bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of a leucine clamp to demonstrate that IGF-I actively stimulates protein synthesis in normal humans
Authors: Russell-Jones D. L. , Umpleby A. M. , Hennessy T. R. , Bowes S. B. , Shojaee-Moradie F. , Hopkins K. D. , Jackson N. C. , Kelly J. M. , Jones R. H. , Sonksen P. H.
Published: December 2017

Insulin-like growth factor I (IGF-I) is thought to mediate the anabolic action of growth hormone. A glucose and amino acid clamp technique was used to investigate the effects of a 3-h intravenous infusion of either 43.7 pmol.kg-1.min-1 (20 micrograms.kg-1.h-1) IGF-I or 3.4 pmol.kg-1.min-1 (0.5 mU.kg-1.min-1) insulin on whole body leucine turnover in five normal human volunteers. During the IGF-I infusion, IGF-I levels increased (P < 0.01; 26.6 +/- 2.8 to 88.9 +/- 14.2 nmol/l) and insulin levels fell (P < 0.05; 0.096 +/- 0.018 to 0.043 +/- 0.009 nmol/l). During the insulin infusion, insulin levels increased (P < 0.01; 0.057 +/- 0.013 to 0.340 +/- 0.099 nmol/l), and there was no change in IGF-I. There was no significant change in leucine production rate (Ra; a measure of protein degradation) during the IGF-I infusion (2.23 +/- 0.17 to 2.13 +/- 0.2 mumol.kg-1.min-1), but there was an increase (P < 0.03) in nonoxidative leucine disposal rate (Rd; a measure of protein synthesis; 1.83 +/- 0.15 to 2.05 +/- 0.21 mumol.kg-1.min-1). In contrast, insulin reduced (P < 0.02) leucine Ra (1.81 +/- 0.24 to 1.47 +/- 0.24 mumol.kg-1.min-1) and had no effect on nonoxidative leucine Rd (1.44 +/- 0.25 to 1.41 +/- 0.22 mumol.kg-1.min-1). We conclude that IGF-I, under conditions of adequate substrate supply, directly increases protein synthesis in contrast to insulin, which exerts its anabolic action by reducing proteolysis.
Altered expression of GLUT-1 and GLUT-3 glucose transporters in neurohypophysis of water-deprived or diabetic rats
Authors: Vannucci S. J. , Maher F. , Koehler E. , Simpson I. A.
Published: December 2017

Progressive dehydration due to water deprivation and streptozotocin diabetes both produce increased activity of the hypothalamoneurohypophysial system and enhanced vasopressin secretion. To determine whether enhanced metabolic activity affects glucose transporter protein expression, this study examined the effect of these conditions on 45-kDa GLUT-1 and the neuronal glucose transporter, GLUT-3, which mediate glucose transport in the rat neurohypophysis. Progressive water deprivation increased hematocrit, plasma electrolytes Na+ and Cl-, and vasopressin over 3 days, relative to the severity of dehydration. Plasma vasopressin increased threefold by 24 h, reaching 4.5-fold by 72 h. These changes were reflected in a 56 and 75% decrease in neurohypophysial vasopressin content by 48 and 72 h, respectively. Significant changes in glucose transporters were also observed at 48 and 72 h, with GLUT-1 increasing by 18 and 44% and GLUT-3 increasing by 42 and 55%, respectively. Streptozotocin-induced diabetes produced increases in hematocrit, plasma Cl-, and vasopressin, although the magnitude of these changes was less than with dehydration. There was a twofold increase in plasma vasopressin by 3 days, commensurate with the onset of overt diabetes, and a threefold increase by 2 wk. These changes were reflected in a 30 and 40% decline in neural lobe vasopressin content, respectively. Despite the difference in the magnitude of hormone response, GLUT-3 increased by the same amount (53%) as in dehydration. GLUT-1, however, was decreased 16% by 3 days and 25% by 1 and 2 wk of diabetes. Although the opposite effects on GLUT-1 may relate to differences in circulating insulin or glucose, this study is the first demonstration of increased expression of GLUT-3 in response to a common hypothalamic signal in these two conditions.
Relationship between sleep stages and metabolic rate in humans
Authors: Fontvieille A. M. , Rising R. , Spraul M. , Larson D. E. , Ravussin E.
Published: December 2017

Differences in sleeping metabolic rate (SMR) among subjects may be related to different levels of energy expenditure associated with sleep stages. The relationship between energy expenditure and sleep stages was investigated overnight in 29 subjects (14 Caucasians and 15 Pima Indians, 18 males and 11 females; mean +/- SD, 31 +/- 7 yr, 83 +/- 26 kg, 27 +/- 11% fat). Sleep stages were determined by electroencephalogram recording, whereas energy expenditure was measured in a 1,000-liter Plexiglas sleep box constructed around a bed as a fast-response open-circuit indirect calorimeter. Eighty-five percent of the interindividual variability in SMR was explained by differences in fat-free mass, fat mass, age, sex, and race (r2 = 0.85). The intra-individual variance in SMR over time was related to sleep stages and to clock time. Within subjects, SMR in stage 3 was significantly lower than in stage 2 (-39 +/- 18 kcal/day; P < 0.05) and rapid eye movement sleep (-51 +/- 23 kcal/day; P < 0.05). Also, sleep stages were associated with different respiratory quotients. Because sleep stages are associated with only small differences in energy metabolism, our results suggest that sleep stages play a minor role in the variance of SMR among subjects. However, the duration of sleep may contribute to the variability of 24-h energy expenditure.
Stimulation of prolactin release by dopamine withdrawal: role of calcium influx
Authors: Gregerson K. A. , Chuknyiska R. , Golesorkhi N.
Published: December 2017

