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313 PHL Lab # 2

Effects and Sites of Action of Different Agonists Drugs (Stimulant or Relaxant)on The Isolated Rabbit Intestine. 313 PHL Lab # 2. Intestine : Is composed of(duodenum,jejunum,ileum). The nervous control of intestine :.

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313 PHL Lab # 2

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  1. Effects and Sites of Action of Different Agonists Drugs (Stimulant or Relaxant)on TheIsolated Rabbit Intestine 313 PHL Lab # 2

  2. Intestine: • Is composed of(duodenum,jejunum,ileum) . The nervous control of intestine: • It is a Smooth muscle & has myogenic contraction (i.e. spontaneous rhythmic contraction). • N.B this rhythmicity due to its pendular movement. • Is involuntary muscle undergoes the control of autonomic nervous system(sympathetic and parasympathetic).

  3. The intestine innervated by ANS : Sympathetic Transmitter:noradrenalin mainly, Adrenaline . Receptors present in (intestine): Adrenergic: α1,B2 Action: inhibitory (↓contraction) relaxation . Parasympathetic Acetylcholine (Ach) . Cholinergic: Central:Nicotinic (Nn) . and peripheral: muscarinic (M3) excitatory (↑contraction) contraction

  4. Types of receptors present in the intestine: Adrenergic. Cholinergic. Histaminergic. Purinergic. Serotinergic.

  5. Drug Acting on Intestine • STMULANTS They are called Spasmogenic • DEPRESSANTS They are called Spasmolytic

  6. Stimulant Drugs (Spasmogenic) A- Autonomic cholinergic stimulants , act on: 1- Central Nicotinic Neuronal receptor agonist (Nn) R (ganglionic stimulant): - Act Nn R present in autonomic ganglia e.g. Nicotine (small doses)= Diluted Nicotine

  7. Mechanism of Action: • Diluted Nicotine Dil.Nicotine stimulates gated ion channels receptors in the cell membrance (activates Nn receptors in the cell membrane) This will activate Na+/K+ channel •  Na+ influx • increase intracellular Na+ •  rapid depolarization and action potential (AP) •  intestinal smooth muscle contraction .

  8. 2)Muscarinic Receptors agonist (cholinomimetic) -Act on muscarinic M3 recptors e.g. Cholinomimetic Ex.: 1-Acetylcholine(Ach) and its derivative : e.g. .Methacholine, Bethanecol, Carbachol. 2- Naturally occurring alkaloid : e.g. Pilocarpine.

  9. Mechanism of Action : 1. Acetylcholine binds with M3R receptors  activation of PLC ( phospholipase C) . 2. PLC hydrolyzes PIP2(phosphotidyl inositol biphosphate) into DAG and IP3 . DAG=diacylglycerol. IP3= inositol triphosphate.

  10. 3. DAG activates Ca+ + channel  increase intracellular Ca+ +. 4.IP3 increase Ca+ + release from intracellular stores. 3,4 increase intracellular Ca+ + intestinal smooth musclecontraction.

  11. Stimulant Drugs (Spasmogenic) B-Direct smooth muscle stimulants (Direct acting stimulant) : e.g. Barium Chloride (Bacl2) Mechanism of Action: BaCl2 stimulates act directly on the muscle fiber increase muscle contraction.

  12. Inhibitory drugs (Spasmolytics) A-Autonomic adrenergic stimulants (sympathomimetic): e.g. Adrenaline, Noradrenaline Mechanism of Action: Adrenaline will stimulate α1 and ß 2 receptors in the intestinal smooth muscle  inhibits tone and motility  decrease intestinal contraction .

  13. Inhibitory drugs (Spasmolytic) B-Direct Inhibitory Drugs : e.g. Mgcl2 Papaverine Mechanism of Action : Mgcl2inhibits the contraction of muscle fiber  muscle relaxation .

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