Reflectance spectroscopy and geochemical analyses of Lake Hoare sediments, Antarctica: implications for remote sensing of the Earth and Mars.

Visible to infrared reflectance spectroscopic analyses (0.3-25 micromoles) have been performed on sediments from the Dry Valleys region of Antarctica. Sample characterization for these sediments includes extensive geochemical analyses and X-ray diffraction (XRD). The reflectance spectra and XRD indicate major amounts of quartz, feldspar, and pyroxene in these samples and lesser amounts of carbonate, mica, chlorite, amphibole, illite, smectite, and organic matter. Calcite is the primary form of carbonate present in these Lake Hoare sediments based on the elemental abundances and spectroscopic features. The particle size distribution of the major and secondary components influences their detection in mixtures and this sensitivity to particle size is manifested differently in the "volume scattering" and "surface scattering" infrared regions. The Christiansen feature lies between these two spectral regimes and is influenced by the spectral properties of both regions. For these mixtures the Christiansen feature was found to be dependent on physical parameters, such as particle size and sample texture, as well as the mineralogy. Semiquantitative spectroscopic detection of calcite and organic material has been tested in these quartz- and feldspar-rich sediments. The relative spectral band depths due to organics and calcite correlate in general with the wt% C from organic matter and carbonate. The amounts of organic matter and carbonate present correlate with high Br and U abundances and high Ca and Sr abundances, respectively. Variation in the elemental abundances was overall minimal, which is consistent with a common sedimentary origin for the forty-two samples studied here from Lake Hoare.

Metabolism of aspartame and its L-phenylalanine methyl ester decomposition product by the porcine gut.

The intestinal metabolism of aspartame (N-L-alpha-aspartyl-L-phenylalanine methyl ester; APM) and its L-phenylalanine methyl ester (PME) decomposition product was evaluated in six young pigs. Equimolar doses (2.5 mmol/kg body weight) of APM, PME, and L-phenylalanine (PHE) administered to the proximal jejunum produced similar increases in portal blood PHE concentrations. Methanol, nondetectable in portal blood after PHE ingestion, increased markedly after administration of either APM or PME. Portal blood aspartate concentrations were unchanged after PME and PHE administration, but increased significantly after APM administration. Increases in portal blood PHE concentrations were significantly greater than were increases in aspartate concentrations following APM administration. Neither APM, PME, nor aspartyl-phenylalanine (AspPhe) were detected in portal or vena caval blood following administration of any test compound. Steady-state perfusion of the small intestine with APM showed a net intraluminal appearance rate of AspPhe at 36% of the disappearance rate of APM. During steady-state PME perfusion, PHE had a significantly greater net appearance rate than during APM perfusion. Methanol appearance rates were slightly, but not significantly, higher during PME than during APM perfusions. The data suggest that (1) APM is hydrolyzed to AspPhe and both APM and PME are hydrolyzed to their constituent amino acids and and methanol prior to entering the portal circulation; (2) AspPhe is an important intraluminal intermediate in aspartame metabolism; and (3) aspartate is rapidly metabolized by the enterocyte.

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover.

Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.

Source of the urinary maltose and maltotriose excreted during intravenous infusion of oligosaccharide solutions in young pigs.

Pigs infused with preparations of glucose oligosaccharides excrete sizeable quantities of maltose in urine despite the absence of maltose in the infused solution. Maltose infused without other oligosaccharides is well utilized. Our studies examined possible sources of excreted maltose. We first examined whether simultaneous infusion of larger oligosaccharides with maltose inhibits maltose utilization. Four young pigs were infused for four days with 20 g/d of a maltose-free oligosaccharide preparation to which tracer quantities of U-14C-maltose were added. Urinary excretion of maltose-plus-maltotriose increased significantly (P less than .05) from a mean +/- SD baseline value of .01 +/- .01 g/d to an overall four-day mean value of 1.33 +/- 0.47 g/d. However, only 10.7 +/- 0.78% of infused 14C-maltose was excreted, indicating that simultaneous infusion of larger oligosaccharides did not inhibit maltose utilization. The second study examined whether maltotriose present in the oligosaccharide mixture was the source of excreted maltose. Four young pigs were infused for three days with 20 g/d of a special preparation of oligosaccharides containing only trace quantities of maltose and maltotriose. Urinary maltose plus maltotriose excretion increased significantly (P less than .05) from a mean +/- SD baseline value of .01 +/- .01 g/d to 1.65 +/- 0.41 g/d during oligosaccharide infusion. The data suggest that excreted maltose and maltotriose arise from the catabolism of larger oligosaccharides.

