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Effect of dietary fat on biliary lipids composition of gallbladder bile in miniature swine (Sus scrofa)
Camp. Biochem. Physiol. Vol. IDOA,No. 3, Printed in Great Britain
pp. 745-748, 1991
COMPARATIVE
0300-9629/91 $3.00 + 0.00 0 1991 PergamonPre&s plc
NUTRITION
PAPERS
EFFECT OF DIETARY FAT ON BILIARY LIPIDS COMPOSITION OF GALLBLADDER BILE IN MINIATURE SWINE (SUS SCROFA) M. C. BALLESTA,E. MARTINEZ-VICTORIA, M. MARAS,I. SEIQUER,J. R. HUERTA~and F. J. MATAIX Instituto de Nutrici6n y Tecnologia de 10s Alimentos, Department0 de Fisiologia, Facultad de Farmacia, Universidad de Granada, 18071 Granada, Spain (Received 2 January 1991) Abstract-l. Weaning animals (34 days old) were fed for 6 months with four diets that differed only in the quantity and quality of fat sources (control group 3.2% (w/w), lard-fed group 7.6% (w/w), olive-oil-fed group 10.4% (w/w), and sunflower-oil-fed group 10.5% (w/w). Samples were collected and assessed after animals were killed at 6 months of age. 2. Our results show that the quality of fat did not alter biliary lipids composition of the gallbladder bile composition in miniature swine after 6 months adaptation to the diet, except for a significant increase of the phospholipid concentration in the lard-fed group with regard to the control group. 3. The highest and lowest bile cholesterol saturation indices were observed in sunflower and lard-fed groups, respectively showing in all cases saturation indices far from the saturation point.
INTRODUCTION Dietary fat quantity and quality induce changes in the lipid composition of bile (Ladas et al., 1984; Juste et al., 1983) just as do the enterohepatic circulation (Juste et al., 1985), food intake (Traynor et al., 1984) or fasting (Bloch et al., 1980).
With regard to dietary fat quality in man, it has been pointed out that the long chain triglycerides (LCT) stimulate gallbladder emptying and increased duodenal bile salt concentration, compared to the medium chain triglicerydes (MCT) (Ladas et al., 1984). Also in man, an overdose of olive oil intake induces a slight increase of bile cholesterol concentration whereas no modification is observed when an overdose of maize oil was given (Schuller et al., 1980). Moreover, when feeding a diet containing a standard quantity of olive oil, increased bile acids have been observed as occur when feeding a maize-oil-based regimen, although the latter resulted in decreased cholesterol saturation index (CSI), although not significantly important, has been observed as compared to the control diet (Kholmeier et al., 1980). In studies performed on pigs, Juste et al. (1983) studied how the amount of dietary fat affected bile secretion in the pig, and found that bile flow rate and bile acid secretion rose with dietary fat content ranging between 2 and IO%, but failed to rise further after feeding with a diet containing 20% fat. In the latter case only, was an increase observed in biliary phospholipids. A positive correlation was also found between the amount of dietary fat and the biliary secretion of cholesterol. Cholesterol is bile soluble as a result of the capacity of bile salts and phospholipids to maintain cholesterol in micellar solution (Admirand et al., 1968).
The relative solubility of cholesterol in bile is determined by bile CSI. Values exceeding 1 indicated the presence of supersaturated bile (Kholmeier et al., 1980) and in general a high degree of supersaturation is associated with lithogenicity (Drapers et al., 1987), being the orderly sequence occurring in the lithogenesis as follows: (a) alteration in biliary lipids, (b) nucleation of cholesterol crystals in presumably supersaturated bile and (c) stone formation (Holzbach et al., 1976). Bile cholesterol saturation index is affected by multiple factors among which dietary habits, and more specifically changes in dietary macronutrients, play an important role. In pig, an increased CSI ratio has been found in animals fed on 10% sunflower oil as compared to those fed on 2-10% lard-based diet (Juste et al., 1985). It has also been documented that, in man, hepatic bile collected in fasting conditions is more lithogenic than hepatic or gallbladder bile in response to food intake (Metzger et al., 1973). The purpose of this study on miniature pigs, was to determine whether the long-term adaptation to diets that differed only in the fat source (different degrees of saturation) influenced the biliary lipid composition of the gallbladder bile and the CSI. MATRRULSANDMETHODS Animals
and diet
A total of 24 miniature pigs (Sus scrofa) weighing 20-57 kg were studied. The pigs were supplied by the Comunidad Autonoma de Madrid to the Gregorio Maraii611 Hospital. After weaning (34 days old) animals were randomly allocated to four equal experimental groups being fed four test diets until they were aged 6 months. Experimental groups and diets were as follows: Control group (C) was fed a standard swine stock diet (developing
745
M.C. BALLESTAetal.
