- Email: [email protected]
Study of cold + restraint stress gastric lesions in spontaneously hypertensive, Wistar and Sprague-Dawley rats
Life Sciences Vol. 12, Part I, pp . 519-527, 1973 Printed in Great Britain
Pergamon Press
STUDY OF COLD + RESTRAINT STRESS GASTRIC LESIONS IN SPONTANEOUSLY HYPERTENSIVE, WISTAR AND SPRAGUE-DAWLEY RATS Marvin M . Goldenberg Pharmacology Section, Pharmacometrics Division, Research and Development Department, Norwich Pharmacal Company, Division of Morton-Norwich Products, Inc ., Norwich, New York 13815
(Received 29 January 1973; in final form 7 March 1973) SUMMARY The object of this study was to determine whether the development of gastric lesions induced by cold-+-restraint stress differed among the Spontaneously Hypertensive (Wistar-derived), Wistar, and Sprague-Dawley (SD) rats . The incidence of gastric lesions (% of rats with lesions) was found to be significantly greater in the SO rat than in the other two types . The increased sussceptibillty of the SD strain to lesion formation was tentatively attributed to differences in hereditary factors and also to less variation in sensitivity within this rat strain . The incidence of gastric lesions was significantly higher in the Spontaneously Hypertensive (SH) than in the normotensive Wistar rat . Evidence from the literature suggests that the SH rat synthesizes more catecholamines in the adrenal glands than the normotensive Wistar rat, and thus under stress these amines may contribute to gastric lesion formation by virtue of their mucosal vascular constriction and gastric ischemia potential . The SD and the SH rat were estimated to have the same average lesions/stomach values significantly higher than in Wistar rats - following cold-+restraint stress . The technique of inducing gastric ulcers in fasted rats by means of cold-+-restraint stress has been described (1,2,3,4) .
The characteristic
appearance of these lesions, however, has not been resolved ; Brodie at at . (4) found hemorrhage in the glandular or corpus portion of the rat stomach, whereas Senay and Levine (3) described distinct ulceration extending to or through the submucosa of the corpus .
Restraint stress (without cold) induces
gastric mucosal vascular engorgement or vascular congestion within one-half hour, and ultimately leads to mucosal ulceration (5) .
Mucosal vascular
congestion is under vagus nerve control and may be associated with the
519
.
520
Incidence of Cold-Restraint Stress Induced Ulcers
Vol. 12, No. 11
occurrence of restraint-induced ulcers (6) . Recently, an inbred strain of rats (Wistar-derived) was developed in which hypertension occurred spontaneously several months after birth ; these were designated Spontaneously Hypertensive (SH) rats (8) .
Under chronic
stress conditions (immobilization for 2-10 hours/day) these rats maintained elevated blood pressures for periods as long as 1 month after final exposure to stress while the adrenal glands showed intense hyperemia and the thymus glands were atrophied (9) . The present study was conducted to determine whether there was a difference in the susceptibility of the stomach of the SH, Wistar, or Sprague-Dawley (SD) rat to hemorrhagic-lesion formation following cold-+-restraint stress . Of particular interest was whether the incidence of gastric lesions in SH rats was similar to that found in their normotensive genetic counterpart, the Wistar rat strain .
MATERIALS AND METHODS Male SO and Wistar rats (Charles River Breeding Laboratories, Inc .) and male SH rats (descendents of Wistar-Kyoto rats obtained from Okamoto and Aoki (8) and subsequently bred and raised at the Norwich Pharmacal Company), ranging in weight from 210-310 g, were fasted 27 hr before the experiment . Each rat was restrained by placing it in a cylindrical metal can (4-3/4 x 2-1/2 in) with an opening (about 1 in diameter) at one end for head protrusion only and closed at the other end with a large rubber stopper (having a 1/2 in opening to accommodate protrusion of the tail) . secured the rubber stopper to the can .
A strip of adhesive tape
To restrict head movement, a piece
of masking tape was positioned lightly around the neck of the rat and affixed to the can .
Each restrained rat was then exposed to the cold (7°C) by placing
in a refrigerator .
