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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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Effects and Sites of Action of Different Agonists Drugs (Stimulant or Relaxant) on TheIsolated Rabbit Intestine 313 PHL Lab # 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 nervous system(sympathetic and parasympathetic).
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
Types of receptors present in the intestine: Adrenergic. Cholinergic. Histaminergic. Purinergic. Serotinergic.
Stimulant Drugs (Spasmogenic) A- Autonomic cholinergic stimulants , act on: 1-Nicotinic Neuronal receptor: e.g. Nicotine (small doses)= Diluted Nicotine Mechanism of Action: Diluted Nicotine activates Nn receptors in the cell membrane. This will activate Na+/K+ channel Na+ influx increase intracellular Na+ rapid depolarization intestinal smooth muscle contraction .
2)Muscarinic Receptors (M3 subtypes): e.g. Cholinomimetic 1-Acetylcholine or its derivative : e.g. .Methacholine, Bethanecol, Carbachol. 2- Naturally occurring alkaloid : e.g. Pilocarpine.
Mechanism of Action : 1. Acetylcholine binds with M3 receptors activation of PLC ( phospholipase C) . 2. PLC hydrolyzes PIP2(phosphotidyl inositol biphosphate) into DAG and IP3 . DAG=diacylglycerol. IP3= inositol triphosphate.
3. DAG activates Ca+ + channel increase intracellular Ca+ +. 4.IP3 increase Ca+ + release from intracellular stores. 3,4 increase intracellular Ca+ + intestinal smooth musclecontraction.
Stimulant Drugs (Spasmogenic) B-Direct smooth muscle stimulants : e.g. Barium Chloride Mechanism of Action: BaCl2 stimulates the muscle fiber increase muscle contraction.
Inhibitory drugs (Spasmolytics) A-Autonomic adrenergic stimulants: 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 .
Inhibitory drugs (Spasmolytic) B-Direct Inhibitory Drugs : e.g. Mgcl2 Papaverine Mechanism of Action : Mgcl2inhibits the contraction of muscle fiber muscle relaxation .