Toxicology

1. •
Pharmacology 1 (3443)
•
Spring 2020
•
Lab 7
Faculty of Pharmacy
Department of Pharmacology
& Toxicology

2. Determination of the site of action
of
Different cardiac stimulant &
depressant drugs
using
Isolated Frog Heart

3. M2
NN
NN
1
Drugs
Depressants Stimulants
Nn agonist (e.g. Dil. nicotine) β-agonist (e.g. Isoprenaline)
M agonist (e.g. Ach) Direct stimulant (e.g. Ca2+)
Direct depressant (e.g. K+ )

4. Setup

5. -ve chronotropic
-ve chronotropic
-ve inotropic
-ve inotropic
Depressants
Stimulants
+ve chronotropic
+ve chronotropic
+ve inotropic
+ve inotropic

6. Agonists and blockers used in the
experiment
Receptor Agonist Blocker
β Isoprenaline Propranolol
Nn Dil. nicotine Hexamethonium
M Ach Atropine

7. Steps to test if a drug acts on a
certain receptor
UNK
AGONIST
Before self
WASH
Before self
WASH
AGONIST
Allow self
WASH
BLOCKER
Allow self
WASH
Start
If no action  Unk
acts on the blocked
receptor
If there is still action 
Unk doesn’t act on the
blocked receptor 
Test another receptor

8. Why is the agonist added after the
blocker?
To test for complete blockade of the
receptor.
Why is the agonist added before the
blocker?
To test for the sensitivity of the receptor
to the added agonist.

9. PROCEDURE
1. Inject the unk drug
2. Determine the lag time & self
washing time

10. a) If the unk is stimulant:
- Add Isoprenaline (allow self washing)
- Add the following 3 consecutively (before
self washing)
No stimulation 
Unk is β agonist
Stimulation 
Unk is directly acting
Prop Isop Unk

11. Unk is
DIRECT
Unk is
β1
agonist
Unk Isop
Prop
Isop
Unk

12. b) If the unknown is depressant:
 Test for nicotinic action:
- Add dil. Nicotine
- Add the following 3:
No depression 
Unk is Nn agonist
Depression 
continue the experiment
Hexa. Dil. nic. Unk

13.  Test for muscarinic action:
- Add Ach
- Add the following 3:
No depression 
Unk is M agonist
Depression 
Unk is directly acting
Atrop. Ach Unk

14. 0.1
Dil. Nic.
0.1
Hexam.
0.1
Dil. Nic
0.1
Unk
0.1
Unk
Site of action:
Nicotinic agonist
Unknown may be Dil nicotine

15. 0.1
Dil. Nic.
0.2
Hexam.
0.1
Dil. Nic.
0.1
Unk
0.1
Unk
0.1
ACh
0.1
Atrop
0.1
ACh 0.1
Unk
Site of action:
Muscarinic agonist
Unknown may be ACh

16. 0.1
Ach
0.1
Hexam.
0.1
Atrop
0.1
Unk
0.1
Dil. Nic.
0.1
Dil. Nic.
0.1
Unk
0.1
ACh 0.1
Unk
Site of action:
Direct acting Depressant
Unknown may be K+