Alpha-adrenoceptor antagonist

Djavan B, Chappie C, Milani S, Marberger M. State of the art on the efficacy and tolerability of alpha, adrenoceptor antagonists in patients with lower urinary tract symptoms suggestive of benign prostatic hyperplasia. Urology 2004 64 1081-1088. 

Pellejero, T., Monti, J. M., Baglietto, J. et al. (1984). Effects of methoxamine and alpha-adrenoceptor antagonists, prazosin and yohimbine, on the sleep-wake cycle of the rat. Sleep 7, 365-72. 

Baraban, J. M., and Aghajanian, G. K. (1980) Suppression of serotonergic neuronal firing by alpha-adrenoceptor antagonists Evidence against GABA mediation. Eur. J. Pharmacol., 66 287-294. 

Elliott HE, Jones CR, Vincent J, et al The alpha adrenoceptor antagonist properties of idazoxan in normal subjects. Chn Pharmacol Ther 36 190-196, 1984... 

Alpha-adrenoceptor antagonists inhibit the activation of a adrenoceptors by catecholamines. In the cardiovascular system these receptors are mainly located on the surface of smooth muscle cells in the walls of arteries and veins. On activation, they mediate an increase in intracellular free calcium, which induces smooth muscle contraction. Inhibition by an a antagonist causes arterial or venous vasodilatation. The postsynaptic effect is mainly mediated by ol adrenoceptors whereas o2 adrenoceptors are found on the presynaptic membranes of the sympathetic neurones. Activation of o2-adreno-ceptors results in auto-inhibition of catecholamine release. 

Alpha-adrenoceptor antagonists are used as antihypertensives and to reduce afterload in the treatment of heart failure. Urapidil and, to a lesser extent, ketanserin are used in the treatment of essential hypertension and acute perioperative hypertension. In contrast to other vasodilators urapidil does not increase intracranial pressure when given intravenously, making it preferable for use in neurosurgical interventions. The effects of the excessive catecholamine concentrations in patients with phaeochromocytoma can be treated by the non-selective ol- and o2-adrenoceptor antagonists phentolamine or phenoxybenzamine. 

The benefit of combining an alpha-adrenoceptor antagonist with a 5-alpha-reductase inhibitor has been assessed in men with benign prostatic hyperplasia (23). Modified-release alfuzosin was more effective than finasteride, with no additional benefit in combining the drugs. The adverse effects of alpha-blockade were postural hypotension, hypotension, headache, dizziness, and malaise the adverse effects of finasteride were ejaculatory disorders and impotence. 

In the phenothiazine series of neuroleptics, thioridazine has less antimuscarinic potency than chlorpromazine, but appears to be equally active as an antagonist of 5-HT2 and D2 receptors like chlorpromazine, however, it is a potent alpha] adrenoceptor antagonist. In contrast, the potent phenothiazine neuroleptic perphenazine is only slightly less selective in blocking D2 receptors than haloperidol but, unlike the latter, has a greater antagonistic effect on histamine receptors. 

Prazosin is an a i-selective adrenoceptor antagonist which causes vasodilation and a fall in BP. Alpha-adrenoceptor antagonists also have a favourable effect on blood lipids and are useful for people with raised cholesterol. However, orthostatic hypotension may occur during treatment because prazosin interferes with the postural reflexes, which are triggered when a patient stands up from a supine or sitting position. 

Alpha-adrenoceptor antagonists are useful antihypertensives they block the vasoconstrictor effects of a-receptor stimulation. There is sometimes a problem with postural hypotension as reflexes which normally raise BP on standing are interrupted. These agents have a beneficial effect on blood lipids. 

In one patient who took 900 mg of phenelzine, there was a marked excess of urinary and plasma catecholamines, analogous to pheochromocytoma, and the patient was successfully managed with alpha-adrenoceptor antagonists (44). In another patient, who probably... 

Trazodone (SEDA-7,19-21) is a triazolopyridine derivative that selectively but weakly inhibits 5-hydroxytrypta-mine (5-HT) re-uptake and is an alpha-adrenoceptor antagonist at both presynaptic and postsynaptic receptors (1). During long-term administration it down-regulates serotonin receptors (2). 

Neuroleptic drugs can intensify the effects of alpha-adrenoceptor antagonists, for example phentolamine, causing severe hypotension (552). 

Chlorpromazine is a phenothiazine with a large range of pharmacological actions it is a dopamine receptor antagonist, an alpha-adrenoceptor antagonist, a muscarinic antagonist, and an antihistamine. 

Hypotension is the most commonly observed cardiovascular adverse effect of neuroleptic drugs, particularly after administration of those that are also potent alpha-adrenoceptor antagonists, such as chlorpromazine, thioridazine, and clozapine (34). A central mechanism involving the vasomotor regulatory center may also contribute to the lowering of blood pressure. 

Alpha-adrenoceptor antagonists. Prazosin, afluzosin, indoramin, terazosin and doxazosin are all a-adrenoceptor blockers, with selectivity for the a -subtype. They cause significant increases (compared to placebo) in objective measures such as maximal... 

The postsjmaptic alpha-adrenoceptor antagonists, indor-amin, prazosin, and related quinazoline derivatives, block alphai-adrenoceptor-mediated vasoconstriction of peripheral blood vessels (both arterial and venous) and are effectively peripheral vasodilators (1,2). Qualitatively and quantitatively common adverse effects are generally similar, although indoramin has additional effects on other neurotransmitter systems and therefore tends to be considered separately. Their use in benign prostatic hyperplasia has been reviewed (3,4). 

Narayan P, Man In t Veld AJ. Clinical pharmacology of modern antihypertensive agents and their interaction with alpha-adrenoceptor antagonists. Br J Urol 1998 81(Suppl 1) 6-16. 

Buflomedil hydrochloride is a vasoactive drug with a variety of actions. It is an alpha-adrenoceptor antagonist and a weak calcium channel blocker. It inhibits platelet aggregation and improves erythrocyte deformability. However, its mechanism of action in peripheral vascular disease is not known. 

Moxisylyte is an alpha-adrenoceptor antagonist with vasodilatory activity (1). It is used orally in the treatment of peripheral vascular disease and by intracavernosal injection in erectile dysfunction. 

Phentolamine is a non-selective alpha-adrenoceptor antagonist. It is used to treat hypertensive crises attributable to the effects of noradrenahne, as in pheochromo-cytoma and during the interaction of monoamine oxidase inhibitors with amine-containing medicaments and foods (1). Its adverse effects are similar to those of phenoxy-benzamine. 

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