bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of VMH obesity: in vivo insulin secretion and tissue insulin sensitivity
Authors: Penicaud L. , Kinebanyan M. F. , Ferre P. , Morin J. , Kande J. , Smadja C. , Marfaing-Jallat P. , Picon L.
Published: December 2017

Euglycemic-hyperinsulinemic clamps coupled with an injection of [2-3H]deoxyglucose were performed in rats 1 or 6 wk after lesion of the ventromedial hypothalamus (VMH) and their age-matched controls. In the basal state, glucose utilization was not different in controls and VMH rats in all the tissues studied except in white adipose tissue where it was greatly increased after the lesion. When insulinemia was clamped at 850 microU/ml, glucose utilization was less important in glycolytic and normal in oxidative muscles in animals 1 wk after the lesion (VMH1) compared with controls. In animals 6 wk after the lesion (VMH6), all the muscles utilized less glucose than those of controls. In white adipose tissue, glucose utilization was increased twice more in VMH1 and returned to normal in VMH6. These data demonstrate a progressive development of insulin resistance in muscles. Simultaneously, there is a transient insulin hypersensitivity in white adipose tissue. This, together with a hypersecretion of insulin, could contribute to the development of body fat mass by redirecting glucose towards adipose tissue.
Increased ACTH response to corticotropin-releasing factor in cold-adapted rats in vivo
Authors: Uehara A. , Habara Y. , Kuroshima A. , Sekiya C. , Takasugi Y. , Namiki M.
Published: December 2017

We have recently reported that chronically repeated restraint stress results in improved cold tolerance in rats via an increased activity of nonshivering thermogenesis, a characteristic metabolic change observed during cold adaptation, suggesting the presence of cross-adaptation between cold and stress. It is well established that the hypothalamic-pituitary-adrenal (HPA) axis is activated in various stress responses. In the present study, therefore, we examined whether cold adaptation would alter the adrenocorticotropic hormone (ACTH)-releasing state in vivo using freely moving, conscious rats chronically implanted with intra-atrial cannulas. There was no difference in the basal levels of plasma ACTH between warm control and cold-adapted rats. On the other hand, the ACTH response to the intravenous administration of corticotropin-releasing factor (CRF; 2 micrograms/animal) was significantly elevated in cold-adapted rats. However, the injection of 10 micrograms of CRF, which was considered as a dose to elicit the maximal ACTH response, resulted in similar ACTH release patterns between the two groups. These changes in the responsiveness of ACTH secretion have been observed in rats chronically exposed to stressful conditions. The results demonstrated in the present study, therefore, provide further evidence for our hypothesis that there may exist cross-adaptation between cold and nonthermal stress.
Glucose recycling and production in glycogenosis type I and III: stable isotope technique study
Authors: Kalderon B. , Korman S. H. , Gutman A. , Lapidot A.
Published: December 2017

Glucose carbon recycling, endogenous glucose production, and glucose turnover rates were measured, by stable isotope methodology, in five patients with glycogen storage disease type I (GSD-I), two patients with glycogen storage disease type III (GSD-III), and three control children. A primed-constant infusion of D-[U-13C]glucose was administered nasogastrically to fasted subjects. The isotopic enrichments and 13C isotopomer distribution of plasma glucose were measured by chemical ionization gas chromatography mass spectroscopy. In response to increasing rates of glucose infusion, endogenous glucose production decreased, whereas the rate of glucose appearance or total glucose flux increased. Recycling of infused D-[U-13C]-glucose, calculated from changes in the isotopomer distribution of plasma [13C]glucose, was not detectable in GSD-I but reached 50% in GSD-III. In GSD-I the gluconeogenic pool was found to be highly labeled and recycled, whereas plasma glucose was diluted but not recycled. It is suggested that in GSD-I dilution of plasma glucose is due to release of glucose from branch points in glycogen. We propose that studies of the extent of glucose recycling and of isotopic enrichment of gluconeogenic precursors can be used as a noninvasive test for diagnosis of GSD-I and other defects in glucose production.
Selective in vitro reversal of the insulin resistance of glucose transport in denervated rat skeletal muscle
Authors: Sowell M. O. , Dutton S. L. , Buse M. G.
Published: December 2017

Denervation (24 h) of skeletal muscle causes severe postreceptor insulin resistance of glucose transport and glycogen synthesis that is demonstrable in isolated muscles after short (30 min) preincubations. After longer preincubations (2-4 h), the insulin response of glucose transport increased to normal, whereas glycogen synthesis remained insulin resistant. Basal and insulin-stimulated amino acid transport were significantly lower in denervated muscles than in controls after short or long incubations, although the percentage stimulation of transport by insulin was not significantly different. The development of glucose transport insulin resistance after denervation was not attributable to increased sensitivity to glucocorticoids or adenosine. The selective in vitro reversal of glucose transport insulin resistance was not dependent on medium composition, did not require protein or prostaglandin synthesis, and could not be attributed to release of a positive regulator into the medium. The data suggest 1) the insulin receptor in muscle stimulates glucose transport by a signaling pathway that is not shared by other insulin-sensitive effector systems, and 2) denervation may affect insulin receptor signal transduction at more than one site.
Differential roles of splanchnic and peripheral tissues in determining diurnal fluctuation of glucose tolerance
Authors: Verrillo A. , De Teresa A. , Martino C. , Di Chiara G. , Pinto M. , Verrillo L. , Torello F. , Gattoni A.
Published: December 2017

