313 PHL Lab 2 Effects and Sites of
313 PHL Lab # 2 Effects and Sites of Action of Different Agonists Drugs (Stimulant or Relaxant) on The Isolated Rabbit Intestine
The nervous control of intestine: Intestine : ØIs composed of(duodenum, jejunum, ileum). ØIt is a Smooth muscle has myogenic contraction (i. e. spontaneous rhythmic contraction). N. B this rhythmicity due to its pendular movement. ØIs 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: α 1, B 2 Action: inhibitory (↓contraction) relaxation. Parasympathetic Acetylcholine (Ach). Cholinergic: Central: Nicotinic (Nn). and peripheral: muscarinic (M 3) excitatory (↑contraction) contraction
Types of receptors present in the intestine: Ø Adrenergic. Ø Cholinergic. Ø Histaminergic. Ø Purinergic. Ø 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 (M 3 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 M 3 receptors activation of PLC ( phospholipase C). 2. PLC hydrolyzes PIP 2(phosphotidyl inositol biphosphate) into DAG and IP 3. DAG=diacylglycerol. IP 3= inositol triphosphate.
3. DAG activates Ca+ + channel increase intracellular Ca+ +. 4. IP 3 increase Ca+ + release from intracellular stores. 3, 4 increase intracellular Ca+ + intestinal smooth muscle contraction.
Stimulant Drugs (Spasmogenic) B-Direct smooth muscle stimulants : e. g. Barium Chloride Mechanism of Action: Ba. Cl 2 stimulates the muscle fiber increase muscle contraction.
Inhibitory drugs (Spasmolytics) A-Autonomic adrenergic stimulants: e. g. Adrenaline, Noradrenaline Mechanism of Action: Adrenaline will stimulate α 1 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. Mgcl 2 Papaverine nism of Action : Mgcl 2 inhibits the contraction of muscle fiber muscle relaxation.
- Slides: 12