Fatty acid metabolism and ketone formation in the suckling rat

Rat milk triacylglycerols contain 35% medium-chain length fatty acids. About 70% of ingested medium-chain fatty acids are released from milk triacylglycerols in the stomach and small intestine and are absorbed directly into the portal venous system. Based on studies with the perfused suckling rat liver and in vivo studies with 2-tetradecylglycidic acid, an inhibitor of long-chain fatty acid oxidation, it is estimated that medium-chain fatty acids provide 75-80% of the substrate for ketogenesis. The preferential use of medium-chain fatty acids for ketogenesis spares long-chain fatty acids for complex lipid and membrane biosynthesis during this period of rapid growth. Although medium-chain fatty acids are the major substrate for ketogenesis, this pathway accounts for only 15% of the utilization of ingested medium-chain fatty acids, the rest presumably being oxidized directly in extrahepatic tissues.     

Dietary regulation of mammary lipogenesis in lactating rats.

The proportion of medium-chain fatty acids (C8:0, C10:0 and C12:0) in rat milk increased significantly between day 4 and day 8 of lactation and for the remainder of lactation these acids comprised 40-50mol% of the total fatty acids. The milk fatty acid composition from day 8 was markedly dependent on the presence of dietary fat and altered to include the major fatty acids of the fats (peanut oil, coconut oil and linseed oil). The distribution of fatty acids made within the gland, however, was independent of dietary lipid and C8:0, C10:0 and C12:0 acids accounted for over 70% of the fatty acids made. The rates of lipogenesis in both the mammary gland and liver determined in vivo after the administration of 3H2O were affected by the presence of dietary lipid. In the mammary gland the rate for rats fed a diet containing peanut oil for 7 days was only one fifth that for rats fed a fat-free diet. Coconut oil also suppressed lipogenesis. Both dietary fats also suppressed lipogenesis in the liver.     

Milk lipid digestion in the neonatal dog: the combined actions of gastric and bile salt stimulated lipases

Intragastric lipolysis may be particularly important for the digestion of milk lipid since milk fat globules are resistant to pancreatic lipase without prior disruption; milk bile salt stimulated lipase (BSSL) may supplement further intestinal hydrolysis. Previous information on gastric lipolysis has been based primarily on in vitro studies using artificial lipid emulsions containing a single component fatty acid and have focused on the preferential release of medium-chain fatty acids. The actual contribution of these enzymes to overall fat digestion in vivo on natural substrates has rarely been studied, however. The neonatal dog is an excellent model in the study of lipid digestion because, like the human, milk lipids are high in long-chain unsaturated fatty acids, milk contains BSSL and gastric lipase is the predominant lipolytic enzyme acting in the stomach. We used a combination of in vivo studies with in vitro incubations to investigate digestion of milk lipid by gastric and milk (BSSL) lipases in the suckling dog. In the first 4 weeks postpartum, 14-41% and 42-60% of milk triacylglycerol was hydrolyzed to primarily diacylglycerol and free fatty acid (FFA) in the first 30 and 60 min in the stomach, respectively. Milk lipid contained high levels (63%) of long-chain unsaturated fatty acids, which were preferentially released as FFA during in vivo gastric lipolysis, consistent with the actions and stereospecificity of gastric lipase. While levels of hydrolysis in gastric aspirates were significantly different (by age and time in stomach) at the start of in vitro studies, total hydrolysis in all incubation systems plateaued at about 65%, suggesting product inhibition by the long-chain FFA, but to a much lesser degree than previously expected from in vitro studies. The magnitude of in vivo intragastric lipolysis was 3- to 6-times greater than that predicted by in vitro assays using either milk lipid or labeled emulsion as substrate, respectively. Prior exposure to intragastric lipolysis resulted in 30% hydrolysis by BSSL compared to 5% hydrolysis without prior exposure. We suggest that previous in vitro studies have largely underestimated the actual degree of intragastric lipolysis that can occur and its activity on long-chain fatty acids; this study indicates the importance of the combined mechanisms of gastric lipase and BSSL to fat digestion in the suckling neonate.     

Minor amounts of plasma medium-chain fatty acids and no improved time trial performance after consuming lipids.

