bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of hepatic insulin-like growth factor II gene expression by thyroid hormones in fetal sheep near term
Authors: Forhead Alison J. , Li Juan , Gilmour R. Stewart , Fowden Abigail L.
Published: December 2017

The effects of thyroid hormones on hepatic insulin-like growth factor (IGF) II gene expression and their interaction with cortisol in the ontogenic control of this gene were investigated in fetal sheep during late gestation (term 145 ± 2 days) and after experimental manipulation of fetal plasma hormone concentrations. In intact fetuses, a significant decrease in hepatic IGF-II mRNA abundance was observed between 127–130 and 142–145 days of gestation, which coincided with the normal prepartum rise in plasma cortisol and triiodothyronine (T3) concentrations. This ontogenic decline in hepatic IGF-II gene expression was abolished in fetuses in which the prepartum rise in plasma T3, but not cortisol, was prevented by fetal thyroidectomy. At 127–130 days, downregulation of hepatic IGF-II mRNA abundance was induced prematurely in intact fetuses by an infusion of cortisol for 5 days (2–3 mg ⋅ kg−1⋅ day−1iv). Plasma concentrations of cortisol and T3in the cortisol-infused intact fetuses were increased to values seen close to term. Similar findings were observed in thyroidectomized fetuses, in which, despite thyroidectomy, cortisol infusion significantly increased plasma T3concentrations and caused a premature decrease in hepatic IGF-II mRNA levels. However, in intact fetuses at 127–130 days, the increasing of T3concentrations alone by exogenous T3infusion (8–12 μg ⋅ kg−1⋅ day−1iv for 5 days) had no effect on hepatic IGF-II mRNA levels. Overall, a decrease in hepatic IGF-II mRNA abundance was only observed in fetuses in which there were concurrent increases in plasma cortisol and T3concentrations. When observations from all fetuses were considered, irrespective of gestational age or treatment, hepatic IGF-II mRNA levels were negatively correlated with plasma cortisol and T3but not thyroxine concentrations. Partial correlation analysis of hepatic IGF-II, cortisol, and T3values showed that the plasma concentration of cortisol in the fetus had the predominant effect on hepatic IGF-II mRNA abundance. These findings show that T3may mediate, in part, the maturational effects of cortisol on hepatic IGF-II gene expression but that it is ineffective without a concomitant rise in fetal plasma cortisol. Hence, increased concentrations of both cortisol and T3appear necessary to induce downregulation of hepatic IGF-II mRNA abundance in fetal sheep close to term.
Tricarboxylic acid cycle intermediate pool size and estimated cycle flux in human muscle during exercise
Authors: Gibala Martin J. , MacLean Dave A. , Graham Terry E. , Saltin Bengt
Published: December 2017

We examined the relationship between tricarboxylic acid (TCA) cycle intermediate (TCAI) pool size, TCA cycle flux (calculated from leg O2uptake), and pyruvate dehydrogenase activity (PDHa) in human skeletal muscle. Six males performed moderate leg extensor exercise for 10 min, followed immediately by intense exercise until exhaustion (3.8 ± 0.5 min). The sum of seven measured TCAI (ΣTCAI) increased ( P ≤ 0.05) from 1.39 ± 0.11 at rest to 2.88 ± 0.31 after 10 min and to 5.38 ± 0.31 mmol/kg dry wt at exhaustion. TCA cycle flux increased ∼70-fold during submaximal exercise and was ∼100-fold higher than rest at exhaustion. PDHacorresponded to 77 and 90% of TCA cycle flux during submaximal and maximal exercise, respectively. The present data demonstrate that a tremendous increase in TCA cycle flux can occur in skeletal muscle despite a relatively small change in TCAI pool size. It is suggested that the increase in ΣTCAI during exercise may primarily reflect an imbalance between the rate of pyruvate production and its rate of oxidation in the TCA cycle.
Leptin induction of UCP1 gene expression is dependent on sympathetic innervation
Authors: Scarpace Philip J. , Matheny Michael
Published: December 2017

We previously demonstrated that leptin increases uncoupling protein 1 (UCP1) and lipoprotein lipase (LPL) gene expression in brown adipose tissue (BAT) of rats. To determine whether the induction of these transcripts is dependent on sympathetic innervation of BAT, we unilaterally surgically denervated interscapular BAT in both pair-fed and leptin (0.9 mg/day by infusion)-treated rats. In pair-fed rats, the level of UCP1 mRNA in the denervated BAT pad was 30–47% less than in the innervated pad. In the intact BAT pad, leptin administration increased UCP1 mRNA levels by nearly 2.5-fold compared with pair-fed rats. In contrast, in the denervated BAT pad, there was no increase in UCP1 gene expression. When LPL mRNA was examined in pair-fed rats, there was no difference between innervated and denervated BAT pads. With leptin administration, LPL gene expression increased by 75% in both the innervated and denervated BAT pads. β3-Adrenergic receptor mRNA was unaffected by either denervation or leptin, whereas uncoupling protein 2 mRNA levels were increased in epididymal white adipose tissue (WAT) but not in perirenal WAT. CGP-12177, a specific β3-adrenergic receptor agonist, induced nearly a fourfold increase in UCP1 and a twofold increase in LPL gene expression in both the innervated and denervated BAT pads. These data indicate that the leptin induction of UCP1 gene expression in BAT is dependent on sympathetic innervation but that the leptin induction of LPL gene expression is not.
Analysis of the paired-tracer method of determining cell uptake
Authors: Watson Philip D.
Published: December 2017

