Influence of Glucagon on the Human Jejunum

Vol. 67, No.6

67:1114-1118, 1974 Copyright© 1974 by The Williams & Wilkins Co.

GASTROENTEROLOGY

Printed in U.S.A.

INFLUENCE OF GLUCAGON ON THE HUMAN JEJUNUM T. HICKS AND

L. A.

TURNBERG,

M.D., F.R.C.P.

Department of Gastroenterology, Manchester Royal Infirmary, Manchester, England

Porcine pancreatic glucagon given by intravenous infusion reduced absorption of Na+, Cl - , and water in the human jejunum. A doseresponse curve for glucagon indicated that the effect on ion transport was maximal to 0.6 J.Lg per kg-hr, and this effect decreased as the dose was increased, until, at a dose of 2.7 J.Lg per kg-hr, ion transport was unaffected. The mean transit time was increased by glucagon in a dose of 1.2 J.Lg kg-hr, and the calculated volume and diameter of the jejunum was also increased. The levels of plasma concentration calculated to have been achieved by these infusions were above those reported under physiological conditions, but they were within the range which could conceivably be found in pathological conditions where these observations may have some relevance. Recent evidence has suggested that glucagon may influence intestinal ion transport1-3 and gastrointestinal motility.•· 5 Glucagon induced a net intestinal secretion of salt and water in dogs, and, when a small background dose of pentagastrin was given, a massive watery diarrhea resulted, 6 prompting comparisons with cholera. 6 • 7 In man and dogs, gastric, jejunal, and colonic motility was also markedly inhibited by glucagon. 4 • 5 These observations raise the possibility that this hormone may be concerned in the control of normal intestinal absorptive and secretory function and motility, or in the pathogenesis of disturbances in these functions, and investigations were performed to assess these possibilities in man.

Methods In order to measure jejunal net transport of salt and water, the triple lumen tube perfusion Received November 15, 1973. Accepted June 17, 1974. Address requests for reprints to: Dr. L. A. Turnberg, Department of Medicine, Hope Hospital , Eccles Old Road, Salford 6, England . The authors are grateful to the Medical Research Council, The Wellcome Foundation, and the Board of Governors of the United Manchester Hospitals for the financial support for this project.

technique of Cooper et al. 8 was used in a group of 22 normal adult volunteers who were healthy students, with an age range of 18 to 34 years. The tube was sited radiologically with the infusion port at or just beyond the level of the ligament of Treitz. After an overnight fast, the jejunum was perfused at 10 ml per min with an isotonic saline solution (NaCl, 140 mEq per liter) containing the poorly absorbed marker, polyethylene glycol4000. After a 30-min equilibration period, perfusion was continued for a 60-min control collection period. This was followed by a similar perfusion study, but, on this occasion, a commercially available porcine pancreatic glucagon (Eli Lilly and Co., Indianapolis, Ind.) was infused intravenously during the whole period. An intravenous infusion of isotonic saline was continued during the whole of the control and study periods through an infusion set at the rate of 250 ml per hr . During the study period, the saline was changed to a saline plus glucagon solution infused at the same rate. Fresh glucagon was made up and diluted for each test, and only one dose level was tested in each individual study. The number of studies at each dose of glucagon is indicated under "Results" and in figure 2. In 7 subjects, the mean transit time of a bolus of dye down the test segment of intestine was measured after collections for the ion transport determinations had been obtained in six of these seven studies. In the seventh study, ion transport measurements were not possible because of accidental contamination of speci-

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December 1974

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GLUCAGON ON HUMAN JEJUNUM

mens . The transit time determinations were made according to the method of Dillard et al. 9 ; a single rapid pulse of bromosulfophthalein was injected through the infusion tube during the constant infusion of saline (10 ml per min), and samples were taken at 1-min intervals from an aspiration point 40 em distally. The dose of glucagon used in these studies was 1.2 llg per kg·hr. Sodium was measured with an E.E.L. flame photometer, chloride with an E.E.L. chloridemeter, and polyethylene glycol by the turbidometric method of Hyden. 10 Bromosulfophthalein was measured colorimetrically.

data for the effects of these two doses of glucagon did not reach statistical significance when taken separately, when the results of both doses were combined, the difference between control values and glucagon values were significant (P < 0.05) (fig. 1.). No obvious effect on transport was detected in 4 subjects given 0.3 J.~,g per kg-hr of glucagon, and doses of 1.9 (4 subjects) and 2.7 J.~,g per kg-hr (2 subjects) exerted an apparently diminishing effect compared with a dose.of0.6 J.~,g per kg-hr (fig. 2.). The effects of different doses on chloride and water transport mirrored that shown for sodium transport (fig. 2.). In 3 subjects given more than 5 J.~,g per kg-hr, nausea and vomiting occurred and the tests had to be terminated. In the 7 subjects in whom a mean transit time (MTT) was measured, glucagon caused a significant increase in MTT (fig. 3.). The mean volume of the test segment of intestine was calculated from the flow rate and MTT using the formula:

