Cardiovascular SystemPrepared by Marc Walters, M.D., Portland Community College
Before solving these mini-cases, we'll provide some information regarding cell membrane receptors. A receptor
agonist stimulates receptors. A receptor
antagonist, or blocker, binds the receptor but doesn't stimulate it; an antagonist usually has the opposite effect of an agonist. Table I includes the locations of some adrenergic (sympathetic) and cholinergic (usually parasympathetic) receptors:
Table I
| Organ or Variable Affected |
Effects of sympathetic stimulation: |
Adrenergic receptor on target organ |
Effects of Parasympa- thetic stimulation: |
Cholinergic receptor on target organ |
| Heart rate |
Increase |
Beta1 |
Decrease |
ACh |
| Heart Contractility |
Increase |
Beta1 |
Decrease |
ACh |
| Skin & mucous membrane arteries |
Constrict |
Alpha1 |
|
|
| Bronchi: |
Dilate |
Beta2 |
Constrict |
ACh |
Here are two examples of how to relate the information displayed in Table I to agonists & antagonists:
a. A Beta
1 receptor antagonist slows the heart rate.
b. An ACh agonist causes bronchoconstriction.
Table II lists some receptor agonists and antagonists that could be used in treating the clinical cases. The drugs listed in this table are not necessarily the one used most often to treat the conditions in the cases and may not be the most appropriate type of treatment. However, studying these drugs and their effects will help you better understand the relationship between the autonomic system and the cardiovascular system.
Table II
| Drug |
Effects on Receptor |
| Atenolol |
Beta1 blocker (=antagonist) |
| Propranolol |
Beta1, Beta2 receptor blocker |
| Prazosin |
Alpha1 receptor blocker |
| Atropine |
ACh receptor blocker |
| |
|
| Phenylephrine |
Alpha1 agonist |
| Dobutamine |
Beta1 agonist |
| Albuterol |
Beta2 agonist |
| Norepinephrine |
Alpha1, Alpha2, Beta1 agonist with predominantly alpha 1 agonist properties |
Case 1
Richard Thompson is a 35-year-old male whose blood pressure was consistently tested at approximately 145/100 despite following a low-sodium diet, omitting alcohol, and beginning an exercise program. He has no symptoms related to this elevated blood pressure. He has a history of asthma.
QUESTIONS
Answer the questions below to demonstrate your knowledge.
Answers are available in the Instructor Resources section of this site.
