Effect of intravenous lipid on gastric acid secretion stimulated by intravenous amino acids

GASTROENTEROLOGY

79:873-876, 1980

Effect of Intravenous Lipid on Gastric Acid Secretion Stimulated by Intravenous Amino Acids ALBERT A. VARNER, JON 1. ISENBERG, JANET D. ELASHOFF, CORNELIS B. H. W. LAMERS, VERNON MAXWELL, and ARTHUR A. SHULKES Department of Medicine, University of California at Los Angeles, and University of California at San Diego, the Center for Ulcer Research and Education (CURE), and the Wadsworth VA Hopsital Center, Los Angeles, California

Intraduodenal fat is a potent inhibitor of all farms of gastric acid secretion in humans. Studies were performed in random order on 3 separate days in 5 normal subjects to determine if intravenous fat (Intralipid) altered gastric acid secretion stimulated by intravenous amino acids in humans. Mean (*SE) gastric acid output during a 4-hr intravenous amino acid infusion (21 g L-amino acids; Freamine II) plus glucose (50 g, to maintain isocaloric and isoosmolar solutions) was 43.2 f 3.2 meq/ hr. Intraduodenal fat fusion (20 g of Intralipid) significantly (IJ < 0.02) suppressed amino acid-stimulated acid output. Interestingly, intravenous fat (20 g of Intralipid) also significantly Cp < 0.02) inhibited acid secretion (14.8 f 6.3 meq/ hr); similar to the effect observed with intraduodenal fat (22.7 f 4.9 meq/ hr). Serum levels of CCK, gastrin, and GIP were measured at 30-min intervals throughout each study. Cholecystokinin and GIP increased signijïcantly from basal during intraduodenal fat infusion. There were no other Received March 6, 1980. Accepted May 23.1980. Address requests for reprints to: Jon 1. Isenberg, M.D., Department of Medicine, Division of Gastroenterology, H-811D, University Hospital, 225 Dickinson Street, San Diego, California 92103. These studies were supported by the National Institute of Arthritis, Metabolism and Digestive Disease Grant #AM 17328 to the Center for Ulcer Research and Education, and Veterans Administration Research Grants. Dr. C. B. H. W. Lamers was supported by the Netherlands Organization for the Advancement of Pure Reserach (ZWO). Dr. Arthur Shulkes was supported by the University of Melbourne, Australia. This paper was presented in part at Digestive Disease Week, New Orleans, Louisiana, May 23, 1979, and published in abstract form in GASTROENTEROLOGY 76:1264,1979. We would like to thank Mrs. Jennifer Abcarian-Lagos for secretarial assistance, and Mr. Daniel Hogan for technical assistance. 0 1980 by the American Gastroenterological Association 0016-5085/80/110673-04$02.25

changes in serum CKK, gastrin, or GIP during any of the other tests. It is concluded that in normal subjects intravenous fat is a potent inhibitor of intravenous amino acid-stimulated gastric acid secretion, similar in effect to intraduodenal fat. The inhibitory effect of inttavenous fat on amino acid-stimulated gastric acid secretion is probably not mediated by release of either CCK or GIP. Circulating fat may play a role in the control of some farms of gastric acid secretion. Intraduodenal fat is a well-recognized and potent inhibitor of gastric acid secretion in both animals and humans.‘- This effect is due to neural and/or humora1 inhibitor factors originating in the duodenum or proximal smal1 intestine. There is evidente, however, that indicates that absorption of fat is necessary for its full inhibitory effect.“” It was therefore our purpose to examine the effect of intravenous fat infusion on amino acid-stimulated gastric acid secretion in humans in order to determine if parenterally infused lipid also inhibited gastric secretion. The responses to intravenous fat were contrasted with intraduodenal infusions of equivalent amounts of fat. To determine whether circulating levels of CCK, gastrin, or GIP were influenced by intravenous fat, each hormone was measured at frequent intervals during each study.

Methods Five normal male subjects mean age of 47 yr (range: 39-59 yr) tient gave informed consent, and proved by the Wadsworth V.A. Human Use Committee.

in good health with a were studied. Each pathese studies Hospita1

were ap-

Research

and

874

VARNER

Table

1.

GASTROENTEROLOGY

ET AL.

