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3Effect of agonist and antagonists on guinea pig ileum.pptx

1. This experiment examines the effect of histamine and the H1 antagonist mepyramine on guinea pig ileum. 2. Histamine causes contraction of the smooth muscle in guinea pig ileum, while mepyramine blocks the H1 receptor and antagonizes the effect of histamine. 3. The concentration-response curve of histamine is shifted to the right in a parallel fashion by mepyramine without suppression of the maximal response, indicating competitive antagonism.

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Effect of agonist and antagonists on guinea pig ileum Experiment No. 3 Pharmacology-III Practical B.Pharm Semester-VI Dr. Sameer H. Sawant, Assistant Professor Pharmacology, Dr. Sameer H. Sawant, SIOP
Requirements: 1.Animals – Guinea pig (300 to 600 g, overnight fasted) 2.Drugs – Histamine stock solution (1 mg/ml), Mepyramine stock solution (1 mg/ml) 3.Physiological solution: Tyrode • Instruments – Student organ bath, lever, plasticin, Sherrington rotating drum and kymograph paper. Dr. Sameer H. Sawant, SIOP
Theory/Principle: • Histamine is an autocoid having profound physiological effect in the body • Besides the triple response caused by it, histamine has spasmogenic response on intestinal smooth muscle • Mepyramine (pyrilamine) is a selective H1-histamine receptor antagonist • Overnight fasted animals are used to get better response of drugs on intestinal smooth muscle Dr. Sameer H. Sawant, SIOP
Cont. • By acting on H1-histamine receptors it causes the contraction of intestinal smooth muscle • Guinea pig is highly sensitive to histamine • The guinea pig ileal preparation is very commonly used for isolated tissue work • It is sensitive to histamine in nanogram/ml concentrations. Dr. Sameer H. Sawant, SIOP
Procedure: 1.The guinea pig is sacrificed by a blow on the head and carotid bleeding. 2.Cut open the abdomen and lift the caecum to trace the ileocecal junction. 3.Cut and remove a few centimeters long of the ileal portion and immediately place it in the watch glass containing Tyrode solution. 4.Trim the mesentery and with gentle care clean the contents of the ileum by pushing the Tyrode solution into the lumen of the ileum. Dr. Sameer H. Sawant, SIOP
Cont. 5. Utmost care should be taken to avoid any damage to the gut muscle. 6. Cut the ileum into small segments of 2-3 cm long. 7. Take one piece of ileum of 2-3 cm long and tie the thread to top and the bottom ends without closing the lumen 8. Mount the tissue in the organ bath containing Tyrode solution maintained at 32-35˚ C and bubbled with O2 or air. Dr. Sameer H. Sawant, SIOP
Cont. 9. A tension of 0.5 g is applied and the tissue is allowed to equilibrate for 30 min before adding drugs to the organ bath. 10. Record concentration dependent responses due to histamine using frontal writing lever. 11. Contact time of 30 sec, and 5 min time cycle are kept for proper recording of the responses. 12. Record at least 4 concentration dependent-responses due to histamine. Dr. Sameer H. Sawant, SIOP
Cont. 13.Add Mepyramine (1-2 µg/ml) to the reservoir containing Tyrode solution and irrigate the tissue with Mepyramine containing Tyrode for 30 min. 14.Repeat the concentration-response curve of histamine in the presence of mepyramine. 15.Label and fix the tracing and plot the graph. Calculate the EC50 values and note the nature of antagonism. Dr. Sameer H. Sawant, SIOP
Inference: • Concentration-response curve of histamine is shifted to the right in a Parallel fashion Without suppression of the maximal response by Mepyramine • The nature of antagonism is of competitive type Dr. Sameer H. Sawant, SIOP