growth factor (HGF). Thus, they are physiological agonists to each other.

Physiological antagonists

*There are several substances that have

antihistaminergic Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provides re ...

action despite not being

ligands In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electro ...

for the

histamine receptor The histamine receptors are a class of G protein–coupled receptors which bind histamine as their primary endogenous ligand. There are four known histamine receptors: * H1 receptor * H2 receptor * H3 receptor * H4 receptor Comparison There ...

. For instance, epinephrine raises arterial pressure through vasoconstriction mediated by A1-

adrenergic receptor The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like beta ...

activation, in contrast to

histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered in ...

, which lowers arterial pressure. Thus, despite not being true antihistamines because they do not bind to and block the histamine receptor, epinephrine and other such substances are physiological antagonists to histamine.

References

Medical terminology Pharmacodynamics Physiology Receptor agonists {{biochemistry-stub