To identify the mechanisms and the sites of the diurnal fluctuation in glucose tolerance in humans, we selectively quantitated the components of net splanchnic glucose balance, i.e., splanchnic glucose uptake and hepatic glucose output, as well as peripheral glucose uptake, by combining tritiated glucose infusion with hepatic and femoral venous catheterization. The studies were carried out in 11 healthy volunteers at 8:00 A.M. and at 6:00 P.M. on different days after 12 h of fasting. After intravenous glucose infusion (6.5 mg.kg-1.min-1 for 120 min) blood glucose rose twofold at 8:00 A.M. and threefold at 6:00 P.M. (P less than 0.01). Insulin levels did not differ significantly between the two series of tests. Splanchnic glucose balance switched from the net output of the basal state to a net uptake in both morning and afternoon studies. However, this effect was more marked at 6:00 P.M. than at 8:00 A.M. (at 60-120 min, P less than 0.05). The different pattern of splanchnic glucose balance was entirely accounted for by a greater rise in splanchnic glucose uptake in the afternoon, as the suppression of endogenous glucose output by the glucose load was practically complete in both series of studies. In contrast, glucose uptake by leg tissues increased less at 6:00 P.M. than at 8:00 A.M. (at 30-60 min, P less than 0.05; at 75 and 90 min, P less than 0.01; at 105 and 120 min, P less than 0.005). These data indicate that the mechanism responsible for the reduced glucose tolerance later in the day resides in the peripheral tissues whose ability to dispose of a glucose load is drastically decreased.
Oscillatory insulin secretion in perifused isolated rat islets
Authors: Bergstrom R. W. , Fujimoto W. Y. , Teller D. C. , de Haen C.
Published: December 2017

After a step-function increase in glucose concentration, insulin secretion by perifused isolated rat islets of Langerhans showed oscillations superimposed on the well-known first- and second-phase secretory components. The oscillations were sustained for the length of the experiment and corresponded to at least four cycles. This established the existence of an oscillatory pacemaker with a narrow dispersion of periodicities intrinsic to the islets and showed that synchronization of islet action could be achieved by a step-function increase in glucose concentration. The observed period of 16 min is similar to the period of oscillatory insulin secretion in a number of intact organisms. This argues for identity of pacemakers in vivo and in isolated islets. This means that neural or other forms of interislet communication are not prerequisites for oscillatory insulin secretion. Theophylline increased the length of the oscillatory period, suggesting the periodicity of the pacemaker of insulin secretion can be metabolically regulated. This observation also provided a basis for explaining fine tuning of oscillatory periods by the nervous system.
Human variation in skeletal muscle fiber-type proportion and enzyme activities
Authors: Simoneau J. A. , Bouchard C.
Published: December 2017

The purpose of the present study was to describe the extent of the variation in some of the common characteristics of human skeletal muscle. A total of 418 biopsies was obtained from the vastus lateralis muscle of 270 healthy sedentary and 148 physically active individuals of both sexes. The lowest and highest proportion of type I muscle fiber observed were 15 and 85%, respectively. Coefficients of variation (CV) reached approximately 30% for the proportion of types I and IIA fibers and were two times higher for the proportion of type IIB fiber. The smallest and largest mean muscle fiber cross-sectional areas (CSA) were approximately 1,100 microns 2 and 9,500 microns 2, respectively. Mean CSA of the various fiber types exhibited CV of approximately 23%. CV reached 30% for the activity of creatine kinase, ranged between 28 and 41% for the glycolytic enzyme markers, and between 34 and 44% for the aerobic-oxidative enzyme markers. The mean proportion of type I fiber was lower in male than in female muscles, whereas the mean CSA of all fiber types was smaller in female than in male muscles. Levels of glycolytic enzyme markers were higher in male than in female skeletal muscles. However, activities of aerobic-oxidative enzyme markers were similar in males and females. These results reveal the existence of large interindividual variability and gender differences in the most common characteristics of the human skeletal muscle.
Endothelin-1 activates phospholipase C and mobilizes Ca2+ from extra- and intracellular pools in osteoblastic cells
Authors: Takuwa Y. , Ohue Y. , Takuwa N. , Yamashita K.
Published: December 2017

The effect of endothelin-1 (ET), a novel vasoactive peptide derived from endothelial cells, on osteoblastic MC3T3-E1 cells was studied. ET specifically binds to a single class of high-affinity receptors in MC3T3-E1 cells and induces phospholipase C activation with the production of two second messengers, inositol trisphosphate and 1,2-diacylglycerol, and a biphasic increase in intracellular free Ca2+ concentration ([Ca2+]i), which consists of an initial transient increase and an ensuing sustained plateau, as measured with a fluorescent indicator, fura-2. The second plateau phase but not the initial transient increase in [Ca2+]i induced by ET is abolished by removal of extracellular Ca2+ but not by either nicardipine, verapamil, or diltiazem. The ET-stimulated production of inositol trisphosphate is not abolished by removal of extracellular Ca2+, indicating that ET-stimulated phospholipase C activation is not a consequence of an increase in Ca2+ influx across the plasma membrane. ET causes stimulation of DNA synthesis and reduction of alkaline phosphatase activity in MC3T3-E1 cells. A protein kinase C activator phorbol 12,13-dibutyrate mimics these effects of ET. The results demonstrate that ET activates the inositol lipid signaling pathway and induces mobilization of Ca2+ from both extra- and intracellular pools and activation of protein kinase C in osteoblastic MC3T3-E1 cells.
Lipogenic enzyme activities and mRNA in rat adipose tissue at weaning
Authors: Coupe C. , Perdereau D. , Ferre P. , Hitier Y. , Narkewicz M. , Girard J.
Published: December 2017

