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Antral and duodenal acidification
Antral and Duodenal Acidification Effect on Pentagastrin-Stimulated
M. H. Wheeler, MD, FRCS (Eng),’
Acid Secretion in the Dog
Edinburgh, Scotland
FL J. Prescott, MSc, PhD, Edinburgh, Scotland A. P. M. Forrest, MD, ChM, FRCS (Edinb, Eng, and Glasg), Edinburgh, Scotland
We have previously reported the failure of acidification of the innervated canine antrum to influence the secretory response to pentagastrin of both vagally innervated and denervated fundic pouches [I]. In these same preparations, antral acidification did inhibit acid secretion stimulated by endogenous gastrin, released from the antrum by irrigation with 0.5 per cent acetylcholine bromide solution. These findings were in agreement with those of Preshaw [Z], who used gastrin to stimulate gastric secretion, but were contrary to those of Williams and Forrest [3] and Coelho et al [4] with respect to pentagastrin. In all these studies, gastrointestinal continuity was re-established by gastroduodenostomy after construction of the antral pouches. In this preparation, it is possible that the secretory responses of the indicator pouches could be influenced by acid from the main stomach entering the duodenum and activating the duodenal inhibitory system. The present investigation was designed to examine the effect of antral acidification on pentagastrin-induced gastric secretion of a denervated fundic pouch, with and without diversion of the From the Department of Clinical Surgery, University of Edinburgh, Teviot Place, Edinburgh. Scotland. This work was supported by the Wellcome Trust, from which I3 Wheeler received a full-time grant. Reprint requests should be addressed to Dr A. P. M. Forrest, Department of Clinical Surgery, University of Edinburgh, Teviot Place, Edinburgh, Scotland. ’ Present address: University Hospital of Wales, Heath Park, Cardiff. South Wales, United Kingdom.
Vofume 128, September 1974
acid stream from the duodenum by a gastric fistula. Because opening the fistula allowed monitoring of the secretion from the innervated main stomach, the effect of antral acidification, on both innervated and denervated gastric mucosa, could be assessed simultaneously in the same animal. Material and Methods The studies were carried out in three dogs, weighing 9.0 to 14.0 kg, each prepared with a vagally denervated (separated) fundic [5] and vagally innervated (mucosal septal) antral pouch [S]. The methods of constructing and testing the pouches have been described previously 171. Gastrointestinal continuity was reestablished by gastroduodenostomy and, in addition, each animal was provided with a gastric fistula of the vagally innervated main stomach. A Gregory Type D cannula (Down Hros., Surrey, England) was used for the fistula and was placed just proximal to the site of the gastroduodenostomy. near the greater curve. Secretory studies were begun at least six weeks after operation. The animals were fasted for eighteen hours before testing, and a forty-eight hour period was allowed between experiments. Any test in which an animal vomited or demonstrated signs of nausea, such as restlessness and salivation, was terminated and the result was rejected. Pentagastrin Studies. Control Series: In each dog the maximal acid secretory response of the fundic pouch to pentagastrin was first obtained by the administration of
Wheeler, Prescott, and Forrest
GASTRIC flSlULA
bogJ
T
Oog H
f Antral
cl
pcrturalc
cl
Dog J prrt”satr
A “,,a,
pti 7.0
pti 7 0 pn I 0
Ia
/yJj pH1.0
i . E E ,
150
z 0 ‘D 0 f =
10.0
GASTRIC FISTULA OPEN 15
i . ,Dce E I Pmlogoslrm
II I 1 5,ug / kg body wtlhr
I
II
1
Figure 2. Acid secretory responses collected from the gastric tlstulas. Method of antral perfusion and presentation of data as in Figure 1. 1
II
Figure 1. Fundic pouch acid secretory responses to intravenous infuskns oi pentagastrin in three dogs with vagaily denervated hmdk pouches and gastric flstulas during antral pouch perfusion with isotonic saline at pH 7.0 and Isotonic saline at pH 1.0 at a rate of 1 ml per minute. Each column represents the mean of the second hour outputs of acid ImEq/hour) in each two hour collection period oblalned from two four hour tests in each animal. Sequence of antral pH change k: I, pH 7.0 to pH 1.0; II, pH 1.0 topH 7.0. increasing doses of pentagastrin (Peptavlon, ICI 50, 123; Imperial Chemical Industries, Macclesfield, England) starting at 1.5 pg per kg of body weight per hour given by continuous intravenous infusion. The dose was doubled every seventy-five minutes, until a further increase failed to produce a higher output than that produced by the preceding dose [8]. The maximal acid output from the pouch was expressed as the mean of the last two fifteen minute collections during the period in which this maximal response occurred. Each test was performed three times in each dog, and the mean maximal output of aa id was expressed in mEq per 15 minutes. The gastric fistula remained closed throughout.