Oligosaccharides as an intravenous energy source in postsurgical patients: utilization when infused with glucose, amino acids, and lipid emulsion.

Utilization of intravenously administered oligosaccharides was evaluated in postsurgical patients by infusing oligosaccharides simultaneously with glucose, amino acids, and lipid emulsion for 4 d postoperatively. Seven patients were infused with a nutritional regimen providing glucose, amino acids, lipid emulsion, and oligosaccharides and seven patients received a similar regimen without oligosaccharides. Patients infused with oligosaccharides received an overall mean (+/- SD) of 144 +/- 41.0 g oligosaccharides per day. The mean overall excretion of total glucose (free plus oligosaccharide-bound) was significantly greater in patients infused with oligosaccharides (65.1 +/- 33.2 g/d) than in controls (1.83 +/- 1.55 g/d). Overall oligosaccharide utilization for the 4-d period was 48.7 +/- 10.1%. Plasma oligosaccharide concentrations increased from a baseline value of 2.43 +/- 1.90 mg/dL to 58.1 +/- 42.3 mg/dL after 4 d of oligosaccharide infusion, suggesting accumulation.

Method for evaluating utilization of infused oligosaccharides in postsurgical patients.

Oligosaccharides are potential sources of carbohydrate-derived energy for use in parenteral nutrition regimens. Clinical studies indicate that although some patients utilize infused oligosaccharides well, many patients do not. These results suggest that oligosaccharides might be useful as a parenteral energy source for selected patients. This report describes a method, suitable for use by nursing staff on the ward, to determine oligosaccharide utilization and identify patients utilizing oligosaccharides well. Oligosaccharides excreted in urine are hydrolyzed enymatically to glucose using alpha-glucosidase and alpha-amylase, and the glucose released is measured by a test tape method. The results obtained agree well with the acid hydrolysis-spectrophotometric assay for oligosaccharide excretion used in earlier studies. The method readily identified postsurgical patients utilizing infused oligosaccharides poorly in both prospective and retrospective studies.

Utilization of intravenously administered glycogen by young pigs.

Previous studies evaluated solutions of small oligosaccharides as potential sources of carbohydrate-derived energy for patients fed intravenously. Although results with these solutions were disappointing, the data suggested that very large oligosaccharides were potential sources of intravenous carbohydrate. To test this hypothesis, four young pigs (3.6 +/- 0.2 kg; mean +/- SD) were infused with sterile solutions for a 6-d period. On days 1 and 6, a balanced isotonic electrolyte solution was infused. On days 2-5 a 9% solution of glycogen was infused at a rate providing 17.7 +/- 0.77 g/d. For each study day the remaining portion of the energy, protein, essential fatty acids and micronutrients was supplied enterally. No adverse reactions were noted during glycogen infusion, and the animals continued to grow. Glycogen utilization was 66.4 +/- 4.3%. Of the total carbohydrate excreted, 85.4% was composed of oligosaccharides of maltotetraose size or larger. Free glucose accounted for 3.5% of the total excreted, while maltose plus maltotriose accounted for 11.1%. Plasma concentrations of oligosaccharide-bound glucose increased during glycogen infusion, rising from a base-line value of 11.0 +/- 14 mg/dL to an overall mean value for the 4-d period of 100.3 +/- 31.6 mg/dL.

Effects of equimolar doses of L-methionine, D-methionine and L-methionine-dl-sulfoxide on plasma and urinary amino acid levels in normal adult humans.

