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

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  .

. From 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

Receptors Nicotinic Classification Agonist



Nicotine SD



Lobeline SD Muscarinic H 1 5-HT 2 H 2 Angiotensin II Vasopressin Adrenergic Adrenergic ACh Histamine Serotonin Histamine Angiotensin Vasopressin Adrenaline (α, β) Phenylephrine, α adrenergic Isoprenaline, β adrenergic Blocker Ganglion Blockers



Depolarizing , Nicotine Large Dose (initial stimulation followed by block of ganglion)



Competitive , Chlorisondamine (Ganglion block without stimulation) or mecamylamine Anti muscarinics i.e Atropine Mepyramine, Cyproheptadine Methysergide, Cyproheptadine Cimetidine Saralasin Papaverine (direct acting spasmolytic) Phentolamine , α adrenergic blocker + Propranolol , β adrenergic blocker Phentolamine , α adrenergic blocker Propranolol , β adrenergic blocker

APPARATUS FOR RECORDING CONTRACTIONS OF ISOLATED RABBIT’S INTESTINE

Parts of apparatus (PowerLab)

CONCEPTS

– – – – – – – – – –

NIC (SD)



stimulation of N N 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) Parasymp ganglia no response indicating BLOCKADE of ACh ---



Atropine Activation of muscarinic receptors – Blocks muscarinic receptors by competing ệ ACh.

ACh after Atropine



no change indicating complete blockade of Muscarinic receptors.

Adrenaline – Activation of Adrenoceptors (



,



) -- intestinal tone and motility.

 

of Propranolol – Phentolamine



- Blockade of

 

receptors Blockade of



receptors ADR after Phentolamine+Propranolol Adrenoceptors (



,



) are blocked ---



No effects ---



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