European Journal of Pharmacology, 37 (1976) 197--201
197
© North-Holland Publishing Company, Amsterdam -- Printed in The Netherlands
Short communication I N T R A G A S T R I C NaHCO3 P E R F U S I O N AND VAGAL-INDUCED U L C E R F O R M A T I O N IN THE RAT STOMACH CLIVE W. OGLE, CHI H. CHO and SOTER DAI
Department of Pharmacology, Faculty of Medicine, University of Hong Kong, Hong Kong Received 24 February 1976, accepted 9 March 1976
C.W. OGLE, C.H. CHO and S. DAI, Intragastric NaHC03 perfusion and vagal-induced ulcer formation in the rat stomach, European J. Pharmacol. 37 (1976) 197--201. The effects of electrical vagal stimulation on gastric acid output and ulcer formation were studied in rats intragastrically perfused with saline or NaHCO3 solutions. Vagal stimulation produced a 100% incidence of glandular lesions and a significant increase in total acid output in saline-perfused stomachs. Antacid perfusion failed to prevent ulcer formation despite complete neutralization of the increased acid output. It is concluded that vagal-induced gastric glandular lesions are not acid dependent. Intragastric NaHCO3 perfusion
Vagus
Gastric ulceration
1. Introduction Substantial evidence points to the role of the vagus nerve in the aetiology of stress-induced gastric ulcer formation in the rat (Watanabe, 1966; Takagi and Okabe, 1970; Brodie and Hooke, 1971; Dai and Ogle, 1974, 1975). Gastric acid appears not to be responsible for stress ulcer formation, as n o t only does antacid administration fail to prevent ulceration b u t also acid secretion is reduced by stress in conscious pylorus-ligated rats (Dai and Ogle, 1974). Recently, Cho et al. (1976) have shown that direct electrical vagal stimulation in rats produces gastric glandular ulcers which are similar in appearance to those induced by stress. However, no measurements of gastric acid o u t p u t were made in this study with anaesthetized animals. Gastric acid secretion has been shown to be increased by electrical vagal stimulation in the pylorus-ligated rat (Watanabe, 1966) and in the isolated perfused dog stomach (Lanciault et al., 1975}, and it has also been reported that the presence (Skillman and Silen, 1972} and the degree of severity (Hase et al., 1975) of stress-induced
ulcers depend on the acidity of the gastric secretion. The purpose of the present study was to examine the effects of electrical vagal stimulation on gastric acid o u t p u t and on glandular ulcer formation in the perfused rat stomach in situ, and to determine whether increased gastric acid secretion does influence the formation of these ulcers.
2. Materials and methods 2.1. General
Male Wistar rats, weighing 200--300 g, were starved for 24 h before use b u t allowed free access only to 8% sucrose in 0.2% NaC1 (w/v). The animals, anaesthetized with i.p. injections of urethane (1.25 g/kg), were kept warm with a heating lamp during the experiment. Body temperature was maintained at 37 ° C. Following tracheal cannulation, positive ventilation was provided by a Palmer respiration pump at a rate of 70 strokes/min (stroke volume of 1 m i l l 0 0 g b o d y weight).
198 All experiments were carried out over a total period of 2 h 8 min, after which the animals were sacrificed and their stomachs examined by an independent observer for the presence or absence of mucosal lesions (Dai and Ogle, 1974).
2.2. Electrical vagal stimulation
C.W. OGLE ET AL. cm from the pylorus, until its tip entered the pyloric opening. The tube was gently tied in place with a ligature over the duodenum before exteriorizing the distal end through an incision in the flank. Prewarmed (37°C) solutions of NaC1 0.9% (w/v, saline) or NaHCO3 0.18% (w/v) were perfused through the oesophageal tube at a rate of 6.3 ml/16 min and the perfusate collected from the exteriorized end of the pyloric tube. The total acid in each sample, collected at 16-min intervals, was determined (Dai and Ogle, 1974). Each 16-min collection of perfusate included the 1-min rest period which immediately followed a 15-rain period of stimulation (or no stimulation in shamoperated controls). The concentration of NaHCO~ in the perfusion solution was determined by finding the total dose of antacid required to neutralize completely the total gastric acid produced by 8 15-min periods of vagal stimulation (including the 8 1-min periods following the stimulation periods).