Withdrawal of dopamine (DA), a neurotransmitter that inhibits prolactin (PRL) release from the anterior pituitary, stimulates PRL release with transient (30- to 45-min) secretory rates that exceed those observed before application of DA ("PRL rebound"). Using patch-clamp methods on identified rat lactotropes, we have demonstrated that a period of increased Ca(2+)-spiking activity follows recovery from the DA-induced hyperpolarization. The present experiments used dissociated pituitary cells to identify the relative roles of adenosine 3',5'-cyclic monophosphate (cAMP), inositol phosphates, and the enhanced influx of Ca2+ in the rebound secretion of PRL. Rebound secretion of PRL after DA withdrawal was completely blocked by the Ca2+ channel blocker verapamil (20 microM), which also inhibited spontaneous Ca(2+)-spiking activity. DA-induced changes in cAMP levels could be completely dissociated from the PRL rebound. Production of inositol phosphates rose after DA withdrawal but was secondary to the influx of Ca2+. These data demonstrate that influx of extracellular Ca2+ through verapamil-sensitive channels is a critical step in inducing PRL release after DA withdrawal. This finding supports our theory that DA-induced hyperpolarization recruits previously inactivated Ca2+ channels and upon DA washout the enhanced influx of Ca2+ through these voltage-regulated channels supports the rebound release of PRL.
Altered skeletal pattern of gene expression in response to spaceflight and hindlimb elevation
Authors: Bikle D. D. , Harris J. , Halloran B. P. , Morey-Holton E.
Published: December 2017

Spaceflight leads to osteopenia, in part by inhibiting bone formation. Using an animal model (hindlimb elevation) that simulates the weightlessness of spaceflight, we and others showed a reversible inhibition of bone formation and bone mineralization. In this study, we have measured the mRNA levels of insulin-like growth factor I (IGF-I), IGF-I receptor (IGF-IR), alkaline phosphatase, and osteocalcin in the tibiae of rats flown aboard National Aeronautics and Space Administration Shuttle Flight STS-54 and compared the results with those obtained from their ground-based controls and from the bones of hindlimb-elevated animals. Spaceflight and hindlimb elevation transiently increase the mRNA levels for IGF-I, IGF-IR, and alkaline phosphatase but decrease the mRNA levels for osteocalcin. The changes in osteocalcin and alkaline phosphatase mRNA levels are consistent with a shift toward decreased maturation, whereas the rise in IGF-I and IGF-IR mRNA levels may indicate a compensatory response to the fall in bone formation. We conclude that skeletal unloading during spaceflight or hindlimb elevation resets the pattern of gene expression in the osteoblast, giving it a less mature profile.
Differential release of tumor necrosis factor and IL-6 from adrenal zona glomerulosa cells in vitro
Authors: Judd A. M. , MacLeod R. M.
Published: December 2017

In previous studies, rat adrenal zona glomerulosa (ZG) cells were demonstrated to release interleukin-6 (IL-6). In the current study, cultures of ZG cells and bioassays for tumor necrosis factor (TNF) and IL-6 were used to determine if ZG cells release TNF and to define more fully the factors that regulate ZG IL-6 release. ZG cells released IL-6 and TNF, and this release was stimulated by lipopolysaccharide, interleukin-1 alpha, interleukin-1 beta, a protein kinase C activator, and a calcium ionophore without affecting intracellular adenosine 3', 5'-cyclic monophosphate (cAMP) content. In contrast, adrenocorticotropic hormone (ACTH) increased the intracellular cAMP content, increased basal and secretagogue-stimulated IL-6 release but decreased basal and secretagogue-stimulated TNF release. The effects of ACTH on IL-6 and TNF release may be mediated by increases in intracellular cAMP because ACTH and dibutyryl cAMP modified IL-6 and TNF release in an identical manner. Therefore, IL-6 and TNF release from ZG cells can be differentially regulated. Because IL-6 and TNF modify adrenal steroid release, the adrenal production of these cytokines may have a role in the stress response.
Estimating body composition in late gestation: a new hydration constant for body density and total body water
Authors: Catalano P. M. , Wong W. W. , Drago N. M. , Amini S. B.
Published: December 2017

Twenty women underwent body density (DB) measurements using underwater weighing with correction of residual lung volume by nitrogen dilution and total body water (TBW) using isotope dilution of 18O to estimate body composition at 30 wk of gestation. DB and TBW were used as independent variables in the same equation. The hydration constant (HC) of fat-free mass (FFM) was estimated as 0.762; based on this HC, new body composition equations for both DB and TBW were derived. These equations were prospectively tested in an additional 20 women at 30 wk of gestation. No significant differences were detected between estimates of percent body fat (%F) using either the newly derived DB or TBW equations and estimates of %F using both DB and TBW. Ten of these forty women were evaluated postpartum. There was no significant difference in %F estimated by either TBW or DB compared with standard equations (hydration of FFM = 0.72) and %F using both DB and TBW. These results highlight the importance of either measuring both DB and TBW or using an appropriate hydration constant for FFM in estimating body composition during pregnancy or conditions associated with increased body water.
Effects of BRL-47672 on growth, beta 2-adrenoceptors, and adenylyl cyclase activation in female rats
Authors: Sillence M. N. , Matthews M. L. , Moore N. G. , Reich M. M.
Published: December 2017

