Energetic Substrates Research Articles

In vitro alanine utilization by rat interscapular brown adipose tissue

The in vitro oxidation to CO 2 and tissue incorporation of alanine label by pieces of rat interscapular brown adipose tissue (IBAT) has been investigated. Insulin increased both uptake and oxidation of alanine, as well as the incorporation of alanine label into tissue. This effect only was observed in the presence of glucose in the incubation medium. Noradrenaline hampered alanine incorporation, not affecting its rate of oxidation. IBAT from 4-h cold-exposed rats showed a higher alanine utilization than that of controls; however, IBAT pieces from both 36-h starved and 30-day cold-exposed rats presented lower rates of alanine utilization. The main fate of alanine taken up by the IBAT pieces was its oxidation to CO 2. Part of the label was also incorporated into the fatty acid fraction of lipids. The results obtained in this study agree with a possible role of alanine as alternative energetic substrate for IBAT.

Laser-excited hot-electron induced desorption: A theoretical model applied to NO/Pt(111)

We present a theoretical model for stimulated desorption due to the interaction of energetic substrate carriers with molecular adsorbates. The model is based on the premise that optically excited hot electrons scatter into an unoccupied valence electron resonance of the adsorbate, thus forming a temporary negative molecular ion which then experiences an enhanced attraction towards the substrate. Neutralization of the ion returns the adsorbed molecule to one of the continuum states of the molecule/substrate potential energy surface, possibly in an internally excited state. The consequences of such a model are worked out using semiclassical wave packet dynamics which, in the short time limit relevant to the present situation, can be brought to an analytic realization. The model provides considerable insight into recent experiments on the laser-induced desorption of NO from Pt(111).

Meal-feeding and physical effort. 1. Metabolic changes induced by exercise training

To evaluate the consequences of the combination of meal-feeding (which causes in the long term several adaptations that lead to saving stored energetic substrates), rats subjected to a 2-hr feeding/22-hr fasting schedule were forced to swim 30 min everyday at a fixed hour during four weeks. The results indicate that meal-fed exercised rats: 1) increase food intake above that found in the nonexercising and the corresponding (nonfood-restricted) controls; 2) did not lose weight (in contrast to the controls); 3) initially had a high glycogen mobilization but at the end of the fourth week started to save hepatic glycogen again, despite the intense energy demanding exercise; 4) maintained a slight hyperglycemia; 5) mobilized less free fatty acids than the nonexercising meal-fed rats, probably due to higher insulinemia; 6) had a lower content of ascorbic acid in the adrenal glands in comparison to the control exercising rats; this suggests that the exercise was less stressful in the latter group.

Effect of low temperatures on glucose-induced insulin secretion and glucose metabolism in isolated pancreatic islets of the rat

The direct effect of hypothermia on the inhibition of insulin secretion may result from inhibition of the availability of energetic substrates and/or the lack of metabolic signals. In order to verify this hypothesis, the insulin secretion and the main metabolic glucose pathways were measured during the incubation of rat islets. In the presence of 16.7 mmol glucose/l and at 37 degrees C, insulin secretion was 925 +/- 119 microU/2 h per ten islets. With the same experimental conditions, glucose utilization, determined as the formation of 3H2O from [5-3H]glucose was 2225 +/- 184 pmol/2 h per ten islets, glucose oxidation measured as the formation of 14CO2 from [U-14C]glucose was 673 +/- 51 pmol/2 h per ten islets, pentose cycle determined as the formation of 14CO2 from either [1-14C]glucose or [6-14C]glucose was 37 +/- 5 pmol/2 h per ten islets; glucose oxidation by the tricarboxilic acid cycle, calculated to be the difference between glucose oxidation and pentose cycle values, was 636 pmol/2 h per ten islets. Hypothermia highly inhibited glucose-induced insulin secretion and glucose utilization. Inhibition of insulin secretion was partial at 27 degrees C since it was 2.5 times lower than that at 37 degrees C, and it was complete at 17 degrees C. Glucose oxidation in the tricarboxilic acid cycle was markedly inhibited by hypothermia since the inhibition coefficient (Q10) between 37 and 27 degrees C was 5. In contrast, glucose oxidation in the pentose phosphate shunt was enhanced at 27 degrees C, reaching 92 +/- 17 pmol/2 h per ten islets, and it was inhibited relatively little at 17 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Action of ornithine α ketoglutarate on DNA synthesis by human fibroblasts

