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the first letter of the Greek alphabet, α; used to denote the first position in a classification system; as, in names of chemical compounds, to distinguish the first in a series of isomers, or to indicate the position of substituent atoms or groups; also used to distinguish types of radioactive decay, brain waves or rhythms, adrenergic receptors, and secretory cells that stain with acid dyes, such as the alpha cells of the pancreas.
alpha-adrenergic blocking agent (alpha-blocker) (alpha-blocking agent) any of a group of drugs that selectively inhibit the activity of alpha receptors in the sympathetic nervous system. As with beta-adrenergic blocking agents, alpha-blocking agents compete with the catecholamines at peripheral autonomic receptor sites. This group includes ergot and its derivatives, and phentolamine.
alpha chain disease the most common heavy chain disease, occurring predominantly in young adults in the Mediterranean area, and characterized by plasma cell infiltration of the lamina propria of the small intestine resulting in malabsorption with diarrhea, abdominal pain, and weight loss, or, exceedingly rarely, by pulmonary involvement. The gastrointestinal form is immunoproliferative small intestine disease.
alpha-fetoprotein (AFP) a plasma protein produced by the fetal liver, yolk sac, and gastrointestinal tract and also by hepatocellular carcinoma, germ cell neoplasms, and other cancers in adults; elevated levels may also be seen in benign liver disease such as cirrhosis and viral hepatitis. The serum AFP level is used to monitor the effectiveness of cancer treatment.

During pregnancy some AFP crosses from the amniotic fluid to the mother's blood. If the fetus has a neural tube defect, large amounts of AFP will be found in the amniotic fluid and maternal blood. Blood screening tests for serum AFP can thus be done as a first step in the screening process; if test results are positive, further testing is indicated to diagnose the defect.
alpha particles a type of emission produced by the disintegration of a radioactive substance. The atoms of radioactive elements such as uranium and radium are very unstable, continuously breaking apart with explosive violence and emitting particulate and nonparticulate types of radiation. The alpha particles, consisting of two protons and two neutrons, have an electrical charge and form streams of tremendous energy when they are released from the disintegrating atoms. These streams of energy (alpha rays) can be used in treatment of various malignancies. See also radiation and radiation therapy.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

α-ad·re·ner·gic block·ing a·gent

a class of drugs that competes with α-adrenergic agonists for available receptor sites; some compete for both α1 and α2 receptors (for example, phentolamine, phenoxybenzamine hydrochloride), whereas others are primarily either α1 (for example, prazosin, terazosin) or α2 receptor blocking agents (for example, yohimbine).
Farlex Partner Medical Dictionary © Farlex 2012


A drug that blocks or counteracts the effects of epinephrine and other molecules that stimulate alpha-receptors, leading to various physiological reactions such as vasodilation and a decrease in blood pressure. Also called alpha-adrenergic antagonist, alpha-adrenergic blocker.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

alpha-adrenergic antagonist 

An adrenergic blocking agent which produces miosis and a slight reduction in intraocular pressure. It is used mainly to reverse the mydriatic effect of sympathomimetic drugs (e.g. phenylephrine hydrochloride), or even some antimuscarinic drugs (e.g. tropicamide). Common agents include dapiprazole and moxisylyte (thymoxamine). Syn. alpha-blocker. See sympatholytic drugs.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
Alpha-blockers versus placebo with/without analgesics for distal ureteric stones
About 9,000 alpha-blocker patients had a fracture versus 3,351 matched patients on other antihypertensives; "9,000 patients out of 70,000 is a huge number.
(i) Preoperative preparation with alpha-blockers first and then with beta-blockers, when preparing a patient for an adrenalectomy due to a pheochromocytoma, is of utmost importance in order to decrease the risk of intraoperative hemodynamic instability.
Patients using only one type of antihypertensive drug before the development of NOF were categorized as single users based on the antihypertensive drug class prescribed, including loop or thiazide diuretics, alpha-blockers, beta-blockers, CCBs, ACE inhibitors, and ARBs.
In the urology setting, LUTS and medications treating LUTS, such as alpha-blockers, can increase the risk for falls and are areas where interventions can optimize care.
Alpha-blockers don't work in everyone, though, and they can cause side effects like dizziness, headache, and postural hypotension (light-headedness after standing up).
Alpha-blockers have been used to treat symptoms of nocturia in men, resulting in measureable, albeit modest, improvements in symptoms related to bladder outlet obstruction.
A warning will pop up on prescribing software when you prescribe a phosphodiesterase inhibitor in patients who are taking alpha-blockers. This is a common situation, because BPH and ED both become more common with age.
Three meta analyses have confirmed a positive effect of alpha-blocker therapy on the stone expulsion rates.
Many doctors prescribe a combination alpha-blocker and 5-ARI for men with larger prostates (in 2010, the FDA approved Jalyn, a pill containing dutasteride and tamsulosin).