Nasal mucosa, vasoconstriction

Topical and systemic decongestants are sympathomimetic agents that act on adrenergic receptors in the nasal mucosa to produce vasoconstriction, shrink swollen mucosa, and improve ventilation. Decongestants work well in combination with antihistamines when nasal congestion is part of the clinical picture. 

Vasoconstriction induced by an a-sympathomimetic is followed by a phase of enhanced blood flow (reactive hyperemia, A). This reaction can be observed after the application of a-sympa-thomimetics (naphazoline, tetrahydro-zoline, xylometazoline) to the nasal mucosa. Initially, vasoconstriction reduces mucosal blood flow and, hence, capillary pressure. Fluid exuded into the interstitial space is drained through the veins, thus shrinking the nasal mucosa. 

Due to the reduced supply of fluid, secretion of nasal mucus decreases. In coryza, nasal patency is restored. However, after vasoconstriction subsides, reactive hyperemia causes renewed exudation of plasma fluid into the interstitial space, the nose is stuffy again, and the patient feels a need to reapply decongestant. In this way, a vicious cycle threatens. Besides rebound congestion, persistent use of a decongestant entails the risk of atrophic damage caused by prolonged hypoxia of the nasal mucosa. 

Functional antagonists of mediators of allergy, a) a-Sympathomi-metics, such as naphazoline, oxymeta-zoline, and tetrahydrozoline, are applied topically to the conjunctival and nasal mucosa to produce local vasoconstriction, and decongestion and to dry up secretions (p. 90), e.g., in hay fever. Since they may cause mucosal damage, their use should be short-term. 

Some of the indirectly acting adrenomimetic amines are used primarily for their vasoconstrictive properties. They are applied locally to the nasal mucosa or to the eye. Other amines are used as bronchodilators, while still others are used exclusively for their ability to stimulate the CNS. Many noncatecholamine adrenomimetic amines resist enzymatic destruction, have prolonged actions, and are orally effective. The indirectly acting drugs are effective only when given in large doses, and they often produce tachyphylaxis. 

Mechanism of Action A direct-acting sympathomimetic amine that acts on alpha-adrenergic receptors in arterioles of the nasal mucosa to produce constriction. Therapeutic Effect Causes vasoconstriction resulting in decreased blood flow and decreased nasal congestion. 

Mechanism of Action A sympathomimetic that directly acts on alpha-adrenergic receptors in arterioles of the nasal mucosa to produce vasoconstriction resulting in decreased blood flow. Therapeutic Effect Decreased nasal congestion. Pharmacokinetics Onset of acf ion occurs wif hin 5-10 minuf es for a duration of action of 5-6 hours. Well absorbed fhrough nasal mucosa. May also be systemically absorbed from bofh nasal mucosa and gasfroinfesfinal (GI) fracf. Half-life Unknown. 

There are major differences in receptor types predominantly expressed in the various vascular beds (Table 9-4). The skin vessels have predominantly receptors and constrict in response to epinephrine and norepinephrine, as do the splanchnic vessels. Vessels in skeletal muscle may constrict or dilate depending on whether a or 13 receptors are activated. The blood vessels of the nasal mucosa express a, receptors, and local vasoconstriction induced by sympathomimetics explains their decongestant action (see Therapeutic Uses of Sympathomimetic Drugs). 

All exert a rapid and potent vasoconstricting effect when applied directly to the nasal mucosa. They should only be used for short periods as rebound congestion can occur. 

By inhalation a local anaesthetic effect and vasoconstriction of the vessels in the nasal mucosa are obtained. 

When used topically as a nasal decongestant, the drug comes in direct contact with the nasal mucosa, causing vasoconstriction within mucosal vessels that have dilated due to the vasodilatory... 

Vasoconstriction in the nasal mucosa is the basis for the widespread use of alpha agonists as topical decongestants. The answer is (A). 

Nasal decongestant sprays such as phenylephrine and oxymetazoline that reduce inflammation by vasoconstriction are often used in sinusitis. Use should be limited to the recommended duration of the product to prevent rebound congestion. Oral decongestants may also aid in nasal or sinus patency. To reduce mucociliary function, irrigation of the nasal cavity with saline and steam inhalation may be used to increase mucosal moisture, and mucolytics (e.g., guaifenesin) maybe used to decrease the viscosity of nasal secretions. Antihistamines should not be used for acute bacterial sinusitis in view of their anticholinergic effects that can dry mucosa and disturb clearance of mucosal secretions. 

MecHanism of Action A sympathomimetic that directly stimulates alpha-adrenergic and beta-adrenergic receptors. Therapeutic Effect Produces vasoconstriction of respiratory tract mucosa shrinks nasal mucous membranes reduces edema and nasal congestion. 

Pseudoephedrine is an orally active sympathomimetic amine exerting its decongestant action by acting directly on a-adrenergic receptors in the respiratory tract mucosa producing vasoconstriction resulting in shrinkage of swollen nasal mucous membranes, reduction of tissue hyperemia, edema, and nasal... 

Acts directly on alpha-adrenergic receptors and to a lesser extent on beta-adrenergic receptors, producing vasoconstriction of respiratory tract mucosa, which causes shrinkage of nasal mucous membranes, edema, and nasal congestion... 

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