Test Solutions

lntravenous 1. Amino acids Glucose Water ll. Amino acids Fat NaCl 111. Amino acids Glucose

Water

g

ml

lntraduodenal

g

ml

21 50

250

NaCl

1.8

200

21 20 6.7 21 50

250 200 134 250 200 134

NaCl

1.8

200

Fat

20

200

200 134

Constituents of the intravenous and intraduodenal infusions administered in random order over 4 hr on 3 separate test days. The amino acids were in the form of Freamine 11, and fat in the form of lntralipid. Each of the intravenous infusions contained a total volume of 584 ml and 305 kcal and were equiosmolar 890 mosm/ kg.

A double-lumen gastroduodenal (Dreiling) tube was modifïed by attaching two pediatrie endotracheal balloons adjacent to one another on either side of the radioopaque marker that separates the gastric from duodenal aspirating holes. A polyethylene tube (PE 150) was attached to the tube assembly so that its distal tip was 1 cm beyond the distal, duodenal balloon. After an overnight fast, the tube assembly was passed under fluoroscopic control until the radioopaque marker was in the proximal duodenum. The distal balloon was inflated with 20 ml of air. The tube assembly was slowly withdrawn until the balloon became anchored at the pylorus. The proximal ballon was then inflated with 20 ml of air in the distal gastric antrum. This secured the balloons so that they straddled the pylorus and prevented flow in either direction across the pylorus. Validation studies using these techniques have been previously described.7 Gastric secretions were collected continuously during a l-hr basal period and during the 4-hr test periods using a pump (Stedman, New York, N.Y.) with 7-10 mmHg negative pressure plus manual aspiration at 5- to 7-min intervals. Gastric aspirates were divided into 15-min samples. Volume was measured to the nearest milliliter. Titratable acidity was determined by titration of O.l-ml portions of each i5-min sample to pH 7.0 with 0.2 M NaOH on an automatic titrator (Radiometer, Copenhagen). Each subject was studied on 3 separate days over a lOday period. After the l-hr basal period, 21.5 g of 15 Lamino acids (250 ml of 8.5% Freamine 11) as a stimulant for gastric acid secretion was infused intravenously over 4 hr using a precisely calibrated infusion pump (IVAC-Ivac Corp., San Diego, Calif.) On 1 of the 3 test days, 50 g of glucose in a volume of 334 ml was infused intravenously with the amino acids over the 4 hr. This served as a control.

The addition of glucose to the amino acid solution permitted an equivalent amount of volume and calories to be infused intravenously when compared with the study when fat plus amino acids were infused intravenously. On another day, 20 g of fat (200 ml of 10% Intralipid) plus 6.7 g of NaCI (134 ml of 5% NaCI) were infused intravenously with the amino acids over 4 hr. NaCI was added to the amino

Vol. 79, No. 5, Part

‘1

acid solution on the day fat was tested to make the two solutions equiosmolar and of equal volume. Therefore, al1 intravenous solutions were equal in calories, volume, and osmolarity. On a 3rd day, the 21 g of amino acids plus 50 g of glucose were administered intravenously, plus 20 g, 300 ml of 10% Intralipid, was infused over the 4 hr into the proximal duodenum via the polyethylene tube. As an additional control measure to obtain an equal volume of duodenal infusate 200 ml of 0.15 M NaCl were infused intraduodenally during the two tests when intravenous glucose or intravenous fat was infused along with the amino acids (Table 1). The three tests were conducted in random order. In 4 of the subjects, 7 ml of blood was withdrawn from an arm vein via an indwelling (19 Ga) scalp-vein needle at 30-min intervals during the 5 hr of each test. The blood was allowed to clot, was centrifuged, and the serum was removed and frozen (-2O’C) until assayed for gastrin, CCK, and GIP. Samples were coded and analyzed without knowledge of the test conditions. The CCK-gastrin antiserum (5135) was raised in a rabbit against synthetic desulfated octapeptide of CCK (CCKSquibb) conjugated to bovine serum albumin. This antiserum bound al1 known molecular forms of CCK and gastrin. The inhibition dose (ID,,) was equal for synthetic unsulfated CCK8 (Squibb), porcine CCK33 (V. Mutt, Karolinska Institute, Stockholm), and gastrin: 3-4 fmol/ml incubation mixture. The concentration of the CCK-like immunoreactivity was obtained by subtracting the gastrin concentration, as measured with gastrin-specific antiserum 1611, from the result obtained with antiserum 5135. Gastrin was measured using antiserum 1611, which binds al1 known molecular forms of gastrin and has only 10

r

;i

IV AMINO

ACID

NORMAL SUBJECTS n=5

Et3

INFUSION-

: T

i

T

T,‘I

t

IV GLUCOSE

? f

xHx,,/x

6_

!S k 40’ 8

a

2_

-1

Figure

1.

