antagonist

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antagonist

 [an-tag´o-nist]
antagonistic muscle. (see illustration.)
1. a substance that tends to nullify the action of another, as a drug that binds to a cellular receptor for a hormone, neurotransmitter, or another drug blocking the action of that substance without producing any physiologic effect itself. See also blocking agent.
2. a tooth in one jaw that articulates with one in the other jaw.
α-adrenergic antagonist alpha-adrenergic blocking agent.
β-adrenergic antagonist beta-adrenergic blocking agent.
folic acid antagonist see folic acid antagonist.
H1 receptor antagonist any of a large number of agents that block the action of histamine by competitive binding to the H1 receptor. Such agents also have sedative, anticholinergic, and antiemetic effects, the exact effect varying from drug to drug, and are used for the relief of allergic symptoms and as antiemetics, antivertigo agents, sedatives, and antidyskinetics in parkinsonism. This group is traditionally called the antihistamines.
H2 receptor antagonist an agent that blocks the action of histamine by competitive binding to the H2 receptor; used to inhibit gastric secretion in the treatment of peptic ulcer.

an·tag·o·nist

(an-tag'ŏ-nist),
Something opposing or resisting the action of another; certain structures, agents, diseases, or physiologic processes that tend to neutralize or impede the action or effect of others. Compare: synergist.

antagonist

(ăn-tăg′ə-nĭst)
n.
1. Physiology A muscle that counteracts the action of another muscle, the agonist.
2. A drug or chemical substance that interferes with the physiological action of another, especially by combining with and blocking its receptor.

an·tag′o·nis′tic adj.
an·tag′o·nis′ti·cal·ly adv.

antagonist

Anatomy
A muscle that opposes the movement of agonist muscles and returns a limb to its initial position.

Pharmacology
A substance that partially or completely nullifies the effect of another agent; a chemical entity that is not naturally found in the body which occupies a receptor, produces no physiologic effects and prevents endogenous and exogenous chemicals from producing an effect on that receptor.

an·tag·o·nist

(an-tag'ŏ-nist)
Something opposing or resisting the action of another; any structure, agent, disease, or physiologic process that tends to neutralize or impede some action or effect.
Compare: synergist

antagonist

1. A muscle that acts to oppose the action of another muscle (the agonist).
2. A drug that counteracts or neutralizes the action of another drug. The antonym of antagonist is agonist.

Antagonist

A substance that tends to nullify the action of another.
Mentioned in: Withdrawal Syndromes

antagonist 

1. An antagonistic muscle.
2. A substance (e.g. a drug, hormone or neurotransmitter) that depresses the action of an agonist or binds to a cell receptor without eliciting a physiological response (e.g. excitation or inhibition). Examples: atropine and hyoscine which block the effect of acetylcholine acting on cholinergic receptors and timolol which blocks adrenergic receptors. See agonist.

an·tag·o·nist

(an-tag'ŏ-nist)
Something opposing or resisting the action of another; certain structures, agents, diseases, or physiologic processes that tend to neutralize or impede the action or effect of others.
Compare: synergist
References in periodicals archive ?
Therefore, in the present study, we investigated the effects of H1 and/or H2 receptor antagonists on emotional memory consolidation.
When endoscopic healing was confirmed in the study patients, omeprazole therapy was discontinued, and all patients received 6 months of maintenance therapy with H2 receptor antagonists. During or after this maintenance therapy, 3 patients with reflux esophagitis and 4 patients with duodenal ulcers had a relapse of their disease.
In this regard, H2 receptor antagonists (H2RA), a class of histamine blockers hold a prominent position since distant past.
Sucralfate is an effective choice for medical treatment, whereas proton pump inhibitors and H2 receptor antagonists can be used as a supportive treatment.
Furthermore, H2 receptor antagonists increased the risk of nosocomial pneumonia, but only in this same subgroup receiving enteral nutrition.
If an ulcer is the cause of anemia, first-line treatments usually include either H2 receptor antagonists such as famotidine (Pepcid) or cimetidine (Tagamet), or proton pump inhibitors such as omeprazole (Prilosec) or lansoprazole (Prevacid).
H2 receptor antagonists (H2 blockers), including cimetidine (Tagamet), famotidine (Pepcid), nizatidine (Axid) and ranitidine (Zantac).