NE has, in general, rather feeble β 2 activity this activity is greatly increased in epinephrine by the addition of a methyl group.
Increase in the size of the alkyl substituent increases β receptor activity (e.g., isoproterenol). The effects of amino substitution are most readily seen in the actions of catecholamines on α and β receptors. This rule applies with few exceptions to all types of action. By far the greatest sympathomimetic activity occurs when two carbon atoms separate the ring from the amino group. Separation of Aromatic Ring and Amino Group. Despite the multiplicity of the sites of action of sympathomimetic amines, several generalizations can be made ( Table 12–1). Many directly acting sympathomimetic drugs influence both α and β receptors, but the ratio of activities varies among drugs in a continuous spectrum from predominantly α activity ( phenylephrine) to predominantly β activity ( isoproterenol). Since o-dihydroxybenzene is also known as catechol, sympathomimetic amines with these hydroxyl substitutions in the aromatic ring are termed catecholamines. NE, epinephrine, DA, isoproterenol, and a few other agents have hydroxyl groups substituted at positions 3 and 4 of the benzene ring. The structure permits substitutions to be made on the aromatic ring, the α- and β-carbon atoms, and the terminal amino group to yield a variety of compounds with sympathomimetic activity. β-Phenylethylamine ( Table 12–1) can be viewed as the parent compound of the sympathomimetic amines, consisting of a benzene ring and an ethylamine side chain. Prejunctional actions that either inhibit or facilitate the release of neurotransmitters, the inhibitory action being physiologically more important.Ĭhemistry and Structure-Activity Relationship of Sympathomimetic Amines.
ALPHA 2 ADRENERGIC AGONIST FREE
Metabolic actions, such as an increase in the rate of glycogenolysis in liver and muscle and liberation of free fatty acids from adipose tissue.Įndocrine actions, such as modulation (increasing or decreasing) of the secretion of insulin, renin, and pituitary hormones.Īctions in the central nervous system (CNS), such as respiratory stimulation, an increase in wakefulness and psychomotor activity, and a reduction in appetite.
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.Ī 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.Ī cardiac excitatory action that increases heart rate and force of contraction.
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