Effect of drugs on gastrointestinal motility

BACKGROUND

Intestinal motility is regulated by the enteric nervous system of the gut (Auerbachs and Meissners plexuses) and the activity of this system can be modified by autonomic nervous system. Hence effect of sympathomimetic and parasympathomimetic drugs on intestinal motility can be studied by using isolated piece of intestine.

Parasympathomimetic drugs stimulate enteric neurons to release acetylcholine at neuromuscular junctions and enhance muscle tone and rhythmicity of intestine. Sympathomimetic drugs acts on alpha and beta receptors and releases adrenaline which in turn prevents release of acetylcholine and inhibits muscle tone and rhythmicity.¹

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Many animal models can be employed to study intestinal motility of symapathetic and parasympathetic drugs. Guinea pig ileum is advantageous for assay purposes as it produces steady baseline for studying effects of drugs.

Rabbit intestine (ileum, deuodenum, jejunum) usually jejunum is used for the effects of pendular movements (continuous contraction and relaxation-Finkelman method).² In the present study rabbit ileum is selected for estimating the effects of selected drugs on intestinal motility.

REQUIREMENTS

Animals: Medium sized rabbit

Drugs: Adrenaline/Acetylcholine- 10 ug/ml, Atropine sulphate- 100 ug/ml, isoproterenol/isoprenaline 10 ug/ml, Propranolol- 1 mg/ml, Phenylephrine- 10 ug/ml, phentolamine- 0.1 ug/ml

Solutions: Tyrode solution

Apparatus used: Kymograph, Dissecting board, Dissecting instruments, scissors, petriplates, Syringe, Frontal writing lever, water bath with temperature controlling unit, organ bath with aeration tube

PROCEDURE

The procedure adopted for the study is the modified Finkleman method developed by Walker and Scott.² Select a medium sized rabbit for the study.

Fast the animal for 24 hours prior to experiment as food in gut results in messy dissection and flushing of gut contents may damage the intestine. Before sacrificing the rabbit, prepare Tyrodes Ringer solution and place about 250 ml of this solution in an ice cold flask.

Sacrifice the animal by cervical decapitation without use of anesthetic as it may affect the gut motility. Shave the abdomen of the animal and vacuum the surface to remove adhered fur. Make a midline incision through the skin and abdominal muscles.

Locate ileum and a part of ileum was taken 10 cm away from ileocaecal valve. An optimal length of tissue (5-6 cms) is cut carefully and tie the thread to antimesenteric border on both sides and place them in the Tyrode solution (extra pieces of ileum can be stoted in ice cold Tyrode solution so that they are viable for hours. In ice cold solution the motility will ceases but after placing them in warm solution the tissue gets relaxed and shows motility within 5-10 minutes).

Record the rhythmic activity of the ileum by using frontal writing lever and kymograph. Suspend the tissue in organ bath of Tyrode solution (100 ml) at 37⁰c with adequate oxygen supply (mixture of 95% O₂ and 5% of Co₂).

Step

Tie one end of the thread of the tissue to fixed point inside the organ bath and the other end to the lever for recording contractions on the kymograph. Stabilise the tissue in the solution to the conditions for about 30 minutes. Ensure the lever should be placed horizontally and record the normal contractions followed by effects of drugs on muscles.

After recording normal contractions inject the drugs one by one and observe for force of contraction and tone (normal, increased or decreased), frequency of contractions (per minute) before and after drug administration.

Inject 0.1 ml of drugs in the succession order in the organ bath and the responses are recorded. After noting the effect of every drug, drain the muscle bath and refill with fresh warm Tyrode solution (100 ml). Take the control (without drug) reading before and after each drug response.

Maintain wash out period for 15-20 minutes for change of every drug and check the next drug response only the when the tone and amplitude returned to original value approximately. The drug and dose name should be mentioned in the recording after taking response of each drug.

Order of adding drugs

1. 0.1 ml of Ach- 1.0 ml of Ach- 0.1 ml of NE- 1.0 ml of NE (these drugs are postganglionic neurotransmitters of parasympathetic and sympathetic system. Ach increases contraction and NE relaxes the tissue)
2. 1.0 ml of phenylephrine- 1.0 ml of isoproterenol (phenylephrine causes contraction by inhibiting adenylate cyclase- alpha adrenergic agonists; isoproterenol causes relaxation by showing beta agonist action)
3. Add drugs one after one (1 and 2) to check for their activity. After taking response of each drug drain the solution and refill the bath with warm Tyrode solution and proceed with next drug.
4. 1.0 ml of phenatolamine (alpha adrenergic blocker). Wait for 2 minutes then proceed for adding 1.0 ml of phenylephrine (to check for alpha receptor blockade, if they are blocked no response is seen)
5. 1.0 ml of propranolol (beta adrenergic blocker). Wait for 2 minutes then proceed for adding 1.0 ml of isoproterenol (to check for beta receptor blockade, if they are blocked no response is seen)
6. 1.0 ml of atropine- wait for 3 minutes- add 1.0 ml of Ach- (to check for parasympatholytic activity of atropine)

CONCLUSION

The effect of drugs on intestinal motility can be easily interpreted by the responses taken on kymograph.

REFERENCES

1. Furness JB. Enteric nervous system. Scholarpedia. 2007;2(10):4064.
2. Peddireddy MKR. In vitro Evaluation Techniques for Gastrointestinal Motility. Indian J Pharmaceutical Education Res. 2011;45(2):184-91.
3. Walker RL, Scott CC. Use of the Rabbit Intestine in Smooth Muscle Pharmacology Experiments: A New Approach. Available at: http://www.ableweb.org/volumes/vol-9/1-walker.pdf. Accessed on 15 October 2016.

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