The morpholine compound BRL-47672 has a chemical structure similar to that of clenbuterol and causes similar anabolic effects in rats but has no actions on beta 2-adrenoceptors in vitro. It has been argued therefore that beta 2-adrenoceptors do not mediate the anabolic effects of this family of compounds. In the present study BRL-47672 was shown to bind to rat beta 2-adrenoceptors with low affinity (dissociation constant 16 microM) relative to clenbuterol (48 nM) and to be a very weak activator of adenylyl cyclase activity in rat skeletal muscle membranes in vitro. In contrast, acute administration of the drug to anesthetized rats in vivo caused an increase in muscle adenosine 3',5'-cyclic monophosphate output, and chronic treatment of conscious rats for > 6 days caused a significant increase in weight gain (69%) accounted for by increased muscle growth. The anabolic effects of BRL-47672 were not counteracted by daily injections of the drug ICI-118551 (2 mg/day) but were prevented when the same beta 2-antagonist was administered in the diet (200 mg/kg feed, equivalent to 4.3 mg/day). The beta 1-adrenoceptor selective antagonist CGP-20712A fed in the diet (200 mg/kg feed) failed to attenuate the response to BRL-47672. These results support the conclusion that BRL-47672 has little direct action on beta 2-adrenoceptors but suggest that the compound is metabolized rapidly in vivo to a potent beta 2-agonist. Thus the stimulation of muscle growth by BRL-47672 is via beta 2-adrenoceptors, with no contribution to this response from beta 1- or beta 3-adrenoceptor activation.
Identification of 3,3'-T2S as a fetal thyroid hormone derivative in maternal urine in sheep
Authors: Wu S. Y. , Polk D. , Fisher D. A. , Huang W. S. , Reviczky A. L. , Chen W. L.
Published: December 2017

We measured 3,3'-diiodothyronine sulfate (T2S) in serum and urine (n = 5–6) obtained from euthyroid fetal (94–145 days of gestation, term = 150 days), newborn, and adult sheep and in serum and urine samples from ovine fetuses 13 days after total thyroidectomy conducted between 110 and 113 gestation days (n = 5). Sham-operated twin fetuses served as controls (n = 5). Mean serum T2S concentrations increased progressively from 94 days (74 ng/dl) to 130 days (420 ng/dl), decreasing thereafter to 145 days (197 ng/dl). T2S concentrations in fetal urine peaked at 110 days (117 ng/dl). In hypothyroid fetuses, mean serum and urine T2S were 60 and 53% of control values. To assess the possibility that the T2S in maternal serum/urine is derived from fetal serum 3,5,3'-triiodothyronine (T3), we measured T3, T3 sulfate (T3S), and T2S in fetal serum and in maternal serum and urine after bolus infusion of T3 to the fetus (n = 4). Additionally, T3, T3S, and T2S concentrations were measured in maternal serum and urine after T3 infusion to the maternal ewes (n = 4). Fetal T3 infusion rapidly increased fetal serum T3S and T2S. Maternal serum and urine T3S and T2S concentrations increased, whereas T3 concentrations remained unchanged. Maternal T3 infusion increased in serum and urine T3S and T2S levels, but the levels, relative to T3, were less than values measured after fetal T3 infusion. We conclude that T2S is a normal thyroid hormone metabolite in the ovine fetus and suggest that a major pathway of fetal T2S production is T3 to T3S to T2S.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of acute glucagon removal on metabolic response to infection in conscious dog
Authors: McGuinness O. P. , Lacy D. B. , Anderson J.
Published: December 2017

This study examined the acute role of glucagon in sustaining the increased hepatic gluconeogenesis observed in the conscious infected dog. After a basal sampling period, arterial glucagon levels were selectively decreased for 180 min by a peripheral infusion of somatostatin and basal intraportal infusion of insulin (GGN deficient; n = 6). In a separate protocol (GGN replaced; n = 5) glucagon was also infused intraportally to maintain the glucagon level at that seen during sepsis. Tracer and arteriovenous difference techniques were used to assess hepatic glucose metabolism and gluconeogenesis. In the GGN-deficient group the arterial plasma glucagon level fell from 416 +/- 49 to 88 +/- 21 pg/ml, whereas in the GGN-replaced group it remained elevated throughout (321 +/- 48 to 248 +/- 22 pg/ml). When glucagon was reduced, endogenous glucose production decreased by 1.6 +/- 0.3 mg.kg-1.min-1, and an exogenous glucose infusion was required to maintain euglycemia. Glucose metabolism remained unaltered when glucagon was replaced. When glucagon was deleted, net hepatic gluconeogenic precursor uptake was not altered. In contrast, the efficiency of gluconeogenesis was decreased by 33% compared with the GGN-replaced group. Liver biopsies taken at the end of the experiment indicated that a diversion of gluconeogenic carbon to glycogen accounted for 50% of the fall in gluconeogenic efficiency. In summary, the basal hyperglucagonemia seen during an infection helps sustain glucose production both through its effects on hepatic glycogen metabolism and on gluconeogenic efficiency.
Forearm muscle insulin resistance during hypoglycemia: role of adrenergic mechanisms and hypoglycemia per se
Authors: Capaldo B. , Napoli R. , Guida R. , Di Bonito P. , Antoniello S. , Auletta M. , Pardo F. , Rendina V. , Sacca L.
Published: December 2017

The forearm perfusion technique was used 1) to quantify the muscle metabolism of glucose and gluconeogenic precursors in response to insulin-induced hypoglycemia and 2) to assess the role of catecholamines and glucose concentration, pe se. Insulin (0.5 mU.kg-1.min-1) was infused for 4 h in three groups of healthy volunteers. In group I (n = 6), blood glucose (BG) was maintained at its basal level (4.5 +/- 0.1 mmol/l). In group II (n = 7), BG was allowed to fall to approximately 3 mmol/l. Group III (n = 6) was similar to group II except that propranolol was infused also. In addition, at 240 min, hypoglycemia was locally corrected by intrabrachial glucose infusion while maintaining the systemic milieu unperturbed. In group I, forearm glucose uptake (FGU) increased from 4.7 +/- 1.3 to a mean value of 37.8 +/- 5.0 mumol.l-1.min-1, whereas in group II it remained unchanged (8.3 +/- 2.0 mumol.l-1.min-1). In group III, propranolol partially prevented the suppression of FGU that increased to 21.6 +/- 5.2 mumol.l-1.min-1 (P < 0.05 vs. group II). Local correction of hypoglycemia normalized the FGU response (36.5 +/- 8.0 mumol.l-1.min-1). Muscle release of lactate, but not of alanine, was slightly higher during hypoglycemia (P = not significant). Forearm blood flow remained unchanged in groups I and III, whereas it increased by approximately 40% in group II (P < 0.05). It is concluded that, during mild hypoglycemia 1) extreme insulin resistance develops in the skeletal muscle, mediated by beta-adrenergic stimulation and reduced glucose mass effect and 2) mobilization of gluconeogenic precursors is only weakly activated.
Thermogenesis after a mixed meal: role of leg and splanchnic tissues in men and women
Authors: Jensen M. D. , Johnson C. M. , Cryer P. E. , Murray M. J.
Published: December 2017

