bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of protein malnutrition on neutral amino acid transport by rat hepatocytes during development
Authors: Gomez-Angelats M. , Ruiz-Montasell B. , Felipe A. , Marin J. J. , Casado F. J. , Pastor-Anglada M.
Published: December 2017

Hepatocytes from suckling rats whose mothers were fed a low-protein diet (9% protein) showed a lower capacity for Na(+)-dependent L-alanine uptake [due to a decrease in maximal uptake rate (Vmax) of a low-affinity component of transport] and were not able to respond to insulin or glucagon, whereas those from suckling pups whose mothers were fed the control diet (17% protein) had already developed the ability to upregulate L-alanine transport after hormone treatment. When animals from low-protein-fed mothers were weaned onto a hypoprotein diet, the overall capacity for Na(+)-dependent L-alanine uptake (apparent Vmax) and its responsiveness to pancreatic hormones were restored. Hepatocytes from these animals showed a lower response to glucocorticoid treatment. Amino acid availability was dramatically decreased in suckling and weanling rats fed a low-protein diet. These results support the hypothesis that nutrient supply is an important factor in the proper development of hepatic transport functions during the suckling-weaning transition.
Mechanism of hyperosmolality stimulation of ANP secretion: its dependency on calcium and sodium
Authors: Schiebinger R. J. , Joseph C. M. , Li Y. , Cragoe E. J.
Published: December 2017

The calcium dependency of hyperosmolality stimulation of atrial natriuretic peptide (ANP) secretion was determined using isolated superfused nonbeating rat left atrium. Increasing osmolality by 65, 85, and 100 mosmol/kgH2O by superfusion with sucrose produced a peak rise in ANP secretion of 1.8-, 2.0-, and 2.7-fold. To determine whether calcium influx played a role in osmolality (osm)-stimulated ANP secretion, atria were superfused with 2 mM lanthanum, a calcium antagonist. Lanthanum inhibited by 85% the response to a 100 mosmol/kgH2O increase in osm. The voltage-dependent calcium channel blocker isradipine had no effect on osm-stimulated ANP secretion, suggesting that calcium influx via voltage-dependent calcium channels was not playing a significant role. Likewise, depleting sarcoplasmic reticulum calcium with 1 microM ryanodine did not block the response to osm, suggesting that calcium influx was not adequate to induce consequential release of calcium from the sarcoplasmic reticulum. To determine whether calcium influx was via Na(+)-Ca2+ exchange, we determined the sodium dependency of osm-stimulated ANP secretion. Replacement of sodium with lithium or choline blocked the secretory response to 100 mosmol/kgH2O. We conclude that osm-stimulated ANP secretion is calcium and sodium dependent. Calcium influx via Na(+)-Ca2+ exchange is highly implicated as the mechanism of cellular calcium entry.
Synergism between IL-1 beta and TNF-alpha on the activity of the pituitary-adrenal axis and on food intake of rats
Authors: Van der Meer M. J. , Sweep C. G. , Pesman G. J. , Borm G. F. , Hermus A. R.
Published: December 2017

We investigated the effects of separate and combined intraperitoneal administration for 3 days of recombinant human interleukin-1 beta (IL-1) and recombinant human tumor necrosis factor-alpha (TNF) on plasma adrenocorticotropic hormone (ACTH) and corticosterone (B) levels, adrenal weight, food intake, and rectal temperature. Rats were equipped with a jugular cannula for daily blood sampling and with an intraperitoneally implanted Alzet osmotic minipump loaded with either saline, IL-1 (2.0 micrograms/day), TNF (0.2, 2.0, or 10.0 micrograms/day), or IL-1 in combination with TNF. Plasma ACTH and B levels and adrenal weight were significantly increased, in a dose-dependent way, by simultaneous infusion of IL-1 and TNF but not by administration of either cytokine alone. Chronic administration of IL-1 alone induced a significant decrease in food intake and a significant elevation of rectal temperature, whereas infusion of only the highest dose of TNF significantly elevated rectal temperature. Coinfusion of IL-1 and TNF induced both effects in a dose-dependent and synergistic way. Our data show that simultaneous infusion of IL-1 and TNF in rats has a synergistic effect on the activity of the pituitary-adrenal axis as well as on food intake and rectal temperature. The existence of two pathways, which act synergistically, may increase the sensitivity of the host to respond to subtle inflammatory stimuli.
Mechanisms of action of somatostatin on human TSH-secreting adenoma cells
Authors: Takano K. , Ajima M. , Teramoto A. , Hata K. , Yamashita N.
Published: December 2017

The mechanisms of somatostatin (SRIH) action on thyroid-stimulating hormone (TSH) secretion were examined using human TSH-secreting adenoma cells. SRIH (10(-7) M) inhibited TSH secretion through a pertussis toxin-sensitive G protein. SRIH also inhibited forskolin- and 8-bromo-adenosine 3',5'-cyclic monophosphate (8-BrcAMP)-induced TSH secretion. The mechanisms of this inhibition were investigated by measuring intracellular Ca2+ concentration ([Ca2+]i) and by electrophysiological experiments. Application of 10(-7) M SRIH reduced the [Ca2+]i, whereas forskolin and 8-BrcAMP increased the [Ca2+]i. Simultaneous application of SRIH abolished the forskolin-and the 8-BrcAMP-induced [Ca2+]i increase, indicating that the SRIH-induced decrease in [Ca2+]i was independent of the reduction in intracellular cAMP. Under current clamp using the whole cell clamp, 10(-7) M SRIH hyperpolarized the membrane and arrested Ca(2+)-dependent action potentials, which accounted for the SRIH-induced decrease in [Ca2+]i. Voltage clamp experiments revealed that this membrane hyperpolarization resulted from the activation of an inward-rectifying K+ current through a pertussis toxin-sensitive G protein. Intracellular injection of cAMP (100 microM) through the patch pipette did not abolish the SRIH-induced K+ current, indicating that the activation of SRIH-induced K+ channels was independent of intracellular cAMP. From these data, we concluded that SRIH-induced membrane hyperpolarization was responsible for the [Ca2+]i decrease, which in turn inhibited TSH secretion. Application of thyrotropin-releasing hormone (TRH; 10(-7) M) caused an increase in the [Ca2+]i, composed of an initial transient increase followed by a sustained increase. SRIH inhibited the sustained increase in [Ca2+]i. SRIH also inhibited the TRH-induced decrease in the membrane conductance.(ABSTRACT TRUNCATED AT 250 WORDS)
Ascorbate concentration in osteoblastic cells is elevated by transforming growth factor-beta
Authors: Wilson J. X. , Dixon S. J.
Published: December 2017