The paired-tracer method has been used extensively for determining cell uptake of numerous substances, although the method of calculating uptake has no published theoretical support. We have investigated the effect of capillary permeability of the tracers on v, the uptake rate calculated directly from the ratio of tracer venous concentrations. For a simple mathematical model of plasma-tissue movement of lactate and an analytic expression for v, it has been shown that values of v calculated in the first moments after tracer injection depend almost entirely on the differences in tracer permeability-surface area product (PS). The model indicates v would never give the correct value of cell uptake. It is also shown that PS differences alone can explain the published values for lactate uptake obtained from v in skeletal muscle of the rat and dog.
Bidirectional regulation of uncoupling protein-3 and GLUT-4 mRNA in skeletal muscle by cold
Authors: Lin Baozhen , Coughlin Sean , Pilch Paul F.
Published: December 2017

To elucidate the possible role of the mitochondrial uncoupling protein (UCP)-3 in skeletal muscle as a regulator of adaptive thermogenesis and energy balance, we examined the modulation by cold exposure (5°C) of UCP-3 and glucose transporter isoform GLUT-4 mRNAs in male Sprague-Dawley rats. In skeletal muscle, UCP-3 and GLUT-4 mRNAs increased two- to threefold between 6 and 24 h of cold exposure and then decreased to 50% of the control value after 6 days in the cold. In contrast, skeletal muscle UCP-2 mRNA showed a small increase on day 3 and returned to normal after 6 days. The bidirectional regulation of UCP-3 and GLUT-4 mRNAs in skeletal muscle by cold suggests that UCP-3 may be a major mediator of acute adaptive thermogenesis but then is downregulated, along with GLUT-4, in the chronic state to preserve energy. In contrast, cold exposure caused only transient changes of UCP-2 and GLUT-4 mRNA in heart. These data are consistent with the necessity of the heart to continuously expend energy to maintain blood circulation, regardless of environmental conditions.
Acute effects of triiodothyronine on glucose and fatty acid metabolism during reperfusion of ischemic rat hearts
Authors: Liu Que , Clanachan Alexander S. , Lopaschuk Gary D.
Published: December 2017

Clinical studies have demonstrated improved myocardial recovery after severe ischemia in response to acute triiodothyronine (T3) treatment. We determined whether T3 improves the recovery of ischemic hearts by improving energy substrate metabolism. Isolated working rat hearts were perfused with 5.5 mM glucose and 1.2 mM palmitate and were subjected to 30 min of no-flow ischemia. Glycolysis, glucose oxidation, and palmitate oxidation were measured during aerobic reperfusion by adding [5-3H]glucose, [U-14C]glucose, or [9,10-3H]palmitate to the perfusate, respectively. During reperfusion, cardiac work in untreated hearts recovered to a lesser extent than myocardial O2 consumption (MV˙o 2), resulting in a decreased recovery of cardiac efficiency, which recovered to only 25% of preischemic values. Treatment of hearts with T3 (10 nM) before ischemia increased glucose oxidation during reperfusion, which was associated with a significant increase in pyruvate dehydrogenase (PDH) activity, the rate-limiting enzyme for glucose oxidation. In contrast, T3 had no effect on MV˙o 2, glycolysis, or palmitate oxidation. This resulted in a significant decrease in H+ production from glycolysis uncoupled from glucose oxidation (2.7 ± 0.3 and 1.9 ± 0.3 μmol ⋅ g dry wt−1 ⋅ min−1in control and T3-treated hearts, respectively, P < 0.05), as well as a 3.2-fold improvement in cardiac work and a 2.3-fold increase in cardiac efficiency compared with untreated postischemic hearts ( P < 0.05). These data suggest that T3 can exert acute effects that improve the coupling of glycolysis to glucose oxidation, thereby decreasing H+ production and increasing cardiac efficiency as well as contractile function during reperfusion of the postischemic heart.
Regulation of glucose production by NEFA and gluconeogenic precursors during chronic glucagon infusion
Authors: McGuinness Owen P. , Ejiofor Joseph , Audoly Laurent P. , Schrom Nancy
Published: December 2017

We previously reported that simulation of the chronic hyperglucagonemia seen during infection was unable to recreate the infection-induced increase in hepatic glucose production. However, chronic hyperglucagonemia was accompanied by a fall in the arterial levels of gluconeogenic precursors as opposed to a rise as is seen during infection. Thus our aim was to determine whether an infusion of gluconeogenic precursors could increase hepatic glucose production in a setting of hyperglucagonemia. Studies were done in 11 conscious chronically catheterized dogs in which sampling (artery and portal and hepatic veins) and infusion catheters (splenic vein) were implanted 17 days before study. Forty-eight hours before infusion of gluconeogenic (GNG) precursors, a sterile fibrinogen clot was placed into the peritoneal cavity. Glucagon was infused over the subsequent 48-h period to simulate the increased glucagon levels (∼500 pg/ml) seen during infection. On the day of the experiment, somatostatin was infused peripherally, and basal insulin and simulated glucagon were infused intraportally. After a basal period, a two-step increase in lactate and alanine was initiated (120 min/step; n= 5). Lactate (Δ479 ± 25 and Δ1,780 ± 85 μM; expressed as change from basal in periods I and II, respectively) and alanine (Δ94 ± 13 and Δ287 ± 44 μM) levels were increased. Despite increases in net hepatic GNG precursor uptake (Δ0.7 ± 0.3 and Δ1.1 ± 0.4 mg glucose ⋅ kg−1⋅ min−1), net hepatic glucose output did not increase. Because nonesterified fatty acid (NEFA) levels fell, in a second series of studies, the fall in NEFA was eliminated. Intralipid and heparin were infused during the two-step substrate infusion to maintain the NEFA levels constant in period I and increase NEFA availability in period II (Δ −29 ± 29 and Δ689 ± 186 μM; n = 6). In the presence of similar increases in net hepatic GNG precursor uptake and despite increases in arterial glucose levels (Δ17 ± 5 and Δ38 ± 12 mg/dl), net hepatic glucose output increased (Δ0.6 ± 0.1 and Δ0.7 ± 0.2 mg ⋅ kg−1⋅ min−1). In summary, a chronic increase in glucagon, when combined with an acute increase in gluconeogenic precursor and maintenance of NEFA supply, increases hepatic glucose output as is seen during infection.
Impaired phasic insulin and amylin secretion in diabetic rats
Authors: Leahy Jack L. , Fineman Mark S.
Published: December 2017

