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Institut für Ernährungswissenschaften, Martin-Luther-Universität Halle-Wittenberg, Emil-Abderhaldenstraße 26, D-06108 Halle/Saale, Germany and * Institut für Biochemie und Lebensmittelchemie, Universität Hamburg, Grindelallee 117, D-20146 Hamburg, Germany
2To whom correspondence should be addressed. E-mail: eder{at}landw.uni-halle.de.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • conjugated linoleic acid • lactation • mammary gland • liver • rat
Several studies showed that dietary conjugated linoleic acids (CLAs)3 exert many biological effects in humans and animals (1–4). In lactating animals and nursing women, dietary CLA caused a reduction in milk fat concentration (2,4,5). Fatty acids used for triacylglycerol synthesis in the mammary gland derive mainly from 2 different sources, either de novo fatty acid synthesis or uptake of fatty acids from circulating lipoproteins, which are released by the action of lipoprotein lipase (LPL). Fatty acids derived from de novo fatty acid synthesis are mainly medium-chain fatty acids with 8–14 carbon atoms, whereas those released from lipoproteins by LPL reflect those of the diet and are typically long-chain fatty acids with 18–22 carbon atoms (6,7). The fatty acid composition of milk lipids can be strongly altered by dietary manipulation of de novo fatty acid synthesis in the mammary gland or the uptake of fatty acids from lipoproteins into the mammary gland. For example, feeding a high-fat diet causes an increase in long-chain fatty acids (>80 g/100 g of total fatty acids) in the milk of rats by stimulating fatty acid uptake from lipoproteins by LPL; feeding a low-fat diet increases the proportions of medium-chain fatty acids (>50 g/100 g of total fatty acids) in the milk by stimulating de novo fatty acid synthesis in the mammary gland (8,9).
Some studies demonstrated that the reduced milk fat concentration of lactating animals fed CLA diets might be due to an inhibitory effect of trans-10, cis-12 CLA on enzymes involved in de novo fatty acid synthesis (4,5). However, it is not known whether dietary CLA also influences the uptake of fatty acids from lipoproteins. Until now, only one study dealt with the effects of dietary CLA on LPL in mammary glands (4). In that study, trans-10, cis-12 CLA reduced gene expression of LPL in the mammary gland of dairy cows. This suggests that dietary CLA inhibits the uptake of fatty acids from triglyceride-rich lipoproteins into the mammary gland. Although the effects of dietary CLA on plasma lipids are contradictory (10–13), some studies showed that dietary CLA lowers the concentration of triglyceride-rich lipoproteins in plasma (10,11), which are the substrates of LPL. Therefore, a reduced milk fat concentration could also be the result of reduced concentrations of triacylglycerols in the plasma. Triglyceride-rich lipoproteins are formed in the liver and secreted into the blood. There is a close relation between hepatic fatty acid metabolism and the formation of VLDL in the liver. CLA was shown to lower both apolipoprotein B synthesis and triacylglycerol secretion in HepG2 cells (14,15). However, it was also shown that CLA activates hepatic peroxisome proliferator-activated receptor 
(PPAR) and enhances ß-oxidation of fatty acids in the liver (16–18) and thereby could reduce the concentration of triacylglycerols in plasma. The aim of our study was to study the relation between possible activation of hepatic PPAR and milk fat concentration in lactating rats fed a dietary CLA supplement.
To gain knowledge about milk fat synthesis, we determined the concentrations of triacylglycerols and fatty acids in the milk and gene expression of lipogenic enzymes and LPL in the mammary gland. The concentrations of medium-chain fatty acids (derived from de novo fatty acid synthesis) and long-chain fatty acids (derived from plasma lipoproteins) in particular were determined to yield information about the sources used for milk fat synthesis. To study the hepatic lipid metabolism, we proposed to measure lipid concentrations in the liver (triacylglycerols, cholesterol and phospholipids), hepatic gene expression of PPAR and some of its target genes (acyl-CoA oxidase, catalase), and the expression of genes encoding enzymes involved in de novo fatty acid synthesis (fatty acid synthase, acetyl-CoA carboxylase).
Milk is the only source of nutrients for suckling pups. We assume that a reduced milk fat concentration might affect growth and survival of the offspring during the suckling period. Therefore, we also examined the development and mortality of the suckling pups.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Diets and feeding.