Both vagus nerves were exposed in the neck and ligated to prevent any central effects of electrical stimulation. An electrode was placed under the left vagus, distal to the ligature. Electrical stimulation, with a stimulator (E & M Instrument Co., Inc.) delivering rectangular impulses of 2 msec duration at a strength of 5 V and a frequency of 20 Hz, was given continuously for 15-min periods. Each 15-min period was followed by a 1-min rest period without stimulation. Each experiment comprised 8 15-min stimulation periods separated by 7 l-rain periods, and included an 8th l-rain rest period which followed the last stimulation period. Sham-operated controls had their vagus nerves similarly exposed and ligated, but no stimulation was given through the electrode placed distal to the ligature on the left vagus. Bilateral sub-diaphragmatic vagotomy (vagotomy) was carried out through a central abdominal incision, and completeness ensured by resecting all the vagal branches to the stomach.
Atropine sulphate (E. Merck), 0.8 mg/kg body weight, expressed as the salt, was injected s.c. 15 min before starting the experiment. Similar volumes of saline were given to the controls by the same route. Sodium bicarbonate (NaHCO3, BDH) was used in the perfusions.
2.3. In tragastric perfusion
2.5. Statistical analysis
A modified perfusion technique basically similar to the m e t h o d described by Smith et al. (1970) was adopted. The oesophagus was cannulated at the cervical level with a polythene tube (2 mm o.d.), inserted until its tip reached the cardiac end of the stomach. It was then secured in place by a ligature around the oesophagus at the cannulation site. The pyloric end of the stomach was cannulated through a central abdominal incision. A polythene tube (4 mm o.d.) was inserted through a small incision in the duodenum, about 1.5
The data were analysed by means of Student's t-test or by the xZ-test.
2.4. Drugs
3. Results
3.1. The effects o f atropine, vagotomy or intragastric N a H C 0 3 perfusion on vagal-induced glandular ulcers Untreated and saline-treated sham-operated rats had a lesion incidence of 0% and 20% re-
NaHCO3 AND VAGAL-INDUCED GASTRIC ULCERS IN RATS
spectively (table 1A). The lesions appeared as occasional petechiae in the glandular segment of the stomach. Electrical vagal stimulation, however, induced a 100% incidence of lesions in both untreated and saline-treated rats (table 1B); this was significant when compared with their corresponding non-stimulated controls (p < 0.01 for both). The lesions were mainly haemorrhagic ulcers located only in the glandular segment of the gastric mucosa.
The incidence of occasional petechiae seen in atropine-treated or vagotomized sham-operated rats was also low (25% and 10% respectively, table 1A). A low incidence of petechiae of similar scatter was likewise seen in the atropine-treated or vagotomized rats that were stimulated (25% and 8% respectively, table 1B), b u t their lesion incidence was significantly different from that of the stimulated untreated or saline-treated rats (p < 0.01 for both). Atropine or vagotomy thus provided significant protection against haemorrhagic ulceration induced by electrical vagal stimulation. Untreated sham-operated rats receiving
199
either saline or NaHCO3 intragastric perfusions had a low incidence of lesions which also appeared as occasional petechiae in the glandular mucosa (33% and 27% respectively, table 1A). The lesion incidence in these two groups of animals did not differ significantly among the groups and from those of the other sham-operated controls (table 1A). Lesion incidence increased significantly to 100% when untreated saline-perfused rats received vagal stimulation (p < 0.01, when compared with their non-stimulated control). The size, and the surrounding haemorrhagic discolouration of the ulcers appeared to be slightly less when compared with the lesions in the non-perfused vagal stimulated untreated or saline-treated rats (table 1B). Intragastric NaHCO3 perfusion did not protect against these vagal-induced glandular lesions. The lesion incidence was 100%, which was significant when compared with the non-stimulated control group perfused with NaHCO3 (p < 0.01), and the appearance of the glandular lesions was similar to those seen in the stimulated untreated rats receiving saline perfusions.
