beta-blocker

blocker /block·er/ (blok´er) something that blocks or obstructs passage, activity, etc.

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α-blocker  alpha-adrenergic blocking agent; see adrenergic blocking agent.

β-blocker  beta-adrenergic blocking agent; see adrenergic blocking agent.

calcium channel blocker  calcium channel blocking agent.

potassium channel blocker  potassium channel blocking agent.

sodium channel blocker  sodium channel blocking agent.

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beta-blocker

n.

A drug that opposes the excitatory effects of norepinephrine released from sympathetic nerve endings at beta-adrenergic receptors and is used for the treatment of angina, hypertension, arrhythmia, and migraine. Also called beta-adrenergic blocking agent.

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Beta-blocker

A drug that blocks some of the effects of fight-or-flight hormone adrenaline (epinephrine and norepinephrine), slowing the heart rate and lowering the blood pressure.

Mentioned in: Coronary Artery Disease

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beta [ba´tah]

second letter of the Greek alphabet, β; used to denote the second position in a classification system. Often used in names of chemical compounds to distinguish one of two or more isomers or to indicate the position of substituent atoms or groups in certain compounds. Also used to distinguish types of radioactive decay; brain rhythms or waves; adrenergic receptors; secretory cells of the various organs of the body that stain with basic dyes, such as the beta cells of the pancreas; and the type of hemolytic streptococci that produce a zone of decolorization when grown on blood media.

beta-adrenergic blocking agent (beta-blocker) any of a group of drugs that block the action of epinephrine at beta-adrenergic receptors on cells of effector organs. There are two types of these receptors: β₁-receptors in the myocardium and β₂-receptors in the bronchial and vascular smooth muscles. The principal effects of beta-adrenergic stimulation are increased heart rate and contractility, vasodilation of the arterioles that supply the skeletal muscles, and relaxation of bronchial muscles.

Because of their effects on the heart, these agents are used to treat angina pectoris, hypertension, and cardiac arrhythmias. And, because they decrease the workload of the heart, they are effective in reducing the long-term risk of mortality and reinfarction after recovery from the acute phase of a myocardial infarction. They are an important adjunct in treatment of heart failure and are also used for prophylaxis of migraine.

Nonselective beta-adrenergic blocking agents affect both types of receptors and can produce bronchospasm in patients with asthma or chronic obstructive pulmonary disease. If such patients need one of these drugs, they should be given a cardioselective one that preferentially blocks the β₁-receptors in the heart.

Nonselective agents include propranolol (Inderal), used for treatment of angina, hypertension, arrhythmias, and migraine and for prophylaxis after the acute phase of a myocardial infarction; nadolol (Corgard), used for treatment of angina and hypertension; and timolol, used as an ophthalmic preparation (Timoptic) for treatment of glaucoma and as an oral preparation (Blocadren) for treatment of hypertension and for prophylaxis after the acute phase of a myocardial infarction. Cardioselective beta-adrenergic blocking agents are used for treatment of hypertension and include atenolol (Tenormin) and metoprolol (Lopressor).

beta particles negatively charged particles emitted by radioactive elements, the result of disintegration of neutrons; their source is the unstable atoms of radioactive metals such as radium and uranium. There are three general types of emissions from radioactive substances: alpha and beta particles and gamma rays. Beta particles are less penetrating than gamma rays and may be used to treat certain conditions on or near the surface of the body. See also radiation and radiation therapy.

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blocker [blok´er]

something that blocks or obstructs a passage or activity; see also antagonist and blocking agent.

α-blocker alpha-adrenergic blocking agent.

β-blocker (beta-blocker) beta-adrenergic blocking agent.

calcium channel blocker calcium channel blocking agent.

potassium channel blocker potassium channel blocking agent.

sodium channel blocker sodium channel blocking agent.