Results The maximal effect on ion transport was noted in 5 subjects given glucagon in a dose of0.6 {.lg per kg-hr, where net absorption of water was reduced from a mean of 78.6 ml per hr to a net secretion of 1.16 ml per hr; sodium and chloride absorption were reduced from 9.8 and 10 .3 mEq per hr to a net secretion of 1.86 and 1.3 mEq per hr, respectively. A dose of 1.2 J.~,g per kg-hr in 6 subjects also reduced absorption of water from a mean value of 50 .6 ml per hr to 4.2 Volume = MTT x flow rate ml per hr; sodium absorption was reduced from 6 .0 mEq per hr to a net secretion of This parameter was also significantly in0.88 mEq per hr, and chloride absorption creased, as was the calculated diameter of from 5 .3 to 1.8 mEq per hr. Although the the intestine (fig. 3.), suggesting t hat glu-20

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each pair of histograms represents the mean of control values, and the second the mean value during glucagon administration. One standard error of the mean is indicated . The negative sign on the axes indicates net absorption , and the positive sign, net secretion ; n = 11.

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Vol . 67, No . 6

cagon had dilated the small intestine and and our results demonstrate that glucagon slowed the rate of transit of fluid through is capable of inducing net intestinal secretion in man also. The dose of glucagon of it. 0.6 J.Lg per kg-hr, at which a maximal effect on ion transport was observed, can be Discussion calculated to have probably achieved In the dog jejunum, glucagon has been steady state levels within the plasma some shown to induce a net intestinal secretion, 1 2 to 3 times the levels normally found in plasma under physiological conditions. The dose of 0.3 J.Lg per kg-hr, which was shown not to influence ion transport, probably provides a plasma level at the upper limit of the normal range, at about 250 pg per ml. These observations suggest that in the physiological range glucagon exerts little or no influence on ion transport, and .:rE +10 this is compatible with the recent observations of Whalen and co-workers" who reported in abstract that glucagon, released endogenously by alanine infusion, did not influence ion transport. The reduced effect on ion transport of ' ' ' higher doses of glucagon in our studies is 0 - - - - - - - - - - - - - - - - - - - ::.......~- • unexplained, but could have resulted, for instance, from the local accumulation at a receptor site of inactivated glucagon, -5 which could reduce the accessibility of the receptor to active glucagon. GLUCAGON DOSE ( pg / kg / hour) The inhibition of jejunal motility conFIG. 2. The changes in Na+ transport produced by firms earlier reports of an effect of glucagon various doses of glucagon. One standard error of the on gastrointestinal motility. 4 • 5 It is possimean is indicated. On the vertical axis, the positive ble that this effect, in contradistinction to sign indicates reduction in net absorption. There were only two points obtained at the highest dose . Changes the effect on ion transport , is physiological , in Cl - absorption were almost identical with those since Whalen et al.'' demonstrated that shown here for Na + n = 4 at 0.3 ; 5 at 0.6; 6 at 1.2; 4 at endogenously released glucagon did influence human jejunal motility. 1.9; and 2 at 2.7 Jig per kg-hr. 40

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FIG. 3. The influence of glucagon (1.2 11g per kg-hr) on transit time and on the calculated volume and mean diameter of the test segment of jejunum. The points on the left of each set of lines are control values, and those on the right are values obtained during glucagon administration.

December 1974

GLUCAGON ON HUMAN JEJUNUM

The possibility that the influence of glucagon on ion transport was secondary to its effect on motility cannot be excluded, since little is known of the influence of motility on transport. Another possibility, that the influence on transport was secondary to an effect of glucagon on intestinal blood flow, cannot be excluded either. All subjects given glucagon in doses greater than 0.3 JJ.g per kg-hr developed a sharp attack of watery diarrhea after the infusion was stopped, lasting approximately 2 hr. Unfortunately, this was not quantitated, but it was clear to the investigators and to the subjects of the studies that it was more marked than had previously been noted after intestinal perfusion with saline for similar periods of time in the absence of glucagon. It seems likely that the diarrhea produced in these subjects was related to the combination of inhibition of ion and water absorption with inhibition of intestinal motility. The combination of depressed salt and water absorption with a flaccid immobile intestine would tend to cause fluid to be evacuated at a similar rate to that at which it entered from endogenous secretions and infused fluid. The observation of Barbezat and Grossman 6 that glucagon alone did not induce diarrhea in dogs or in 2 human subjects, while its combination with pentagastrin did, is not incompatible with this observation. In their studies, fluid was not infused into the intestine, and it may be required in order for diarrhea to be produced by glucagon alone. The lack of reports of diarrhea in patients given prolonged courses of large doses of glucagon for resistent heart failure 12 ' 13 may also be due to the lack of intraluminal fluid infused, as in our studies, or secreted, as with our much lower doses of glucagon. Although an effect on ion transport was only observed at probably unphysiological levels , it is possible that this effect may have relevance to certain pathological conditions in which elevated levels may be found. Patients with the "dumping syndrome, " in which diarrhea may be a prominent feature, have been shown to have elevated levels of enteroglucagon, 14 a hormone resembling glucagon, liberated from