TABLE 1 Effects of drugs or of vagotomy on the incidence of gastric glandular lesions induced by vagal stimulation. Treatment
Number of rats
Number of rats with glandular haemorrhagic ulcers and/or petechiae
A. Non-stimulated sham-operated groups Untreated Saline (0.2 ml s.c.) Atropine (0.8 mg/kg s.c.) Vagotorny Saline perfusion (untreated) NaHCO 3 perfusion (untreated)
10 10 12 10 12 11
0 2 3 1 4 3
B. Vagal-stimulated groups Untreated Saline (0.2 ml s.c.) Atropine (0.8 mg/kg s.c.) Vagotomy Saline perfusion (untreated) NaHCO s perfusion (untreated)
12 12 12 12 12 12
12 12 3 1 12 12
(20%) (25%) (10%) (33%) (27%)
* (100%) * (100%) 1" (25%) t (8%) * (100%) * (100%)
* p < 0.01 when compared with its o w n n o n - s t i m u l a t e d c o n t r o l . t P < 0.01 when compared with the untreated or saline-treated stimulated groups.
200
C.W. OGLE ET AL.
TABLE 2 Effect of vagal stimulation on gastric acid secretion. The values are the means ± S.E.M. Time (min)
Total acidity (pequiv HC1/100 g body weight/16 min) Intragastric saline perfusion (12 rats)
Intragastric NaHCO3 perfusion (11 rats)
--16 0
5.17 ± 1.17 4.35 ± 0.24
0 0
16 32 48 64 80 96 112 128
No vagal stimulation 3.50 ± 0.50 3.47 ± 0.41 2.47 ± 0.45 2.29 ± 0.29 2.04 ± 0.16 2.50 ± 0.55 2.36 ± 0.40 2.00 -+ 0.21
0 0 0 0 0 0 0 0
Intragastric saline perfusion (12 rats) 5.17 ± 1.86 4.22 ± 1.81
Vagal stimulation ± 2.60 * +_ 3.57 ** ± 4.35 ** ± 3.60 ** ± 3.19 ** ± 2.51 ** ± 1.89 ** ± 1.73 **
10.30 16.74 17.50 14.97 12.34 10.51 9.23 7.11
Intragastric NaHCO 3 perfusion (12 rats) 0
0 0 0 0 0 0 0 0
* p < 0.02. ** p < 0.01 when compared with its corresponding non-stimulated control.
3.2. The effect o f vagal stimulation on gastric acid secretion in perfused stomachs Vagal s t i m u l a t i o n significantly increased t h e t o t a l gastric acid o u t p u t in u n t r e a t e d rats intragastrically p e r f u s e d w i t h saline (table 2). M a x i m u m acid o u t p u t o c c u r r e d d u r i n g the 3 15-min s t i m u l a t i o n p e r i o d , a n d a gradual fall in t o t a l acid c o n t e n t was seen in t h e subseq u e n t 16-min p e r f u s a t e samples. T h e vagal-ind u c e d increases in acid o u t p u t in all t h e 16m i n s a m p l e s w e r e significantly g r e a t e r t h a n their corresponding non-stimulated untreated c o n t r o l s receiving saline p e r f u s i o n s (table 2). No acid was d e t e c t e d in t h e 1 6 - m i n s a m p l e s o f gastric p e r f u s a t e o f n o n - s t i m u l a t e d or s t i m u l a t e d rats receiving NaHCO3, indicating t h a t c o m p l e t e n e u t r a l i z a t i o n was a c h i e v e d even u n d e r c o n d i t i o n s o f increased acid outp u t p r o d u c e d b y vagal s t i m u l a t i o n .