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beta

the second letter of the Greek alphabet, B or β; used to denote the second position in a chemical classification system. Often used in names of chemical compounds to distinguish one of two or more isomers or to indicate the position of substituent atoms or groups in certain compounds. Also used to distinguish types of radioactive decay; brain rhythms or waves; adrenergic receptors; secretory cells of the various organs of the body that stain with basic dyes, such as the beta cells of the pancreas; and the type of hemolysis induced by bacteria that results in a zone of complete hemolysis when grown on blood agar, except for staphylococci.

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beta adrenergic

see adrenergic.

beta-adrenergic receptors,

β-adrenergic receptors specific sites on effector cells that respond to epinephrine. There are two types: β₁-receptors, found in the heart and small intestine, and β₂-receptors, found in the bronchi, blood vessels and uterus.

beta agonists

see adrenergic.

beta barrels

a form of secondary structure of a polypeptide in which β strands of amino acids are wound into a super secondary structure; usually interconnected by α helical regions of the polypeptide on the outside of the molecule.

beta-blocker

a drug that blocks the action of epinephrine at beta-adrenergic receptors on cells of effector organs. There are two types of these receptors: β₁-receptors in the myocardium and β₂-receptors in the bronchial and vascular smooth muscles. The principal effects of beta-adrenergic stimulation are increased heart rate and contractility, vasodilation of the arterioles that supply the skeletal muscles, and relaxation of bronchial muscles.

beta brain waves

those having a frequency of more than 10 hertz (pulsations per second); seen during wakefulness. See also electroencephalography.

beta-carboline indoleamine alkaloid

poisoning causes a nervous syndrome of hyper- or hypomotility, muscle tremor, flexed paresis of fore- or hindlimbs, hypermetria, walking backwards, convulsions. A plant poison found in Peganum, Tribulus, Kallstroemia spp.

beta carbon

carbon-3 of a molecule or the carbon atom two on from the function group of a molecule, the carbon(s) of which are not included in the lettering.

beta-endorphin

hormone secreted by central nervous system, hypothalamus, gastrointestinal tract. See also endorphin.

beta fibrillosis

see amyloidosis.

beta-folded domains

compact, locally folded region of tertiary structure containing the β-sheets or β-turns.

beta hemolysin

is a sphingomyelinase and is produced by staphylococci. It produces partial hemolysis of sheep and cattle erythrocytes. It appears to have little pathogenic effect. See also beta hemolysis.

beta-hydroxy-beta-methylglutaryl coenzyme A

1. intermediate in the formation of ketones.

2. key starting compound in the synthesis of cholesterol.

beta-hydroxybutyrate

salt of the major circulating ketone body in animals, formed from the reduction of acetoacetic acid.

beta-hydroxybutyrate dehydrogenase

mitochondrial enzyme catalyzing the NADH-linked-reduction of acetoacetate to β-hydroxybutyrate.

beta-ketobutyric acid

acetoacetic acid.

beta particle

an electron emitted from a nucleus.

beta radiation

see radiation injury, radiotherapy.

beta sheet (β-sheet)

a common structural feature of many proteins in which the single polypeptide chain is folded back and forth upon itself with each folded section running in an opposite direction to its nearest neighbors. The folded sections are held together by hydrogen bonds and the arrangement which occurs, particularly in the core of proteins, confers great stability on the molecule.

beta subunit

second-named chain (or subunit) occurring in the functional organization of macromolecules, usually proteins, containing two or more chains.

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beta-blocker 

A drug that blocks or reduces the action of neurotransmitters on beta-adrenergic receptors. It reduces secretion of aqueous humour and consequently intraocular pressure and it is used in the treatment of glaucoma. Common beta-blockers include timolol maleate, betaxolol hydrochloride, carteolol hydrochloride, levobunolol hydrochloride and metipranolol. Timolol is often used together with another agent (combination drugs), e.g. timolol and brimonidine, timolol and dorzolamide, timolol and latanoprost. Syn. beta-adrenergic antagonist; beta-adrenergic blocking agent. See adrenergic receptors; miotics; sympatholytic drugs.