Three hours later, the rat was taken from the cold en-
vironment and sacrificed by an overdose of ether, and the stomach was removed
Vol. 12, No. II
Incidence of Cold-Restraint Stress Induced Ulcers
and rinsed with tap water .
521
In control experiments, fasted male rats of the
3 strains were not subjected to 3 hr cold-+-restraint stress, but their stomachs were removed and studied for gastric lesions . The stomach was opened by making an initial incision along the limiting ridge and then cutting along the greater curvature to expose the corpus or glandular portion and finally cutting the forestomach (nonglandular portion) so that the entire interior surface of the stomach was visible .
If food or
The stomach was
fecal material were present, the stomach was discarded .
lightly rinsed with tap water to remove any loosely-clinging debris .
Using
a cotton swab, the stomach was carefully scrutinized for hemorrhagic lesions by examining it with a low-power magnifying lens (Dazor Floating Fixture) . Gastric or hemorrhagic lesions were considered positive if they could not be removed by firm wiping of the surface with a cotton swab .
The size of the
lesions was variable (1-5 mm) and only the total number of lesions divided by the total number of rats stressed in each group was included in the calculation of the average number of lesions per stomach .
Interstrain differences
in the number of lesions were assessed for statistical significance by the one-way analysis of variance (18) .
Strains were compared, in pairs, as to
x2 test for a 2 x 2 the proportions of rats forming lesions, by means of the contingency table (18) .
RESULTS The appearance of gastric lesions in the corpus or glandular portion after 3-hr cold-+-restraint stress was grossly similar in the stomachs of SD, Wistar, and SN rats .
The lesions were characterized by multi-shaped, multi-sized
superficial hemorrhagic (black or deeply-red) areas frequently situated parallel to and near the crest of the rugae . the forestomach or pyloric region .
No lesions were observed in
The stomachs in all 3 strains of rats
were in a state of contraction when extirpated from the body .
No gastric
Incidence of Cold-Restraint Stress Induced Ulcers
522
Vol. 12, No . 11
lesions were present in nonstressed rats of any strain, and the stomachs were not contracted . TABLE 1 Effect of 3 Hour Cold-+-Restraint Stress in 3 Rat Strains No . of Rats
Rat Strain
S
_
of (tats-
with Gastric Lesions
- Average -No . of Lesions per Stanacha
Sprague-Dawley
47
89 .4
3 .0 + 0 .4b
Spontaneously-Hypertensive (Wistar-Derived)
42
69 .1
3 .1 + 0 .6c
Wistar
47
34 .4
0 .7 + 0 .2
a Obtained by dividing the total number of lesions in each strain by the total number of rats studied in that strain . b Number of gastric lesions in the SO strain was not significantly different (P>0 .05) from that in SH strain but was significantly different (P<0 .01) from that in the Wistar strain . c Number of gastric lesions in the SH strain was significantly different (P<0 .01) from that in the Wistar strain . As shown in Table 1, the incidence of gastric lesions was greatest in the SO rat following cold-+-restraint stress for 3 hours .
The stomach of the Wis-
tar rat demonstrated the most resistance to lesion formation, of the 3 groups of stressed rats .
More specifically, the occurrence of gastric lesions in
these stressed SO rats was more than twice that in Wistar rats under the same conditions .
The stomach of the SH rat, derived from the Wistar strain, was
apparently affected more by cold-+-restraint stress than the stomach of its normintensive counterpart strain ; i .e ., as indicated from the results of the x2 analysis (Table 2), the incidence of gastric lesions in the SH rat was significantly greater than in the Wistar strain but significantly less than in the SO strain .
The SH rat when restrained was the most vocal and visibly-
enraged of the rats studied . gastric lesions in the SH rat .
Restraint alone for 3 hr failed to induce
Vol. 12, No . 11
Incidence of Cold-Restraint Stress Induced Ulcers
523
TABLE 2 2 x 2 XZ Values for Interstrain Differences in Percentages of Rats Exhibiting Gastric Lesions (Pair-Wise) SO SH
SH
4 .48a
Wistar
--
28 .14b
9 .52b
a Significantly different value - Xi (P-0 .05) - 3 .84. b Significantly different value (P-0 .01) - 6 .635 . Xi It was interesting to note that despite the more frequent occurrence of gastric lesions in the SO strain, the average number of lesions/stomach was similar to that found in the SH rat after cold-+-restraint stress for 3 hr (Table 1) .
