METHODS AND TECHNICS

Exertion Ulcers in the Rat

Andr~ Robert, MD, PhD, J. I. Northam, MA, J. E. Nezamis, BS and J. P. Phillips, BS

Gastric ulcers were produced in rats by forced muscular exercise ("exertion ulcers"). These ulcers were multiple, bleeding, located in the corpus, consisted of hemorrhagic necrosis of the mucosa, and could easily be counted. The ani- mals were fasted overnight prior to exertion. Female rats were more sensitive than males to this type of ulcer. Agents known to reduce gastric acidity (anti- cholinergics, antacids, mercuric acetate) prevented their formation, as did prednisolone. Neither adrenalectomy nor administration of desoxycorticosterone affected these ulcers. During exertion, volume and acidity of gastric juice were reduced. Although the pathogenesis of these ulcers remains to be elucidated, the following chain of events is offered as a hypothesis: Exertion (severe stress) -> vascular shock --> impairment of gastric circulation ~ gastric anoxia --> decreased resistance to autedigestion --> ulcers.

Since exertion ulcers can be graded quantitatively (incidence, severity, and number of ulcers are expressed as such, and also are combined as an "ulcer index"), and are prevented by antiulcer drugs on a dose-dependent basis, this technic is proposed as an assay for antiulcer agents. Its main advantages are rapidity (2 hr and 45 rain), simplicity, reproducibility and quantitation.

Several methods have been described which produce gastric ulcers in the rat. In the most frequently used, ulcers are pro- duced by pylorus ligation (Shay ulcers) (1), restraint (2), administration of corti-

colds (steroid-induced ulcers) (3, 4), phenylbutazone (5), reserpine (6-8), sero- tonin (9, 10), and histamine releasers (11, 12). Other methods, less commonly used, include ulcers produced by injection of formalin into the gastric wall (13), by excision (14) or cauterization (15) of a portion of the mucosa, and by the Mann-

From the ExperimentaI Biology Division, The Upjohn Company, Kalamazoo, Mich.

Address for reprint requests: Dr. Andrd Robert, Experimental Biology, The Upjohn Company, Kala- mazoo, Mich 49001.

Williamson operation (for jejunal ulcers) (16). Several years ago, Selye (17, 18) and

Dalton (19) reported that stressing agents (eg, exposure to cold, spinal cord transec-

tion, forced muscular exercise and formal- dehyde) produced acute gastric ulcers in the rat during the first phase of the general adaptat ion syndrome-- the alarm reaction. In this communication, a technic is de- scribed which produces "exertion ulcers" with regularity. Of the various stressing conditions, forced muscular exercise was chosen as being one of the simplest to produce, leading regularly to formation of ulcers in the shortest time. This procedure can be used as a quantitative assay to test antiulcer agents

Digestive Diseases, Vol. 15, No. 5 (May 1970) 497

METHODS

A cylindrical cage, 90 cm long by 48 cm in diameter, was suspended on a stand and connected to a motor (Fig 1). The inside of the cage was divided by sheet metal part i t ions into 7.5 cm spaces. Female rats of 195-215 g body weight were fasted oxernight (water allowed). The following morning these animals (usually l0 per group) were trans- ferred to the cylindrical cage which was then rotated at 12 rpm for three periods of 45 min each separated by two rest periods of 15 rain each; the total durat ion was 2 hr and 45 min. Variations in durat ion were studied in prel iminary experiments, and it was found that this schedule ga~e the most uniform results. Rotation forces the animals to r u n

at the bot tom of the cage. After completing their third running cycle, they were killed with chloro- form; their stomachs were removed, opened along the greater curvature, rinsed with lukewarm water, and examined with a × 2 hinocular magnifier for ulcerations. The stomachs of all groups were coded aud mixed so that the examiner did not know the

t reatment given. In each group, the ulcers were

expressed as an "ulcer index" the sum of (1)

percent incidence (dixided by 10) of animals with

ulcers; (2) average sexerity of ulcers in phases

ROBERT ETAL

(from a scale of 0 to 3+) rated as the most severe ulcer for each stomach; and (3) average number of ulcers per stomach. Maximum values for the ulcer index ranged from 19 to 23. The following rating scale was a d o p t e d and found to be useful when referring to the relative activity of potential antiul- cer agents:

Inhibition (%) Degree of activity

0-20 Inactive 21-35 Slightly active 36-60 Moderately active 61-90 Very active 91-100 Total ulcer prevention

Variation RESULTS

Variat ion in percent inhibi t ion of tile ul- cer index was studied by assaying one very active antiulcer agent (methscopolamine bromide, 3 mg/kg , given orally) on five occasions dur ing a 5 week period. Percent inhibi t ion varied from 61 to 77 (all "very active" according to the above scale) with

498

Fig 1. Rotating cage used to produce exertion ulcers.