The activities and mRNA concentrations of two lipogenic enzymes, fatty acid synthetase and acetyl-CoA carboxylase, and one enzyme involved in glyceroneogenesis, phosphoenolpyruvate carboxykinase (PEPCK), were measured in rat white adipose tissue during the suckling-weaning transition. Activities and mRNA concentrations of lipogenic enzymes were low in suckling rats, whereas activity and mRNA concentration of PEPCK were high. At weaning to a high-carbohydrate diet, the rapid increase in lipogenic enzymes mRNA (10- to 20-fold) and decrease in PEPCK mRNA (10-fold) were followed by parallel changes in enzyme activities. In contrast, weaning to a high-fat diet prevented these modifications. Force feeding suckling rats with carbohydrates induced a rise in blood glucose and plasma insulin concentrations. During these experiments, mRNA concentrations increased 10- to 20-fold for lipogenic enzymes and decreased 5-fold for PEPCK in less than 6 h, whereas all enzyme activities did not vary. This suggests a pretranslational regulation of gene expression. Force feeding suckling rats with a mixture of fat devoid of carbohydrate induced a slight increase in plasma insulin concentration and a fall in PEPCK mRNA but was not accompanied by a rise in lipogenic enzyme mRNAs. This suggested that insulin is a prime regulator of PEPCK gene expression, whereas glucose and insulin act synergistically in the regulation of lipogenic enzyme gene expression.
Underestimation of glucose turnover corrected with high-performance liquid chromatography purification of [6-3H]glucose
Authors: Schwenk W. F. , Butler P. C. , Haymond M. W. , Rizza R. A.
Published: December 2017

We have recently reported that during infusion of commercially available [6-3H]glucose, a radioactive nonglucose contaminant may accumulate in plasma causing errors in the measurement of glucose turnover. To determine whether purification of this tracer by HPLC (high-performance liquid chromatography) before infusion would eliminate the contaminant in plasma and remove the underestimation of glucose turnover reported during hyperinsulinemia, four normal subjects each underwent two 5-h euglycemic clamps during infusion of insulin (1 mU.kg-1.min-1). Glucose turnover was measured with either commercially available [6-3H]glucose or with HPLC-purified [6-3H]glucose. HPLC analysis of samples from the clamps done with commercially available [6-3H]glucose showed that 9.7% of the infused tracer and 26% of the "plasma glucose 3H radioactivity" were contaminants. In contrast, no contaminant was observed in the plasma during infusion of HPLC-purified [6-3H]glucose. During the last hour of the clamp, mean glucose turnover using commercially available [6-3H]glucose was less (P less than 0.01) than the mean glucose infusion rate (7.6 +/- 0.3 vs. 10.5 +/- 0.3 mg.kg-1.min-1) yielding apparent "negative" (P less than 0.001) hepatic glucose release. In contrast, when HPLC-purified [6-3H]glucose was employed, glucose turnover equaled the glucose infusion rate (10.4 +/- 0.9 vs. 10.2 +/- 0.9 mg.kg-1.min-1) and hepatic glucose release was no longer negative. We conclude that removal of a tritiated nonglucose contaminant in [6-3H]glucose by HPLC yields correct estimations of glucose turnover at steady state.
Effects of a growth hormone pulse on total and forearm substrate fluxes in humans
Authors: Moller N. , Jorgensen J. O. , Schmitz O. , Moller J. , Christiansen J. , Alberti K. G. , Orskov H.
Published: December 2017

Under physiological circumstances growth hormone (GH) is secreted in bursts after the onset of sleep and a few hours postprandially. Because most relevant studies have employed constant or repeated infusion of high doses of GH, the possible metabolic effects of such bursts are largely unknown. We have studied seven healthy, male subjects for 7 h after an intravenous bolus of 1) 140 micrograms GH and 2) saline. When injected, serum GH rose to a peak of 21 +/- 3 micrograms/l 10 min after injection. GH caused 1) a rapid, sustained 55% decrease in forearm glucose uptake (P less than 0.05) followed by increases toward control values, 2) a delayed 5 mg/100 ml decrease in plasma glucose (P less than 0.05), and 3) significant 60-250% increases (P less than 0.05) in all measured lipid intermediates (nonesterified fatty acids, 3-hydroxybutyrate, and glycerol) 120-160 min after administration followed by decreases to below control values (P less than 0.05). GH did not influence circulating levels of insulin, C-peptide, glucagon, or insulin-like growth factor I (IGF-I), or isotopically determined glucose turnover. Physiological bursts of GH secretion appear to have acute insulin antagonistic effects with maximal effect on lipolysis after 2 h. These effects are reversed after 4 h. Therefore, GH could play a key role in regulation of diurnal rhythms of substrate levels and fuel utilization in humans.
The role of pituitary beta-endorphin in mediating corticotropin-releasing factor-induced antinociception
Authors: Hargreaves K. M. , Flores C. M. , Dionne R. A. , Mueller G. P.
Published: December 2017

The hypothesis that blood-borne beta-endorphin modulates nociception was examined with corticotropin-releasing factor (CRF) as a potent and selective agent to stimulate its release from the pituitary gland. Intravenously administered CRF produced a dose-related antinociception in rats as determined by measuring paw-lick latencies on a 50 degrees C hot plate. A dose of 25 nmol/kg of CRF was comparable in both magnitude and duration of antinociception to a 7,500 nmol/kg (= 2.5 mg/kg) dose of morphine sulfate. The antinociceptive effect of CRF was blocked by both hypophysectomy and dexamethasone pretreatment, suggesting that it was mediated by hormone release from the anterior pituitary corticotrophs. Furthermore, the effect of CRF was antagonized by 1) naltrexone, 2) naltrexone methyl bromide, and 3) passive immunization with anti-beta-endorphin antiserum. Together, these data support the hypothesis that opiate-active, beta-endorphin, released by pituitary corticotrophs, participates in the physiological modulation of nociception in rats.
Placental lactogen receptors in maternal sheep liver: effects of fasting and refeeding
Authors: Freemark M. , Comer M. , Mularoni T. , D'Ercole A. J. , Grandis A. , Kodack L.
Published: December 2017