According to the one-way analysis of variance, the Wistar strain
was significantly the least susceptible to gastric lesion formation, with about 1 lesion/stomach observed . DISCUSSION These findings indicate that it is imperative to select the proper strain of rat for induction of cold-+-restraint-stress gastric lesions when conducting a short term (3 hr) study.
The SO strain was found to be more susceptible
to 3 hr cold + restraint than the Wistar strain .
That is, both the incidence
and the number of gastric lesions were greater in the SO than in the Wistar strain .
Investigators have used the Wistar rat very little in cold-+-
restraint-stress studies .
Nuryobayashi et al . (7) exposed Wistar rats to
cold-water+-restraint for 4 to 5 hr to obtain 10 to 11 gastric lesions per stomach, but only 3 to 5 rats were studied .
On the contrary, the SO strain
(3) and the Holtzman strain (2) are frequently used and have been shown to be susceptible to cold-+-restraint-stress forming gastric lesions after an hour or two of exposure .
524
Incidence of Cold-Restraint Stress Induced Ulcers
Vol . 12, No. 11
The greater susceptibility of the SD rat in gastric lesion formation as opposed to the Wistar rat, regardless of genetic hypertension, may be due to the dissimilarity in the hereditary factors between the two strains of rat. Since the literature is replete with examples of interstrain differences (rat, mouse, dog, rabbit) in physiologic, pharmacologic, or infectious responses to various drugs or to experimental techniques and procedures (19), it is not surprising to note the relative resistance of one strain to induction of gastric lesions as compared to another one .
By selective breeding of rats
with the same genotypes, it is possible to obtain colonies of rats either sensitive or resistant to a given procedure (17) .
Martin at at . (20) de-
scribed the potential difficulty in using Wistar rats to induce gastric ulcers by immobilization (no cold) since two distinct lines of rats, one sensitive and the other resistant to stress ulcers, were found.
Sines (21), on the
other hand, used the Sprague-Dawley rat strain for selective breeding of rats which were highly susceptible to stress-induced gastric lesions .
In
the 4th generation of selective breeding, Sines (22,23) recorded a 100% frequency of ulceration in these sensitive Sprague-Dawley rats along with a line of susceptible rats which were smaller and more emotional than unselected rats .
The colony of SD rats used in the present study may have
far fewer resistant than sensitive rats, in comparison to the Wistar colony . The Wistar-derived SH rat was more susceptible to cold-+-restraint-stress gastric lesions than its normotensive Wistar counterpart.
That is, both the
incidence (% of animals) and the number of lesions per stomach in the SH rat were greater than in the Wistar rat . planation for these differences .
There is no definitive, specific ex-
Perhaps greater amounts of catecholamines
are synthesized and released from the adrenal glands of SH rats than from those of normotensive Wistar rats when subjected to cold-+-restraint stress . Nagatsu at at . (10) reported that the levels of tyrosine hydroxylase and dopamine ß-hydroxylase in the adrenal glands of SH rats were twice as high
Vol. 12, No . 11
Incidence of Cold-Restraint Stress Induced Ulcers
as in normal Wistar rats .
525
Both adrenal enzymes are involved in the biosyn-
thesis of catecholamines, and inhibitors of these two enzymes have a hypotensive effect in SH rats (11) .
Furthermore, Ozaki at at . (12) found that the
concentration of norepinephrine in the adrenal glands of SH rats doubles 4-6 months after birth .
The catecholamines norepinephrine and epinephrine,
and phenylephrine, another vasopressor agent, were reported to induce hemorrhage and ulcers in rats as a result of their vasoconstricting property (13,14,15) .
Thus, if the theories of Guth and co-workers (5,6) and Brodie
and co-workers (2,4,16) are now taken into consideration, i .e ., mucosal vascular engorgement results in the subsequent formation of restraint ulcers independent of the amount of acid secretion into the stomach, then the incidence of gastric lesion formation in SH rats should be greater than that in normotensive Wistar rats, since catecholamine levels are higher in the adrenal glands of SH than in those of normotensive rats (12) and greater amounts of catecholamines may be released via stress in the SH rat.
