![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
1To whom correspondence should be addressed. E-mail: hara{at}chem.agr.hokudai.ac.jp.
 |
ABSTRACT |
|---|
 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
KEY WORDS: • soybean phosphatidylcholine • gastric emptying • food intake • cholecystokinin • rats
Excess food intake causes obesity, which is a serious risk factor in several life-style-related diseases, such as diabetes and hyperlipidemia. Suppression of food intake is important for the prevention of obesity. Moreover, suppression of increased appetite is very important for preventing the development of complications associated with diabetes.
Fat has been shown to suppress short-term food intake in humans (1 ) and a variety of animals (2 ,3 ); it also delays gastric emptying (4 –6 ). Dietary fat is a strong secretagogue of a gut hormone, cholecystokinin (CCK), which is produced in the I-cells in the small intestinal mucosa and is released into the blood. Endogenous CCK plays a role in the inhibition of gastric emptying and in the signaling of satiety. Previous studies showed that a CCK-A receptor-mediated pathway (5 –9 ) is responsible for the effects of dietary lipid-induced CCK release.
Phosphatidylcholine (PC) from biliary sources plays an important role in intestinal lipid absorption (10 ). A previous study showed that dietary PC does not increase triglyceride (TG) absorption (11 ). However, we demonstrated that the intestinal administration of triglyceride containing soybean PC increased the lymphatic output of TG (unpublished data). Raybould et al. (6 ) showed that chylomicron formation is important for the stimulation of CCK secretion by luminal fat and the inhibition of gastric emptying caused by CCK secretion. These results suggest that lipids containing lecithin, which promotes the lymphatic output of chylomicron, enhanced the suppressive effect on gastric emptying and food intake via CCK secretion.
The aim of the present study was to determine whether dietary PC has a greater suppressive effect on gastric emptying and food intake than PC-free oil and whether CCK is involved in the effects of PC.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Experiment 1. Male Wistar rats (Japan SLC, Hamamatsu, Japan), aged 6 wk, were fed a semipurified casein sucrose-based diet (AIN 76 formula) for 5 d. After 24 h of food deprivation, rats were divided into five groups (n = 6/group) and fed 2 g of test diet. The experiment diets contained 20 g lipids/100 g; lipid sources for the test diet were soybean oil (Wako Pure Chemical) and lecithin (60 g soybean lecithin/100 g, Wako Pure Chemical). Test lipids were soybean oil (SO) and SO partially replaced by lecithin (soybean lecithin concentrations: 14, 20, 25 and 50 g lecithin/100 g lipid). The rats were killed under ether anesthesia 3 h after feeding. The stomach was immediately removed after ligation of the pylorus and the end of the esophagus. Gastric contents were collected and the amounts of lipid, protein and sugar were measured.
Experiments 2 and 3. Male Wistar rats (Japan SLC), aged 9 wk, were fed a semipurified casein sucrose-based diet for 5 d. Silicone catheters (Silascon SH No. 00; 0.5-mm i.d., 1.0-mm o.d.; Kaneka Medix, Osaka, Japan) were implanted into the duodenum and the jugular vein (Experiment 3) under anesthesia (sodium pentobarbital, 40 mg/kg body). After a 7-d recovery period, rats were deprived of food for 24 h before the experiment. The test solution, consisting of 100 g test lipid/L, was emulsified with sodium taurocholate (10 g/L) using a sonicator (150 W for 1.5 min, SONICATOR, 5202, Ohtake Seisakusyo, Tokyo, Japan). The lipids in the 0.5-mL test solution for these experiments were as follows: 50 mg soybean oil (Wako Pure Chemical; SO) or 37.5 mg soybean oil plus 12.5 mg lecithin (92% soybean phosphatidylcholine, Epikuron 200, Lucas Meyer, Hamburg, Germany; LE1, 25% lecithin) in Experiment 2; and SO, LE1 or 25 mg soybean oil plus 25 mg lecithin (LE2, 50% lecithin) in Experiment 3.