Medium-chain triacylglycerols (MCT) have a potential glycogen-saving effect during exercise due to rapid hydrolysis and oxidation. However, studies comparing intake of carbohydrates (CHO) plus 80-90 g MCT with intake of CHO alone have revealed different results. The present study tested performance after consumption of specific structured triacylglycerol, consisting of a mixture of medium-chain fatty acids and long-chain fatty acids, to prevent the adverse effects observed by MCT (pure medium-chain fatty acids) regarding gastrointestinal distress. Seven well-trained subjects cycled 3 h at 55% of maximum O2 uptake during which they ingested CHO or CHO plus specific structured triacylglycerols. Immediately after the constant-load cycling, the subjects performed a time trial of approximately 50-min duration. Breath and blood samples were obtained regularly during the experiment. Fatty acid composition of plasma triacylglycerols, fatty acids, and phospholipids was determined. Performance was similar after administration of CHO plus specific structured triacylglycerol [medium-, long-, and medium-chain fatty acid (MLM)] compared with CHO (50.0 +/- 1.8 and 50.8 +/- 3.6 min, respectively). No plasma 8:0 was detected in the plasma lipid classes, but the amount of phospholipid fatty acids was significantly higher after CHO+MLM compared with CHO intake. The lacking time trial improvement after intake of medium-chain fatty acids might be due to no available 8:0 in the systemic circulation. A higher level of plasma phospholipid fatty acids in the CHO+MLM compared with the CHO group was probably due to endogenous phospholipid release into chylomicrons.     

Intestinal absorption of specific structured triacylglycerols

To clarify the intestinal absorption pathway of medium-chain fatty acids from MLM-type structured triacylglycerols containing both medium- and long-chain fatty acids, we studied the lymphatic transport of 1,3-dioctanoyl-2-linoleoyl-sn-glycerol (8:0/18:2/8:0), 1,3-didecanoyl-2-linoleoyl-sn-glycerol (10:0/18:2/10:0), and 1,3-didodecanoyl-2-linoleoyl-sn-glycerol (12:0/18:2/12:0) in a rat model. Safflower oil was used in the absorption study in order to compare the absorption of medium-chain fatty acids and long-chain fatty acids. The triacylglycerol species of lymph lipids were separated on a reversed-phase high performance liquid chromatograph (RP-HPLC) and identified by atmospheric pressure chemical ionization mass spectrometry. The composition of triacylglycerols was quantified by RP-HPLC with evaporative light scattering detection. The intact MLM-type triacylglycerols were detected in the lymph lipids after administration of the specific structured triacylglycerols (STAG). The recoveries of 8:0/18:2/8:0, 10:0/18:2/10:0, and 12:0/18:2/12:0 were 0.6%, 12%, and 5%, respectively. Several new triacylglycerol species were detected in the lymph lipids, including MLL-, LLL-, and MMM-type triacylglycerols.From the present study we conclude that the medium-chain fatty acids from STAG, in addition to absorption into the portal blood as free fatty acids, are absorbed by the same pathway as the conventional long-chain triacylglycerols, that is, they are hydrolyzed into free fatty acids, absorbed and activated into CoA, and reacylated into triacylglycerols in the enterocyte. The hydrolysis of MLM-type STAG is predominantly partial hydrolysis, whereas part of the STAG can also be hydrolyzed to free glycerol and free fatty acids.     

Inhibition of FASN reduces the synthesis of medium-chain fatty acids in goat mammary gland

Fatty acid synthase (FASN) is known as a crucial enzyme of cellular de novo fatty acid synthesis in mammary gland which has been proved as the main source of short and medium-chain fatty acids of milk. However, the regulatory role of FASN in goat-specific milk fatty acids composition remains unclear. We cloned and analyzed the full-length of FASN gene from the mammary gland of Capra hircus (Xinong Saanen dairy goat) (DQ 915966). Comparative gene expression analysis suggested that FASN is predominantly expressed in fat, small intestine and mammary gland tissues, and expresses higher level at lactation period. Inhibition of FASN activity by different concentrations (0, 5, 15, 25 and 35 μM) of orlistat, a natural inhibitor of FASN, resulted in decreased expression of acetyl-CoA carboxylase α (ACCα), lipoprotein lipase and heart-type fatty acid binding protein (H-FABP) in a concentration-dependent manner in goat mammary gland epithelial cells (GMEC). Similar results were also obtained by silencing of FASN. Additionally, reduction of FASN expression also led to apparent decline of the relative content of decanoic acid (C10:0) and lauric acid (C12:0) in GMEC. Our study provides a direct evidence for inhibition of FASN reduces cellular medium-chain fatty acids synthesis in GMEC.     