Transforming growth factor-beta modulates the proliferation, differentiation, and synthetic activity of osteoblasts, but its mechanisms of action are not fully understood. Because ascorbate also influences osteoblast differentiation and is a cofactor for collagen synthesis, the present study examined the effect of transforming growth factor-beta on the initial rate of transport and steady-state concentration of ascorbate in an osteoblastic cell line. UMR-106 rat osteosarcoma cells accumulated reduced vitamin C from culture medium. Virtually all accumulation of ascorbate was accomplished by a saturable Na(+)-dependent transport mechanism. Transforming growth factor-beta increased the initial rate of ascorbate transport, measured in either attached or suspended cells. Within 24 h, the growth factor also increased the steady-state intracellular concentration of ascorbate, without significantly changing cell volume or the DNA or protein content of cultures. These data provide evidence that Na(+)-ascorbate cotransport activity controls ascorbate concentration in osteoblasts. Furthermore, the results indicate that both the transport rate and steady-state concentration of ascorbate in these cells are regulated by transforming growth factor-beta.
SAM prevents impairment of glucose-stimulated insulin secretion caused by hexose deprivation or starvation
Authors: Conget I. , Zhang T. M. , Eizirik D. L. , Malaisse W. J.
Published: December 2017

Succinic acid monomethyl ester (SAM) was recently proposed as an insulinotropic tool in non-insulin-dependent diabetes mellitus. Three models were now used to investigate whether SAM protects the B-cell against the impairment of glucose-stimulated insulin release caused by either glucose deprivation or starvation. In the first model, preincubation of the islets for 180 min at low glucose concentration in the presence of SAM prevented the decrease in the secretory response to D-glucose otherwise observed during a subsequent incubation. In the second model, an impaired secretory response to D-glucose was observed after 3-day culture at low (2.8 or 5.6 mM) as distinct from high (11.1 mM) hexose concentration and the presence of SAM in the culture medium again protected against this anomaly. In the third model, the infusion of SAM for 3 days to starved rats restored the secretory potential of isolated islets to a level comparable to that otherwise found in fed rats. Thus, during glucose deprivation or starvation, SAM is indeed able to maintain B-cell responsiveness to D-glucose.
Metabolism of (R,S)-1,3-butanediol acetoacetate esters, potential parenteral and enteral nutrients in conscious pigs
Authors: Desrochers S. , Dubreuil P. , Brunet J. , Jette M. , David F. , Landau B. R. , Brunengraber H.
Published: December 2017

The (R,S)-1,3-butanediol-acetoacetate monoesters and diester are nonionized sodium-free precursors of ketone bodies (beta-hydroxybutyrate and acetoacetate). They represent a convenient form of ketone body administration for parenteral and enteral nutrition. We have studied the metabolism of the esters in the conscious pig, an animal in which ketogenesis is congenitally impaired. Some pigs were infused for 3 h, intravenously or intragastrically, with the esters or with (R,S)-1,3-butanediol at 30% of the hourly caloric requirement. Other pigs were given intragastric boluses of esters or of (R,S)-1,3-butanediol at 15% of the daily caloric requirement. Our data show that continuous infusion of the esters at 30% of the caloric requirement leads to low concentrations of (R,S)-1,3-butanediol (0.1 mM) and total ketone bodies (0.5 mM). In pigs given intragastric boluses of esters at 15% of the daily caloric requirement, concentrations of (R,S)-1,3-butanediol and total ketone bodies peaked briefly at 2-3 and 5 mM, respectively. No deleterious side effects were observed in any group, including no hypoglycemia and no acidosis. Thus the (R,S)-1,3-butanediol acetoacetate esters appears to be well utilized as a nutrient by the pig despite its impaired ketogenesis.
Glutamine prevents downregulation of myosin heavy chain synthesis and muscle atrophy from glucocorticoids
Authors: Hickson R. C. , Czerwinski S. M. , Wegrzyn L. E.
Published: December 2017

The aims of this study were to determine whether glutamine infusion prevents the decline in protein synthesis and muscle wasting associated with repeated glucocorticoid treatment. Hormone (cortisol acetate, 100 mg.kg body wt-1.day-1) and vehicle (carboxymethyl cellulose)-treated female rats were infused with either saline or glutamine (240 mM, 0.75 ml/h) for a 7-day period. Glutamine infusion attenuated the decline of plantaris muscle glutamine concentration (3.0 +/- 0.2 vs. 2.3 +/- 0.2 mumol/g) and prevented > 70% of the total muscle mass losses due to the glucocorticoid injections. Fractional synthesis rates of myosin heavy chain (MHC) and total protein were determined after constant [3H]leucine infusion from the leucyl-tRNA precursor pool, which was similar in all groups (range 4.8 +/- 0.5 to 6.3 +/- 0.4 disintegrations.min-1.pmol-1). MHC synthesis rates (%/day) in plantaris muscles were reduced to approximately 40% of controls (4.2/9.4). Although glutamine had no effect on MHC synthesis in vehicle-treated animals (10.1/9.4), it prevented 50% (7.6/4.2) of the hormone-induced decline in MHC synthesis rates. The same results were obtained with total protein synthesis measurements. Changes in muscle mass did not appear related to estimates of protein breakdown. In conclusion, these data show that glutamine infusion is effective therapy in counteracting glucocorticoid-induced muscle atrophy. Atrophy attenuation appears related to maintaining muscle glutamine levels, which in turn may limit the glucocorticoid-mediated downregulation of MHC synthesis.
Mathematical model of beta-cell glucose metabolism and insulin release. I. Glucokinase as glucosensor hypothesis
Authors: Sweet I. R. , Matschinsky F. M.
Published: December 2017

