Metabolic Partitioning Research Articles

Effect of Chronic Treatment with Lacidipine or Lisinopril on Intracellular Partitioning of Glucose Metabolism in Type 2 Diabetes Mellitus

Effect of Chronic Treatment with Lacidipine or Lisinopril on Intracellular Partitioning of Glucose Metabolism in Type 2 Diabetes Mellitus

Stable isotope distribution in the major metabolites of source and sink organs of Solanum tuberosum L.: a powerful tool in the study of metabolic partitioning in intact plants

A method was developed for the purification of main intermediates and storage products of leaves and tubers of potato for analysis of their 13C content. The method was tested for recovery of metabolites and carbon isotope discrimination during the purification process. Leaf metabolite δ13C values showed an enrichment of starch relative to sucrose and citrate. This result is in agreement with previous findings in other higher plants and indicates the existence of isotope discrimination steps during transport and metabolism of triose-phosphates in potato leaf mesophyll cells. Active anaplerotic replenishment of the tricarboxylic acid cycle in the leaves of the plants investigated was also deduced from the significant 13C enrichment of malate relative to citrate and asparagine/aspartate relative to glutamine/glutamate. Analysis of tuber metabolite δ13C values showed no difference between starch and sucrose. However, tuber sucrose appeared significantly enriched compared with leaf sucrose and also relative to tuber citrate and malate. This finding suggests the existence of sites of isotopic discrimination during sucrose processing in developing tubers. It also confirms that metabolic cycles of sucrose synthesis and breakdown and of hexose-phosphate/triose-phosphate interconversion, which have been described in excised tuber tissue, also occur in intact organs. The δ13C values were also used to estimate the metabolic rate of carbon oxidation in developing tubers on the assumption that pyruvate dehydrogenase is the main site of isotopic discrimination in the tuber cells. The result obtained was in agreement with the available literature, suggesting that analyses of natural isotopic distribution in plant products may be a useful tool for the study of metabolic processes and sink-source relationships in intact plants.

Cysteine Sulfinic Acid Decarboxylase mRNA Abundance Decreases in Rats Fed a High-Protein Diet

The partitioning of cysteine metabolism between sulfate and taurine biosynthetic pathways may be regulated in part by the activity of cysteine sulfinic acid decarboxylase (CSAD). CSAD activity is repressed by high-protein feeding, and we have previously reported that changes in CSAD activity are correlated with changes in CSAD protein. We conducted experiments to determine the relative expression of CSAD mRNA in rats fed 18 or 60% casein diets. In rats fed a 60% casein diet for 1 wk, hepatic CSAD activity and CSAD protein were 16 and 36%, respectively, of the values measured in rats fed the 18% casein diet. CSAD mRNA abundance in rats fed the 60% casein diet was 14% of the CSAD mRNA abundance in rats fed an 18% casein diet. The time course of the change in CSAD activity and mRNA abundance was examined in rats fed 18 or 60% casein diets for 48 h. Within 6 h of switching rats to a 60% casein diet, CSAD activity was decreased by 20% and after 48 h, activity was decreased 47% compared to activity measured at baseline. CSAD mRNA abundance was decreased 54% within 12 h of feeding rats a high-protein diet and remained depressed at 48 h. In a parallel group of rats fed the 18% casein diet, CSAD activity and CSAD mRNA were not significantly different from baseline values at 48 h. The decreased expression of CSAD mRNA in rats fed a high-protein diet is consistent with decreases in both CSAD enzyme activity and CSAD protein. Our results suggest dietary protein may regulate CSAD at the level of mRNA.

Influence of lipid content of testmeal on gastrointestinal handling and metabolic partitioning of dietary lipid in young men.

Influence of lipid content of testmeal on gastrointestinal handling and metabolic partitioning of dietary lipid in young men.

