1. Effect & Sites of Action of Different Agonist Drugs on The Isolated Rabbit Intestine
Lab # 1

2. Purpose of Pharmacological Experiments
Qualitative
To determine the activity & mechanism of drugs action e.g. analgesic, effect on blood pressure
Quantitative
To assay (measure) the activity of drugs e.g. toxic level

3. Types of pharmacological experiments
In vivo
Study the action of drugs on the whole body (intact animal)
There is interference by compensatory mechanisms of body
Easier to study effect of drugs
In vitro
Study the action of drugs on pieces of tissue
There is no interference by compensatory mechanisms of body
Easier to study MOA & potency of drugs

4. In vitro experiments
- In vitro experiments involve the use of isolated organ or muscle
- Conditions of the experiment should be kept similar to body
Experiment conditions:
1- Electrolytes
2- Nutrients
3- Physiological pH
4- Constant temperature
5- Aeration

5. Electrolytes Physiological solution: Ex. Tyrode’s & Kreb’s
Ingredients:
1- Nacl → adjust the tonicity
2- Ca+2, K+, Mg+2 → for normal contraction
3- Sodium bicarbonate → to render the pH similar to that of blood
4- NaH2PO4 → to compensate for any change in the pH
5- Glucose → nutrient

6. Aeration Examples Pure oxygen → for heart tissues Air → for intestine
Carbogen (95% O2, 5% CO2) → used for uterus

7. Temperature Temperature should be kept constant during the experiment
Physiological temp. (37°C) is needed for mammalian tissues e.g. rabbit intestine
The temp. should be reduced in some experiments to decrease spontaneous contraction e.g. isolated guinea-pig ileum
Amphibian tissues can survive in room temp. e.g. isolated frog rectus abdominis

8. Intestine Intestine is composed of duodenum, jejunum & ileum
It is a smooth muscle & has myogenic contraction
The intestine is involuntary structure which undergoes the control of nervous system

9. Autonomic nervous system innervations of the intestine
Sympathetic
Parasympathetic
CNS AG e
CNS AG e
PGF PostGF
PGF PostGF
Key:
AG= autonomic ganglion
E= effector organ
PGF= preganglionic fiber
POSTGF= postganglionic fiber

10. Autonomic nervous system innervations of the intestine
Sympathetic
Transmitter: NA, Adrenaline
Receptors
(intestine): adrenergic
a1, b2
Action
(intestine): inhibitory (↓cont.)
Parasympathetic
Ach
cholinergic
a-central-Nicotinic (Nn)
b-periphral-muscarinic(M3)
excitatory (↑cont.)

11. Drugs Acting on Intestine
1- STIMULANTS
They are called Spasmogenic
2- DEPRESSANTS
They are called Spasmolytic

12. Stimulants 1- Autonomic Cholinergic stimulant
A- Central nicotinic neuronal (Nn) R agonist (ganglionic stimulant)
- Act on Nn R present in autonomic ganglia
- Ex. Small dose of nicotine ( dil. Nicotine)
- MOA of dil.nicotine:
Dil. Nicotine stimulates Gs protein in cell membrane
→ activates Na channels → rapid ↑ intracellular Na
→ depolarization and AP → contraction

13. Stimulants B- Muscarinic receptors agonist (cholinomimetic)
- Act on muscarinic M3 receptors
- Ex.: 1- Ach & its derivatives e.g. methachloine, bethanecol, carbacol
2- Naturally occurring alkaloids e.g. Pilocarpine
- MOA of Ach:
Ach ++ M3R → ++ Phospholipase C
→ Splitting of phosphatidylinositol biphosphate (PIP2) into:
1- DAG (diacylglycerol) → ↑opening of Calcium channels
2- IP3 (inositol triphosphate) → mobilization of cal. from its stores
1, 2 lead to ↑ intracellular calcium → contraction

14. Stimulants 2- Direct acting stimulant e.g. Bacl2
- Acts directly on muscle fibers

15. Depressants 1- Autonomic adrenergic stimulants (sympathomimetic)
- e.g. adrenaline & noradrenaline
- They bind to a1, b2 receptors causing relaxation
2- Direct depressants
e.g. Mgcl2 & papaverine

16. Experiment N
Dil.nic. Ach Bacl adr Mgcl2

17. Definitions Dose cycle: time between different drug additions
Contact time: time from addition of drug until its removal by washing

18. ↑ amplitude
↓ amplitude

19. ↑ tone
↓ tone

20. ↑ tone & amplitude
↓ tone & amplitude