To determine the relative contribution of splanchnic and leg tissues to postprandial thermogenesis, systemic and regional oxygen consumption rates were measured in nine women and eight men before and for 6 h after the consumption of a mixed meal that provided one-third of the daily energy needs. In women, the increase in splanchnic oxygen uptake accounted for 63 +/- 12% of the postprandial increase in oxygen consumption, whereas in men it accounted for 35 +/- 14% (P = not significant between women and men). Leg oxygen uptake accounted for 11 +/- 4 and 10 +/- 3% of the increase in postprandial oxygen consumption in women and men, respectively. The combined data suggest that approximately 48% of postprandial thermogenesis over 6 h occurs in splanchnic tissues, whereas 30-35% occurs in skeletal muscle. Thus the increase in oxygen consumption after a mixed meal is primarily localized to splanchnic tissues, and major reductions in postprandial thermogenesis are unlikely to be attributable solely to abnormalities of skeletal muscle metabolism.
Effects of lactate on glucose metabolism in healthy subjects and in severely injured hyperglycemic patients
Authors: Tappy L. , Cayeux M. C. , Schneiter P. , Schindler C. , Temler E. , Jequier E. , Chiolero R.
Published: December 2017

Hepatic glucose production is autoregulated during infusion of gluconeogenic precursors. In hyperglycemic patients with multiple trauma, hepatic glucose production and gluconeogenesis are increased, suggesting that autoregulation of hepatic glucose production may be defective. To better understand the mechanisms of autoregulation and its possible alterations in metabolic stress, lactate was coinfused with glucose in healthy volunteers and in hyperglycemic patients with multiple trauma or critical illness. In healthy volunteers, infusion of glucose alone nearly abolished endogenous glucose production. Lactate increased gluconeogenesis (as indicated by a decrease in net carbohydrate oxidation with no change in total [13C]carbohydrate oxidation) but did not increase endogenous glucose production. In patients with metabolic stress, endogenous glucose production was not suppressed by exogenous glucose, but lactate did not further increase hepatic glucose production. It is concluded that 1) in healthy humans, autoregulation of hepatic glucose production during infusion of lactate is still present when glycogenolysis is suppressed by exogenous glucose and 2) autoregulation of hepatic glucose production is not abolished in hyperglycemic patients with metabolic stress.
Glutamine-glutamate exchange between placenta and fetal liver
Authors: Vaughn P. R. , Lobo C. , Battaglia F. C. , Fennessey P. V. , Wilkening R. B. , Meschia G.
Published: December 2017

The hypothesis that glutamine shuttles nitrogen between placenta and fetal liver via interconversion with glutamate was explored by infusing L-[1,2-13C2]glutamine in six fetal sheep chronically catheterized for sampling of the umbilical and hepatic circulations. Fetal plasma glutamine disposal rate was 19.9 +/- 1.3 mumol.min-1.kg fetus-1. Entry of glutamine from the placenta accounted for approximately 60% of the total glutamine entry rate in fetal plasma. Glutamine was taken up by fetal liver, and 45.3 +/- 7.9% of the glutamine taken up was released as glutamate. The fetal liver released large quantities of glutamate, as evidenced by a sixfold increase in plasma glutamate concentration in the blood flowing through the left hepatic lobe and a hepatic glutamate output-to-O2 uptake molar ratio of 0.149 +/- 0.013. In conjunction with a previous study of fetal glutamate metabolism, these data demonstrate that glutamine entering the fetal circulation is converted to glutamate by the fetal liver at a rate of approximately 3-4 mumol.min-1.kg fetus-1.
Alterations in specific protein-tyrosine phosphatases accompany insulin resistance of streptozotocin diabetes
Authors: Ahmad F. , Goldstein B. J.
Published: December 2017

To test whether protein tyrosine phosphatases (PTPases) may play a role in the insulin resistance of insulinopenic diabetes, we assessed PTPase activity as well as the protein and mRNA abundance of three major candidate PTPases in subcellular fractions of liver and skeletal muscle of streptozotocin-diabetic rats before and after insulin treatment. PTPase activity against the insulin receptor in liver and muscle cytosol increased to 120-125% of control in the diabetic animals and by an additional 5-10% after insulin treatment. In the particulate fraction, PTPase activity decreased to 65-70% of control in diabetic liver and muscle and increased to 115-120% of control after insulin treatment. Protein for the leukocyte common antigen-related PTPase paralleled the changes in the PTPase activity in the particulate fraction. SH-PTP2/syp and PTPase 1B were both significantly increased in diabetes. SH-PTP2/syp also exhibited an increased ratio of particulate to cytosol distribution in diabetic tissues (1.8-1.9) that was reversed after insulin treatment (0.79-0.95). Northern analysis suggested that the PTPases were regulated at a pretranslational level. These changes in the abundance and distribution of specific PTPases may be involved in the pathogenesis of insulin resistance in insulinopenic diabetes.
Activation of the ATP-ubiquitin-proteasome pathway in skeletal muscle of cachectic rats bearing a hepatoma
Authors: Baracos V. E. , DeVivo C. , Hoyle D. H. , Goldberg A. L.
Published: December 2017

