Alpha-Adrenergic Receptor Blockers

Bronchial asthma Overt cardiac failure AV block ( 1st degree) 

Alpha-adrenergic agents can cause marked hypotension after the first dose, especially in the upright position, with syncope and other postural symptoms 

Dosage must be individualized Initial dosage is 1 mg given once daily Depending on standing blood pressure, dose may increased to 2 mg and then if necessary to 4 mg, 8 mg, or 16 mg 

After 2 or 3 days, dosage may be titrated in increments of too mg BID every 2 or 3 days usual maintenance range is 200 mg to 400 mg twice daily 

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Phenoxybenzamine is a noncompetitive alpha-adrenergic-receptor blocker, and its action cannot be nuUifled by increasing the amount of agoinst, or agoinsts. It causes epinephrine reversal in that the administration of epinephrine after pretreatment with phenoxybenzamine elicits vasodilation, and, conversely, phenoxybenzamine reverses epinephrine-mediated vasoconstriction to vasodilation (see also Figure 37). 

I. Pharmacology. Phentolamine is a competitive presynaptic and postsynaptic alpha-adrenergic receptor blocker that produces peripheral vasodilation. By acting on both venous and arterial vessels, it decreases total peripheral resistance and venous return. It may also stimulate beta-adrenergic receptors, causing cardiac stimulation. Phentolamine has a rapid onset of action (usually 2 minutes) and short duration of effect (approximately 15-20 minutes). 

Some of the side effects due to beta blockers such as the slowing of heart rate can be counteracted by administration of drugs which antagonize the alpha adrenergic receptors. The... 

Alpha-adrenergic blockers inhibit the response at the alpha-adrenergic receptor sites. There are two types of alpha-adrenergic blockers ... 

Selective Alpha-adrenergic Blockers Affect a specific alpha-adrenergic receptor site... 

Nonselective Alpha-adrenergic Blockers Affect multiple alpha-adrenergic receptor sites... 

Alpha-adrenergic blockers inhibit the response at the alpha-adrenergic receptor sites. There are two types of alpha-adrenergic blockers selective and nonse-lective blockers. Both types decrease symptoms of benign prostatic hypertrophy (BPH) (enlarged prostate) and promote vasodilation and treat peripheral vascular disease such as Raynaud s disease. 

Adrenergic receptor blocker (Alpha) - in vitro (rat, aorta), cone, used not stated (Alpha-1) - in vitro (rat, aorta) 101... 

Adrenergic receptor blocker Yohimbine, alpha Indole alkaloid 815... 

Deficiency of adrenal medullary catecholamines appears to give no ill effects, and replacement therapy is therefore not used, but adrenal medullary tumours, phaeochromocytomas, secrete excess catecholamines often causing hypertension with dramatic episodes of headache, palpitations, pallor, sweating and anxiety. This condition is normally treated surgically, but preoperative preparation is mandatory to avoid catastrophic effects of surges of catecholamine release. A combination of alpha- and beta-adrenergic receptor blockade is normally used, with drugs such as phenoxybenzamine or doxazosin as alpha-blockers, and propranolol as a non-selective beta-blocker. 

Alpha-adrenergic antagonists are used primarily as antihypertensive drugs because of their ability to block vascular alpha-1 receptors. Beta-adrenergic antagonists (beta blockers) are administered primarily for their inhibitory effects on myocardial function and are used in the prevention and treatment of hypertension, angina pectoris, arrhythmias, and myocardial reinfarction. Many of the drugs introduced in this chapter are discussed further in chapters that deal with the specific clinical conditions (e.g., hypertension, asthma, and other disorders). 

This category includes ACE inhibitors, adrenergic neurone blockers, alpha-blockers, angiotensin II receptor antagonists and centrally acting vasodilatory antihypertensives. 

ACE INHIBITORS, ADRENERGIC NEURONE BLOCKERS, ALPHA-BLOCKERS, ANGIOTENSIN II RECEPTOR ANTAGONISTS, CENTRALLY ACTING AND VASODILATOR ANTIHYPERTENSIVES ... 

In this chapter we summarize some aspects of the structure-functional relationship of the ala and alb-adrenergic receptor subtypes related to the receptor activation process as well as the effect of different alpha-blockers on the constitutive activity of the receptor. Molecular modeling of the ala and alb-adrenergic receptor subtypes and computational simulation of receptor dynamics were useful to interpret the experimental findings derived from site directed mutagenesis studies. 2000 Elsevier Science B.V. All rights reserved. 

Labetalol hydrochloride is an alpha-adrenergic blocker/beta-adrenergic blocker that selectively blocks alpha-1 receptors and nonselectively blocks beta receptors to decrease BP, heart rate, and myocardial oxygen demand. It is indicated in the management of hypertension. 

Tamsulosin is an alpha -adrenergic blocker that selectively blocks alphai-adrenergic receptors, causing relaxation of prostate smooth muscle resulting in an increase in urinary flow rate and a reduction in symptoms of BPH. It is used in the treatment of signs and symptoms of benign prostatic hyperplasia (BPH). 

Alpha blockers Alpha adrenergic antagonists compete with endogenous catecholamines for binding at and CC receptors. Because norepinephrine and epinephrine cannot bind to a receptor that is occupied by an antagonist, the actions of catecholamines at... 

Alpha and beta blockers compete with endogenous agonists for adrenergic receptors. Antagonist occupation of al receptors inhibits vasoconstriction and occupation of pi receptors prevents adrenergic stimulation of the heart. 

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