332
Series I: The first series of tests to study antral inhibition was also carried out with the gastric fistula closed. Pentagastrin in a dose producing approximately 50 per cent maximal acid stimulation (1.5 pg per kg of body weight per hour) was administered by continuous intravenous infusion into a foreleg vein at a rate of 3.33 ml per hour for four hours, using a Palmer pump (C. F. Palmer, London, England). At the onset of acid stimulation, the antral pouch was perfused with isotonic saline. For the first two hours of the test, the pH of the perfusate was 7.0; for the second two hours of the test, 1.0. This pattern of antral pH change was employed in two tests in each animal. In two additional tests the order of pH was reversed; the perfusion of the antrum was begun at pH 1.0 and changed to pH 7.0 after two hours. The system of perfusion of the pyloric antrum has been described previously [7]: a peristaltic pump (Model MHRE, Watson-Marlow Ltd., Marlow, Rucks., England) was employed to ensure a constant rate of antral perfusion (1 ml per minute) via a Kay double-lumen gastrostomy tube (J. G. Franklin and Sons I,td., London, England). Series II: In the second series of tests, pentagastrin was administered intravenously in the same dose with
The American Journal of Surgery
Antral and Duodenal Acidification
1 o-
the gastric fistula open. Gastric secretion was collected simultaneously from the gastric fistula and fundic pouch, but each animal also received an intravenous infusion of 154 mM of sodium chloride at a rate of 80 ml per hour, delivered by peristaltic pump. This was to compensate for the excess fluid loss from the gastric fistula. Four such tests were performed in each animal,
Antrol 09-
0.01 N sodium hydroxide to pH 7.0 using an E.I.L. Model 24 Titrimeter, (Electronic Instruments Ltd., Richmond, Surrey, England). The acid output was calculated in mEq per fifteen minutes. In the meat tests, an aliquot proportional to the volume of each fifteen minute collection was pooled into thirty minute samples for pepsin estimation. The concentration of pepsin was determined in 0.1 ml of each pooled specimen in duplicate by the method of Klotz and Duvall (9) and expressed in micrograms of standard Sigma pepsin per milliliter of juice. The outputs were calculated in micrograms per thirty minutes. Statistical Analysis. Pentagastrin studies: As the acid outputs followed a lognormal distribution, the differences between the log acid outputs [IO] during the second hour of each period when the antrum was perfused at pH 7.0 and those when the antral pH was 1.0 were calculated. These differences were subjected to an analysis of variances [II] to determine whether there was any evidence of inhibition of acid secretion from either the fundic pouch or main stomach. Meat studies: The means of the arithmetic values of the total outputs of acid and pepsin over the four hour period after ingestion of the meal, without antral perfusion, were compared by t tests [12] with those during antral perfusion at pH 7.0 and 1.0. Arithmetic values were employed in the statistical analysis, rather than the logarithms used previously because of the occurrence of isolated zero readings.
Voiwne
128, September 1974
Cl
s
e .
and antral perfusion was identical to that employed in series I. Meat Studies. To confirm that the pouch preparations were capable of demonstrating that acidification of the antrum would effect an inhibitory response, an additional group of tests was carried out in which the stimulus of gastric secretion was the ingestion of uncooked minced ox heart (25 gm per kg of body weight). At the time of feeding, antral perfusion was commenced with either isotonic saline at pH 7.0 or an isotonic solution of hydrochloric acid in saline at pH 1.0 at a rate of 1 ml per minute. Perfusion was continued for four hours after ingestion of the meal. The pH of the effluent fluid was checked at hourly intervals and did not differ from that of the perfusate. Each test was performed three times in each dog. Control studies were performed, again three times in each dog, in which the antral pouch was not perfused.
