Insulin-Induced Gastric Acid Secretion in Young Men

Vol. 50, No.1 Printed in U.S .A.

GASTROENTEROLOGY

Copyright © 1966 by The Williams & Wilkins Co.

INSULIN-INDUCED GASTRIC ACID SECRETION IN YOUNG MEN Test reproducibility and correlation with the auglDented histalDine test KENNETH

A.

RUBEL,

M.D.

Gastroenterology Research Laboratory, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa

Two years after Banting and Best reported the successful preparation of insulin (1922), the effects of the hormone on gastric secretion were reported. l Variations in insulin potency and dosage and limitations of experimental design, however, prevented consistent demonstrations of the secretory stimulating effect of hypoglycemia for another decade. In 1931, LaBarre and de Cespedes2 showed that interrupting the vagus nerves prevented the insulin secretory response, and in 1946 HollanderS proposed that the hypoglycemic stimulus be'used to determine the completeness of therapeutic vagotomy in a test which measured changes in gastric acid concentration. Kay's introduction of the augmented histamine test in 1953 demonstrated that the measurement of acid production was reproducible.l 2 Subsequently, in tests of insulin-induced gastric secretion, there has been a trend toward measuring acid production instead of changes in acid concentration.4 - 6 , 15, 16 Although the reproducibility of the various indices of acid production has been measured for the augmented histamine test, no such information is availReceived July 26; 1965. Accepted September 14, 1965. Address requests for reprints to: Dr. Kenneth A. Rubel, Gastroenterology Research Laboratory, University of Iowa College of Medicine, Iowa City, Iowa 52241. This investigation was supported in part by a United States Public Realth Service general research support grant administered by the University of Iowa College of M edicine, by Training Grant 5-TI-AM-5390 from the National Institute of Arthritis and Metabolic Diseases, and by Research Grant AM-09022-0l from the National Institute of Arthritis and Metabolic Diseases. ' 24

able for the insulin test. For the augmented histamine test Baron showed that the maximal acid output obtained during any 30-min pE)riod was the most reproducible index of secretion. 9 Ross and Kay used the 30-min maximal acid output following insulin to study secretory function in patients with vagotomies but did not study the reproducibility of the measurement. 16 The present paper reports for insulin-induced gastric secretion the reproducibility of maximal acid output determinations for periods of 15, 30, 60, and 120 min. In addition it compares the 30-min maximal acid outputs following augmented histamine tests and insulin tests in the same subjects. Method

Reproducibility of the insulin test was studied in 25 healthy men of an average age of 22 years. None had known disease of the gastrointestinal tract. Duplicate tests were done on each subject at an average interval of 7 days. After the subject had fasted overnight, a rubber nasogastric tube (16 Fr) was passed into the stomach with fluoroscopic guidance, and the tip was placed along the greater curvature at the left vertebral border. Gastric suction, 40 to 50 mm Hg, was interrupted every minute during collection, and patients frequently alternated body position between supine and left lateral decubitus. After the fasting stomach contents were aspirated, 0.15 units per kg of body weight of regular insulin were given intravenously, and eight consecutive IS-min samples of gastric juice were collected. Venous blood was drawn 30 and 60 min after the insulin inj ection for glucose determination by the SomogyiNelson method 7 in the hospital laboratory.

January 1966

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INSULIN-INDUCED GASTRIC ACID SECRETION