Studies
are in progress to define more clearly the mechanisms involved in evoking stress lesions in the SH rat. The mean number of gastric lesions in the SO and SH rat was the same . This paradoxical finding reflected the criterion used to define a hemorrhagic response in this study, i .e ., one gastric lesion was considered to be a posi tive response while the absence of a single lesion signified a negative response .
In the nearly 90% of the SO rats exhibiting positive gastric lesions,
about 1/3 of these had at least one lesion whereas in the nearly 70% of the SH rats showing positive gastric lesions, only about 1/6 of these had one lesion and the rest had multiple lesions .
526
Vol. 12, No. 11
Incidence of Cold-Restraint Stress Induced Ulcers REFERENCES
1.
R .G . BARTLETT, V.C . BOHR and R.H . HELMENDACH, Proc . Soc. Exp . Biol . & Med. 395-396 (1954) .
2.
D.A . BRODIE and L .S . VALITSKI, Proc . Soc. Exp. Biol . & Med . ]U, 998-1001 (1963) .
3.
jam,
E .C . SENAY and R.J . LEVINE, Proc . Soc. Exp. Biol . & Med.
1221-1223
(1967) . 4.
D .A . BRODIE, V .J . LOTTI and B .G . BAUER, Am . J . Dig . Dis . ]i, 111-120 (1970) .
5.
P .H . GUTH and P. HALL, Gastroenterology ,`L 562-570 (1966) .
6.
P .H . GUTH and X. KOZBUR, Am . J . Dig . Dis . U,, 530-535 (1968) .
7.
T . MURYOBAYASHI, M. FUJIWARA and K. SHIMAMOTO, Jap . J . Pharmacol . ]$, 299-311 (1968) .
8.
K. OKAMOTO and K. AOKI . Jap. Circul . J .
9.
K. OKAMOTO, Int. Rev . Exp . Path .
10 .
227-270 (1969) .
1,
1013-1014 (1971) .
I . NAGATSU, T . NAGATSU, K. MIZUTANI, H . UMEZAWA, M . MATSUZAKI and T . TAKEUCHI, Nature
12 .
282-293 (1963) .
I . NAGATSU, T. NAGATSU, K. MIZUTANI, H . UMEZAWA, M . MATSUZAKI and T . TAKEUCHI, Experientia
11 .
7,
3,
L,
381-382 (1971) .
M. OZAKI, Y . SUZUKI, Y . YAMORI and K . OKAMOTO, Jap . Circ . J .
AL,
1367-
1372 (1968) . 13 .
B. DJAHANGUIRI, S . HEMMATI, D. SADEGHI and A . FIROOZABODI, Med. Pharmacol . Exp . ].,, 427-433 (1967) .
L,
243-246 (1969) .
14 .
B. DJAHANGUIRI, A. POUSTI and M. HEMMATI, Pharmacology
15 .
D .M . NICOLOFF, E.T . PETER, A.S . LEONARD and O.H . WANGENSTEIN, J . Am . Med . Assoc. ]2],, 383-385 (1965) .
16 .
D .A . BRODIE and K.F . HOOKE, Digestion g, 193-204 (1971) .
17 .
W. KALOW, Annals N.Y . Acad . Sci .
18 .
G.W . SNEDECOR, Statistical Methods , Iowa State University Press (1957) .
IU,
694-697 (1968) .
Vol. 12, No. 11 19 .
Incidence of Cold-Restraint Stress Induced Ulcers
527
B. CALESNICK, Drill's Pharmacology in Medicine , McGraw-Hill Book Co ., P. 99 (1971) .
20 .
M.S . MARTIN, F. MARTIN, C . ANDRE and R. LAMBERT, Cast . rend . Soc . Biol . 2126-212 8 (1968) .
21 .
J .0. SINES, J . Camp . Physiol . Psychol .
22 .
J.0 . SINES, J . Genet . Psychol .
23 .
J .0 . SINES, J . Psychosom. Res .