Digestive Diseases, Vol. 15, No. 5 (May 1970)

EXERTION ULCERS

a mean of 68% and a s tandard deviation of 6.7% (a percent s tandard deviation of 10%).

Variation in the ulcer index for control groups was studied from data collected in 121 separate, consecutive assays (with l0 animals/assay). A summary of these data follows:

Response Mean ~SD

Incidence (%) 99.1 3.4 Severity (0 to 3+) 1.6 .3 Ulcers (per stomach) 9.6 2.3

Control Ulcer Index 21.1 2.6 (or 12.3%)

T h e value of the control" ulcer index is most closely correlated with the number of ulcers per stomach; percent incidence (in groups of 10 rats) was 100% in 112 of the 121 assays. When this occurs, an incidence of 80% in the exper imenta l group is a quick indicator of borderl ine slight activi- ty. Therefore, in assessing the potency of antiulcer agents, a difference in ulcer index between control and exper imenta l groups of 20~o or less was not considered signifi- cant.

Appearance of Animals

Toward the end of each of the three cycles, animals showed fatigue and ran in- termittently. They laid on their side and slid against the turning cage for 3-5 min at a time, after which they resumed running. After complet ion of the last cycle, they often stayed motionless for a few minutes, with tachypnea and tachycardia. Wi th in 10 min, however, they had recovered. In most cases, the skin of the paws was damaged due to friction against the rotat ing cage.

Exertion Ulcers

Ulcers were found in the gastric corpus only (Fig 2 ) I t h e port ion of the stomach containing the three types of gastric cells (parietal, zymogenic and mucus) . T h e an-

truin, whose mucosa is composed exclusive- ly o[ mucus glands, was always intact. Simi- larly, the forestomach, which is structurally identical with the esophagus and is devoid of glands, and the duodenum were not affected. T h e ulcers appeared as black spots (5-15/s tomach) , more or less round, rang-

ing in size from pinpoint to 3 mm. They could be counted easily. T h e black materi- al consisted of partially digested blood ooz- ing from the ulcers but embedded in the mucosa. On histologic examinat ion, the lesion involved only the mucosa (Fig 3) and appeared to be init iated by an in- tramucosal hemorrhage leading to necrosis of a segment of the mucosa. Since the ulcers were bleeding, the contents of long segments of the small intestine were black because of digested blood.

Fed vs Fasted State

T h e ulcerogenic effect of exertion in animals fasted overnight was compared with that of rats fed until t ime of exertion. Feeding completely prevented formation of these ulcers.

Animals in groups of 10 each were killed from 0 to 72 hr after terminat ion of exer- tion. T h e ulcer index diminished by half dur ing the first day, whether animals re- mained fasted or were refed. After 2 days, the lesions had healed ahnost completely in fed rats whereas it was still t)resent in 70% of fasted anials (Tal)le 1) .

Sex

When male and female rats of the same body weight (195-205 g) were exerted,

,~:o~ less than in ulcerations in males were ~,~/o female animals (Table 2). Since male rats eat more than females, their stomachs at the time of fasting may have contained more food than that of the females. Conse- quently, dur ing the overnight fasting, the stomach of male rats woul(I take longer to

Dige~/tive Diseases, Vol. 15, No. 5 (May 1970) 499

ROBERT ETAL

Fig 2. Exertion ulcers, gross appearance. Top. Stomach of control rat. Bottom. Stomachs of rats with exertion ulcers located in corpus. Forestomach (upper portion) is not affected and antrum (arrow) usually is either not ulcerated (right) or has very small erosions (left).