The colonial cyanobacterium Trichodesmium as a physical and nutritional substrate for the harpacticoid copepod Macrosetella gracilis

The pelagic harpacticoid copepod Macrosetella gracilis uses the colonial cyanobacterium Trichodesmium not only as a physical substrate for juvenile development, but also as a food source. By associating itself with a buoyant colonial cyanobacterium, M.gracilis has developed a successful mode of life for existence in the plankton. Further evidence of M.gracills ' dependence on Trichodesmium as a physical substrate is demonstrated by previously undescribed microscopic observations of a gravid M.gracilis female attaching eggs to a Trichodesmium colony. Shipboard experiments investigating the ingestion and assimilation of Trichodesmium carbon (C) were conducted in September 1991 and January/February 1992 in waters of the Bahamas and the Caribbean, respectively. Macrosetella gracilis not only ingested, but rapidly incorporated, cyanobacterial organic matter into its own cellular material. Utilization of ingested Trichodesmium by M.gracilis was investigated by assessing the metabolic partitioning and incorporation of 14 C-labelled Trichodesmium into copepod lipids, proteins, polysaccharides and low-molecular-weight (LMW) compounds using sequential biochemical fractionation techniques. Despite variations in grazing rates between the two sites and times (September 1991,0.017 μg C * μg −1 C h −1 ; January 1992, 0.134 μg C * μg −1 C h −1 , the partitioning of incorporated C into the different biochemical fractions was relatively consistent. There was rapid assimilation of ingested C into the LMW (˜60%) and polysaccharide fractions (˜30%) in the first few hours, with a subsequent increase in the percent C incorporated into protein. On average, ˜21% of the Trichodesmium C ingested by M.gracilis was assimilated. Therefore, M.gracilis is an important secondary link in the food web of oligotrophic waters where Trichodesmium is abundant.

Carbohydrate metabolism in human platelets in a low glucose medium under aerobic conditions

The metabolism of human platelets has been the subject of investigation for at least three decades, at the level of basic metabolism, and because of the increasing requirement for platelet storage. Platelets are relatively active metabolically and are typical cells in terms of fuels and metabolic pathways. They contain glycogen and utilize glucose and demonstrate aerobic glycolysis and carbohydrate oxidation. Both glycolysis and carbohydrate oxidation contribute significantly to total ATP turnover, so platelets are an ideal system in which to study the partitioning of carbohydrate metabolism between the two available fuels and the two available pathways, in the presence of adequate oxygen. We have designed a system whereby we can study carbohydrate metabolism in relatively pure human platelets, under sterile conditions, over long periods. The system enables us to determine total ATP turnover and, with the aid of a mathematical model, the contribution to this turnover of glycolysis and the oxidation of glucose/glycogen and lactate. When glucose and glycogen are present, most of the glucose and glycogen utilised is converted to lactate, but lactate is being oxidised at this time. When glucose/glycogen stores are exhausted lactate oxidation continues and increases with time with the result that carbohydrate oxidation accounts for 41% of total ATP turnover over 48 h.

Evidence for intracellular partitioning of serine and glycine metabolism in Chinese hamster ovary cells.

Serine hydroxymethyltransferase (SHMT) is the primary enzyme in the interconversion of serine and glycine. The roles of mitochondrial and cytosolic SHMT in the interconversion of serine and glycine were determined in two Chinese hamster ovary (CHO) cell lines that both contain cytosolic SHMT but either have (CHOm+) or lacK (CHOm-) mitochondrial SHMT. Mitochondrial SHMT activity was significantly reduced in CHOm- (0.24 +/- 0.11 nmol/min per mg of mitochondrial protein) compared with CHOm+ (3.21 +/- 0.66 nmol/min per mg of mitochondrial protein; P = 0.02) cells, whereas cytosolic SHMT activity was similar in CHOm- and CHOm+ cells (1.09 +/- 0.31 and 1.53 +/- 0.12 nmol/min per mg of cytosolic protein respectively; P = 0.57). In CHOm+ and CHOm- cells, the relative flux of glycine to serine measured with either [1-13C]- or [2-13C]-glycine was similar (CHOm-: 538 +/- 82 nmol/24 per mg of DNA; CHOm+: 616 +/- 88 nmol/24 h per mg of DNA; P = 0.42). In contrast, the relative flux of serine to glycine measured with [1-13C]serine was low in CHOm- cells (80 +/- 28 nmol/24 h per mg of DNA) compared with CHOm+ cells (3080 +/- 320 nmol/24 h per mg of DNA; P = 0.0001). The rate of glycine production determined by [1-(13)C]glycine dilution was lower in CHOm- (1200 +/- 200 nmol/24 h per mg of DNA) than CHOm+ (10200 +/- 1800 nmol/24 h per mg of DNA; P = 0.03) cells, whereas glycine utilization was similar in the two cell lines. Serine production was similar in the two cell lines but serine utilization was lower in CHOm- (3800 +/- 1200 mu mol/24 h per mg of DNA) than CHOm+ (6600 +/- 1000 nmol/24 h per mg of DNA; P = 0.0002) cells. Increasing the serine concentration in the medium resulted in an increase in glycine production in CHOm+ but not in CHOm- cells. Intracellular studies with [1-13C]serine confirm the findings of decreased glycine production from serine. In CHO cells there is partitioning of intracellular serine and glycine metabolism. Our data support the hypothesis that mitochondrial SHMT is the primary pathway for serine into glycine interconversion.