Ornithine alpha ketoglutarate (OKG) is largely used in clinical nutrition for its anabolic effects. However, the mechanism of its action remains questionable. We investigated the effect of OKG on the rate of DNA synthesis in human fibroblasts. The in vitro experimental procedure required to demonstrate in cell culture the anabolic effects of OKG observed in vivo was found to be glutamine-free and serum-poor medium with sparse cells. In these conditions, OKG induced a significant increase in [3H]thymidine incorporation compared to untreated control cells. This effect was dose-dependent and was observed in all the cultures tested. Taken individually, the two constituents of OKG, i.e. alpha KG and Orn, also showed a stimulatory effect, but did not demonstrate a dose-dependent response. Concomitant analysis of extracellular aminoacids showed in alpha KG-treated cultures an increase in glutamate and a decrease in aspartate, suggesting a cellular transamination of alpha KG. Glutamine, which is the preferential energetic substrate of fibroblasts, can be produced from glutamate and might play a role in the action of OKG. Moreover, OKG induced a rise in the cellular polyamine content. This, in association with the inhibitory effect on OKG action of difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, suggests a link between the polyamine biosynthesis pathway and the anabolic effect of OKG.

Effect of valproate on renal metabolism in the intact dog

Valproate is an antiepileptic drug known to induce hyperammonemia in humans. This hyperammonemia might result from a reduced detoxification of ammonium in the liver and/or from an accelerated renal ammoniagenesis. Six dogs with normal acid-base equilibrium and eight dogs with chronic metabolic acidosis were infused with valproate directly into their left renal artery in order to obtain arterial concentrations around 3 to 4 mM. The arterial ammonium concentration rose only in chronically acidotic dogs, whereas the lactate concentration and the lactate/pyruvate ratio increased in both groups. The urinary excretion of lactate and pyruvate increased markedly but the urinary excretion of other relevant metabolites remained minimal. Renal glutamine utilization and ammonium production were not changed by valproate administration in normal dogs but increased modestly in acidotic dogs. However, renal lactate utilization was drastically reduced and in fact, changed into a net production of lactate. Valproate strikingly reduced the renal cortical concentrations of glutamine, glutamate, alphaketoglutarate and citrate, and more modestly those of malate, oxaloacetate, aspartate, alanine and ATP. By contrast, the tissue lactate concentration and the lactate/pyruvate ratio were markedly increased. In experiments with brush border membrane vesicles, valproate inhibited the lactate transporter. These results suggest that high concentrations of valproate drastically inhibited the proximal reabsorption and the proximal and distal oxidation of lactate and pyruvate. Valproate probably became itself a significant energetic substrate for the kidney.

Metabolic and structural adaptations to exercise in chronic intermittent fasted rats.

The effect of repetitive alternance of 3 days fasting and 3 days refeeding on morphological and biochemical ability to perform exercise was investigated in adult male rats. At the end of 10 wk of chronic intermittent fasting, the rats had consumed 20% less food but were able to maintain their initial body weight. Intermittent fasted rats (IF) had significantly lower carcass fat but had maintained the percent contribution of proteins to total carcass weight. The relative mass of liver, heart, kidney, and muscles was not affected by such dietary manipulation. Both glycolytic and oxidative enzyme capacities were reduced in IF rat muscles. In response to exercise (2 h of swimming), control rats displayed hypoglycemia, whereas IF rats were able to maintain plasma glucose level in spite of a reduced energy supply from liver (low glycogen stores) and adipose tissue (low plasma free fatty acid levels). This had been obtained by accumulating glycogen and triglycerides in muscles and by deriving energy for muscular contraction from the in situ breakdown of these energetic substrates. In addition, although IF rats displayed a markedly reduced liver protein content, the liver exercise-induced protein breakdown was abolished in these animals.

