This document describes a simulation experiment to study the effects of various drugs on blood pressure and heart rate in a pithed rat model. The drugs tested include acetylcholine (ACh), glyceryl trinitrate (GTN), an NO synthase inhibitor (L-NOArg), and atropine. The simulation involves recording changes after intravenous injection of these drugs, alone and in combination. A series of questions about the mechanisms and clinical uses of organic nitrates in angina treatment are also provided, along with answers.

1. PROBLEM2 2021
1 CVSSimulation forPHASEIIMBBS PHARMACOLOGYSTUDENTS (https://doctoru.weebly.com/)
PROBLEM 2: Organic Nitrates and Endothelium
Object
1. Demonstrate the effect of given drugs on Rat CVS
2. Draw (use pencil ONLY) the tracing of changes on arterial blood pressure and heart rate following
intravenous injection of the given drugs
3. Make relevant observation table
4. Complete the set of questions
Methods
Select “Pithed”. Record the effect of the following on arterial blood pressure and heart rate:
(i) Intravenous injection (select mid-range concentrations from the menu) of:
acetylcholine (ACh)
glyceryl trinitrate (GTN)
(ii) Inject 50 mg kg-1
of the NO synthase inhibitor L-NOArg.
(iii) Repeat the injections of ACh and GTN.
(v) Inject 5 mg kg-1
atropine.
(vi) Repeat the injections of ACh and GTN.

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Drugs
Drugs affecting the cardiovascular and their receptors.
Drug Receptor
Acetylcholine Cholinoceptor agonist
Glyceryl Trinitrate Nitric oxide
Atropine Muscarinic cholinoceptor antagonist
L-NOArg Nitric oxide synthase inhibitor
Receptors
Receptor types and drug targets present on the heart and blood vessel and action on tissues.
Tissue Receptor / target Action
Heart Muscarinic cholinoceptor Decreases heart rate and force
Blood vessels Nitric Oxide Vasodilation

3. PROBLEM2 2021
3 CVSSimulation forPHASEIIMBBS PHARMACOLOGYSTUDENTS (https://doctoru.weebly.com/)
Draw (use pencil ONLY) tracings of changes on ABP & HR
ACh:
GTN:
L-NOArg+ACh:
L-NOArg+GTN:
Atropine+ACh:
Atropine+GTN:

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Observation Table - pithed rat simulation
Intervention Systolic ABP
mmHg
Diastolic
ABP
mmHg
Heart rate
Beats/min
Control – before drug
After acetylcholine
Change due to ACh
Control – before drug
After glyceryl trinitrate
Change due to GTN
Control
After L-NOArg+ACh
Change due to L-NOArg+ACh
Control
After L-NOArg+GTN

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Change due to L-NOArg+GTN
Control
After atropine+ACh
Change due to atropine+ACh
Control
After atropine+GTN
Change due to atropine+GTN

6. PROBLEM2 2021
6 CVSSimulation forPHASEIIMBBS PHARMACOLOGYSTUDENTS (https://doctoru.weebly.com/)
Set of Questions (with answers)
1. What two mechanistic strategies are used in the treatment of angina?
1. Increase oxygen supply to the myocardium
2. Decrease myocardial oxygen demand
2. What types of drugs can increase oxygen supply?
Nitrates; calcium channel blockers (CCBs)
3. What types of drugs can decrease oxygen demand?
Nitrates; CCBs; β-blockers
4. What is the drug of choice for immediate relief of anginal symptoms?
Sublingual nitroglycerin (NTG)
5. What is the mechanism of action of nitrates?
Nitrates form nitrites; nitrites form nitric oxide (NO); NO activates guanylyl cyclase to
increase cGMP; increased cGMP leads to increased relaxation of vascular smooth
muscle.
6. How does cGMP lead to relaxation of vascular smooth muscle?
Causes dephosphorylation of myosin light chains
7. How do nitrates increase oxygen supply?
Dilation of coronary vessels which leads to increased blood supply
8. How do nitrates decrease oxygen demand?
Dilation of large veins which leads to preload reduction; decreased preload reduces the
amount of work done by the heart; decreased amount of work results in decreased
myocardial oxygen requirement
9. What are the adverse effects of nitrates?
Headache; hypotension; reflex tachycardia; facial flushing; methemoglobinemia
10. Why must patients have at least a 10-to 12-hour “nitrate-free” interval every day?
Tolerance (tachyphylaxis) develops to nitrates if given on a continuous (around-the-
clock) basis
11. Nitrates are contraindicated in patients taking which drugs?
1. Sildenafil 2. Vardenafil 3. Tadalafil
12. Methemoglobin formation, specifically by amyl nitrite, can be used to treat what type of
poisoning?
Cyanide
13. What are the common formulations of nitrates?
NTG; isosorbide mononitrate; isosorbide dinitrate
14. What is the time to peak effect of sublingual NTG?
2 minutes
15. What is the dosing frequency of sublingual NTG during an anginal episode?
Every 5 minutes for a maximum of three doses
16. How do β-blockers work in the treatment of angina?
Inhibition of β 1 -adrenoceptors which leads to decreased CO, HR, and force of
contraction, thereby reducing the workload of the heart and oxygen demand
17. Do α-blockers increase oxygen supply?
No
18. For each of the following CCBs, state whether their primary effects are on the myocardium or peripheral
vasculature:
Verapamil -Myocardium (greater negative inotropic effects)
Dihydropyridines -Peripheral vasculature (more potent vasodilators)
(DHP;nifedipine, amlodipine, felodipine, isradipine, nicardipine) Diltiazem-Myocardium
19. How do CCBs work in the treatment of angina?

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Block vascular L-type calcium channels which leads to decreased heart contractility and
increased vasodilation
20. How can ACh lower blood pressure?
ACh binds to ACh receptors in the vasculature leading to increased synthesis of nitric
oxide (NO) via second messenger pathways. An increase in NO leads to vasodilation.
21. NO is also known as what?
Endothelial-derived relaxation factor (EDRF)
22. What amino acid is a precursor of NO synthesis?
Arginine
23. What does ACh do to the ciliary muscle of the eye?
Increased contraction which leads to increased accommodation
24. How does ACh cause miosis?
Increased contraction of the circular muscle in the iris.
REFERENCES
1. Dempster J. Strathclyde Pharmacology Simulations Software. 2021. University of Strathclyde.
2. Gleason J. Deja Review: Pharmacology.