Insulin and the partitioning of hepatic fatty acid metabolism.

Conference Article| August 01 1995 Insulin and the partitioning of hepatic fatty acid metabolism V. A. Zammit V. A. Zammit 1Hannah Research Institute, Ayr, KA6 5HL, Scotland, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1995) 23 (3): 506–511. https://doi.org/10.1042/bst0230506 Article history Received: February 24 1995 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation V. A. Zammit; Insulin and the partitioning of hepatic fatty acid metabolism. Biochem Soc Trans 1 August 1995; 23 (3): 506–511. doi: https://doi.org/10.1042/bst0230506 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search Keywords: ACC, acetyl-CoA carboxylase, apoB, apolipoprotein B, CPT I, carnitine palmitoyltransferase, DAG, diacylglycerol, GPAT, glycerol-3-phosphate acyltransferase, PDH, pyruvate dehydrogenase, TAG, triacylglycerol, VLDL, very-low-density lipoprotein This content is only available as a PDF. © 1995 Biochemical Society1995 Article PDF first page preview Close Modal You do not currently have access to this content.

Development of Metabolic Partitioning of Energy in Young Calves

Modifications in thermal demand and energy partitioning in newborn calves were determined over time via indirect calorimetry. One-week-old calves were fed milk replacer at 70 and 110% of the metabolizable energy requirements for maintenance, at ambient temperatures of 7.5 or 19°C, over two consecutive but separately monitored 7-d balance periods. During wk l, N digestibility, energy digestibility, and energy metabolizability were lower than during wk 2. Heat production decreased, but retention of energy and fat increased, between balance periods. During wk l, initial IgG concentration in serum was positively correlated with digestibilities of N and energy, and hemoglobin concentration was negatively correlated with heat production. Regression analysis revealed that predicted basal metabolic rate, efficiency of metabolizable energy use, and metabolizable energy requirements for maintenance were lower for wk 2 than for wk 1. Decreased energy utilization in calves on restricted feedings is related to an increase in the utilization of protein as an energy source. Young calves need at least 2 wk to adapt to the combination of new environmental temperature and low feeding amount. Metabolic partitioning of energy may indicate completion of the adaptation stage.

Dietary fat is shunted away from oxidation, toward storage in obese Zucker rats.

Previous measurements of lipoprotein lipase (LPL) activity in adipose tissue (ATLPL) of lean and obese Zucker rats have consistently documented increased activity in obese rats relative to lean. Since LPL is considered to be rate limiting for the delivery of triglyceride fatty acids (TGFA) to muscle and adipose tissue, these data have been used to suggest that the metabolic partitioning of TGFA favors storage over oxidation in obese rats. To document the partitioning of TGFA directly, the fate of 14C labeled oleic acid (42nmols) was fed to lean, obese, and obese Zucker rats fed a hypocaloric diet designed to chronically reduce weight 25% below that of obese controls (reduced-obese). The amount of 14C recovered in CO2 over 6 hours following ingestion was significantly less in obese rats compared to lean (0.45 +/- 0.06 vs. 0.88 +/- 0.09nmols, p = .0004) and less still in the reduced obese group (0.34 +/- 0.06nmols p = .00003). Six hours after ingestion, the quantity of label found in adipose tissue was significantly greater in the obese rats compared to lean (14.51 +/- 1.92 vs. 1.38 +/- 0.29nmols p < .00001), but was intermediate in the reduced-obese group (9.23 +/- 0.98nmols p = .0003). At 2.2 hours there was significantly more label in skeletal muscle of lean rats compared to either obese or reduced-obese (2.33 +/- 0.24; 1.35 +/- 0.04nmols p = .01; 1.41 +/- 0.27nm p = .02). However, at 6 hours these differences between groups were no longer present. These finding Indicate that dietary fat is shunted away from oxidation toward storage in obese Zucker rats. Additionally it appears that there may be a relative block in the oxidation of TGFA that is taken up by skeletal muscle in obese rats. Finally the relative normalization of this partitioning defect in reduced-obese rats is at variance with what was suggested by previous measurements of tissue specific levels of LPL, and suggests an enhanced recirculation of fatty acids from adipose tissue to muscle in reduced-obese rats. This could occur through increased delivery of non-esterified fatty acids (NEFA) to muscle as a result of an increase in net lipolysis.