empty, an event that could explain the reduct ion in ulceration found in these ani- mals. T o el iminate this factor of variable food intake, males and females were force- fed equal amounts of a med ium carbohy- drate fluid diet for 6 days. Ti le schedule of feeding was as follows: Day 1, 8 ml of the diet given in late afternoon; Day 2, 8 ml AM and 9 ml PM; and Days 3-6, 10 ml twice a day. Food was then withheld for 2 ½ days, after which the animals were submit ted to exertion. Prel iminary experiments had shown that a high content in corn oil, needed to keep this diet in stable suspen-

sion, rendered tile stomachs somewhat resistant to ulcers unless the fasting interval prior to exert ion was extended to about 2 days. When these pair-fed animals were submit ted to exertion, ulcerations were still reduced by 34% in male rats when com- pared with female rats (Table 2), an indi- cation that the sex difference in susceptibili- ty to ulcers is only partially related to the amoun t of food intake.

I n f l u e n c e of t h e A d r e n a l s

Adrenalectomy. Animals were adrenalec- tomized 5 days prior to exert ion and given

500 Digestive Diseases, Vol. 15, No. 5 (May 1970)

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Fig 3. Exertion ulcers, histologic appearance. Upper left. Normal gastric wall. (H&E, X28) Upper right. Well localized ulcer consisting of necrotic tissue mass with two central intramucosal hemorrhages (black areas). (PAS, X28) Lower left. Diffuse necrosis extending between arrows. (PAS, X28) Lower right. Crater formation, with necrotic tissue at base of ulcer. (PAS, X28)

0.9% NaC1 to drink. Control, nonadren- alectomized rats also received NaC1 0.9% for the same time period. Adrenalectomy did not influence ulcerations.

Prednisolone. Prednisolone, suspended in aI~ aqueous vehicle containing sodium car- boxymethylcellulose, was administered at

the doses (rag per rat) indicated in Tab l e 3 in a single subcutaneous injection either at the t ime of exertion, or 16 or 24 hr before. When given at exertion, prednisolone had no effect. When injected several hours prior to exertion, prednisolone, at levels of 0.5, 1 and 2 mg, inhibi ted ulcers (the

Digestive Diseases, Vol. 15, No. 5 (May 1970) 501

ROBERT ET AL

Table 1. Healing Time of Exertion Ulcers

Imme. diately Fed after after Fasted after exert ion (hr) exert ion (hr)

exert ion (0 hr) 6 24 48 72 24 48

Ulcers Incidence (%) 100 100 80* 70t 20t 92f 17f Severity (0 to 3+) 1.5 1.2 0.5t 0.4t OAt 0.6t 0.1t Ulcers/stomach 10.8 7.4 1.8f 1.5f 0.3f 1.7f 0.7t Ulcer index 22.3 18.6 10.3 8.9 2.4 11.5 2.5 Inhib i t ion (%)$ - - 17 54 60 89 48 89

* p < 0.05 when values are compared with those of the ' '0 hr " group. t P < 0.01 when values are compared with those of the "0 h r "g roup . $ Values express percent inhib i t ion of ulcer index when compared to group ki l led at 0 hr, that is,

immedia te ly at the end of exert ion.

degree depending on the dose). The re was no appreciable difference between 16 and 24 hr.

Oesoxycorticosterone. Desoxycorticoster- one (5 mg sc either at t ime of exertion or 20 hr before) did not influence exert ion ulcers.

Effect of P h a r m a c o l o g i c Agents

,Anflchollnerglc. M e t h s c o p o l a m i n e bro- mide (Pamine) * was administered orally in 1 ml of water, once, immediate ly prior to exertion, to groups of 10 rats each at the doses indicated in T a b l e 4. Th i s compound inhibi ted exert ion ulcers and the effect was dose-dependent.

Anfocid. An antacid preparat ion, Mal- cogel,* containing 130 mg of magnes ium trisilicate and 66 mg of a luminum hydrox- ide per ml, was administered orally either once (prior to exer t ion) , twice (before the first and tile third runn ing cycles) or three times (before each of the three runn ing cycles) to groups of I0 rats each. Control animals received identical volumes of water. Ti le results (Table 5) indicate that

*The Upjohn Company, Kalamazoo, Mich.

ulcerations were prevented ill relation to the amount of antacid given.