In all the tests, gastric juice was collected at fifteen minute intervals. The volume was measured in milliliters and the acidity was determined by titration with
EI
08-
”
// a
NOW
pH 7 0
pHl0
07-
: %
perfusato
“5 06-
5 p8
05
6 f oh-
03-
0 2pco
01
Ol-
Figure 3. Mean acid secretory with vagatly denervated fundic after ingestion of a meat meal. from the resutts of nine tests in
responses of three dogs pouches in the four hours Each value was obtained the three dogs.
Results
Pentagastrin Stimulation. For each dog there were results from three methods of collection of gastric acid: (1) from the fundic pouch, with the gastric fistula closed; (2) from the fundic pouch, with the gastric fistula open; (3) from the gastric fistula. Figures 1 and 2 illustrate the mean acid outputs (mEq/hr) for each animal during the second hour of each two hour collection period. In each case there were duplicate results both when the order of administration of perfusate was pH 7.0 followed by pH 1.0 and when the order of administration was pH 1.0 followed by pH 7.0. An analysis of variance showed that no significant inhibition of acid secretion occurred during antral acidification with any method of collection. Furthermore, opening the gastric fistula and diverting acid from the main stomach to the exterior had no significant effect on the acid output of the fundic pouch. Meat Stimulation. Acid output: The mean acid outputs pear
over in Figure
the
four
3. There
hour
period
of the
was no difference
tests
ap-
between
333
Wheeler, Prescott, and Forrest
2.5,
Antral
porfusatr
#
None
[7
pH 7.0
pH
z
t-0
_
E” 2
1.5-
5 .5
B
x
s f
-
-
“.S
lo-
O-8 -
06-
OL-
02-
Figure 4. Mean pepsin secretory responses of three dogs with vagally denervated fundic pouches in the four hours after ingestion of a meat meal. Each value was obtained from the results of nine tests in the three dogs. N.S. = not significant (p > 0.05).
the acid outputs in the control tests and those during antral perfusion at pH 7.0. Significant inhibition occurred with antral acidification. Pepsin output: The mean pepsin outputs after stimulation by meat are shown in Figure 4. Although the mean pepsin outputs when the antrum was perfused with acid were numerically lower than both the mean pepsin outputs without perfusion and those when the- antrum was perfused at pH 7.0, this apparent inhibition was not statistically significant at the 5 per cent level. Comments
We have been unable to determine that acidification of the innervated pyloric antrum can influence pentagastrin-induced acid secretion from denervated fundic pouches of the canine stomach, even when the acid stream is diverted from the duodenum. The duodenal inhibitory mechanism, by which acid in the duodenum can depress acid se-
334
cretion of a fundic pouch [13-161 was prevented from acting by opening the gastric fistula. Such a maneuver has been shown to enhance the acid secretory response of denervated pouches to gastrin [17-191 and pentagastrin [20] stimulation. Nor, in the present studies, did the prevention of duodenal acidification unmask an inhibitory effect of antral acidification on the acid secretion collected from the main stomach via the gastric fistula. It therefore seems clear that the inhibitory action of antral acidification is mediated by a diminished release or formation of endogenous gastrin. No evidence is provided for the existence of either a hormonal or neuronal antral inhibitory mechanism active against pentagastrin-induced secretion. The studies performed first with the fistula closed and then with it open showed that diverting the acid stream from the duodenum did not, in itself, influence the acid output of the fundic pouch. These results are contrary to those of Way and Grossman [20] but are in agreement with the observations of Konturek and Johnson [21], who reported that exogenous acidification of the innervated duodenal bulb failed to inhibit pentagastrininduced secretion from denervated pouches, although it did inhibit secretion from the innervated main stomach. Because separation of the duodenal bulb from the pylorus abolished this inhibitory effect on the main stomach, it was concluded that an enterogastric reflex was involved in the duodenal inhibitory mechanism. Support for the role of the nervous system in the duodenal inhibition of gastric secretion has been provided by other workers [22,23]. When a single feeding of ox heart was provided as a physiologic stimulus to gastric secretion, antral acidification inhibited the acid secretory response of the denervated fundic pouches. These findings are in agreement with those of many other workers [3,24,25] and confirm that the antral pouch preparations used in our study were capable of initiating inhibition of the acid secretory response to a truly physiologic stimulus. Such inhibition resulted from diminished vagal gastrin release after a decrease in antral pH. The finding that antral acidification did not significantly suppress the pepsin secretory response to a meat meal is in agreement with other reported observations [3,26]. Thus it seems that in these tests vagal gastrin did not play a significant role in the stimulation of pepsin secretion.