Changes in plasma fatty acids indicate change in nutritional status in developing Weddell seal pups

The concentrations and the fatty acid compositions (weight percent) of three plasma lipid fractions (phospholipids, cholesteryl esters, and triacylglycerols) were examined in five Weddell seal pups through suckling, the post-weaning fast and periods of independent foraging. The principal plasma fatty acids in Weddell seal pups during suckling were the same as those previously reported for milk samples collected from lactating Weddell seals. In contrast to the stable milk fatty acid composition suggested by the previous study, significant changes in the fatty acid composition of plasma lipids occurred during suckling. These included an increase in the weight% of 20:4(n-6) and 18:0 in phospholipids, an increase of 20:4(n-6) in cholesteryl esters, and an increase of 20:1(n-9) and a decrease of 20:5(n-3) in triacylglycerols. Weaning and the subsequent fasting period were accompanied by a dramatic drop in the plasma concentration and 14:0 content of triacylglycerols and by marked decrease and increase in the weight% of 20:1(n-9) and 20:5(n-3), respectively, in this lipid fraction. Weight% of 14:0 in triacylglycerols and/or plasma concentration of triacylglycerols clearly distinguish post-weaning from suckling. However, fasting versus foraging pups could not be clearly distinguished. Received: 7 October 1996 / Accepted: 20 May 1997     

Changes in the yield, and carbohydrate, lipid and protein content of milk during lactation in the rat

The milk yield and composition was studied during the first three lactations of a group of rats. Milk yield increased steadily throughout the three lactations, but was somewhat lower during the first than subsequent lactations. Protein concentration was similar during all three lactations and varied little with stage of lactation. In contrast the lactose concentration, which was reasonably constant for the first 8 days post partum, increased thereafter two-fold by the end of the period studied in all three lactations. However, the N-acetyl-neuraminyl lactose concentration showed somewhat reciprocal changes. Considerable variations in the triacylglycerol concentration was found during the first lactation but few changes were observed during subsequent lactations. The free fatty acid concentration was at all times low and showed no significant changes during or between lactations. At most stages of lactation in raw milk, the major fatty acids are palmitate, oleate and linoleate. However, as lactation progresses there is an increase in the proportion of medium-chain saturated fatty acids and a corresponding decrease in the proportion of long chain unsaturated fatty acids in milk fat. Clearly the composition of milk is not invariable but changes both during and between lactations. Such changes may be expected to have some influence on the metabolism of the offspring.     

Prenatal and postnatal transfer of fatty acids from mother to pup in the hooded seal

Unlike most mammals, hooded seal (Cystophora cristata) pups are born with a substantial layer of adipose tissue. Subsequently, during the brief lactation period of only 4 days, fasting mothers mobilize enormous amounts of lipid from blubber and secrete milk (60% fat) at rates of 10 kg·day^-1. Pups gain 7 kg·day^-1 due primarily to the deposition of fat in blubber. We measured blubber content and fatty acid composition of blubber and milk in hooded seal mother-pup pairs at birth and over the 4-day lactation period to examine the nature and source of fetal lipids, the incorporation of maternal blubber fatty acids into milk lipid, and patterns of fatty acid deposition in suckling young. The fatty acid composition of the blubber of the newborn was notably different from that of its mother. Fetal deposition was likely due to a combination of both fetal synthesis and direct placental transfer of maternal circulating fatty acids. The blubber of the newborn was characterized by high levels (>90% of total fatty acids) of saturated and monounsaturated fatty acids of primarily endogenous origin. In particular, the fetus appeared to have high Δ-9 desaturase activity as evidenced by the large amounts of 14:1n-5 (4.2%) and 16:1n-7 (37.0%) in newborn blubber compared to maternal blubber (0.2% and 14.1%, respectively). Nevertheless, essential and long-chain polyunsaturated fatty acids of the n-3 and n-6 families, which could only have originated by direct transfer from the mother, comprised>7% of pup blubber fatty acids and indicated greater rates of placental transfer than found in humans. In hooded seal mothers, rapid lipid transfer during the brief lactation period appeared to be facilitated by direct incorporation of mobilized fatty acids into milk. Although some differences in proportions of specific fatty acids were found between milk and maternal blubber, most of these differences declined over the course of lactation. However, selective mobilization of 20:5n-3 from maternal blubber into milk was apparent throughout lactation and resulted in elevated levels in pup blubber at weaning compared to maternal blubber. Ingested fatty acids were deposited directly and without modification into the blubber of pups, and by 4 days the fatty acid composition of pup blubber was virtually identical to that of the milk consumed.     