0 TIME

2 (30 min

4

6

8

PERIODS)

Mean (+- SE) 30-min acid outputs before (-1 and 0) and during 4-hr intravenous infusion of 21.5 g of L-amino acids (Feamine 11). “+ IV glucose” depicts the results when 50 g of glucose was infused intravenously plus the amino acids; “+ IV fat” indicated the responses when 20 g of fat (lntralipid) was infused intravenously; and, “+ intraduodenal fat” indicates the responses when 20 g of fat was infused intraduodenally. The responses to “+ IV fat” and “+ intraduodenal fat” were each significantly (P < 0.05) different than the response to “+ IV glucose” from periods 4-8.

November

INTRAVENOUS

1980

100

z 1

NORMAL

t IV FAT

Gastrointestinal

Figure 2. Individual 4-hr total acid outputs in response to a 4-hr intravenous infusion of 21.5 g of L-amino acids. “+ IV glucose, ” “+ IV fat,” and “+ intraduodenal fat” as described in the legend to Figure 1. The mean (t SE) responses were: 43.2 & 3.2, 14.8 f 8.3, and 12.7 f 4.9 meq/ 4 hr, respectively. The responses to “+ IV fat” and “+ intraduodenal fat” were each significantly (P < 0.02) less than the response to “+ IV glucose.”

2% crossreactivity with CCK. The ID, of this antiserum was 1 fmol/ml incubation mixture. Antisera to GIP was raised in rabbits immunized with pure porcine GIP (kindly provided by John Brown, University of British Columbia). The ID,, was generally 70 fmol/ml. Secretin, glucagon, and GIP did not crossreact with the antibody at concentrations several orders of magnitude higher than the GIP standard. Al1 samples for the present study were measured within the one assay. The intraassay coefficient of variation for 10 estimations was 5.6%. Hormone results are expressed as mean (+ SE) change from basal during each test according to the following equations:

AB = (H+30 - H,) + (H,,

+ H,/z;

(1)

- HR) . . . + (H+m - Hd/W

where H, = average basal hormone level, B = individual change from basal, and H_,,, H,, H,,, H, . . . = serum hormone leve1 at -30, 0, 30, 60, etc., minutes before or after starting intravenous amino acid infusion. Student’s t-tests for paired and unpaired values were used in statistical analysis.R Differente was considered significant if P was less than 0.05. Results are expressed as mean f SE.

Hormones

The mean (+ SE) change from basal hormone leve1 over the 4 hr in each test is included in Table 2. The only two values significantly different from zero were the CCK and GIP responses during infusion of intravenous amino acids plus duodenal fat, The increases in these hormones were anticipated since the intraduodenal fat is a potent releaser of both CCK and GIP.” Intraduodenal fat, however, had no significant effect on serum gastrin. Also, the other two studies had no significant effect on serum CCK, GIP, or gastrin (Table 2).

Discussion The results of this study indicate that in normal subjects, intravenous infusion of fat, in the form of Intralipid, is a potent inhibitor of gastric acid secretion stimulated by intravenous amino acids. Interestingly, the suppression produced by intravenous fat was almost identical with that produced by intraduodenal fat, one of the most potent enteric nonpharmacologic methods of inhibiting gastric acid secretion. These human observations are in accord with studies in Shay rats, where intravenous infusion of Intralipd markedly inhibited gastric acid secretion.lo,‘l In addition, there is evidente that sug-

Table 2. Mean (*SE) Change in Serum Hormones from Basal (fmoI/mI) i.v. AA + CHO i.v. AA + Fat i.d. NaCl i.d. NaCl

Results Secretory

875

tINTRADUo!:TmL

H, = H-,,

ACID SECRETION

acids plus glucose. Of interest is the response to intravenous amino acids plus intravenous fat. The infusion of intravenous fat plus intravenous amino acids virtually abolished the secretory response. In fact, the response to intraduodenal fat and intravenous fat were almost identical (Figures 1 and 2). The mean (*SE) total 4-hr acid outputs in response to intravenous amino acids plus intravenous fat and intravenous amino acids plus intraduodenal fat (14.8 f 6.3 and 12.7 & 4.9 meq/ hr, respectively) were significantly (P < 0.02) less than response to intravenous amino acids plus glucose, 43.2 + 3.2 meq/ hr.

