The effect of secretion on hydrogen ion transport in the duodenum and jejunum

JOURNAL

OF SURGICAL

RESEARCH

The Effect

20, 461-411 (1976)

of Secretin

on Hydrogen

in the Duodenum RAPHAEL

Ion Transport

and Jejunum

S. CHUNG, M.D., GEOFFREY M. JOHNSON, B.S., AND LAWRENCE DENBESTEN, M.D.

Department ofsurgery, Veterans Administration Hospital and University of Iowa College of Medicine, Iowa City, Iowa 52242 Submitted for publication December 31, 1975

One of the best examples of homeostasis in physiology must be the remarkable ability of the duodenum to maintain a near neutral pH, despite proximity to an acid secreting organ. It has been shown that, even after diversion of bile and pancreatic juices, acid instilled into the duodenum rapidly disappears from the lumen [2-4, 7, lo] In the cat, which has only a short segment of Brunner’s gland bearing area, we found that passive diffusion, occurring concomitantly with neutralization, accounted for the mucosal mechanism of acid disposal [l]. Since the amount of bicarbonate secreted in the cat duodenum is modest, we conclude that passive diffusion plays a major role. Because of the close relationship between secretin release and acidification of the intestines, the effect of secretin on this mucosal mechanism for acid disposal at various levels of the upper small intestine is examined in the study. MATERIAL AND METHODS The animal model employed was the cat under ketamine anesthesia [ 11. After diversion of bile and pancreatic juices, the first 5 cm of the duodenum was cannulated for perfusion, with the inlet cannula introduced through an incision on the antral side of the pylorus so as to include the first centimeter of the duodenum in the perfusion circuit. When lower duodenum was studied, the 5 cm segment was measured cephalad from the ligament of Trietz. When the jejunum was studied, a 5 cm segment 10 cm distal to the ligament was cannulated. The perfusion circuit was a recirculating system of 35 ml ca-

pacity, consisting of a roller pump, a heat exchanger, and a reservoir (Fig. 1). At the circulation rate of 20 ml/min, it took 3 set for the solution in the duodenum to reach the reservoir. The solution contained Na+ at 150 mM; Cl-, 110 mM; SOh2-, 20 mM; 10 g/liter of polyethylene glycol (Carbowax 4000) and 14CPEG at 30 &i/liter. It had an osmolality (308 mOsm/kg H,O) identical to that of cat serum. Continuous titration to a specified pH took place in the reservoir, mixing being achieved by a magnetic stirrer and air bubbling. The titrant was delivered to the reservoir from a Harvard pump (Model 930A, Harvard Instruments, Mass.) equipped with an infinitely variable manual speed control. In actual titration, once a correct speed has been found, only minimal adjustment needs to be made to achieve a constant pH. Titrant volume was recorded by a parallel channel of the Harvard pump delivering into a preweighed vessel. The H+ contained in the titrant is equal to the H+ removed by the duodenal mucosa during the period of titration. The experiments were randomized to iv infusion of either GIH secretin at 3 CU/kg/hr or the equivalent volume of saline via the femoral vein. Histological sections of the intestines were taken in approximately half of the experiments to look for the extent and state of Brunner’s gland bearing area, as well as any mucosal structural changes induced by perfusion at various pH. Statistical analysis of results comprised of examination of relationship between two variables by means of regression lines by the method of least squares [8], and comparison of re-

467 Copyright D 1976 by Academic Press, Inc. All rights of reproduction in any form reserved.

468

JOURNAL

OF SURGICAL

RESEARCH:

VOL. 20, NO. 5, MAY

1976

Tiirant in Harvard

FIG. 1. In viva titration-perfused

gression lines by comparison of slopes and elevations after ascertaining homogeniety of variances [8]. The Student’s t test for paired variates were also performed to determine statistically significant difference between means. RESULTS

circuit.

and y-intercept = 6.3. No statistically significant difference was detected between the two regression lines either in the variance, intercept, or slope (P > 0.1). Eflect of secretin on the rate of removal of H+ from the lower duodenum and jejunum (Table 1). No significant change in any of the

values was discernible when secretin was

Rate of removal of H+ from the lower infused intravenously, as shown in Table 1. duodenum and jejunum (Table 1). As When these values were plotted against

shown in Table 1, the rate of H+ removal increases as pH decreases. No significant difference was detected between any of the values for lower duodenum and jejunum. When these values were plotted against the luminal H+ concentrations as converted from the pH values, the regression statistics were: for the lower duodenum (Fig. 2), r = 0.932, slope = 4.0 (ml/30 min/g wet weight of gut perfused), and y-intercept = 8.2 (pmole/30 min/g wet weight of gut perfused); and for the jejunum (Fig. 3) r = 0.962, slope = 4.62,

respective pH expressed as H+ concentration, the regression statistics were: for the lower duodenum (Fig. 2), r = 0.947, slope = 0.947, slope = 4.9, and y-intercept = 7.0; and for the jejunum (Fig. 3), r = 0.918, slope = 4.6, and y-intercept = 8.5. None of the lines were significantly different with or without secretin infusion (P > 0.1). Eflect of luminal Hf concentration on H+ removal from upper duodenal lumen (Table