To quantitatively test the theory that glucokinase controls the rate of glucose metabolism and therefore the rate of insulin secretion, a minimal mathematical model of glycolysis in the pancreatic beta-cell was developed. The model represents our current hypothesis of how the normal beta-cell transduces the glucose signal. In this report, the model was used to address questions regarding the control strength of transport, hexokinase, glucose-6-phosphatase, and phosphofructokinase in the metabolism of glucose. The hypothesis that fructose 6-phosphate and a protein regulator modulate glucokinase activity was evaluated by simulation analysis, as was the possibility that glucose-6-phosphatase, working in concert with phosphofructokinase, can modulate the glucose-sensing system. It was found that, in the absence of glucose-6-phosphatase, transport, hexokinase, and phosphofructokinase do not greatly influence the rate of glucose metabolism unless their activities are dramatically altered from the measured values. Glucose metabolism was profoundly affected by the activity of glucokinase. However, in the presence of glucose-6-phosphatase, the ratio of glucose-6-phosphatase to phosphofructokinase activities was a very important parameter, and this potential control mechanism deserves more attention. The results further support the notion that glucokinase is indeed the glucosensor of the beta-cell and that modeling the system in toto provides quantitative evaluation needed to interpret the experimental tests of hypotheses.
Quantification of carbohydrate oxidation by respiratory gas exchange and isotopic tracers
Authors: Glamour T. S. , McCullough A. J. , Sauer P. J. , Kalhan S. C.
Published: December 2017

Estimates of glucose oxidation measured by indirect respiratory calorimetry and by [U-13C]glucose tracer were compared as a function of respiratory exchange ratio (RER) in 14 studies performed on 9 healthy adult subjects. RER was varied between 0.7 and 1.04, either by fasting or by infusing glucose. 13C enrichment of plasma glucose and expired CO2 were measured by mass spectrometry. The two methods gave similar results when the nonprotein respiratory quotient (NPRQ) was between 0.76 and 0.90. Glucose oxidation by the tracer method was quantified to be higher than that by respiratory calorimetry when NPRQ was < 0.76; it was lower than the respiratory calorimetry estimate when NPRQ was > 0.90. The discrepancy between the two methods at low RER may represent the contribution of gluconeogenesis, whereas, at high RER, the discrepancy may be the consequence of lipogenesis. We conclude that respiratory calorimetry and [13C]glucose tracer give comparable results only in a narrow range of RER. These data are important when the disposal of glucose is compared using these techniques in different metabolic states with varying respiratory quotients.
Effects of caffeine ingestion on NE kinetics, fat oxidation, and energy expenditure in younger and older men
Authors: Arciero P. J. , Gardner A. W. , Calles-Escandon J. , Benowitz N. L. , Poehlman E. T.
Published: December 2017

Age-related differences in energy expenditure, fat oxidation, and norepinephrine (NE) kinetics after caffeine ingestion were examined using a placebo-controlled double-blind study in 10 older (O, 65-80 yr) and 10 younger (Y, 19-26 yr) men who were moderate consumers of caffeine. Caffeine ingestion resulted in similar increases in Y and O men for plasma caffeine levels (Y = 89 +/- 100 to 6,340 +/- 1,938 ng/ml, P < 0.05; O = 124 +/- 38 to 7,066 +/- 2,366 ng/ml, P < 0.05) and energy expenditure (Y = 11%, 1.38 +/- 0.15 to 1.52 +/- 0.22 kcal/min, P < 0.05; O = 9.5%, 1.15 +/- 0.13 to 1.26 +/- 0.20 kcal/min, P < 0.05). However, caffeine ingestion increased fatty acid concentrations (362 +/- 159 to 803 +/- 253 mumol/l, P < 0.05) and tended to increase rate of appearance of fatty acids (624 +/- 376 to 1,394 +/- 1,331 mumol/l, P = 0.07) in younger but not older men. Rates of fat oxidation and NE appearance and clearance did not significantly differ from baseline values in either group. In conclusion, older and younger men show a similar thermogenic response to caffeine ingestion, whereas older men show a smaller increase in fatty acid availability after a caffeine challenge. These metabolic differences are not related to alterations in NE kinetics or fat oxidation.
Synthesis and parallel secretion of rat intestinal alkaline phosphatase and a surfactant-like particle protein
Authors: Alpers D. H. , Zhang Y. , Ahnen D. J.
Published: December 2017