Gastric emptying was assessed by a modified phenol red recovery technique (12 ,13 ), as described below. Rats were deprived of food overnight and deprived of water for 3 h before the experiment, and then divided into six groups. Rats from three groups were administered an intraperitoneal injection of 500 µg/kg body of the selective CCK-A receptor antagonist, devazepide (ML Laboratories plc, Liverpool, UK); rats from the other groups received its vehicle [5% dimethyl sulfoxide (DMSO)/5% Tween 80/90% saline] 10 min before an intraduodenal infusion of the two test lipid emulsions or saline. Twenty minutes after the intraduodenal lipid infusion (0.5 mL emulsion for 30 s), 4 mL of phenol red (60 mg/L in saline), as a nonabsorbable dilution marker, was administered into the stomach of rats in all groups using a feeding tube (5 Fr, Terumo, Tokyo, Japan) equipped with a 5-mL syringe. Gastric contents were collected 15 min after administration of the marker. To wash the interior of the stomach, 3 mL of saline was instilled into the stomach twice and collected. The gastric contents and wash-out solution were combined, filtered and the absorbance was measured.
The effects of lecithin and devazepide on food intake (meal size) were assessed by the method described below. Rats were deprived of food overnight and deprived of water for 3 h before the experiment. The rats were then administered an intraperitoneal injection of 500 µg/kg body of the selective CCK-A receptor antagonist, devazepide, or its vehicle (5% DMSO/5% Tween 80/90% saline) 10 min before intraduodenal infusion of the 0.5-mL lipid emulsion or saline for 30 min. Fifteen minutes after the end of intraduodenal infusion, the rats were given 15 g of a basal diet for 60 min. After the 60-min ingestion period, the remaining diet was collected and the weight of the uneaten portion was measured. The weight of the ingested diet was calculated by subtraction of the weight of the uneaten portion from the weight of the total diet given. Spilled food was carefully collected and weighed and the meal size was corrected. Each rat was used repeatedly for experiments and allowed an interval of 3–4 d between treatments. Each rat was subjected to three to four of the eight different treatments (four different test solutions with or without devazepide).
Analyses. Protein levels in the gastric contents and diet were measured as total nitrogen content and determined by the micro-Kjeldahl method (14 ). Sugar in the gastric contents and diet was determined as total sugar content by the phenol-sulfuric acid method (15 ). Lipid in the gastric contents and diet was extracted with chloroform/methanol (2:1, v/v) according to the method of Folch et al. (16 ) and measured by weight after the complete evaporation of the extraction solvent. Phenol red in the gastric contents was measured spectrophotometrically at 560 nm after adequate dilution and alkalization with NaOH.
Calculations and statistics. The gastric emptying rate of each nutrient (lipid, protein and sugar) was estimated as the nutrient excreted from the stomach (amount of intake minus the amount remaining) and expressed as a percentage of the nutrient given in the 2-g test diet (Experiment 1). In Experiment 2, the gastric emptying rate was calculated as the percentage of phenol red solution emptied from the stomach.
Data were analyzed by one-way (Fig. 1) or two-way (Figs. 2 and 3) ANOVA. Duncan’s multiple range test was used to determine whether means were significantly different (P < 0.05). Values are means ± SEM.
|
|
|
|
RESULTS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
As the proportion of lecithin in the lipid of the test diet increased, the gastric emptying rate of the dietary lipid in the test diets 3 h after feeding decreased (Fig. 1A ). Rats in all groups ate 2 g of test diet within 5 min, and there were no differences in consumption time among groups. Suppressive effects on lipid emptying were observed from 1.5 to 6 h after consumption of the test diet (data not shown). The gastric emptying rate of protein was decreased to half after feeding with all test diets containing lecithin except for the diet containing lipid with 50% lecithin (Fig. 1 B). Ingested sugar was almost entirely emptied from the stomach 3 h after feeding in all of the groups.
Experiment 2: gastric emptying rate of phenol red solution.
The gastric emptying rate of phenol red solution in rats that were not treated with devazepide was slower in the group administered lecithin than in those administered soybean oil or saline (Fig. 2 ; P < 0.05). Infusion of soybean oil alone did not reduce the gastric emptying rate. Gastric emptying rates did not differ among the three groups of devazepide-treated rats. The rate in treated rats administered lecithin was greater than that in untreated controls fed lecithin.