4. D i s c u s s i o n
Electrical vagal s t i m u l a t i o n p r o d u c e d a 100% i n c i d e n c e o f lesions o n l y in t h e glandu-
lar s e g m e n t o f t h e r a t s t o m a c h . T h e s e vagali n d u c e d h a e m o r r h a g i c ulcers a n d p e t e c h i a e in a n a e s t h e t i z e d rats were similar in size, a p p e a r a n c e a n d l o c a t i o n t o g l a n d u l a r m u c o s a l lesions f o u n d in c o n s c i o u s p y l o r u s - l i g a t e d rats stressed b y r e s t r a i n t a n d 4°C f o r 2 h (Dai a n d Ogle, 1974). F o r m a t i o n o f t h e vagal-induced lesions was p r e v e n t e d b y a t r o p i n e t r e a t m e n t or b y s u b - d i a p h r a g m a t i c v a g o t o m y . Stress-induced h a e m o r r h a g i c ulcers a n d p e t e c h i a e have also b e e n f o u n d t o be p r e v e n t e d b y a t r o p i n e or b y v a g o t o m y (Takagi a n d O k a b e , 1 9 7 0 ; Dai a n d Ogle, 1 9 7 4 ) . T h e insignificant c h a n g e s in b l o o d pressure a n d h e a r t r a t e o b s e r v e d in this s t u d y were similar to t h e findings o f C h o et al. ( 1 9 7 6 ) , a n d c o n s e q u e n t l y h a v e n o t b e e n p r e s e n t e d in this c o m m u n i c a t i o n . G l a n d u l a r ulcer f o r m a t i o n f o l l o w i n g vagal s t i m u l a t i o n in t h e r a t can, t h e r e f o r e , be a t t r i b u t e d to t h e dir e c t a c t i o n o f t h e vagus n e r v e on t h e s t o m a c h a n d n o t to t h e b l o o d pressure falls i n d u c e d b y stimulation. T h e severity, i n d i c a t e d b y lesion size a n d degree o f h a e m o r r h a g i c d i s c o l o u r a t i o n , o f t h e vagal-induced glandular ulcers in saline-perf u s e d s t o m a c h s a p p e a r e d t o be less w h e n c o m -
NaHCO3 AND VAGAL-INDUCED GASTRIC ULCERS IN RATS pared with vagal-stimulated stomachs which were n o t perfused. However, the scatter and the number of the lesions were similar in these two groups. The somewhat lessened severity of the vagal-induced ulcers in saline-perfused stomachs could be due to the intragastric concentration of the increased acid outp u t being reduced by the perfusion. Intragastric perfusion with NaHCO3 failed to prevent ulceration although it completely neutralized the vagal-induced increase in acid output. The appearance and the incidence of the vagal-induced glandular ulcers in NaHCO3-perfused stomachs could not be differentiated from those seen in the saline-perfused stomachs. Thus, it appears that although gastric acidity can influence t h e severity of these glandular ulcers to a limited extent, their formation is due to another factor. These ulcers are probably produced by increased vagal-induced gastric contractions. As stress-induced ulcers are t h o u g h t to be caused by increased gastric contractions with consequent mucosal microcirculatory changes leading to ischaemia and ulceration (Dai and Ogle, 1974, 1975), the similarity between these ulcers and those produced by direct vagal stimulation indicates t h a t stress also produces its ulcer effects primarily through the vagus nerve. The present findings do n o t support the hypothesis of Skillman and Silen (1971) t h a t gastric acid is a prerequisite for stress ulcer formation, but are n o t at variance with the suggestion of Hase et al. (1975) t h a t the severity of these ulcers may be influenced by acidity. It can be concluded that this study n o t only confirms and extends t h e observations of Cho et al. (1976) but also provides a better insight into the aetiology and stress-induced ulcers. Direct evidence, from electrical vagal stimulation and intragastric NaHCO3 perfusion,
201
is now presented to support the idea that stress-induced glandular ulcers in rats are indeed produced by vagal overactivity and to confirm that the formation of these ulcers is n o t acid dependent.
Acknowledgements T h e authors wish to t h a n k Professor M.B. Roberts for reading the manuscript.
