Practical Pharmacology III third year B. Pharm

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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