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Effects of Agonists on Rabbit Intestine - Smooth Muscle Control

Understand the impact of stimulant and relaxant drugs on isolated rabbit intestine and the role of neurotransmitters on smooth muscle contraction. Explore various receptor types and mechanisms of action for different agonist drugs.

riley-mcdonald
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Effects of Agonists on Rabbit Intestine - Smooth Muscle Control

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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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