References Brodie, D.A. and K.F. Hooke, 1971, The effect of vasoactive agents on stress-inducedgastrichemorrhage in the rat, Digestion 4,193. Cho, C.H., C.W. Ogle and S. Dai, 1976, Acute gastric ulcer formation in response to electricalvagal stimulation in rats, European J. Pharmacol. 35,215. Dai, S. and C.W. Ogle, 1974, Gastric ulcers induced by acid accumulation and by stress in pylorus-occluded rats, European J. Pharmacol. 26, 15. Dai, S. and C.W. Ogle, 1975, Effects of stress and of autonomic blockers on gastric microcirculation in
rats, European J. Pharmacol. 30, 86. Hase, T., P.R. Anderson and B. Mehlman, 1975, Significance of gastric secretory changes in the pathogenesis of stress ulcers, Amer. J. Digest. Dis. 20, 443. Lanciault, G., J.E. Shaw, J. Urquhart, L.S. Adair and F.P. Brooks, 1975, Response of the isolated perfused stomach of the dog to electrical vagal stimulation, Gastroenterology 68, 294. Skillman, J.J. and W. Silen, 1972, Stress ulcers, Lancet 2, 1303. Smith, G.M., A.J. Lawrence, D.G. Colin-Jonesand H.O. Schild, 1970, The assay of gastrin using the perfused rat stomach, Brit. J. Pharmacol. 38,206. Takagi, K. and S. Okabe, 1970, Studies of the mechanism involved in the production of stress and stressatropine ulcers in rats, European J. Pharmacol. 10, 378. Watanabe, K., 1966, Some pharmacological factors involved in formation and prevention of stress ulcers in rats, Chem. Pharm. Bull. (Tokyo) 14, 101.
197
© North-Holland Publishing Company, Amsterdam -- Printed in The Netherlands
Short communication I N T R A G A S T R I C NaHCO3 P E R F U S I O N AND VAGAL-INDUCED U L C E R F O R M A T I O N IN THE RAT STOMACH CLIVE W. OGLE, CHI H. CHO and SOTER DAI
Department of Pharmacology, Faculty of Medicine, University of Hong Kong, Hong Kong Received 24 February 1976, accepted 9 March 1976
C.W. OGLE, C.H. CHO and S. DAI, Intragastric NaHC03 perfusion and vagal-induced ulcer formation in the rat stomach, European J. Pharmacol. 37 (1976) 197--201. The effects of electrical vagal stimulation on gastric acid output and ulcer formation were studied in rats intragastrically perfused with saline or NaHCO3 solutions. Vagal stimulation produced a 100% incidence of glandular lesions and a significant increase in total acid output in saline-perfused stomachs. Antacid perfusion failed to prevent ulcer formation despite complete neutralization of the increased acid output. It is concluded that vagal-induced gastric glandular lesions are not acid dependent. Intragastric NaHCO3 perfusion
Vagus
Gastric ulceration
1. Introduction Substantial evidence points to the role of the vagus nerve in the aetiology of stress-induced gastric ulcer formation in the rat (Watanabe, 1966; Takagi and Okabe, 1970; Brodie and Hooke, 1971; Dai and Ogle, 1974, 1975). Gastric acid appears not to be responsible for stress ulcer formation, as n o t only does antacid administration fail to prevent ulceration b u t also acid secretion is reduced by stress in conscious pylorus-ligated rats (Dai and Ogle, 1974). Recently, Cho et al. (1976) have shown that direct electrical vagal stimulation in rats produces gastric glandular ulcers which are similar in appearance to those induced by stress. However, no measurements of gastric acid o u t p u t were made in this study with anaesthetized animals. Gastric acid secretion has been shown to be increased by electrical vagal stimulation in the pylorus-ligated rat (Watanabe, 1966) and in the isolated perfused dog stomach (Lanciault et al., 1975}, and it has also been reported that the presence (Skillman and Silen, 1972} and the degree of severity (Hase et al., 1975) of stress-induced
ulcers depend on the acidity of the gastric secretion. The purpose of the present study was to examine the effects of electrical vagal stimulation on gastric acid o u t p u t and on glandular ulcer formation in the perfused rat stomach in situ, and to determine whether increased gastric acid secretion does influence the formation of these ulcers.
2. Materials and methods 2.1. General
Male Wistar rats, weighing 200--300 g, were starved for 24 h before use b u t allowed free access only to 8% sucrose in 0.2% NaC1 (w/v). The animals, anaesthetized with i.p. injections of urethane (1.25 g/kg), were kept warm with a heating lamp during the experiment. Body temperature was maintained at 37 ° C. Following tracheal cannulation, positive ventilation was provided by a Palmer respiration pump at a rate of 70 strokes/min (stroke volume of 1 m i l l 0 0 g b o d y weight).
198 All experiments were carried out over a total period of 2 h 8 min, after which the animals were sacrificed and their stomachs examined by an independent observer for the presence or absence of mucosal lesions (Dai and Ogle, 1974).
