Adrenoceptor Antagonists

Drugs that produce responses by interacting with adrenoceptors are referred to as adrenoceptor agonists or adrenergic agonists. Norepinephrine and isoproterenol are examples of such compounds. Agents that inhibit responses mediated by adrenoceptor activation are known as adrenoceptor antagonists, adrenergic antagonists, or adrenergic blocking agents. Prazosin and propranolol are examples of receptor-blocking drugs. The pharmacology of the adrenoceptor antagonists is described in this chapter. Norepinephrine is released from the varicosities of the postganglionic sympathetic nerves during neural activity and interacts with the adrenoceptors of the effector organ, producing the characteristic response of the effector. This occurs because norepinephrine has an affinity for the receptors and possesses intrinsic activity; that is, it has the capacity to activate the receptors. Circulating catecholamines and other directly acting adrenomimetic drugs also interact with these receptors. The adrenergic blocking agents also have an affinity for the adrenoceptors. The antagonists, however, have only limited or no capacity to activate the receptors; that is, they have little or negligible intrinsic activity.The blocking drugs compete with adrenomimetic substances for access to the receptors. Thus, these agents reduce the effects produced by both sympathetic nerve stimulation and by exogenously administered adrenomimetics. This action forms the basis for their therapeutic and investigational use. D R U G L I S T Adrenoceptor Antagonists