The American
Journal ol Surgery
Antral and Duodenal Acidification
Summary In three dogs, each prepared with an innervated antral pouch, vagally denervated fundic pouch, and a gastric fistula of the main stomach, gastric secretion was stimulated by intravenous infusion of a submaximal dose of pentagastrin. Antral acidification at pH 1.0 did not inhibit the acid secretory response of the fundic pouch during tests in which the gastric fistula was closed. When the gastric fistula was opened, acidification did not affect the acid secretion of either the denervated fundic pouch or innervated main stomach. Diversion of acid from the duodenum did not influence the over-all level of acid secretion from the fundic pouch. Antral acidification did inhibit the acid secretory response of the fundic pouch after ingestion of a meat meal (25 gm per kg of body weight), although pepsin outputs remained unchanged. The results provide no support for the existence of either an antral inhibitory hormone or. inhibitory neural reflex active against pentagastrin-stimulated gastric secretion in the dog. Antral inhibition of gastric secretion is the result of a diminished release or formation of endogenous gastrin. Acknowledgment: We wish to thank Dr Morton I. Grossman for his valuable suggestions and advice regarding this project. The pentagastrin used in this study was generously supplied by Imperial Chemical Industries Ltd., England. The authors are grateful to Mrs M. Coyle for her technical assistance.
References 1. Wheeler MH, Prescott RJ. Forrest APM: Antral acidification and the gastric secretory response to pentagastrin and acetylcholine in dogs. Br J Surg in press. 2. Preshaw RM: Antral acidification and the gastric secretory response to sham feeding and gastrin in dogs. Rev Can Biol26: 305, 1967. 3. Williams CB, Forrest APM: Effect of antral acidification on acid secretion induced by meat and pentagastrin. Gastroenterology57: 399, 1969. 4. Coelho R, Bombeck CT, Pissidis AG, et al (unpublished data): Ciied by Miller B, Bombeck CT, Schumer W, et al: Vagotomy limited to the parietal cell mass. Arch Surg 103: 153,
volume 129, september 1974
1971. 5. Heidenhain R: Ueber die Absonderung der Fundusdrusen des Magens. Pfliigers Arch 19: 148, 1879. 6. Forrest APM: The importance of the innervation of the pyloric antrum in the control of gastric secretion in dogs. Proceedings of the 20th International Congress of Physiology. Brussels, 1956, p 299. 7. Wheeler MH, Prescott RJ. Forrest APM: The effect of antral acidification on acid secretion stimulated by pentagastrin. Br J Surg60: 197, 1973. 8. Andersson S, Grossman Ml: Effect on vagal denervation of pouches on gastric secretion in dogs with intact or resected antrums. GastroenteroIogy48: 449, 1965. 9. Klotz AP, Duvall MR: The laboratory determination of pepsin in gastric juice with radioactive iodinated albumin. J Lab C/in Med50: 753, 1957. 10. Gaddum JH: Lognormal distributions. Nature 156: 463, 1945. 11. Snedecor GW, Cochran WG: Statistical Methods, 6th ed. Ames, Iowa. Iowa State University Press, 1967, p 369. 12. Fisher RA: Statistical Methods for Research Workers, 10th ed. London, Oliver and Boyd, 1948, p 114. 13. Day JJ, Webster DR: The autoregulation of the gastric secretion. Am J Dig Dis 2: 527, 1935. 14. Jones TW, Harkins HN: The mechanism of inhibition of gastric acid secretion by the duodenum. Gastroenterology 37: 81, 1959. 