Rats implanted with Yoshida ascites hepatoma (YAH) show a rapid and selective loss of muscle protein due mainly to a marked increase (63-95%) in the rate of protein degradation (compared with rates in muscles of pair-fed controls). To define which proteolytic pathways contribute to this increase, epitrochlearis muscles from YAH-bearing and control rats were incubated under conditions that modify different proteolytic systems. Overall proteolysis in either group of rats was not affected by removal of Ca2+ or by blocking the Ca(2+)-dependent proteolytic system. Inhibition of lysosomal function with methylamine reduced proteolysis (-12%) in muscles from YAH-bearing rats, but not in muscles of pair-fed rats. When ATP production was also inhibited, the remaining accelerated proteolysis in muscles of tumor-bearing rats fell to control levels. Muscles of YAH-bearing rats showed increased levels of ubiquitin-conjugated proteins and a 27-kDa proteasome subunit in Western blot analysis. Levels of mRNA encoding components of proteolytic systems were quantitated using Northern hybridization analysis. Although their total RNA content decreased 20-38%, pale muscles of YAH-bearing rats showed increased levels of ubiquitin mRNA (590-880%) and mRNA for multiple subunits of the proteasome (100-215%). Liver, kidney, heart, and brain showed no weight loss and no change in these mRNA species. Muscles of YAH-bearing rats also showed small increases (30-40%) in mRNA for cathepsins B and D, but not for calpain I or heat shock protein 70. Our findings suggest that accelerated muscle proteolysis and muscle wasting in tumor-bearing rats result primarily from activation of the ATP-dependent pathway involving ubiquitin and the proteasome.
Insulin-like growth factor binding protein-3 inhibits porcine granulosa cell function in vitro
Authors: Samaras S. E. , Hammond J. M.
Published: December 2017

Recombinant human insulin-like growth factor binding protein-3 (rhIGFBP-3) effects on basal, insulin-like growth factor I (IGF-I)-, and follicle-stimulating hormone (FSH)-stimulated progesterone (P4) secretion and [3H]aminoisobutyric acid (AIB) uptake by primary porcine granulosa cells (MDGs) and MDGs that have been passaged once (MDGp1) were assessed. Cells were treated concurrently or were preincubated with rhIGFBP-3 followed by treatment. rhIGFBP-3 had no effect on MDG or MDGp1 cell numbers after 24 h. Cotreatment with rhIGFBP-3 inhibited P4 secretion after treatment with FSH, IGF-I, and FSH plus IGF-I. FSH did not stimulate [3H]AIB uptake. However, the IGF-I-stimulated increase in [3H]AIB uptake was completely prevented by concurrent treatment with IGFBP-3. Preincubation of MDGp1 cells with IGFBP-3 dose dependently inhibited FSH- and IGF-I-stimulated P4 secretion. This inhibition was associated with increased cell association of the binding protein and increased IGF-I binding to the cells. These results indicate that IGFBP-3 is inhibitory to a variety of crucial functions in porcine granulosa cells, supporting a role for it in the regulation of granulosa cell function.
Differential effect of maturation on insulin- vs. contraction-stimulated glucose transport in Zucker rats
Authors: Dolan P. L. , Boyd S. G. , Dohm G. L.
Published: December 2017

Insulin-stimulated glucose transport has been shown to decline during maturation in lean rats. To determine whether this maturation-induced decrease occurred in the muscle of obese rats and whether the contraction-stimulated pathway for glucose transport was similarly affected, glucose transport rates were measured in insulin- and electrically stimulated skeletal muscle during hindlimb perfusion of 10- and 29-wk-old lean and obese male Zucker rats. Glucose transporter (GLUT-4) protein was also measured. Insulin-stimulated glucose transport rates were significantly decreased (36–56%) in 29-wk compared with 10-wk-old lean rats. There was no maturation-related decrease in GLUT-4. Insulin-mediated glucose transport was unaltered by maturation in skeletal muscle of obese rats. Differential effects of maturation on lean and obese rats caused the effect of obesity on maximally insulin-stimulated glucose transport to be much greater in 10- than 29-wk-old animals. Maturation had no effect on contraction-stimulated glucose transport rates in either lean or obese animals. The combined effect of maximal insulin plus contraction was not altered with maturity in lean animals but was significantly increased in 29- compared with 10-wk-old obese rats. Absence of a change in GLUT-4 content together with uncompromised contraction-stimulated glucose transport suggests that the maturation-induced decrease in insulin-stimulated glucose transport in lean rats is due to a defect in the insulin signaling pathway.
Sterol metabolism in fetal, newborn, and suckled lambs and their response to cholesterol after weaning
Authors: Cavender C. P. , Turley S. D. , Dietschy J. M.
Published: December 2017

Several aspects of cholesterol metabolism were studied in lambs at six stages of development. The first three stages involved fetal lambs with gestational ages (fertilization set at -150 days) of -73 days (early fetal), -42 days (midfetal), and -14 days (late fetal). The other groups comprised newborn (0 days), suckled (17 days), and weaned (105 days) lambs. The liver, kidney, spleen, and brain actively synthesized cholesterol at all stages of development, but hepatic synthesis in the suckled lambs was markedly suppressed compared with that in their newborn and weaned counterparts. Whereas intestinal sterol synthesis was very low in all the fetal lambs, the converse was true in the neonatal animals. The total cholesterol concentration in the liver, intestine, kidney, and spleen remained relatively constant at all stages of growth, whereas in brain tissue it increased throughout development. Plasma total and low-density-lipoprotein cholesterol levels were lowest in the late fetal lambs and highest in the suckled animals. The metabolic response of weaned lambs to a dietary cholesterol challenge was similar to that reported for various monogastric species.
Polyunsaturated fatty acids recruit brown adipose tissue: increased UCP content and NST capacity
Authors: Sadurskis A. , Dicker A. , Cannon B. , Nedergaard J.
Published: December 2017

