Duodenal rapeseed oil infusion in early and midlactation cows. 5. Milk fatty acids and adipose tissue lipogenic activities

Lipogenic activities of perirenal adipose tissue were investigated in early (wk 3) and midlactation (wk 19 to 26) cows that received a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In midlactation, oil infusion resulted in a decreased rate of fatty acid synthesis from acetate and a decreased rate of the activities of fatty acid synthetase and glucose-6-phosphate dehydrogenase, whereas lipoprotein lipase activity tended to increase. The rate of glucose incorporation into glyceride-glycerol and the activities of glycerol-3-phosphate dehydrogenase and malic enzyme were not significantly affected. Fatty acid C14:0 content of perirenal adipose tissue was decreased, and fatty acid C18:2 and C18:3 contents were increased in oil-infused cows. In early lactation, rates of acetate incorporation into fatty acids and activities of fatty acid synthetase and lipoprotein lipase were very low. Activities of glucose-6-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase were lower in the early than in the midlactation trial. Oil infusion did not change the measured parameters. In both trials, percentages and yields of milk fatty acids C18:1, C18:2, and C18:3 were increased, whereas those of C14:0 and C16:0 were decreased by oil. Calculated transfer rates of absorbed fatty acid C18:2 from oil to milk fat were 16 to 26%. Results suggested that oil fatty acids affected adipose and mammary de novo lipogenesis in a direct way without affecting fatty acid esterification in adipose tissue or total fat secretion in mammary tissue.     

Mammary lipid metabolism and milk fatty acid secretion in alpine goats fed vegetable lipids

Fourteen Alpine goats at midlactation were fed a diet of hay and concentrate (55:45), without (control) or with formaldehyde-treated linseed (FLS) or oleic sunflower oil (OSO) at 11.2 or 3.5% of dry matter intake, respectively, in a 3 x 3 Latin Square design with three 3-wk periods. Milk yield was lower in goats fed FLS than control or OSO (2.13 vs. 2.32 kg/d). Milk fat content was higher with FLS or OSO than control (40.8 vs. 33.8 g/kg). Formaldehyde-treated linseed and OSO caused a significant decrease (23 and 18%, respectively) of C10 to C17 fatty acids secretion compared with control. The secretion of cis-9 C18:1 and cis-9, trans-11 C18:2 were increased 1.44- and 1.54-fold for FLS and 1.78- and 1.36-fold for OSO, compared with control. The C18:3 (n-3) secretion was increased 2.61-fold with FLS compared with control. Milk cis-9 C14:1/C14:0, cis-9 C16:1/C16:0, and cis-9 C18:1/C18:0 ratios decreased with the supplemented diets compared with control. Mammary stearoyl-CoA desaturase mRNA and activity were decreased by the lipid supplements, whereas no significant change was observed for acetyl-CoA carboxylase and fatty acid synthase. The activities of glucose-6-phosphate dehydrogenase, malic enzyme, and glycerol-3-phosphate dehydrogenase were not affected by the lipid supplements. Mammary lipoprotein lipase mRNA increased with OSO, whereas lipoprotein lipase activity tended to decrease with FLS compared with control. Milk lipoprotein lipase activity sharply decreased with lipid supplement (by 59 and 71%, for FLS and OSO, respectively). The changes in milk fatty acid profile due to FLS and OSO supplements were partly related to changes in the levels of mammary enzyme activities or mRNA.     

NADP-linked dehydrogenases in secreted milk

The activities of glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, malic enzyme, lactate dehydrogenase and malate dehydrogenase have been determined in secreted milk from sows, rats and rabbits. Within each species, although there was considerable variation in the absolute activities of these enzymes, the relative activities were similar to those observed for, or previously published for mammary homogenates. The only exception was milk glucose 6-phosphate dehydrogenase which tended to lose activity upon prolonged storage in the mammary gland. These results suggest that the pattern of milk enzymes can be an accurate reflection of that occurring in the mammary gland.     

