1. 351 PHL
5th lecture
Effect of Certain Agonist and Their Antagonist on Isolated Guinea Pig Ileum
Awatif B. Al-Backer

2. It’s the lower part of the small intestine. Involuntry muscle.
Guinea Pig Ileum
It’s the lower part of the small intestine.
Involuntry muscle.
Recives sympathetic & parasympathetic innervations.
Advantages of GPI:
No myogenic contraction
More sensitive to histamine
Awatif B. Al-Backer

3. Types of receptors in GPI
1- Cholinergic receptors
2- Serotonergic or tryptaminergic receptors (5-HT1→5-HT7)
3- Histaminergic receptors
Awatif B. Al-Backer

4. Cholinergic receptors
1- Nn R
Agonist: Dil. Nicotine
Antagonist: Conc. Nicotine
2- M3R
Agonist: Ach
Antagonist: Atropine
Awatif B. Al-Backer

5. Serotonergic or tryptaminergic receptors
Serotonin = 5-HT(5-hydroxytryptamine)
5-HT receptors in GPI:
5-HT2A
Agonist: serotonin
Antagonist: ketanserin
methysergide
cyproheptadine (blocks 5-HT2A & H1)
Awatif B. Al-Backer

6. Histaminergic receptors
R subtype
Distribution
Action
Agonist
Antagonist H1
Smooth muscles
contraction
Histamine
Mepyramine
cyproheptadine H2
Gastric mucosa
Gastric acid secretion
Cimetidine
Ranitidine H3
Presynaptic
Autoregulation of H release
Thioperamide
N.B. Histamine acts by stimulating Gs protein → ↑ cAMP → ↑ [Calcium]ic → contraction
Awatif B. Al-Backer

7. e.g. Barium chloride (Bacl2) Direct spasmolytic: e.g. Papaverine
Direct acting drugs
Direct spasmogen:
e.g. Barium chloride (Bacl2)
Direct spasmolytic:
e.g. Papaverine
Awatif B. Al-Backer

8. Experiment Awatif B. Al-Backer Keys: Hist.=histamine AH= antihistamine
N W+N W+N W+N
Ach
0.1ml
Hist.
0.1ml
W+N
0.1ml
Bacl2
W+N
AH 0.2 ml
Hist. 0.1ml
Ach 0.1ml
5-HT 0.1ml
Atropine 0.1ml
Bacl2 0.1ml
Papaverine 0.1ml
Keys:
Hist.=histamine
AH= antihistamine
5-HT=serotonin
Awatif B. Al-Backer

9. Experiment
Identification of site of action of an unknown drug using isolated guinea-pig ileum
N N W+N W+N W+N
0.1 ml ml
Ach Hist.
Unk.
0.1 ml ml Unk ml 0.2 ml Unk.
Atrop. Ach AH Hist
Keys:
Ach= acetylcholine
Hist.=histamine
AH= antihistamine
Unk.= unknown
Awatif B. Al-Backer