Maximal Acid Response in Pavlov Pouch Cats to Pentagastrin and Feeding Alone and in Combination

GASTHOENTEHOLO(;y

Copyri~ht

Vol. 65, No.1

()f):fl 11- fl9, 197:~

Printed in U.S .A.

© 197:1 by The Williams & Wilkins Co.

MAXIMAL ACID RESPONSE IN PAVLOV POUCH CATS TO PENTAGASTRIN AND FEEDING ALONE AND IN COMBINATION SvEN-OLOF SvENSSON, M .D. ,

AND

SvERRE EMAS, M.D.

Departments of Surgery and Experimental Surgery, Allmiinna Sjukhuset, Malmo, Sweden

In cats with both gastric fistulae (GF) and Pavlov pouches (PP), the PP acid response to a single intravenous injection of 2-deoxy-n-glucose (100 mg per kg) was unaltered by closing the GF. This suggested that the PP was vagally innervated and that duodenal acidification by closing the GF did not inhibit vagally stimulated PP secretion in cats. The maximum of the dose-response curve for PP acid output (GF closed) to graded doses of intravenous pentagastrin and graded meat meals was equal. Based on our previous findings that the maximal response to feeding amounted to 70% of that to pentagastrin in cats with vagally denervated pouches, this study showed that vagal impulses to the PP during feeding increased the action of endogenous gastrin released in amounts that alone produced submaximal response. Since concomitant maximal stimulation with pentagastrin did not increase the PP response to feeding, the increase of vagal tone by feeding did not potentiate the maximal response to pentagastrin. These results therefore suggested that the increased vagal tone to the PP evoked by feeding increased submaximal responses to gastrin but did not potentiate the maximal response. In cats the maximal acid response from the vagally denervated fundic pouch (Heidenhain pouch, HP) to feeding a meat meal amounted to 70% of the maximal HP response to intravenous pentagastrin. 2 No

comparison has been published of the maximal acid response from the vagally innervated fundic pouch (Pavlov pouch, PP) to feeding and exogenous gastrin in cats or dogs. In dogs the maximal PP response to feeding exceeded the response to histamine. 3 It is reasonable to assume that feeding releases similar amounts of gastrin in HP 2 and PP cats. A comparison of the maximal acid response of the PP to feeding and pentagastrin might therefore reveal if vagal impulses to the PP during feeding elevated the acid response to endogenously released gastrin. Feeding and pentagastrin, in doses that alone produced maximal acid response from the PP, were also combined to study the effect of vagal impulses on the maximal acid response to pentagastrin.

Received December 4, 1972. Accepted March 6, 1973. This study was reported at the Meeting of the European Gastro Club, Erlangen, West Germany, 1972. 1 Address requests for reprints to: Dr. Sverre EmAs, Department of Surgery, Karolinska Sjukhuset, 104 01 Stockholm 60, Sweden. Financial support from the Swedish Medical Research Council (Grant No. B71-17X-2324-04C) , The Faculty of Medicine, University of Lund, Sweden, and Svenska Sallskapet for Medicinsk Forskning is gratefully acknowledged. Pentagastrin (Peptavlon) was generously supplied by Imperial Chemical Industries Ltd. , Cheshire, England, and by Mr. P. E . Hornkvist, AB Scanmeda, Gothenburg, Sweden. The authors are grateful to Miss Gertie Ranelycke for skillful technical assistance.

Methods Nine adult cats (weight 2.8 to 4.5 kg) were provided with vagally innervated, mucosal sep54

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RESPONSE TO PENTAGASTRIN AND FEEDING IN CATS

tal fundic pouches (PP) according to the method described by Thomas. 4 A plastic cannula• drained the PP. During the same operation the cats were also provided with gastric fistulae (GF) to drain the vagally innervated main stomach. The gastric cannula was placed just proximal to the pyloric gland area near the greater curvature. 5 Three to 4 weeks were allowed for recovery after surgery. The PP was drained freely and to compensate for the electrolyte loss, most cats were injected with electrolyte solutions subcutaneously two or three times a week. By doing so the cats remained in good condition. To ensure that the mucosal septum between the PP and the main stomach was intact, the PP was filled with methylene blue solution at a pressure of 10 em of water and secretion collected from the GF. Two dye tests were carried out on each cat with 6-month interval. In addition, the mucosal septum was inspected when the cats were killed. Before the secretory studies, food but not water was withheld for 18 hr. During experiments the cats were placed in sling frames . 6 Secretion from the PP or from the PP and GF was collected in 15-min periods and the acid output in milliequivalents determined by titration as described previously." Basal secretion was collected for at least two 15-min periods before stimulation of acid secretion. In two or three experiments on each cat, 2-deoxy-n-glucose (2 DG) (Sigma Chemical Co., St. Louis , Mo .) dissolved in saline (0.15 M NaCl solution) was injected intravenously in a dose of 100 mg per kg of body weight (100 mg per ml). Acid secretion from the GF and PP was then collected for 4 hr. In another two to four experiments with 2 DG on each cat, the acid response from the PP was determined with the GF closed. At least 1 week elapsed between the 2 DG experiments. The PP acid responses to different doses of pentagastrin (Imperial Chemical Industries Pharmaceuticals, Cheshire, England) or feeding different amounts of meat were determined with the GF closed. In the pentagastrin experiments, saline was infused intravenously at a rate of 12.5 ml per hr (infusion pump) during collection of basal secretion . Pentagastrin was then added to the saline infusion in doses of 0.5 , 2, 4, 8, 16, 32, or 64 J.!g per kg of body weight per hr and infused for 3 hr. In the feeding experiments, the amounts of meat were 3, 6.3, 12.5, 25, and 50 g. The composition of the meat in this and a previous study 2 was the same. Feeding was completed within 2 min except for a few experiments with 25 and 50 g of meat in