CNS depressonf. Chlorpromazinewas ad- ministered subcutaneously, once, to groups of 10 rats each, immediately prior to exer- tion at the doses indicated in Tab l e 6. T h e degree of inhibi t ion was dose-dependent. Dur ing exertion, the number of actively runn ing ra ts diminished as the closes in- creased. Other animals given the same doses of chlorpromazine but not submitted to exert ion were also increasingly lethargic relative to the dose.

Table 2. Influence of Sex on Exertion Ulcers

Fed ad l ib i tum Force-fed

Females Males Females Males

No. of animals 10 15 20 14 Exertion ulcers

Incidence (%) 100 60* 95 77 Severity

(0 to 3+) 1.8 0.7* 1.2 1.1 Ulcers/stomach 6.2 1.4" 7.0 3.9* Ulcer index 18.0 8.1 17.7 11.7 Inhibi t ion (%) - - 55 - - 34

* p < 0.01 when values are compared with those of corresponding female group.

S0Z Digestive Diseases, Vol. 15, No. 5 (May 1970)

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Table 3. Effect of Prednisolone on Exertion Ulcers

Dose of prednisolone (mg/rat )

0.5 1 2

Time of UI- Ul- Ul- UI. injection cer cer % cer % cer % (hr pre- in- in- Inhi- in. Inhi- in- Inhi-

exertion) dex dex bit ion dex bit ion dex bit ion

24 23.3 18.1 22 15.0 36 4.4 81 16 19.7 16.8 15 12.7 36 7.8 60 0 20.6 20.4 1 23.0 --11 22.7 --10

Table 4. Effect of Methscopolamine Bromide on Exertion Ulcers

Methscopoiamine dose

Water (pg/rat)

Ulcers alone 50 100 250 500 1000

Incidence (%) 100 100 60* 50* 40* 10"

Severity ( 0 t o 3 + ) 1.6 1.3 0.7* 0.4* 0.4* 0.1"

Ulcers/ stomach 10.6 9.6 2.2* 3.2* 1.5" 0.1"

Ulcer index 22.2 20.9 8.9 8.6 5.9 1.2 Inhibit ion

(%) 6 60 61 73 95

* p < 0.01 when values are compared with group given water alone.

Mercuric acetate. M e r c u r i c aceta te was

previously reported to inhibit acid secre- tion and to increase 1)oth volume of gastric juice (20,21) and mucus (21) secretion. When administered orally at a dose known to reduce acid secretion by 65% (1 ml of 5 X 10-~ tool) (21), this compound inhib- ited ulceration (ulcer index decreased by 30~'o). Higher closes, given to groups of 10 each, completely prevented ulcer formation (Table 7).

Effect of Exert ion on Gastr ic Secre t ion

-Rats were fasted fo r l ½ days, starting at 4 PM, after which their pylorus was ligated

under ether anesthesia; 5-10 rain later, they were submitted to exertion. At au- topsy (3 hr after pylorus l igation), gastric juice was collected and analyzed for (1) titratable acidity with N a O H 0.01 N to p H 8.5 (glass electrode) ; (2) hexosamine (used as an estimation o f mucus) (22)

Table 5. Effect of an Antacid on Exertion Ulcers

Amount and frequency

2m l 2m l 2m l 2.5ml X 1 X 2 X 3 X 3

RATS GIVEN WATER ONLY

Incidence (%) 100 100 100 100 Severity (0 to 3+) 1.4 1.5 1.4 1.7 Ulcers/stomach 9.0 10.9 7.1 14.2 Ulcer index 20.4 22.4 18.5 25.9

RATS GIVEN MALCOGEL

Incidence (%) 90 80* 50? 10t Severity (0 to 3+) 1.2 0.6 0.5t 0.1t Ulcers/stomach 4.2* 3.0t 0.8f 0.2t Ulcer index 14.4 11.6 6.3 1.3 Inhibi t ion (%) (from

water groups) 29 48 66 95

* p < 0.05when values are compared with those of corresponding water group.

t P < 0.01 when values are compared with those of corresponding water group.