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the intestinal tract. Although high plasma levels of vasoactive intestinal polypeptide have been reported 15 in patients with the severe cholera-like diarrhea of the VernerMorrison syndrome, it remains possible that in some of these patients glucagon may also play a role. A number of the gastrointestinal hormones have recently been reported to influence intestinal ion transport. 2 • 16 - 18 These have been shown to reduce net ion absorption or induce net ion secretion. Exogenous pentagastrin, 18 secretin, 1 7 cholecystokinin, 16 and the more recently isolated polypeptides, gastric inhibitory polypeptide, and vasoactive intestinal polypeptide 1 have each been shown to be capable of inducing a net intestinal secretion, or at least of reducing net absorption in animals, and some have also been demonstrated to be active in man. However, a physiological role in intestinal transport for any of these hormones or glucagon remains speculative. REFERENCES 1. Barbezat GO: Stimulation of intestinal secretion by polypeptide hormones. Scand J Gastroenterol 8 (suppl 22):1-21, 1973 2. Ganeshappa KP, Whalen GE, Meade RC, et al: The effect of glucagon on jejunal motility, electrolyte and water absorption in man (abstr). Clin Res 19:658, 1971 3. Mekhjian H, King D, Sanzenbacher L, et al: Glucagon (GI) and Secretin (Se) inhibit water and electrolyte transport in the human jejunum (abstr). Gastroenterology 62:782, 1972 4. Kock NG, Darle N, Dotevall G: Inhibition of intestinal motility in man by glucagon given intraportally. Gastroenterology 53:88-92, 1967 5. Necheles H, Sporn J, Walker L: Effect of glucagon on gastrointestinal motility. Am J Gastroenterology 45:34-39, 1966 6. Barbezat GO, Grossman MI : Cholera like diarrhoea induced by glucagon plus gastrin. Lancet 1:1025- 1026, 1971 7. Barbezat GO, Grossman MI: Intestinal secretion: stimulation by peptides. Science 1974:422-424, 1971 8. Cooper H, Levitan R, Fordtran JS, et al: A method for studying absorption of water and solute from the human small intestine. Gastroenterology 50: 1-7, 1966 9. Dillard RL, Eastman H, Fordtran JS: Volume flow relationships during the transport of fluid through the human small intestine. Gastroenterology 49: 58-66, 1965

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10. Hyden S: A turbidometric method for determination of higher polyethylene glycols in biological materials. Ann R Agri Col! Sweden 22:139- 145, 1956 11. Whalen GE, Wu WC, Ganeshappa KP, eta!: The effect of endogenous glucagon on human small bowel function (abstr.) Gastroenterology 64:822, 1973 12. Murtagh JG, Binnion PF, La! S, eta!: Haemodynamic effects of glucagon. Br Heart J 32: 307-315, 1970 13. Vanden Ark, Reynolds EW : Clinical evaluation of glucagon by continuous infusion in the treatment of low cardiac output states. Am Heart J 79:481487, 1970 14. Bloom SR, Royston CMS, Thompson JPS: En-

15.

16.

17.

18.

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teroglucagon release in the dumpsing syndrome. Lancet 2:789-791, 1972 Bloom SR, Polack JM, Pearse AGE: Vaso-active intestinal peptide and watery-diarrhoea syndrome. Lancet 2:14- 16, 1973 Moritz M, Finkelstein G, Meshkinpour H, et a!: Effect of secretin and cholescystokinin on the transport of electrolyte and water in human jejunum. Gastroenterology 64:76-80, 1973 Hicks T, Turnberg LA: The influence of secretin on ion transport in the human jejunum. Gut 14: 485- 490, 1972 Modigliani R, Mary JY, Bernier JJ : The effect of pentagastrin upon movements of water, electrolysts and glucose across the human jejunum and ileum. Digestion 9:208- 219, 1973