Alpha adrenergic blockers Health Dictionary

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Alpha Adrenergic Blockers: From 1 Different Sources

Also called adrenoceptor-blocking agents or alpha blockers, these drugs stop the stimulation of alpha-adrenergic receptors at the nerve endings of the SYMPATHETIC NERVOUS SYSTEM by HORMONES with ADRENALINE-like characteristics. The drugs dilate the arteries, causing a fall in blood pressure, so they are used to treat HYPERTENSION and also benign enlargement of the PROSTATE GLAND. Examples of this group of drugs are doxazosin, indoramin, phentolamine and prazosin. The drugs should be used with caution as some may cause a severe drop in blood pressure when ?rst taken.
Health Source: Medical Dictionary
Author: Health Dictionary

Beta Blockers

Drugs used to slow the response to epinephrine (released by the adrenal medulla), usually to attempt controlling high blood pressure... beta blockers

Adrenergic

Functions that are dominated by epinephrine (the blood hormone) or norepinephrine (local sympathetic adrenergic nerve stimulus)... adrenergic

Calcium-channel Blockers

Calcium-channel blockers inhibit the inward ?ow of calcium through the specialised slow channels of cardiac and arterial smooth-muscle cells. By thus relaxing the smooth muscle, they have important applications in the treatment of HYPERTENSION and ANGINA PECTORIS. Various types of calcium-channel blockers are available in the United Kingdom; these di?er in their sites of action, leading to notable di?erences in their therapeutic effects. All the drugs are rapidly and completely absorbed, but extensive ?rst-pass metabolism in the liver reduces bioavailability to around one-?fth. Their hypotensive e?ect is additive with that of beta blockers (see BETA-ADRENOCEPTOR-BLOCKING DRUGS); the two should, therefore, be used together with great caution – if at all. Calcium-channel blockers are particularly useful when beta blockers are contraindicated, for example in asthmatics. However, they should be prescribed for hypertension only when THIAZIDES and beta blockers have failed, are contraindicated or not tolerated.

Verapamil, the longest-available, is used to treat angina and hypertension. It is the only calcium-channel blocker e?ective against cardiac ARRHYTHMIA and it is the drug of choice in terminating supraventricular tachycardia. It may precipitate heart failure, and cause HYPOTENSION at high doses. Nifedipine and diltiazem act more on the vessels and less on the myocardium than verapamil; they have no antiarrhythmic activity. They are used in the prophylaxis and treatment of angina, and in hypertension. Nicardipine and similar drugs act mainly on the vessels, but are valuable in the treatment of hypertension and angina. Important di?erences exist between di?erent calcium-channel blockers so their use must be carefully assessed. They should not be stopped suddenty, as this may precipitate angina. (See also HEART, DISEASES OF.)... calcium-channel blockers

Alpha-antitrypsin Deficiency

A rare genetic disorder in which a person is missing the enzyme alpha1-antitrypsin, which protects the body from damage by other enzymes.

The disease mainly affects tissues in the lungs, resulting in emphysema, and the liver, causing cirrhosis.

The effects of alpha1-antitrypsin deficiency may not become apparent until after the age of 30.

There is no cure, but symptoms can be relieved by drug treatment.

In severe cases, a liver transplant may be a possibility.... alpha-antitrypsin deficiency

Alpha-fetoprotein

A protein that is produced in the liver and gastrointestinal tract of the fetus and by some abnormal tissues in adults.

Alpha-fetoprotein (AFP) can be measured in the maternal blood from the latter part of the 1st trimester of pregnancy, and its concentration rises between the 15th and 20th weeks.

Raised levels of are associated with fetal neural tube defects, such as spina bifida or anencephaly, and certain kidney abnormalities. High levels of also occur in multiple pregnancies (see pregnancy, multiple) and threatened or actual miscarriage. levels may be unusually low if the fetus has Down’s syndrome. For this reason, measurement of blood is included in blood tests, which are used to screen pregnant women for an increased risk of Down’s syndrome.

levels are commonly raised in adults with hepatoma (see liver cancer), cancerous teratoma of the testes or ovaries, or cancer of the pancreas, stomach, or lung.

For this reason, is known as a tumour marker.

(AFP) levels can be used to monitor the results of treatment of certain cancers; increasing levels after surgery or chemotherapy may indicate tumour recurrence.

