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 ?
This was consistent with results obtained in Kenya [37] where the prevalence of antifolate markers remained high despite withdrawal of SP from national treatment guidelines.
Part 7 2-[aminobenzoates]- and 2-[aminobenzoylglutamate]-quinoxalines as classical antifolate agents.
Effects of antifolates: cotrimoxazole and pyrimethamine-sulphadoxine on gametocytes in children with acute, symptomatic, uncomplicated Plasmodium falciparum malaria.
Studies provided the collaborators with the information they needed to exploit this feature of cancer cells and to develop an antifolate that would be more effectively transported into the cells via RFC-1.
Molecular data on Plasmodium falciparum chloroquine and antifolate resistance : a public health tool.
We first addressed the question of whether tHcy could serve as a marker of folate status in patients with psoriasis, rheumatoid arthritis, or cancer who were treated with a wide range of doses of the antifolate agent methotrexate (3).
Methotrexate, a folate antagonist, was originally developed as an anticancer agent, (34) In addition to its antifolate action, methotrexate has been proposed to inhibit T-cell proliferation via effects on purine and pyrimidine metabolism; to inhibit transmethylation reactions required for T-cell cytotoxicity; to promote the release of adenosine, an endogenous anti-inflammatory mediator; and to interfere with glutathione metabolism, and hence, alter the recruitment of monocytes to the inflamed joint.
(Nasdaq:CHTP), Charlotte, N.C., has begun dosing volunteers in its bioequivalence study of CH-1504, an orally available metabolically inert antifolate which has demonstrated potential anti-inflammatory and anti-tumor properties.
Allos has two product candidates in late-stage clinical development: EFAPROXYN (efaproxiral), a radiation sensitizer currently under evaluation in a pivotal Phase 3 trial in women with brain metastases originating from breast cancer, and PDX (pralatrexate), a novel, next-generation antifolate currently under evaluation in a pivotal Phase 2 trial in patients with relapsed or refractory peripheral T-cell lymphoma.
Evidence for a localized conversion of endogenous tetrahydrofolate cofactors to dihydrofolate as an important element in antifolate action in murine leukemia cells.
In addition, there have been reports of neural tube defects thought to be secondary to the antifolate activity of TMP (Eur.