In order to compare the augmented histamine test and the insulin test, nine patients with duodenal ulcers and three healthy volunteers were studied by both methods. For the histamine response, either histamine acid phosphate (0.04 mg per kg of body weight) or betazole (1.0 or 1.5 mg per kg of body weight) was injected subcutaneously. These doses of betazole do not stimulate secretion maximally, but were chosen because they elicit a response comparable to that produced by 0.04 mg per kg of body weight of histamine acid phosphate.8 Chlortrimeton, 20 mg, was given by intramuscular injection 30 min before histamine, but no antihistamine was used before betazole. Following histamine or betazole injection, four 15-min samples of gastric juice were aspirated. All gastric aspirates were analyzed in the same way. The volume was measured and a lO-ml aliquot was titrated electrometrically to pH 7.0 using 0.1 N NaOH. The milliequivalents of acid in each specimen were then calculated . The 30-min maximal acid output was calculated for the augmented histamine response. 9 For the insulin response, the total 120-min acid output was determined and the maximal acid output (MAO) was calculated for periods of 15, 30, and 60 min. The 30- and 60-min MAO periods consist of consecutive 15-min intervals and the MAO is the largest amount of acid (milliequivalents) produced during any such period. For each period the following were calculated: (a) mean MAO; (b) coefficient correlating the results of the first and second tests; and (c) mean difference between the individual MAO values of the two tests calculated as follows: Mean difference ~15 (larger MAO - smaller MAO)

25

Results

The quantity of acid secreted during successive 15-min periods is shown (table 1, fig. 1) as the mean and 1 SD of 50 tests in 25 subjects. Following intravenous insulin, the rate of acid production rose abruptly in

1. The amount of gastric acid (milliequivalents) aspirated during successive 15-min collection periods following regular insulin, 0.15 units per kg, iv, in 50 tests in 25 subjects

T AB LE

Period

S ta tis tical measure 1

2

3

45

---

_6_1_7_

1_ 8_

1.31 2.26 5.61 6.95 5.99 5.29 5.05 4.39

Mean

±

±

±

±

±

±

±

±

±

l.09 1.94 2.99 3.31 3.20 2.79 2.92 2.90

SD

11.0

-S.D. 9.0 1-

:t;: 7.0

~ ~

5.0

1.0 PERIOD I 1 I 2 I 3 I 4 I 5 I 6 I 7 I 8 I MINUTES 15 30 45 60 75 90 105 120

FIO. 1. The mean ::±: SD amount of gastric acid (milliequivalents) aspirated during successive 15min collection periods following regular insulin, 0.15 units per kg, iv, in 50 tests in 25 subjects.

the 30 to 45-min period, was highest between 45 to 60 min; and though it decreased thereafter, the rate was elevated moderately 2 hr after injection. The mean and 1 SD of the lowest blood glucose concentration measured during the first and second insulin tests was, respectively, 42.6 ± 22.5 and 33.8 ± 18.1 mg per 100 m!. Only three subjects failed to show clear-cut increases in gastric acid production. In two of these the blood glucose concentrations were less than 40 mg per 100 ml in each test. In the third, the values were less than 50 mg per 100 m!. Table 2 summarizes for each of the two insulin tests the mean MAO for each period. The means of the first and second tests are identical for the 30-min MAO and

26

HUBEL

in close agreement for the 15- and 50-min MAO. The coefficients correiating 10 the results of the two tests are listed in the final column.

Vol. 50 , N o.1 4. The 30-min MAO in 13 subjects following the insulin and augmented histamine tests

TABLE

30-minMAO S~bject

Insulin

O~~5~-7.IO~~15--~2~O~~2~5--d30~~35

INSULIN 30 MIN. MAO (mEq) FIG. 2. Correlation of the gastric acid secretion, expressed as the 3O-min maximal acid output, following standard doses of histamine and insulin. 2. The mean insulin maximal acid output (MAO) obtained in 25 subjects in duplicate tests for MAO periods of 15, 30, 60, and 120 min. The coefficient correlating the first and second tests is also shown

TABLE

Mean MAO MAO period

I

1st

min

15 30 60

120

2nd

Correlation coefficient

mcq

8.5 14.3 24.1 35.4

8.2 14 .3 25.3 38.4

0.67 0.76 0.77 0.77

3. The mean difference between the paired individual values of the two insulin tests for each MAO period (see formula) expressed as milliequivalents and as percentage of the MAO obtained on the first test