Application of atmospheric pressure chemical ionization liquid chromatography–mass spectrometry in identification of lymph triacylglycerols

Atmospheric pressure chemical ionization liquid chromatography–mass spectrometry was used in the identification of triacylglycerol molecular species in lymph samples from rats given either a structured lipid or safflower oil. The structured lipid was MLM-type (M, medium-chain fatty acid; L, long-chain fatty acid) and manufactured from caprylic acid (8:0) and the oil (safflower oil or high-oleic sunflower oil). The triacylglycerol composition of lymph varied significantly between structured triacylglycerols and safflower oil. Diacylglycerol fragment ions were found for all triacylglycerols and we could also observe the ammonium adduct molecular ion [M+NH₄]⁺ for all the triacylglycerols at the selected conditions. Protonated molecular ions were formed from triacylglycerols containing unsaturated fatty acids, and fatty acid fragment ions were also observed in the case of strong fragmentation. The lymph triacylglycerols were identified from their ammonium adduct molecular ions and diacylglycerol fragment ions. In addition to the intact MLM-type structured triacylglycerols, the MLL- and LLL-type triacylglycerols were also identified. The absorption pathway of MLM-type structured triacylglycerols is most likely the same as that of conventional long-chain triacylglycerols, i.e. they were hydrolyzed into 2-monoacylglycerol and medium-chain fatty acids, which were then used for resynthesis of triacylglycerols. The present study thereby also demonstrates the possibility to study the absorption pathway of triacylglycerol via identification of triacylglycerol species in biological samples.     

Nervonic acid is transferred from the maternal diet to milk and tissues of suckling rat pups

Three experiments were designed to investigate the metabolism of dietary nervonic acid (24:1n-9, NA) during reproduction in the rat. The first experiment determined the effect of early development on the sphingomyelin (SM) composition of rat heart and liver tissues. Rats were fed a standard chow diet and the SM fatty acid composition of the hearts and livers were analyzed of 18-20 day old fetuses, 14 day old sucklings and adult rats. The 18:0 content of SM decreases with age, while 23:0 and iso 24:0 increase with age. In the second experiment pregnant rats were fed diets supplemented with either canola, corn or peanut oil to determine the effect of diets high in 24:1n-9 and 24:0 on liver and heart SM at birth and after 14 days of suckling. Pups from the dams fed the corn oil diet had elevated 24:2n-6 in SM from heart and liver at birth, but the content of NA was not altered by dietary fat type. In the third experiment oil mixtures were designed to provide elevated levels of 22:1 and 24:1 (canola-N25), 22:0 and 24:0 (peanut-flax) or <0.01% of these fatty acids (olive-flax) and were supplemented to the diets of lactating rats. Canola-N25 oil supplemented to lactating rats resulted in increased 24:1n-9 and 24:1/24:0 with decreased 22:0 and 24:0 in milk SM relative to the other groups. The SM composition of livers of the suckling rats showed significant changes reflecting the changes in milk SM composition after 6 days of milk consumption. These experiments suggest that dietary NA and is not readily transferred across the placental barrier but does readily cross the mammary epithelium and is incorporated into milk SM. In addition, NA in milk appears to cross the intestinal epithelium where it is incorporated into the SM of heart and liver of suckling rats.     