Behavior of [14c]‐4‐nitrophenol and [14c]‐3,4‐dichloroaniline in lab sediment‐water systems. 1. Metabolic fate and partitioning of radioactivity

AbstractUsing a standard screening procedure, the fate of [14C]‐4‐nitrophenol and [14C]‐3,4‐dichloroamline was studied in lab sediment‐water systems; incubation intervals ranged from 4 h to 90 d. The sediments were collected from a creek, a pond, and a drainage ditch of a fruit‐growing plantation, and were characterized. Both compounds and their transformation products were sorbed to the sediments in large quantities; radioactivity left in the water phase was below 11 % after termination of the experiments. Besides minor amounts of 14CO2, 3,4‐dichloroaniline was converted to predominantly nonextractable residues, presumably without preceding microbial transformation of the 3,4‐dichloroaniline moiety. Two main end products were observed in the 4‐nitrophenol experiments, namely nonextractable residues and 14CO2. Data obtained from the sediment exhibiting highest microbial activity probably indicated a further mineralization of 4‐nitrophenol‐derived sediment‐bound residues. On the whole, 4‐nitrophenol presumably shows low persistence and accumulation in sediment‐water systems, whereas due to its stability the toxicity of sediment‐sorbed 3,4‐dichloroaniline should be examined.

Multicompartmental analysis of triiodothyronine kinetics in hypothyroid patients treated orally or intravenously with triiodothyronine.

Kinetic studies were performed with i.v. 125I T3 in four athyreotic women on two occasions each, once while they were taking oral T3 (30 micrograms T3 every 12 h) and again while on i.v. T3 replacement (same dosage schedule). The kinetic data were analyzed by a 7-compartment model, representing the plasma volume, the fast and slow peripheral exchange compartments, the iodide pool (as a delay compartment prior to appearance in the urine), the intestine (as a delay compartment before appearance in the feces), and the urine and feces. Modeling was done by the SAAM methodology. All data sets, and also the mean data treated as though they were data from a single subject, were fitted for the two limit solutions in which all metabolism was assumed to be in one or the other of the exchange compartments. The mean data set was also fitted to a solution in which limits were imposed on the excretion parameters and the partition of metabolism between the 2 peripheral exchange compartments was estimated. We found that steady-state parameters for removal of T3 from the circulation (the MCRs and DRs) were increased during the i.v. T3 replacement period compared with the oral replacement period, especially in the fast exchange compartment. Measured serum stable T3 levels (RIA) were lower in the i.v. than in the oral study, both at 8 and at 12 h after the most recent T3 dose. These values corresponded to similar differences in the circulating T3 levels projected from the model, although the T3 values projected from the model were greater than the measured T3 levels for unknown reasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of variable insulinemia and glycemia on in vivo glycolysis and glucose storage in dogs.

To determine the impact of variable plasma insulin concentrations and glycemia on the partitioning of whole body glucose metabolism between glycolysis and glucose storage, we estimated endogenous hepatic glucose production and rates of in vivo glycolytic flux (GF) and glucose storage (GS) in six normal dogs from the generation of plasma tritiated water (3H2O) and [3-3H]glucose specific activity during 150 min of somatostatin euglycemic (E) and hyperglycemic (H) clamps at hypoinsulinemic, basal, intermediate, and high insulin levels. During both E and H clamps, overall rates of GF and GS increased with the rising insulin levels, but the relative contributions to in vivo glucose disposal of GF decreased, whereas GS rose progressively with increasing insulin levels. The relative contribution of GS during H to overall glucose disposal was greater at the lower insulin level. In addition, in absolute terms, GF and GS were significantly higher (P < 0.05) during H than during E at all insulin levels. Moreover, the incremental rise in GF induced by H was equal for the low to intermediate insulin levels tested, independent of the prevailing free fatty acid (FFA) levels. However, when whole body glucose disposal rates were matched, GF and GS rates were independent of the coexisting glycemia, insulin, and/or FFA levels. We conclude that 1) insulin has a major impact on the intracellular fate of infused glucose, with a lesser but significant effect of hyperglycemia per se on these processes; 2) the magnitude of the hyperglycemia-induced increase in GF is independent of the prevailing insulin level from low to intermediate levels; and 3) in vivo GF and GS are dependent on the net rate of glucose uptake into cells but independent of absolute FFA levels or whether glucose uptake is stimulated by raised insulin or glucose levels.

