Agonist – a type of chemical

An agonist is a type of chemical known as a ligand. It binds to a receptor. It is a compound that can bind to and cause activation of a receptor, thus mimicking an endogenous ligand or neurotransmitter. It activates (switches on) the receptor to produce a response. In Pharmacology, it is a chemical substance capable of activating a receptor to induce a full or partial pharmacological response.

An agonist causes an action. It is a substance that acts like another substance and therefore stimulates an action. There are also antagonists which block the action of the agonists, and there are inverse agonists which cause an action opposite to that of the agonist. It is a chemical that binds to a receptor and activates the receptor to produce a biological response.

Agonist is a drug or substance that binds to a receptor inside a cell or on its surface and causes the same action as the substance that normally binds to the receptor.

This is typical of the systems which regulate the body. Being able to control activity is the basis of homeostasis. It is a chemical substance capable of combining with a specific receptor on a cell and initiating the same reaction or activity typically produced by the binding endogenous substance.
Types of agonists

• Receptors can be activated by either endogenous or exogenous agonists. Both types result in a biological response. Agonists and most natural ligands bind to receptors in their inactive state and quickly induce an active receptor conformation that initiates cell signaling. Endogenous agonists include hormones and neurotransmitters. Exogenous agonists include drugs.
• A substance which causes the same bodily responses, but does not bind to the same receptor is called a physiological agonist. The active receptor state initiates signaling because of its structural complementariness with coupling proteins that activate signaling pathways, such as G proteins and G protein-coupled receptor kinases.
• An endogenous agonist for a specific receptor is a compound normally created by the body that ties to and enacts that receptor. For instance, the endogenous agonist for serotonin receptors is serotonin, and the endogenous agonist for dopamine receptors is dopamine. 
• Full agonists tie to and initiate a receptor with the most extreme reaction that an agonist can inspire at the receptor. One illustration of a medication that can go about as a full agonist is isoproterenol, which imitates the activity of adrenaline at β adrenoreceptors. Another model is morphine, which copies the activities of endorphins at μ-narcotic receptors all through the focal sensory system. Notwithstanding, a medication can go about as a full agonist in certain tissues and as a fractional agonist in different tissues, contingent on the overall quantities of receptors and contrasts in receptor coupling.[medical reference needed] 
• A co-agonist works with other co-agonists to create the ideal impact together. NMDA receptor actuation requires the limiting of both glutamate, glycine and D-serine co-agonists. Calcium can likewise go about as a co-agonist at the IP3 receptor. 
• A particular agonist is particular for a particular sort of receptor. For example buspirone is a specific agonist for serotonin 5-HT1A. 
• Fractional agonists (like buspirone, aripiprazole, buprenorphine, or norclozapine) additionally tie and enact a given receptor, yet have just halfway viability at the receptor comparative with a full agonist, even at maximal receptor inhabitance. Specialists like buprenorphine are utilized to treat narcotic reliance therefore, as they produce milder impacts on the narcotic receptor with lower reliance and misuse potential. 
• An opposite agonist is a specialist that ties to a similar receptor restricting site as an agonist for that receptor and restrains the constitutive action of the receptor. Converse agonists apply the inverse pharmacological impact of a receptor agonist, not simply a shortfall of the agonist impact as seen with a rival. A model is the cannabinoid reverse agonist rimonabant. 
• A superagonist is a term utilized by some to recognize a compound that is equipped for delivering a more noteworthy reaction than the endogenous agonist for the objective receptor. It very well may be contended that the endogenous agonist is just an incomplete agonist in that tissue. 
• An irreversible agonist is a sort of agonist that ties forever to a receptor through the arrangement of covalent bonds. A couple of these have been portrayed, including Paracetamol. 
• A one-sided agonist is a specialist that ties to a receptor without influencing a similar sign transduction pathway. Oliceridine is a µ-narcotic receptor agonist that has been portrayed to be practically specific towards G protein and away from β-arrestin2 pathways.

Examples

The endogenous agonist for serotonin receptors is serotonin, and the endogenous agonist for dopamine receptors is dopamine.
Morphine is an exogenous agonist. It mimics the actions of endorphins at certain receptors in the central nervous system.
Agonist is the opposite of antagonist. Antagonists and agonists are key players in the chemistry of the human body and in pharmacology. These are drugs or naturally occurring substances that activate physiologic receptors, whereas antagonists are drugs that block those receptors.

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