Semipurified diets, composed according to the recommendations of ASNS (19), were used for rat diets. The basal diet consisted of (g/kg diet): casein, 200; cornstarch, 400; saccharose, 268; cellulose, 30; fat, 40; mineral mixture, 40; vitamin mixture, 20; DL-methionine, 2. Two experimental diets, which differed in fat type, were used. The SFO diet contained 30 g sunflower oil (Palmin) and 10 g soybean oil (C. Thywissen)/kg diet; the CLA diet contained 30 g CLA oil (Strengthfood) and 10 g soybean oil/kg diet. The CLA oil contained 54 g CLA isomers/100 g CLA oil, which is equivalent to 1.47 g CLA/100 g diet. The fatty acid compositions of total lipids of the 2 experimental fats were similar except for the concentrations of 18:2(n-6) and CLA (Table 1). Total lipids in the SFO diet contained <0.1 g CLA/100 g total fatty acids, whereas total lipids in the CLA diet contained 40.9 g CLA/100 g total fatty acids. The CLA oil contained a large number of CLA isomers. Among them, trans-10, cis-12 CLA, cis-11, trans-13 CLA, cis-9, trans-11 CLA, and trans-8, cis-10 CLA were the major CLAs contributing 
65% of total CLA.
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Sample collection. On the day of parturition, 3 pups from each dam were randomly separated, anesthetized with diethyl ether, killed by decapitation, and frozen with liquid nitrogen; 2 pups from each dam were used for carcass analysis, and 1 pup from each dam was used for determination of hepatic lipid concentrations. Milk samples were collected on d 10 of lactation at 1000 h as previously reported (21). Milk samples were stored at –20°C pending analysis. On d 17 of lactation, the dams were anesthetized with diethyl ether and killed by decapitation. Blood from the dams was collected into heparinized polyethylene tubes (Sarstedt) and plasma was separated by centrifugation (1100 x g, 10 min) at 4°C and stored at –80°C. The liver and mammary gland were excised immediately, frozen with liquid nitrogen, and stored at –80°C until analysis. For analysis of biochemical variables and growth development, only 10 dams from the SFO group and 8 dams from the CLA group and the corresponding pups were used for the following reasons: first, 1 and 2 rats were not pregnant in the SFO group and the CLA group, respectively; second, 1 dam within each treatment group was excluded from analysis in order to wet-nurse the remaining pups after adjustment to 10 pups per dam; and third, 1 dam within the CLA group was excluded from analysis due to devouring the whole litter directly after parturition. For analysis of CLA isomeric distribution in the milk, only 9 milk samples in the SFO group and 6 milk samples in the CLA group were used due to insufficient sample amounts in 1 and 2 dams, respectively. The remaining milk variables were determined in the milk from 10 and 8 dams in the SFO and CLA groups, respectively.
Lipids in liver, milk, diets and carcass. Total lipids of milk, liver, carcass, and dietary lipids were extracted with a mixture of hexane and isopropanol (3:2, v/v) (22). The fatty acid composition of total lipids in the diet, milk, and the liver of the pups was determined by GC as described recently (23). The amounts of individual CLA in the CLA-oil and in milk total lipids were determined by GC analysis and silver-ion HPLC according to Sehat et al. (24).
Total cholesterol in liver and plasma and triacylglycerol concentrations in liver, plasma, and milk total lipids were determined using enzymatic reagent kits as described previously (25). Hepatic concentrations of cardiolipin (CL), phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), and sphingomyelin (SM) were quantified by HPLC as previously reported (25).
Carcass composition of newborn pups. Analysis of carcass composition of newborn pups was performed after homogenization and freeze-drying. Head and gastrointestinal tract were removed from newborn pups and not included in the analysis. The hide was not removed from these rats. Carcass total lipids were determined gravimetrically by evaporating the solvent from an aliquot of the hexane-isopropanol extract. Carcass protein was measured using the bicinchoninic acid (BCA) protein assay kit (Pierce; no. 23225).
Milk nutrients. Lactose concentration in the milk was determined by an enzymatic reagent kit from Boehringer (Catalog no. 10986119035). Milk protein was measured as carcass protein. Triacylglycerols in the milk were determined as described above. Milk energy content was calculated based on Atwater factors; lactose and protein each contributed 17 MJ/kg and triacylglycerols contributed 38 MJ/kg.