Plasma and urinary amino acid levels were measured in four normal adult subject administered equimolar quantities (0.0605 mmol/kg body wt) of L-methionine, D-methionine and L-methionine-dl-sulfoxide in a randomized crossover design. Plasma total methionine concentrations increased significantly (P less than 0.05) over base line (3.7 +/- 1.2 mumol/dl; mean +/- SD) after loading with each compound. Mean peak plasma methionine levels were 9.8 +/- 1.1, 14.4 +/- 2.3 and 5.2 +/- 1.0 mumol/dl after loading with L-methionine, D-methionine and L-methionine sulfoxide, respectively. D-Methionine accounted for the increased plasma levels seen after D-methionine loading. None of the three compounds affected plasma cystine, cysteine or taurine concentrations. Plasma methionine sulfoxide concentrations were not affected by loading with D- or L-methionine but increased significantly after ingestion of L-methionine sulfoxide. Urinary methionine excretion was 20 times higher after ingestion of D-methionine than after ingestion of L-methionine or L-methionine sulfoxide, with the increase due to D-methionine excretion. Urinary excretion of methionine sulfoxide and its N-acetyl derivatives was not significantly higher after loading with methionine sulfoxide. The data indicate that adult humans do not utilize D-methionine efficiently as a methionine source but probably do utilize L-methionine-dl-sulfoxide.

Utilization of parenterally administered glucose oligosaccharides when infused with glucose and amino acids in postsurgical patients.

Utilization of intravenously administered oligosaccharides was tested in postsurgical patients by infusing them simultaneously with glucose and amino acids. Thirty two patients were infused with one of two parenteral regimens for four-day periods. Twenty-two patients received a nutritional regimen providing 46 g glucose, 32.5 g amino acids, and 45 g oligosaccharides per liter, while the remaining ten patients received the same solution without oligosaccharides. Patients infused with the test solution received an overall four-day mean +/- SD of 106 +/- 24.2 g oligosaccharide per day. The mean overall four-day excretion of total glucose (free plus oligosaccharide bound) was significantly higher (P less than 0.001) in patients infused with oligosaccharides (46.1 +/- 29.0 g/d) than in reference patients (1.19 +/- 1.20 g/d). Of the total carbohydrate excreted in patients receiving oligosaccharides, 11.3 +/- 13.1 g/d were glucose, 14.8 +/- 13.1 g/d were maltose plus maltotriose, and 20.8 +/- 19.3 g/d were oligosaccharides of maltotetraose size or larger. Although overall utilization of infused oligosaccharide for all patients was only 58.5% +/- 23.1%, three of the patients showed unexpectedly good utilization (94.6% +/- 1.24%).

Intravenous lipid emulsions in the treatment of essential fatty acid deficiency: studies in young pigs.

Essential fatty acid deficiency (EFAD) occurs in infants fed fat-free mixtures of glucose and amino acids. Although infusion of lipid emulsion rapidly reverses clinical symptoms, little is known about effects on tissue fatty acids. To study this question, five groups (n = 4/group) of neonatal pigs were studied. Three groups (I, II, and V) were made EFAD by feeding diets without essential fatty acids (EFA) for days 5 to 33 of life. Groups III and IV were fed a control diet. By 33 days, animals fed the deficient diet showed clinical symptoms and biochemical signs of EFAD. On days 33 to 54 of life, group I animals were fed the EFA-deficient diet and infused with lipid emulsion, providing 3.6% of energy as linoleic acid; group II animals were fed the deficient diet and infused with linoleic acid at 7.2% of energy; group V animals were fed the deficient diet with no lipid emulsion; group III and IV animals were fed the EFA-deficient diet and provided EFA intravenously. Infusion of lipid emulsion rapidly reversed clinical symptoms of EFAD and returned plasma phospholipid omega 6 fatty acids levels to normal. However, erythrocyte and liver phospholipid omega 6 fatty acid content and adipose tissue reserves of omega 6 fatty acids normalized more slowly. Three weeks of infusion of linoleic acid at 3.6% of energy and 2 weeks of infusion at 7.2% of energy were required to return erythrocyte phospholipid fatty acids to normal. Liver phospholipid fatty acid composition still showed biochemical evidence of EFAD in animals treated with linoleic acid at 3.6% of energy for 3 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

Portal and vena caval plasma methionine concentrations in young pigs administered L-methionine, N-acetyl-L-methionine and N-acetyl-D-methionine.