We have proposed that a hyperstimulated insulin secretion causing β-cell degranulation is the basis for the impaired glucose-potentiated insulin secretion in type 2 diabetes (“overworked β-cell”). To confirm this idea, we previously investigated tolbutamide-infused euglycemic rats. Two novel kinds of β-cell dysfunction were observed: altered phasic glucose-potentiated insulin secretion with preferential sparing of the first phase and a raised secreted ratio of amylin to insulin. The current study tested these parameters in 90% (intact β-cell insulin stores) and 95% (markedly lowered insulin stores) pancreatectomized (Px) diabetic rats. Rats underwent pancreas perfusion 5–6 wk postsurgery. Controls showed nonchanging insulin secretion during a 20-min perfusion of 16.7 mM glucose + 10 mM arginine. In contrast, both Px groups showed an altered phasic pattern, with the first phase being supernormal (for the β-cell mass) but the second phase reduced in tandem with the insulin content. Amylin secretion from control and 90% Px rats paralleled the insulin output, so that the amylin-to-insulin ratio averaged 0.12 ± 0.03% in the controls and 0.16 ± 0.01% in the 90% Px rats over the two secretory phases. In contrast, the amylin-to-insulin ratio in 95% Px rats equaled that of controls during the first phase (0.12 ± 0.1%) but was twice normal during the second phase (0.32 ± 0.4%). These results confirm the validity of the overworked β-cell schema by showing identical β-cell functional defects in Px rats and tolbutamide-infused normoglycemic rats.
Palmitate transport and fatty acid transporters in red and white muscles
Authors: Bonen A. , Luiken J. J. F. P. , Liu S. , Dyck D. J. , Kiens B. , Kristiansen S. , Turcotte L. P. , Van Der Vusse G. J. , Glatz J. F. C.
Published: December 2017

We performed studies 1) to investigate the kinetics of palmitate transport into giant sarcolemmal vesicles, 2) to determine whether the transport capacity is greater in red muscles than in white muscles, and 3) to determine whether putative long-chain fatty acid (LCFA) transporters are more abundant in red than in white muscles. For these studies we used giant sarcolemmal vesicles, which contained cytoplasmic fatty acid binding protein (FABPc), an intravesicular fatty acid sink. Intravesicular FABPcconcentrations were sufficiently high so as not to limit the uptake of palmitate under conditions of maximal palmitate uptake (i.e., 4.5-fold excess in white and 31.3-fold excess in red muscle vesicles). All of the palmitate taken up was recovered as unesterified palmitate. Palmitate uptake was reduced by phloretin (−50%), sulfo- N-succinimidyl oleate (−43%), anti-plasma membrane-bound FABP (FABPpm, −30%), trypsin (−45%), and when incubation temperature was lowered to 0°C (−70%). Palmitate uptake was also reduced by excess oleate (−65%), but not by excess octanoate or by glucose. Kinetic studies showed that maximal transport was 1.8-fold greater in red vesicles than in white vesicles. The Michaelis-Menten constant in both types of vesicles was ∼6 nM. Fatty acid transport protein mRNA and fatty acid translocase (FAT) mRNA were about fivefold greater in red muscles than in white muscles. FAT/CD36 and FABPpmproteins in red vesicles or in homogenates were greater than in white vesicles or homogenates ( P < 0.05). These studies provide the first evidence of a protein-mediated LCFA transport system in skeletal muscle. In this tissue, palmitate transport rates are greater in red than in white muscles because more LCFA transporters are available.
Lower activity of oxidative key enzymes and smaller fiber areas in skeletal muscle of postobese women
Authors: Raben Anne , Mygind Elsebeth , Astrup Arne
Published: December 2017

Muscle fiber morphology and activities of four key enzymes, as well as energy metabolism, were determined in nine normal-weight postobese women and nine matched control subjects. No differences in fiber type composition, but a smaller mean fiber area and area of fiber types I and IIb, were found in postobese compared with control subjects ( P < 0.05). The activities of β-hydroxyacyl-CoA dehydrogenase (HADH) and citrate synthase (CS) were 20% lower in postobese than in control subjects ( P < 0.05). However, the activities of lactate dehydrogenase and lipoprotein lipase were not significantly different between postobese and control subjects. Basal metabolic rate and respiratory exchange ratio were also similar, but maximal oxygen uptake (V˙o2 max) tended to be lower in postobese than in control subjects ( P = 0.06). When adjustments were made for differences inV˙o2 max, HADH and CS were not different between postobese and control subjects. In conclusion, these data suggest that smaller fiber areas and lower enzyme activities, i.e., markers of aerobic capacity of skeletal muscle, but not fiber composition, may be factors predisposing to obesity.
Restoration of insulin-like growth factor I action in skeletal muscle of old mice
Authors: Willis P. E. , Chadan S. G. , Baracos V. , Parkhouse W. S.
Published: December 2017

This study examined the effects of long-term chronic voluntary wheel exercise on the ability of insulin-like growth factor I (IGF-I) to stimulate rates of protein synthesis in the soleus muscle of old C57Bl/6 mice. Factors contributing to any changes in hormone action were analyzed at the level of hormone receptor binding, protein content, and gene expression. Chronic exercise resulted in an increased skeletal muscle mass (10–22%) and a 56% increase in IGF-I-stimulated rates of protein synthesis ( P < 0.05). IGF-I receptor mRNA was increased 46%, IGF-Ireceptor protein was increased 65%, and the binding capacity of the IGF-I high-affinity site was increased sixfold ( P < 0.05) with chronic wheel exercise. Insulin receptor protein content was decreased 35% ( P < 0.05), whereas GLUT-4 content was increased 47% with chronic exercise ( P < 0.05). This study demonstrates that old animals retain a plasticity for IGF I receptor and glucose transporter expression that may have valuable physiological consequences.
Altered ATP sensitivity of ATP-dependent K+channels in diabetic rat hearts
Authors: Shimoni Y. , Light P. E. , French R. J.
Published: December 2017