Rat intestinal microvillous alkaline phosphatases are secreted bidirectionally from the enterocyte attached to a phospholipid-rich membrane (surfactant-like particle). To determine the intracellular pathways for newly synthesized alkaline phosphatases and for the extracellular enzyme-particle complex in the intestinal mucosa, pulse-chase experiments were performed. Synthesis of both isoforms of alkaline phosphatase in fasted rats peaked in the Golgi at 15–30 min and in the microvillous membrane at 60 min, without intermediate localization in the basolateral membranes. A second peak of incorporation was found at 15–30 min in scrapings obtained from the apical surface of the enterocytes. These results demonstrate a dominant direct Golgi-to-microvillous membrane transport for newly synthesized alkaline phosphatase. An additional precursor pool(s) appears responsible for the early appearance of enzyme in the lumen. Newly synthesized alkaline phosphatase isoforms and the 97-kDa protein of surfactant-like particles showed parallel patterns of appearance in enterocytes, luminal washings, and lamina propria after triacylglycerol feeding and were preferentially secreted into the lumen and lamina propria at times (5-7 h) when enterocyte content of these newly synthesized proteins had declined toward basal rates. Enhanced secretion of newly synthesized proteins for hours after fat feeding could explain the prolonged rise in serum and luminal washings of both the enzyme and the particle.
Arachidonic acid increases cytosolic calcium and stimulates hormone release in rat lactotrophs
Authors: Roudbaraki M. M. , Vacher P. , Drouhault R.
Published: December 2017

Arachidonic acid (AA) released from membrane phospholipids after activation of surface receptors causes cellular signaling actions in neurons and endocrine cells, including stimulation of prolactin (PRL) release from dissociated rat pituitary cells and clonal cells of the GH3 pituitary tumor line. In the present study, we investigated the effect of exogenous AA on PRL release from dispersed pituitary cells and tried to elucidate the mechanism involved in this process. The effects of AA on cytosolic Ca2+ concentration ([Ca2+]i) were studied using dual-emission microspectrofluorometry in identification lactotrophs and on PRL release in dispersed pituitary cell populations. AA had a dose-dependent effect on [Ca2+]i. At 1 microM, the Ca2+ increase was biphasic: a mobilization of intracellular Ca2+ from intracellular stores was followed by stimulation of Ca2+ influx. For lower concentrations (10 and 100 nM), only the stimulation of Ca2+ influx was observed. AA-induced Ca2+ influx and PRL release were not due to the stimulation of a phorbol 12-myristate 13-acetate-sensitive protein kinase C. In the same way, AA-stimulated PRL release and intracellular Ca2+ increase were independent of intracellular thapsigargin-sensitive Ca2+ pools. Furthermore, blockade of Ca2+ channels suppressed AA-induced PRL release. We hypothesize that Ca2+ influx plays a major role in AA-induced PRL release.
Receptor-mediated clearance of G-CSF derivative nartograstim in bone marrow of rats
Authors: Kuwabara T. , Uchimura T. , Kobayashi H. , Kobayashi S. , Sugiyama Y.
Published: December 2017

To clarify the role of the granulocyte colony-stimulating factor (G-CSF) receptor in the nonlinear elimination of a recombinant human G-CSF derivative, nartograstim (NTG), the accompanying changes in the in vivo NTG total body clearance at steady state (CLss) or the early-phase tissue uptake clearance (CLuptake) in rats were compared with the change in the number of G-CSF receptors in bone marrow. The infusion rate-dependent decrease in CLss in control rats confirmed the existence of a saturable elimination mechanism for NTG. The Michaelis-Menten constant (Km) and maximal velocity for this saturable process were estimated to be 107 pM and 15.5 pmol.h-1.kg-1, respectively. The Km for this saturable process was comparable with the dissociation constant (Kd) for the specific binding of NTG to bone marrow cells. After administration of excess NTG, the CLuptake of tracer amounts of 1251-NTG by bone marrow and spleen, which corresponds to the receptor density in the tissues, was reduced at 2 h but gradually recovered. This change in CLuptake corresponds well to the change in the in vitro NTG-binding capacity in each isolated cell. This reduction in CLuptake might be due to the downregulation of G-CSF receptors on the cell surface. On the other hand, the saturable CLss in cyclophosphamide-treated rats was 17% of that in control rats, whereas the saturable CLss in rats given NTG repeatedly was twofold greater than in controls, which is associated with the upregulation of G-CSF receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
The insulin action-fiber type relationship in humans is muscle group specific
Authors: Hickey M. S. , Weidner M. D. , Gavigan K. E. , Zheng D. , Tyndall G. L. , Houmard J. A.
Published: December 2017

The purpose of the present investigation was to determine the relationship between skeletal muscle characteristics, adiposity, and in vivo insulin action. Percutaneous muscle biopsies of the vastus lateralis (VL) and gastrocnemius (G) muscles were obtained from twenty-two sedentary male subjects. Insulin sensitivity (SI) and glucose effectiveness (SG) were determined from minimal model analysis, and indexes of regional and overall adiposity were obtained. SI was positively related to the citrate synthase activity from the VL (r = 0.50, P < 0.01) but unrelated to the citrate synthase activity from the G (r = 0.28). Similarly, SI was inversely related to the percentage of type IIb fibers in the VL (r = -0.47, P < 0.01) but unrelated to the percentage of type IIb fibers in the G (r = 0.06). SG was unrelated to fiber type, oxidative capacity, or adiposity. These data suggest that oxidative capacity and other characteristics related to VL skeletal muscle fiber type are determinants of in vivo insulin action but that this relationship cannot be extended to all muscle groups. Finally, neither skeletal muscle characteristics nor adiposity appears to be a determinant of SG in sedentary males.
Regulation of alpha 2-adrenergic receptor expression and signaling in pancreatic beta-cells
Authors: Hamamdzic D. , Duzic E. , Sherlock J. D. , Lanier S. M.
Published: December 2017

