Binding Affinity
Definition
How tightly a molecule holds its receptor, reported as a dissociation constant where a lower number means tighter binding. Affinity alone does not predict the size of a response: that also depends on how well the bound molecule activates the receptor.
What this means for research sourcing
Mechanistic terms like this describe how research compounds behave in vitro. See the mechanism overviews for compounds Volta stocks.
Related Terms in Pharmacology
EC50
The concentration producing half of a compound's maximum effect in a given assay. It is a potency measure and is only comparable between compounds tested in the same system, which is why cross-paper EC50 comparisons mislead so often.
Potency
How little of a compound is needed to produce a given effect. A more potent molecule works at a lower concentration, which says nothing about whether its maximum achievable effect is larger.
Receptor Selectivity
How far a compound acts on its intended receptor rather than on related ones. Selectivity is the difference between a GHRP that raises growth hormone alone and one that also moves cortisol and prolactin.
Desensitization
A fall in receptor responsiveness under prolonged or repeated stimulation, achieved by internalising receptors or expressing fewer of them. It is one mechanism behind an effect that fades while exposure continues.
Tachyphylaxis
Response falling away rapidly over a few administrations rather than gradually, which separates it from slower desensitization. Reports of it appear with melanocortin agonists and with some growth hormone releasing peptides.
Downregulation
A reduction in the number of receptors a cell presents, in response to sustained stimulation. It is slower than desensitization and is the usual reason a protocol in the literature includes periods without administration.
Dose-Response Curve
A plot of effect against amount administered. A clean curve is among the stronger indications that an observed effect is real rather than noise, and the gap between the amount that first works and the amount that harms is the therapeutic window.
GLP-1 (Glucagon-Like Peptide-1)
An incretin released from the small intestine after a meal. It raises insulin secretion when glucose is high, suppresses glucagon, slows gastric emptying and signals fullness centrally. Its native half-life is about two minutes.