313 PHL Lab # 3 Effect of Certain Agonists & Their Antagonists on The Isolated Rabbit Intestine

Effect of stimulant drugs (spasmogens)and their blocker: 1-Drugs act on neuronal nicotinic (Nn) Receptors: Agonist Dil. Nicotine (0.01%, 0.1ml) Antagonist : Conc. Nicotine (0.1%, 0.1ml) 2-Drugs act on muscarinic (M3) Receptors: Ach (0.01%, 0.1ml) Atropine (0.1ml, 0.1%)

1-Drugs act on neuronal nicotinic (Nn) Receptors: Agonist Dil. Nicotine (0.01%, 0.1ml) MOA: Dil. Nicotine act on Nn receptor → activates Na-K channels → rapid ↑ intracellular Na → rapid depolarization → increase contraction .

Antagonist : Conc. Nicotine (0.1%, 0.1ml) - Conc. Nicotine is depolarizing ganglionic blocker MOA: It causes an initial increase in amplitude due to its initial depolarization (↑contraction) → Followed by successive depolarization → transmission failure & muscular fatigue (blocker of the receptors) .

2-Drugs act on muscarinic (M3) Receptors: Agonist : Ach (0.01%, 0.1ml) MOA : Ach stimulates M3R → ++ Phospholipase C → Hydrolysis of (PIP2) into: 1- DAG → opening of Calcium channels → Ca++ influx → contraction 2- IP3 → mobilization of ca++ from its stores ↑ intracellular calcium →contraction

Antagonist: Atropine (0.1ml, 0.1%) MOA: It is a reversible, competitive, specific, non-selective muscarinic blocker.