15. Andersson S: Inhibitory effects of hydrochloric acid in antrum and duodenum on gastric secretory responses to test meal in Pavlov and Heidenhain pouch dogs. Acta phvsiol Stand 49: 23 1, 1960. 16. Andersson S: Inhibitory effects of hydrochloric acid in the duodenum on gastrin-stimulated gastric secretion in Heidenhain pouch dogs. Acta Physiol Stand 50: 105, 1960. 17. Wormsley KG, Grossman Ml: Inhibition of gastric acid secretion by secretin and by endogenous acid in the duodenum. Gastroenterology47: 72, 1964. 18. Konturek S, Grossman Ml: Localization of the mechanism for inhibition of gastric secretion by acid in intestine. Gastfoenterology49: 74, 1965. 19. Cooke AR: Observations on the effect of diversion of acid from the duodenum in response to gastrin and histamine. Gastroenteroiogy 55: 268, 1968. 20. Way LM, Grossman Ml: Gastric and pancreatic response to acid in the duodenum after partial duodenectomy. Am J Physiol220: 1016, 1971. 21. Konturek SJ, Johnson LR: Evidence for an enterogastric reflex for the inhibition of acid secretion. Gastroenterology 61: 667, 1971. 22. Code CF. Watkinson G: Importance of vagal innervation in the regulatory effect of acid in the duodenum on gastric secretion of acid. J Physioll30: 233, 1955. 23. Sircus W: Studies on the mechanisms in the duodenum inhibiting gastric secretion. Q J Exp physiol43: 114, 1958. 24. Margolus BD. Harrison RC: Inhibition of the intestinal phase of gastric secretion by antral inhibitor substance. Surg Forum 7: 360, 1956. 25. Duval MK, Fagella RM, Price WE: The mechanism of antral regulation of gastric secretion: antral pouch studies. Surgery49: 569, 1961. 26. Preshaw RM, Cooke AR, Grossman Ml: Sham feeding and pancreatic secretion in the dog. Gastroenterology 50: 171, 1966.
335
M. H. Wheeler, MD, FRCS (Eng),’
Acid Secretion in the Dog
Edinburgh, Scotland
FL J. Prescott, MSc, PhD, Edinburgh, Scotland A. P. M. Forrest, MD, ChM, FRCS (Edinb, Eng, and Glasg), Edinburgh, Scotland
We have previously reported the failure of acidification of the innervated canine antrum to influence the secretory response to pentagastrin of both vagally innervated and denervated fundic pouches [I]. In these same preparations, antral acidification did inhibit acid secretion stimulated by endogenous gastrin, released from the antrum by irrigation with 0.5 per cent acetylcholine bromide solution. These findings were in agreement with those of Preshaw [Z], who used gastrin to stimulate gastric secretion, but were contrary to those of Williams and Forrest [3] and Coelho et al [4] with respect to pentagastrin. In all these studies, gastrointestinal continuity was re-established by gastroduodenostomy after construction of the antral pouches. In this preparation, it is possible that the secretory responses of the indicator pouches could be influenced by acid from the main stomach entering the duodenum and activating the duodenal inhibitory system. The present investigation was designed to examine the effect of antral acidification on pentagastrin-induced gastric secretion of a denervated fundic pouch, with and without diversion of the From the Department of Clinical Surgery, University of Edinburgh, Teviot Place, Edinburgh. Scotland. This work was supported by the Wellcome Trust, from which I3 Wheeler received a full-time grant. Reprint requests should be addressed to Dr A. P. M. Forrest, Department of Clinical Surgery, University of Edinburgh, Teviot Place, Edinburgh, Scotland. ’ Present address: University Hospital of Wales, Heath Park, Cardiff. South Wales, United Kingdom.