U,
615-617 (1959) .
]Q1, 209-217 (1962) . 1, 120-126 (1961) .
Pergamon Press
STUDY OF COLD + RESTRAINT STRESS GASTRIC LESIONS IN SPONTANEOUSLY HYPERTENSIVE, WISTAR AND SPRAGUE-DAWLEY RATS Marvin M . Goldenberg Pharmacology Section, Pharmacometrics Division, Research and Development Department, Norwich Pharmacal Company, Division of Morton-Norwich Products, Inc ., Norwich, New York 13815
(Received 29 January 1973; in final form 7 March 1973) SUMMARY The object of this study was to determine whether the development of gastric lesions induced by cold-+-restraint stress differed among the Spontaneously Hypertensive (Wistar-derived), Wistar, and Sprague-Dawley (SD) rats . The incidence of gastric lesions (% of rats with lesions) was found to be significantly greater in the SO rat than in the other two types . The increased sussceptibillty of the SD strain to lesion formation was tentatively attributed to differences in hereditary factors and also to less variation in sensitivity within this rat strain . The incidence of gastric lesions was significantly higher in the Spontaneously Hypertensive (SH) than in the normotensive Wistar rat . Evidence from the literature suggests that the SH rat synthesizes more catecholamines in the adrenal glands than the normotensive Wistar rat, and thus under stress these amines may contribute to gastric lesion formation by virtue of their mucosal vascular constriction and gastric ischemia potential . The SD and the SH rat were estimated to have the same average lesions/stomach values significantly higher than in Wistar rats - following cold-+restraint stress . The technique of inducing gastric ulcers in fasted rats by means of cold-+-restraint stress has been described (1,2,3,4) .
The characteristic
appearance of these lesions, however, has not been resolved ; Brodie at at . (4) found hemorrhage in the glandular or corpus portion of the rat stomach, whereas Senay and Levine (3) described distinct ulceration extending to or through the submucosa of the corpus .
Restraint stress (without cold) induces
gastric mucosal vascular engorgement or vascular congestion within one-half hour, and ultimately leads to mucosal ulceration (5) .
Mucosal vascular
congestion is under vagus nerve control and may be associated with the
519
.
520
Incidence of Cold-Restraint Stress Induced Ulcers
Vol. 12, No. 11
occurrence of restraint-induced ulcers (6) . Recently, an inbred strain of rats (Wistar-derived) was developed in which hypertension occurred spontaneously several months after birth ; these were designated Spontaneously Hypertensive (SH) rats (8) .
Under chronic
stress conditions (immobilization for 2-10 hours/day) these rats maintained elevated blood pressures for periods as long as 1 month after final exposure to stress while the adrenal glands showed intense hyperemia and the thymus glands were atrophied (9) . The present study was conducted to determine whether there was a difference in the susceptibility of the stomach of the SH, Wistar, or Sprague-Dawley (SD) rat to hemorrhagic-lesion formation following cold-+-restraint stress . Of particular interest was whether the incidence of gastric lesions in SH rats was similar to that found in their normotensive genetic counterpart, the Wistar rat strain .
MATERIALS AND METHODS Male SO and Wistar rats (Charles River Breeding Laboratories, Inc .) and male SH rats (descendents of Wistar-Kyoto rats obtained from Okamoto and Aoki (8) and subsequently bred and raised at the Norwich Pharmacal Company), ranging in weight from 210-310 g, were fasted 27 hr before the experiment . Each rat was restrained by placing it in a cylindrical metal can (4-3/4 x 2-1/2 in) with an opening (about 1 in diameter) at one end for head protrusion only and closed at the other end with a large rubber stopper (having a 1/2 in opening to accommodate protrusion of the tail) . secured the rubber stopper to the can .
A strip of adhesive tape
To restrict head movement, a piece
of masking tape was positioned lightly around the neck of the rat and affixed to the can .
Each restrained rat was then exposed to the cold (7°C) by placing
in a refrigerator .
Three hours later, the rat was taken from the cold en-
vironment and sacrificed by an overdose of ether, and the stomach was removed
Vol. 12, No. II
Incidence of Cold-Restraint Stress Induced Ulcers
and rinsed with tap water .