146
Table 1. Composition of macronutrients Diet
Control (C) 3930.0 177.0 32.0 670.0 50.0 71.0 19.3 7.8 72.9
Energy (kcal/kg) Brut protein (g/kg) Fats (g/kg) Carbohydrates (g/kg) Fibre (g/kg) Ash (g/kg) Protein (% energy) Fats (% energy) Carbohydrates (% energy)
of the experimental diets Olive (0)
Lard (L) 3930.0 170.0 76.0 650.0 37.0 67.0 17.2 17.3 65.6
Sunflower (S)
3930.0 193.0 104.0 594.0 43.0 66.0 18.9 22.9 58.2
3930.0 201 .o 105.0 562.0 44.0 88.0 20.1 23.6 56.2
Table 2. Fatty acid composition of the experimental diets Diet
Control (C)
Lard (L)
Olive (0)
Sunflower (S)
21.1 22.9 31.5
21.2 34.9 24.1
13.8 62.9 16.3
10.6 26.2 52.9
Palmitic (%) Oleic (%) Linoleic (%)
The fatty acid contents are expressed as a percentage of total.
swine NANTA R, Madrid, Spain). The lard group (L) was fed a basal feeding regimen for pigs (AVICU, S.A., Guadalajara, Spain) which contained the following ingredients: barley, bran, soy, salt, phosphate, carbonate, enriched with a mineral and vitamin mixture. This fat-free chow was supplemented with animal fat (bovine lard). Sunflower group (S): the basal feeding regimen was supplemented with sunflower oil (Koipesol R. Koipe, S. A.). Olive-oil group (0): the basal feeding regimen was supplemented with virgin olive oil (Patrimonio Comunal Olivarero). Detailed dietary macronutrients and fatty acids are shown in Tables 1 and 2, respectively. Procedure and sample collection
Animals of each experimental months’ feeding on the respective period, swine were anesthetized S.A.) and gallbladder bile was syringe and subsequently divided stored at -20°C until analysis.
group were killed after 6 diets. After a 24 hr fasting with Ethrane R (Abbot, collected into a sterilized into three vacutainers and
Phospholipids were determined by standard calorimetry (Boehringer, No. 691844). Cholesterol was also determined by standard calorimetry (Boehringer methods CHOD-PAP, no. 237576) based on an enzymatic reaction according to Seidel et al. (1981) after previous removal of proteins and bile pigments according to Lcvin et al. (1961). Bile acids were determined according to an enzymatic method with 3 a-hydroxysteroid dehydrogenase (STEROGNOST 3 a-Pho; Nyegaard & Co. AS. Oslo).
0
Statistical analyses
All the results were expressed as means f SEM. Data were compared following a one way analysis of variance (One Way, SPSS/PC+) subjected to Scheff&‘s test to compare the four groups. Student’s r-test was also used to compare the mean differences between the groups. Differences were considered significant if P < 0.05. RESULTS
Sample analysis
260
In all case results are expressed as mmol/l. The critical tables of cholesterol solubility constructedby Carey were used to calculate the percentage of cholesterol present at saturation (Carey, 1978). To calculate the CSI of a sample (Thomas and Hoffmann, 1973), one takes actual mole per cent of cholesterol in the sample and divides this by the mole per cent of cholesterol present at saturation, determined by the tables of Carey (Carey, 1978).
