Uptake Of AA Research Articles

The transport of vitamin C in the isolated human near-term placenta

We investigated the specific uptake (reference: [H 3]- l-glucose) as a measure of membrane transfer of [C 14]-labeled l-ascorbic acid (AA), l-dehydroascorbic acid (DHA) and diketogulonic acid using the single injection, double tracer dilution method in the artificially perfused lobe of the near-term human placenta. The uptake of DHA (40–60%) on both the fetal and the maternal side was 3–6 times higher than the uptake of AA, whereas an uptake of diketogulonic acid was not detected. AA transport was slightly higher on the maternal side. Uptake of DHA was suppressed by phloretin and cytocholasin B, whereas AA transfer was not affected. Low sodium concentrations inhibited the uptake of DHA. d-glucose (> 20 mmol/l) inhibited the DHA uptake, and DHA inhibited d-glucose uptake but not l-alanine uptake. The K m value (self inhibition) for DHA was 6–14 mmol/l. Vitamin C enters the trophoblast predominantly as l-dehydroascorbic acid. Its transfer through the microvillous and basal membrane might use the glucose transporter, however, a specific sodium-dependent pathway is not ruled out. Our transfer data suggest an intracellular pool of vitamin C which fills up with increasing plasma DHA-concentrations.

Effect of Graded Levels of Duodenal Infusions of Casein on Mammary Uptake in Lactating Cows. 2. Individual Amino Acids

The experiment examined patterns of mammary uptake of individual AA when graded amounts of calcium caseinate (0, 177, 362, and 762 g/d) were infused duodenally into four lactating cows. Six blood samples were collected over 12h from the subcutaneous abdominal vein and the carotid. Mammary blood flow was measured by an ultrasonic flow probe implanted around the external pudic artery. Infusions of casein linearly increased the arterial concentrations of all essential AA and several nonessential AA (Pro, Tyr, Orn, and Cit) and increased, or tended to increase, linearly the mammary arteriovenous differences of all AA except Glu and Ala. Absorption ability of the mammary gland was not reduced in vivo. Relationships between mammary arteriovenous differences and arterial concentrations were positive and linear in every cow for all AA except Asn, Ser, Gly, and Ala. Some essential AA (Lys, Arg, and branched-chain AA) were therefore taken up in excess of their output into milk proteins, but others (His, Thr, Met, and Phe) were almost exclusively extracted by the udder in a direct ratio to their output. As infusions of casein increase, Phe becomes probably the most critical AA for milk synthesis.

The arachidonic acid cascade, eicosanoids, and signal transduction.

Eicosanoid biosynthesis in animal cells either results from agonist-stimulated phospholipase activation (endogenous pathway) or from lipoprotein receptor-mediated uptake and lysosomal lipid hydrolase-dependent release of AA (exogenous pathway) (see Fig. 1 for schematic representation). LDL stimulates eicosanoid formation through delivery of substrate AA to enzymes of oxidative AA metabolism. The classical LDL receptor is a control point of the effects of LDL AA on eicosanoid formation in different tissues: LDL AA metabolism occurs in several cell types of mesenchymal and epithelial origin and generates the formation of distinct eicosanoid patterns in each case. The LDL AA pathway does appear to couple directly to the PGH synthase reaction, whereas it does not couple directly to the 5-lipoxygenase reaction. We expect that a more complete characterization of the LDL unsaturated fatty acid pathway in different tissue will yield additional information on the biochemistry of lipoproteins, AA, and eicosanoids.

Effect of Graded Levels of Duodenal Infusions of Casein on Mammary Uptake in Lactating Cows. 1. Major Nutrients

Effects of duodenally infused casein on milk secretion were investigated by coupling measurements of mammary blood flow and arteriovenous differences. Four lactating cows were given a continuous duodenal infusion of 0, 177, 352, and 762g of calcium caseinate/d according to a Latin square design. Diets, formulated to meet 90% of energy and protein recommendations, consisted of a ratio of corn silage:concentrate of 76:24 supplemented with dehydrated alfalfa. Yields of milk, protein, and fat increased linearly with casein infusions (by up to 2.6 kg/d, 126 g/d, and 133 g/d, respectively) as did milk protein content (by up to 2.2 g/kg). Mammary blood flow and insulin, prolactin, and growth hormone in plasma were not affected by added casein. Concentrations of arterial acetate, glucose, BHBA, and NEFA remained unchanged, but their uptake by the udder increased by 3, 18, 22, and 91%, respectively, between the control and high casein treatments. Plasma arterial concentrations and the mammary uptake of essential and nonessential AA increased linearly with casein infusions. Although arterial concentrations increased to a much greater degree for essential AA than for nonessential AA, the increased udder extraction was higher for nonessential AA. The main part of the added AA (90%) was extracted by the udder. However, a direct transfer of supplementary-extracted AA into milk did not occur, thus increasing AA availability for other metabolic pathways.