Table 6. Effect of Chlorpromazine on Exertion Ulcers

Chlorpromazine dose (mg/rat )

Sal ine alone 0.1 0.25 0.5 1.0

Exertion ulcers Incidence (%) 100 100 70* 50* 0 Severity (0 to 3+) 2.3 1.6 0.9* 0.6* Ulcers/stomach 11.3 7.0 3.1" 1.5" Ulcer index 23.6 18.6 11.0 7.1 0 Inhibi t ion (%) 21 53 70 100

No. of act ively running rats 10/10 8/10 7/10 3/10 2/10

* p < 0.01 when values are compared with those of saline group.

Digestive Diseases, Vol. 15, No. 5 (May 1970) 503

Table 7. Effect of Mercuric Acetate on Exertion Ulcers

M ercuric acetate dose (1 ml)

5 X 5 X 7 X Exertion Water 10-4 10-a 10-a ulcers alone tool mol mol

Incidence (%) 100 100 0 0 Severity (0 to 3+) 1.6 0.8* - - - - Ulcers/stomach 11.2 5.2t - - - - Ulcer index 22.8 16.0 0 0 Inhibition (%) - - 30 100 100

* p < 0.01 when values are compared with those of water group.

t P < 0.05 when values are compared with those of water group.

followng a modification (22) of Boas' method (23); and (3) pepsin, modified (21) after Anson (24). Control rats were

not submit ted to exertion. Volume and acid secretion were significantly reduced dur ing exert ion (Table 8) but hexosamine (mucus) and pepsin were not changed.

Table 8. Effect of Exertion on Gastric Secretion

(%) Rest Exertion Inhi.

(M ± SE) (M :E SE) bition

No. of animals 15 15 - - Gastric juice

Volume(ml /3hr) 5.8:E0.5 3 . 7 ~ 0 . 2 36* Titratable Acid

Concentration (mEq/l i ter) 91 ~ 5 61 -4- 4 33*

Output (mEq/3 hr) .656 ~: 0.06 .358 -4- 0.02 45*

Hexosamine (mg/3hr) 1.54~0.07 1.52<0.06 1

Pepsin (mEq Tyrosine/3 hot .204 =k 0.02 .185-4- 0.01 9

Values following -4- sign refer to standard error of the mean.

* p < 0.01. tAmoun t of tyrosine, released pe r 10 min of

incubation with hemoglobin, during the 3 hr of gastric juice secretion.

ROBERT ET AL

D I S C U S S I O N

T h e exert ion ulcer technic had advan- tages as an assay. I t is rapid (2 hr and 45 ra in) , simple (no surgery, no special prepa- ra t ion of the animals other than overnight fasting), reproducible, and quanti tat ive (ulcers are rated in terms of incidence,

severity, number per stomach, and ulcer index) . Usually, to test antiulcer agents, a single adminis t ra t ion of a compound is required, except for very quick acting agents where a repeat dose may be needed. I[ a compound is part icularly insoluble and expected to be absorbed slowly from the injection site, as is the case for predniso- lone, it should be injected the night before and the amount of deposit found under the skin noted at autopsy. In the case of oral administrat ion, absorption is usually rapid enough so that the agent can be given immediately prior to exertion. As for any other nicer assay, the resemblance between h u m a n and animal ulcers cannot be as- sessed with certainty, and, unlike the com- mon peptic ulcer, exertion ulcers ate acute and involve the mucosa only. However, exert ion ulcers respond to the usual antiul- cer the rapy- -namely , anticholinergics, ant- acids, and tranquilizers. A disadvantage of the exert ion ulcer assay is that agents re- ducing muscular activity, such as CNS de- pressants, may inhibi t ulcers simply be- cause the animals do not actively run. For this reason, 15 rain before the end of the assay, the animals must be observed to ascertain that the treated rats are running the same as the controls. T h e same criti- cism can be raised for restraint ulcers, in which case the animals must be awake and struggling in order to develop ulcers. In Tab l e 9 the technics most frequently used to study ulcer formation in the rat are listed, and their main advantages are indi- cated.

504 Digestive Diseases, Vol. 15, No. 5 (May 1970)

EXERTION ULCERS

Shay

Restraint

Table 9.

