Drugs that act as vasoconstrictor sympathomimetics

Question 1

What are alpha receptors important for?

Answer 1

In the blood vessel wall, the presence of A receptors in vascular smooth muscle cells is important for controlling vascular reactivity to sympathetic nervous stimulation.

Question 2

Vasoconstrictor sympathomimetic drugs- how do A agonists raise blood pressure?

Answer 2

A agonists raise BP by constricting peripheral arterioles.

Question 3

What is the prevalence and action of pseudoephedrine?

Answer 3

Ephedrine’s stereoisomer, pseudoephedrine, is much more widely encountered. It has a similar action to ephedrine (it stimulates noradrenaline release from sympathetic nerves) but is much less potent. It also has some direct A agonist activity.

Question 4

How are phenylephrine and pseudoephedrine used in nasal congestion?

Answer 4

Phenylephrine and pseudoephrine cause vasoconstriction in the inflamed mucous membranes, reducing nasal secretions and stuffiness. Their particular value is in symptomatic relief of nasal and sinus congestion in colds, flu and allergic conditions.

Question 5

What happens when A1 receptors are stimulated?

Answer 5

In response to A1 receptor stimulation (by noradrenaline or adrenaline), a signal transduction cascade is enacted which results in high intracellular Ca concentrations, resulting in smooth muscle contraction.
A1 receptor stimulation therefore promotes vasoconstriction.

Question 6

What class is is phenylephrine and what is it used for?

Answer 6

Phenylephrine is a directly acting sympathomimetic used to raise BP in emergency but can reduce perfusion to vital organs

Question 7

What class is ephedrine and what does it do?

Answer 7

Ephedrine is an indirectly acting sympathomimetic stimulating NAd release, so causes dual A and B action

Question 8

Name some other drugs used for nasal decongestion

Answer 8

Naphazoline, xylometazoline and antazoline are structurally related A1 agonists, al used topically as nasal drops for nasal congestion.