Activation of alpha 2-adrenergic receptors (alpha 2-AR) in pancreatic beta-cells inhibits insulin secretion in response to various stimuli, and acute or long-term regulation of alpha 2-AR receptor-mediated effects may influence the tissue response to glucose dishomeostasis. As an initial approach to this issue, we determined the effect of various metabolic and hormonal treatments on alpha 2-AR expression and coupling in the pancreatic beta-cell lines HIT-T15 and RIN-5AH. Radioligand binding studies ([3H]RX-821002) and RNA blot analysis indicate that both pancreatic beta-cell lines express the alpha 2A/D-AR subtype [for HIT-T15 the maximum binding (Bmax) = 113 +/- 28; for RIN-5AH Bmax = 93 +/- 18 fmol/mg of cellular protein]. Treatment of HIT-T15 or RIN-5AH cells with glucocorticoids [dexamethasone, hydrocortisone, or prednisolone (1 microM)] increased alpha 2-AR mRNA level and receptor protein density three- to fivefold. The glucocorticoid-induced increase in receptor density in HIT-T15 cells was associated with 1) an increase in the amount of receptors coupled to G protein as determined by analysis of high-affinity 5'-guanylyl imidodiphosphate-sensitive binding of [3H]UK-14304, a selective alpha 2-AR agonist, and 2) a greater inhibition of forskolin-induced elevation of cellular adenosine 3',5'-cyclic monophosphate after receptor activation. Receptor density in HIT-T15 cells was not altered by different growth conditions, insulin (1 microM), phorbol 12-myristate 13-acetate (1 microM), or the sex steroids testosterone and progesterone (1 microM). These data indicate that glucocorticoids upregulate alpha 2-AR expression and signaling in pancreatic beta-cells. Such regulation may operate in a cell-specific manner, allowing discrete modulation of tissue responses to glucose dishomeostasis.
A limitation in the use of mass isotopomer distributions to measure gluconeogenesis in fasting humans
Authors: Landau B. R. , Fernandez C. A. , Previs S. F. , Ekberg K. , Chandramouli V. , Wahren J. , Kalhan S. C. , Brunengraber H.
Published: December 2017

The use of distributions of mass isotopomers in glucose from [U-13C]glycerol to estimate fractional rates of gluconeogenesis was examined. [U-13C]glycerol was infused into normal subjects who ingested acetaminophen and fasted for 60 h. Isotopomer distributions were measured by mass spectrometry in blood glucose and in glucuronic acid from urinary acetaminophen glucuronide. The distributions are incompatible with glucose production solely via gluconeogenesis from a single pool of triose phosphates. Rather, with the assumption of a single enriched triose phosphate pool, the distributions indicate, despite the 60 h of fasting, about as much glucose formation from an unlabeled glucose source as from that pool. Therefore the data indicate cellular heterogeneity in glycerol's metabolism, so that two or more pools with significantly different enrichments were the source of the glucose and glucuronic acid. This heterogeneity is related to much greater concentrations of glycerol in periportal than in pericentral zones of the liver lobule. Beyond evidence for heterogeneity, the findings emphasize a limitation in applying analyses of mass isotopomer distributions to measure polymer biosynthesis in the presence of heterogeneity in the precursor pool.
A compartmental model of 3-methylhistidine metabolism in humans
Authors: Rathmacher J. A. , Flakoll P. J. , Nissen S. L.
Published: December 2017

Urinary 3-methylhistidine (3MH) excretion has been proposed as a noninvasive in vivo marker of muscle protein breakdown, but such analysis requires quantitative collection of urine and yields few details about the metabolism of 3MH. In this study, we propose that data from a single bolus dose of tracer and serial blood samples over 72 h can be described by a kinetic model that defines 3MH metabolism in humans. Plasma concentration of the tracer was described by a linear time-invariant three-compartment model. The model defines masses and fluxes of 3MH within the subjects and, in particular, the intracellular de novo production of 3MH. The de novo production of 3MH as calculated by the model was not different from that calculated via the traditional collection of urinary 3MH (3.09 vs 2.57 mumol.kg-1.day-1, respectively; P > 0.30). These data indicate that 3MH production can be measured by a compartmental model that can be used to measure muscle proteolysis without quantitative urine collections.
Stimulatory effect of glutamine on glycogen accumulation in human skeletal muscle
Authors: Varnier M. , Leese G. P. , Thompson J. , Rennie M. J.
Published: December 2017

To determine whether glutamine can stimulate human muscle glycogen synthesis, we studied in groups of six subjects the effect after exercise of infusion of glutamine, alanine+glycine, or saline. The subjects cycled for 90 min at 70-140% maximal oxygen consumption to deplete muscle glycogen; then primed constant infusions of glutamine (30 mg/kg; 50 mg.kg-1.h-1) or an isonitrogenous, isoenergetic mixture of alanine+glycine or NaCl (0.9%) were administered. Muscle glutamine remained constant during saline infusion, decreased 18% during alanine+glycine infusion (P < 0.001), but rose 16% during glutamine infusion (P < 0.001). By 2 h after exercise, muscle glycogen concentration had increased more in the glutamine-infused group than in the saline or alanine+glycine controls (+2.8 +/- 0.6, +0.8 +/- 0.4, and +0.9 +/- 0.4 mumol/g wet wt, respectively, P < 0.05, glutamine vs. saline or alanine+glycine). Labeling of glycogen by tracer [U-13C]glucose was similar in glutamine and saline groups, suggesting no effect of glutamine on the fractional rate of blood glucose incorporation into glycogen. The results suggest that, after exercise, increased availability of glutamine promotes muscle glycogen accumulation by mechanisms possibly including diversion of glutamine carbon to glycogen.
Simultaneous treatment with IGF-I and GH additively increases anabolism in parenterally fed rats
Authors: Lo H. C. , Hinton P. S. , Peterson C. A. , Ney D. M.
Published: December 2017

