Question

Many pharmaceuticals act on the autonomic nervous system; either by mimicking Ach or NE and activating their receptors, or by blocking their receptors. Each of these drugs can have side effects.

Choose any one of the following pharmaceuticals and:

1) state whether it is targeting sympathetic or parasympathetic effectors based on the receptor type,

2) explain why/how it could have the treatment effect, and

3) predict which of the listed side effects it would have, with a brief explanation why.

Your explanations should focus on the activities of the sympathetic and parasympathetic nervous systems and their receptors. You may lump sympathetic receptor types together with the exception of those on most blood vessels, blood vessels serving skeletal muscle, the heart, and bronchi. Your explanations don’t need to be 100% correct for the specific drug, just logical predictions based on what we know about the ANS.

Here is the list of pharmaceuticals to choose from. Please choose ONE:

a)     A drug that blocks muscarinic receptors- used to prepare eyes for eye examinations

b)     A drug that activates muscarinic receptors- used to treat Sjogrens syndrome, an autoimmune disease that affects salivary glands

c)    A drug that activates alpha-1 receptors- used to decrease nasal congestion

d)    A drug that blocks beta-1 and beta-2 receptors- used to regulate heart rhythm and other cardiovascular treatments

e)     A drug that blocks alpha-1 receptors- used to regulate blood pressure

And here are the possible side effects. Remember, you are predicting which of these side effects your chosen drug is likely to cause based on the drug’s mechanism of action:

-Pupil dilation (need to shield eyes in bright light)

-Pupil constriction

-Dry mouth

-Decreased gastrointestinal motility (may interfere with absorption of other pharmaceuticals)

-Slow heart rate (bradycardia)

-Rapid heart rate (tachycardia)

-Laryngismus (constriction of the upper airway)

-Bronchodilation

-Bronchoconstriction

-Vasoconstriction (increased blood pressure)

-Vasodilation (decreased blood pressure)

Answer 1

I have chose the drug (d) that blocks beta-1 and beta-2 receptors and is used to regulate heart rhythm and other cardiovascular treatments. This class of drugs is called non-selective beta blockers as they block both beta 1 and beta 2 receptors. Propranol is one of the most commonly prescribed non-selective beta blockers.

Choose any one of the following pharmaceuticals and:

1) state whether it is targeting sympathetic or parasympathetic effectors based on the receptor type,

Ans: The drug targets the sympathetic effectors as it blocks the beta-1 and beta-2 adrenergic receptors.

2) explain why/how it could have the treatment effect, and

Ans: Beta blockers block the effect of the hormone epinephrine on the heart. As a result, the force of contraction and the heart rate are reduced. A similar effect can be seen in the blood vessels. The blockade of the beta receptors in the blood vessels will cause the smooth muscles in the arteries to relax thereby causing vasodilation. Vasodilation reduces the systemic vascular resistance and there is a fall in blood pressure. To summarise, beta blockers reduce heart rate, force of contraction of the heart and the blood pressure.

3) predict which of the listed side effects it would have, with a brief explanation why.

Beta blockers will have the following side effects. The explanation for each of the side effect has been explained.

-Dry mouth - Beta blockers block the autonomic ganglia that regulate secretion of saliva from the salivary glands. Hence they are known to cause dry mouth.

-Slow heart rate (bradycardia) - The effect of norepinephrine on the beta receptors of the heart is blocked by beta blockers.

-Bronchoconstriction -  Bronchoconstriction occurs because sympathetic nerves innervating the bronchioles normally activate β2-adrenoceptors that promote bronchodilation.

-Vasodilation (decreased blood pressure) - The beta receptors in the blood vessels are blocked. The smooth muscles relax and there is vasodialtion which decreases the blood pressure.