The effects of streptozotocin-induced diabetes (5–7 days or 7 wk) on cardiac ATP-sensitive potassium channels (KATPchannels) were investigated with the use of single-channel and action potential recordings from dissociated ventricular myocytes isolated from control and diabetic rat hearts. In inside-out patches from diabetic myocytes (5–7 days), the IC50for ATP inhibition was 82 ± 7.2 μM (mean ± SE, n = 8), twice that in controls (43 ± 3.6 μM, n = 12). For 7-wk diabetic rats, the IC50was 75 ± 2.3 μM ( n = 6). Increasing internal ADP concentration attenuated ATP-induced inhibition in both controls and diabetics. On reducing the internal pH from 7.4 to 6.8, both control and diabetic myocytes showed a 1.7-fold increase in the IC50for ATP inhibition. No differences were observed in either intraburst kinetics or unitary conductance of single channels from control and diabetic myocytes. In diabetic myocytes, action potential duration at 90% repolarization (APD90) was longer and more variable than in controls and was significantly shortened by application of the KATPchannel opener cromakalim (50 μM). Cromakalim scarcely affected APD90in controls. Computer simulation of the longer diabetic APD90required a lower background conductance during the plateau phase in addition to small, measured changes in the delayed rectifier current, transient outward current, and ATP-sensitive K+current (KATPcurrent, IKATP). The simulations reproduced the enhanced sensitivity of the diabetic APD90to changes in IKATP. These results have important implications for cardiac function in diabetics and their treatment by sulfonylureas.
Increased plasma Gln and Leu Raand inappropriately low muscle protein synthesis rate in AIDS wasting
Authors: Yarasheski Kevin E. , Zachwieja Jeffrey J. , Gischler Jennifer , Crowley Jan , Horgan Mary M. , Powderly William G.
Published: December 2017

Muscle protein wasting occurs in human immunodeficiency virus (HIV)-infected individuals and is often the initial indication of acquired immunodeficiency syndrome (AIDS). Little is known about the alterations in muscle protein metabolism that occur with HIV infection. Nine subjects with AIDS wasting (CD4 < 200/mm3), chronic stable opportunistic infections (OI), and ≥10% weight loss, fourteen HIV-infected men and one woman (CD4 > 200/mm3) without wasting or OI (asymptomatic), and six HIV-seronegative lean men (control) received a constant intravenous infusion of [1-13C]leucine (Leu) and [2-15N]glutamine (Gln). Plasma Leu and Gln rate of appearance (Ra), whole body Leu turnover, disposal and oxidation rates, and [13C]Leu incorporation rate into mixed muscle protein were assessed. Total body muscle mass/fat-free mass was greater in controls (53%) than in AIDS wasting (43%; P = 0.04). Fasting whole body proteolysis and synthesis rates were increased above control in the HIV+ asymptomatic group and in the AIDS-wasting group ( P = 0.009). Whole body Leu oxidation rate was greater in the HIV+ asymptomatic group than in the control and AIDS-wasting groups ( P < 0.05). Fasting mixed muscle protein synthesis rate was increased in the asymptomatic subjects (0.048%/h; P = 0.01) but was similar in AIDS-wasting and control subjects (0.035 vs. 0.037%/h). Plasma Gln Rawas increased in AIDS-wasting subjects but was similar in control and HIV+ asymptomatic subjects ( P < 0.001). These findings suggest that AIDS wasting results from 1) a preferential reduction in muscle protein, 2) a failure to sustain an elevated rate of mixed muscle protein synthesis while whole body protein synthesis is increased, and 3) a significant increase in Gln release into the circulation, probably from muscle. Several interesting explanations for the increased Gln Rain AIDS wasting exist.
A modified high-fat diet induces insulin resistance in rat skeletal muscle but not adipocytes
Authors: Wilkes Jason J. , Bonen Arend , Bell Rhonda C.
Published: December 2017

We hypothesized that variation in dietary fatty acid composition in rats fed a high-fat diet had tissue-specific effects on glucose uptake sufficient to maintain normal glucose tolerance. Rats were fed one of three diets for 3 wk. The isocaloric high-fat-mixed oil (HF-mixed) diet and the high-fat-safflower oil (HF-saff) diet both provided 60% kcal fat, but fat composition differed [HF-mixed = saturated, polyunsaturated (n-3 and n-6), and monounsaturated fatty acids; HF-saff = polyunsaturated fatty acids (mainly n-6)]. The control diet was high carbohydrate (HCHO, 10% kcal fat). Insulin-stimulated 3- O-methylglucose uptake into perfused hindlimb muscles was reduced in rats fed HF-saff and HF-mixed diets compared with those fed HCHO diet ( P< 0.02). Basal uptake increased in HF-saff- and HF-mixed-fed rats vs. HCHO-fed rats ( P < 0.04). In adipocytes, HF-saff feeding decreased 2-deoxyglucose uptake vs. HF-mixed feeding and HCHO feeding ( P< 0.05), but 2-deoxyglucose uptake in HF-mixed-fed rats did not differ from that in HCHO-fed rats ( P> 0.05). Glucose tolerance was significantly reduced in HF-saff-fed rats but was unaffected by the HF-mixed diet. Therefore, in skeletal muscle of rats, 1) feeding a diet high in fat induces a reduction in insulin-stimulated glucose uptake but 2) provides an increase in basal glucose uptake. In contrast, 3) in adipocytes, insulin-stimulated glucose transport is reduced only when the high-fat diet is high in n-6 polyunsaturated fatty acids but not when fat comes from these mixed sources. Glucose intolerance becomes evident when insulin resistance is seen in multiple tissues.
Lactate clamp: a method to measure lactate utilization in vivo
Authors: Gao Jiaping , Islam Mohammad A. , Brennan Christine M. , Dunning Beth E. , Foley James E.
Published: December 2017