The concentration of biliary acids in bile gallbladder did not differ significantly in the four exper-
imental groups, although in the lard-fed group, values were slightly increased (Fig. 1). The cholesterol content was similar in all groups (Fig. 2) and we found the highest mean value in the sunflower-fed group and the lowest one in the olive-oil group. Phospholipid concentration evidenced a significant increase (P < 0.05) in miniature pigs fed on animal fat (bovine lard) (Fig. 3). Finally, the CSI did not
r
convol
lard
Sunfkaiver
OliiO
Fig. 1. Bile acid concentration (mmol/l) in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6), with their standard errors represented by vertical bars. Mean values for the four dietary groups were significantly different: ‘P < 0.05.
Fig. 2. Cholesterol concentration (mmol/l) in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6), with their standard errors represented by tical bars. Mean values for the four dietary groups were significantly different: *P < 0.05.
Dietary fats and gallbladder bile 18 a
18
1
‘*
g
‘:
g
8
E n
4 2 0
l
T
Control
Lard
Sunflower
Olii
Fig. 3. Phospholipid concentration (mmol/l) in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6), with their standard errors represented by vertical bars. Mean values
for the four dietary groups were significantly different: *P < 0.05. differ significantly in the four experimental groups (Fig. 4) ranging from 0.22 to 0.32 with mean values far from the saturation point. The highest saturation indices were shown in the sunflower-oil-fed group. DISCUSSION
According to these results, neither the quantity nor the quality of dietary fat (lard, olive or sunflower oil) alter significantly the biliary lipid composition of gallbladder bile in miniature swine when compared to a control group fed on a standard chow diet, except for the concentration of phospholipids that increase significantly in lard bovine group. On the other hand, the highest values of all parameters measured were reported in the bovine-lard-fed group (rich in saturated fatty acids). If we compared our results in miniature pig to those reported by Juste et al. (1983) in large white pigs (L-W) we noticed that in L-W pigs an increase of phospholipids occurs when diet has at least 10% of lard, while in our experiments, this increase occurred with a lower quantity of dietary fat, more specifically 7.5% of bovine lard, perhaps because of the different times of adaptation to the diet used in both studies. Besides, bile salts concentration were markedly decreased in L-W pigs fed with diets that have 2-20%
.$ z
0.30
iiii 0.20
e $
of pig-lard as compared to values obtained in miniature pigs in all the experimental groups. On the other hand, in control and olive-oil groups, phospholipids were similar to values reported in L-W animals fed 2 and 10% pig-lard diets whereas in bovine-lard and sunflower-oil groups, values of phospholipids are similar to those reported for L-W fed a 20% pig-lard diet. Cholesterol concentration was always higher in miniature swine fed any of the four different diets. In another experimental study performed on L-W swine (Juste et al., 1986) it has been documented that when feeding a 10% (w/w) sunflower-oil diet or pig-lard diet, the concentration of bile salts was similar in both groups, whereas concentrations of phospholipids and cholesterol were higher in the sunflower-oil-fed group. When comparing these results to those obtained in miniature swine fed bovine lard and sunflower oil, we found that both phospholipids and bile salts were increased in miniature swine fed lard, and only cholesterol was slightly higher in sunflower oil-fed animals. These differences are probably due to the fact that values found in L-W are the mean of 24 hr bile sampling, meanwhile the values obtained in our experimental study responded to precise gallbladder bile sampling and it is known that flow rate and bile composition change throughout the day (Metzger et al., 1973). If we observe the values obtained only in miniature swine, we see that values of biliary lipids when fed an olive-oil diet are similar to those obtained in control group, whereas in sunflower and bovine-lard groups, values of biliary lipids are higher. We only found significant differences in the concentration of phospholipids between control and bovine-lard groups. If we compare the concentrations of biliary lipids in miniature swine to normal values substantiated in humans (Schuller et al., 1980) we observe that miniature swine show a concentration of bile salts much higher and cholesterol and phospholipids concentrations lower than that reported in man. So this study suggests that miniature swine are not similar to man when considering the biliary lipid composition. Finally, we observed that in all the experimental feeding regimens, the CSI ratio is far from the saturation point (CSI c 1) which shows that in minature swine and under this experimental design, the quantity and quality of dietary fat do not significantly affect bile CSI ratio. However, the highest and lowest CSI ratios were reported in sunflower oil- and lardbased diets respectively which would agree with the results reported in L-W swine when fed sunflower or pig lard (Juste et al., 1985). REFERENCES
0.10
3 5
0
747
Control
Lard
Sunflower
Olii
Fig. 4. Cholesterol saturation index in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6) with their standard error represented by bars. Mean values for the four dietary groups were significantly different: *P c 0.05.
