Adrenergic Agonists And Antagonists I Catecholamines And Sympathomimetic Drugs

Actions of catecholamines and sympathomimetic agents can be classified into seven broad types: (1) peripheral excitatory actions on smooth muscles (e.g., in blood vessels supplying skin, kidney, and mucous membranes) and on gland cells (e.g., in salivary and sweat glands); (2) peripheral inhibitory action on certain other types of smooth muscle (e.g., in the wall of the gut, bronchial tree, and blood vessels supplying skeletal muscle); (3) cardiac excitatory action (increased rate and force of contraction); (4) metabolic actions (e.g., enhanced glycogenolysis in liver and muscle, accelerated liberation of free fatty acids from adipose tissue); (5) endocrine actions (e.g., modulation of secretion of insulin, renin, and pituitary hormones); (6) actions in the central nervous system (CNS) (e.g., respiratory stimulation, increased wakefulness and psychomotor activity, reduced appetite); and (7) prejunctional actions (inhibition or facilitation of neurotransmitter release, inhibition being physiologically more important). Not all sympathomimetic drugs show each of the above types of action to the same degree; however, many of their differences are only quantitative.

Understanding the pharmacological properties of sympathomimetics and their antagonists depends on knowledge of the classification, distribution, and mechanism of action of a and b adrenergic receptors (see Tables 6-1, 6-6, 6-7, Figure 10-1, and Table 10-6).

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