Effects of physiological hyperinsulinemia on the intracellular metabolic partition of plasma glucose

Methodology for assessing the glycolytic and oxidative fluxes from plasma glucose, by measuring 3H2O and 14CO2 rates of production during [3-3H]- and [U-14C]glucose infusion, was tested in healthy subjects. In study 1, during staircase 3H2O infusion in six subjects, calculated rates of 3H2O appearance agreed closely with 3H2O infusion rates. In study 2, when [2-3H]glucose and NaH14CO3 were infused in four subjects in the basal state and during a 4-h euglycemic insulin (approximately 70 microU/ml) clamp, accurate estimates of the rates of [2-3H]glucose detritiation were obtained (94-97% of the expected values), and the recovery factor of NaH14CO3 did not change during hyperinsulinemia. In study 3, 11 subjects underwent a 4-h euglycemic insulin (approximately 70 microU/ml) clamp with [3-3H]- and [U-14C]glucose infusion and measurement of gaseous exchanges by indirect calorimetry to estimate the rates of total glycolysis, glycogen synthesis, glucose oxidation, nonoxidative glycolysis, hepatic glucose production, glucose recycling, and glucose conversion to fat. Hyperinsulinemia stimulated glycogen synthesis above baseline more than glycolysis [increment of 4.78 +/- 0.37 vs. 2.0 +/- 0.17 mg.min-1 x kg-1 of lean body mass (LBM), respectively, P < 0.01] and incompletely suppressed (approximately 87%) hepatic glucose production. The major component of nonoxidative glycolysis shifted from glucose recycling in the postabsorptive state (approximately 57% of nonoxidative glycolysis) to glucose conversion to fat during hyperinsulinemia (approximately 59% of nonoxidative glycolysis). Lipid oxidation during the insulin clamp was negatively correlated with both isotopic glucose oxidation (r = -0.822, P < 0.002) and glycolysis (r = -0.582, P < 0.07). In conclusion, in healthy subjects, glycogen synthesis plays a greater role than glycolysis and glucose oxidation in determining insulin-mediated glucose disposal. Part of insulin-mediated increase in glycolysis/oxidation might be secondary to the relief of the competition between fat and glucose for oxidation.

Peroxisomal beta-oxidation is a significant pathway for catabolism of fatty acids in a marine teleost.

Hepatic beta-oxidation is characterized in a marine teleost, Myoxocephalus octodecimspinosus, to determine mitochondrial and peroxisomal substrate selectivity as well as metabolic partitioning. Substrate selectivity is broad for peroxisomal beta-oxidation. Acyl CoA oxidase activities, with all unsaturated substrates measured, are at least 35% of activity with palmitoyl CoA (16:0), a saturated substrate. Mitochondrial selectivities are more pronounced. Carnitine palmitoyltransferase activity with a monounsaturate, palmitoleoyl CoA (16:1), is nearly 40% greater than activity with palmitoyl CoA, whereas activities with two polyunsaturates are < 10% of activity with the saturate. The presence of polyunsaturated acyl CoA esters inhibits up to 70% the oxidation of palmitoyl CoA by intact peroxisomes. Acyl CoA hydrolase activity is localized to peroxisomal fractions prepared by density-gradient centrifugation. Hydrolytic activity in these fractions is nearly twofold the activity of beta-oxidation. Estimates for metabolic partitioning suggest that at least 50% of hepatic beta-oxidation may be initiated by the peroxisomal compartment.