Vofume 128, September 1974
acid stream from the duodenum by a gastric fistula. Because opening the fistula allowed monitoring of the secretion from the innervated main stomach, the effect of antral acidification, on both innervated and denervated gastric mucosa, could be assessed simultaneously in the same animal. Material and Methods The studies were carried out in three dogs, weighing 9.0 to 14.0 kg, each prepared with a vagally denervated (separated) fundic [5] and vagally innervated (mucosal septal) antral pouch [S]. The methods of constructing and testing the pouches have been described previously 171. Gastrointestinal continuity was reestablished by gastroduodenostomy and, in addition, each animal was provided with a gastric fistula of the vagally innervated main stomach. A Gregory Type D cannula (Down Hros., Surrey, England) was used for the fistula and was placed just proximal to the site of the gastroduodenostomy. near the greater curve. Secretory studies were begun at least six weeks after operation. The animals were fasted for eighteen hours before testing, and a forty-eight hour period was allowed between experiments. Any test in which an animal vomited or demonstrated signs of nausea, such as restlessness and salivation, was terminated and the result was rejected. Pentagastrin Studies. Control Series: In each dog the maximal acid secretory response of the fundic pouch to pentagastrin was first obtained by the administration of
Wheeler, Prescott, and Forrest
GASTRIC flSlULA
bogJ
T
Oog H
f Antral
cl
pcrturalc
cl
Dog J prrt”satr
A “,,a,
pti 7.0
pti 7 0 pn I 0
Ia
/yJj pH1.0
i . E E ,
150
z 0 ‘D 0 f =
10.0
GASTRIC FISTULA OPEN 15
i . ,Dce E I Pmlogoslrm
II I 1 5,ug / kg body wtlhr
I
II
1
Figure 2. Acid secretory responses collected from the gastric tlstulas. Method of antral perfusion and presentation of data as in Figure 1. 1
II
Figure 1. Fundic pouch acid secretory responses to intravenous infuskns oi pentagastrin in three dogs with vagaily denervated hmdk pouches and gastric flstulas during antral pouch perfusion with isotonic saline at pH 7.0 and Isotonic saline at pH 1.0 at a rate of 1 ml per minute. Each column represents the mean of the second hour outputs of acid ImEq/hour) in each two hour collection period oblalned from two four hour tests in each animal. Sequence of antral pH change k: I, pH 7.0 to pH 1.0; II, pH 1.0 topH 7.0. increasing doses of pentagastrin (Peptavlon, ICI 50, 123; Imperial Chemical Industries, Macclesfield, England) starting at 1.5 pg per kg of body weight per hour given by continuous intravenous infusion. The dose was doubled every seventy-five minutes, until a further increase failed to produce a higher output than that produced by the preceding dose [8]. The maximal acid output from the pouch was expressed as the mean of the last two fifteen minute collections during the period in which this maximal response occurred. Each test was performed three times in each dog, and the mean maximal output of aa id was expressed in mEq per 15 minutes. The gastric fistula remained closed throughout.
332
Series I: The first series of tests to study antral inhibition was also carried out with the gastric fistula closed. Pentagastrin in a dose producing approximately 50 per cent maximal acid stimulation (1.5 pg per kg of body weight per hour) was administered by continuous intravenous infusion into a foreleg vein at a rate of 3.33 ml per hour for four hours, using a Palmer pump (C. F. Palmer, London, England). At the onset of acid stimulation, the antral pouch was perfused with isotonic saline. For the first two hours of the test, the pH of the perfusate was 7.0; for the second two hours of the test, 1.0. This pattern of antral pH change was employed in two tests in each animal. In two additional tests the order of pH was reversed; the perfusion of the antrum was begun at pH 1.0 and changed to pH 7.0 after two hours. The system of perfusion of the pyloric antrum has been described previously [7]: a peristaltic pump (Model MHRE, Watson-Marlow Ltd., Marlow, Rucks., England) was employed to ensure a constant rate of antral perfusion (1 ml per minute) via a Kay double-lumen gastrostomy tube (J. G. Franklin and Sons I,td., London, England). Series II: In the second series of tests, pentagastrin was administered intravenously in the same dose with
The American Journal of Surgery
Antral and Duodenal Acidification
1 o-