Admirand W. H. and Small D. M. (1968) The physicochemical basis of cholesterol gallstone formation in man. J. clin. Invest. 47, 1043-1052. Bloch H. M., Thorthon J. R. and Heaton, K. W. (1980) Effect of fasting on the composition of gallbladder bile. Gut 21, 1087-1089. Carey M. C. (1978) Critical tables for calculating the cholesterol saturation of the native bile. J. Lipid Rex 19. 945-955.
748
M.C. BALLESTAetal.
Drapers J. A. G., Groen A. K., Stout J. P. J., Nordam C., Hoek F. J.. Jansen P. L. M. and Tvtaat G. N. J. (1987) Quantification of cholesterol nucleation promoting activity in human gallbladder bile. C/in. C&m. Acta 165, 295-302. Holxbach R. T., Corbusier C., Marsh M. and Naito H. K. (1976) The process of cholesterol cholelitiasis by diet in the prairie dog: a physiochochemical characterization. J. Lab. Clin. Med. 987-988. Juste C., Demame Y. and Corring T. (1983) Response of bile flow, biliary lipids and bile acid pool in the pig to quantitative variations in dietary fats. J. Nutr. 113, 1691-1701. Juste C., Corring T. and Demame Y. (1985) Effect du regime lipidique sur la saturation de la bile en cholesterol chew le p&c. Effect of a lipid diet on cholesterol saturation in the bile of pigs. Reprod. Nutr. Dbelop. 25, 815. Juste C., Demame Y. and Corring T. (1986) Effet du niveau et de la qualite de linger6 lipidique sur la secretion biliaire du vorc en croissance. Rerwod. Nutr. Divelou. 26, 1191. Kholmeier M., Oster P., Schellenberg B. Stiehl A. and Schilier G. (1980) Effect of lipid lowering diets on bile lipids in healthy young men. Proceedings of the IIIrd
International Congress on the Biological Value of Olive Gil, pp. 2855305. Ladas S.D., Isaacs P.E.T., Murphy G. M. and Slader G. E. (1984) Comparison of the effects of medium chain triglycerides containing liquid meals on gallbladder and small intestinal function in normal man. Gur 2S, 405-411. Levin S. J., Jhonston C. G. and Boyle A. J. (1961) Spectrophotometric determination of several bile acids as conjugates extraction with athyl-acetate. Analyf. Chem. 33, 1407. Seidel J., Schulmberger H. and Klose S. (1981) Boehringer Manmheim Gmbh. J. c/in. Chem. Bio&em..l9, 838. Schuller A.. Diax-Rubio M.. Esteban J. and Errot L. (1980) Variaciones de la compo&ion de la bilis en relation a 1; grass de la dieta. Proceedings of the IIIrd International Congress on the Biological Value of Olive Oil, pp 263-272. Thomas P. J. and Hofmann A. F. (1973) A simple calculation of the lithogenic index of bile: expressing biliary lipid composition on rectangular coordenates. Gastroenrerologi 65, 698-700. Traynor 0. J., Dozois R. R. and Dimagno E. P. (1984) Canine interdigestive and postprandial gallbladder motility and emptying. Am. J. Physiol. 246, G426-G432.