A lactate clamp method has been developed to quantify the whole body lactate utilization in conscious, unstressed rats. Dichloroacetate (DCA), a known lactate utilization enhancer, was used to validate the method. Fasting blood lactate concentrations before the clamps were identical for DCA-treated (1 mmol/kg) and control groups (1.65 ± 0.37 vs. 1.65 ± 0.19 mM). The animals received a primed continuous lactate infusion for 90 min at variable rates to clamp the blood lactate concentration at 2 mM. The steady-state (60–90 min) lactate infusion rate, which represents the whole body lactate utilization in DCA-treated animals, was 144% higher than that in the control animals (13.2 ± 1.0 vs. 5.4 ± 1.1 mg ⋅ kg−1 ⋅ min−1; P < 0.001). The markedly increased lactate infusion rate indicates an enhanced lactate flux by DCA. To determine whether the increased lactate infusion by DCA reflected reduced endogenous lactate production, lactate production was measured. The results indicate that endogenous lactate production was not affected by DCA. In conclusion, the lactate clamp provides a sensitive and reliable method to assess lactate utilization in vivo, a dynamic measurement that may not be clearly demonstrated by blood lactate concentrations per se.
Ligand-induced downregulation of receptor-mediated clearance of hepatocyte growth factor in rats
Authors: Liu Ke-Xin , Kato Yukio , Kino Ichiro , Nakamura Toshikazu , Sugiyama Yuichi
Published: December 2017

The change in tissue uptake clearance of125I-labeled hepatocyte growth factor (HGF) after an intravenous injection of an excess (120 μg/kg) of unlabeled HGF was examined in rats. The heparin-washable component of the hepatic uptake clearance of125I-HGF was only slightly changed, whereas the heparin-resistant component was significantly reduced 30 min after injection of excess HGF, followed by gradual recovery with a half-life of 3.2 h. Because the former clearance mainly represents125I-HGF association with heparan sulfate proteoglycan on the cell surface and/or extracellular matrix, whereas the latter includes relatively specific clearance, such as receptor-mediated endocytosis, this result suggests that injection of excess HGF selectively causes downregulation of receptor-mediated HGF clearance in the liver. Downregulation could also be observed for HGF receptor density in isolated liver plasma membrane, assessed by Western blot analysis by means of anti-receptor antibody, 30 min after injection of excess unlabeled HGF, supporting the hypothesis that the overall elimination of HGF from the systemic circulation can be affected by a change in HGF receptor density on the liver cell surface.
13C NMR measurements of human gluconeogenic fluxes after ingestion of [U-13C]propionate, phenylacetate, and acetaminophen
Authors: Jones John G. , Solomon Michael A. , Sherry A. Dean , Jeffrey F. M. H. , Malloy Craig R.
Published: December 2017

Anaplerotic, pyruvate recycling, and gluconeogenic fluxes were measured by13C isotopomer analysis of plasma glucose, urinary phenylacetylglutamine, and urinary glucuronide in normal, 24-h-fasted individuals after ingestion of [U-13C]propionate, phenylacetate, and acetaminophen. Plasma glucose isotopomer analysis reported a total anaplerotic flux of 5.92 ± 1.03 (SD) relative to citrate synthase. This was not significantly different from glucuronide and phenylacetylglutamine analyses (6.08 ± 1.16 and 7.14 ± 1.94, respectively). Estimates of pyruvate recycling from glucose and glucuronide isotopomer distributions were almost identical (3.55 ± 0.99 and 3.66 ± 1.11, respectively), whereas phenylacetylglutamine reported a significantly higher estimate (5.74 ± 2.13). As a consequence, net gluconeogenic flux reported by phenylacetylglutamine (1.41 ± 0.28) was significantly less than that reported by glucose (2.37 ± 0.64) and glucuronide (2.42 ± 0.76). This difference in fluxes detected by analysis of phenylacetylglutamine vs. hexose is likely due to compartmentation of hepatic metabolism of propionate. Net gluconeogenic flux estimates made by use of this stable isotope method are in good agreement with recent measurements in humans with [14C]propionate.
Testosterone injection stimulates net protein synthesis but not tissue amino acid transport
Authors: Ferrando Arny A. , Tipton Kevin D. , Doyle David , Phillips Stuart M. , Cortiella Joaquin , Wolfe Robert R.
Published: December 2017

Testosterone administration (T) increases lean body mass and muscle protein synthesis. We investigated the effects of short-term T on leg muscle protein kinetics and transport of selected amino acids by use of a model based on arteriovenous sampling and muscle biopsy. Fractional synthesis (FSR) and breakdown (FBR) rates of skeletal muscle protein were also directly calculated. Seven healthy men were studied before and 5 days after intramuscular injection of 200 mg of testosterone enanthate. Protein synthesis increased twofold after injection ( P < 0.05), whereas protein breakdown was unchanged. FSR and FBR calculations were in accordance, because FSR increased twofold ( P < 0.05) without a concomitant change in FBR. Net balance between synthesis and breakdown became more positive with both methodologies ( P< 0.05) and was not different from zero. T injection increased arteriovenous essential and nonessential nitrogen balance across the leg ( P < 0.05) in the fasted state, without increasing amino acid transport. Thus T administration leads to an increased net protein synthesis and reutilization of intracellular amino acids in skeletal muscle.
A mathematical model of luteinizing hormone release from ovine pituitary cells in perifusion
Authors: Heinze K. , Keener R. W. , Midgley A. R.
Published: December 2017