55

which it was completed within 15 min. Acid secretion from the PP was collected for 5 hr after feeding. Only one dose of pentagastrin or meat was given during each test with at least 1 or 2 (pentagastrin) days between tests . Each cat underwent two to four tests with each dose of pentagastrin or meat in randomized order. In 17 experiments the PP acid response to combined stimulation with pentagastrin and feeding was determined (GF closed). Each of the 9 cats received that dose of pentagastrin that produced maximal acid response. One half-hour after the start of the continuous pentagastrin infusion, the cats were fed the amount of meat that alone produced maximal response. Secretion was collected for 4 hr after the start of the pentagastrin infusion. The acid response to 2 DG and to each dose of pentagastrin or meat is the mean of the mean 15-min peak acid outputs( ± SEM; n = 9) in each of 9 cats (19 to 28 experiments with each dose). The mean maximal response (MR) to pentagastrin and meat for the 9 cats was calculated from the maximum of the mean dose-response curve': for each cat. The differences between the maximal responses to pentagastrin, feeding , and combined stimulation, and between the peak response to '7 DG and pentagastrin were evaluated for each cat by the Wilcoxon-Mann- Whitney test. 8 The probabilities of the differences for the cats were then combined.• The same method was used to evaluate the differences between the peak acid responses of the mean curve to pentagastrin , feeding, and combined stimulation. The ratios of the acid response to 2 DG and pentagastrin in' the GF and PP were compared by the t-test 8 for paired values (two-tailed).

Results The peak acid output after 2 DG occurred in the second 15-min period in the main stomach and in the second or third period in the PP (GF open or closed). The mean peak response from the GF was 0.26 ± 0.03 mEq and from the PP 0.16 ± 0.02 mEq. Closing the GF did not alter (P > 0.05) the acid response from the PP (fig. 1); the mean peak response from the PP with the GF closed was 0.17 ± 0.02 mEq. The ratio of the peak acid response to 2 : DG (100 mg per kg of body weight) and to an approximately equipotent dose of pentagastrin (in 7 cats 0.5 J.Lg, in 1 cat 2 J.Lg , and . in 1 cat 4 J.lg per kg per hr) was deter- : mined from 20 experiments with 2 DG and

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Vol . 65, No. 1

SVENSSON AND EMAS

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int ravenous injection of 2-deoxy-o-glucose (100 mg per kg of body weight) in 9 cats with t he gastric fistula (GF) open (20 experiments) or closed (22 experiments). Vertical lines, standard error of mean (n = 9).

21 experiments with pentagastrin (GF open) . The peak response to 2 DG and pentagastrin did not differ (P > 0.05) in the GF or PP (fig . 2), but the ratio of the responses was significantly greater (P < 0.001) in the PP (1.24 ± 0.11) than in the GF (0.85 ± 0.09). During pentagastrin infusion, the peak acid output from the PP (GF closed) occurred in the third to fifth 15-min periods independent of dose (fig. 3) . The mean acid response from the PP increased with increasing doses of pentagastrin (fig. 4, left). The dose required for MR was 16 11-g in 4 cats, 32 11-g in 3 cats, and 64 11-g per kg of body weight per hour in 2 cats. The mean of the MR's was 0.32 ± 0.02 mEq (fig. 5) and the mean response to 64 11-g per kg was 0.31 ± 0.03 mEq (fig. 4, left) . The latter response was regarded as the maximum of the mean dose-response curve . After feeding, the peak acid output from the PP (GF closed) occurred in the second or third 15-min period independent of amount of meat (fig. 6). The duration of the response was roughly related to the amount of meat; with 3 and 6.3 g, acid secretion was close to basal level 2 hr after feeding ; with 25 and 50 g, secretion remained elevated for at least 5 hr (fig. 6) . The mean response increased with increasing amounts of meat (fig. 4, right). Maximal response was produced by 12.5 g of meat in 1 cat, by 25 g in 4 cats and by 50 g in 4 cats. The mean of the MR's was 0.31 ± 0.03 mEq (fig. 5). The maximum of the mean dose-response curve was 0.29 ± 0.03

