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Awatif B. Al-Backer. Guinea Pig Ileum  It’s the lower part of the small intestine.  Involuntry muscle.  Recives sympathetic & parasympathetic innervations.

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Presentation on theme: "Awatif B. Al-Backer. Guinea Pig Ileum  It’s the lower part of the small intestine.  Involuntry muscle.  Recives sympathetic & parasympathetic innervations."— Presentation transcript:

1 Awatif B. Al-Backer

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

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

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

5 Awatif B. Al-Backer 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)

6 Awatif B. Al-Backer Histaminergic receptors R subtype DistributionActionAgonistAntagonist H1H1 Smooth muscles contractionHistamineMepyramine cyproheptadine H2H2 Gastric mucosa Gastric acid secretion HistamineCimetidine Ranitidine H3H3 PresynapticAutoregulation of H release HistamineThioperamide N.B. Histamine acts by stimulating Gs protein → ↑ cAMP → ↑ [Calcium]ic → contraction

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

8 Awatif B. Al-Backer Experiment N W+N W+N W+N Ach 0.1ml Atropine 0.1ml Ach 0.1ml W+N Hist. 0.1ml AH 0.2 ml Hist. 0.1ml W+N 0.1ml Bacl 2 Papaverine 0.1ml Bacl 2 0.1ml Keys: Hist.=histamine AH= antihistamine 5-HT=serotonin 5-HT 0.1ml

9 Awatif B. Al-Backer 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 Ach Hist. 0.1 ml 0.1 ml Unk. 0.2 ml 0.2 ml Unk. Atrop. Ach AH Hist Keys: Ach= acetylcholine Hist.=histamine AH= antihistamine Unk.= unknown Unk.


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