Effect of the Iberian×Duroc reciprocal cross on productive parameters, meat quality and lipogenic enzyme activities

The aim of this study was to investigate the effect of the Iberian×Duroc reciprocal cross on: (i) productive parameters, (ii) physico-chemical traits of three muscles with different oxidative patterns (Longissimus dorsi, Biceps femoris and Psoas maior) and (iii) lipogenic enzyme activities (glucose-6-phosphate dehydrogenase and malic enzyme) in subcutaneous adipose and muscle tissues. Fourteen Duroc-sired (Duroc♂×Iberian♀) and 14 Iberian-sired castrate male pigs (Iberian♂×Duroc♀) were selected at weaning and were reared until 235 days of age. Iberian-sired pigs had significantly higher weight at slaughter (147.7kg vs. 138.8kg, p<0.05) as well as a greater ham and foreleg weight than Duroc-sired pigs. The fatty acid composition of subcutaneous adipose tissue of Duroc-sired pigs showed a higher percentage of C18:0 (13.21% vs. 14.34%, p<0.05) and a lower percentage of monounsaturated fatty acids (47.79% vs. 46.73%, p<0.05) compared to that from Iberian-sired pigs. Contrary to productive parameters, there were no noticeable differences between reciprocal cross in parameters defining meat quality, although there was a clear muscle effect on such parameters with this effect being significant for most of the traits. No differences were found between reciprocal crosses for glucose-6-phosphate dehydrogenase and malic enzymes activities in both muscular and subcutaneous adipose tissues. Lipogenic enzyme activities were considerably higher in subcutaneous adipose tissue compared to muscles. Glucose-6-phosphate dehydrogenase activity did not differ (p>0.05) between muscles, whereas malic enzyme activity was higher (p<0.05) in Psoas maior compared to Biceps femoris and those were higher than in Longissimus dorsi, which was consistent with the positive correlations (p<0.05) found between malic enzyme activity and traits defining oxidative metabolic type. On the contrary, negative correlations (p<0.05) were found between malic enzyme activity and intramuscular fat content, which could suggest that there are differences among muscles in the ability of depositing fatty acids from other tissues.     

Conjugated linoleic acid (CLA) effects on pups growth, milk composition and lipogenic enzymes in lactating rats

Conjugated linoleic acid (CLA) has a range of biological properties, including effects on lipid metabolism, milk and body composition in animals. This study investigated the effects of dietary CLA on lactating rats and development of the suckling pups. Dams were fed either a control diet or the same diet supplemented with 25 g/kg of a fat supplement containing 540 g CLA/kg (final concentration of 13.5 g CLA/kg diet) from parturition to the 15th day post-partum. The CLA mixture used in this study contained the following isomers (per 100 g): cis-9, trans-11 (24 g); cis-10, trans-12 (35 g); cis-8, trans-10 (15 g); cis-11, trans-13 (17 g) and others (9 g). On d 15 post partum, CLA supplementation reduced milk fat content by 33% and pup growth by 21%. The milk fatty acid profile, with decreased content of short and medium chain acids, suggests CLA inhibition was more pronounced for de novo lipid synthesis. Consistent with these results, activities of fatty acid synthase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were reduced by CLA treatment in the mammary gland and liver. In contrast, the activity of NADP-malate dehydrogenase was unchanged.     

Short-term and long-term effects of early nutritional deprivation on adipose tissue growth and metabolism in calves

Two groups of 10 Friesian calves received, respectively, 819 and 1380 g of milk replacer daily between birth and 95 d of age. After weaning, both groups were pair-fed until slaughter at 533 d of age. Body composition, cellularity, and lipogenic activity of kidney and omental fat were determined at 95 and 533 d of age. Milk intake restriction produced a 40% reduction of growth rate and a 68% decrease in lipid deposition between birth and 95 d of age. This was accompanied by a reduced adipose cell hypertrophy without any effect on adipose cell number. Acetate incorporation in isolated cells, glucose 6-phosphate dehydrogenase, NADP-malate dehydrogenase, and lipoprotein lipase activities were lower in restricted animals. Glucose incorporation in isolated fat cells was very slight in both groups. Acetate incorporation and lipogenic enzyme activities were more than 10 times higher in 533-d-old animals that have larger adipocytes than in younger calves. Moreover, kidney fat presented a higher rate of de novo fatty acid synthesis than omental fat. The reverse order was observed for lipoprotein lipase activity. Early postnatal nutrition had no significant effect on lipid deposition between 95 and 533 d of age. There were no significant differences in body composition, adipose tissue cellularity, or metabolism at slaughter.     