Aging Diminishes Serotonin‐Stimulated Arachdonic Acid Uptake and Cholinergic Receptor‐Activated Arachidonic Acid Release in Rat Brain Cortex Membrane

Synaptoneurosomal and synaptosomal fractions from the brain cortex of adult (4-month-old) and aged (27-month-old) rats were used for studies on the uptake and subsequent release of [14C]arachidonic acid ([14C]AA) from brain lipids. The incorporation of AA and the pattern of its uptake into lipids of the aged brain cortex synaptoneurosomes and synaptosomes were not significantly different when compared with those in the adult brain cortex fractions. Serotonin (5-HT), at 10 microM to 1 mM in the presence of pargyline and the agonist of the 5-HT1A receptor, buspirone, stimulated AA uptake into membrane lipids, mainly into phosphatidylinositol, by about 40% exclusively in adult brain synaptoneurosomes. Aging significantly diminished the effect of 5-HT on AA uptake. Synaptoneurosomal and synaptosomal fractions prelabeled with [14C]AA were used subsequently for investigation of voltage-dependent, muscarinic and 5-HT receptor-mediated AA release. Aging diminished markedly carbachol-stimulated Ca(2+)-dependent AA liberation from membrane lipids of synaptoneurosomes and synaptosomes. Moreover, aging decreased voltage-dependent and 5-HT2 receptor-mediated AA release. These results show that aging affects receptor-dependent AA uptake and pre- and postsynaptic receptor-mediated AA release. These modulations of AA incorporation and release in aged brain may be of pathophysiological significance, in view of the importance of these processes for signal transmission in the brain. The changes of receptor-dependent processes of deacylation and reacylation may be responsible for alteration in the function of neuronal cells and may affect learning and memory ability and brain plasticity during aging.

Interorgan movements of amino acid in the pig: effects of dietary fibres

Six non-anaesthetized Large White pigs (mean body weight 59 ± 1.7 kg) were fitted with permanent catheters in the portal vein, the brachiocephalic artery and the right hepatic vein as well as with electromagnetic flow probes around the portal vein and around the hepatic artery. The animals were given a basal none-fibre diet (diet A) alone or together with 6% guar gum (diet B) or 15% purified cellulose (diet C). The diets were given for one week and according to a replicated 3 × 3 latin square design. On the last day of each such adaptation period test meals of 800 g were given prior to blood samplings. These samplings were continued for 8 h. Guar gum strongly reduced the amino acids (aa) and urea absorption as well as the hepatic production of urea. The aa profile of the absorbed mixture was not strongly modified by guar gum ingestion as well as the profile of the hepatic aa uptake. Cellulose at the consumed level had very few effects on the considered parameters.It is suggested that the modulation of intestinal mechanisms by guar gum was sufficient to mediate the latter internal metabolic effects.

Effect of stress hormones on transsplanchnic balance of exogenous amino acids in healthy man

The effect of stress hormones on transsplanchnic balance of basal and infused amino acids (AA: Val, Met, Ile, Leu, Phe, Lys, His) was investigated in healthy men without and with added epinephrine (EPI) and dexamethasone (DEX). Concentrations of AA and blood glucose were measured in arterial and hepatic venous blood before and after primed-continuous (t = 120 minutes) AA infusion without (group I: controls; n = 6, 24 ± 3 years), and with intravenous (IV) EPI infusion (group II: 6 μg/min, t = −75 to 120 minutes; n = 6, 26 ± 5 years) or oral DEX pretreatment (group III: 6 mg/d for 2 days; n = 7, 26 ± 3 years). In the absence of exogenous AA, EPI was demonstrated to increase estimated hepatic plasma flow (EHPF, mL/min: 1,019 ± 133 [mean ± SD] v 737 ± 153; P < .01), splanchnic output of glucose (SGO), and splanchnic uptake of total AA (nmol/kg · min: 4,657 ± 2,014 v 2,802 ± 704; P < .05), of Gln (+78%) and of Gly (+100%). DEX did not affect EHPF or SGO, but doubled basal splanchnic AA uptake (5,446 ± 3,635 nmol/kg · min) and increased that of Gln by 110%. Following AA administration, total splanchnic AA uptake was consistently increased (group I, 8,577 ± 2,380; II, 8,957 ± 3,714; III, 10,757 ± 2,689 nmol/kg · min) as was splanchnic Gln uptake, both of which did not differ versus controls following EPI or DEX exposure. However, metabolic clearance rate (MCR, L/min) of infused AA was elevated by 40% (Met) to 85% (Leu) versus controls in subjects receiving EPI, but unchanged in those receiving oral DEX. These data (1) demonstrate augmented basal splanchnic Gln and total AA uptake after stress hormone exposure; (2) show failure of stress hormones to affect splanchnic uptake of exogenous AA; and (3) provide evidence that EPI, but not DEX, promotes a marked increase in total AA clearance, which potentially may occur in both splanchnic and peripheral tissues.