We compared the effects of recombinant human insulin-like growth factor I [rhIGF-I, 800 micrograms/day, coinfused with total parenteral nutrition (TPN)], growth hormone (rhGH, 800 micrograms/day, subcutaneous injection twice daily), and simultaneous treatment with rhIGF-I and rhGH (800 + 800 micrograms/day) in rats subjected to surgical stress and maintained with TPN. Weight gain induced by IGF-I plus GH was double that shown by IGF-I or GH alone. Although weight gain was similar with IGF-I or GH, IGF-I selectively increased heart, kidney, thymus, spleen, and small intestine mass, whereas GH selectively increased gastrocnemius muscle mass. IGF-I and/or GH increased carcass protein and water while decreasing fat. Serum total and free IGF-I levels were highest with IGF-I plus GH. Serum rat GH levels were reduced with IGF-I and/or GH. IGF-I given with GH reversed the GH-induced increase in serum insulin. In summary, IGF-I and GH show tissue-specific anabolic effects, and simultaneous treatment with IGF-I plus GH additively increases anabolism during TPN.
Receptor discrimination and control of agonist-antagonist binding
Authors: Tallarida R. J.
Published: December 2017

The law of mass action is the common model for the interaction of agonist and antagonist compounds with cellular receptors. Parameters of the interaction, obtained from functional and radioligand-binding studies, allow discrimination and subtyping of receptors and aid in understanding specific mechanisms. This article reviews the theory and associated mathematical models and graphical transformations of data that underlie the determination of receptor parameters. The main theory assumes that agonist and antagonist compounds bind to cells that have a fixed number of receptors and provides the framework for obtaining drug-receptor parameters from data and their graphical transformations. Conditions that produce a change in receptor number, a newer concept in pharmacology, can have an important effect on the parameter values derived in the usual way. This review concludes with a discussion of the quantitative study of receptor-mediated feedback control of endogenous ligands, a very new topic with potentially important implications for understanding antagonist effectiveness, loss of control, and chaos in regulated mass action binding.
Estimation of glucose-alanine-lactate-glutamine cycles in postabsorptive humans: role of skeletal muscle
Authors: Perriello G. , Jorde R. , Nurjhan N. , Stumvoll M. , Dailey G. , Jenssen T. , Bier D. M. , Gerich J. E.
Published: December 2017

To evaluate transfer of carbon between plasma glucose and plasma alanine (glucose-alanine cycle) and lactate (Cori cycle), to assess the contribution of skeletal muscle to these cycles, and to determine whether a glucose-glutamine cycle exists in postabsorptive humans, we infused 11 normal overnight-fasted volunteers with [2-3H]glucose, [6-14C]glucose, and [3-13C]alanine to isotopic steady state and in 7 of these simultaneously measured forearm net balance, uptake, and release of labeled and unlabeled glucose, lactate, and alanine. We found that 40.9 +/- 3.3, 66.8 +/- 3.2, and 13.4 +/- 1.1%, respectively, of plasma alanine, lactate, and glutamine carbon came from plasma glucose. More plasma glucose was converted to plasma alanine than could be derived from plasma alanine (1.89 +/- 0.20 vs. 1.48 +/- 0.15 mumol.kg-1.min-1, P < 0.001). A similar direction of net carbon flux was found for lactate (8.5 vs. 4.2 mumol.kg-1.min-1), with only glutamine adding more carbon to plasma glucose than was received from it (1.0 vs. 0.75 mumol.kg-1.min-1). Skeletal muscle accounted for 50.2 +/- 3.9 and 45.5 +/- 5.7% of the overall appearance of alanine and lactate in plasma and 54.2 +/- 5.4 and 36.4 +/- 4.2% of their respective origins from plasma glucose. Skeletal muscle release of alanine and lactate that had been formed from plasma glucose accounted for 19.1 +/- 2.1 and 48.4 +/- 4.8%, respectively, of muscle glucose uptake and 42.4 +/- 5.5 and 49.9 +/- 5.8% of the overall release of alanine and lactate from muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
Pulsatile insulin secretion accounts for 70% of total insulin secretion during fasting
Authors: Porksen N. , Munn S. , Steers J. , Vore S. , Veldhuis J. , Butler P.
Published: December 2017

The purpose of the present study was to determine the contributions of discrete insulin secretory bursts vs. basal insulin release to total insulin secretion in vivo. Quantification of the partitioning of pulsatile and basal insulin secretion is complicated by physiological delivery of these pulses into the portal vein and the absence of validated methods of measuring the rates of pulsatile and basal insulin secretion in vivo. We therefore 1) developed a canine model with chronically implanted portal vein catheters, 2) validated an established deconvolution technique as well as a novel direct catheterization technique (Clustcath) for measurement of pulsatile and nonpulsatile insulin secretion rates in this model, and 3) applied these methods to study insulin secretion in the overnight-fasted dog in vivo to determine the contribution of pulsatile vs. basal insulin secretion to total rates of endogenous insulin secretion. Rates of total, pulsatile, and nonpulsatile endogenous insulin secretion measured by Cluscath closely parallel those measured by deconvolution analysis (54 +/- 15 vs. 51 +/- 11, 38 +/- 12 vs. 36 +/- 11, and 16 +/- 4 vs. 14 +/- 4 pmol/min, respectively). Clustcath and deconvolution indicated that the majority of insulin was secreted as pulses (70 +/- 6 and 66 +/- 7%, respectively). These data infer that any process that selectively decreases the pulsatile component of insulin secretion (e.g., diabetes mellitus) will likely have a major impact on total insulin secretion.
Diurnal rhythmicity of human cholesterol synthesis: normal pattern and adaptation to simulated "jet lag"
Authors: Cella L. K. , Van Cauter E. , Schoeller D. A.
Published: December 2017