T ABLE

Difference between paired tests MAO period Mean ± so

min

15 30 60 120

(Mean ± so/1st MAO) X 100

%

mcq

1.6 2.4 3.9 6.8

± ± ± ±

1.4 2.1 3.8 6.4

18.6 16.5 16.2 19 .2

± ± ± ±

16.5 14.7 15.8 18.1

Histamine

meq

tneq

J. G. R.M . D. M. D. B. B. G. S. W. S. J . C. B. L. F . L.M. C. V. 2 C. V. , B. T.

32.8 31.0 30.7 23.7 20.8 20.0 17.4 15.3 13.5 12.1 10.5 9.0 7.8

29.4 9.4 27.4 15 .9 22.9 13 .3 15.8 7.2 13.6 7.5 12. 3 12.0 15.9

Mean

17.2

15 .5

Table 3 gives the mean difference between the paired individual values of the two tests calculated from the formula (see above). It also expresses the mean difference as a percentage of the MAO obtained on the first test and therefore shows a comparison of test variability for each period. Thus, the percentage difference between the first and second tests is least for the 30- and 50-min MAO and greatest for the I5-min ,MAO and I20-min collection. Table 4 lists the 30-min MAO's obtained when insulin tests and augmented histamine tests were performed in the same subjects (fig. 2). The mean 30-min MAO is greater after insulin than after histamine. The correlation coefficient is 0.47. Discussion

The difference in the secretory response among subjects is reflected in the large standard deviations shown in table 1. This variation was not the result of an inadequate hypoglycemic stimulus since 22 subjects out of 25 showed an unequivocal increase in gastric acid production. Such an increase is evidence that the critical hypoglycemic threshold for stimulation has been attained. Two of the remaining three subjects who showed a less impressive increase in acid secretion had blood glucose

January 1966

I NSULIN -IN D UCED GASTRIC ACID SECRETION

concentrations of less than 40 mg per 100 ml. The last nine subjects in the study had higher blood glucose determinations despite clear symptomatic and secretory evidence of hypoglycemia. These values are therefore regarded as erroneously elevated. No decrease in acid secretion was seen during the 15- to 30-min period of collection, in contrast to the results of Olson and NechelesY It is possible that this effect is dosage-related since they administered a standard dose of 25 units of insulin in contrast to an average of 12 units in this study. Table 2 shows the close agreement of mean values for the MAO's in the two insulin tests at each time period, and this is reflected in the correlation coefficients. When the values for the mean difference between the first and second tests are expressed as a percentage of the MAO obtained in the first test (table 3), it is apparent that the mean percent difference between the two insulin tests is least for the MAO's at 30 min (16.5% ) and 60 min (16.2%) . Studies of the reproducibility of the augmented histamine test by Kay12 showed that the mean difference that occurred between paired tests in the same subjects was about 5% when the 15 to 45-min collection was used as the test period. More recent studies by Baron 9 used different measures of reproducibility than those used in this study so that no comparison can be made. The remarkably small difference between repeated tests reported by Kay, however, indicates that the insulin test shows considerably greater variability than the augmented histamine test. Baron showed that in the augmented histamine test, the 30-min maximal acid output (comparable to the 30-min MAO in this study) was the most reproducible measurement. Because of the reproducibility of the insulin 30-min MAO and the obvious advantage of using similar measurements in tests of gastric acid secretion, the 30-min MAO should be used as the st andard measurement of maximal acid secretory rate following insulin . As shown by Ihre 13 and Hunt/ 4 the acid secretory responses following histamine and those followin g insulin have a