SUBJECTS n=5

t IV GLUCOSE

LIPID AND GASTRIC

Results

CCK GIP Gastrin

The results of two of the tests were expected (Figure 1): that is, (a) intravenous amino acids plus glucose significantly stimulated gastric acid secretion, and (b) infusion of intraduodenal fat significantly inhibited the response to intravenous amino

a Indicates

0.4 f 2.2 5.1 f

-3.8

f

10.0 4.1

0.3 + 2.4

-28.2 -1.4

f

16.6

f 3.0

i.v. AA + CHO i.d. Fat 8.3 f 1.9'

63.9

f

2.0 f

15.2” 2.0

a significant (Pc 0.05) change from basal. The only changes that were significant were increases in CCK and GIP during intraduodenal fat infusion plus i.v. AA + CHO. i.v. = intravenous, i.d. = intraduodenal, AA = amino acids, and CHO = glucose.

876

GASTROENTEROLOGY

VARNER ET AL.

fat must be absorbed in orgests that intraduodenal der to exert its full inhibitory effect. Menguy demonstrated that the inhibitory effect of intraduodenal olive oil was impaired in the absente of bile and pancreatic juice, and conversely, the inhibitory effect was enhanced by the addition of pancreatic juice and bile.” In dogs, intraduodenal fat had little inhibitory effect on meal- or histamine-stimulated gastric acid secretion in the absente of pancreatic juice.” Konturek and Grossman observed a positive correlation between the amount of fat absorbed in jejunal loops and the degree of inhibition of gastric acid secretion in dogs.” Also, they observed less inhibition of gastric acid secretion when fat was instilled into distal smal1 intestinal loops when compared with loops of proximal smal1 intestine. These observations suggest that enteric lipid inhibits gastric acid secretion by at least two mechanisms: Firstly, fat in the proximal smal1 intestine, particularly in presence of bile and pancreatic juice that may assist in the passage of fat across the intestinal unstirred water layer, inhibits gastric acid secretion by either neural and/or humoral factors, and secondly, after fat is absorbed it also appears to have a direct inhibitory effect on acid secretion. It is not known how intravenous fat exerted its inhibitory effect. Possible mechanisms would be a direct effect on or near the parietal cell, stimulation of inhibitory nerves, or the release of inhibitory hormones (“enterogastrones”). Our results do not point to any one of these mechanisms more than another. However, the results of this study indicate that cir-

Vol. 79, No. 5, Part 1

culating fat, in the form of Intralipid, is a potent inhibitor of gastric acid secretion in humans.

References 1.

2.

3. 4.

5. 6.

10. ll.

12.

Johnson LR, Grossman MI: Intestinal hormones as inhibitors of gastric secretion. Gastroenterology 60:120-144, 1971 Johnston D, Duthie HL: Effect of fat in the duodenum on gastric acid secretion before and after vagotomy in man. Stand J Gastroenter 4:561-567, 1969 Windsor CWO, Cockel R, Lee MJR: Inhibition of gastric secretion in man by intestinal fat infusion. Gut 10:135-141, 1969 Johnson LR, Grossman MI: Effects of fat, secretin and cholecystokinin on histamine-stimulated gastric secretion. Am J Physiol 216:1176-1179, 1969 Sircus W: Studies on the mechanisms in the duodenum inhibiting gastric secretion. Q J Exp Phys Surg 4~114-133, 1958 Menguy R: Studies on the role of pancreatic and biliary secretions in the mechanism of gastric inhibition by fat. Surgery 48:195-200, 1960 Isenberg JI, Ippoliti AF, Maxwell VL: Perfusion of the proximal smal1 intestine with peptone stimulates gastric acid secretion in man. Gastroenterology 73:746-752, 1977 Cochran WG, Snedecor GW: In: Statistical Methods. Sixth edition. Ames, Iowa, Iowa State University Press, 1967 Brown JC, Dryburgh JR. Moccia P, et al: The current status of GIP. In: Gastrointestinal Hormones. A Symposium. Edited by JC Thompson. Austin and London, University of Texas Press, 1975, p 537 Baume PE, Meng HC, Law DH: Intravenous fat emulsion and gastric secretion in the rat. Am J Dig Dis ll:l-9. 1966 Vecchioni R. d’Amico D, Cordiano C, et al: Gastric secretions upon intravenous administration of Iipidic emulsions. Acts Chir Ital 22 (Suppl 1):129-136, 1966 Konturek S, Grossman MI: Effect of perfusion of intestinal loops with acid, fat, or dextrose on gastric secretion. Gastroenterology 49:481-489, 1965