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FIG. 2. Mean peak acid output( ± SEM, n = 9) to intravenous injection of 2-deoxy-o-glucose (2 DG, 100 mg per kg) and continuous intravenous infusion of approximately equipotent doses of pentagastrin (PG) in 9 cats with gastric fistulae and Pavlov pouches. Each cat was tested two or three times with each stimul ant.

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FIG. 3. Acid output during continuous intravenous infusion of different doses of pentagastrin in 9 cats with P avlov pouches (gastric fistula closed). Each curve represents t he mean of 19 to 28 experiments. Dose of pentagastrin in micrograms per kil ogram of body weight per hour to the right of each curve.

mEq and was produced by 50 g of meat (fig. 4, right). The MR's (fig. 5) or the maximum of the mean dose-response curve for pentagastrin and feeding (fig. 4) did not differ (P > 0.05). In 17 experiments on 9 cats, the peak of the mean curve for PP acid output to feeding during concomitant maximal pentagastrin stimulation was 0. 35 ± 0.03 mEq, to pentagastrin alone 0.29 ± 0.02 mEq, and to feeding alone 0.30 ± 0.03 mEq (fig. 7); the figures did not differ (P > 0.05). Similarly, the mean of the mean peak response for each cat (1st postprandial hr) to combined stimulation (0.37 ± 0.03 mEq), and the mean maximal response to pentagastrin (0.32 ± 0.02) and feeding

RESPONSE TO PENTAGASTRIN AND FEEDING IN CATS

July 1973

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release . In this study, closing the GF did not alter the PP response to 2 DG. The PP was therefore regarded as vagally inner0.30 vated. The unaltered PP response could 0 mean that small amounts of gastrin is re~ Cl .~ 0.20 Li E ~ leased in spite of closing the GF, or-if <( ll'> ~ vagal release of gastrin was blocked-that ::.:: "'- 0.10 <( t>' ~ gastrin is of minor importance for the PP 'ljltJ ~ a.. E 0 response to vagal stimulation by 2 DG in cats. The ratio of the peak acid response FIG. 5. Mean peak ac id outp ut ( ± SEM, n = 9) to to 2 DG and pentagastrin was greater in feeding durin g concomitant maximal pentagastrin the PP than the GF although the response (PG) stim ul at ion (17 experiments), and the mean maximal response to pentagastrin (28 experim ents) to 2 DG and to the doses of pentagastrin and feeding alone (24 experiments) in 9 cats with selected did not differ significantly in the Pavlov pouches (gastric fistula closed). Pentagastrin GF or PP. This suggested that the degree an d meat was given in doses t h at produced maximal of vagal innervation of the PP was satisresponse in each cat. factory . Duodenal acidification of the intact alone (0.31 ± 0.03) did not differ (P > duodenum by closing the GF did not in0.05) (fig. 5). hibit gastrin 10 or pentagastrin-stimulated 11 acid secretion from the HP in cats. In this Discussion study the acid response from the main No leakage was detected between the GF stomach drained to the duodenum did not and the PP by the dye test in the 9 cats alter the vagally (2 DG) induced acid used in the study but another 4 cats were secretion from the PP. This is in keeping discarded because of leakage. In our expe- with our previous statement that the rience the risk for leakage appears to be duodenal acid inhibitory mechanism is greater in PP cats than in PP dogs and the probably without physiological signifidye test is therefore regularly applied to cance in t he cat. 11 To our knowledge there are no studies cats. In cats 2 DG produced a small peak acid comparing the maximal acid response from response from the HP (0.06 mEq) when the the PP or the vagally innervated stomach GF was open . 2 Closing the GF abolished to feeding and exogenous gastrin or penthe HP response to 2 DG which was as- tagastrin. In man, Rune 12 estimated the cribed to acid inhibition of vagal gastrin ·. acid secretion after a test meal and maxi..... :::> a.. ..... :::>

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Vol. 65, No.!