Effects of nicotinamide and oxythiamine on the lipogenic parameters of the adipose tissue of mice with non-insulin-dependent type of experimental diabetes mellitus and hyperinsulinemia]

The influence of nicotinamide and oxythiamine on the activity of NADPH-producing dehydrogenases of glucoso-6-phosphate, 6-phosphogluconate, malate, isocitrate, as well as concentration and synthesis rate of fatty acids in fatty tissue were studied in experiments on mice with genetically conditioned non-insulin-dependent diabetes and hyperinsulinemia. It has been established that in these diseases the synthesis of fatty acids and their inclusion into lipids are activated without increasing the above enzymes activity. It is shown that nicotinamide and oxythiamine inhibit inclusion of C from glucose into free fatty acids, antivitamin intensifies lipolysis in the fatty tissue of the diseased animals.     

Seasonal effects of prepartum and postpartum fat and niacin feeding on lactation performance and lipid metabolism

Control, prilled fat (5% of ration DM), niacin (12 g/d), or fat and niacin treatments were fed to 39 Holstein cows beginning 17 d prior to expected calving through 15 wk postpartum to determine effects on hepatic lipid content, plasma ketone concentration, and lactation performance. Cows were blocked according to season of calving (cool = November 1 through April 1; warm = April 2 through August 1). Fat supplementation tended to increase milk yield but only for cows that calved in the warm season. Milk composition was not affected by treatments. Fat supplementation did not decrease BW loss in early lactation but increased rate of BW gain af ter 8 wk postpartum. Dry matter intake and glucose, nonesterified fatty acid, and beta-hydroxybutyrate concentrations in plasma were not different among treatments. Fat and niacin supplementation tended to increase hepatic total lipid and triglyceride content. Between 17 d prior to expected calving and 1 to 2 d postpartum, hepatic lipid content increased approximately 2-fold and triglyceride content increased 6- to 10-fold. Hepatic lipid and triglyceride contents were greater postpartum during the warm season than the cool season and were greater at 5 wk than at freshening during the warm season but lower at 5 wk than at freshening during the cool season. The cause of the dramatic increase in hepatic lipid and triglyceride content prepartum is unknown.     

Candida albicans SOU1 encodes a sorbose reductase required for L-sorbose utilization

Previous work in our laboratory showed that L-sorbose utilization in Candida albicans is subject to a novel form of regulation which involves a reversible increase or decrease in the copy number of chromosome 5. Furthermore, the structural gene SOU1 is required for L-sorbose utilization and encodes a member of the short chain dehydrogenase family. However, the precise function of SOU1 was not known and neither was the pathway for L-sorbose utilization. We have now expressed SOU1 at a high level from a replicative plasmid having a constitutive ADH1 promoter and purified a version of Sou1p tagged with the FLAG epitope at the N-terminus. Sou1FLAGNp has a sorbose reductase activity which utilizes NADPH as a co-factor and converts L-sorbose to D-sorbitol. It can also less efficiently utilize fructose as a substrate with NADPH as a co-factor, converting fructose to mannitol. In agreement with prediction, the purified enzyme has a subunit molecular weight of 31 kDa and a pI of about 4.8. It probably consists of four identical subunits and has a pH optimum of 6.2. The L-sorbose utilization pathway in C. albicans probably converts L-sorbose to fructose-6-phosphate via D-sorbitol as an intermediate. The first step is catalysed by Sou1p. We also found that C. albicans extracts have a D-sorbitol-6-phosphate dehydrogenase activity, not encoded by SOU1, which utilizes NADP as a co-factor. This activity has not been described previously in yeasts and may be involved in the conversion of phosphorylated D-sorbitol to fructose-6-phosphate or glucose-6-phosphate.     