Factors affecting goat milk production and quality

Differences between production systems based on grazing and browsing vs. use of harvested feedstuffs in confinement largely depend on specific feedstuffs and plants available and being consumed. Low forage nutrient ingestion should have relatively greater impact on tissue mobilization than milk production in early than later periods of lactation, with a transition to proportionally greater change in milk production in late lactation. However, low body condition at kidding would limit tissue energy mobilization and restrict impact of level of nutrient intake to milk yield and, likewise, tissue mobilization would be less with one vs. two or three milkings per day. As lactation advances after freshening, fat and protein levels decrease with increasing milk yield, and when production declines in mid- to late lactation, fat and protein concentrations increase. Milk production generally peaks at a parity of 3 or 4, thereafter declining slowly. Elevated somatic cell count alone in dairy goats is not a valid indication of mammary infection. Extended lactations offer opportunities to minimize or avoid seasonal fluctuations in milk production and lessen production costs. If differences in performance between suckled and machine-milked dairy goats occur, they may be restricted to or of greater magnitude during the suckling period compared with post-weaning, and differences in milk yield will either be absent or less with one kid compared with greater litter sizes. The magnitude of effects of milking frequency on milk yield is less for goats of low vs. high production potential and with low vs. high diet quality. Likewise, the effect of milking frequency is greater in early and mid-lactation when yield is higher than in late lactation, along with a shorter period of peak production with one vs. two daily milkings. Physical form of the diet can affect production and composition of goat milk, although effects appear of smaller magnitude than in dairy cattle. When tissue is mobilized to support milk production in early lactation, levels of C18:0 and C18:1 cis in milk increase and levels of medium-chain fatty acids decline. Effects of elevated levels of dietary fatty acids on specific long-chain fatty acids in milk and milk products vary with the fatty acid profile of fat sources used.     

Effect of different contents of extruded linseed in the sow diet on piglet fatty acid composition and hepatic desaturase expression during the post-natal period

n-3 polyunsaturated fatty acids (n-3 PUFA) contribute to the normal growth and development of numerous organs in the piglet. The fatty acid composition of piglet tissues is linked to the fatty acid composition of sow milk and, consequently, to the composition of sow diet during the gestation and lactation period. In this study, we investigated the impact of different contents of extruded linseed in the sow diet on the fatty acid composition and desaturase gene expression of piglets. Sows received a diet containing either sunflower oil (low 18:3n-3 with 18:3n-3 representing 3% of total fatty acids) or a mixture of extruded linseed and sunflower oil (medium 18:3n-3 with 9% of 18:3n-3) or extruded linseed (high 18:3n-3 with 27% of 18:3n-3) during gestation and lactation. Fatty acid composition was evaluated on sow milk and on different piglet tissues at days 0, 7, 14, 21 and 28. The postnatal evolution of delta5 (D5D) and delta6 (D6D) desaturase mRNA expression was also measured in the liver of low 18:3n-3 and high 18:3n-3 piglets. The milk of high 18:3n-3 sows had higher proportions of n-3PUFA than that of low 18:3n-3 and medium 18:3n-3 sows. Piglets suckling the high 18:3n-3 sows had greater proportions of 18:3n-3, 20:5n-3, 22:5n-3 and 22:6n-3 in the liver, and of 22:5n-3 and 22:6n-3 in the brain than low 18:3n-3 and medium 18:3n-3 piglets. D5D and D6D mRNA expressions in piglet liver were not affected by the maternal diet at any age. In conclusion, extruded linseed in the sow diet modifies the n-3PUFA status of piglets during the postnatal period. However, a minimal content of 18:3n-3 in the sow diet is necessary to increase the n-3PUFA level in piglet liver and brain. Moreover, modifications in the n-3PUFA fatty acid composition of piglet tissue seem linked to the availability of 18:3n-3 in maternal milk and not to desaturase enzyme expression.     

Comparative study of triacylglycerol fatty acids in milk from two Leporidae species: rabbit (Oryctolagus cuniculus) and hare (Lepus europaeus).

1. Fatty-acid composition of hare milk triacylglycerols markedly differed from that of rabbit milk and was essentially characterized by a 2.1 times lower concentration of medium-chain fatty-acids (M.C.F.A.). 2. Consequently, very high levels (greater than 70 moles %) of M.C.F.A., previously reported for rabbit milk, cannot be considered as a general characteristic of the Leporidae. 3. General tendencies recorded for intramolecular fatty acid distribution in hare milk triacylglycerols agreed with those reported for other animal species.     

Formation and degradation of dicarboxylic acids in relation to alterations in fatty acid oxidation in rats.