To examine the effect of polyunsaturated fatty acids (PUFA) on brown adipose tissue recruitment and on the capacity for nonshivering thermogenesis (NST), mice were fed a diet with a standard fat content (9%) and a normal PUFA content (1.6%) (controls) or a high-PUFA content (4.3%) for 2-3 wk. The resting metabolic rate was somewhat lower in the high-PUFA group, probably due to a lower physical activity whereas the capacity for NST (estimated as the metabolic response to a norepinephrine injection) was higher in the high-PUFA group. There was no significant effect on brown adipose tissue wet weight, protein content, or cytochrome-c oxidase content, but the amount of the uncoupling protein thermogenin (UCP), measured immunologically, was significantly increased in the high-PUFA mice (totally by 41%). It was concluded that short-term feeding of a high-PUFA diet may recruit brown adipose tissue thermogenic capacity; it was speculated that earlier-reported recruiting effects of high-fat diets may not be due solely to the high total fat content of the diet but perhaps also to a specific recruiting property of the high-PUFA diets generally used in this type of investigation.
Skeletal muscle pyruvate dehydrogenase activity during maximal exercise in humans
Authors: Putman C. T. , Jones N. L. , Lands L. C. , Bragg T. M. , Hollidge-Horvat M. G. , Heigenhauser G. J.
Published: December 2017

The regulation of the active form of pyruvate dehydrogenase (PDHa) and related metabolic events were examined in human skeletal muscle during repeated bouts of maximum exercise. Seven subjects completed three consecutive 30-s bouts of maximum isokinetic cycling, separated by 4 min of recovery. Biopsies of the vastus lateralis were taken before and immediately after each bout. PDHa increased from 0.45 +/- 0.15 to 2.96 +/- 0.38, 1.10 +/- 0.11 to 2.91 +/- 0.11, and 1.28 +/- 0.18 to 2.82 +/- 0.32 mmol.min-1.kg wet wt-1 during bouts 1, 2, and 3, respectively. Glycolytic flux was 13-fold greater than PDHa in bouts 1 and 2 and 4-fold greater during bout 3. This discrepancy between the rate of pyruvate production and oxidation resulted in substantial lactate accumulation to 89.5 +/- 11.6 in bout 1, 130.8 +/- 13.8 in bout 2, and 106.6 +/- 10.1 mmol/kg dry wt in bout 3. These events coincided with an increase in the mitochondrial oxidation state, as reflected by a fall in mitochondrial NADH/NAD, indicating that muscle lactate production during exercise was not an O2-dependent process in our subjects. During exercise the primary factor regulating PDHa transformation was probably intracellular Ca2+. In contrast, the primary regulatory factors causing greater PDHa during recovery were lower ATP/ADP and NADH/NAD and increased concentrations of pyruvate and H+. Greater PDHa during recovery facilitated continued oxidation of the lactate load between exercise bouts.
Quantification of incorporation of [15N]ammonia into plasma amino acids and urea
Authors: Patterson B. W. , Carraro F. , Klein S. , Wolfe R. R.
Published: December 2017

The incorporation of 15N into individual plasma amino acids and urea was quantified in five human subjects who received 15NH4Cl either orally or intravenously for 6 h. After oral tracer administration, the highest enrichment was achieved by arginine, followed by urea and glutamine; distribution of 15N within glutamine was 55% amide and 45% amino N. Glutamine achieved the highest enrichment after the intravenous administration of tracer, with a distribution of 92% amide and 8% amino N. The relative distribution pattern of 15N incorporation was quantified from the rate at which 15N initially appeared in each plasma component. Amino acids (especially arginine, glutamine, and glutamate) accounted for greater than one-half (54%) of the orally administered tracer that was initially recovered in plasma components, compared with 46% initial appearance for urea; for the intravenous tracer, amino acids accounted for 78% of initial appearance of tracer compared with 22% for urea. Our results highlight the involvement of the splanchnic bed in the utilization of orally administered ammonia (preferential incorporation of oral tracer into arginine, urea, glutamate, and the amino N of glutamine) in contrast to the preferential incorporation of systemically administered ammonia into the amide N of glutamine and alanine.
Measuring gluconeogenesis with [2-13C]glycerol and mass isotopomer distribution analysis of glucose
Authors: Peroni O. , Large V. , Beylot M.
Published: December 2017

We tested the validity of the use of [2-13C]glycerol and of the mass isotopomer distribution analysis of glucose for measuring gluconeogenesis in vitro and in vivo. When isolated rat livers (starved for 48 h) were infused with labeled glycerol without or with lactate+pyruvate, gluconeogenesis accounted for > 90% of glucose production. When glucose was added to the infusate so that glucose produced by the liver represented only 80 or 45% of total glucose output, this dilution could be calculated from the mass isotopomer distribution of glucose. When postabsorptive and starved rats were infused with [2-13C]glycerol, gluconeogenesis accounted for 54 +/- 2 and 89 +/- 1%, respectively, of glucose production. However, accurate measures could be obtained, particularly in postabsorptive rats, only with high tracer infusion rates (representing > or = 50% of endogenous glycerol production rate). In both groups of rats, these infusion rates resulted in an increase in total glycerol turnover rate and gluconeogenesis from glycerol. In addition, hepatic concentration of glycerol 3-phosphate was increased. In conclusion, [2-13C]glycerol infusion and mass isotopomer distribution analysis of glucose appear to be useful methods for studies of gluconeogenesis in vitro and in vivo; however, accurate measurements in vivo can be obtained only at the expense of some perturbation of the metabolic pathway studied.
Distinguishable substrate pools for muscle glyconeogenesis in lactate-supplemented recovery from exercise
Authors: Ryan C. , Radziuk J.
Published: December 2017