We model the effect of gonadotropin-releasing hormone (GnRH) on the production of luteinizing hormone (LH) by the ovine pituitary. GnRH, released by the hypothalamus, stimulates the secretion of LH from the pituitary. If stimulus pulses are regular, LH response will follow a similar pattern. However, during application of GnRH at high frequencies or concentrations or with continuous application, the pituitary delivers a decreased release of LH (termed desensitization). The proposed mathematical model consists of a system of nonlinear differential equations and incorporates two possible mechanisms to account for this observed behavior: desensitized receptor and limited, available LH. Desensitization was provoked experimentally in vitro by using ovine pituitary cells in a perifusion system. The model was fit to resulting experimental data by using maximum-likelihood estimation. Consideration of smaller models revealed that the desensitized receptor is significant. Limited, available LH was significant in three of four chambers. Throughout, the proposed model was in excellent agreement with experimental data.
Pinealectomy causes glucose intolerance and decreases adipose cell responsiveness to insulin in rats
Authors: Lima Fabio B. , Machado Ubiratan F. , Bartol Ione , Seraphim Patricia M. , Sumida Doris H. , Moraes Solange M. F. , Hell Naomi S. , Okamoto Maristela M. , Saad Mario J. A. , Carvalho Carla R. O. , Cipolla-Neto José
Published: December 2017

Although the pineal gland influences several physiological systems, only a few studies have investigated its role in the intermediary metabolism. In the present study, male Wistar rats, pinealectomized or sham-operated 6 wk before the experiment, were submitted to both intravenous glucose tolerance tests (IVGTT) and insulin binding as well as glucose transport assays in isolated adipocytes. The insulin receptor tyrosine kinase activity was assessed in liver and muscle. The insulin secretory response during the IVGTT was impaired, particularly in the afternoon, and the glucose transport responsiveness was 33% lower in pinealectomized rats. However, no difference was observed in the insulin receptor number of adipocytes between groups as well as in insulin-stimulated tyrosine kinase activity, indicating that the initial steps in the insulin signaling were well conserved. Conversely, a 40% reduction in adipose tissue GLUT-4 content was detected. In conclusion, pinealectomy is responsible for both impaired insulin secretion and action, emphasizing the influence of the pineal gland on glucose metabolism.
Localization and quantification of glucose transporters in liver of growth-retarded fetal and neonatal rats
Authors: Lane Robert H. , Crawford Susan E. , Flozak Annette S. , Simmons Rebecca A.
Published: December 2017

To determine whether altered transport of glucose into the hepatocyte may be an important factor contributing to abnormal hepatic glucose metabolism in the intrauterine growth-retarded (IUGR) fetus and newborn, we measured glucose transport (glucose uptake, GLUT protein, and mRNA) and localization of GLUT protein in liver of control (sham operated) and IUGR fetal ( day 20) and postnatal (1, 4, 14, and 21 days) rats. GLUT-1 and -2 proteins were localized to the hepatocyte. Glucose uptake and GLUT-1 protein and mRNA levels were increased in IUGR fetal and neonatal liver. GLUT-2 protein and mRNA levels were low in IUGR and control fetal liver. After birth, GLUT-2 abundance did not differ from controls. Run-on experiments showed that the rate of transcription of GLUT-1 and -2 did not differ between IUGR and control rats. However, the transcription rate of GLUT-1 decreased with age, and the GLUT-2 transcription rate increased with age. These studies indicate that the metabolic and physiological factors that cause IUGR also alter glucose transporter expression in fetal liver.
Glucose production during an IVGTT by deconvolution: validation with the tracer-to-tracee clamp technique
Authors: Vicini Paolo , Zachwieja Jeffrey J. , Yarasheski Kevin E. , Bier Dennis M. , Caumo Andrea , Cobelli Claudio
Published: December 2017

Recently, a new method, based on a two-compartment minimal model and deconvolution [A. Caumo and C. Cobelli. Am. J. Physiol 264 ( Endocrinol. Metab.. 37): E829–E841, 1993; P. Vicini, G. Sparacino, A. Caumo, and C. Cobelli. Comput. Meth. Prog. Biomed. 52: 147–156, 1997], has been proposed to estimate endogenous glucose production (EGP) from labeled intravenous glucose tolerance test (IVGTT) data. Our aim here is to compare this EGP profile with that independently obtained with the reference method, based on the tracer-to-tracee ratio (TTR) clamp. An insulin-modified (0.03 U/kg body wt infused over 5 min) [6,6-2H2]glucose-labeled IVGTT (0.33 g/kg of glucose) was performed in 10 normal subjects. A second tracer ([U-13C]glucose) was also infused during the test in a variable fashion to clamp endogenous glucose TTR. The TTR clamp was quite successful. As a result, the EGP profile, reconstructed from [U-13C]glucose data with the models of Steele and Radziuk, were almost superimposable. The deconvolution-obtained EGP profile, calculated from [6,6-2H2]glucose data, showed remarkable agreement with that obtained from the TTR clamp. Some differences between the two profiles were noted in the estimated basal EGP and in the initial modalities of EGP inhibition. A high interindividual variability was also observed with both methods in the resumption of EGP to baseline; variability was high in both the timing and the extent of resumption. In conclusion, the use of the two-compartment minimal model of the IVGTT and deconvolution allows the estimation of a profile of EGP that is in very good agreement with that independently obtained with a TTR clamp.
Fas regulates germ cell apoptosis in the human testis in vitro
Authors: Pentikäinen Virve , Erkkilä Krista , Dunkel Leo
Published: December 2017