However, levels are also raised in some noncancerous conditions, including viral and alcoholic hepatitis and cirrhosis.... alpha-fetoprotein

Adrenergic Receptors

The sites in the body on which ADRENALINE and comparable stimulants of the SYMPATHETIC NERVOUS SYSTEM act. Drugs which have an adrenaline-like action are described as being adrenergic. There are ?ve di?erent types of adrenergic receptors, known as alpha1, alpha2, beta1, beta2 and beta3 respectively. Stimulation of alpha receptors leads to constriction of the bronchi, constriction of the blood vessels with consequent rise in blood pressure, and dilatation of the pupils of the eyes. Stimulation of beta1 receptors quickens the rate and output of the heart, while stimulation of beta2 receptors dilates the bronchi. Beta3 receptors are now known to mediate so-called non-shivering thermogenesis, a way of producing heat from specialised fat cells that is particularly relevant to the human infant.

For long it had been realised that in certain cases of ASTHMA, adrenaline had not the usual bene?cial e?ect of dilating the bronchi during an attack; rather it made the asthma worse. This was due to its acting on both the alpha and beta adrenergic receptors. A derivative, isoprenaline, was therefore produced which acted only on the beta receptors. This had an excellent e?ect in dilating the bronchi, but unfortunately also affected the heart, speeding it up and increasing its output – an undesirable e?ect which meant that isoprenaline had to be used with great care. In due course drugs were produced, such as salbutamol, which act predominantly on the beta2 adrenergic receptors in the bronchi and have relatively little e?ect on the heart.

The converse of this story was the search for what became known as BETA-ADRENOCEPTORBLOCKING DRUGS, or beta-adrenergic-blocking drugs. The theoretical argument was that if such drugs could be synthesised, they could be of value in taking the strain o? the heart – for example: stress ? stimulation of the output of adrenaline ? stimulation of the heart ? increased work for the heart. A drug that could prevent this train of events would be of value, for example in the treatment of ANGINA PECTORIS. Now there is a series of beta-adrenoceptor-blocking drugs of use not only in angina pectoris, but also in various other heart conditions such as disorders of rhythm, as well as high blood pressure. They are also proving valuable in the treatment of anxiety states by preventing disturbing features such as palpitations. Some are useful in the treatment of migraine.... adrenergic receptors

Alpha

(Greek) The firstborn child; the first letter of the Greek alphabet... alpha

Alpha (i) Error

See “Type I error”.... alpha (i) error

Alpha (i) Statistic

A statistic commonly used to reflect the reliability of a measurement scale. See “reliability”.... alpha (i) statistic

Alpha-feto Protein

A protein produced in the gut and liver of the FETUS. Abnormality in the fetus, such as neural tube defect, may result in raised levels of alphafeto protein in the maternal blood. In DOWN’S (DOWN) SYNDROME, levels may be abnormally low. In either case, screening of the pregnancy should be carried out, including AMNIOCENTESIS to check the amount of alpha-feto protein in the amniotic ?uid. The protein may also be produced in some abnormal tissues in the adult – in patients with liver cancer, for example.... alpha-feto protein

Alpha-blocker Drugs

A group of drugs used to treat hypertension (high blood pressure) and urinary symptoms due to enlargement of the prostate gland. Alpha-blockers are also used to treat urinary retention caused by an enlarged prostate gland (see prostate, enlarged). Side effects of the drugs may include dizziness and fatigue due to a sudden drop in blood pressure, nausea, dry mouth, and drowsiness.... alpha-blocker drugs

Alpha Agonist

see sympathomimetic.... alpha agonist

Alpha Blocker

(alpha-adrenergic blocker) a drug that prevents the stimulation of alpha *adrenoceptors at the nerve endings of the sympathetic nervous system by noradrenaline and adrenaline: it therefore causes relaxation of smooth muscle, including widening of arteries (vasodilatation) and a drop in blood pressure. Alpha blockers include *doxazosin, *phentolamine, *phenoxybenzamine, *indoramin, *prazosin, *alfuzosin, and *tamsulosin.... alpha blocker

Alpha-glucosidase Inhibitor

any member of a group of *oral hypoglycaemic drugs, including acarbose (Glucobay), used for treating type 2 *diabetes mellitus. They reduce the breakdown and absorption of carbohydrates in the intestine by blocking the action of an important enzyme (?-glucosidase) in this process. Side-effects include flatulence and diarrhoea.... alpha-glucosidase inhibitor

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