Enzyme activities in mammary glands and liver. For determination of enzyme activities, aliquots of liver and mammary gland were homogenized in a buffer containing 0.25 mol sucrose/L and 0.1 mol phosphate/L (pH 7.4). Hepatic catalase activity was measured spectrophotometrically in liver homogenate according to Aebi (26). For the measurement of fatty acid synthase (FAS) activity in the mammary gland, homogenates were centrifuged at 105,000 x g for 10 min and the supernatants were used for enzyme assays. FAS activity in the mammary gland was determined according to the method of Nepokroeff et al. (27). Activities were related to the protein concentrations of the samples determined using BCA protein assay kit (Pierce).
Relative mRNA concentrations.
Isolation of total RNA from liver and mammary gland and cDNA synthesis were performed as described previously (21). The relative quantities of SREBP-1c, PPAR, FAS, and LPL mRNA compared with glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) mRNA were determined by means of semiquantitative RT-PCR as reported previously (28). Relative quantities of AcCx and catalase mRNA were determined by quantitative real-time RT-PCR as described previously (28). Specific primers coding for these genes were obtained from Roth. Results are expressed as the ratio of the target gene mRNA to the reference gene (GAPDH) mRNA. The primer sequences used for RT-PCR were as follows: 5'-GCATGGCCTTCCGTGTTCC-3' (forward) and 5'-GGGTGGTCCAGGGTTTCTTACTC-3' (reverse) for rat GAPDH; 5'-TCTTCAACTGGCTGGAGGAAG-3' (forward) and 5'-TATGCCTTGCTGGGGTTTTCT-3' (reverse) for rat LPL; 5'-CCTCCCCTGGTGGCTGCTACAA-3' (forward) and 5'-CCTGGGGTGGGCGGTCTTT-3' (reverse) for rat FAS; 5'-CCCTCTCTCCAGCTTCCAGCCC-3' (forward) and 5'-CCACAAGCGTCTTCTCAGCCATG-3' (reverse) for rat PPAR; 5'-GGAGCCATGGATTGCACATT-3' (forward) and 5'-AGGAAGGCTTCCAGAGAGGA-3' (reverse) for rat SREBP-1c; 5'-GATGGGGGCCTGCTCCTGTCCTA-3' (forward) and 5'-CGCCCCTGGTCGCTTGATGTA-3' (reverse) for rat AcCx; 5'-CTTTCTTGCTTGCCTTCCTTCTCC-3' (forward) and 5'-GCCGTTTCACCGCCTCGTA-3' (reverse) for rat ACO and 5'-TCTTGTTCAGCGACCGAGGGATTC-3' (forward) and 5'-GGTGGCGGTGAGTGTCTGGGTAAG-3' (reverse) for rat catalase.
Statistics. Means of the 2 groups were compared by Student’s t test. Because 2 pups from each dam were used for the determination of the carcass composition, observations within 1 dam were repeated measurements. Therefore, an ANOVA including the factors diet and dam and their interaction was used to evaluate data of carcass composition. Values in the text are means ± SD. Means were considered significantly different at P < 0.05.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Liver weights, lipid concentrations, and activities and relative mRNA concentrations of enzymes involved in lipid metabolism.
Relative liver weights (expressed per 100 g of body weight) were lower in dams fed the CLA diet than in those fed the SFO diet (Table 2). Absolute liver weights tended to be lower in CLA-fed dams than in those fed the SFO diet (P < 0.15). Dams fed the CLA diet had higher concentrations of PC, PI, and SM, but lower concentrations of cholesterol and triacylglycerols in the liver than those fed the SFO diet. Hepatic concentrations of PE and PS tended to be higher in CLA-fed dams than in SFO-fed dams (P < 0.15), whereas the concentration of CL did not differ between the 2 groups. The sum of CL, PE, PC, PI, PS, and SM was higher in dams fed the CLA diet than in those fed the SFO diet. The relative mRNA concentrations of PPAR, ACO, and catalase and the activity of catalase in the liver were higher in CLA-fed dams than in SFO-fed dams. mRNA concentrations of SREBP-1c, FAS, and AcCx in the liver did not differ between groups.
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Activity of FAS and relative mRNA concentrations of FAS and LPL in the mammary gland. The mRNA concentration of LPL in the mammary gland was lower in CLA-fed dams than in SFO-fed dams (Table 3). The activity and the mRNA concentration of FAS in the mammary gland were also lower in dams fed the CLA diet than in those fed the SFO diet.
