3 Adrenergic receptor antagonist with epinephrine

Epinephrine can produce severe hypertension when used with a nonselective P receptor antagonist due to the unopposed stimulation of a receptors when vascular receptors are blocked. Such paradoxical hypertensive responses to p adrenergic receptor antagonists have been observed in patients with hypoglycemia or pheochromocytoma, during withdrawal from clonidine, following administration of Epi as a therapeutic agent, or in association with the iUicit use of cocaine. 

Receptor antagonists are not the drugs of choice in patients with pheochromocytoma, because a vasoconstrictor response to epinephrine can still result from activation of unblocked vascular (X2 adrenergic receptors, Receptor antagonists are attractive drugs for hypertensive patients with benign prostatic hyperplasia, since they also improve urinary symptoms. 

The effect of catecholamines on System A activity has been tested in freshly isolated cells as well. Freychet and his colleagues (50,57) showed that most of the stimulatory action of epinephrine was mediated by a-adrenergic receptors. Phentolamine blocked about 90% of the epinephrine-induced transport, while the )9-antagonist propanolol reduced the hormonal stimulation by only 15% (50). Furthermore, epinephrine was more potent by an order of magnitude than isoproterenol with respect to enhancement of transport (50). 

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... 

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