Activity of key enzymes involved in glucose and triglyceride catabolism during bovine oocyte maturation in vitro

Little is known about the metabolic profile of cumulus-oocyte complexes (COCs) during maturation. The aim of this study was to determine the differential participation of enzymatic activity in cumulus cells and the oocyte during in vitro maturation of bovine oocytes, by measuring the activity of key enzymes involved in the regulation of glycolysis (phosphofructokinase), the pentose phosphate pathway (glucose-6-phosphate dehydrogenase) and lipolysis (lipase). COCs were matured in medium 199 plus 10% (v/v) steer serum for 22-24 h at 39 degrees C in 5% CO(2):95% humidified air. Phosphofructokinase, glucose-6-phosphate dehydrogenase and lipase activities were measured in immature and in vitro matured COCs, denuded oocytes and cumulus cells, respectively. Phosphofructokinase and glucose-6-phosphate dehydrogenase activities (enzymatic units) remained constant during in vitro maturation of COCs, but there was a significant decrease in lipase activity (units) (P < 0.05), as activity in cumulus cells decreased significantly (P < 0.05). For the three enzymes studied, enzyme activity (units) remained unchanged in the oocyte during in vitro maturation. Specific activity increased in the oocyte (P < 0.05) and decreased in cumulus cells as a result of maturation (P < 0.05). In cumulus cells, phosphofructokinase was the most abundant of the three enzymes followed by glucose-6-phosphate dehydrogenase and then lipase (P < 0.05), whereas in the denuded oocyte this order was reversed (P < 0.05). Thus, the metabolism of cumulus cells is adapted to control the flow of metabolites toward the oocyte, which maintains its enzymatic activity even when dissociated from cumulus cells during maturation. The high activity of phosphofructokinase in cumulus cells indicates that glucose is metabolized mainly via the glycolytic pathway in these cells. The greater relative activity of glucose-6-phosphate dehydrogenase recorded in the oocyte indicates that glucose uptake could be directed mainly toward the pentose phosphate pathway. The marked lipolytic activity concentrated in the oocyte indicates an active participation in lipid catabolism during maturation.     

Effect of sunflower-seed oil and linseed oil on tissue lipid metabolism, gene expression, and milk fatty acid secretion in Alpine goats fed maize silage–based diets

Lipid in the diet is known to enhance milk fat secretion and alter milk fatty acid composition in lactating goats. In the current experiment, the contribution of peripheral tissue and mammary gland lipid metabolism to changes in milk fat composition from plant oils was examined. Fourteen Alpine goats in midlactation were used in a 3 × 3 Latin square design with 28-d experimental periods. Treatments comprised maize silage–based diets containing no additional oil (M), sunflower-seed oil (MSO; 6.1% of diet DM), or linseed oil (MLO; 6.2% of diet DM). Compared with the control, milk yield was greater in goats fed MSO (3.37 and 3.62 kg/d, respectively), whereas MLO enhanced milk fat content (+3.9 g/kg), resulting in a 14% increase in milk fat secretion. Both MSO and MLO increased milk lactose secretion by 12 and 8%, respectively, compared with M. Relative to the control, plant oils decreased C10 to C16 secretion (32 and 24%, respectively, for MSO and MLO) and enhanced C18 output in milk (ca. 110%). Diets MSO and MLO increased cis-9 18:1 secretion in milk by 25 and 31%, respectively, compared with M. The outputs of trans-11 18:1 and cis-9, trans-11 18:2 in milk were increased 8.34- and 6.02-fold for MSO and 5.58- and 3.71-fold for MLO compared with M, and MSO increased trans-10 18:1 and trans-10, cis-12 18:2 secretion. Plant oils decreased milk fat cis-9 14:1/14:0; cis-9 16:1/16:0; cis-9 18:1/18:0; and cis-9, trans-11 18:2/trans-11 18:1 concentration ratios but had no effect on mammary stearoyl-CoA desaturase mRNA or activity. Furthermore, changes in milk fatty acid secretion were not associated with alterations in mammary acetyl-CoA carboxylase mRNA and activity, abundance of mRNA encoding for lipoprotein lipase and fatty acid synthase, or malic enzyme and glycerol-3-phosphate dehydrogenase activity in mammary tissue. Mammary lipoprotein lipase activity was increased with MSO relative to MLO. Treatments had no effect on glucose-6-phosphate dehydrogenase, malic enzyme, glycerol-3-phosphate dehydrogenase activity, or mRNA abundance and/or activity of lipoprotein lipase, acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase in liver or adipose tissue. In conclusion, inclusion of sunflower-seed oil and linseed oil in maize silage–based diets alters milk fatty acid secretion in goats via mechanisms independent of changes in mammary, hepatic, or adipose tissue lipogenic gene expression. Furthermore, data provided indications that the regulation of mammary lipogenic responses to plant oils on starch-rich diets differs between the caprine and bovine.     