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Fatty acid composition of total lipids in the milk. The proportion of fatty acids with 8–14 carbon atoms in the milk was lower in CLA-fed dams than in SFO-fed dams (Table 4). The proportion of C16:0 in the milk did not differ between the groups. The milk of dams fed the CLA diet had higher proportions of 18:0, 18:1 and total CLA but lower proportions of 18:2(n-6) than the milk of dams fed the SFO diet. The major CLA isomers found in the milk of CLA-fed rats were cis-11, trans-13 CLA, trans-10, cis-12 CLA, cis-9, trans-11 CLA and trans-8, cis-10 CLA (Fig. 1). In the rats fed the SFO diet, trans-10, trans-12 CLA, trans-9, trans-11 CLA, trans-8, trans-10 CLA, trans-7, trans-9 CLA, cis-11, trans-13 CLA, trans-10, cis-12 CLA, cis-9, trans-11 CLA and trans-8, cis-10 CLA were the only CLA isomers with concentrations > 0.01 g/100 g fatty acids. The cis-9, trans-11 CLA was found to be the most abundant CLA isomer in the milk of rats fed the SFO diet.
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Reproductive performance, development of litters and pups during lactation, and carcass composition and hepatic lipid concentrations of newborn pups. The number of pups per litter, litter weights, and pup weights at d 1 and 8 of lactation did not differ between the groups (Table 5). At d 17 of lactation, the number of pups per litter, litter weights, and pup weights were lower in dams fed the CLA diet than in those fed the SFO diet. Newborn pups from rats fed the CLA diet had a higher protein:fat ratio but lower concentrations of total lipids in the carcass than those from rats fed the SFO diet. Carcass protein did not differ between pups from the 2 groups. Hepatic concentrations of triacylglycerols were markedly lower in newborn pups from CLA-fed dams than in pups from SFO-fed dams [7.4 ± 2.1 (n = 8) vs. 18.2 ± 8.5 (n = 10) µmol/g, P < 0.05]. The concentration of cholesterol in the liver of newborn pups tended to be lower in the CLA group than in the SFO group [19.0 ± 8.4 (n = 8) vs. 29.2 ± 15.4 (n = 10) µmol/g, P < 0.15].
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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65 g/100 g total CLA. The remaining CLA identified consisted of minor isomers in trans/cis-, cis/trans-, trans/trans- and cis/cis-configurations. The CLA isomeric distribution of the supplement used in this study differs markedly from the distribution pattern of natural foods. In natural foods such as milk, milk products, or beef, cis-9, trans-11 CLA is the main CLA isomer. It comprises between 80 and 90 g/100 g total CLA isomers, whereas trans-10, cis-12 CLA and other CLA isomers exist in very low concentrations. In contrast, most dietary CLA supplements contain a large number of CLA isomers (29). Concentrations of total CLA isomers in the CLA diet, amounting to 14.7 g/kg of diet, were much higher than those of Western human diets. Daily CLA consumption of humans in the United States from natural foods was estimated to be in the range between 150 and 210 mg/d (30), which is equivalent to a CLA concentration in the diet of 0.3 g/kg dry matter. The present study therefore should be regarded as a model study showing the potential effects of a high supplementation with various CLA isomers rather than the effects of CLA occurring in natural foods. The trans-10, cis-12 CLA, rather than the cis-9, trans-11 CLA is considered responsible for most of the CLA effects on lipid metabolism in animal studies (31–33), but the effects of minor CLA isomers on the metabolism in animals are unknown. Because the CLA supplement used in this study contained a large number of CLA isomers, it is not known which CLA isomers were mainly responsible for the effects of the CLA supplement in this study.
To study the effect of dietary CLA, we added the CLA supplement to the diet at the expense of sunflower oil. Similar approaches were used by several others and are widely accepted for studying the effects of CLA on animal metabolism (34,35). Nevertheless, one should be aware that in such an approach, the concentration of linoleic acid in the CLA diet is lower than in the control diet, and some effects observed after feeding the CLA diet could be due to lower concentrations of linoleic acid rather than to CLA itself. To avoid metabolic confounding due to insufficient dietary linoleic acid concentrations, we supplemented the diets of both treatment groups with 10 g soybean oil/kg diet. The linoleic acid intake of the rats fed the CLA diet, which was 107, 120, and 230 mg/d during growth, pregnancy, and lactation, respectively, was in excess of the requirement of 100 mg linoleic acid/d for pregnant and lactating rats (36). Therefore, we can exclude the possibility that the effects observed in rats fed the CLA diet were due to a deficiency of linoleic acid.