Evaluation of free fatty acid kinetics during TPN feeding of healthy rats

Free fatty acid (FFA) kinetics were evaluated in TPN-fed healthy rats using a single fatty acid tracer. Rats were divided into three groups according to the nonprotein energetic substrate infused: glucose (A), monoacetoacetin-glucose (B), and lipid emulsion-glucose (C). Fat kinetics were measured by continuous infusion of [1- 14C]palmitate. Total FFA and individual FFA concentrations were measured and turnover and oxidation were determined for the total pool of FFA and for palmitate. Groups A and B were similar in all parameters. Group C had increased total and individual FFA concentrations. Group C appeared to have decreased total plasma FFA turnover and unchanged oxidation compared to groups A and B. Palmitate appeared to have a 400% increase in oxidation and a 50% increase in turnover for rats in Group C when compared to Groups A and B. It is concluded that a single tracer does not accurately reflect plasma FFA during TPN using lipid emulsion.

Effects of muscular exercise on erythrocyte adenosine triphosphate concentration in patients with insulin-dependent diabetes mellitus.

Type I diabetes mellitus represents a metabolic disorder in which intracellular glycolytic pathway is inhibited by insulin deficiency, with the subsequent decreased availability of energetic substrates such as ATP. Some aspects of the energetic metabolism in response to an intensive demand (muscular exercise) were investigated, in a group of 10 ketotic diabetic patients, by measuring erythrocyte adenosine triphosphate (ATP) and blood glucose, free fatty acids (FFA) and lactate levels. In the diabetic subjects, in comparison with normal subjects, the decreased levels of erythrocyte ATP at rest did not increase after exercise, while the increased levels of FFA at rest did not diminish after exercise. The results show that the impaired erythrocyte glycolysis may produce reduced levels of ATP not only at rest, but also after exercise, when muscular contraction results in a manifold increase in cellular energy requirements. In addition, other metabolic systems providing energy for the exercising muscle, such as FFA utilization, are impaired in the ketotic diabetic patients.

A 24-hour fast-induced loss of energetic substrates in the interscapular brown adipose tissue of ‘cafeteria’ rats

The incorporation of tracer-labelled glucose and alanine, as well as the levels of energetic components in interscapular brown adipose tissue of male rats fed either standard or ‘cafeteria’ diet have been studied in fed and 24-hour of food withdrawal situations. The relative amount of brown adipose tissue in cafeteria fed rats was much greater than in controls, whose size and composition were not altered with food withdrawal. Cafeteria fed rats lost significant amounts of both lipid and protein during food withdrawal. Label incorporation was comparable for glucose and alanine except within the lipidic fraction, in which cafeteria fed rats showed a considerably lower efficiency. The loss of protein with food withdrawal and the swift incorporation of alanine into protein, tissue amino acid pools and lipids suggest an easy utilization of these amino acids by both groups of rats. In addition, the loss of energetic substrates observed in the cafeteria fed rats during food withdrawal suggests a continued utilization of energetic substrates by this brown adipose tissue, a condition not observed in the tighter energetic budget of control rats.

Process monitoring of a-C:H plasma deposition

The deposition process of amorphous hydrogenated carbon (a-C:H) in a 13.56 MHz hydrocarbon glow discharge system is investigated. Mass spectrometry was used to measure the relative abundance of the different ionic species. While there is a strong dependence of the mass spectra on the type of hydrocarbon gas (e.g., benzene, hexane, methane), the film properties are independent of the precursor. Spatially resolved spectroscopy of the optical emission was applied to study the interaction between energetic ions and substrate surface. Strong emission from small fragments, such as C, C2, and CH in the vicinity of the negatively self-biased cathode shows the importance of impact-induced fragmentation and explains the independence of film properties of the hydrocarbon process gas. With an electrically heated Langmuir probe we measured the potential, the density and the electron temperature of the plasma. In situ determination of the properties of the growing film, such as refractive index, thickness, absorption, and optical gap, was achieved by recording the reflectivity of the substrate during deposition.

Stable isotope tracers and the determination of fuel fluxes in newborn infants.