SVENSSON AND EMAS

58 ~

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FIG. 7. Acid response to feeding or pentagastrin alone, or in combination , in 9 cats wit h Pavlov pouches (gastric fistula closed). The amoun t of meat and dose of pentagastrin was selected to produce maximal acid response. Each curve represents the mean of 17 to 28 experiments. Vertical lines, standard error of mean (n = 9).

mal stimulation with histamine from the base accumulation in the body caused by the acid loss. He found an approximately equal base accumulation after feeding and histamine which suggested that the responses were equal in man . However, as pointed out by Rune, 12 the acid response to feeding might have been underestimated due to a concomitant bicarbonate response from the pancreas. In dogs the maximal PP acid response to feeding was 34 to 56% higher than the maximal response to histamine. 3 This study shows t hat in cats the maximal peak acid response to feeding and pentagastrin was equal in the PP . This is probably valid also for histamine, since the maximal response to histamine and pentagastrin is equal in the vagally inner-

vated stomach in cats. 7 In the dog experiments with histamine, the GF was open to prevent the release of possible duodenal inhibitors of acid secretion. 3 Closing the GF does not alter the PP response to pentagastrin in cats (unpublished o bseruations). Accordingly, the difference in duodenal acidification in the experiments with histamine in the dogs and with pentagastrin in the cats cannot account for the different findings in dogs and cats: lower response to histamine than to feeding in dogs and equal response to pentagastrin (or histamine) and feeding in cats. If this difference between dogs and cats is due to different composition of the test meals, or represents another species difference, remains to be elucidated. In HP cats, the maximal response to feeding amounted to 70% of the maxim al response to pentagastrin, 2 whereas in PP cats, the maxim al responses were equal. Since the same meat was used in the two studies, it is assumed that feeding released similar amounts of gastrin (and other secretagogues) in HP and PP cats. From our previous 2 and present findings it is therefore concluded that vagal impulses to the PP during feedin g increased the action of endogenous gastrin, released in amounts that alone produced 70% of the maxim al response to pentagastrin . When maximal stimulation with pentagastrin was superimposed on feeding, the PP response tended to be higher but did not differ significantly from the maximal response to feedin g or pentagastrin alone . This means that maxim al pentagastrin stimulation combined with basal vagal tone (pentagas-

July 1973

RESPONSE TO PENTAGASTRIN AND FEEDING IN CATS

trin experiments), or increased vagal tone during feeding, produced equal PP re sponse. It is therefore concluded that, in cats, an increase of vagal tone by feeding did not potentiate the action of pentagas trin at dose levels that produced maximal PP response. In Rune's study 12 in man, the estimated acid response to feeding alone did not differ from the response to feeding and concomitant maximal stimulation with histamine. With respect to the absent potentiation of acid secretion by feeding at maximal secretory rate, cats thus appear to behave as man. The cat might therefore be a satisfactory model for studying the interaction between vagal impulses and gastrin on gastric acid secretion in man. It is evident but deserves to be emphasized that the maximal rate of acid secretion from the innervated oxyntic glands attained experimentally by pentagastrin in cats, and by histamine in man 12 and dogs, 3 is also reached during physiological conditions, namely after a meal. REFERENCES 1. Svensson S-0, Emas S: Acid response in Pavlov pouch cats to pentagastrin and feeding alone or in combination. Acta Hepato-Gastroenterol (in press), 1973 2. Svensson S-0 , Emas S; Acid response to graded doses of pentagastrin and feeding, and effect of atropine in Heidenhain pouch cats. Scand J Gastroenterol (in press), 1973

59

3. Brooks AM , Grossman MI: Maximal acid response of Pavlov pouches to food and histamine. Gut 11:153- 157, 1970 4. Thomas JE : A simplified procedure for preparing an improved Pavlov pouch. Proc Soc Exp Bioi Med 50:58- 61, 1942 5. Emas S: Gastric secretory responses to repeated intravenous infusions of histamine and gastrin in nonanesthetized and anesthetized gastric fistula cats . Gastroenterology 39 :771-782, 1960 6. Emas S, Swan KG , Jacobson ED: Methods of studying gastric secretion, Handbook of Physiology, sect 6: Alimentary Canal, vol 2. Edited by CF Code . American Physiological Society, Washington DC , 1967, p 743-758 7. Borg I, Emas S: Effect of atropine on the gastric acid response to histamine and pentagastrin in conscious cats. Scand J Gastroenterol 5:369-374, 1970 8. Snedecor GW, Cochran WG: Statistical Methods. Sixth edition. Ames, Iowa, Iowa State University Press , 1969 9 . Fisher RA: Statistical Methods for Research Workers. Tenth edition. London, Oliver and Boyd, 1948 10. Stening GF, Johnson LR, Grossman MI: Effect of secretin on acid and pepsin secretion in cat and dog. Gastroenterology 56:468-475, 1969 11. Em asS , Svensson S-0, Borg 1: Effect of duodenal acidification or exogenous secretin on gastric acid secretion stimulated by histamine, pentagastrin and hum an gastrin I in conscious cats. Digestion 5:17-30, 1971 12. Rune SJ: Comparison of the rates of gastric acid secretion in man after ingestion of food and after maximal stimulation with histamine. Gut 7: 344-350, 1966