Our study shows that feeding a CLA supplement to rats during pregnancy and lactation strongly reduces milk fat concentration. This finding agrees with other studies in humans and animals (2,4,5). The observation that rats fed the CLA diet had a reduced mRNA level and FAS activity indicates that CLA lowered the rate of de novo fatty acid synthesis in the mammary gland. This indication is confirmed by the observation of markedly reduced concentrations of medium-chain fatty acids with 8–14 carbon atoms in the milk of rats fed CLA. Fatty acids with 8–14 carbon atoms are the main products of de novo fatty acid synthesis in the mammary gland. The observation that dietary CLA reduces gene expression of lipogenic enzymes in the mammary gland of lactating rats agrees with findings of another study (37). That study, moreover, showed that trans-10, cis-12 CLA is a more potent inhibitor of mammary lipogenesis than cis-9, trans-11 CLA.
In addition to fatty acids synthesized in the mammary gland, fatty acids released from triglyceride-rich lipoproteins by LPL and taken up into the mammary gland are another important source for milk fat synthesis. Those fatty acids largely reflect those of the diet; they are predominately long-chain fatty acids with 18–22 carbon atoms, either saturated or unsaturated (6,7). The finding that the milk of rats fed the CLA supplement also had reduced concentrations of long-chain fatty acids with 18–22 carbon atoms suggests that the CLA supplement impaired the uptake of those fatty acids into the mammary gland, thereby impairing the synthesis of triglycerides with long-chain fatty acids.
Because the concentration of triglycerides in plasma was not lower in rats fed the CLA supplement than in control rats, we assume that the activity of LPL, the key factor in the uptake of circulating lipids by the lactating mammary gland (38), could have been reduced. For technical reasons, we were not able to determine the activity of that enzyme. However, gene expression analysis revealed that mRNA concentrations of LPL in the mammary gland were significantly lower in rats fed the CLA diet than in control rats. We therefore assume that the activity of this enzyme might have been reduced in rats fed CLA. The finding of our study is consistent with a recent study in cows in which abomasally infused trans-10, cis-12 CLA caused a significant reduction of LPL mRNA in mammary glands and a reduction in milk fat concentration (4).
Data from this study therefore suggest that the reduced milk fat concentration in the CLA group was the result of the inhibition of both de novo fatty acid synthesis and uptake of fatty acids from lipoproteins into the mammary gland. However, the finding that milk of CLA-fed rats had a lower ratio of medium-chain fatty acids to long-chain fatty acids than milk of SFO-fed rats suggests that inhibition of de novo fatty acid synthesis was more responsible for the impairment than inhibition of the uptake of fatty acids from plasma lipoproteins.
Our study shows that dietary CLA lowers the concentrations of triacylglycerols and cholesterol and increases the concentration of phospholipids in the liver of lactating rats. These effects might be explained by the activation of hepatic PPAR by dietary CLA. It was shown that CLAs are ligands of PPAR (16–18). Activation of PPAR leads to proliferation of peroxisomes and stimulates the expression of genes encoding proteins of mitochondrial and peroxisomal ß-oxidation (39). Increased mRNA levels of ACO and catalase, both marker enzymes of peroxisomes, indicate that dietary CLA activated PPAR, caused peroxisome proliferation, and enhanced lipid catabolism in the liver. The activation of PPAR leads to reduced concentrations of hepatic triacylglycerols through an increased oxidation of fatty acids (40). Increased concentrations of phospholipids and reduced concentrations of cholesterol in the liver are other responses to the activation of PPAR, which were also observed in other animal studies examining dietary CLA supplements (10,34,41). The finding that hepatic mRNA concentrations of lipogenic enzymes such as FAS and AcCx were not altered in rats fed CLA suggests that CLA did not influence the rate of de novo fatty acid synthesis in the liver. Typically, enhanced fatty acid oxidation in the liver due to activation of PPAR is associated with reduced plasma triacylglycerol concentrations (40). Therefore, it was surprising that plasma triacylglycerol concentrations did not differ between rats fed CLA and control rats. However, this observation suggests that the reduced milk fat concentrations of rats fed CLA were not caused by reduced concentrations of plasma triacylglycerols.