In a recent study we demonstrated that fasting of the pregnant ewe reduces the number of placental lactogen (PL) receptors in fetal sheep liver. In the present study we examined the effects of a 72-h fast on the number and affinity of PL receptors in maternal sheep liver. Fasting caused a 57% reduction in the number of hepatic ovine PL receptors; this effect was reversed by refeeding. There were no changes in the affinity of the PL receptor, the subunit structure of the receptor, or the extent of occupancy of the receptor by endogenous circulating maternal hormones. The number of hepatic PL receptors was correlated positively with the maternal plasma concentrations of glucose and insulin, suggesting that these factors may regulate PL binding to maternal tissues during pregnancy. In addition, PL receptor number was correlated positively with maternal plasma insulin-like growth factor I (IGF-I) concentrations, suggesting that a reduction in hepatic ovine PL binding may contribute to the reduction in maternal IGF-I during fasting. Fasting produced a 72% reduction in the number of ovine growth hormone receptors in maternal liver and an 83% increase in hepatic insulin binding. These findings indicate that fasting of the pregnant ewe reduces the number of PL receptors in maternal and fetal liver. The reduction in PL binding may contribute to maternal and fetal hyposomatomedinemia and may play a role in the pathogenesis of the intrauterine growth retardation that accompanies maternal nutritional deprivation.
Sustained stimulation of aldosterone production by angiotensin II is potentiated by nickel
Authors: Spat A. , Balla I. , Balla T. , Enyedi P. , Hajnoczky G. , Rohacs T.
Published: December 2017

Angiotensin-induced aldosterone production by superfused adrenal glomerulosa cells was potentiated by Ni2+ (0.1 mM), added either at the onset of stimulation with angiotensin II or 1 h later. Nickel did not influence the effect of adrenocorticotropic hormone or potassium on aldosterone production. Nickel failed to modify angiotensin-induced changes in phospholipid metabolism or the formation of inositol phosphates and slightly reduced the enhancement of 45Ca influx. Uptake of Ni2+ into glomerulosa cells was increased by depolarization in a dihydropyridine-insensitive manner. Because nickel selectively potentiates the sustained phase of the response to a calcium-mobilizing hormone, it may serve as a suitable tool in elucidating the signal transduction process during the sustained phase of stimulation.
Regulatory effect of cholecystokinin on subsequent insulin binding to pancreatic acini
Authors: Okabayashi Y. , Otsuki M. , Nakamura T. , Koide M. , Hasegawa H. , Okutani T. , Kido Y.
Published: December 2017

We investigated the regulatory effect of cholecystokinin (CCK) on subsequent insulin binding to pancreatic acinar cells. Rat isolated acini were preincubated with various concentrations of CCK octapeptide (CCK-8) at 37 degrees C. Acini were then washed, resuspended in the binding buffer, and incubated with 8.3 pM 125I-labeled insulin for 60 min at 37 degrees C. Pretreatment with CCK-8 caused inhibition of subsequent 125I-insulin binding that was time and concentration dependent. Significant inhibition was observed with 3 pM CCK-8. Computer analysis of the competition-inhibition study with a nonlinear least-squares curve-fitting program revealed that CCK-8 pretreatment of acini reduced the receptor affinity of the high-affinity binding site. This inhibitory action of CCK-8 was not due to the alteration in degradation or internalization of the tracer. When acini were pretreated with 100 pM CCK-8 for 120 min at 4 degrees C, a reduction in the receptor affinity of the high-affinity binding site was also observed. In pancreatic membrane prepared from acini preincubated with 100 pM CCK-8 for 120 min at 37 degrees C, displacement of 125I-insulin (83 pM) by unlabeled insulin (24 degrees C, 1 h) revealed that CCK-8 inhibited 125I-insulin binding by altering the receptor affinity of the high-affinity binding site. In acinar preparations the inhibitory effect of CCK-8 on 125I-insulin binding was abolished when acini were preincubated with CCK-8 and CCK receptor antagonist L 374718 at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of 1,25 dihydroxyvitamin D3 on isolated islets from vitamin D3-deprived rats
Authors: Billaudel B. J. , Faure A. G. , Sutter B. C.
Published: December 2017

Insulin release is impaired by vitamin D3 deficiency but can be restored by in vivo administration of 1,25 dihydroxyvitamin D3 [1,25(OH)2D3]. A direct influence of 1,25(OH)2D3 on the B-cell was studied in vitro with islets from 5-wk vitamin D3-deprived rats. This hormone (10(-12) to 10(-6) mol/l) added to the incubation medium had a stimulatory dose-dependent effect on insulin response to 8.3 mmol/l glucose 6 h later. Moreover, perifusion experiments performed after different times of incubation demonstrated that after 6 h 1,25(OH)2D3 increased in particular the first phase of insulin response to 16.7 mmol/l glucose. The 45Ca fluxes, followed in parallel, were never modified by 1,25(OH)2D3 in the absence of glucose but were enhanced during the glucose stimulus, whereas 86Rb fluxes were never affected by 1,25(OH)2D3. These results demonstrated that 1,25(OH)2D3 acts in vitro on B-cells, but with a 6-h delay to potentiate the glucose-induced insulin release, concomitant with intracellular calcium redistribution.
Exercise-enhanced activation of glycogen synthase in human skeletal muscle
Authors: Bak J. F. , Pedersen O.
Published: December 2017