The Fas-Fas ligand (FasL) system has been implicated in maintaining the immune privileged nature of the testis. The present report concerns the role of the Fas-FasL system in regulating germ cell apoptosis, another important function of this system in the human testis. Fas was localized immunohistochemically to the same types of germ cells that were identified as apoptotic, namely spermatocytes and spermatids. Strong expression of Fas was also observed in Western blot analysis of the human testis. Furthermore, an antagonistic antibody to the FasL blocked germ cell apoptosis induced in vitro by incubating segments of seminiferous tubules under serum- and hormone-free conditions (i.e., without survival factors). Thus Fas appears to mediate germ cell apoptosis. A universal caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone, also inhibited germ cell death, suggesting that Fas-associated germ cell apoptosis is mediated via the caspase pathway. The present results suggest an important role for the Fas-FasL system in the regulation of germ cell apoptosis in the human testis.
Effects of sex steroid hormones on regional fat depots as assessed by magnetic resonance imaging in transsexuals
Authors: Elbers J. M. H. , Asscheman H. , Seidell J. C. , Gooren L. J. G.
Published: December 2017

We investigated prospectively the effect of sex steroids on regional fat depots and thigh muscle mass in adult transsexuals. Ethinyl estradiol in combination with cyproterone acetate, a progestational antiandrogen, was given to 20 male-to-female (M-F) transsexuals, and parenteral testosterone esters were given to 17 female-to-male (F-M) transsexuals. Before and after 12 mo of cross-sex hormone administration, several anthropometric measurements (weight, skinfolds, body circumferences, and bioimpedance) were performed, and transverse magnetic resonance images were obtained at the level of the abdomen, hip, and thigh to quantify fat depots (subcutaneous and visceral) and muscle areas. We observed that treatment with ethinyl estradiol in M-F transsexuals induced a significant increase in all subcutaneous fat depots, with a lesser but proportional and significant increase in the visceral fat depot and a decrease in thigh muscle area. Testosterone administration in F-M transsexuals markedly increased thigh muscle area, reduced subcutaneous fat deposition at all levels measured, but slightly increased the visceral fat area. We conclude that sex steroid hormones are important determinants of the sex-specific localization of body fat.
Discrimination, adjusted correlation, and equivalence of imprecise tests: application to glucose tolerance
Authors: Levy Jonathan , Morris Richard , Hammersley Margaret , Turner Robert
Published: December 2017

Comparison studies between physiological tests are often unsatisfactory for assessing their ability to distinguish between subjects. We recommend a simple but comprehensive protocol, using duplicate testing, that compares tests using 1) the discriminant ratio (DR) between the underlying between- and within-subject SDs, 2) correlation coefficients adjusted for attenuation due to test imprecision, and 3) unbiased estimation of the underlying linear relationship between test results. The following five alternative methods for assessing glucose tolerance were compared: fasting plasma glucose (FPG) as a single sample or as the mean of three 5-min samples (FPG3); the 1- and 2-h glucose during a low-dose intravenous glucose infusion (CIG); and the 2-h plasma glucose from a 75-g oral glucose tolerance test (OGTT). All tests had similar DRs ranging from 2.6 to 4.2. The adjusted correlation between FPG and CIG tests approached unity, and those between OGTT and other tests were ∼0.9, showing that FPG3provides similar information to the OGTT. FPG concentrations of 6.0 and 7.1 were found equivalent to the 1985 World Health Organization OGTT thresholds for impaired glucose tolerance and diabetes (7.8 and 11.1 mmol/l).
GLUT-1 or GLUT-4 transgenes in obese mice improve glucose tolerance but do not prevent insulin resistance
Authors: Marshall Bess Adkins , Hansen Polly A. , Ensor Nancy J. , Ogden M. Allison , Mueckler Mike
Published: December 2017

Insulin-stimulated glucose uptake is defective in patients with type 2 diabetes. To determine whether transgenic glucose transporter overexpression in muscle can prevent diabetes induced by a high-fat, high-sugar diet, singly (GLUT-1, GLUT-4) and doubly (GLUT-1 and -4) transgenic mice were placed on a high-fat, high-sugar diet or a standard chow diet. On the high-fat, high-sugar diet, wild-type but not transgenic mice developed fasting hyperglycemia and glucose intolerance (peak glucose of 337 ± 19 vs. 185–209 mg/dl in the same groups on the high-fat, high-sugar diet and 293 ± 13 vs. 166–194 mg/dl on standard chow). Hyperinsulinemic clamps showed that transporter overexpression elevated insulin-stimulated glucose utilization on standard chow (49 ± 4 mg ⋅ kg−1⋅ min−1in wild-type vs. 61 ± 4, 67 ± 5, and 63 ± 6 mg ⋅ kg−1⋅ min−1in GLUT-1, GLUT-4, and GLUT-1 and -4 transgenic mice given 20 mU ⋅ kg−1⋅ min−1insulin, and 54 ± 7, 85 ± 4, and 98 ± 11 in wild-type, GLUT-1, and GLUT-4 mice given 60–80 mU ⋅ kg−1⋅ min−1insulin). On the high-fat, high-sugar diet, wild-type and GLUT-1 mice developed marked insulin resistance, but GLUT-4 and GLUT-1 and -4 mice were somewhat protected (glucose utilization during hyperinsulinemic clamp of 28.5 ± 3.4 vs. 42.4 ± 5.9, 51.2 ± 8.1, and 55.9 ± 4.9 mg ⋅ kg−1⋅ min−1in wild type, GLUT-1, GLUT-4, GLUT-1 and -4 mice). These data demonstrate that overexpression of GLUT-1 and/or GLUT-4 enhances whole body glucose utilization and prevents the development of fasting hyperglycemia and glucose intolerance induced by a high-fat, high-sugar diet. GLUT-4 overexpression improves the insulin resistance induced by the diet. We conclude that upregulation of glucose transporters in skeletal muscle may be an effective therapeutic approach to the treatment of human type 2 diabetes.
Decreased hexosamine biosynthesis in GH-deficient dwarf rat muscle. Reversal with GH, but not IGF-I, therapy
Authors: Robinson Katherine A. , Willi Steven M. , Bingel Sarah , Buse Maria G.
Published: December 2017

