In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a receptor and cause some form of cellular/tissue response, e.g. a change in the electrical activity of a cell. There are three main ways the action of the receptor can be classified: relay of signal, amplification, or integration. Relaying sends the signal onward, amplification increases the effect of a single ligand, and integration allows the signal to be incorporated into another biochemical pathway.
A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of receptor proteins. They are sometimes called blockers; examples include alpha blockers, beta blockers, and calcium channel blockers. In pharmacology, antagonists have affinity but no efficacy for their cognate receptors, and binding will disrupt the interaction and inhibit the function of an agonist or inverse agonist at receptors. Antagonists mediate their effects by binding to the active site or to the allosteric site on a receptor, or they may interact at unique binding sites not normally involved in the biological regulation of the receptor's activity. Antagonist activity may be reversible or irreversible depending on the longevity of the antagonist–receptor complex, which, in turn, depends on the nature of antagonist–receptor binding. The majority of drug antagonists achieve their potency by competing with endogenous ligands or substrates at structurally defined binding sites on receptors.
Drug interactions occur when a drug's mechanism of action is disrupted by the concomitant administration of substances such as foods, beverages, or other drugs. The cause is often inhibition of, or less effective action, of the specific receptors available to the drug. This influences drug molecules to bind to secondary targets, which may result in an array of unwanted side-effects.
An opioid antagonist, or opioid receptor antagonist, is a receptor antagonist that acts on one or more of the opioid receptors.
An antagonist is a character opposing the protagonist in literature.
Nitrendipine is a dihydropyridine calcium channel blocker. It is used in the treatment of primary (essential) hypertension to decrease blood pressure and can reduce the cardiotoxicity of cocaine.
Chemical antagonists impede the normal function of a system. They function to invert the effects of other molecules. The effects of antagonists can be seen after they have encountered an agonist, and as a result, the effects of the agonist is neutralized. Antagonists such as dopamine antagonist slow down movement in lab rats. Although they hinder the joining of enzymes to substrates, Antagonists can be beneficial. For example, not only do angiotensin receptor blockers, and angiotensin-converting enzyme (ACE) inhibitors work to lower blood pressure, but they also counter the effects of renal disease in diabetic and non-diabetic patients. Chelating agents, such as calcium di sodium defeated, fall into the category of antagonists and operate to minimize the lethal effects of heavy metals such as mercury or lead.
Saclofen is a competitive antagonist for the GABAB receptor. This drug is an analogue of the GABAB agonist baclofen. The GABAB receptor is heptahelical receptor, expressed as an obligate heterodimer, which couples to the Gi/o class of heterotrimeric G-proteins. The action of saclofen on the central nervous system is understandably modest, because G-proteins rely on an enzyme cascade to alter cell behavior while ionotropic receptors immediately change the ionic permeability of the neuronal plasma membrane, thus changing its firing patterns. These particular receptors, presynaptically inhibit N- and P/Q- voltage-gated calcium channels (VGCCs) via a direct interaction of the dissociated beta gamma subunit of the g-protein with the intracellular loop between the 1st and 2nd domain of the VGCC's alpha-subunit; postsynaptically, these potentiate Kir currents. Both result in inhibitory effects.
7-Hydroxymitragynine is a terpenoid indole alkaloid from the plant Mitragyna speciosa, commonly known as Kratom. It is often referred to as ‘7-OH’. It was first described in 1994 and is a natural product derived from the mitragynine present in the Kratom leaf. It is considered an oxidized derivative and active metabolite of mitragynine. 7-OH binds to opioid receptors like mitragynine, but research suggests that 7-OH binds with greater potency and contributes heavily to the analgesic activity of mitragynine as a metabolite.
αVβ3 is a type of integrin that is a receptor for vitronectin. It consists of two components, integrin alpha V and integrin beta 3 (CD61), and is expressed by platelets. Furthermore, it is a receptor for phagocytosis on macrophages or dendritic cells.
LY-320,135 is a drug used in scientific research which acts as a selective antagonist of the cannabinoid receptor CB1. It was developed by Eli Lilly and Company in the 1990s.
In pharmacology the term agonist-antagonist or mixed agonist/antagonist is used to refer to a drug which under some conditions behaves as an agonist while under other conditions, behaves as an antagonist.
A vasopressin receptor antagonist (VRA) is an agent that interferes with action at the vasopressin receptors. Most commonly VRAs are used in the treatment of hyponatremia, especially in patients with congestive heart failure, liver cirrhosis or SIADH.
17-Phenylandrostenol (17-PA), or (3α,5α)-17-phenylandrost-16-en-3-ol, is a steroid drug which binds to GABAA receptors. It acts as an antagonist against the sedative effects of neuroactive steroids, but has little effect when administered by itself, and does not block the effects of benzodiazepines or barbiturates.
A receptor modulator, or receptor ligand, is a general term for a substance, endogenous or exogenous, that binds to and regulates the activity of chemical receptors. They are ligands that can act on different parts of receptors and regulate activity in a positive, negative, or neutral direction with varying degrees of efficacy. Categories of these modulators include receptor agonists and receptor antagonists, as well as receptor partial agonists, inverse agonists, orthosteric modulators, and allosteric modulators, Examples of receptor modulators in modern medicine include CFTR modulators, selective androgen receptor modulators (SARMs), and muscarinic ACh receptor modulators.
6β-Naltrexol, or 6β-hydroxynaltrexone, is a peripherally-selective opioid receptor antagonist related to naltrexone. It is a major active metabolite of naltrexone formed by hepatic dihydrodiol dehydrogenase enzymes. With naltrexone therapy, 6β-naltrexol is present at approximately 10- to 30-fold higher concentrations than naltrexone at steady state due to extensive first-pass metabolism of naltrexone into 6β-naltrexol. In addition to being an active metabolite of naltrexone, 6β-naltrexol was itself studied for the treatment of opioid-induced constipation. It was found to be effective and well-tolerated, and did not precipitate opioid withdrawal symptoms or interfere with opioid pain relief, but development was not further pursued.
(R,R)-Tetrahydrochrysene ((R,R)-THC) is a drug used to study the estrogen receptors (ERs) in scientific research. It is an ERβ antagonist and an ERα agonist with 10-fold higher affinity for ERβ relative to ERα. (R,R)-THC is a silent antagonist of ERβ, and, uniquely relative to other known ERβ antagonists, a passive antagonist of the receptor.
