Peptic Ulcer Disease and its Screening

Lesions occur mainly in the lumen and in the antrum, the no of ulcers is noted and severity recorded with the following scores
0= no ulcers
1= superficial ulcers
2= deep ulcers
3= perforation
the volume of the gastric content is measured.
After centrifugation ,acidity is determined by titration with 0.1N NaOH

EVALUATION
An ulcer index UI is calculated
UI=UN+US+UPX10-1
UN=average of no of ulcers per animal
US=average of severity of score(0,1,2,3)
UP=percentage of animals with ulcers
Ulcer index and acidity of the gastric content of treated animals are compared with controls. using various doses, dose response curves can be established for ulcer formation and gastric acid secretion.
ID50 values can be caluculated by probit analysis where by 0% corresponds to no and 100% to maximal stimulated gastric acid output.

Critical assessment of the method
The “ shay-rat “ as been proven to be valuable tool to evaluate antiulcer drug with various mechanisms of action.

Stress Ulcer Through Immobilization Stress.
Principle:
Psychogenic factors such as stress, play a major role in the pathogenisis of gastric ulcers in man .
The first report of the use of restraint (device used in aiding the immobilization ) as stress factor was published by Selye.
Purpose.
study the effect of antiulcer drugs on immobilization stress in rats.

Requirements:
animals-10 female wister rats( 150-170g)

conditions-Food and water are withdrawn 24hrs before experiment.

route: oral /SC

Procedure:
1. Groups of 10 rats/dose of test drug and for control are used.
2. Food and water are withdrawn 24 hours before the expt.
3. After oral/s.c administration of the test compound or the placebo solution the animals are slightly anesthetized with ether.
4. Both lower and upper extremities are fixed together and the animals wrapped in wire gaze.
5. They are horizontally suspended in the dark at 200 for 24hours and finally sacrificed in CO2 anesthesia.
6. The stomach is removed ,fixed on a cork plate and the number and severity of ulcers is recorded with a stereomicroscope using the following scores,
   0= no ulcers
   1= superficial ulcers
   2= deep ulcers
   3= perforation

CRITICAL ASSESSMENT OF THE METHOD
The experimental model resembles the psychogenic factors in the pathogenesis of gastric ulcers in patients.therefore it is not surprising that not only antacids,anticholinergics, H2 antagonists,proton-pump nhibitors,but also psychotropic drugs,like neuroleptics,have been antagonists,proton-pump inhibitors,but also psychotropic drugs,like neuroleptics,have been found to be effective in this test.the test is being used in final drug evaluation only.

STRESS ULCERS BY COLD WATER IMMERSION
PRINCIPLE: -cooling of rats in water during the restraint period accelerates the occurrence of gastric ulcers and shortens the time of necessary immobilization

Req: -
animals:8-10 rats(150-200g)

route:oral

conditions:individual restraint cages in water

Procedure:-
Animals are taken,test compound is given orally .then placed vertically in individual restraint cages in water at 220c for one hour(in the last method restraint was used for 24 hours)
they are removed ,dried and injected intravenously via tail vein 30mg/kg evans blue.
10 min later ,they are sacrificed in CO2 anesthesia and their stomachs removed.
Formol-saline(2%v/v)is then injected into the totally ligated stomachs for overnight storage.
Next day, the stomachs are opened along the greater curvature,washed in warm water,and examined under a 3 fold magnifier.
The lengths of the longes diameters of the lesions are measured and summated to give a total lesion score(in mm) for each animal,the mean count for each group being calculated.

EVALUATION
The mean score in control rats is about 25(range20-28).inhibition of the lesion production is expressed as percentage value.

Critical assessment of the method
Like other stress models,the test resembling the psychogenic factor for ulcer disease in human beings,is used for final drug evaluation only.

INDOMETHACIN INDUCED ULCERS IN RATS
PRINCIPLE:- NSAIDs ,like Indomethacin and acetyl salicylic acid ,induce gastric lesions in man and in experimental animals by inhibition of gastric cyclo-oxygenase resulting in less formation of prostacyclin,the predominant prostanoid produced in the gastric mucosa.

Req: -

animals:8-10  rats (150-200g)

route:oral.

Procedure:
The test drugs are administered orally in 0.1% tween 80 solution.10min prior to oral Indomethacin in a dose of 20mg/kg.
6hours later,the rats are sacrificed in CO2anesthesia and their stomachs removed.
Formol-saline(2%v/v)is then injected into the totally ligated stomachs for overnight storage.
Next day, the stomachs are opened along the greater curvature,washed in warm water,and examined under a 3 fold magnifier.
The lengths of the longes diameters of the lesions are measured and summated to give a total lesion score(in mm) for each animal,the mean count for each group being calculated.

EVALUATION
The mean score in control rats is about 25(range20-28).inhibition of the lesion production is expressed as percentage value.

Modification of the method
Instead of Indomethacin,gastric lesions can be induced by intravenous or oral doses of aspirin which can be prevented by exogenous PGE2 OR PGI2.

Critical assessment of the method
Cold stress induced ulcer formation ,an be inhibited by H2 receptor antagonists have only protective effects.

CYSTEAMINE –INDUCED DUODENAL ULCERS IN RAT
Principle: -
Duodenal ulcers can be induced in rats by repeated  administration of cysteamine or propionitrile in rats.

Req:-male Sprague Dawley rats(with 200g initial weight)

Procedure
Male Sprague Dawley rats are taken .
Cysteamine HCL is administered three times on day 1 in a dose of 280mg/kg orally.
Protective drugs,such as H2 antagonists ,are given 30min prior cysteamine treatment.
Rats are sacrificed on 3rd day.

For histological evaluation
The stomach and duodenum are fixed in 10% aqueous buffered formaldehyde and paraffin – embedded sections are stained with hematoxylin and eosin.
Duodenal ulcers develop in the anterior and posterior wall of the proximal duodenum, about 2-4mm from the pylorus.
The more severe ulcers, located on the anterior wall, frequently perforate, resisting in focal or generalized peritonitis or penetrate and the liver . the opposite ulcer invariably penetrates in to the pancreas.

NOW YOU CAN ALSO PUBLISH YOUR ARTICLE ONLINE.

SUBMIT YOUR ARTICLE/PROJECT AT articles@pharmatutor.org

Subscribe to Pharmatutor Job Alerts by Email

FIND OUT MORE ARTICLES AT OUR DATABASE