M ethod

Steroid.induced

Phenylbutazone

Reserpine

Histamine releasers

Exertion

Advantages and Disadvantages of Various Ulcer Inducing Technics in the Rat

Advantages

Permits detection of antiulcer agents acting through inhibition of gastric secretion

Stress-induced ulcers May simulate clinical acute

ulcers May have psychic component Can be made quantitative

Simu.lates corresponding clin- ical condition

Quantitative Simulates corresponding clin-

ical condition Simulates corresponding clin-

ical condition Rapid, simple technic

Stress-induced ulcers May simulate clinical acute

ulcers May have psychic component Simple, rapid technic Quantitative

Disadvantages

Ulcers are in the nonglandular portion

Difficult to quantitate Requires surgery Relatively low ulcer incidence in

fasted rats Higher incidence in fed rats, but

compounds retarding gastric empty- ing cannot be used

Agents slowing down muscular activity cannot be used

Oral treatment during restraint technically difficult

May not be related to other forms of clinical ulcers

Special form of ulcer

Special form of ulcer

Special form of ulcer May not have clinical equivalent Agents slowing down muscular

activity cannot be used

Noble and Collip (25) devised a rota t ing drum to produce shock in rats and guinea pigs. Shock was produced, not by running, but by bumping over obstacles prot ruding inside the drum, and gastrointestinal ulcers were observed only in surviving animals, after they had been removed from the drum. Ulceration in these animals was ac- companied by extreme vascular dilation, engorgement, and congestion of the mesen- tory and bowel. Such visceral changes were not observed in our experiments, and ani- mals never died dur ing or after exertion. Lillehei and ~¥angensteen (26) placed dogs on a treadmill for 3-4 h r / day for 6 days and found that such a procedure increased the incidence of ulcers produced by daily administrat ion of his tamine in

1)eeswax, a l though muscular exercise by itself was not ulcerogenic. These authors postulated that dur ing muscular exercise blood flowed preferentially to the muscles and that such a shift would favor develop- ment of ulcers by causing mucosal ischemia. In a later publ icat ion (27), the}' demonstra ted a similar effect of hemor- rhagic shock. In our experiments, in con- trast to the Lillebei and Wangensteen studies, exert ion by itself did produce ul- cers. I t may be that rat stomachs are more sensitive to shock than dog stomachs or that the intensity of stress in our case was ,greater.

T h e higher susceptibility of female rats to exertion ulcers is contrary to the human sex incidence of peptic ulcer. Female rats

Digestive Diseases, Vol. 15, No. 5 (May 1970) 505

were also f o u n d to be m o r e sensi t ive than

males to ulcers p r o d u c e d by the t echn ic o1 r e s t r a i n t (28, 29) W h e t h e r this sex differ- ence is a gene t ic charac te r i s t i c has no t been d e t e r m i n e d .

O v e r n i g h t fas t ing is necessary for exer- t ion ulcers to deve lop m a x i m a l l y . T h i s m a y

be due p r i n c i p a l l y to two reasons: A n y stress p roduces more severe d a m a g e in a fas ted t h a n in a fed s tate and s t renuous

e x e r t i o n is no excep t ion ; absence of food in the s tomach render s the mucosa m o r e v u l n e r a b l e because i t is t hen in con tac t wi th concen t r a t ed , unbu f f e r ed gastr ic juice .

T h e a n t i u l c e r p r o p e r t y of m e r c u r i c ace- ta te is p resumal ) ly due to a c o m b i n a t i o n of i n h i b i t i o n of ac id f o r m a t i o n a n d s t imula-

t ion of mucus , as d e m o n s t r a t e d ea r l i e r (20,- 21) . T h i s c o m p o u n d was also shown to

reduce by ha l f peps in secre t ion (21).

As to the e t io logy of e x e r t i o n ulcers,

gast r ic hype r sec re t i on can be r u l e d ou t s ince v o l u m e a n d ac id secre t ion were actu-

a l ly decreased d u r i n g exer t ion . ] t is more l ike ly tha t phys ica l e x h a u s t i o n consequen t

to s t r enuous e x e r t i o n p roduces a t e m p o r a r y s tate of shock w i th consequen t i m p a i r m e n t

in gas t r ic c i r cu la t ion , a l t h o u g h no b l o o d flow s tudies were p e r f o r m e d to test this hypothes is . T h e shock w o u l d resu l t in local anox ia , h e m o r r h a g e , a n d p a r t i a l d iges t ion ,

by gas t r ic ju ice a l r eady present , of the

affected areas. Such a cha in of events he lps also to e x p l a i n the benef ic ia l effect of pred-

n iso lone . T h i s h o r m o n e , by c o u n t e r a c t i n g the effects of shock, w o u l d a l low ma in t e - nance of nea r n o r m a l b l o o d pressure dur- ing e x e r t i o n and, thus, p r even t u lcer for- ma t i on . Psychic factors also may c o n t r i b u t e

to f o r m a t i o n of these ulcers.