Dicarboxylic acids are excreted in urine when fatty acid oxidation is increased (ketosis) or inhibited (defects in beta-oxidation) and in Reye's syndrome. omega-Hydroxylation and omega-oxidation of C6-C12 fatty acids were measured by mass spectrometry in rat liver microsomes and homogenates, and beta-oxidation of the dicarboxylic acids in liver homogenates and isolated mitochondria and peroxisomes. Medium-chain fatty acids formed large amounts of medium-chain dicarboxylic acids, which were easily beta-oxidized both in vitro and in vivo, in contrast to the long-chain C16-dicarboxylic acid, which was toxic to starved rats. Increment of fatty acid oxidation in rats by starvation or diabetes increased C6:C10 dicarboxylic acid ratio in rats fed medium-chain triacylglycerols, and increased short-chain dicarboxylic acid excretion in urine in rats fed medium-chain dicarboxylic acids. Valproate, which inhibits fatty acid oxidation and may induce Reye like syndromes, caused the pattern of C6-C10-dicarboxylic aciduria seen in beta-oxidation defects, but only in starved rats. It is suggested, that the origin of urinary short-chain dicarboxylic acids is omega-oxidized medium-chain fatty acids, which after peroxisomal beta-oxidation accumulate as C6-C8-dicarboxylic acids. C10-C12-dicarboxylic acids were also metabolized in the mitochondria, but did not accumulate as C6-C8-dicarboxylic acids, indicating that beta-oxidation was completed beyond the level of adipyl CoA.     

DGAT1 underlies large genetic variation in milk-fat composition of dairy cows

Dietary fat may play a role in the aetiology of many chronic diseases. Milk and milk-derived foods contribute substantially to dietary fat, but have a fat composition that is not optimal for human health. We measured the fat composition of milk samples in 1918 Dutch Holstein Friesian cows in their first lactation and estimated genetic parameters for fatty acids. Substantial genetic variation in milk-fat composition was found: heritabilities were high for short- and medium-chain fatty acids (C4:0-C16:0) and moderate for long-chain fatty acids (saturated and unsaturated C18). We genotyped 1762 cows for the DGAT1 K232A polymorphism, which is known to affect milk-fat percentage, to study the effect of the polymorphism on milk-fat composition. We found that the DGAT1 K232A polymorphism has a clear influence on milk-fat composition. The DGAT1 allele that encodes lysine (K) at position 232 (232K) is associated with more saturated fat; a larger fraction of C16:0; and smaller fractions of C14:0, unsaturated C18 and conjugated linoleic acid (P < 0.001). We conclude that selective breeding can make a significant contribution to change the fat composition of cow's milk.     

Intestinal responsiveness to experimental colitis in young rats is altered by maternal diet

Increasing evidence suggests that fetal and neonatal nutrition impacts later health. Aims of the present study were to determine the effect of maternal dietary fat composition on intestinal phospholipid fatty acids and responsiveness to experimental colitis in suckling rat pups. Female rats were fed isocaloric diets varying only in fat composition throughout gestation and lactation. The oils used were high (8%) in n-3 [canola oil (18:3n-3)], n-6 (72%) [safflower oil (18:2n-6)], or n-9 (78%) [high oleic acid safflower oil (18:1n-9)] fatty acids, n = 6/group. Colitis was induced on postnatal day 15 by intrarectal 2,4-dinitrobenzene sulfonic acid (DNBS) administration with vehicle (50% ethanol) and procedure (0.9% saline) controls. Jejunal and colonic phospholipids and milk fatty acids were determined. The distal colon was assessed for macroscopic damage, histology, and MPO activity. The 18:2n-6 maternal diet increased n-6 fatty acids, whereas the 18:3n-3 diet increased n-3 fatty acids in milk and pup jejunal and colonic phospholipids. Maternal diet, milk, and pup intestinal n-6-to-n-3 fatty acid ratios increased significantly in order: high 18:3n-3 < high 18:1n-9 < high 18:2n-6. DNBS administration in pups in the high 18:2n-6 group led to severe colitis with higher colonic damage scores and MPO activity than in the 18:1n-9 and 18:3n-3 groups. High maternal dietary 18:3n-3 intake was associated with colonic damage scores and MPO activity, which were not significantly different from ethanol controls. We demonstrate that maternal dietary fat influences the composition of intestinal lipids and responsiveness to experimental colitis in nursing offspring.     