The diurnal rhythm of cholesterol synthesis was determined by deuterium incorporation from body water in five normolipemic men studied during a 24-h baseline period and on the 1st, 2nd, and 4th days of a simulated 12-h time zone shift achieved by delaying sleep times and, starting on the 2nd day, meal-times. Profiles of plasma cortisol and thyrotropin (TSH) were obtained simultaneously. Under baseline conditions, cholesterol synthetic rates varied from essentially zero in the morning to maximal values around midnight. On the 1st shifted day, this diurnal variation was unaltered despite sleep-wake reversal. The diurnal pattern of cholesterol synthesis, however, was shifted 5 h on the 2nd shifted day and approximately 12 h on the 4th. The diurnal variation of synthetic rate cholesterol fractional synthesis and plasma cortisol levels was negatively correlated on both the baseline day and the 1st shifted day. A positive correlation with the TSH rhythm was found on the 1st day only. During the 2nd and 4th days, the rhythm of cholesterol synthesis adapted faster than the rhythms of cortisol and TSH. These findings indicate that cholesterol synthesis is not acutely entrained by the sleep-wake cycle nor is it primarily entrained by the circadian clock.
Insulin regulates circulating insulin-like growth factors and some of their binding proteins in lactating cows
Authors: McGuire M. A. , Dwyer D. A. , Harrell R. J. , Bauman D. E.
Published: December 2017

Four lactating Holstein cows were subjected to a hyperinsulinemic-euglycemic clamp to evaluate the effects of insulin on circulating concentrations of insulin-like growth factors (IGF) and their binding proteins (IGFBP). Baseline blood samples were taken every 4 h for 2 days. For the 4-day clamp, insulin was infused (1 microgram.kg body wt-1.h-1) into the jugular vein and exogenous glucose was infused to maintain euglycemia. Circulating insulin was increased approximately fivefold, while glucose was maintained within 10% of baseline concentrations by infusion of 0.15 g.kg body wt-1.h-1 glucose. Hyperinsulinemia-euglycemia approximately doubled IGF-I (145 vs. 286 ng/ml, SE = 20) while decreasing circulating IGF-II (285 vs. 180 ng/ml, SE = 32). Densitometry of Western blots demonstrated no change in IGFBP-3 or a 30,000 relative molecular weight (M(r)) band during the clamp. However, IGFBP-2 decreased 73% and a 26,000 M(r) band decreased 58% by the end of the clamp. Therefore, insulin, directly or via secondary changes, increased circulating concentrations of IGF-I while decreasing concentrations of IGF-II, IGFBP-2, and a 26,000 M(r) IGFBP in lactating cows.
Persistence of metabolic consequences in the progeny of rats fed a HC formula in their early postnatal life
Authors: Vadlamudi S. , Kalhan S. C. , Patel M. S.
Published: December 2017

First-generation (1-) male and female rat pups were either reared artificially on a high-carbohydrate (HC) or a high-fat (HF) formula or nursed by mother (MF) from day 4 and weaned onto a stock diet on day 24. 1-HC rats compared with sex-matched control rats (1-HF and 1-MF) were hyperinsulinemic and mildly obese by day 60. We investigated the effect of maternal hyperinsulinemia on the second generation (2-) by intragroup breeding. The 2-HC male and female rats were hyperinsulinemic on day 45, had significantly increased growth rate from approximately day 60 onward, and became obese as evidenced by increased adipose tissue mass due to hypertrophy on day 100. The lipogenic capacity of liver and adipose tissues was significantly higher in the 2-HC than in control rats. Thus the metabolic changes that occurred in the first-generation rats fed a HC formula during early postnatal life not only persisted into their adult life but were also passed on to the next generation.
Expression of IGF-II and IGF binding proteins in differentiating human intestinal Caco-2 cells
Authors: Zhang Y. , Wick D. A. , Seetharam B. , Dahms N. M.
Published: December 2017

The mitogenic and metabolic effects of insulin-like growth factor-II (IGF-II) can be modulated by six distinct IGF binding proteins (IGFBPs). As a first step toward understanding the role of IGFs and their binding proteins in intestinal epithelial cell differentiation, the expression of IGF-II and IGFBPs was characterized in the human colon adenocarcinoma Caco-2 cell line. Northern blot analysis revealed two IGF-II transcripts of 5.4 and 4.5 kb, and ribonuclease protection assays indicated that IGF-II mRNA levels are regulated during Caco-2 differentiation. A specific radioimmunoassay detected IGF-II in serum-free conditioned medium, the level of which was three- to fivefold higher in proliferating cells than in differentiated cells. Immunoprecipitation and ligand blot analyses of conditioned medium demonstrated that IGFBP-2, IGFBP-3, IGFBP-4, and IGFBP-6 are synthesized by Caco-2 cells, with IGFBP-2 and IGFBP-4 being the major IGFBPs secreted, and that the levels of IGFBP-2 and IGFBP-6 decreased as differentiation proceeded. These results indicate that the expression of IGF-II, IGFBP-2, and IGFBP-6 is regulated in a differentiation-dependent manner in Caco-2 cells.
Urea cycle intermediate kinetics and nitrate excretion at normal and "therapeutic" intakes of arginine in humans
Authors: Beaumier L. , Castillo L. , Ajami A. M. , Young V. R.
Published: December 2017

We investigated the effects of a high dietary supplement of arginine on plasma arginine, ornithine, and leucine kinetics and on urea production and excretion in five healthy young adult men. Subjects received either 56 or 561 mg arginine.kg-1.day-1 for 6 days via a complete L-amino acid diet, and on day 7 a tracer protocol (first 3 h fasted; next 5 h fed) was conducted, involving primed constant intragastric infusions of L-[15N2-guanidino,5,5-2H2]arginine, L-[5-13C]ornithine, L-[5,5,5-2H3]leucine, and [15N2]urea, with a prime of H13CO3. Plasma arginine and ornithine fluxes increased significantly (P < 0.05) with arginine supplementation, as did the rate of conversion of plasma labeled arginine to ornithine (P < 0.05) and rate of ornithine oxidation (P < 0.001). However, absolute changes in ornithine kinetics were less than those for arginine or those based on changes expected from the change in arginine intake, implying a complex compartmentation in both whole body arginine and ornithine metabolism. The plasma NO3 concentration, daily output of total NO3, and conversion of [15N]arginine to NO3 did not differ between the diets. Urea production and excretion were reduced significantly with arginine supplementation, suggesting an anabolic effect on the whole body nitrogen economy, possibly via the raised plasma insulin levels (P = 0.013) during the prandial phase.
Insulin-like growth factor I accelerates protein synthesis in skeletal muscle during sepsis
Authors: Jurasinski C. V. , Vary T. C.
Published: December 2017

