Catecholamine adrenergic antagonists

In animals, the hemorrhagic effects of acrylonitrile exposure on the adrenals may be reduced by prior exposure of the animals to adrenergic blockers or chemicals that deplete the adrenal cortex of catecholamines (Silver et al. 1987 Szabo et al. 1980). It is difficult to judge whether adrenergic antagonists would have a similar protective effect in humans, because effects of acrylonitrile on the adrenal have not been described in humans. 

Yohimbine, a tree-bark derivative also known as yohimbe, is widely used as an aphrodisiac. This can be explained by yohimbine s central 2 -adrenergic antagonistic effects, which increase catecholamines and improves mood. However, some investigators believe that yohimbine has peripheral proerectogenic effects. It has been postulated that... 

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... 

The major circulating hormones that influence vascular smooth muscle tone are the catecholamines epinephrine and norepinephrine. These hormones are released from the adrenal medulla in response to sympathetic nervous stimulation. In humans, 80% of catecholamine secretion is epinephrine and 20% is norepinephrine. Stimulation of cy-adrenergic receptors causes vasoconstriction. The selective a,-adrenergic receptor antagonist, prazosin, is effective in management of hypertension because it causes arterial and venous smooth muscle to relax. 

Agents that decrease catecholamines are used for the treatment of mania (e.g, DA antagonists and a2-adrenergic agonists). 

Carvedilol, medroxalol, and bucindolol are nonselective 3-receptor antagonists with some capacity to block 04-adrenergic receptors. Carvedilol antagonizes the actions of catecholamines more potently at 3 receptors than at a. receptors. 

Hoffman BB. Catecholamines, sympathomimetic dmgs, and adrenergic receptor antagonists. In Hardman, JG, et al, eds. The Pharmacological Basis of Therapeutics. 10th ed. New York McGraw-Hill 2001. 

Another cardiac response to catecholamine release is Increased vulnerability to ventricular fibrillation. Recent studies (13) have shown that bromocriptine produced an increase of 50% in the ventricular fibrillation threshold In anesthetized dogs, and that pretreatment with the peripheral D-2 dopamine antagonist domperidone abolished this effect. This suggests that adrenergic induced cardiac arrhythmia may be inhibited by peripheral presynaptic dopamine agonists. 

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