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313 PHL Lab #1 Introduction & Dose Response Curve of Different Doses of Acetylcholine

313 PHL Lab #1 Introduction & Dose Response Curve of Different Doses of Acetylcholine. Purpose of Pharmacological Experiments :. The pharmacological experiments largely divided in to : Qualitative : - To determine ( analyze) the activity of drug (i.e. analgesic,

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313 PHL Lab #1 Introduction & Dose Response Curve of Different Doses of Acetylcholine

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  1. 313PHL Lab #1 Introduction & Dose Response Curve of Different Doses of Acetylcholine

  2. Purpose of Pharmacological Experiments : The pharmacological experiments largely divided in to : Qualitative : - To determine ( analyze) the activity of drug (i.e. analgesic, hypotensive and hypoglycemic). -To determine mechanism of drugs action. Quantitative: To assay (measure) the potency of drugs (e.g. toxic level, therapeutic level, LD50).

  3. Types of pharmacological experiments : A- In vitro experiments - Study the action of drugs on isolated preparation: 1) Tissue e.g. (intestine, ileum) . 2) Organ e.g. (heart) . • Advantages: • Easier to study MOA (qualitative) . • Easier to study its potency (quantitative) e.g. DRC on rectus abdominis. • Disadvantages : • There is no interference by compensatory mechanisms of body that may affect the direct action of drug  not easy to study the chemical and biological effect of the drug.

  4. B- In vivo experiments • Study the action of drugs on the whole body (intact) . • Advantages: • Observe the direct drug action(actual effect) . • Easier to study the chemical and biological effect . • Disadvantages : -Difficulty to determine the exact mechanism of action .

  5. In vitro experiments 1) Experimental conditions: An isolated organ or muscle should be bathed in a suitable media that is resemble to the normal condition in the body regarding (pH,osmolarity,temperature) . Therefore, tissue is bathed in solution containing: .1- Electrolytes 2- Nutrients . .3- Adjusted Physiological pH .4- Constant temperature 5- Aeration .

  6. : 2) Physiological Salt Solution • According to different tissue to be used, there is a different physiological solution prepared. • But all or most of them contain the following ingredients at different concentrations: 1-Nacl → to adjust the isotonicity. 2- Glucose → nutrient . 3-Ca+2, K+, sometimes Mg+2 as CL salt → to maintain normal muscle contraction.

  7. 3- Sodium bicarbonate → to adjust pH similar to that of blood . 4- NaH2PO4 (sodium di hydrogen phosphate) buffer→ to compensate for any change in pH . The two most commonly used physiological solutions are Tyrode’sand Krebs .

  8. 3) Aeration: Physiological salt solutions should be aerated by a suitable gas : 1- Pure oxygen → for heart tissues. 2- Normal air → for intestine. 3- Carbogen (95% O2, 5% CO2) → used for uterus .

  9. 3)Temperature: • Mammalian tissue must be bathed in a warmed solution adjusted at 37ºCe.g. Isolated rabbit intestine . • The temperature should be decreased in some experiments to reduce the myogenic contraction, the warmed solution adjusted at 32ºCe.g. Guinea-pig ileum. • Amphibian tissues survive at room temperature (25ºC)e.g.frog rectus abdominis .

  10. Dose cycle & contact time Dose cycle (NT): the time between different drugs addition. Contact time (CT): the duration of drug presence in the organ bath until its removal by washing . • CT= 30 sec, NT=60 sec, washing 3 times 30 sec for each total cycle time = 3 min.

  11. Apparatus for experiments with isolated amphibian and mammalian tissue: Physiograph and thermostatically controlled organ bath. Drugs acting on the isolated tissue: • isolated rabbit intestine has normal myogenic contraction which is under the control of the Autonomic nervous system (ANS). • The effect of drugs that act on the intestine could be a stimulatory i.e. increase in the intestinal contraction or inhibitory i.e. decrease in the intestinal contraction.

  12. The intestine innervated by ANS : Sympathetic Transmitter:noradrenalin mainly, Adrenaline . Receptors present in (intestine): Adrenergic: α1,B2 Action: inhibitory (↓contraction) relaxation . Parasympathetic Acetylcholine (Ach) . Cholinergic: Central:Nicotinic (Nn) . and peripheral: muscarinic (M3) excitatory (↑contraction) contraction

  13. This increase or decrease in muscle contraction is observed as follows: ↑ amplitude ↓ amplitude

  14. Or ↑ tone ↓ tone

  15. Or ↑ tone & amplitude ↓ tone & amplitude

  16. The effect of different doses of acetylcholine on smooth muscle of intestine: N 0.05 0.1 0.2 0.3 0.4 Ach Ach Ach Ach Ach

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