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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 ?
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.
Some physicians combine Proscar with alpha-blockers.
For patients with increased urinary frequency or urgency that does not improve a few months after starting an alpha-blocker, antimuscarinic drugs such as solifenacin (Vesicare) and tolterodine (Detrol) may be in order.
Tamsulosin has been the most studied alpha-blocker in MET.
Patients with pregnancy or lactation, history of previous surgery on the ipsilateral ureter, solitary kidney, urinary tract infection, moderate or severe hydronephrosis, currently on alpha-blocker therapy, known allergy to tamsulosin, contraindications for non-steroidal anti-inflammatory agents (e.
3,8-10) In the Antihypertensive and Lipid-Lowering to Prevent Heart Attack Trial (ALLHAT), treatment initiated with the thiazide-type diuretic (THZD) chlorthalidone (CHT) reduced systolic BP (SBP) by 4 mm Hg more than treatment based on the angiotensin-converting enzyme inhibitor (ACEI) lisinopril or the alpha-blocker doxazosin in black ALLHAT participants who were receiving similar background antihypertensive drug treatment.
Early use of drugs known as 5-alpha reductase inhibitors (5-ARIs) may reduce the risk of clinical progression in men taking an alpha-blocker medication for benign prostatic hyperplasia (BPH, or enlarged prostate), suggests a study in the August issue of Pharmacy & Therapeutics.
4] The selective alpha-blocker silodosin was recently made available in Canada and offers another option.