The present study was undertaken to elucidate aspects of the regulatory mechanisms leading to enhanced glucose metabolism and insulin sensitivity of muscle after physical exertion. Biopsies were obtained from the vastus lateralis muscle of healthy volunteers before and after 60 min of bicycle exercise at 60% of their maximal aerobic capacity. Insulin binding to wheat germ agglutinin-purified muscle insulin receptors as well as basal and insulin-stimulated receptor kinase activity toward an exogenous substrate were unaltered by exercise. Muscle glycogen levels diminished from 3.35 +/- 0.26 to 1.85 +/- 0.13 mg/100 mg muscle (P less than 0.01) and the half-maximal activation constant of glycogen synthase for glucose 6-phosphate decreased from 0.62 +/- 0.05 to 0.25 +/- 0.02 mM (P less than 0.001). Total glycogen synthase activity was unchanged. In the absence of phosphatase inhibitors, glucose 6-phosphate-independent glycogen synthase activity of the crude enzyme extract increased during in vitro incubation. The initial rate of activation (through dephosphorylations) of glycogen synthase was 0.18 +/- 0.06 vs. 0.37 +/- 0.03 U.min-1.mg-1 protein before and after exercise, respectively (P less than 0.02). The total as well as the glycogen-associated phosphoprotein phosphatase activity was, however, unaffected by exercise.
Relationship of resting metabolic rate to body composition and protein turnover
Authors: Welle S. , Nair K. S.
Published: December 2017

This study examined whether variability among healthy young adults in resting metabolic rate, normalized for the amount of metabolically active tissue (assessed by total body potassium), is related to protein turnover. Resting metabolic rate was measured by indirect calorimetry for 2 h in 26 men and 21 women, 19-33 yr old, with simultaneous estimation of protein turnover during a 4-h infusion of L-[1-13C]leucine. After adjusting metabolic rate for total body potassium, the standard deviation was only 89 kcal/day, or 5.5% of the average value. There was a high correlation between leucine flux (an index of proteolysis) and metabolic rate (r = 0.84) and between the nonoxidized portion of leucine flux (an index of protein synthesis) and metabolic rate (r = 0.83). This relationship was weaker, but still significant, after adjusting leucine metabolism and metabolic rate for total body potassium (r = 0.36 for leucine flux vs. metabolic rate, r = 0.33 for nonoxidized portion of leucine flux vs. metabolic rate, P less than 0.05). The regression analysis suggested that the contribution of protein turnover to resting metabolic rate was approximately 20% in an average subject. Metabolic rate and protein turnover were highest in the subjects with the greatest amount of body fat, even after accounting for differences in whole body potassium. Neither resting metabolic rate nor protein turnover was related to total or free concentrations of thyroxine or triiodothyronine, within the euthyroid range.(ABSTRACT TRUNCATED AT 250 WORDS)
Defective thermoregulatory thermogenesis does not cause onset of obesity in Zucker rats
Authors: Kaul R. , Heldmaier G. , Schmidt I.
Published: December 2017

To test whether or not the onset of obesity in fatty (fa/fa) Zucker rats is caused by decreased thermoregulatory thermogenesis, pups were artificially reared above their lower critical temperature from 3 or 4 days of age. Littermates were continuously fed identical amounts of synthetic rat milk while body temperature (Tc) and oxygen consumption rate (VO2) were continuously recorded. When the daily mean Tc of all pups was held greater than 37 degrees C, neither Tc nor VO2 differed between fa/fa and genetically lean (Fa/-) pups during the first 2 wk of life. Tc and VO2 were significantly elevated in Fa/- pups during the third postnatal week. At both 16 and 21 days of age, fa/fa pups were identified by their low Tc during a brief cold exposure. Body fat and fat-free dry mass of fa/fa and Fa/- littermates differed at 21 but not at 16 days of age. The excess energy deposited as fat was partly derived from decreased nonthermoregulatory energy expenditure and decreased synthesis of lean body mass. Calculations support the speculation that a greater extraction of energy from the synthetic diet additionally supports the excess fat deposition. Decreased thermoregulatory thermogenesis and excess fat storage appear to be secondary and independent consequences of the primary genetic lesion.
Quantitative role of splanchnic region in leucine metabolism: L-[1-13C,15N]leucine and substrate balance studies
Authors: Yu Y. M. , Wagner D. A. , Tredget E. E. , Walaszewski J. A. , Burke J. F. , Young V. R.
Published: December 2017

The role of the splanchnic region (Sp) in whole body leucine metabolism was assessed in six chronically catheterized fasting mongrel dogs and in eight dogs during constant enteral feeding of a complete amino acid solution (0.24 g.kg-1.h-1). We used primed continuous intravenous infusions of L-[1-13C,15N]leucine and L-[1-14C]leucine and measurements of arteriovenous isotope and leucine balance across the gut, liver, and Sp. In the fasted condition, 3.5% of arterial leucine supply was oxidized in the Sp, accounting for 13% of total body leucine oxidation, with 10% by liver. With amino acid feeding 1) leucine carbon and nitrogen fluxes and oxidation were increased (P less than 0.01) at the whole body level; 2) the percent of whole body leucine oxidation occurring in the Sp and liver increased (P less than 0.01) to 41 and 27%, respectively; 3) fractional metabolic utilization of leucine delivered to the Sp was reduced (P less than 0.01) from 47 to 35%; 4) the deamination rate of leucine in the gut was increased (P less than 0.05), along with an increased reamination rate of alpha-ketoisocaproic acid in the Sp (P less than 0.05). These findings reveal that the Sp accounts for a small fraction of whole body leucine oxidation during the fasting condition, but it plays a quantitatively important role in total body leucine oxidation during amino acid feeding; the gut and liver play cooperative roles in controlling leucine supply to peripheral tissues.
Hepatic nerves are not essential to the increase in hepatic glucose production during muscular work
Authors: Wasserman D. H. , Williams P. E. , Lacy D. B. , Bracy D. , Cherrington A. D.
Published: December 2017

