OVERVIEW: ACTIONS OF CATECHOLAMINES AND SYMPATHOMIMETIC DRUGS
Most of the actions of catecholamines and sympathomimetic agents can be classified into seven broad types:
A peripheral excitatory action on certain types of smooth muscle, such as those in blood vessels supplying skin, kidney, and mucous membranes; and on gland cells, such as those in salivary and sweat glands.
A peripheral inhibitory action on certain other types of smooth muscle, such as those in the wall of the gut, in the bronchial tree, and in blood vessels supplying skeletal muscle.
A cardiac excitatory action that increases heart rate and force of contraction.
Metabolic actions, such as an increase in the rate of glycogenolysis in liver and muscle and liberation of free fatty acids from adipose tissue.
Endocrine actions, such as modulation (increasing or decreasing) of the secretion of insulin, renin, and pituitary hormones.
Actions in the CNS, such as respiratory stimulation, an increase in wakefulness and psychomotor activity, and a reduction in appetite.
Prejunctional actions that either inhibit or facilitate the release of neurotransmitters, the inhibitory action being physiologically more important.
Many of these actions and the receptors that mediate them are summarized in Tables 8–1 and 8–6. Not all sympathomimetic drugs show each of the types of action to the same degree; however, many of the differences in their effects are only quantitative. The pharmacological properties of these drugs as a class are described in detail for the prototypical agent, epinephrine (EPI). Appreciation of the pharmacological properties of the drugs described in this chapter depends on an understanding of the classification, distribution, and mechanism of action of α and β adrenergic receptors (Chapter 8).
AAAD: l-aromatic amino acid decarboxylase
ACEI: angiotensin-converting enzyme inhibitor
ADHD: attention-deficit/hyperactivity disorder
BPH: benign prostatic hyperplasia
CNS: central nervous system
COPD: chronic obstructive pulmonary disease
FDA: Food and Drug Administration
HDL: high-density lipoprotein
HMG CoA: 3-hydroxy-3-methylglutaryl coenzyme A
5HT: 5-hydroxytryptamine (serotonin)
INE: isoproterenol (Isopropyl NE)
LABA: long-acting β2 adrenergic agonist
LDL: low-density lipoprotein
MAO: monoamine oxidase
NET: NE transporter
NPY: neuropeptide Y
PVR: peripheral vascular resistance
ROS: reactive oxygen species
VLABA: very long-acting β2 adrenergic agonist
CLASSIFICATION OF SYMPATHOMIMETIC DRUGS
Catecholamines and sympathomimetic drugs are classified as direct-acting, indirect-acting, or mixed-acting sympathomimetics (Figure 12–1). Direct-acting sympathomimetic drugs act directly on one or more of the adrenergic receptors. These agents may exhibit considerable selectivity for a specific receptor subtype (e.g., phenylephrine for α1, terbutaline for β2) or may have no or minimal selectivity and act on several receptor types (e.g., EPI for α1, α2, β1, β2, and β3 receptors; NE for α1...