Effect of vitamin E on arachidonic acid peroxidation and its binding to Chinese hamster V79 cell DNA

Following 24 h incubation in standard culture medium (containing 2 μM of arachidonic acid, AA), and 10 and 20 μM supplemented AA, approx. 55, 40 and 33%, respectively, of the fatty acid was incorporated into Chinese hamster V79 cell lipids. The AA content of cell increased 5 to 7-fold with the 10 and 20 μM supplementations of AA and, there was a correspondingly marked decrease in the proportion of AA incorporated into phospholipids (94 vs. 50 and 32%), whereas an increased percentage of AA was recovered in triacylglycerols (1 vs. 30 and 50%) and free fatty acids (1 vs. 3 and 8%). AA at 12 and 22 μM induced a 50 and 80% increase, respectively, in cellular content of thiobarbituric acid reactive substances (TBARS), an indication of increased peroxidation of cell lipids. This formation of TBARS was inhibited by vitamin E but not by indomethacin or SKF-525. Binding of [ 3H]AA-derived counts to DNA increased in parallel to the levels of cellular lipid peroxidation. Vitamin E added to the culture medium at 10 −4 was readily taken up by the cells within 48 h and significantly reduced both lipid peroxidation and binding of AA-derived counts to DNA, without affecting AA uptake. Cell vitamin E content was significantly reduced following 24 h incubation in the presence of 10 and 20 μM supplemented AA. This study indicates that products of lipid peroxidation can bind to DNA in cultured cells, and points to a potential cyto- and geno-toxic risk posed by increased cellular AA content relative to anti-oxidant defenses.

Renal epithelial amino acid concentrations in mercury-induced and postischemic acute renal failure

The concentration of 18 α-amino acids (AAs) in plasma and renal cortical cell water were measured 3 or 24 hr after 1 hr of unilateral renal artery clamping or 24 or 48 hr after 15 mg/kg body weight HgCl 2 injection sc as a test of epithelial integrity. Cellular glycine (Gly), hydroxyproline (Hpr), ornithine (Orn), phenylalanine (Phe), serine (Ser), and tryptophan (Trp) concentrations were depressed 24 hr after HgCl 2 ( p < 0.05), but the remaining 12 AAs were not distinguishable from control despite the presence of severe renal failure. Arginine (Arg), glutamic acid (Glu), and valine (Val) also were decreased ( P < 0.05) 24 hr later, but concentrations of half of all measured AAs were still normal. Cellular alanine (Ala), Arg, Glu, Gly, Phe, and Ser concentrations were decreased 3 hr after ischemia, p < 0.05, but 12 AAs were unchanged and only Arg, Phe, Ser, and threonine (Thr) were reduced 24 hr after ischemia was reversed. Concentrations of even the most affected AAs remained notably higher than in plasma in both forms of acute renal failure (ARF). Total loss of AAs from a small proportion of tubular cells would be hidden by essentially normal concentrations in the rest, and such losses may well have occurred. Unless cellular AAs in ARF are almost completely bound, however, the well-maintained cell:plasma AA concentration ratios indicate that cellular energetics were adequate for AA uptake and that epithelial permeability to AAs in the vast majority of cells was not greatly disturbed. Such findings suggest that most of the epithelium, although seriously damaged, had remained viable.

1446 VASCULAR PROSTAGLANDIN I2 ACTIVITY AS A FUNCTION OF GESTATIONAL AGE

PGI2 formation by vascular tissue plays an important role in maintaining the fetal-placental unit. Recently, an abnormality in PGI2 production has been reported in fetal vessels from women with pre-eclampsia, when compared to term deliveries. The gestational ages of the infants evaluated was however <38 wks. (Prostaglandins 20:105, ′80). Since a decrease in PGI2 formation by fetal vessels may be implicated in a variety of placental insufficiency syndromes, it is important to determine if PGI2 production differs in term neonates compared to prematures. We evaluated PGI2 activity from umbilical arteries of infants of various gestational ages in comparison to paired, full term control neonates. Group I consisted of 7 infants (28 to 32 wks) who were compared to simultaneously evaluated 7 term neonates. Group II comprised 8 infants (33 to 36 wks) who were compared to 8 paired term controls. Mean uptake of 14C Arachidonic Acid (A.A.) into the vessels of the term controls and Grp I prematures was similar at 8603 ± 1314 (1SD), and 8555 ± 3281 cpm per 30 mgms tissue. The production of 6-Keto-PGF1α (the end product of PGI2) was similar (4.6 ± 1.7% vs 4.5 ± 1.4%). Values for Grp II prematures were also similar to paired term control values. Uptake of 14C AA into the vascular tissues of the term controls and Grp II prematures were similar at 10170 ± 3059 and 10023 ± 2322 cpm. 6-Keto-PGF1α was also similar at 4.7 ± 0.9%, and 4.8 ± 1.2%. PGI2 activity is not age dependent during the gestational ages of 28 weeks to term.