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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.

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).


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.

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.
References in periodicals archive ?
Corticosteroid therapy, as an adjunct to alpha-blocker therapy, may be effective in improving expulsion rates.
In patients with symptoms of OAB, the addition of an antimuscarinic agent such as solifenacin, fesoterodine, tolterodine, or oxybutynin following initial treatment with an alpha1a-selective alpha-blocker has been shown to improve persistent storage symptoms to a greater degree than the alpha-blocker alone.
The other Stanford authors on the alpha-blocker study are research assistant Tseday Alehegn and research associate Jun Ma, MD, PhD, along with researchers at Wake Forest University, the Massachusetts Institute of Technology and Boston University.
39) Alpha-blockers as a treatment option are included in EUA guidelines in case of BPH with bothersome LUTS with no absolute indication for surgery.
9,10] In this study we evaluate the relationship between LUTS and bladder wall thickness and investigate if alpha-blocker treatment with alfuzosin improves BWT.
The study indicates that the combination of certain alpha-blocker drugs used for prostrate treatment and drops used to enlarge the pupil can cause irregular iris behavior during surgery.
McVary, a professor of surgery at Northwestern University, Chicago, described his results as "somewhat provocative" and the benefits as comparable to others reported on the use of alpha-blockers for LUTS.
There was some disagreement with respect to the attempt to use an alpha-blocker after TURP.
Food and Drug Administration (FDA) instituted a new label warning for Flomax and other alpha-blocker drugs that reads: "The patient's ophthalmologist should be prepared for possible modifications to their surgical technique.
Flomax(R) (tamsulosin hydrochloride) is the most widely prescribed alpha-blocker indicated for the treatment of the signs and symptoms of BPH in the United States.
For those men with smaller prostates and/or low prostate-specific antigen (PSA), the guidelines recommend monotherapy with an alpha-blocker as the primary pharmacotherapy.