呼吸代谢参与粉红单端孢侵染厚皮甜瓜果实不同阶段的防御反应

目的：探讨三羧酸（tricarboxylic acid cycle，TCA）循环和磷酸戊糖途径（pentose phosphate pathway，PPP）在病原真菌侵染果实中的作用。方法：用粉红单端孢（Trichothecium roseum）接种‘玉金香’厚皮甜瓜果实，观察（22±2）℃、相对湿度55%～60%条件下病斑直径的变化，测定接种果实病健交界处组织TCA循环和PPP关键酶活力以及中间产物含量的变化，分析不同侵染阶段TCA循环和PPP发挥的作用。结果：果实病斑直径在接种后24 h内无明显变化，48 h时明显增大，72 h时显著高于对照组（P＜0.05）。与对照组相比，接种粉红单端孢显著降低了早期果实的异柠檬酸脱氢酶活力（P＜0.05），而显著提高了苹果酸脱氢酶（malate dehydrogenase，MDH）活力（P＜0.05），24 h时MDH活力是对照组的2.14 倍；显著提高了早期果实烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide，NAD）和还原型烟酰胺腺嘌呤二核苷酸含量（P＜0.05），24 h时分别高出对照组50.37%和50.31%；激活了果实的NAD激酶，显著提高了后期葡萄糖-6-磷酸脱氢酶和6-磷酸葡萄糖酸脱氢酶的活力（P＜0.05），48 h时分别是对照组的1.83 倍和2.51 倍；显著促进了后期果实烟酰胺腺嘌呤二核苷酸磷酸和葡萄糖-6-磷酸的合成（P＜0.05）；显著降低了早期和中期果实核糖-5-磷酸异构酶活力和核酮糖-5-磷酸含量（P＜0.05）。结论：粉红单端孢侵染厚皮甜瓜早期诱导了果实组织TCA循环，后期促进了PPP，说明TCA循环参与了更多果实早期的抗病防御，而PPP在后期寄主防御反应中发挥更大的作用。     

Turnover of hexosamines in the lens and glycoproteins in the blood of rats given a xylose-containing diet

To elucidate the action of xylose admixtures during the biotechnological production of monosaccharides, rats were given rations containing xylose that comprised 2.10 and 20% of the total amount of carbohydrates. Hexosamines of the lens and general blood globulin fraction were isolated and their turnover was investigated. The activity of glucoso-6-phosphate dehydrogenase, and the content of reduced and oxidized glutathione were assayed in the eyes and red blood cells. The content of xylose was determined in the plasma, eyes and red blood cells. Xylose inclusion into the ration of rats induced a pronounced increase in the half-life of hexosamines in the lens. The general blood globulin fraction turnover was unchanged. The activity of glucoso-6-phosphate dehydrogenase and the amount of total and reduced glutathione in red blood cells were decreased. Xylose content in the eyes and red blood cells was unchanged, while in the plasma it rose proportionally to the increase of its amount in the ration.     

Two mechanisms for oxidation of cytosolic NADPH by Kluyveromyces lactis mitochondria

Null mutations in the structural gene encoding phosphoglucose isomerase completely abolish activity of this glycolytic enzyme in Kluyveromyces lactis and Saccharomyces cerevisiae. In S. cerevisiae, the pgi1 null mutation abolishes growth on glucose, whereas K.lactis rag2 null mutants still grow on glucose. It has been proposed that, in the latter case, growth on glucose is made possible by an ability of K. lactis mitochondria to oxidize cytosolic NADPH. This would allow for a re-routing of glucose dissimilation via the pentose-phosphate pathway. Consistent with this hypothesis, mitochondria of S. cerevisiae cannot oxidize NADPH. In the present study, the ability of K. lactis mitochondria to oxidize cytosolic NADPH was experimentally investigated. Respiration-competent mitochondria were isolated from aerobic, glucose-limited chemostat cultures of the wild-type K. lactis strain CBS 2359 and from an isogenic rag2Delta strain. Oxygen-uptake experiments confirmed the presence of a mitochondrial NADPH dehydrogenase in K.lactis. This activity was ca. 2.5-fold higher in the rag2Delta mutant than in the wild-type strain. In contrast to mitochondria from wild-type K. lactis, mitochondria from the rag2Delta mutant exhibited high rates of ethanol-dependent oxygen uptake. Subcellular fractionation studies demonstrated that, in the rag2Delta mutant, a mitochondrial alcohol dehydrogenase was present and that activity of a cytosolic NADPH-dependent 'acetaldehyde reductase' was also increased. These observations indicate that two mechanisms may participate in mitochondrial oxidation of cytosolic NADPH by K. lactis mitochondria: (a) direct oxidation of cytosolic NADPH by a mitochondrial NADPH dehydrogenase; and (b) a two-compartment transhydrogenase cycle involving NADP(+)- and NAD(+)-dependent alcohol dehydrogenases.     

