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

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 Atropine

H1 Histamine Mepyramine, Cyproheptadine

5-HT2 Serotonin Methysergide, Cyproheptadine

H2 Histamine Cimetidine

Angiotensin II Angiotensin Saralasin

Vasopressin Vasopressin Papaverine (direct acting spasmolytic)

Adrenergic

Adrenergic 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

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