The formation of muscle glycogen from substrates other than glucose (glyconeogenesis) has now been demonstrated 1) from circulating lactate when this lactate is elevated and 2) from intramuscular substrate, which equilibrates with the products of local glucose metabolism but not with circulating lactate [Am. J. Physiol. 267 (Endocrinol. Metab. 30): E210-E218, 1994]. The purpose of the present studies was to examine the interaction of recovery from low-intensity exercise (4-h swim) and supplementation with exogenous lactate in determining the distribution of carbon flux between these two pathways for the glyconeogenic process in the gastrocnemius muscles. Ten protocols were defined using [14C]bicarbonate (no local incorporation into glycogen), [U-14C]lactate (tracks circulating lactate), and recycled [1-14C]glucose (tracks local substrate formation and glyconeogenesis). During recovery, lactate was infused to increase circulating concentrations 15- to 20-fold. Glucose and saline infusions during recovery were used as controls. The results indicate that prior exercise primarily promotes the local incorporation of recycled glucose label produced within the muscle into glycogen. Exogenous lactate stimulates the incorporation of circulating lactate into muscle glycogen. The contribution of the two substrate pools to glycogen synthesis appears to be additive, indicating the independence of muscle glycogenesis from these two sources.
Insulin resistance after hypertension induced by the nitric oxide synthesis inhibitor L-NMMA in rats
Authors: Baron A. D. , Zhu J. S. , Marshall S. , Irsula O. , Brechtel G. , Keech C.
Published: December 2017

To explore the relationship between insulin resistance and hypertension, we examined whether acute induction of hypertension can engender insulin resistance. For this purpose we measured rates of insulin-mediated glucose uptake in awake unstressed rats with the euglycemic hyperinsulinemic (12 microns.kg-1.min-1) clamp technique during infusions of saline alone or after induction of hypertension by bolus administration of NG-monomethyl-L-arginine (L-NMMA, 30 and 15 mg/kg), a competitive inhibitor of nitric oxide synthase. Arterial pressure was approximately 20% greater with L-NMMA bolus than with saline alone. Isotopically determined steady-state rates of glucose uptake were 36 +/- 1 mg.kg-1.min-1 during saline alone and 26 +/- 2 and 19 +/- 1 mg.kg-1.min-1 with low- and high-dose L-NMMA (P < 0.001 vs. saline), respectively. To rule out that insulin resistance induced by L-NMMA was adrenergically mediated, clamp studies were repeated with alpha- and beta-blockade. Rates of glucose uptake remained approximately 20% below those observed with saline alone (P < 0.001). A significant inverse correlation was observed between the height of the blood pressure and the rate of glucose uptake (r = 0.32, P = 0.04). In conclusion, acute induction of hypertension with L-NMMA can cause marked insulin resistance. We postulate that reduced skeletal muscle perfusion and/or sympathetic nervous system activation may contribute to insulin resistance induced by L-NMMA.
Effect of meal timing on diurnal rhythm of human cholesterol synthesis
Authors: Cella L. K. , Van Cauter E. , Schoeller D. A.
Published: December 2017

To test whether the diurnal rhythm of cholesterol synthesis in humans is entrained to meal timing, the effect of a 6.5-h delay of mealtimes was investigated in four normal lipidemic male subjects. Cholesterol fractional synthetic rate was measured by deuterium incorporation from body water using blood sampling every 2 h. The baseline was a 24-h control period in which three Western-style meals were consumed at 0700, 1150, and 1640, followed by 3 days in which meals were delayed by 6.5 h, i.e., meals consumed at 1330, 1820, and 2310 without changing the sleep-wake and light-dark cycles. Cholesterol synthesis was maximal at 2200 +/- 0200 and minimal at 1130 +/- 0050 on the baseline day. On day 1 of the shifted meals, the maximum was delayed 6.0 +/- 0.5 h and the nadir was not changed. On day 3, the maximum was delayed 8.6 +/- 3.7 h and the minimum was delayed 6.5 +/- 2.4 h from baseline. The mean amplitude of the cholesterol rhythm was significantly greater on day 3,233 +/- 35%, compared with baseline which was 109 +/- 15%. A strong negative correlation (r = -0.66 +/- 0.10) was found between the rhythms of cholesterol synthesis and cortisol during the baseline day, but there was a phase delay in the rhythm of cholesterol synthesis relative to cortisol on day 1 and day 3. Findings indicate that the 24-h variation in cholesterol synthesis is strongly dependent on meal timing.
Effects of protein, methionine, or chloride on acid-base balance and on cysteine catabolism
Authors: Bella D. L. , Stipanuk M. H.
Published: December 2017

Metabolism of cysteine to sulfate results in production of H+, whereas metabolism of cysteine to taurine does not. Rats were fed a basal low-protein diet or a diet with excess protein, methionine, or chloride for 2-3 wk, and effects of these treatments on acid-base homeostasis and on cysteine metabolism were determined. Hepatocytes from rats fed diets with excess methionine, but not from rats fed diets with excess protein or chloride, catabolized a high proportion of cysteine to taurine (32% vs. 4-7% for other groups), and intact rats fed excess methionine excreted more sulfur as taurine (51% of total sulfur vs. 1-6% for other groups). The formation of taurine vs. sulfate as the end product of cysteine catabolism provides a metabolic compensation that minimizes the acid load in rats fed excess sulfur amino acids. However, increased production of taurine vs. sulfate is not a general adaptive response to acidogenic diets.
Recording of a large-conductance chloride channel in normal rat lactotrophs
Authors: Fahmi M. , Garcia L. , Taupignon A. , Dufy B. , Sartor P.
Published: December 2017