Sepsis causes an inhibition of protein synthesis in gastrocnemius that is resistant to the anabolic effects of insulin. The purpose of the present studies was to investigate the effect of recombinant human insulin-like growth factor I (IGF-I) on protein synthesis during a 30-min perfusion of the isolated rat hindlimb from septic rats. Inclusion of IGF-I (1 or 10 nM) in the perfusate stimulated protein synthesis in gastrocnemius of septic rats 2.5-fold and restored rates of protein synthesis to those observed in control rats. The stimulation of protein synthesis did not result from an increase in the RNA content but was correlated with a 2.5-fold increase in the translational efficiency. The enhanced translational efficiency was accompanied by a 33 and 55% decrease in the abundance of free 40S and 60S ribosomal subunits, respectively, indicating that IGF-I accelerated peptide-chain initiation relative to elongation/termination. These studies provide evidence that IGF-I can accelerate protein synthesis in gastrocnemius during chronic sepsis by reversing the sepsis-induced inhibition of peptide-chain initiation.
Effect of training on epinephrine-stimulated lipolysis determined by microdialysis in human adipose tissue
Authors: Stallknecht B. , Simonsen L. , Bulow J. , Vinten J. , Galbo H.
Published: December 2017

Trained humans (Tr) have a higher fat oxidation during submaximal physical work than sedentary humans (Sed). To investigate whether this reflects a higher adipose tissue lipolytic sensitivity to catecholamines, we infused epinephrine (0.3 nmol.kg-1.min-1) for 65 min in six athletes and six sedentary young men. Glycerol was measured in arterial blood, and intercellular glycerol concentrations in abdominal subcutaneous adipose tissue were measured by microdialysis. Adipose tissue blood flow was measured by 133Xe-washout technique. From these measurements adipose tissue lipolysis was calculated. During epinephrine infusion intercellular glycerol concentrations were lower, but adipose tissue blood flow was higher in trained compared with sedentary subjects (P < 0.05). Glycerol output from subcutaneous tissue (Tr: 604 +/- 322 nmol.100 g-1.min-1; Sed: 689 +/- 203; mean +/- SD) as well as arterial glycerol concentrations (Tr: 129 +/- 36 microM; Sed: 119 +/- 56) did not differ between groups. It is concluded that in intact subcutaneous adipose tissue epinephrine-stimulated blood flow is enhanced, whereas lipolytic sensitivity to epinephrine is the same in trained compared with untrained subjects.
Cyclical variation of plasma lipids, apolipoproteins, and lipoprotein(a) during menstrual cycle of normal women
Authors: Tonolo G. , Ciccarese M. , Brizzi P. , Milia S. , Dessole S. , Puddu L. , Secchi G. , Maioli M.
Published: December 2017

We report herein the effects of cyclical variations of endogenous sex steroids during the menstrual cycle on plasma lipids and apolipoproteins (apo) in normal women. We examined 16 normal women (age range 25-36 yr) with normal menstrual cycles of 28-31 days. The study covered the period from the 1st day of a menstrual phase (basal) until the 1st day of the following menstrual phase. During the study all women maintained a normolipidic diet (30% fat). Plasma total cholesterol and low-density-lipoprotein cholesterol were significantly higher than basal in the preovulatory phase until progesterone started to increase in the postovulatory phase [day +8 from luteinizing hormone (LH) surge]. High-density-lipoprotein cholesterol was significantly higher than basal from day -1 to the day after LH surge, whereas plasma apoAI levels were significantly higher from day -8 to day +8 (from LH surge). Plasma apo(a) increased significantly during the luteal phase in four women characterized by a single S4 band and lower basal plasma levels of apo(a). Our results indicate that endogenous female sex steroids have significant effects on the circulating levels of plasma lipids and apolipoproteins, including apo(a). More work needs to be done to elucidate the significance of the observed apo(a) changes, and the different phases of the menstrual cycle must be taken into account when evaluating the lipidic risk profile in premenopausal women.
Gut mucosal protein synthesis measured using intravenous and intragastric delivery of stable tracer amino acids
Authors: Nakshabendi I. M. , Obeidat W. , Russell R. I. , Downie S. , Smith K. , Rennie M. J.
Published: December 2017

We measured the rates of mucosal protein synthesis during the simultaneous delivery of [1-13C]leucine and [1-13C]valine delivered either intragastrically or intravenously to investigate any influence of the route of supply of the tracers. Dependent on the route, there were marked differences in the gradient of labeling between the plasma and intramucosal leucine and valine; i.e., for intravenous tracers the ratio was 1.73 +/- 0.16, but for intragastric tracers it was 0.65 +/- 0.12 (P < 0.05). Incorporation of intravenous tracer into mucosal protein was linear with time, and irrespective of tracer route, the calculated fractional rates of protein synthesis were identical when based on the intracellular labeling of the leucine or valine tracer, i.e., with intravenous 2.58 +/- 0.32%/h and with intragastric 2.45 +/- 0.36%/h. The results demonstrate that a robust and reproducible method of measurement of gastrointestinal mucosal protein synthesis has been developed and that use of either intragastric or intravenous routes of tracer administration gives comparable results. The high rates measured suggest that the gastrointestinal mucosa contributes substantially to whole body protein synthesis in normal healthy subjects.