After birth, newborns adapt from the in utero situation of a continuous fuel supply to the postnatal situation of feeding and fasting periods. In order to maintain adequate fluxes of energetic substrates to their various organs and tissues, neonates must rapidly activate the release of glucose, free fatty acids and ketone bodies into the blood stream. This review will summarize some of the techniques and results available today regarding the in vivo kinetics of an energetic substrate in early postnatal life: the rate of production of this substrate, the overall rate of its uptake by the tissues, its rate of oxidation and contribution to the total caloric demand, the rate of conversion of a precursor into this substrate.

Ultrastructure of the gill of the hydrothermal vent bivalveCalyptogena magnifica, with a discussion of its nutrition

Calyptogena magnifica Boss and Turner, 1980, a new Vesicomyidae found during the Galapagos expedition in hydrothermal vents of the East Pacific Rise, was collected in the same Rise at 21°N during the “Oasis” expedition (March 1982), and samples of the gill were fixed for ultrastructural observations. The large size and structure of the gill indicate that this is the organ mainly involved in the nutritional processes ofC. magnifica. Despite the classic structural appearance of the external cilia of its gill, and an obvious production of mucus,C. magnifica is not a filter-feeder, as it does not use filtering processes to provide its major source of nutrition. Negligible particulate transfer is evidenced by reduction of the ciliary groove, of the labial palps and of the digestive tube, as well as by the absence of mucous strings. Histological and ultrastructural observations endorse the hypothesis that endocellular chemoautotrophic bacteria play an important role in the nutrition of the clam. Except for a superficial zone of ciliated cells, most of the gill tissue is comprised of cells which appear to be bacteriocytes, and which are perfectly integrated into the gill tissue and contain abundant and normally reproducing bacteria. The differences observed in the structure of the bacteriocytes suggest a cyclic process of their colonization by bacteria, their possible resorption, and their replacement by new bacteria-infected cells. Energetic substrates (sulfides and organic molecules) are probably directly absorbed by the bacteriocytes through the microvilli of the epithelial cells. Abundant fingerprint-like mitochondria in ciliate cells attest to a particularly high metabolic activity, perhaps related to active biosynthesis.

Influence of a “cafeteria” diet on heat production during postnatal development of the rat

1. 1. Despite different food availability for pregnant rats, the maternal diet had no effect on the weight of the pups at birth. 2. 2. There were no differences in thermogenesis during lactation in pups from dams that received cafeteria diet during pregnancy and after parturition. 3. 3. Both groups of pups grew faster than controls with, however, indistinguishable thermogenesis rates for all pups. 4. 4. After weaning, relative heat production decreased in all groups, even though cafeteria rats showed higher rates than the controls. 5. 5. The higher availability of energetic substrates resulted in increased growth in pups, but only after weaning was the heat output enhanced.

Permissive effect of glutamine on the differentiation of fetal mouse small intestine in organ culture

The proximal third of the small intestine of 15-day-old mouse embryo can be cultured for 72 h at 37° C. When Trowell-T8 medium is used, the integrity of the explants is maintained, but villi do not form and absorptive cells are poorly differentiated. However, when Leibovitz L-15 or RPMI-1640 medium is used, one can observe the formation of medium-sized villi, and absorptive cells in the explants are more differentiated. Since the chemical composition of T8 medium is quite different from that of the other two media, we decided to test the importance of two major differences, i.e., three amino acids and five vitamins, in order to find out which element(s) is necessary to permit the formation of intestinal villi. Subsequent testing demonstrated that the three amino acids are responsible for the effect on differentiation, and that glutamine is the only critical difference between T8 and the two other media. The results show that the addition of L–glutamine to T8 medium permits (1) the formation of villi, (2) the initiation of absorptive cell differentiation, (3) an increase in DNA synthesis, and finally, (4) an increase in the number of epithelial cells. These findings indicate that undifferentiated fetal mouse small intestine is able to express its phenotype in organ culture, even without any extrinsic regulatory influences, provided that L-glutamine is present at a sufficient level in the culture medium. The use of inhibitors indicated that L-glutamine may be essential as an energetic substrate and/or a precursor for glucosamine.