pp. 745-748, 1991
COMPARATIVE
0300-9629/91 $3.00 + 0.00 0 1991 PergamonPre&s plc
NUTRITION
PAPERS
EFFECT OF DIETARY FAT ON BILIARY LIPIDS COMPOSITION OF GALLBLADDER BILE IN MINIATURE SWINE (SUS SCROFA) M. C. BALLESTA,E. MARTINEZ-VICTORIA, M. MARAS,I. SEIQUER,J. R. HUERTA~and F. J. MATAIX Instituto de Nutrici6n y Tecnologia de 10s Alimentos, Department0 de Fisiologia, Facultad de Farmacia, Universidad de Granada, 18071 Granada, Spain (Received 2 January 1991) Abstract-l. Weaning animals (34 days old) were fed for 6 months with four diets that differed only in the quantity and quality of fat sources (control group 3.2% (w/w), lard-fed group 7.6% (w/w), olive-oil-fed group 10.4% (w/w), and sunflower-oil-fed group 10.5% (w/w). Samples were collected and assessed after animals were killed at 6 months of age. 2. Our results show that the quality of fat did not alter biliary lipids composition of the gallbladder bile composition in miniature swine after 6 months adaptation to the diet, except for a significant increase of the phospholipid concentration in the lard-fed group with regard to the control group. 3. The highest and lowest bile cholesterol saturation indices were observed in sunflower and lard-fed groups, respectively showing in all cases saturation indices far from the saturation point.
INTRODUCTION Dietary fat quantity and quality induce changes in the lipid composition of bile (Ladas et al., 1984; Juste et al., 1983) just as do the enterohepatic circulation (Juste et al., 1985), food intake (Traynor et al., 1984) or fasting (Bloch et al., 1980).
With regard to dietary fat quality in man, it has been pointed out that the long chain triglycerides (LCT) stimulate gallbladder emptying and increased duodenal bile salt concentration, compared to the medium chain triglicerydes (MCT) (Ladas et al., 1984). Also in man, an overdose of olive oil intake induces a slight increase of bile cholesterol concentration whereas no modification is observed when an overdose of maize oil was given (Schuller et al., 1980). Moreover, when feeding a diet containing a standard quantity of olive oil, increased bile acids have been observed as occur when feeding a maize-oil-based regimen, although the latter resulted in decreased cholesterol saturation index (CSI), although not significantly important, has been observed as compared to the control diet (Kholmeier et al., 1980). In studies performed on pigs, Juste et al. (1983) studied how the amount of dietary fat affected bile secretion in the pig, and found that bile flow rate and bile acid secretion rose with dietary fat content ranging between 2 and IO%, but failed to rise further after feeding with a diet containing 20% fat. In the latter case only, was an increase observed in biliary phospholipids. A positive correlation was also found between the amount of dietary fat and the biliary secretion of cholesterol. Cholesterol is bile soluble as a result of the capacity of bile salts and phospholipids to maintain cholesterol in micellar solution (Admirand et al., 1968).
The relative solubility of cholesterol in bile is determined by bile CSI. Values exceeding 1 indicated the presence of supersaturated bile (Kholmeier et al., 1980) and in general a high degree of supersaturation is associated with lithogenicity (Drapers et al., 1987), being the orderly sequence occurring in the lithogenesis as follows: (a) alteration in biliary lipids, (b) nucleation of cholesterol crystals in presumably supersaturated bile and (c) stone formation (Holzbach et al., 1976). Bile cholesterol saturation index is affected by multiple factors among which dietary habits, and more specifically changes in dietary macronutrients, play an important role. In pig, an increased CSI ratio has been found in animals fed on 10% sunflower oil as compared to those fed on 2-10% lard-based diet (Juste et al., 1985). It has also been documented that, in man, hepatic bile collected in fasting conditions is more lithogenic than hepatic or gallbladder bile in response to food intake (Metzger et al., 1973). The purpose of this study on miniature pigs, was to determine whether the long-term adaptation to diets that differed only in the fat source (different degrees of saturation) influenced the biliary lipid composition of the gallbladder bile and the CSI. MATRRULSANDMETHODS Animals
and diet
A total of 24 miniature pigs (Sus scrofa) weighing 20-57 kg were studied. The pigs were supplied by the Comunidad Autonoma de Madrid to the Gregorio Maraii611 Hospital. After weaning (34 days old) animals were randomly allocated to four equal experimental groups being fed four test diets until they were aged 6 months. Experimental groups and diets were as follows: Control group (C) was fed a standard swine stock diet (developing
745
M.C. BALLESTAetal.