N-Acyl-methionine derivatives have been proposed as replacements for methionine in supplementing food products low in this amino acid. We studied the effects of N-acetyl-L-methionine, N-acetyl-D-methionine and L-methionine loads (2 mmol/kg body weight) on portal and vena caval plasma amino acid concentrations in young pigs (n = 4). L-Methionine loading significantly increased mean (+/- SD) portal and vena caval plasma methionine concentrations from baseline values of 6.44 +/- 1.03 and 6.63 +/- 0.99 mumol/100 ml, respectively, to mean peak values of 340 +/- 75.0 and 265 +/- 49.8 mumol/100 ml, respectively. N-Acetyl-L-methionine loading increased mean peak portal and vena caval plasma methionine concentrations to 291 +/- 85 and 220 +/- 51.6 mumol/100 ml, respectively. N-Acetyl-L-methionine could not be detected in either portal or vena caval plasma. In contrast, N-acetyl-D-methionine loading produced only a small rise in mean peak portal and vena caval plasma methionine concentrations (13.0 +/- 4.31 and 8.62 +/- 1.71 mumol/100 ml, respectively). Concentrations of N-acetyl-D-methionine increased from baseline values of 0 mumol/100 ml to mean peak values of 251 +/- 32.0 and 234 +/- 72.3 mumol/100 ml, respectively, in portal and vena caval plasma. These data explain the poor utilization of N-acetyl-D-methionine as a methionine source.

Effect of meal components on peripheral and portal plasma glutamate levels in young pigs administered large doses of monosodium-L-glutamate.

Mean peak plasma glutamate concentrations and area under the plasma glutamate concentration-time curve are much lower in adult humans ingesting monosodium L-glutamate (MSG) in formula than in water. The present study investigated the effects of individual meal components on portal and vena caval plasma glutamate concentration in young pigs administered MSG. Portal vein catheters and gastrojejunal tubes were placed in four young male pigs, and the animals were allowed to recover. Each animal was then administered four water solutions providing 500 mg/kg body weight MSG in a Latin square design. One solution provided only MSG; the second provided MSG and 1 g/kg body weight metabolizable carbohydrate (partially hydrolyzed corn starch); the third provided MSG and 1 g/kg body weight nonmetabolizable carbohydrate (beta-cellobiose); and the fourth provided MSG and 0.4 g/kg body weight of an amino acid mixture (Aminosyn, Abbott Laboratories, North Chicago, Ill). Mean peak plasma glutamate concentration and area under the plasma glutamate concentration-time curve were significantly lower (P less than 0.05) in both portal and vena caval blood when MSG was administered with metabolizable carbohydrate than when administered in water. Simultaneous ingestion of MSG with nonmetabolizable carbohydrate (beta-cellobiose) or amino acids had no significant effect on either mean peak portal or vena caval plasma glutamate concentration or area under the plasma glutamate concentration-time curves when compared to values observed when MSG was administered alone. The data suggest that metabolizable carbohydrate is the meal component affecting plasma glutamate concentration.

Utilization of intravenously administered beta-cellobiose and maltose by young pigs.

Intravenous solutions of glucose oligosaccharides are potential sources of carbohydrate-derived energy for patients requiring intravenous feeding. Relatively little is known about utilization of glucose oligosaccharides linked by beta-glucosidic bonds. We compared the utilization of maltose (alpha-D-glucosyl-1,4-D-glucose) and beta-cellobiose (beta-D-glucosyl-1,4-D-glucose) when administered intravenously (19 g per day) to young pigs for a 5-day period. Animals infused with maltose excreted 15% of the infused disaccharide over the 5-day infusion period. No evidence of maltose accumulation was noted in plasma, and kidney morphology was normal. Animals infused with beta-cellobiose excreted 95% of the infused disaccharide in the urine. The mean (+/- SD) plasma total glucose concentration increased significantly over base-line values of 114 +/- 39 mg/dl to a value of 180 +/- 28 mg/dl during cellobiose infusion, indicating accumulation of cellobiose in body water. Kidney morphology in cellobiose-infused animals was normal. Intravenously infused beta-cellobiose is poorly utilized by the pig when compared with the utilization of its alpha-1,4 linked isomer, maltose.

Utilization of intravenously infused glucose-oligosaccharides in fasted and fed pigs.