Le fermenteur rumen

The two main pregastric compartments of ruminants (rumen and reticulum) can be compared to an anaerobic fermenter which allows them to use energetic and nitrogen substrates which are indigestible by monogastric animals. The aim of this bibliographic review is to describe the main features (characteristics) of this fermenter, focusing on the role of microbes (bacteria, protozoa and fungi), on the degradation of cell-wall carbohydrates (cellulose, hemicelluloses, pectic substances), on nitrogen digestion and finally on the utilisation of the major minerals and trace elements.

Influence of Sertoli cell products upon the in vitro survival of isolated spermatocytes and spermatids

We have investigated the effect of Sertoli cell products upon the in vitro survival of isolated pachytene spermatocytes and round spermatids using co-cultures without contact between the somatic and germ cells. 3H-leucine incorporation was measured in such conditions at different culture times and compared with that of isolated germ cells incubated in presence of different energetic substrates. Dependence upon pyruvate and Sertoli cell products with respect to lactate is shown and discussed for both cell types; differences in pyruvate requirement are reported between meiotic and haploid cells.

The neuroendocrine response to multiple trauma.

AbstractThe neuroendocrine response to multiple trauma is a coordinated, complex, changing response which has as its objective maintenance of life by preserving oxygen delivery and the mobilization and utilization of the synthetic and energetic substrates required by the body.The afferent system is composed of neural input from the various chemoceptors, nociceptors, and baroceptors which monitor normal bodily function, in addition to the effects of plasma factors directly on the brain (e.g., glucose and amino acids). The efferent system is composed of the autonomic nervous system and the output of the anterior and posterior pituitary and other hormones. The efferent response is shown by measurements of ACTH, arginine vasopressin, growth hormone, prolactin, norepinephrineepinephrine, and opiate peptides. This efferent output then modulates the response of the pancreatic islets with the observed changes in glucagon and insulin and of the adrenal glands with additional changes in the catechol‐amines and cortisol. The renin‐angiotensin‐aldosterone system involving the kidney and adrenal gland is another responding system.The preceding relationships are discussed in some detail. Restoration of normal neuroendocrine function is best achieved by prompt restoration of blood volume, relief of pain and anxiety, restoration of normal food intake, excision of damaged tissue, and prevention of subsequent organ failure (e.g., pulmonary).

Fatty acid levels in blood of cyclostomes and fish

Experimental data obtained on cyclostomes and fish concerning the levels of plasma fatty acids (PFA), their biological role as an energetic substrate, various factors affecting PFA and mechanisms involved in the control of their level are reviewed.

Free fatty acid turnover and oxygen consumption. Effects of noradrenaline in nonfasted and nonanesthetized cold-adapted rats

The effects of a 3-h noradrenaline (NA) infusion (1.5 μg kg−1 min−1) on the O2 consumption, the respiratory quotient (RQ), the concentration of plasma free fatty acids (FFA), and the rates of appearance (Ra) and disappearance (Rd) of plasma FFA were studied in nonfasted and nonanesthetized control and cold-adapted rats. To calculate the Ra FFA and Rd FFA, [1-14C]palmitate complexed to albumin was infused as a tracer. The concentrations of glucose and lactate in blood were also determined before and during the NA infusion. The enhanced O2 consumption produced by NA in cold-adapted rats was associated with a decreased RQ. The Ra FFA and Rd FFA were more enhanced by NA in cold-adapted than in control rats whereas the plasma FFA concentration was less elevated in cold-adapted rats. The blood lactate was barely increased by the NA infusion in cold-adapted rats and was not modified in control rats. Blood glucose was increased by NA in both control and cold-adapted rats but to a greater extent in control rats during the last 90 min of NA infusion. These results suggest that the enhanced calorigenic response to NA observed in nonfasted and nonanesthetized cold-adapted rats is related, at least partly, to an enhanced lipid metabolism; the RQ is low and Ra FFA and Rd FFA are greatly increased. However, the contribution of other energetic substrates like glucose will also be investigated in further studies.