Space Allowance and Type of Housing for Growing Cattle: A Review of Performance and Possible Relation to Neuroendocrine Function

Abstract This paper reviews the effect of space allowance, feeding space and floor type in loose housing and the effect of tie stalls versus loose housing on voluntary feed intake, daily gain, feed conversion ratio, carcass and meat quality, and health. Possible physiological mechanisms involved in mediating housing-induced differences in performance are discussed. Furthermore, animal well-being, practical implications and need for future research are commented. From the review the following conclusions are made: (1) Reduced space allowance from 4.7 to 1.5 m2 per animal changes feed intake, daily gain and feed conversion ratio to 92, 81 and 115%, respectively, for bulls and steers weighing 250–500 kg. (2) Only minor differences in performance are expected in animals kept on deep bedding and slatted floors when animals are compared at the same space allowance. (3) Reducing space at feed manger to less than one per animal in loose housing systems may reduce performance, but more data are needed to quantify the effects. (4) Compared to tethered animals, loose-housed animals (≥4.7 m2 per animal) eat approximately 4% more and have an approximately 4% higher feed conversion ratio, probably due to increased exercise. (5) Loose-housed animals tend to have a higher conformation score and area of longissimus dorsi, less fat, darker meat and a tendency for tougher meat compared to tethered animals. (6) Loose-housed animals have a higher risk of inflamed legs and hoof problems compared to tethered animals. Loose-housed animals also have a higher risk of liver abscesses when they are fed high amounts of concentrates. A low space allowance on slatted floors increases the risk of tail tip lesions. Differences in performance due to space allowance are probably caused by stress. Stress results in changed levels of a multiplicity of hormones orchestrated by the neuropeptides corticotropin releasing factor (CRF), somatostatin (SS) and the catecholamines. A stress-induced reduction of feed intake may be mediated by increased levels of SS, CRF and possibly insulin, glucagon and gastrin. Evidence for the involvement of GH, ACTH, cortisol and testosterone, however, is weak. The mechanisms mediating stress-induced increase on feed conversion ratios are complex and not well understood in ruminants. However, stress may change the function of the gastrointestinal tract, nutrients absorbed, partitioning of nutrients and metabolism. A number of hormones are involved in these mechanisms, including somatotropic hormones. It is concluded that a low space allowance threatens the well-being of bulls and steers.

Alterations in Carbohydrate Intermediates in the Endosperm of Starch-Deficient Maize (Zea mays L.) Genotypes

Metabolite levels in kernels of selected starch-deficient mutants of maize (Zea mays L.) were investigated to gain insight into partitioning of carbohydrate metabolism during kernel development. Several free sugars, hexose phosphates, triose phosphates, fructose-2,6-bisphosphate, and pyrophosphate were measured in normal, shrunken, shrunken-2, amylose extender dull waxy, and brittle genotypes, which were in a near-isogenic W64A background. These mutants were selected to include at least one lesion in both the cytosolic (shrunken) and amyloplastic (shrunken-2) compartments. All the starch-deficient genotypes contained elevated levels of fructose-2,6-bisphosphate and triose phosphates but reduced levels of pyrophosphate, indicating an enhanced glycolytic utilization of carbohydrates in response to the reduced utilization of sugars for starch synthesis. The shrunken kernels (sucrose synthase deficient) contained reduced levels of glucose-1-phosphate, glucose-6-phosphate, and fructose-6-phosphate, and this reduction paralleled the reduction in starch accumulation, but levels of triose phosphates were elevated. In shrunken-2 kernels, glucose-1-phosphate, glucose-6-phosphate, and fructose-6-phosphate, dihydroxyacetone phosphate, and glyceraldehyde-3-phosphate were increased, but fructose-1,6-bisphosphate was lower. These findings support the view that hexose phosphate transport across the amyloplast envelope is more important for starch biosynthesis than transport of triose phosphates. The amylose extender dull waxy mutation showed less dramatic effects on hexose phosphates, but the triose phosphates were greatly increased. The brittle mutation, which has an unknown lesion, showed distinctly similar changes in metabolite levels with shrunken-2, suggesting that the lesion may be associated with the amyloplast.

Altered partition of threonine metabolism in pigs by protein-free feeding or starvation