the gastric fistula open. Gastric secretion was collected simultaneously from the gastric fistula and fundic pouch, but each animal also received an intravenous infusion of 154 mM of sodium chloride at a rate of 80 ml per hour, delivered by peristaltic pump. This was to compensate for the excess fluid loss from the gastric fistula. Four such tests were performed in each animal,
Antrol 09-
0.01 N sodium hydroxide to pH 7.0 using an E.I.L. Model 24 Titrimeter, (Electronic Instruments Ltd., Richmond, Surrey, England). The acid output was calculated in mEq per fifteen minutes. In the meat tests, an aliquot proportional to the volume of each fifteen minute collection was pooled into thirty minute samples for pepsin estimation. The concentration of pepsin was determined in 0.1 ml of each pooled specimen in duplicate by the method of Klotz and Duvall (9) and expressed in micrograms of standard Sigma pepsin per milliliter of juice. The outputs were calculated in micrograms per thirty minutes. Statistical Analysis. Pentagastrin studies: As the acid outputs followed a lognormal distribution, the differences between the log acid outputs [IO] during the second hour of each period when the antrum was perfused at pH 7.0 and those when the antral pH was 1.0 were calculated. These differences were subjected to an analysis of variances [II] to determine whether there was any evidence of inhibition of acid secretion from either the fundic pouch or main stomach. Meat studies: The means of the arithmetic values of the total outputs of acid and pepsin over the four hour period after ingestion of the meal, without antral perfusion, were compared by t tests [12] with those during antral perfusion at pH 7.0 and 1.0. Arithmetic values were employed in the statistical analysis, rather than the logarithms used previously because of the occurrence of isolated zero readings.
Voiwne
128, September 1974
Cl
s
e .
and antral perfusion was identical to that employed in series I. Meat Studies. To confirm that the pouch preparations were capable of demonstrating that acidification of the antrum would effect an inhibitory response, an additional group of tests was carried out in which the stimulus of gastric secretion was the ingestion of uncooked minced ox heart (25 gm per kg of body weight). At the time of feeding, antral perfusion was commenced with either isotonic saline at pH 7.0 or an isotonic solution of hydrochloric acid in saline at pH 1.0 at a rate of 1 ml per minute. Perfusion was continued for four hours after ingestion of the meal. The pH of the effluent fluid was checked at hourly intervals and did not differ from that of the perfusate. Each test was performed three times in each dog. Control studies were performed, again three times in each dog, in which the antral pouch was not perfused.
In all the tests, gastric juice was collected at fifteen minute intervals. The volume was measured in milliliters and the acidity was determined by titration with
EI
08-
”
// a
NOW
pH 7 0
pHl0
07-
: %
perfusato
“5 06-
5 p8
05
6 f oh-
03-
0 2pco
01
Ol-
Figure 3. Mean acid secretory with vagatly denervated fundic after ingestion of a meat meal. from the resutts of nine tests in
responses of three dogs pouches in the four hours Each value was obtained the three dogs.
Results
Pentagastrin Stimulation. For each dog there were results from three methods of collection of gastric acid: (1) from the fundic pouch, with the gastric fistula closed; (2) from the fundic pouch, with the gastric fistula open; (3) from the gastric fistula. Figures 1 and 2 illustrate the mean acid outputs (mEq/hr) for each animal during the second hour of each two hour collection period. In each case there were duplicate results both when the order of administration of perfusate was pH 7.0 followed by pH 1.0 and when the order of administration was pH 1.0 followed by pH 7.0. An analysis of variance showed that no significant inhibition of acid secretion occurred during antral acidification with any method of collection. Furthermore, opening the gastric fistula and diverting acid from the main stomach to the exterior had no significant effect on the acid output of the fundic pouch. Meat Stimulation. Acid output: The mean acid outputs pear
over in Figure
the
four
3. There
hour
period
of the
was no difference
tests
ap-
between
333
Wheeler, Prescott, and Forrest
2.5,
Antral
porfusatr
#
None
[7
pH 7.0
pH
z
t-0
_
E” 2
1.5-
5 .5
B
x
s f
-
-
“.S
lo-
O-8 -
06-
OL-
02-
Figure 4. Mean pepsin secretory responses of three dogs with vagally denervated fundic pouches in the four hours after ingestion of a meat meal. Each value was obtained from the results of nine tests in the three dogs. N.S. = not significant (p > 0.05).