Membrane current fluctuations resembling channel openings and closings were observed in the whole cell configuration of the patch-clamp technique in normal rat lactotrophs in primary culture. Using high-gain head stage in whole cell configuration, we characterized the nature and pharmacological properties of the ionic channel underlying these fluctuations. This channel, found in small numbers (< 10 per cell), was specific for Cl- because its reversal potential varied with Cl- gradients, according to the Nernst equation, and its unitary amplitude was linearly related to membrane potential from -100 to 0 mV. Slope conductance was close to 100 pS. Analyzing open times, we demonstrated its Ca2+ and potential dependence. Four sublevels were observed. We suggest that this channel, belonging to the background Cl- channel group, takes part in the regulation of intracellular Cl- concentration of normal rat lactotrophs.
Infusion of labeled KIC is more accurate than labeled leucine to determine human muscle protein synthesis
Authors: Chinkes D. , Klein S. , Zhang X. J. , Wolfe R. R.
Published: December 2017

The leucine constant infusion method is the most commonly used method for measuring fractional synthetic rates (FSR) of muscle protein. However, this method has been criticized because of the uncertainty involved in measuring precursor pool enrichment. We present an alternative method for measuring muscle FSR by giving a constant infusion of alpha-[1-13C]ketoisocaproate (alpha-[1-13C]KIC). We infused alpha-[1-13C]KIC and [5,5,5-2H3]leucine for 4 h in five volunteers and took plasma samples half-hourly and muscle biopsies at 1 and 4 h of isotope infusion. When KIC was infused, intramuscular free leucine enrichment was the same as arterial leucine enrichment. However, when labeled leucine was infused, intramuscular free leucine enrichment was only 76 +/- 3% of arterial KIC enrichment, which agrees with previous reports that plasma KIC enrichment does not accurately reflect intramuscular leucine enrichment. We obtained an FSR of 2.25 +/- 0.12%/day by use of this method, which agrees with a previous report using tRNA bound leucine as the precursor. In conclusion, the KIC infusion method overcomes the theoretical limitations of the leucine infusion.
Protein turnover during puberty in normal children
Authors: Arslanian S. A. , Kalhan S. C.
Published: December 2017

To investigate whether insulin resistance of puberty involves protein metabolism, we compared whole body leucine kinetics in 20 prepubertal Tanner I (TI), and 21 pubertal Tanner II-IV (TII-IV) healthy children. Leucine flux (LRa), oxidation (LOX), and nonoxidative disposal (NOXLD) were measured during primed constant infusion of [1-13C]leucine at baseline and during a stepwise hyperinsulinemic (10 and 40 mU.m-2.min-1)euglycemic clamp in combination with indirect calorimetry. At baseline LRa and LOX were lower in TII-IV vs. TI [LRa: 3.59 +/- 0.17 vs. 4.05 +/- 0.18 mumol.min-1.kg-1 fat-free mass (FFM), P = 0.036; LOX: 0.45 +/- 0.03 vs. 0.59 +/- 0.04 mumol.min-1. FFM-1, P = 0.005], but NOXLD was similar. Insulin-like growth factor I (IGF-I) levels correlated inversely with LRa, NOXLD, and LOX. Energy expenditure correlated positively with LRa, LOX, and NOXLD. During the clamp absolute and percent suppression in LRa were significantly lower in TII-IV than TI. In conclusion, 1) proteolysis and protein oxidation are lower during puberty compared with prepuberty, whereas protein synthesis is unchanged; 2) insulin action in inhibiting proteolysis is decreased during puberty; and 3) increased pubertal IGF-I levels may play a role in decreased protein degradation.
Effects of systemic GHRH on sleep in intact and hypophysectomized rats
Authors: Obal F. , Floyd R. , Kapas L. , Bodosi B. , Krueger J. M.
Published: December 2017

The role of pituitary growth hormone (GH) in the mediation of enhanced sleep elicited by GH-releasing hormone (GHRH) was studied in the rat. Intact and hypophysectomized (HYPOX) rats received systemic injections of GHRH or physiological saline. GHRH (0.5, 5.0, or 50 micrograms/kg in the intact rats and 0.5 or 50 micrograms/kg in HYPOX rats) was injected 6 h after light onset (P.M. injection) or just before light onset (A.M. injection, 0.5 microgram/kg in both A.M. groups). Sleep-wake activity and brain cortical temperature were recorded for 23 h (12 h light + 11 h dark). A.M. injection of GHRH did not alter sleep in normal or HYPOX rats. Each dose of P.M. GHRH increased rapid-eye-movement sleep (REMS) during 6 h postinjection in the intact rats. Hypophysectomy abolished the REMS-promoting activity of GHRH. P.M. injection of 0.5 microgram/kg GHRH increased non-REM sleep (NREMS) and enhanced electroencephalogram slow-wave activity during NREMS in both the intact and the HYPOX rats. The NREMS-promoting activity disappeared when the dose of GHRH was increased in the intact rats, whereas a tendency to enhanced NREMS was still observed after 50 micrograms/kg GHRH in the HYPOX rats. GHRH stimulated GH secretion dose dependently in the intact rats. A.M. injection of 0.5 microgram/kg GHRH tended to be less effective in stimulating GH release than the same dose administered P.M. The results confirm the time-of-day variations in the GHRH effects on sleep previously reported in human subjects. It is likely that pituitary GH is involved in the mediation of the REMS-promoting activity of GHRH but not in the NREMS-promoting activity of GHRH. Nevertheless, the results do not exclude the possibility that GH may modulate NREMS.