Enhanced glucose flux via the hexosamine biosynthesis pathway (HNSP) has been implicated in insulin resistance. We measuredl-glutamine:d-fructose-6-phosphate amidotransferase activity (GFAT, a rate-limiting enzyme) and concentrations of UDP- N-acetyl hexosamines (UDP-HexNAc, major products of HNSP) in muscle and liver of growth hormone (GH)-deficient male dwarf (dw) rats. All parameters measured, except body weight, were similar in 5-wk-old control and dw rats. Muscle GFAT activity declined progressively with age in controls and dw rats but was consistently 30–60% lower in 8- to 14-wk-old dw rats vs. age-matched controls; UDP-HexNAc concentrations in muscle were concomitantly 30% lower in dw rats vs. controls ( P < 0.01). Concentrations of UDP-hexoses, GDP-mannose, and UDP in muscle were similar in control and dw rats. Muscle HNSP activity was similarly diminished in fed and fasted dw rats. In liver, only a small difference in GFAT activity was evident between controls and dw rats, and no differences in UDP-HexNAc concentrations were observed. Treatment with recombinant human GH (rhGH) for 5 days restored UDP-HexNAc to control levels in dw muscles ( P < 0.01) and partially restored GFAT activity. Insulin-like growth factor I treatment was ineffective. We conclude that GH participates in HNSP regulation in muscle.
Contribution of protein kinase C to ET-1-induced proliferation in human myometrial cells
Authors: Tertrin-Clary C. , Eude I. , Fournier T. , Paris B. , Breuiller-Fouché M. , Ferré F.
Published: December 2017

The role of protein kinase C (PKC) in endothelin-1 (ET-1)-induced proliferation of human myometrial cells was investigated. ET-1 dose dependently stimulated DNA synthesis and the number of cultured myometrial cells. Inhibition of PKC by calphostin C or Ro-31-8220 or downregulation of PKC eliminated the proliferative effects of ET-1. The failure of two protein tyrosine kinase (PTK) inhibitors (tyrphostin 51 and tyrphostin 23) to affect ET-1-induced proliferation supports the hypothesis of noninvolvement of the tyrosine kinase signaling pathway in this process. The expression and distribution of PKC isoforms were examined by Western blot analysis. The five PKC isoforms (PKC-α, -β1, -β2, -ζ, -ε) evidenced in human myometrial tissue were found to be differentially expressed in myometrial cells, with a predominant expression of PKC-α and PKC-ζ. Treatment with phorbol 12,13-dibutyrate (PDBu) resulted in the translocation of all five isoforms to the particulate fraction, whereas ET-1 induced a selective increase in particulate PKC-β1, PKC-β2, and PKC-ε. Our findings that multiple PKC isoforms are differentially responsive to ET-1 or PDBu suggest that they play distinct roles in the myometrial growth process.
Many LH peaks are needed to physiologically stimulate testosterone secretion: modulation by fasting and NPY
Authors: Pierroz Dominique D. , Aebi Audrey C. , Huhtaniemi Ilpo T. , Aubert Michel L.
Published: December 2017

The pulsatile luteinizing hormone (LH) and testosterone secretions were studied during serial blood collections performed at 7-min time intervals in the male rat. In fed rats, a discontinuous pattern of LH secretion was observed. Periods without secretion alternated with active secretory episodes consisting in trains of three to four LH peaks that triggered testosterone secretion usually 1–2 h later. The magnitude of the testosterone response was not correlated with the amplitude of the LH peaks. Isolated, single peaks of LH did not evoke clear testosterone responses. Forty-eight hours after initiation of fasting, testosterone secretion was markedly decreased, but integrated LH secretion was only partly reduced. Chronic infusion of neuropeptide Y (NPY; 18 μg/day, icv) reduced testosterone secretion to very low levels and abolished pulsatile LH secretion or testosterone response to isolated LH peaks. In conclusion, the stimulation of testosterone secretion by LH necessitates several LH peaks organized in a proper sequence, and the testosterone response is not immediate. Low testosterone secretion in fasting rats appears to result from disappearance of coordinated, multiple LH peaks of sufficient size. Inhibition of the gonadotropic axis achieved by central NPY administration is due to either absence of LH peak “clusters” or occurrence of nonfunctional single LH peaks.
Muscle contractile activity increases fatty acid metabolism and transport and FAT/CD36
Authors: Bonen Arend , Dyck David. J. , Ibrahimi Azeddine , Abumrad Nada A.
Published: December 2017

We have examined whether 1) fatty acid (FA) uptake, 2) FA transporter expression, and 3) FA metabolism are increased when the oxidative capacity of skeletal muscle is increased. The oxidative capacities of red and white tibialis anterior and extensor digitorum longus muscles were increased via chronic stimulation (10 Hz, 24 h/day for 7 days). The contralateral muscles served as controls. After 7 days of increased muscle activity 1) palmitate uptake by giant sarcolemmal vesicles was increased twofold ( P < 0.05), 2) the expression of FA translocase (FAT)/CD36 was increased at both the mRNA (3.2- to 10-fold) and protein (3.4-fold) levels, and 3) palmitate oxidation and esterification into triacylglycerols and phospholipids were increased 1.5-, 2.7-, and 1.7-fold, respectively ( P < 0.05). These data show that when the oxidative capacity of muscle is increased, there is a parallel increase in the rate of FA transport and FA transporters at the sarcolemmal membrane, which is associated with the enhanced expression of the membrane transporter FAT/CD36.