2.2. Electrical vagal stimulation
C.W. OGLE ET AL. cm from the pylorus, until its tip entered the pyloric opening. The tube was gently tied in place with a ligature over the duodenum before exteriorizing the distal end through an incision in the flank. Prewarmed (37°C) solutions of NaC1 0.9% (w/v, saline) or NaHCO3 0.18% (w/v) were perfused through the oesophageal tube at a rate of 6.3 ml/16 min and the perfusate collected from the exteriorized end of the pyloric tube. The total acid in each sample, collected at 16-min intervals, was determined (Dai and Ogle, 1974). Each 16-min collection of perfusate included the 1-min rest period which immediately followed a 15-rain period of stimulation (or no stimulation in shamoperated controls). The concentration of NaHCO~ in the perfusion solution was determined by finding the total dose of antacid required to neutralize completely the total gastric acid produced by 8 15-min periods of vagal stimulation (including the 8 1-min periods following the stimulation periods).
Both vagus nerves were exposed in the neck and ligated to prevent any central effects of electrical stimulation. An electrode was placed under the left vagus, distal to the ligature. Electrical stimulation, with a stimulator (E & M Instrument Co., Inc.) delivering rectangular impulses of 2 msec duration at a strength of 5 V and a frequency of 20 Hz, was given continuously for 15-min periods. Each 15-min period was followed by a 1-min rest period without stimulation. Each experiment comprised 8 15-min stimulation periods separated by 7 l-rain periods, and included an 8th l-rain rest period which followed the last stimulation period. Sham-operated controls had their vagus nerves similarly exposed and ligated, but no stimulation was given through the electrode placed distal to the ligature on the left vagus. Bilateral sub-diaphragmatic vagotomy (vagotomy) was carried out through a central abdominal incision, and completeness ensured by resecting all the vagal branches to the stomach.
Atropine sulphate (E. Merck), 0.8 mg/kg body weight, expressed as the salt, was injected s.c. 15 min before starting the experiment. Similar volumes of saline were given to the controls by the same route. Sodium bicarbonate (NaHCO3, BDH) was used in the perfusions.
2.3. In tragastric perfusion
2.5. Statistical analysis
A modified perfusion technique basically similar to the m e t h o d described by Smith et al. (1970) was adopted. The oesophagus was cannulated at the cervical level with a polythene tube (2 mm o.d.), inserted until its tip reached the cardiac end of the stomach. It was then secured in place by a ligature around the oesophagus at the cannulation site. The pyloric end of the stomach was cannulated through a central abdominal incision. A polythene tube (4 mm o.d.) was inserted through a small incision in the duodenum, about 1.5
The data were analysed by means of Student's t-test or by the xZ-test.
2.4. Drugs
3. Results
3.1. The effects o f atropine, vagotomy or intragastric N a H C 0 3 perfusion on vagal-induced glandular ulcers Untreated and saline-treated sham-operated rats had a lesion incidence of 0% and 20% re-
NaHCO3 AND VAGAL-INDUCED GASTRIC ULCERS IN RATS
spectively (table 1A). The lesions appeared as occasional petechiae in the glandular segment of the stomach. Electrical vagal stimulation, however, induced a 100% incidence of lesions in both untreated and saline-treated rats (table 1B); this was significant when compared with their corresponding non-stimulated controls (p < 0.01 for both). The lesions were mainly haemorrhagic ulcers located only in the glandular segment of the gastric mucosa.
The incidence of occasional petechiae seen in atropine-treated or vagotomized sham-operated rats was also low (25% and 10% respectively, table 1A). A low incidence of petechiae of similar scatter was likewise seen in the atropine-treated or vagotomized rats that were stimulated (25% and 8% respectively, table 1B), b u t their lesion incidence was significantly different from that of the stimulated untreated or saline-treated rats (p < 0.01 for both). Atropine or vagotomy thus provided significant protection against haemorrhagic ulceration induced by electrical vagal stimulation. Untreated sham-operated rats receiving
199
either saline or NaHCO3 intragastric perfusions had a low incidence of lesions which also appeared as occasional petechiae in the glandular mucosa (33% and 27% respectively, table 1A). The lesion incidence in these two groups of animals did not differ significantly among the groups and from those of the other sham-operated controls (table 1A). Lesion incidence increased significantly to 100% when untreated saline-perfused rats received vagal stimulation (p < 0.01, when compared with their non-stimulated control). The size, and the surrounding haemorrhagic discolouration of the ulcers appeared to be slightly less when compared with the lesions in the non-perfused vagal stimulated untreated or saline-treated rats (table 1B). Intragastric NaHCO3 perfusion did not protect against these vagal-induced glandular lesions. The lesion incidence was 100%, which was significant when compared with the non-stimulated control group perfused with NaHCO3 (p < 0.01), and the appearance of the glandular lesions was similar to those seen in the stimulated untreated rats receiving saline perfusions.