I ). No significant difference existed between the values obtained in this portion of the

TABLE I Hydrogen Ion Disposal in the Duodenum and Jejunum’ Secretin, iv

Saline, iv PH 2.0 2.3 3.0 4.5 6.0

U Duodenum

L Duodenum

Jejunum

U Duodenum

L Duodenum

Jejunum

70 f 9 46 zt 7 21 zt4 18 + 5 8+1

47 i 7 31 lt4 19 zt 3 7%2 3*1

51 ~6 30 f 4 18 + 3 6&2 2*0

88 f 12 82 zt 7 81 +7 74* 14 86h 16

54 + 8 35 f 5 17 * 4 8+3 2&O

52 * 9 34 i 5 23 zt 4 7&2 2&O

’ Results are mean cated in the text.

l

SE, (n = 5) pm/30 min/g wet weight of intestine perfused. Statistical

significances are indi-

CHUNG,

JOHNSON

AND

DENBESTEN:

SECRETIN

AND

HYDROGEN

469

ION TRANSPORT

2 3 60 k9 t

. -Control

%

0 -GM

\h

$ 40 F t

Secretin

I=mean+ SE (N=51

3 cd ho/ hr IV

I I

Y

_ (r

i)

i

- GIH Secretin =meo”

f

SE

3cu/kg/hr

IV

(N=5)

FIG. 2. Effect of secretin on Hf loss in the lower duodenum.

small intestine and that of the lower duodenum and jejunum at pH of 3 and 6 (Table 1). However, significantly greater H+ removal was encountered at pH 2.3 and 2 (P < 0.002, P < 0.05, respectively). The regression statistics were: r = 0.952, slope = 5.9, y-intercept = 13.8. This plot is significantly different from the corresponding plots obtained with the lower duodenum and jejunum (P = 0.025). Effect of secretin on H+ removal from the upper duodenum (Table I, Fig. 4). As shown

I 0%I

I IPH 301

/LlPH 4 51 I(PH 6.01

FIG. 4. duodenum.

5 IPH 2.31

IO IPH 2.01

Lummal [H] in mM

Effect of secretin on H+ loss in the upper

scopically at any portion of the small intestine after perfusion for 2 hr at any of the pH studied. The Brunner’s gland never extended below the level of the pancreatic duct, which occurred at the middle of the upper duodenum, i.e., 2-2.5 cm from pylorus. At pH 2.3 and below, and at all pH when secretin was infused, there was markedly decreased size of globlet cells in the Brunner’s gland, denoting a decrease in the mucin content of these glands.

in Table 1 and Fig. 4, a significantly increased Hf removal occurred at all pH when secretin was infused intravenously, (P < 0.001 for pH 3 and below, P < 0.01 for pH 2.3, P < 0.05 for pH 2). There was no trend for the mean H+ removal to increase with increasing luDISCUSSION minal H+ concentration under secretin infuThe results are clear-cut in that exogenous sion as none of these values were significantly secretin does not cause any changes in the different from one another (P > 0.01). rate of mucosal removal of H+ in either the Histological changes. No definite evidence lower duodenum or the jejunum. It is of structural damage was detectable microreasonable to conclude therefore that endogenous secretin, as for example released 2 60. .-Control during the perfusion of these portions of up. O-GIH Secretin 3 cu/kg/hr IV .32 h per small intestine at pH 2, also does not P I=mean? SE (N=5) \h 40. affect mucosal H+ transport. In the upper : duodenum, however, secretin does signifi;? T cantly increase Hf removal when infused \ ?? 20 intravenously. Further, in the absence of P t i exogenous secretin, increased Hf removal is also seen in the upper duodenum at pH 2.3 and 2, compared with the values obtained at the corresponding pH in the lower duodenum FIG. 3. Effect of secretin on H+ loss in thejejunum. and jejunum. Although we cannot predict the

470

JOURNAL

OF SURGICAL

RESEARCH:

response of physiological dose of endogenous secretin by extrapolations of results obtained with maximal dose of exogenous secretin, these findings are suggestive that the presence of the Brunner’s glands are responsible for the differences between the results obtained in the proximal duodenum and the rest of the upper small intestine. Either endogenous secretin or the local effect of perfusion at pH 2.3 and 2 caused an increase in the Brunner’s gland secretion, accounting for the difference in response in the upper duodenum. For this reason we conclude that there is no demonstrable difference in the rate of passive H+ diffusion at this level of the small intestine attributable to secretin. In the cat, stimulation of Brunner’s gland occurs with the intravenous injection of intestinal mucosal extracts containing secretin [4]. Work with purified hormones confirmed the results in both the cat and the dog [6]. During digestion, the contribution by the Brunner’s glands to alkalinization of the upper duodenum is probably very small compared to the pancreatic juice secreted under a similar level of stimulation. However, at the basal state in the anesthetized cat, perfusion of duodenum at pH 2 produced a bicarbonate secretion by the pancreas [l] in the same range of magnitude as that obtained from Brunner’s glands deduced from data in this study. The observation that the total H+ removal capacity of the upper duodenum under secretin infusion did not rise significantly at pH 2.3 and 2 over that seen at higher pH deserves some comment. The unchanged total H+ removal capacity may result from a decrease in either the output of the alkaline secretion from Brunner’s glands, or a decrease in mucosal transport of H+. AS secretin clearly did not affect mucosal transport of H+ in the lower duodenum and jejunum, it is reasonable to assume that the former possibility is the likely explanation. We can offer no clues as to why the output from Brunner’s gland did not hold up at low pH. Perhaps the glands did not function

VOL. 20, NO. 5, MAY

1976

optimally in a low pH, since such a pH for any prolonged period does not occur naturally in the upper duodenum. Griffith and Harkins [5] noted the protective effect of Brunner’s glands in the upper duodenum, and advanced this as one of the arguments for preference of Billroth I to Billroth II gastrectomy. Our data indicate that the segment of small bowel bearing Brunner’s glands does have marginal superiority in H+ removal, even though this is dwarfed entirely in comparison to the wellknown neutralizing capacity of the pancreas occurring during digestion. However, after gastric operations, when gastric emptying may be altered and basal acid secretion diminished, it is doubtful if the Brunner’s gland is ever stimulated to a degree comparable to perfusion at pH 2 in this experimental preparation. Our data also suggests that there is no difference in H+ diffusion rates between the point of small intestine employed for either the Billroth I or II anastomosis. Actual pH measurement of these parts of the small intestine after the two operations will be required to make conclusive statements regarding the relative proneness for stoma1ulcers in these operations. SUMMARY To measure the capacity of the upper small intestine to dispose of acid in the absence of bile and pancreatic juice, in viva titrations were performed in cat upper duodenum, lower duodenum, and jejunum to various pH levels in a recirculating perfusion circuit in groups of five cats. The effect of secretin in this capacity to dispose of acid was investigated by repeating the experiment with intravenous infusion of GIH secretin at 3 CU/kg/hr. Identical results were obtained in the lower duodenum and jejunum, but significant increase in rate of H+ removal was seen in the upper duodenum at all pH levels. Histological examination showed that the Brunner’s glands did not extend for more than half of the length of upper duodenum, and are not found in either the lower duodenum or jejunum. No morphological

CHUNG, JOHNSON AND DENBESTEN: SECRETIN AND HYDROGEN

changes were detectable other than depletion of mucin in Brunner’s glands in animals stimulated with secretin. It is concluded that the only effect secretin has on H+ transport in the upper small intestine is to increase alkaline secretion from, for example, Brunner’s glands, resulting in a larger amount of neutralization. REFERENCES

47 1

hormone controlling Brunner’s glands. Quart. J. Exp. Physiol. 251329, 1935. 5. Griffith, C. A.. and Harkins. H. N.The role of Brunner’s glands in the intrinsic resistance of the duodenum to acid-peptic digestion. Ann. Surg. 143:160, 1956. 6 Himal, H. S., Moqtaderi, F., Kark, A. E., and Rudick, J. Hormonal regulation of duodenal secretion Effects of glucagon and secretin. In D. 8. Skinner and P. A. Ebert (Eds.), Current Topics in Surgical Research, Vol. 3, p. 453. Academic Press, New York, 1971. 7 King, C. R., and Schloerb, P. R. Gastric juice neutralization in the duodenum. Surg. Gynecol. Obsrer. 135:22, 1972. 8. Snedecor, 1. W., and Cochran, W. G. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, Iowa, 1967. 9. Stening, G. F., and Grossman, M. 1. Hormonal control of Brunner’s glands. Gustroenterology 56:1047, 1969. 10. Winship, D. H., Caflisch, C. R., and Schulte, W. J. Acid loss in the human duodenum. J. Appl. Physiol. 32:585, 1972. I

I. Chung, R. S. K., Johnson, G. M., and DenBesten, L. The role of the proximal duodenal mucosa in the overall provisions for acid disposal in the upper G. 1. tract.Surg. Forum. 24:389,1975. 2. Dorricott, N. J., Fiddian-Green, R. G., and Silen, W. Mechanisms of acid disposal in canine duodenum. Amer. J. Physiol. 228:269,1975. 3. Florey, H. W., and Harding, H. E. The functions of Brunner’s glands and the pyloric end of the stomach. J. Puthol. Bacterial. 37:431,1933. 4. Florey, H. W., and Harding, H. E. The nature of the

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