521
In control experiments, fasted male rats of the
3 strains were not subjected to 3 hr cold-+-restraint stress, but their stomachs were removed and studied for gastric lesions . The stomach was opened by making an initial incision along the limiting ridge and then cutting along the greater curvature to expose the corpus or glandular portion and finally cutting the forestomach (nonglandular portion) so that the entire interior surface of the stomach was visible .
If food or
The stomach was
fecal material were present, the stomach was discarded .
lightly rinsed with tap water to remove any loosely-clinging debris .
Using
a cotton swab, the stomach was carefully scrutinized for hemorrhagic lesions by examining it with a low-power magnifying lens (Dazor Floating Fixture) . Gastric or hemorrhagic lesions were considered positive if they could not be removed by firm wiping of the surface with a cotton swab .
The size of the
lesions was variable (1-5 mm) and only the total number of lesions divided by the total number of rats stressed in each group was included in the calculation of the average number of lesions per stomach .
Interstrain differences
in the number of lesions were assessed for statistical significance by the one-way analysis of variance (18) .
Strains were compared, in pairs, as to
x2 test for a 2 x 2 the proportions of rats forming lesions, by means of the contingency table (18) .
RESULTS The appearance of gastric lesions in the corpus or glandular portion after 3-hr cold-+-restraint stress was grossly similar in the stomachs of SD, Wistar, and SN rats .
The lesions were characterized by multi-shaped, multi-sized
superficial hemorrhagic (black or deeply-red) areas frequently situated parallel to and near the crest of the rugae . the forestomach or pyloric region .
No lesions were observed in
The stomachs in all 3 strains of rats
were in a state of contraction when extirpated from the body .
No gastric
Incidence of Cold-Restraint Stress Induced Ulcers
522
Vol. 12, No . 11
lesions were present in nonstressed rats of any strain, and the stomachs were not contracted . TABLE 1 Effect of 3 Hour Cold-+-Restraint Stress in 3 Rat Strains No . of Rats
Rat Strain
S
_
of (tats-
with Gastric Lesions
- Average -No . of Lesions per Stanacha
Sprague-Dawley
47
89 .4
3 .0 + 0 .4b
Spontaneously-Hypertensive (Wistar-Derived)
42
69 .1
3 .1 + 0 .6c
Wistar
47
34 .4
0 .7 + 0 .2
a Obtained by dividing the total number of lesions in each strain by the total number of rats studied in that strain . b Number of gastric lesions in the SO strain was not significantly different (P>0 .05) from that in SH strain but was significantly different (P<0 .01) from that in the Wistar strain . c Number of gastric lesions in the SH strain was significantly different (P<0 .01) from that in the Wistar strain . As shown in Table 1, the incidence of gastric lesions was greatest in the SO rat following cold-+-restraint stress for 3 hours .
The stomach of the Wis-
tar rat demonstrated the most resistance to lesion formation, of the 3 groups of stressed rats .
More specifically, the occurrence of gastric lesions in
these stressed SO rats was more than twice that in Wistar rats under the same conditions .
The stomach of the SH rat, derived from the Wistar strain, was
apparently affected more by cold-+-restraint stress than the stomach of its normintensive counterpart strain ; i .e ., as indicated from the results of the x2 analysis (Table 2), the incidence of gastric lesions in the SH rat was significantly greater than in the Wistar strain but significantly less than in the SO strain .
The SH rat when restrained was the most vocal and visibly-
enraged of the rats studied . gastric lesions in the SH rat .
Restraint alone for 3 hr failed to induce
Vol. 12, No . 11
Incidence of Cold-Restraint Stress Induced Ulcers
523
TABLE 2 2 x 2 XZ Values for Interstrain Differences in Percentages of Rats Exhibiting Gastric Lesions (Pair-Wise) SO SH
SH
4 .48a
Wistar
--
28 .14b
9 .52b
a Significantly different value - Xi (P-0 .05) - 3 .84. b Significantly different value (P-0 .01) - 6 .635 . Xi It was interesting to note that despite the more frequent occurrence of gastric lesions in the SO strain, the average number of lesions/stomach was similar to that found in the SH rat after cold-+-restraint stress for 3 hr (Table 1) .