TABLE 1 Effects of drugs or of vagotomy on the incidence of gastric glandular lesions induced by vagal stimulation. Treatment
Number of rats
Number of rats with glandular haemorrhagic ulcers and/or petechiae
A. Non-stimulated sham-operated groups Untreated Saline (0.2 ml s.c.) Atropine (0.8 mg/kg s.c.) Vagotorny Saline perfusion (untreated) NaHCO 3 perfusion (untreated)
10 10 12 10 12 11
0 2 3 1 4 3
B. Vagal-stimulated groups Untreated Saline (0.2 ml s.c.) Atropine (0.8 mg/kg s.c.) Vagotomy Saline perfusion (untreated) NaHCO s perfusion (untreated)
12 12 12 12 12 12
12 12 3 1 12 12
(20%) (25%) (10%) (33%) (27%)
* (100%) * (100%) 1" (25%) t (8%) * (100%) * (100%)
* p < 0.01 when compared with its o w n n o n - s t i m u l a t e d c o n t r o l . t P < 0.01 when compared with the untreated or saline-treated stimulated groups.
200
C.W. OGLE ET AL.
TABLE 2 Effect of vagal stimulation on gastric acid secretion. The values are the means ± S.E.M. Time (min)
Total acidity (pequiv HC1/100 g body weight/16 min) Intragastric saline perfusion (12 rats)
Intragastric NaHCO3 perfusion (11 rats)
--16 0
5.17 ± 1.17 4.35 ± 0.24
0 0
16 32 48 64 80 96 112 128
No vagal stimulation 3.50 ± 0.50 3.47 ± 0.41 2.47 ± 0.45 2.29 ± 0.29 2.04 ± 0.16 2.50 ± 0.55 2.36 ± 0.40 2.00 -+ 0.21
0 0 0 0 0 0 0 0
Intragastric saline perfusion (12 rats) 5.17 ± 1.86 4.22 ± 1.81
Vagal stimulation ± 2.60 * +_ 3.57 ** ± 4.35 ** ± 3.60 ** ± 3.19 ** ± 2.51 ** ± 1.89 ** ± 1.73 **
10.30 16.74 17.50 14.97 12.34 10.51 9.23 7.11
Intragastric NaHCO 3 perfusion (12 rats) 0
0 0 0 0 0 0 0 0
* p < 0.02. ** p < 0.01 when compared with its corresponding non-stimulated control.
3.2. The effect o f vagal stimulation on gastric acid secretion in perfused stomachs Vagal s t i m u l a t i o n significantly increased t h e t o t a l gastric acid o u t p u t in u n t r e a t e d rats intragastrically p e r f u s e d w i t h saline (table 2). M a x i m u m acid o u t p u t o c c u r r e d d u r i n g the 3 15-min s t i m u l a t i o n p e r i o d , a n d a gradual fall in t o t a l acid c o n t e n t was seen in t h e subseq u e n t 16-min p e r f u s a t e samples. T h e vagal-ind u c e d increases in acid o u t p u t in all t h e 16m i n s a m p l e s w e r e significantly g r e a t e r t h a n their corresponding non-stimulated untreated c o n t r o l s receiving saline p e r f u s i o n s (table 2). No acid was d e t e c t e d in t h e 1 6 - m i n s a m p l e s o f gastric p e r f u s a t e o f n o n - s t i m u l a t e d or s t i m u l a t e d rats receiving NaHCO3, indicating t h a t c o m p l e t e n e u t r a l i z a t i o n was a c h i e v e d even u n d e r c o n d i t i o n s o f increased acid outp u t p r o d u c e d b y vagal s t i m u l a t i o n .
