b Adrenergic receptor antagonists inhibit the interaction of NE, Epi, and sympathomimetic drugs with b receptors. Detailed knowledge of autonomic tone, localization of b receptor subtypes, effector-response coupling, and the multiplicity of possible actions of these drugs is essential for understanding their pharmacological effects and therapeutic uses (see Tables 6-1, 6-6, 6-7, 6-8, 10-2, 10-6, and Figure 10-3). Effects of b adrenergic antagonists may be predicted from the consequences of b receptor stimulation (generally equivalent to the effects of elevated cyclic AMP). Effects of b antagonists at a particular site depend on the level of receptor stimulation, or tone, at that site. Effects of antagonists are more prominent when receptor stimulation by agonist is high.
b antagonists can be distinguished by: relative specificity for b1 over b2 receptors, intrinsic sym-pathomimetic activity, capacity to block b receptors, differences in lipid solubility, capacity to induce vasodilation, and pharmacokinetic properties. b Adrenergic antagonists may be classified as Non-Subtype Selective (First Generation), ^-Selective (Second Generation), and Antagonists with Additional Cardiovascular Actions (Third Generation). Table 10-4 summarizes pharmacological and pharmacokinetic properties of b receptor antagonists.
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