the acid outputs in the control tests and those during antral perfusion at pH 7.0. Significant inhibition occurred with antral acidification. Pepsin output: The mean pepsin outputs after stimulation by meat are shown in Figure 4. Although the mean pepsin outputs when the antrum was perfused with acid were numerically lower than both the mean pepsin outputs without perfusion and those when the- antrum was perfused at pH 7.0, this apparent inhibition was not statistically significant at the 5 per cent level. Comments
We have been unable to determine that acidification of the innervated pyloric antrum can influence pentagastrin-induced acid secretion from denervated fundic pouches of the canine stomach, even when the acid stream is diverted from the duodenum. The duodenal inhibitory mechanism, by which acid in the duodenum can depress acid se-
334
cretion of a fundic pouch [13-161 was prevented from acting by opening the gastric fistula. Such a maneuver has been shown to enhance the acid secretory response of denervated pouches to gastrin [17-191 and pentagastrin [20] stimulation. Nor, in the present studies, did the prevention of duodenal acidification unmask an inhibitory effect of antral acidification on the acid secretion collected from the main stomach via the gastric fistula. It therefore seems clear that the inhibitory action of antral acidification is mediated by a diminished release or formation of endogenous gastrin. No evidence is provided for the existence of either a hormonal or neuronal antral inhibitory mechanism active against pentagastrin-induced secretion. The studies performed first with the fistula closed and then with it open showed that diverting the acid stream from the duodenum did not, in itself, influence the acid output of the fundic pouch. These results are contrary to those of Way and Grossman [20] but are in agreement with the observations of Konturek and Johnson [21], who reported that exogenous acidification of the innervated duodenal bulb failed to inhibit pentagastrininduced secretion from denervated pouches, although it did inhibit secretion from the innervated main stomach. Because separation of the duodenal bulb from the pylorus abolished this inhibitory effect on the main stomach, it was concluded that an enterogastric reflex was involved in the duodenal inhibitory mechanism. Support for the role of the nervous system in the duodenal inhibition of gastric secretion has been provided by other workers [22,23]. When a single feeding of ox heart was provided as a physiologic stimulus to gastric secretion, antral acidification inhibited the acid secretory response of the denervated fundic pouches. These findings are in agreement with those of many other workers [3,24,25] and confirm that the antral pouch preparations used in our study were capable of initiating inhibition of the acid secretory response to a truly physiologic stimulus. Such inhibition resulted from diminished vagal gastrin release after a decrease in antral pH. The finding that antral acidification did not significantly suppress the pepsin secretory response to a meat meal is in agreement with other reported observations [3,26]. Thus it seems that in these tests vagal gastrin did not play a significant role in the stimulation of pepsin secretion.
The American
Journal ol Surgery
Antral and Duodenal Acidification
Summary In three dogs, each prepared with an innervated antral pouch, vagally denervated fundic pouch, and a gastric fistula of the main stomach, gastric secretion was stimulated by intravenous infusion of a submaximal dose of pentagastrin. Antral acidification at pH 1.0 did not inhibit the acid secretory response of the fundic pouch during tests in which the gastric fistula was closed. When the gastric fistula was opened, acidification did not affect the acid secretion of either the denervated fundic pouch or innervated main stomach. Diversion of acid from the duodenum did not influence the over-all level of acid secretion from the fundic pouch. Antral acidification did inhibit the acid secretory response of the fundic pouch after ingestion of a meat meal (25 gm per kg of body weight), although pepsin outputs remained unchanged. The results provide no support for the existence of either an antral inhibitory hormone or. inhibitory neural reflex active against pentagastrin-stimulated gastric secretion in the dog. Antral inhibition of gastric secretion is the result of a diminished release or formation of endogenous gastrin. Acknowledgment: We wish to thank Dr Morton I. Grossman for his valuable suggestions and advice regarding this project. The pentagastrin used in this study was generously supplied by Imperial Chemical Industries Ltd., England. The authors are grateful to Mrs M. Coyle for her technical assistance.
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