Stearoyl-CoA desaturase 1 genotype and stage of lactation influences milk fatty acid composition of Canadian Holstein cows

Single nucleotide polymorphisms in the coding region of the bovine stearoyl-CoA desaturase 1 gene have been predicted to result in p.293A (alanine at amino acid 293) and p.293V (valine at amino acid 293) alleles at the stearoyl-CoA desaturase1 locus. The objectives of this study were to evaluate the extent to which genotypes at the stearoyl-CoA desaturase 1 locus and stage of lactation influence milk fatty acid composition in Canadian Holstein cows. Cows with the p.293AA genotype had higher C10 index, C12 index and C14 index and higher concentrations of C10:1 (10 carbon fatty acid with one double bond), C12:1 (12 carbon fatty acid with one double bond) and myristoleic acid (C14:1) compared with the p.293AV or p.293VV cows. Cows had higher C18 index and total index, and lower C10 index, C12 index, C14 index and CLA index during early lactation compared with the subsequent lactation stages. Early lactation was also characterized by higher concentrations of oleic acid (C18:1 cis -9), vaccenic acid (C18:1 trans -11), linoleic acid (C18:2), monounsaturated fatty acids and total polyunsaturated fatty acids, and lower concentrations of capric acid (C10:0), C10:1, lauric acid (C12:0), C12:1, myristic acid (C14:0), myristoleic acid (C14:1), palmitic acid (C16:0) and total saturated fatty acids compared with the subsequent lactation stages. Neither the stearoyl-CoA desaturase 1 genotype nor the stage of lactation had an influence on conjugated linoleic acid concentrations in milk.     

Mechanisms of inhibition of triacylglycerol hydrolysis by human gastric lipase

In the human stomach, gastric lipase hydrolyzes only 10 to 30% of ingested triacylglycerols because of an inhibition process induced by the long chain free fatty acids generated, which are mostly protonated at gastric pH. The aim of this work was to elucidate the mechanisms by which free fatty acids inhibit further hydrolysis. In vitro experiments examined gastric lipolysis of differently sized phospholipid-triolein emulsions by human gastric juice or purified human gastric lipase, under close to physiological conditions. The lipolysis process was further investigated by scanning electron microscopy, and gastric lipase and free fatty acid movement during lipolysis were followed by fluorescence microscopy. The results demonstrate that: 1) free fatty acids generated during lipolysis partition between the surface and core of lipid droplets with a molar phase distribution coefficient of 7.4 at pH 5.40; 2) the long chain free fatty acids have an inhibitory effect only when generated during lipolysis; 3) inhibition of gastric lipolysis can be delayed by the use of lipid emulsions composed of small-size lipid droplets; 4) the release of free fatty acids during lipolysis induces a marked increase in droplet surface area, leading to the formation of novel particles at the lipid droplet surface; and 5) the gastric lipase is trapped in these free fatty acid-rich particles during their formation. In conclusion, we propose a model in which the sequential physicochemical events occurring during gastric lipolysis lead to the inhibition of further triacylglycerol lipolysis.     

Metabolic effects of intravenous LCT or MCT/LCT lipid emulsions in preterm infants

Most lipid emulsions for parenteral feeding of premature infants are based on long-chain triacylglycerols (LCTs), but inclusion of medium-chain triacylglycerols (MCTs) might provide a more readily oxidizable energy source. The influence of these emulsions on fatty acid composition and metabolism was studied in 12 premature neonates, who were randomly assigned to an LCT emulsion (control) or an emulsion with a mixture of MCT and LCT (1:1). On study day 7, all infants received [13C]linoleic (LA) and [13C]alpha-linolenic acid (ALA) tracers orally. Plasma phospholipid (PL) and triacylglycerol (TG) fatty acid composition and 13C enrichments of plasma PL fatty acids were determined on day 8. After 8 days of lipid infusion, plasma TGs in the MCT/LCT group had higher contents of C8:0 (0.50 +/- 0.60% vs. 0.10 +/- 0.12%; means +/- SD) and C10:0 (0.66 +/- 0.51% vs. 0.15 +/- 0.17%) than controls. LA content of plasma PLs was slightly lower in the MCT/LCT group (16.47 +/- 1.16% vs. 18.57 +/- 2.09%), whereas long-chain polyunsaturated derivatives (LC-PUFAs) of LA and ALA tended to be higher. The tracer distributions between precursors and products (LC-PUFAs) were not significantly different between groups. Both lipid emulsions achieve similar plasma essential fatty acid (EFA) contents and similar proportional conversion of EFAs to LC-PUFAs. The MCT/LCT emulsion seems to protect EFAs and LC-PUFAs from beta-oxidation.