Experiment 3: food intake after duodenal infusion of lipid emulsion.
Food intake for 60 min after 24-h food deprivation was lower in rats infused with lecithin-containing soybean oil than in rats infused with saline (P < 0.05; Fig. 3 ). Food intake was not reduced by the infusion of soybean oil without lecithin. In the devazepide-treated groups, intraduodenal infusion of lipid containing lecithin did not reduce food intake (Fig. 3) .
|
DISCUSSION |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
First, we examined the effect of feeding a diet containing lecithin on the emptying rate of ingested food components from the stomach. Ingestion of a diet containing lecithin delayed the gastric emptying of lipid and protein in the test diet compared with that of a lecithin-free diet (Experiment 1), except for the gastric emptying of protein of rats fed the diet with 50% lecithin. The reason for the exceptional effect of the diet with the highest level of lecithin is not known. We did not observe any adverse effects on rats fed the high level lecithin diet; however, it is possible that this level of lecithin had other effects on the digestion systems. Further, the effect on the gastric emptying of lipids continued for 6 h after consumption of the test diet. We propose several possible mechanisms that may be involved in the suppression of gastric emptying by lecithin. One possible reason for the delay in gastric emptying with a diet containing lecithin is that lecithin is more viscous than soybean oil. Several studies have shown that increasing meal viscosity delays gastric emptying (20 ,21 ). However, this possibility was ruled out in the present study because the duodenal infusion of a lecithin-containing lipid emulsion also delayed gastric emptying of a marker solution.
Repeated results with the duodenal infusion of lecithin-containing soybean oil demonstrated that the action of dietary lecithin on gastric emptying occurred in the intestine (Experiment 2). In these experiments, we used purified soybean phosphatidylcholine and a lipid emulsion containing 25 g lecithin/100 g test lipid according to the results of Experiment 1. We showed previously that the oral or intestinal administration of TG with soybean PC enhances lymphatic output of TG (unpublished data). Chylomicron formation after TG absorption is reported to be important to the stimulation of CCK secretion by dietary lipid, and CCK is a strong suppressor of gastric emptying. These previous results suggest that soybean oil administered with lecithin is absorbed more rapidly than soybean oil alone, leading to rapid chylomicron formation and increased CCK release.
We demonstrated that the suppressive effect of lecithin on gastric emptying was lessened by an injection of a CCK-A receptor antagonist, devazepide (Fig. 2) , indicating that endogenous CCK has an important role in the reduction of gastric emptying and food intake by luminal lecithin, and that CCK-A receptors are involved in the reduction. Our results are consistent with some previous reports showing that lipids inhibit gastric emptying via CCK-A receptors (2 –9 ). CCK receptors exist on the vagus nerve (22 ), and the suppression of gastric emptying by CCK has been blocked by vagotomy (23 ) or the destruction of visceral afferent neurons by capsaicin treatment (7 ). Therefore, it is possible that the regulation of gastric emptying by CCK depends on vagal innervation. Further studies are required to clarify the involvement of the vagus nerve in the suppressive effect of lecithin.
We also showed that the suppressive effect of lecithin on food intake was diminished by an injection of devazepide (Fig. 3)
, indicating that CCK was also related to the suppression of food intake by lecithin. It is not clear from the present study whether the suppression of food intake by lecithin depends on the retardation of gastric emptying. In Experiment 1, rats in all groups ate 2 g of test diet within 
5 min, and rats did not appear to consume the lecithin-containing diet more slowly. Possibly, meal size was too small or the consumption time was too short for the slowing of gastric emptying by lecithin-induced CCK to affect food intake. Another possibility is that lecithin-induced CCK decreases meal size independently of gastric emptying. Using pylorectomized rats, Moran (24
) showed that the reduction on food intake by CCK is partly independent of gastric emptying.