Kinetic aspects of threonine (Thr) metabolism were examined in growing pigs fed a well-balanced diet (C), an isocaloric protein-free diet (PF), or starved (S) for 48 h. With the use of continuous simultaneous infusion of L-[1-13C]Thr, [1-14C]sarcosine, and 2-[1-14C]ketobutyrate (KB) for 10 h, estimates were made of rates of Thr incorporated into protein (S), released from body proteins (B), and oxidized through the catabolic pathways of L-Thr 3-dehydrogenase (TDG) and threonine dehydratase (TDH). In the C group S was 185, B was 138, Thr disposal to glycine (DRThr-Gly) was 47, and Thr disposal to KB (DRThr-KB) was 7 mumol.h-1.kg-1. Consequently, Thr balance was +48 mumol.h-1.kg-1. In the PF-fed pigs, S, B, DRThr-Gly, and DRThr-KB were significantly reduced by 38, 15, 74, and 75%, respectively. In the S group, S, B, and DRThr-Gly were significantly reduced by 47, 17, and 55%, respectively, but DRThr-KB was similar to the C group. DRThr-Gly in all groups was highly correlated with TDG enzyme activity measured in liver homogenates. By contrast with in vivo results, TDH enzyme activity was increased by 88% (P less than 0.05) in the S group and decreased by 27% (not significant) in the PF group compared with the C group. The TDH pathway accounted for 13, 12, and 27% of total Thr oxidation in the C, PF, and S groups, respectively. These results suggest that Thr conservation in protein-depleted states (PF and S groups) occurred mainly by a decrease of Thr oxidation and that the partition through these pathways was only altered when energy was completely withdrawn.

Partition of energy metabolism in the surgical newborn

Variations in energy expenditure (EE) and substrate utilization were investigated in 12 surgical neonates (body weight, 2.81 ± 0.15 kg) receiving total parenteral nutrition (TPN) at an energy intake of 66.34 ± 2.16 kcal/kg/d in a thermoneutral environment of 32°C to 34°C. Respiratory gas exchange was continuously recorded for 12 hours by a computerized, open-circuit indirect calorimeter. Physical activity was monitored on a modified Freymond scale. Urine was collected over 3 days, including the time of the calorimetry study to determine the urinary nitrogen excretion rate. Oxygen consumption, carbon dioxide production, nonprotein respiratory quotient, and EE were calculated according to the principles of indirect calorimetry for each 30-minute period and for the entire 12 hours. During the indirect calorimetry study the patients were receiving a fat-free TPN mixture consisting of 10% glucose and 2% amino acids ( GL AA ) for 8 hours. The fat-free TPN was interupted by an isocaloric and isovolemic infusion of Intralipid 10% (IL) for 4 hours. The effect of physical activity on EE was evaluated separately according to the macronutrient intake ( GL AA for 8 hours v IL for 4 hours) and then combined throughout the 12 hours of intravenous alimentation. The neonates were resting during 80% of the 12-hour study time (range, 38% to 90%). The partition of EE expressed as mean ± SEM in kcal/kg/d was: total EE 48.5 ± 2.1; resting EE 43.9 ± 1.6; energy cost of activity 4.6 ± 1.3. Resting EE ranged from 33 to 51 kcal/kg/d and correlated positively with body weight ( r = .96; P = .0001), body length ( r = .79; P = .002), and body surface area ( r = .95; P = .0001). The coefficient of variation for resting EE was higher between subjects (12%) than between each 30-minute period (9%). No significant differences were found in daily resting EE between 30-minute and 12-hour measurements. Total EE correlated positively with the percentage of time spent for crying/total body movement ( r = .65; P = .012). EE variability among surgical neonates receiving TPN in a thermoneutral environment, depends on interindividual differences during rest and activity. Resting EE can be accurately estimated by indirect calorimetry from 30-minute measurements. Physical activity contributes up to 9% of the total EE. Substrate utilization in these patients was not effected by the vigorous muscular activity.

Regulation of fatty acid metabolism and gluconeogenesis by growth hormone and insulin in sheep hepatocyte cultures. Effects of lactation and pregnancy

Primary monolayer hepatocyte cultures derived from non-mated, pregnant and lactating sheep were used to investigate the interactions between the effects of growth hormone and insulin on (i) the partitioning of fatty acid metabolism between oxidation and esterification, and (ii) the rate of gluconeogenesis. In hepatocytes from lactating sheep the rates of gluconeogenesis, ketogenesis and very-low-density lipoprotein secretion were approx. 2-fold higher than in cells from non-mated or pregnant animals. There was no apparent difference in the rates of fatty acid uptake between the three groups of sheep cells. Growth hormone stimulated gluconeogenesis only in hepatocytes from non-mated sheep. It has no effect on the flux of fatty acid towards ketone body formation. Growth hormone inhibited intracellular accumulation of acylglycerol from exogenous fatty acid. Insulin alone had no such effect, but it blunted the effect of growth hormone when the two hormones were present together. The data suggest that major differences may exist between ruminants and non-ruminants in the response of liver metabolism both to lactation per se and to the effects of growth hormone and insulin.