146
Table 1. Composition of macronutrients Diet
Control (C) 3930.0 177.0 32.0 670.0 50.0 71.0 19.3 7.8 72.9
Energy (kcal/kg) Brut protein (g/kg) Fats (g/kg) Carbohydrates (g/kg) Fibre (g/kg) Ash (g/kg) Protein (% energy) Fats (% energy) Carbohydrates (% energy)
of the experimental diets Olive (0)
Lard (L) 3930.0 170.0 76.0 650.0 37.0 67.0 17.2 17.3 65.6
Sunflower (S)
3930.0 193.0 104.0 594.0 43.0 66.0 18.9 22.9 58.2
3930.0 201 .o 105.0 562.0 44.0 88.0 20.1 23.6 56.2
Table 2. Fatty acid composition of the experimental diets Diet
Control (C)
Lard (L)
Olive (0)
Sunflower (S)
21.1 22.9 31.5
21.2 34.9 24.1
13.8 62.9 16.3
10.6 26.2 52.9
Palmitic (%) Oleic (%) Linoleic (%)
The fatty acid contents are expressed as a percentage of total.
swine NANTA R, Madrid, Spain). The lard group (L) was fed a basal feeding regimen for pigs (AVICU, S.A., Guadalajara, Spain) which contained the following ingredients: barley, bran, soy, salt, phosphate, carbonate, enriched with a mineral and vitamin mixture. This fat-free chow was supplemented with animal fat (bovine lard). Sunflower group (S): the basal feeding regimen was supplemented with sunflower oil (Koipesol R. Koipe, S. A.). Olive-oil group (0): the basal feeding regimen was supplemented with virgin olive oil (Patrimonio Comunal Olivarero). Detailed dietary macronutrients and fatty acids are shown in Tables 1 and 2, respectively. Procedure and sample collection
Animals of each experimental months’ feeding on the respective period, swine were anesthetized S.A.) and gallbladder bile was syringe and subsequently divided stored at -20°C until analysis.
group were killed after 6 diets. After a 24 hr fasting with Ethrane R (Abbot, collected into a sterilized into three vacutainers and
Phospholipids were determined by standard calorimetry (Boehringer, No. 691844). Cholesterol was also determined by standard calorimetry (Boehringer methods CHOD-PAP, no. 237576) based on an enzymatic reaction according to Seidel et al. (1981) after previous removal of proteins and bile pigments according to Lcvin et al. (1961). Bile acids were determined according to an enzymatic method with 3 a-hydroxysteroid dehydrogenase (STEROGNOST 3 a-Pho; Nyegaard & Co. AS. Oslo).
0
Statistical analyses
All the results were expressed as means f SEM. Data were compared following a one way analysis of variance (One Way, SPSS/PC+) subjected to Scheff&‘s test to compare the four groups. Student’s r-test was also used to compare the mean differences between the groups. Differences were considered significant if P < 0.05. RESULTS
Sample analysis
260
In all case results are expressed as mmol/l. The critical tables of cholesterol solubility constructedby Carey were used to calculate the percentage of cholesterol present at saturation (Carey, 1978). To calculate the CSI of a sample (Thomas and Hoffmann, 1973), one takes actual mole per cent of cholesterol in the sample and divides this by the mole per cent of cholesterol present at saturation, determined by the tables of Carey (Carey, 1978).
The concentration of biliary acids in bile gallbladder did not differ significantly in the four exper-
imental groups, although in the lard-fed group, values were slightly increased (Fig. 1). The cholesterol content was similar in all groups (Fig. 2) and we found the highest mean value in the sunflower-fed group and the lowest one in the olive-oil group. Phospholipid concentration evidenced a significant increase (P < 0.05) in miniature pigs fed on animal fat (bovine lard) (Fig. 3). Finally, the CSI did not
r
convol
lard
Sunfkaiver
OliiO
Fig. 1. Bile acid concentration (mmol/l) in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6), with their standard errors represented by vertical bars. Mean values for the four dietary groups were significantly different: ‘P < 0.05.
Fig. 2. Cholesterol concentration (mmol/l) in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6), with their standard errors represented by tical bars. Mean values for the four dietary groups were significantly different: *P < 0.05.
