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

/an·tag·o·nist/ (an-tag´o-nist)
1. a substance that tends to nullify the action of another, as a drug that binds to a cell receptor without eliciting a biological response, blocking binding of substances that could elicit such responses.antagonis´tic
2. antagonistic muscle.
Enlarge picture
Antagonist. The triceps brachii extends the forearm at the elbow while the biceps brachii, its antagonist, flexes the elbow.
3. a tooth in one jaw that articulates with one in the other jaw.

α-adrenergic antagonist  alpha-adrenergic blocking agent; see adrenergic blocking agent.
β-adrenergic antagonist  beta-adrenergic blocking agent; see adrenergic blocking agent.
folic acid antagonist  an antimetabolite, e.g., methotrexate, that interferes with DNA replication and cell division by inhibiting the enzyme dihydrofolate reductase; used in cancer chemotherapy.
H1 receptor antagonist  any of a large number of agents that block the action of histamine by competitive binding to the H1 receptor; they also have sedative, anticholinergic, and antiemetic effects and are used for the relief of allergic symptoms, as antiemetics, as antivertigo agents, and as antidyskinetics in parkinsonism.
H2 receptor antagonist  an agent that blocks the action of histamine by competitive binding to the H2 receptor; used to inhibit acid secretion in the treatment of peptic ulcer.

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

[antagə′nist]
Etymology: Gk, antagonisma, struggle
1 one who contends with or is opposed to another.
2 (in physiology) any agent, such as a drug or muscle, that exerts an opposite action to that of another or competes for the same receptor sites. Kinds of antagonists include the antimetabolite, associated antagonist, direct antagonist, and opioid antagonist. Compare agonist.
3 (in dentistry) a tooth in the upper jaw that articulates during mastication or occlusion with a tooth in the lower jaw. antagonistic, adj., antagonize, v.

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

an agent having a counteractive effect on the action of another agent. (1) In pharmacology, a chemical agent (naturally occurring substance or drug) which prevents cells from responding to a particular agonist by competing at binding sites on or in the cell. (2) With reference to skeletal muscles: one, or a group, which opposes the action of another, e.g. the triceps may 'antagonize' flexion of the elbow by the biceps. Antagonistic pairs of muscles allow coordinated control. See also reciprocal inhibition.

antagonist

something opposing or resisting an agonist, e.g. the action of skeletal muscles (tibialis posterior antagonizes tibialis anterior) or the actions of certain drugs (antihypertensive drugs antagonize the hypertensive effects of adrenaline)

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

antagonist,

n 1. a drug that counteracts, blocks, or abolishes the action of another drug.
n 2. a muscle that acts in opposition to the action of another muscle (e.g., flexor vs. extensor).
n 3. a tooth in one jaw that occludes with a tooth in the other jaw.
antagonist, narcotic,
n a narcotic drug that acts specifically to reverse depression of the central nervous system.
antagonists, insulin,
n.pl the circulating hormonal and nonhormonal substances that stimulate glyconeogenesis (e.g., 11-oxysteroids and S hormones).

antagonist

1. a muscle that counteracts the action of another muscle, its agonist.
2. a drug that binds to a cellular receptor for a hormone, neurotransmitter, or another drug blocking the action of that substance without producing any physiological effect itself.
3. a tooth in one jaw that articulates with one in the other jaw. See also antagonism.
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