According to the one-way analysis of variance, the Wistar strain
was significantly the least susceptible to gastric lesion formation, with about 1 lesion/stomach observed . DISCUSSION These findings indicate that it is imperative to select the proper strain of rat for induction of cold-+-restraint-stress gastric lesions when conducting a short term (3 hr) study.
The SO strain was found to be more susceptible
to 3 hr cold + restraint than the Wistar strain .
That is, both the incidence
and the number of gastric lesions were greater in the SO than in the Wistar strain .
Investigators have used the Wistar rat very little in cold-+-
restraint-stress studies .
Nuryobayashi et al . (7) exposed Wistar rats to
cold-water+-restraint for 4 to 5 hr to obtain 10 to 11 gastric lesions per stomach, but only 3 to 5 rats were studied .
On the contrary, the SO strain
(3) and the Holtzman strain (2) are frequently used and have been shown to be susceptible to cold-+-restraint-stress forming gastric lesions after an hour or two of exposure .
524
Incidence of Cold-Restraint Stress Induced Ulcers
Vol . 12, No. 11
The greater susceptibility of the SD rat in gastric lesion formation as opposed to the Wistar rat, regardless of genetic hypertension, may be due to the dissimilarity in the hereditary factors between the two strains of rat. Since the literature is replete with examples of interstrain differences (rat, mouse, dog, rabbit) in physiologic, pharmacologic, or infectious responses to various drugs or to experimental techniques and procedures (19), it is not surprising to note the relative resistance of one strain to induction of gastric lesions as compared to another one .
By selective breeding of rats
with the same genotypes, it is possible to obtain colonies of rats either sensitive or resistant to a given procedure (17) .
Martin at at . (20) de-
scribed the potential difficulty in using Wistar rats to induce gastric ulcers by immobilization (no cold) since two distinct lines of rats, one sensitive and the other resistant to stress ulcers, were found.
Sines (21), on the
other hand, used the Sprague-Dawley rat strain for selective breeding of rats which were highly susceptible to stress-induced gastric lesions .
In
the 4th generation of selective breeding, Sines (22,23) recorded a 100% frequency of ulceration in these sensitive Sprague-Dawley rats along with a line of susceptible rats which were smaller and more emotional than unselected rats .
The colony of SD rats used in the present study may have
far fewer resistant than sensitive rats, in comparison to the Wistar colony . The Wistar-derived SH rat was more susceptible to cold-+-restraint-stress gastric lesions than its normotensive Wistar counterpart.
That is, both the
incidence (% of animals) and the number of lesions per stomach in the SH rat were greater than in the Wistar rat . planation for these differences .
There is no definitive, specific ex-
Perhaps greater amounts of catecholamines
are synthesized and released from the adrenal glands of SH rats than from those of normotensive Wistar rats when subjected to cold-+-restraint stress . Nagatsu at at . (10) reported that the levels of tyrosine hydroxylase and dopamine ß-hydroxylase in the adrenal glands of SH rats were twice as high
Vol. 12, No . 11
Incidence of Cold-Restraint Stress Induced Ulcers
as in normal Wistar rats .
525
Both adrenal enzymes are involved in the biosyn-
thesis of catecholamines, and inhibitors of these two enzymes have a hypotensive effect in SH rats (11) .
Furthermore, Ozaki at at . (12) found that the
concentration of norepinephrine in the adrenal glands of SH rats doubles 4-6 months after birth .
The catecholamines norepinephrine and epinephrine,
and phenylephrine, another vasopressor agent, were reported to induce hemorrhage and ulcers in rats as a result of their vasoconstricting property (13,14,15) .
Thus, if the theories of Guth and co-workers (5,6) and Brodie
and co-workers (2,4,16) are now taken into consideration, i .e ., mucosal vascular engorgement results in the subsequent formation of restraint ulcers independent of the amount of acid secretion into the stomach, then the incidence of gastric lesion formation in SH rats should be greater than that in normotensive Wistar rats, since catecholamine levels are higher in the adrenal glands of SH than in those of normotensive rats (12) and greater amounts of catecholamines may be released via stress in the SH rat.