The ability of fed or fasted 30-day-old pigs to utilize intravenously administered glucose-oligosaccharides (supplied at 20 g/day) was compared in a randomized crossover design. Six pigs were fed a stock diet from days 10 to 30 of life. A central venous catheter was placed on day 30. From days 30 to 39 of life, either a balanced electrolyte solution or a glucose-oligosaccharide solution was infused through the intravenous (i.v.) catheter. On the first i.v. feeding day, all animals were infused with an isotonic, balanced electrolyte solution and were allowed food and water ad libitum per os. On days 2 through 5 of the i.v. period, 3 animals received glucose-oligosaccharides intravenously (20 g/day), with all other needed nutrients, including energy, supplied enterally. On days 6-9 of the i.v. infusion period these animals continued to receive oligosaccharides intravenously, but were denied food. The other three animals were infused with oligosaccharides in the fed or fasting state in the reverse order. Based on urinary carbohydrate excretion, mean (+/- SD) glucose-oligosaccharide utilization was 92% whether the animals were fed or fasted. These results differ from those observed in fasted human subjects.

Utilization of intravenously administered glucose-oligosaccharides in growing miniature pigs.

The ability of intravenously administered glucose or glucose oligosaccharides to supply 12% of the energy requirement of the growing miniature pig was determined. All pigs were fed a stock diet from days 5-28 of life, and a central venous catheter was inserted at 29 days. For the next 30 days, all pigs were fed both enterally and parenterally. Positive control pigs were fed the stock diet with infusions of an isotonic balanced electrolyte solution. Negative control and test animals were fed a diet containing cellulose to replace 12% of energy. Negative control animals received the balanced electrolyte solution intravenously, while test animals received either intravenous glucose of glucose oligosaccharides at levels providing 12% of energy. Carbohydrate utilization was measured by urinary loss of carbohydrate, as well as by growth and body composition. Chemical analyses of the urine indicated utilization of both glucose and glucose oligosaccharides. Glucose oligosaccharides were utilized less well (85%) than glucose (greater than or equal to 99%). No statistically significant differences in weight gain were noted between groups, although weight gain in negative control animals and those animals infused with glucose oligosaccharide solutions were lower than those in the other groups. Body fat analyses also indicated that glucose oligosaccharide solutions were less effective than glucose as an energy source.

Utilization of intravenously administered maltose by growing miniature pigs.

The ability of intravenously administered maltose or glucose to supply 12% of the energy requirements of growing miniature pigs was compared. All pigs were fed a stock diet from days 5 to 28 of life, and a central venous catheter was placed at 28 days. For the next 30 days, all pigs were fed orally and intravenously. Positive control pigs were fed the stock diet with infusions of an isotonic balanced electrolyte solution. Negative control and test animals were fed a diet containing cellulose to replace 12% of energy. Negative control animals received the balanced electrolyte solution intravenously, while test animals received either intravenous glucose or maltose at levels providing 12% of energy. Carbohydrate utilization was measured by loss of urinary carbohydrate, as well as by growth and body composition. Chemical analyses of the urine indicated utilization of both maltose and glucose, but maltose was utilized less well (87%) than glucose (greater than 99%). Growth and body composition data also indicate maltose utilization. The data suggest a possible role for maltose infusion as a supplemental energy source.

D-methionine utilization in young miniature pigs, adult rabbits, and adult dogs.

Rats and chickens, unlike man, utilize D-methionine efficiently. We have studied urinary excretion of methionine isomers in young miniature pigs, adult rabbits, and adult dogs given D-methionine in an attempt to find an animal model that, like man, utilizes the D-isomer poorly. Six-week-old miniature pigs ingesting a protein-free diet were infused with 8.5% amino acid solutions differing only in methionine isomer content (L- vs DL-) to supply amino acid requirements. Each solution was infused for a 2- or 3-day period in a cross-over design. Plasma methionine levels were significantly higher (p = 0.01) during infusion of the solution providing DL-methionine, with 25% of total plasma methionine present as the D-configuration. However, urinary methionine excretion was similar with both solutions, with D-methionine utilization calculated as greater than 99%. Adult rabbits ingesting DL-methionine (0.14 g/100 g food) showed good utilization of D-methionine, excreting less than 1.3% D-isomer in the urine. Mixed breed dogs given 1.25 g D-methionine in their drinking water excreted less than 0.4% of ingested D-methionine in the urine. These data indicate that the pig, rabbit, and dog utilize D-methionine efficiently, behaving like the rat and chicken rather than man.