A-Adrenergic blocking action

Adenine, 423 Adenyl cyclase, 62 Adiphenine, 91 Adrenal gland extracts, 188 Adrenaline, see epinephrine a-Adrenergic blocking action, 242... 

Risperidone may also cause hypotension via its a-adrenergic blocking actions ( 501). In the elderly, hypotensive side effects can occur, especially if there is any of the following ... 

It possesses considerable a-adrenergic blocking action and consequently induces dilatation... 

Dubiusine (33), homolycorine (26), 8-D-demethylhomolycorine (27), and lycorenine (35) have a hypotensive effect on the arterial pressure of normotensive rats (498). Lycorenine also shows a vasodepressor action ascribed to the maintenance of its a-adrenergic blocking action, and produces bradycardia by modifying vagal activity (499). Another feature of lycorenine is its analgesic activity (20). 

In addition, other chemicals such as a-adrenergic blocking agents like chlorpromazine (O Flaherty and Thomas 1982 Way and Burrows 1976) or oxygen (Burrows et al. 1973 Sheehy and Way 1968) may be used to enhance the protective action of other antidotes. However, the mechanism of their action is not well understood. Further research for a potent and safe antidote, particularly among smoke inhalation victims who have carbon monoxide poisoning, to mitigate cyanide toxicity is desirable. 

Also, as with diuretics, cardiac output is gradually restored, yet the hypotensive effect remains. Labetalol, a unique 8-adrenoblocker best suited to lower blood pressure, combines nonselective 8-adrenergic blocking action on both p - and jSj-receptors with simultaneous blockage of tti-receptors. 

Both drugs are partial agonists at a-adrenergic receptors and at some serotonin and dopamine receptors they also can inhibit the release of endotheUal-derived relaxation factor. They may induce arterial vasoconstriction and have minor actions on the central nervous system. Their a-adrenergic blocking activity is relatively weak compared with those of other ergot alkaloids. 

ANS They have varying degree of a adrenergic blocking activity. They also have weak anti-cholinergic, Hj-antihistaminic and anti 5-HT actions as well. 

Sedation is related to the antihistamine action and the a-adrenergic blocking properties (phenothiazines are therefore very sedative). 

Terazosin has a peripheral postsynaptic alpha,-adrenergic-blocking action, which is thought to account primarily for its effects (see Figure 37). 

It is mostly used as a vasodilator with a-adrenergic blocking activity and direct vasodilator actions. It exhibits a sympathomimetic effect to stimulate the heart, in doing so the BP sometimes gets increased moderately, despite vasodilation. It is foimd to be an effeetive 0C2-antagonist having a free... 

Administration of an aqueous extract of yohimbe at doses of 1 to 1000 ng/kg elicited a dose-dependent increase in mean blood pressure and an increase in medullary blood flow. Both the pressor action and renal medullary vasodilation were blocked by endothelin A and B receptor antagonists in combination. N -nitro-L-arginine methyl ester also inhibited the increase in medullary blood flow induced by yohimbe. The authors of the study concluded that preliminary observations indicate that, in addition to the a-adrenergic antagonist actions that characterize yohimbine, yohimbe possesses endothelin-like actions and affects nitric oxide production in the renal circulation (Ajayi et al. 2003). 

Older tricyclic antidepressants are set in italics. The specificity of action of tricyclic antidepressants (in particular of amitritpyline, imipmmine, doxepine, noitriptyline, maprotiline) is limited because at therapeutic levels ihese drugs also block receptors (H t-histamine, a,-adrenergic, muscarinic). 

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