To establish the role of hepatic nerves in hepatic glycogenolytic and gluconeogenic regulation during exercise, dogs underwent a laparotomy during which the hepatic nerves were either left intact (C; n = 8) or cut (DN; n = 5). At least 17 days after surgery, dogs were studied during 150 min of treadmill exercise (12% grade, 100 m/min). Glucose production (Ra) and gluconeogenesis (GNG) were assessed by combining [3-3H]glucose, [U-14C]alanine, and indocyanine green infusions with arterial, portal vein, and hepatic vein sampling. Glucagon and insulin were similar at rest and exercise in both groups. Norepinephrine rose from 145 +/- 10 to 242 +/- 32 pg/ml by 150 min of exercise in C and from 150 +/- 25 to 333 +/- 83 pg/ml in DN. Epinephrine rose from 66 +/- 7 pg/ml at rest to 108 +/- 10 and 148 +/- 24 pg/ml after 30 and 150 min of exercise in C and from 90 +/- 15 pg/ml at rest to 185 +/- 33 (P less than 0.05 compared with C) and 194 +/- 36 pg/ml after 30 and 150 min of exercise in DN. Plasma glucose fell gradually from 108 +/- 2 and 106 +/- 3 mg/dl at rest to 96 +/- 4 and 92 +/- 8 by the end of exercise in C and DN, respectively. Ra was similar in C and DN rising from 3.2 +/- 0.2 to 8.7 +/- 0.6 and 2.6 +/- 0.2 to 7.5 +/- 1.1 mg.kg-1.min-1, respectively, by the end of exercise. Minimum and maximum rates of GNG from alanine, glycerol, and lactate were elevated in DN compared with C during rest and exercise. However, the exercise-induced changes in GNG were similar in both groups. In conclusion, nerves to the liver are not essential to the increased Ra and glucose homeostasis during moderate-intensity exercise.
Transforming growth factor alpha in developing rats
Authors: Brown P. I. , Lam R. , Lakshmanan J. , Fisher D. A.
Published: December 2017

Transforming growth factor-alpha (TGF-alpha) concentrations were measured in lung, brain, liver, and kidney of rats at three different ages (20 days gestation and 9 and 50 days postnatal). TGF-alpha concentrations were maximal in the lung and brain by 20 days of gestation and showed minimal changes during nursing (day 9) and young adulthood (day 50). The liver, which also showed maximal TGF-alpha concentration by 20 days of gestation, demonstrated a progressive reduction with age to nadir values in the young adult. In contrast to the pattern in other tissues, kidney had the lowest concentration of TGF-alpha in late gestation and showed an increase by 50 days of age. As TGF-alpha acts via the epidermal growth factor (EGF) receptor, its function in development may be analogous to that of EGF. Thus TGF-alpha may have a role in lung maturation and postinjury repair, liver repair and regeneration, and neuronal cell growth.
Quantitative partition of threonine oxidation in pigs: effect of dietary threonine
Authors: Ballevre O. , Cadenhead A. , Calder A. G. , Rees W. D. , Lobley G. E. , Fuller M. F. , Garlick P. J.
Published: December 2017

Kinetic aspects of threonine (Thr) metabolism were examined in eight pigs fed hourly with a diet containing either 0.68% (LT group) or 0.81% (HT group) of Thr (wt/wt), corresponding to 10 and 30% Thr excess, respectively, compared with an "ideal" diet. Primary production (PR) and disposal (DR) rates were obtained for Thr, glycine (Gly), and 2-keto-butyrate (KB) after a 12-h continuous infusion of L-[U-14C]-Thr together with [1-13C]Gly and a 6-h continuous infusion of [1-14C]KB. Transfer of Thr into secondary pools was also monitored, and from these the rates of Thr oxidation through the catabolic pathways of L-Thr 3-dehydrogenase (DR(Thr-Gly)) and threonine dehydratase (DR(Thr-KB)) were estimated. For the LT group the results were (mumol.kg-1.h-1) PR(Thr) 314 +/- 3, PR(Gly) 551 +/- 24, PR(KB) 41 +/- 3, DR(Thr-Gly) 22 +/- 2, and DR(Thr-KB) 7 +/- 1. For the HT group they were PR(Thr) 301 +/- 23, PR(Gly) 598 +/- 55, PR(KB) 39 +/- 4, DR(Thr-Gly) 32 +/- 2, and DR(Thr-KB) 8 +/- 1. The increase in Thr intake (14 mumol.kg-1.h-1, P less than 0.01) induced a commensurate increase in the sum of DR(Thr-Gly) and DR(Thr-KB) (14 mumol.kg-1.h-1, P less than 0.001) when liver was used as the precursor pool. This was mainly due to the increased DR(Thr-Gly) (13 mumol.kg-1.h-1, P less than 0.01); the change in DR(Thr-KB) was not statistically significant. By comparison of intracellular-to-plasma ratios of specific activities (or enrichments) for different tissues with each type of infusion, liver was shown to be the major site of production of Gly and KB from Thr. These data suggest that in fed growing pigs a 30% excess of Thr in the diet does not alter the partition of Thr oxidation, since 80% of Thr oxidation occurs through the L-Thr 3-dehydrogenase pathway for both LT and HT groups.
Effects of testosterone on muscle insulin sensitivity and morphology in female rats
Authors: Holmang A. , Svedberg J. , Jennische E. , Bjorntorp P.
Published: December 2017

