Effect of autonomic drugs on rabbit’s isolated intestine
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Transcript of Effect of autonomic drugs on rabbit’s isolated intestine
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Effect of autonomic drugs on rabbit’s isolated
intestine
Dr Muhammad Raza
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Action of autonomic drugs on the isolated Rabbit’s
intestine • The smooth muscle of small intestine receives both parasympathetic and sysmpathetic innervation.
• PARASYMPATHETIC preganglionic fibres relay in neurons located in the wall of the intestine in myenteric plexus and submucus plexus, and from there the post ganglionic fibres travel to the smooth muscle of intestine.
• SYMPATHETIC preganglionic fibres relay in collateral ganglia OUT SIDE THE WALL OF INTESTINE. From these ganglia, postganglionic fibres arise and run with the blood vessels to supply the small intestine.
• Parasympathetic nerves reach the intestine as preganglionic fibres and isolated intestine contains ONLY PARASYMPATHETIC GANGLIA.
• PARASYMPATHETIC Stimulation intestinal motility whereas sympathetic stimulation it.
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TYPES OF RECEPTORS IN THE ISOLATED RABBIT’S INTESTINE
• Nicotinic cholinoceptors (N) in parasympathetic ganglia
• Muscarinic cholinoceptors (M) in smooth muscle
• Adrenoceptors (, )• Other receptors for histamine,
serotonin, vasopressin
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INNERVATION AND RECEPTORS IN THE ISOLATED INTESTINE
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ClassificationReceptors Agonist Blocker
Nicotinic Nicotine SDLobeline SD
Ganglion BlockersDepolarizing, Nicotine Large Dose (initial stimulation followed by block of ganglion)Competitive, Chlorisondamine (Ganglion block without stimulation) or mecamylamine
Muscarinic ACh Anti muscarinics i.e AtropineH1 Histamine Mepyramine, Cyproheptadine
5-HT2 Serotonin Methysergide, Cyproheptadine
H2 Histamine Cimetidine
Angiotensin II Angiotensin SaralasinVasopressin Vasopressin Papaverine (direct acting spasmolytic)
AdrenergicAdrenergic Adrenaline (α, β) Phentolamine, α adrenergic blocker +
Propranolol, β adrenergic blocker
Phenylephrine, α adrenergic
Phentolamine, α adrenergic blocker
Isoprenaline, β adrenergic
Propranolol, β adrenergic blocker
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APPARATUS FOR RECORDING CONTRACTIONS OF ISOLATED RABBIT’S INTESTINE
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Parts of apparatus (PowerLab)
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CONCEPTS– NIC (SD) stimulation of NN receptors of Parasympathetic
ganglia located in the wall of intestine, cause release of ACh from postganglionic parasympth nerve endings resulting in intestinal stimulation via muscarinic receptors.
– NIC (LD) –Initial stimulation followed by block (DEPOLARIZING GANGLION BLOCK) of the Para-symp ganglia in the wall of the intestine. Chlorisondamine is a Competitive Ganglion blocker without stimulation.
– NIC (SD) after NIC (LD) no response indicating BLOCKADE of Parasymp ganglia
– ACh --- Activation of muscarinic receptors– Atropine – Blocks muscarinic receptors by competing ệ ACh.– ACh after Atropine no change indicating complete blockade of
Muscarinic receptors.– Adrenaline – Activation of Adrenoceptors (, ) --- of
intestinal tone and motility.– Propranolol – Blockade of receptors– Phentolamine -- Blockade of receptors– ADR after Phentolamine+Propranolol --- No effects ---
Adrenoceptors (, ) are blocked
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Effect of unknown stimulant
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Effect of unknown stimulant
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Effect of unknown stimulant
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Effect of unknown stimulant
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Effect of unknown stimulant
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CONCEPTS– Adrenaline Activation of Adrenoceptors
(, ) of intestinal tone and motility.– Propranolol Blockade of receptors– Phentolamine Blockade of receptors– ADR after Phentolamine+Propranolol No
effects Adrenoceptors (, ) are blocked