27

general tendency to be parallel. The average 30-min MAO is larger followin g insulin than following doses of betazole or histamine equivalent to the maximal etimul ating dose of histamine. The large ac id output that follows vagal stimulation may exceed that following histamine beca u ~e the vagus liberates acetycholine and gastrin which acts synergistically to etimul ate acid secretion. The insulin MAO should be used to assess the effect of treatment on Yagusmediated gastric secretion. Such a comparison would be made by contrasting preand post-treatment values obtained in the same subj ects. This differs from the Hollander test which compares post-treatment insulin gastric secretion to that obtained during t he post-treatment basal state. Th c Hollander test provides criteria by which one can judge whether vagus-mediated gastric secretion is present or absent, whereas the insulin MAO assesses t he degree to which vagus-mediated secretion has been altered. Injury of the parietal cells also will cause a decrease in the insulin MAO. In studies in which alteration of both parietal cell and vagus fun ction are anticipated, pre- and post-treatment augmented histamine tests should be used to estimate the secretory change resulting from parietal cell injury. A percentage change in the insulin MAO greater than the percentage change in thc augmented histamine MAO. would indicate inj ury to the gastric secretory nerves.15 We have not previously had a ,yay of assessing in man changes in vagal fu nc tion that are less than total. The insulin MAO should fulfill this need. Summary

1. Duplicate tests of gastric acid secretion following a s t andard intravenous dose of regular insulin have been made in 25 subjects in order to determine the most reproducible measurement. 2. The 30-min maximal acid output (MAO) a nd 60-min MAO showed mean differences between the first and second tests of 16.5 and 16.2%. Because of its similarity to the most reproducible measurem fmt, of the augmented histamine test

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Vol. 50, No.1

HUBEL

and the desirability of using similar measurements in tests of gastric secretion, the 30-min MAO is recommended as the standard for comparison between insulin tests. 3. The insulin 30-min MAO is suggested as a method of evaluating in man changes in gastric secretory function resulting from partial alteration of the vagal efferent network. 4. The acid secretory responses following histamine and those following insulin show a general tendency to parallel.

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REFERENCES

10.

1. Collazo, J. A., and M. Dobreff. 1924. Insulinwirkung auf die Absonderung der Verdauungssafte. Klin. Wschr. 3: 1226. 2. LaBarre, J., and C. de Cespedes. 1931. Sur l'origine parasympathetique de l'hypersecretion gastrique consecutive a l'administration d'insuline. C. R. Soc. Bio!. (Paris) 106: 484-486. 3. Hollander, F. 1946. The insulin test for the presence of intact nerve fibers after vagal operations for peptic ulcer. Gastroenterology 7: 607-614. 4. Karacadag, S., and A. P. Klotz. 1964. A physiologic interpretation of gastric freezing in the human. Amer. J. Dig. Dis. 9: 319-327. 5. Hitchcock, C. R., J. E. Bitter, and R. D. Sutherland. 1964. Clinical evaluation of

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gastric freezing for duodenal ulcer. J. A. M. A.1SS: 409-414. Scott, H. W., H. J. Shull, J. A. O'Neill, Jr., and R. E. Richie. 1964. Experimental and clinical appraisal of gastric freezing for duodenal ulcer. Ann. Surg.159: 769-786. Nelson, N. 1944. A photometric adaptation of the Somogyi method for the determination of glucose. J. Bio!. Chem.153: 375-380. Clark, R. W., and E. Englert. 1963. Betazole vs. histamine for maximal gastric secretion. Clin. Res. 11: 77. (Abstr.) Baron, J. H. 1963. Studies of basal and peak acid output with an augmented histamine test. Gut 4: 136-144. Snedecor, G. W. 1961. Statistical methods. Iowa State University Press, Ames. Olson, W. H., and H. Necheles. 1953. Initial depression of human gastric secretion by insulin. Gastroenterology 24: 362-368. Kay, A. W. 1953. Effect of large doses of histamine on gastric secretion of HC!. Brit. Med. J. 2: 77-80. Ihre, B. 1938. Human gastric secretion. Acta Med. Scand. (Supp!.) 95: 1-226. Hunt. J. N. 1950. An interpretation of histamine and insulin tests in patients with peptic ulceration. Lancet 2: 397--400. Hubel, K. A., L. Faber, T. H. Kent, J. A. Clifton, and E. E. Mason. 1964. The effects of gastric freezing on vitamin B12 absorption, acid secretion, tissue morphology and serum enzymes. Amer. J. Dig. Dis. 9: 328336.