Intact or oophorectomized (OVX) female rats were given moderate doses of testosterone for 12 wk. Insulin-stimulated glucose transport with submaximal insulin concentrations was studied with the euglycemic clamp technique. Glycogen synthesis and 2-deoxy-D-glucose uptake were measured during the clamp in the extensor digitorum longus, white and red portions of the gastrocnemius, and in the soleus muscles by tracer technique. Testosterone treatment resulted in elevations of circulating testosterone, increased plasma insulin concentrations, and a marked decrease in insulin-stimulated glucose transport. In control animals, glycogen synthesis and 2-deoxy-D-glucose transport increased with increasing concentrations of type 1 fibers. Testosterone inhibited glycogen synthesis and 2-deoxy-D-glucose transport to approximately 50% in all muscles except 2-deoxy-D-glucose transport in intact rats. Glycogen synthesis in the liver was not affected. Testosterone administration also resulted in changes in muscle morphology. The relative number of type 1 fibers decreased, whereas type 2 fibers increased. This was most pronounced in red muscles. There was also a decrease in capillary density after testosterone treatment. It was concluded that testosterone administered to female rats is followed by marked insulin resistance. This is correlated to alterations in muscle morphology with fewer type 1 fibers and a lower degree of capillarization, which are both known to be characteristics of insulin-insensitive muscles.
Contribution of liver and skeletal muscle to alanine and lactate metabolism in humans
Authors: Consoli A. , Nurjhan N. , Reilly J. J. , Bier D. M. , Gerich J. E.
Published: December 2017

To quantitate alanine and lactate gluconeogenesis in postabsorptive humans and to test the hypothesis that muscle is the principal source of these precursors, we infused normal volunteers with [3–14C]lactate, [3–13C]alanine, and [6-3H]glucose and calculated alanine and lactate incorporation into plasma glucose corrected for tricarboxylic acid cycle carbon exchange, the systemic appearance of these substrates, and their forearm fractional extraction, uptake, and release. Forearm alanine and lactate fractional extraction averaged 37 +/- 3 and 27 +/- 2%, respectively; muscle alanine release (2.94 +/- 0.27 mumol.kg body wt-1.min-1) accounted for approximately 70% of its systemic appearance (4.18 +/- 0.31 mumol.kg body wt-1.min-1); muscle lactate release (5.51 +/- 0.42 mumol.kg body wt-1.min-1) accounted for approximately 40% of its systemic appearance (12.66 +/- 0.77 mumol.kg body wt-1.min-1); muscle alanine and lactate uptake (1.60 +/- 0.7 and 3.29 +/- 0.36 mumol.kg body wt-1.min-1, respectively) accounted for approximately 30% of their overall disappearance from plasma, whereas alanine and lactate incorporation into plasma glucose (1.83 +/- 0.20 and 4.24 +/- 0.44 mumol.kg body wt-1.min-1, respectively) accounted for approximately 50% of their disappearance from plasma. We therefore conclude that muscle is the major source of plasma alanine and lactate in postabsorptive humans and that factors regulating their release from muscle may thus exert an important influence on hepatic gluconeogenesis.
Effects of insulin on carbohydrate and protein metabolism in voluntary running rats
Authors: Rodnick K. J. , Reaven G. M. , Azhar S. , Goodman M. N. , Mondon C. E.
Published: December 2017

The goal of this study was to assess the effects of voluntary running activity in rats on various aspects of carbohydrate and protein metabolism. After 6 wk of exercise training, rats (ET) were rested for 24 h and their hindquarters, along with those from sedentary control (SC) and dietary control (DC) rats, were perfused with 0, 60, 250, or 6,000 microU/ml insulin. At 0 insulin, glucose clearance was similar for all groups, and it was increased with added insulin. However, the insulin effect was 20–40% greater for ET rats at all insulin concentrations (P less than 0.05). Muscle glycogen deposition also increased with added insulin but showed muscle-specific differences. Specifically, glycogen content of the plantaris muscle was significantly higher in ET compared with SC or DC rats, whereas this pattern was reversed in soleus muscle. In plantaris muscle, insulin stimulated glucose 6-phosphate (G-6-P)-independent (-G-6-P) glycogen synthase activity only in SC and DC rats and increased its affinity for G-6-P at 250 microU/ml in all groups. In contrast, the -G-6-P synthase activity was not increased in soleus muscle and was actually decreased in all groups at 6,000 microU/ml. Tyrosine release was suppressed by insulin in all groups, but this effect was significantly greater at insulin levels of 60 microU/ml (P less than 0.02) in hindquarters from ET rats compared with SC and DC rats. Neither insulin nor exercise training decreased 3-methylhistidine release from perfused hindquarters.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal 25-hydroxyvitamin D-1 alpha-hydroxylase activity and mitochondrial phosphate transport in Hyp mice
Authors: Carpenter T. O. , Shiratori T.
Published: December 2017

The Hyp mouse is a homologue of the X chromosome-linked human disease, familial hypophosphatemic rickets (FHR). In FHR, reduced renal tubular brush-border membrane transport of phosphate results in hypophosphatemia and rickets. Both humans with FHR and Hyp mice have abnormal regulation of 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase), a mitochondrial enzyme found in proximal renal tubular cell epithelia, the apparent site of defective brush-border membrane phosphate transport. No common pathophysiology for these defects has been demonstrated. We hypothesized that phosphate transport may be present in renal mitochondria from Hyp mice and that its regulation may be deranged in parallel with the mitochondrial 1 alpha-hydroxylase. Using inhibitor-stop techniques described for measurement of phosphate transport in liver mitochondria, we examined mitochondria in normal and Hyp mouse kidney and found them to be comparable. We performed manipulations known to alter 1 alpha-hydroxylase differentially in normal and Hyp mice, i.e., phosphorus deprivation and phosphorus loading, and found no effect on mitochondrial phosphate transport. We also subjected Hyp and normal mice to calcium and vitamin D deprivation; this maneuver resulted in no significant changes in mitochondrial phosphate transport in Hyp or normal mice but confirmed the earlier observation that 1 alpha-hydroxylase activity is stimulated to a greater degree in normal mice than Hyp mice after this diet. Furthermore, administration of 1,25-hydroxyvitamin D3 depresses 1 alpha-hydroxylase activity in mitochondria from both normal and Hyp mice but has no effect on mitochondrial phosphate transport. We conclude that the mechanism of abnormal vitamin D metabolism in Hyp mice is not related to a primary defect in renal mitochondrial phosphate transport.
Hormone secretion by isolated perfused pancreas of aging Fischer 344 rats
Authors: Starnes J. W. , Cheong E. , Matschinsky F. M.
Published: December 2017

