Effect of autonomic drugs on rabbit’s isolated intestine Dr Muhammad Raza
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.
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
INNERVATION AND RECEPTORS IN THE ISOLATED INTESTINE
Classification Adrenaline (α, β) Phenylephrine, α adrenergic Receptors Agonist Blocker Nicotinic Nicotine SD Lobeline SD Ganglion Blockers Depolarizing, Nicotine Large Dose (initial stimulation followed by block of ganglion) Competitive, Chlorisondamine (Ganglion block without stimulation) or mecamylamine Muscarinic ACh Anti muscarinics i.e Atropine H1 Histamine Mepyramine, Cyproheptadine 5-HT2 Serotonin Methysergide, Cyproheptadine H2 Cimetidine Angiotensin II Angiotensin Saralasin Vasopressin Papaverine (direct acting spasmolytic) Adrenergic Adrenaline (α, β) Phentolamine, α adrenergic blocker + Propranolol, β adrenergic blocker Phenylephrine, α adrenergic Phentolamine, α adrenergic blocker Isoprenaline, β adrenergic
APPARATUS FOR RECORDING CONTRACTIONS OF ISOLATED RABBIT’S INTESTINE
Parts of apparatus (PowerLab)
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
Effect of unknown stimulant
Effect of unknown stimulant
Effect of unknown stimulant
Effect of unknown stimulant
Effect of unknown stimulant
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