The reduction in milk fat concentration resulted in a reduced energy content in the milk. The production of lipids in the milk is of biological importance for the development of the offspring (8,42). Because maternal milk is the only source of nutrients for the suckling pups, it was not surprising that the reductions in fat and energy in the milk were accompanied by a reduced development of the litter and pup weights during lactation. The finding of the present study is in contrast to a previous study in rats that did not report a reduced survival of the offspring during lactation (43). However, differences between the present and the previous study could be due to a different diet composition, e.g., dietary fat contents (60 vs. 40 g fat/kg diet) or isomeric distribution of the CLA supplement. It was demonstrated that a higher fat content in the diet increases lipid accumulation in the pup carcass (8), which increases the energy stores of the suckling pup and probably decreases mortality. The fatty acid analysis of milk triglycerides showed that the concentration of linoleic acid in the milk of CLA dams was much lower than that in the milk of control dams. Therefore, the question arose whether the increased mortality of pups of the CLA dams could be due a deficiency in essential fatty acids (EFA). To test this, we determined the fatty acid composition of liver lipids in pups after birth and at weaning. The amounts of linoleic acid and arachidonic acid in the liver at weaning were lower in pups of CLA dams than in pups of control dams, as expected, but they were clearly higher than those observed in EFA-deficient rats (44). As a consequence of the lower supply of linoleic acid from the milk, the amount of mead acid [20:3(n-9)] and the ratio at weaning between mead acid and arachidonic acid, both sensitive indicators of EFA deficiency, were higher in CLA pups than in SFO pups. Nevertheless, these indicators were markedly lower than those of EFA-deficient rats (44). Therefore, we assume that the increased mortality of pups of CLA dams was not caused by an insufficient intake of EFA in the milk. Rather, the increased mortality of the suckling pups could be the result of a limited supply of the energy that is required for optimal growth of the offspring. Some studies demonstrated that dietary CLA also influences the amount of milk produced. The effects, in this respect, however, are not quite uniform. Some studies reported a reduced milk production by dietary CLA in various animals species (45,46), whereas one reported increased milk production (47). Because the milk of rats fed the CLA diet contained a large number of CLA isomers, we also cannot exclude the possibility that one or more of those isomers had unfavorable effects on the suckling pups.
The observation that small amounts of CLA were also found in the milk of rats fed the SFO diet supports the indication from a previous study that microorganisms in the digestive tract of monogastric animals are able to synthesize CLA (48), which are probably absorbed and incorporated into tissues and milk lipids. CLAs are also synthesized endogenously from vaccenic acid (trans-11–18:1) via the 
9-desaturase reaction (49). However, the absence of vaccenic acid in the SFO diet does not support this notion.
This study shows that the newborn pups of rat dams fed a diet containing CLA had reduced concentrations of triacylglycerols in the liver, reduced amounts of linoleic acid and arachidonic acid in liver lipids, and an increased protein:fat ratio in their carcass compared with pups of control dams. Increases in the protein:fat ratio of the carcass occur in growing or adult animals fed a dietary CLA supplement (10,31,50). Our study shows for the first time that CLA fed to pregnant rats has similar effects on their fetuses.
In conclusion, the present study suggests that administration of a dietary CLA supplement to pregnant and lactating rats strongly reduces milk fat concentration and energy content of the milk, changes body composition of newborn pups, reduces body weight gains of suckling pups, and increases their mortality. Although the results of our study cannot be extrapolated directly to humans, they suggest that commercially available CLA supplements should be considered critically in pregnant and nursing women.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: AcCx, acetyl-CoA carboxylase; ACO, acyl-CoA oxidase; BCA, bicinchoninic acid; CL, cardiolipin; CLA, conjugated linoleic acid; EFA, essential fatty acid; FAS, fatty acid synthase; GAPDH, glyceraldehyde-3-phosphate-dehydrogenase; LPL, lipoprotein lipase; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; PPAR, peroxisome proliferator-activated receptor ; PS, phosphatidylserine; SM, sphingomyelin; SREBP-1c, sterol regulatory element binding protein-1c.
Manuscript received 16 June 2004. Initial review completed 6 August 2004. Revision accepted 10 September 2004.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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