Dietary fats and gallbladder bile 18 a
18
1
‘*
g
‘:
g
8
E n
4 2 0
l
T
Control
Lard
Sunflower
Olii
Fig. 3. Phospholipid concentration (mmol/l) in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6), with their standard errors represented by vertical bars. Mean values
for the four dietary groups were significantly different: *P < 0.05. differ significantly in the four experimental groups (Fig. 4) ranging from 0.22 to 0.32 with mean values far from the saturation point. The highest saturation indices were shown in the sunflower-oil-fed group. DISCUSSION
According to these results, neither the quantity nor the quality of dietary fat (lard, olive or sunflower oil) alter significantly the biliary lipid composition of gallbladder bile in miniature swine when compared to a control group fed on a standard chow diet, except for the concentration of phospholipids that increase significantly in lard bovine group. On the other hand, the highest values of all parameters measured were reported in the bovine-lard-fed group (rich in saturated fatty acids). If we compared our results in miniature pig to those reported by Juste et al. (1983) in large white pigs (L-W) we noticed that in L-W pigs an increase of phospholipids occurs when diet has at least 10% of lard, while in our experiments, this increase occurred with a lower quantity of dietary fat, more specifically 7.5% of bovine lard, perhaps because of the different times of adaptation to the diet used in both studies. Besides, bile salts concentration were markedly decreased in L-W pigs fed with diets that have 2-20%
.$ z
0.30
iiii 0.20
e $
of pig-lard as compared to values obtained in miniature pigs in all the experimental groups. On the other hand, in control and olive-oil groups, phospholipids were similar to values reported in L-W animals fed 2 and 10% pig-lard diets whereas in bovine-lard and sunflower-oil groups, values of phospholipids are similar to those reported for L-W fed a 20% pig-lard diet. Cholesterol concentration was always higher in miniature swine fed any of the four different diets. In another experimental study performed on L-W swine (Juste et al., 1986) it has been documented that when feeding a 10% (w/w) sunflower-oil diet or pig-lard diet, the concentration of bile salts was similar in both groups, whereas concentrations of phospholipids and cholesterol were higher in the sunflower-oil-fed group. When comparing these results to those obtained in miniature swine fed bovine lard and sunflower oil, we found that both phospholipids and bile salts were increased in miniature swine fed lard, and only cholesterol was slightly higher in sunflower oil-fed animals. These differences are probably due to the fact that values found in L-W are the mean of 24 hr bile sampling, meanwhile the values obtained in our experimental study responded to precise gallbladder bile sampling and it is known that flow rate and bile composition change throughout the day (Metzger et al., 1973). If we observe the values obtained only in miniature swine, we see that values of biliary lipids when fed an olive-oil diet are similar to those obtained in control group, whereas in sunflower and bovine-lard groups, values of biliary lipids are higher. We only found significant differences in the concentration of phospholipids between control and bovine-lard groups. If we compare the concentrations of biliary lipids in miniature swine to normal values substantiated in humans (Schuller et al., 1980) we observe that miniature swine show a concentration of bile salts much higher and cholesterol and phospholipids concentrations lower than that reported in man. So this study suggests that miniature swine are not similar to man when considering the biliary lipid composition. Finally, we observed that in all the experimental feeding regimens, the CSI ratio is far from the saturation point (CSI c 1) which shows that in minature swine and under this experimental design, the quantity and quality of dietary fat do not significantly affect bile CSI ratio. However, the highest and lowest CSI ratios were reported in sunflower oil- and lardbased diets respectively which would agree with the results reported in L-W swine when fed sunflower or pig lard (Juste et al., 1985). REFERENCES
0.10
3 5
0
747
Control
Lard
Sunflower
Olii
Fig. 4. Cholesterol saturation index in gallbladder bile of miniature swine fed on control, bovine lard, olive oil and sunflower oil diets. Values are means (N = 6) with their standard error represented by bars. Mean values for the four dietary groups were significantly different: *P c 0.05.
Admirand W. H. and Small D. M. (1968) The physicochemical basis of cholesterol gallstone formation in man. J. clin. Invest. 47, 1043-1052. Bloch H. M., Thorthon J. R. and Heaton, K. W. (1980) Effect of fasting on the composition of gallbladder bile. Gut 21, 1087-1089. Carey M. C. (1978) Critical tables for calculating the cholesterol saturation of the native bile. J. Lipid Rex 19. 945-955.
748
M.C. BALLESTAetal.
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