Effect of neonatal nutrition on the enzyme activity of liver lysosomes, adipocytes and thrombocytes in young and old rats

The activity of cathepsins A, B, C, D, phospholipases A1 and A2, and aryl sulphatases A and B was studied in hepatic lysosomas, adipocytes of epididymal fatty tissue and in platelets of rats aged 2,5 and 24 months differing in the character of milk feeding. It was found that excessive feeding in the neonatal period resulted in a decrease of the lysosomal proteinase activity by 18-33% in 24-month animals, while phospholipase A2 activity rose 1,4-2.2-fold. Phospholipase A2 activity proved to be also increased in adipocytes of obese rats. Obese rats' platelets were characterized by a drastic (2-3.5-fold) activation of cathepsin C, and phospholipase A1 activity rose by 55% at all the stages of the ontogenesis. It is suggested that the changes in the lysosomal hydrolases activity may reflect the platelet function in the disordered lipoprotein metabolism.     

A toxicological hygiene study of a dye made from abattoir blood for sausage products

Toxicologic and hygienic study of a pigment from abattoir blood--carboxyn (based on carboxyhemoglobin) was conducted on noninbred white rats in subacute (3 months) and chronic (12 months) experiments. The condition of the animals, their bw growth, blood morphology, erythrocyte sedimentation rate, the content of hemoglobin, protein and iron in the blood serum were evaluated. Activity of the following enzymes was studied: catalase and sorbitol dehydrogenase--in the blood serum; glucose 6-phosphate dehydrogenase, lactate dehydrogenase and cytochrome P-450 content--in the liver. Internal organs of the rats were subjected to histological investigation. The data obtained have evidenced the absence of some signs of biotransformation of the red complex of carboxyhemoglobin, or its toxic effect on the experimental animals. It has been concluded that carboxyn can be used as a coloring component in the production of sausage (in the amount of up to 2% of the sausage meat mass).     

Behavior of certain parameters of lipid and energy metabolism. 5. Effects of high-fat and low-fat diets on certain biochemical parameters in rat livers before and after change of diet]

Typical metabolic patterns are detectable in the livers of growing rats after feeding diets with high (25%) or low (2%) fat contents. In view of the elucidation of problems related to the regulation of the metabolic processes, it is of interest to know in what way these metabolic patterns change after short-time change from the one diet to the other and if there are hierarchies. Within 2 days after change of diet, the enzymes glucose-6-phosphate dehydrogenase, NAD-malate dehydrogenase, lactate dehydrogenase, citrate synthase and fatty acid synthase were affected, only the 3'.5'-c AMP-splitting phosphodieterase showed no change. The metabolites lactate and pyruvate also changed, inversely to lactate dehydrogenase activity, the lactate-pyruvate ratio remaining almost constant. Acetyl CoA also responded in a characteristic manner. The single parameters were differently affected by the kind of the change of diet (from high-fat to low-fat diet or inversely). For example, glucose-6-phosphate dehydrogenase responded very rapidly to the change from the high-fat to the low-fat diet, malate dehydrogenase behaved inversely, and citrate synthase responded to both changes. Consequently, the regulatory processes after change of diet start from different sides. It is thinkable that this behaviour is related to the different roles of the determined parameters in fat and energy metabolism.     

