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 An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agon ...

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 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 induces

platelet aggregation Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...

, and so does

hepatocyte growth factor Hepatocyte growth factor (HGF) or scatter factor (SF) is a paracrine cellular growth, motility and morphogenic factor. It is secreted by mesenchymal cells and targets and acts primarily upon epithelial cells and endothelial cells, but also acts on ...

(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 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 Ther ...

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

, 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