R E F E R E N C E S

1. Shay H, Komarov SA, Fels SS, et al: A simple method for the uniform production

ROBERT ETAL

of gastric ulceration in the rat. Gastro- enterology 5:43, 1945

2. Rossi G, Bonfils S, Lieltogh F, et al: Tech- nique nouvelle pour produire des ulcera- tions gastriques chez le rat blanc: l'ulcbre de contrainte. Compt rend Soc Biol 150:

2124, 1956 3. Robert A, Nezamis JE: Ulcerogenic prop-

erty of steroids. Proc Soc Exp Biol Med 99:443, 1958

4. Robert A, Nezamis JE: Histopathology of steroid-induced ulcers. An experimental study in the rat. AMA Arch Path 77:407, 1964

5. Bonfils S, Hardouin JP, Bourel M: I,'ulcbre gastrique du rat par ingestion de phOlyl- butazone. Compt rend Soc Biol 147:2016, 1953

6. Benditt El', Wong RI.: The release of enterochromagfin substance by reserpine. Amer J l 'a th 32:638, 1956

7. Haverback BI. Bogdanski DF: Gastric mu- cosal erosion in the rat following adminis- tration of the serotonin precursor, 5-hy- droxy-tryptophan. Proc Soc Exp Biol Med

95:392, 1957

8. I~aBarre J, Desmarez J J: A propos des ph(.nom~nes hypers(~cr~toires et des mani- festations ulc6reuses gastriques apparaissant chez le rat trait6 par la r6serpine. Compt rend Soc Biol 151:1451, 1957

9. Wilhelmi G: .Cber die ulcerogelm Wirkung yon 5-Hydrox~,,tryptamin am Rattenmagen und deren Beeinflussung durch verschiedene Pharma(a. Helvet Physiol Pharmacol Acta

15:C83, 1957

10. Hedinger C, Veraguth F: Magengeschwfire bei Rat ten unter Behandlung mit 5-Hy- droxytryptamin. Schweiz reed Wschr 87: 1175, 1957

11. Feldberg PD,', Telesnik J: Reduction of tissue histamine by compound 48/80. J Physiol 120:550, 1953

12. Franco-Browder S, Masson GMC, Corcoran AC: Induction of acute gastric lesions by histamine liberators in rats. J Allergy 30:1,

1959

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13. Robert A, Selye H: Effect de la cortisone et de la STH sur l'ulc~re gastrique exp6ri- mental. Ann d'Endocrinol 13:845, 1952

14. Myhre E: Regeneration of the fundic rnu- cosa in rats. Effect of estrone and of castra- tion. AMA Arch Path 62:30, 1956

15. Skoryna SC, Webster DR, Kahn DS: A new method of production of experimental gas- tric ulcer. The effects of hormonal factors on healing. Gastroenterology 34:1, 1958

16. Kuroyanagi Y, Necheles H: Mann-William- son rat. Proc Soc Exp Biol Med 108:771, 1962

17. Selye H: Studies on adaptation. Endocrinol 21:169, 1937

18. Selye H, Macleaw A: Prevention of gastric ulcer formation during the alarm reaction. Amer J Digest Dis 11:319, 1944

19. Dalton AJ: Gastric ul(ers elicited by non- specific damage. Anat Rec 79:85, 1941

20. Seijffers M, Birnl)aum D, Groen J J: Effect of mercury salts on gastric secretion in rats. Gatroenterologia 99:105, 1963

21. Robert A, Nczamis JE, Phillips Jp: Differ- ent properties of two mucigogues, pilocar- pine and mercuric acetate. Amer J Physiol 209:877, 1965

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