Utilization of oxidative pressure for enhanced production of poly-beta-hydroxybutyrate and poly(3-hydroxybutyrate-3-hydroxyvalerate) in Ralstonia eutropha

Ralstonia eutropha was cultivated under oxidative conditions in the presence of hydrogen peroxide and methyl viologen to stimulate the flux of NADPH to the PHA biosynthesis pathway. The effects of oxidants on the biosynthesis of poly-beta-hydroxybutyrate(PHB) and poly(3-hydroxybutyrate-3-hydroxyvalerate)[P(3HB-3HV)] were investigated. The biosynthesis rate and concentrations of PHB and its copolymer P(3HB-3HV) increased significantly under the oxidative pressure of methyl viologen, meanwhile, the molar fraction of 3HV in P(3HB-3HV) remained constant. The effect of methyl viologen on the flux of the intermediate compounds was investigated by measuring the activity of enzymes related to PHB biosynthesis, glucose 6-phosphate dehydrogenase (G6PD), and NADPH level. The oxidant significantly activated the G6PD of R. eutropha, increasing the NADPH level used for the reduction reaction of acetoacetyl-CoA to beta-hydroxybutyryl-CoA, thereby enhancing the biosynthesis of PHB and P(3HB-3HV).     

Duodenal infusion of glucose decreases milk fat production in grass silage-fed dairy cows

Four lactating dairy cows were arranged in a 4 x 4 Latin square design to study the effect of intestinal glucose supply on milk fat synthesis. Glucose (0, 443, 963, and 2398 g/d) was continuously infused in the duodenum over 14-d periods. Grass silage-based diets were formulated to be isoenergetic and isonitrogenous and met 100 and 110% of energy and protein requirements according to INRA (1989). Mammary uptake of nutrients was estimated through assay of arteriovenous differences and blood flow measurements. Glucose infusions decreased arterial concentrations of acetate, beta-hydroxybutyrate, and nonesterified fatty acids linearly and total glycerides curvilinearly. Milk fat yield was slightly decreased (- 52 g/d) between 0 and 963 g/d of glucose and milk fatty acid composition was modified by a marked decrease in long-chain fatty acids and an increase in de novo synthesis. The decrease in long-chain fatty acids, related to the decreased mammary uptake of plasma total glycerides, was likely due to a decrease in lipoprotein lipase and esterification activities. In regards to the evolution of metabolite concentrations in milk, the enhanced de novo synthesis and chain elongation was probably allowed by a greater availability of NADPH synthesized through pentose phosphate pathway. The greatest dose of glucose clearly decreased milk fat yield (-234 g/d). A mammary cell mediated intracellular reaction likely caused a homothetic decrease in milk fatty acids. However, reduced synthesis was not due to a shortage of glycerol-3-phosphate because its milk concentration remained unchanged. In conclusion, changes in exogenous glucose supply, in cows fed a grass silage-based diet, decreased milk fat production and modified milk fatty acid composition.     

Supplementation of dairy cow diets with calcium salts of long-chain fatty acids and nicotinic acid in early lactation.

Forty multiparous Holstein cows were assigned to one of four treatments 15 d postpartum according to milk yield during wk 2 postpartum to examine the effects of supplementing niacin, Ca salts of long-chain fatty acids, and their interaction. Treatments were control, niacin (12 g/d), Ca salts of long-chain fatty acids (3% of dietary DM), or a combination of niacin and Ca salts. On d 99 postpartum, all cows were fed the control treatment for 2 wk to evaluate residual effects. Milk and FCM yields, blood plasma NEFA and beta-hydroxybutyrate concentrations, and apparent total tract hemicellulose digestibility were increased; milk protein percentage, milk SNF percentage, and blood plasma glucose concentrations were reduced by treatments containing the Ca soaps. Niacin supplementation increased milk protein content and yield but reduced blood plasma beta-hydroxybutyrate concentration. During the residual period, in which all cows received the control treatment, milk yield and plasma NEFA concentration remained elevated, milk protein and SNF contents remained depressed, and milk fat content was reduced for cows previously supplemented with Ca salts of long-chain fatty acids. Methionine and phenylalanine uptakes by the mammary gland were enhanced by niacin supplementation. Results indicated that dairy cattle in early lactation yielded more milk when their diets were supplemented with Ca salts of long-chain fatty acids and that niacin supplementation increased milk protein content and yield.