This is the first study investigating hormone secretion by the isolated perfused pancreas of the aged Fischer 344 rat. Nutrient-induced release of insulin, glucagon, and somatostatin in overnight-fasted rats aged 2, 10, 18, 24, and 30 mo was studied. After an equilibration period, the pancreas was perfused for 20 min with buffer A (containing 4.2 mM glucose plus a 3.5 mM mixture of amino acids) then for 20 min with buffer B (containing 8.3 mM glucose and 7.0 mM amino acids). When stimulated by buffer B, the amount of insulin secreted increased (P less than 0.05) from immaturity (2 mo) to adulthood (10-18 mo) because of growth of the organ. From adulthood to very old age an equal amount of insulin was released in all groups during the last 19 min of perfusion with buffer B. Fasting blood glucose levels remained constant throughout life, whereas pancreatic insulin stores and plasma insulin levels rose, reaching peak values at 18 mo. The alpha-cell appeared to be deemphasized relative to the beta-cell during development but not thereafter, as indicated by the findings that from immaturity to adulthood pancreatic glucagon stores expanded less than insulin stores and that glucagon release significantly decreased. Only minor changes in somatostatin release from the delta-cells were observed after the rat reached adulthood. We conclude that the endocrine secretory response of the pancreas is well maintained throughout life in the Fischer 344 rat.
Evidence against important catecholamine compensation for absent glucagon counterregulation
Authors: De Feo P. , Perriello G. , Torlone E. , Fanelli C. , Ventura M. M. , Santeusanio F. , Brunetti P. , Gerich J. E. , Bolli G. B.
Published: December 2017

To assess the counterregulatory role of glucagon and to test the hypothesis that catecholamines can largely compensate for an impaired glucagon response, four studies were performed in seven normal volunteers. In all studies, insulin was infused subcutaneously (15 mU.m-2.min-1) and increased circulating insulin approximately twofold to levels (26 +/- 1 microU/ml) observed with intensive insulin therapy. In study 1, plasma glucose fluxes (D-[3-3H]glucose) and plasma substrate and counterregulatory hormone concentrations were simply monitored; plasma glucose decreased from 87 +/- 2 mg/dl and plateaued at 51 +/- 2 mg/dl for 3 h. In study 2 [pituitary-adrenal-pancreatic (PAP) clamp], secretion of insulin and counterregulatory hormones (except for catecholamines) was prevented by somatostatin (0.5 mg/h i.v.) and metyrapone (0.5 g/4 h per os), and glucagon, cortisol, and growth hormone were reinfused to reproduce the concentrations of study 1. In study 3 (lack of glucagon response), the PAP clamp was performed with maintenance of plasma glucagon at basal levels, and glucose was infused whenever needed to reproduce plasma glucose concentration of study 2. Study 4 was identical to study 3, but exogenous glucose was not infused. The PAP clamp (study 2) reproduced glucose concentrations and fluxes observed in study 1. In studies 3 and 4, isolated lack of glucagon response did not affect glucose utilization but caused an early and persistent decrease in hepatic glucose production (approximately 60%) that caused plasma glucose to decrease to 38 +/- 2 mg/dl (P less than 0.01 vs. control 62 +/- 2 mg/dl), despite compensatory increases in plasma epinephrine. We conclude that, in a model of clinical hypoglycemia, glucagon's effect on hepatic glucose production is a dominant counterregulatory factor in humans and that its absence cannot be compensated for by increased epinephrine secretion.
Utilization of tyrosine dipeptides and acetyltyrosine in normal and uremic humans
Authors: Druml W. , Lochs H. , Roth E. , Hubl W. , Balcke P. , Lenz K.
Published: December 2017

The impact of renal failure on the elimination and hydrolysis of three sources of tyrosine for parenteral nutrition, the dipeptides alanyltyrosine (Ala-Tyr), glycyltyrosine (Gly-Tyr), and N-acetyltyrosine (NAc-Tyr) was investigated in eight patients on regular hemodialysis therapy (HD) and seven healthy controls (CON). In CON, whole body clearance (Ctot) of Ala-Tyr (3,169 +/- 198 ml/min) was higher than Gly-Tyr (1,781 +/- 184, P less than 0.001), and both exceeded NAc-Tyr (284 +/- 24, P less than 0.001). In HD, Ctot of Ala-Tyr was not different from CON, but Ctot of Gly-Tyr (858 +/- 73, P less than 0.001) and NAc-Tyr (129 +/- 30, P less than 0.02) was decreased. The rise in plasma levels of constituent amino acids was higher in Ala-Tyr vs. Gly-Tyr (P less than 0.01). In HD, the pattern was similar, although the increase in Tyr was less than in CON. Plasma Tyr did not increase with NAc-Tyr in either group. Urinary loss of peptides was neglible, but 60% of NAc-Tyr infused was excreted by CON. The half-life of peptides incubated in CON and HD plasma was unchanged for Ala-Tyr (12.3 +/- 0.9 vs. 14.6 +/- 1.9 min) and prolonged for Gly-Tyr in HD (101.7 +/- 4.9 vs. 131.3 +/- 12, P less than 0.05). Thus renal failure does not impair Ala-Tyr disposal and delays Gly-Tyr utilization. These differential effects on peptide assimilation underscore the importance of peptide structure on metabolism. Both peptides, but not NAc-Tyr, may serve as a nutritional substrate in renal failure patients.