4. D i s c u s s i o n
Electrical vagal s t i m u l a t i o n p r o d u c e d a 100% i n c i d e n c e o f lesions o n l y in t h e glandu-
lar s e g m e n t o f t h e r a t s t o m a c h . T h e s e vagali n d u c e d h a e m o r r h a g i c ulcers a n d p e t e c h i a e in a n a e s t h e t i z e d rats were similar in size, a p p e a r a n c e a n d l o c a t i o n t o g l a n d u l a r m u c o s a l lesions f o u n d in c o n s c i o u s p y l o r u s - l i g a t e d rats stressed b y r e s t r a i n t a n d 4°C f o r 2 h (Dai a n d Ogle, 1974). F o r m a t i o n o f t h e vagal-induced lesions was p r e v e n t e d b y a t r o p i n e t r e a t m e n t or b y s u b - d i a p h r a g m a t i c v a g o t o m y . Stress-induced h a e m o r r h a g i c ulcers a n d p e t e c h i a e have also b e e n f o u n d t o be p r e v e n t e d b y a t r o p i n e or b y v a g o t o m y (Takagi a n d O k a b e , 1 9 7 0 ; Dai a n d Ogle, 1 9 7 4 ) . T h e insignificant c h a n g e s in b l o o d pressure a n d h e a r t r a t e o b s e r v e d in this s t u d y were similar to t h e findings o f C h o et al. ( 1 9 7 6 ) , a n d c o n s e q u e n t l y h a v e n o t b e e n p r e s e n t e d in this c o m m u n i c a t i o n . G l a n d u l a r ulcer f o r m a t i o n f o l l o w i n g vagal s t i m u l a t i o n in t h e r a t can, t h e r e f o r e , be a t t r i b u t e d to t h e dir e c t a c t i o n o f t h e vagus n e r v e on t h e s t o m a c h a n d n o t to t h e b l o o d pressure falls i n d u c e d b y stimulation. T h e severity, i n d i c a t e d b y lesion size a n d degree o f h a e m o r r h a g i c d i s c o l o u r a t i o n , o f t h e vagal-induced glandular ulcers in saline-perf u s e d s t o m a c h s a p p e a r e d t o be less w h e n c o m -
NaHCO3 AND VAGAL-INDUCED GASTRIC ULCERS IN RATS pared with vagal-stimulated stomachs which were n o t perfused. However, the scatter and the number of the lesions were similar in these two groups. The somewhat lessened severity of the vagal-induced ulcers in saline-perfused stomachs could be due to the intragastric concentration of the increased acid outp u t being reduced by the perfusion. Intragastric perfusion with NaHCO3 failed to prevent ulceration although it completely neutralized the vagal-induced increase in acid output. The appearance and the incidence of the vagal-induced glandular ulcers in NaHCO3-perfused stomachs could not be differentiated from those seen in the saline-perfused stomachs. Thus, it appears that although gastric acidity can influence t h e severity of these glandular ulcers to a limited extent, their formation is due to another factor. These ulcers are probably produced by increased vagal-induced gastric contractions. As stress-induced ulcers are t h o u g h t to be caused by increased gastric contractions with consequent mucosal microcirculatory changes leading to ischaemia and ulceration (Dai and Ogle, 1974, 1975), the similarity between these ulcers and those produced by direct vagal stimulation indicates t h a t stress also produces its ulcer effects primarily through the vagus nerve. The present findings do n o t support the hypothesis of Skillman and Silen (1971) t h a t gastric acid is a prerequisite for stress ulcer formation, but are n o t at variance with the suggestion of Hase et al. (1975) t h a t the severity of these ulcers may be influenced by acidity. It can be concluded that this study n o t only confirms and extends t h e observations of Cho et al. (1976) but also provides a better insight into the aetiology and stress-induced ulcers. Direct evidence, from electrical vagal stimulation and intragastric NaHCO3 perfusion,
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is now presented to support the idea that stress-induced glandular ulcers in rats are indeed produced by vagal overactivity and to confirm that the formation of these ulcers is n o t acid dependent.
Acknowledgements T h e authors wish to t h a n k Professor M.B. Roberts for reading the manuscript.
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