Studies
are in progress to define more clearly the mechanisms involved in evoking stress lesions in the SH rat. The mean number of gastric lesions in the SO and SH rat was the same . This paradoxical finding reflected the criterion used to define a hemorrhagic response in this study, i .e ., one gastric lesion was considered to be a posi tive response while the absence of a single lesion signified a negative response .
In the nearly 90% of the SO rats exhibiting positive gastric lesions,
about 1/3 of these had at least one lesion whereas in the nearly 70% of the SH rats showing positive gastric lesions, only about 1/6 of these had one lesion and the rest had multiple lesions .
526
Vol. 12, No. 11
Incidence of Cold-Restraint Stress Induced Ulcers REFERENCES
1.
R .G . BARTLETT, V.C . BOHR and R.H . HELMENDACH, Proc . Soc. Exp . Biol . & Med. 395-396 (1954) .
2.
D.A . BRODIE and L .S . VALITSKI, Proc . Soc. Exp. Biol . & Med . ]U, 998-1001 (1963) .
3.
jam,
E .C . SENAY and R.J . LEVINE, Proc . Soc. Exp. Biol . & Med.
1221-1223
(1967) . 4.
D .A . BRODIE, V .J . LOTTI and B .G . BAUER, Am . J . Dig . Dis . ]i, 111-120 (1970) .
5.
P .H . GUTH and P. HALL, Gastroenterology ,`L 562-570 (1966) .
6.
P .H . GUTH and X. KOZBUR, Am . J . Dig . Dis . U,, 530-535 (1968) .
7.
T . MURYOBAYASHI, M. FUJIWARA and K. SHIMAMOTO, Jap . J . Pharmacol . ]$, 299-311 (1968) .
8.
K. OKAMOTO and K. AOKI . Jap. Circul . J .
9.
K. OKAMOTO, Int. Rev . Exp . Path .
10 .
227-270 (1969) .
1,
1013-1014 (1971) .
I . NAGATSU, T . NAGATSU, K. MIZUTANI, H . UMEZAWA, M . MATSUZAKI and T . TAKEUCHI, Nature
12 .
282-293 (1963) .
I . NAGATSU, T. NAGATSU, K. MIZUTANI, H . UMEZAWA, M . MATSUZAKI and T . TAKEUCHI, Experientia
11 .
7,
3,
L,
381-382 (1971) .
M. OZAKI, Y . SUZUKI, Y . YAMORI and K . OKAMOTO, Jap . Circ . J .
AL,
1367-
1372 (1968) . 13 .
B. DJAHANGUIRI, S . HEMMATI, D. SADEGHI and A . FIROOZABODI, Med. Pharmacol . Exp . ].,, 427-433 (1967) .
L,
243-246 (1969) .
14 .
B. DJAHANGUIRI, A. POUSTI and M. HEMMATI, Pharmacology
15 .
D .M . NICOLOFF, E.T . PETER, A.S . LEONARD and O.H . WANGENSTEIN, J . Am . Med . Assoc. ]2],, 383-385 (1965) .
16 .
D .A . BRODIE and K.F . HOOKE, Digestion g, 193-204 (1971) .
17 .
W. KALOW, Annals N.Y . Acad . Sci .
18 .
G.W . SNEDECOR, Statistical Methods , Iowa State University Press (1957) .
IU,
694-697 (1968) .
Vol. 12, No. 11 19 .
Incidence of Cold-Restraint Stress Induced Ulcers
527
B. CALESNICK, Drill's Pharmacology in Medicine , McGraw-Hill Book Co ., P. 99 (1971) .
20 .
M.S . MARTIN, F. MARTIN, C . ANDRE and R. LAMBERT, Cast . rend . Soc . Biol . 2126-212 8 (1968) .
21 .
J .0. SINES, J . Camp . Physiol . Psychol .
22 .
J.0 . SINES, J . Genet . Psychol .
23 .
J .0 . SINES, J . Psychosom. Res .
U,
615-617 (1959) .
]Q1, 209-217 (1962) . 1, 120-126 (1961) .