The suppression of gastric emptying and food intake by lecithin was nearly, but not completely (Figs. 2 and 3) , abolished by intravenous injection of devazepide. This result indicates the possibility that factors other than CCK are involved in the suppressive effects of intestinal lecithin. As described above, we showed that lecithin intake (25 g lecithin/100 g test lipid) enhanced the lymphatic output of TG, which may increase chylomicron formation. Several studies have suggested that the stimulation of apolipoprotein (apo) A-IV production by lipid feeding is associated with the formation of chylomicrons (25 ), and apo A-IV decreases food intake and gastric motor function (2 ,26 ,27 ). Further, other studies showed that the gut hormone peptide YY (PYY) is released from the distal intestine in response to intestinal long-chain fatty acids (28 ) and that this intestinal hormone also inhibited gastric emptying (29 ). Rodriguez et al. (30 ) showed that a bolus dose of [3H] triolein-labeled Intralipid (0.5 mL of a 20 g/100 g emulsion) administered to rats was spread evenly throughout the gut by 15–30 min. It is possible that the duodenally infused lecithin-containing lipid emulsion reached the distal intestine in this study. Although the involvement of apo A-IV and PYY in the lecithin-induced inhibition of gastric emptying and food intake may not be large, the issue of dose requires clarification in the future.
We conclude that lecithin suppresses gastric emptying and food intake. These results depend mainly on the enhancement of CCK release by intestinal lecithin-containing lipids. This effect of lecithin may be associated with efficient TG absorption and chylomicron formation. Use of a lipid containing high levels of lecithin as a food ingredient would be beneficial for therapeutic diets in diabetes or obesity.
|
FOOTNOTES |
|---|
Manuscript received 24 December 2002. Initial review completed 28 January 2003. Revision accepted 16 February 2003.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
1. Greenberg, D. (1992) Cholecystokinin and the satiating effect of fat. Gastroenterology 102:1801-1803.[Medline]
2. Sakata, Y., Fujimoto, K., Ogata, S., Koyama, T., Fukagawa, K., Sakai, T. & Tso, P. (1996) Postabsorptive factors are important for satiation in rats after a lipid meal. Am. J. Physiol. 271:G438-G442.[Medline]
3. Horn, C. C., Tordoff, M. G. & Friedman, M. I. (1996) Does ingested fat produce satiety?. Am. J. Physiol. 270:R761-R765.[Medline]
4. Hunt, J. N. (1968) Control of gastric emptying. Am. J. Dig. Dis. 13:372-375.[Medline]
5. White, W. O., Schwartz, G. J. & Moran, T. H. (2000) Role of endogenous CCK in the inhibition of gastric emptying by peptone and Intralipid in rats. Regul. Pept. 88:47-53.[Medline]
6. Raybould, H. E., Meyer, J. H., Tabrizi, Y., Liddle, R. A. & Tso, P. (1998) Inhibition of gastric emptying in response to intestinal lipid is dependent on chylomicron formation. Am. J. Physiol. 274:R1834-R1838.[Medline]
7. Holzer, H. H., Turkelson, C. M., Solomon, T. E. & Raybould, H. E. (1994) Intestinal lipid inhibits gastric emptying via CCK and a vagal capsaicin-sensitive afferent pathway in rats. Am. J. Physiol. 267:G625-G629.
8. Lloyd, K. C., Holzer, H. H., Zittel, T. T. & Raybould, H. E. (1993) Duodenal lipid inhibits gastric acid secretion by vagal, capsaicin-sensitive afferent pathways in rats. Am. J. Physiol. 264:G659-G663.[Medline]
9. Wank, S. A. (1995) Cholecystokinin receptors. Am. J. Physiol. 269:G628-G646.
10. O’Doherty, P. J., Kasis, G. & Kuksis, A. (1973) Role of luminal lecithin in intestinal fat absorption. Lipids 8:249-255.[Medline]
11. Jiang, Y., Noh, S. K. & Koo, S. I. (2001) Egg phosphatidylcholine decreases the lymphatic absorption of cholesterol in rats. J. Nutr. 131:2358-2363.
12. Feldman, S. & Gibaldi, M. (1968) Effect of bile salts on gastric emptying and intestinal transit in rat. Gastroenterology 54:918-921.[Medline]
13. Feldman, S. & Putcha, L. (1977) Effect of anti-Parkinsonism drugs on gastric emptying and intestinal transit in rat. Pharmacology 15:503-511.[Medline]
14. Ma, T. & Zuazaga, G. (1942) Micro-Kjeldahl determination of nitrogen. A new indication and an improved rapid method. Ind. Eng. Chem. Anal. Ed. 14:280-282.
15. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A. & Smith, F. (1956) Colorimetric method for determination of sugars and related substances. Anal. Chem. 28:350-356.
16. Folch, J., Less, M. & Sloane-Stanley, G. H. (1957) A simple method for the isolation and purification of total lipids from animal tissue. J. Biol. Chem. 226:497-509.
17. Furuse, M., Choi, Y. H., Mabayo, R. T. & Okumura, J. I. (1992) Feeding behavior in rats fed diets containing medium chain triglyceride. Physiol. Behav. 52:815-817.[Medline]
18. Van Wymelbeke, V., Himaya, A., Louis-Sylvestre, J. & Fantino, M. (1998) Influence of medium-chain and long-chain triacylglycerols on the control of food intake in men. Am. J. Clin. Nutr. 68:226-234.[Abstract]
19. Cuche, G., Cuber, J. C. & Malbert, C. H. (2000) Ileal short-chain fatty acids inhibit gastric motility by a humoral pathway. Am. J. Physiol. 279:G925-G930.
20. Haskell, W. L., Spiller, G. A., Jensen, C. D., Ellis, B. K. & Gates, J. E. (1992) Role of water-soluble dietary fiber in the management of elevated plasma cholesterol in healthy subjects. Am. J. Cardiol. 69:433-439.[Medline]
21. Marciani, L., Gowland, P. A., Spiller, R. C., Manoj, P., Moore, R. J., Young, P., Al-Sahab, S., Bush, D., Wright, J. & Fillery-Travis, A. J. (2000) Gastric response to increased meal viscosity assessed by echo-planar magnetic resonance imaging in humans. J. Nutr. 130:122-127.
22. Li, Y., Hao, Y. & Owyang, C. (1997) High-affinity CCK-A receptors on the vagus nerve mediate CCK-stimulated pancreatic secretion in rats. Am. J. Physiol. 273:G679-G685.
23. Smith, G. P., Jerome, C., Cushin, B. J., Eterno, R. & Simansky, K. J. (1981) Abdominal vagotomy blocks the satiety effect of cholecystokinin in the rat. Science (Washington, DC) 213:1036-1037.
24. Moran, T. H. (2000) Cholecystokinin and satiety: current perspectives. Nutrition 16:858-865.[Medline]
25. Hayashi, H., Fujimoto, K., Cardelli, J. A., Nutting, D. F., Bergstedt, S. & Tso, P. (1990) Fat feeding increases size, but not number, of chylomicrons produced by small intestine. Am. J. Physiol. 259:G709-G719.
26. Glatzle, J., Kalogeris, T. J., Zittel, T. T., Guerrini, S., Tso, P. & Raybould, H. E. (2002) Chylomicron components mediate intestinal lipid-induced inhibition of gastric motor function. Am. J. Physiol. 282:G86-G91.
27. Fujimoto, K., Machidori, H., Iwakiri, R., Yamamoto, K., Fujisaki, J., Sakata, T. & Tso, P. (1993) Effect of intravenous administration of apolipoprotein A-IV on patterns of feeding, drinking and ambulatory activity of rats. Brain Res. 608:233-237.[Medline]
28. Hill, F. L., Zhang, T., Gomez, G. & Greeley, G. H., Jr (1991) Peptide YY, a new gut hormone (a mini-review). Steroids 56:77-82.[Medline]
29. Pironi, L., Stanghellini, V., Miglioli, M., Corinaldesi, R., De, , Giorgio, R., Ruggeri, E., Tosetti, C., Poggioli, G., Morselli, , Labate, A. M. & Monetti, N. (1993) Fat-induced ileal brake in humans: a dose-dependent phenomenon correlated to the plasma levels of peptide YY. Gastroenterology 105:733-739.[Medline]
30. Rodriguez, M. D., Kalogeris, T. J., Wang, X. L., Wolf, R. & Tso, P. (1997) Rapid synthesis and secretion of intestinal apolipoprotein A-IV after gastric fat loading in rats. Am. J. Physiol 272:R1170-R1177.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
