bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of short-term fasting on lipid kinetics in lean and obese women
Authors: Horowitz Jeffrey F. , Coppack Simon W. , Paramore Deanna , Cryer Philip E. , Zhao Guohong , Klein Samuel
Published: December 2017

We evaluated whole body and regional adipose tissue lipid kinetics and norepinephrine (NE) spillover during brief fasting in six lean [body mass index (BMI) 21 ± 1 kg/m2] and six upper-body obese (UBO; BMI 36 ± 1 kg/m2) women. At 14 h of fasting, abdominal adipose tissue glycerol and free fatty acid (FFA) release rates were lower ( P = 0.07), but whole body glycerol and FFA rates of appearance (Ra) were greater ( P < 0.05) in obese than in lean subjects. At 22 h of fasting, glycerol and FFA Raincreased less in obese (19.8 ± 7.0 and 87.1 ± 30.3 μmol/min, respectively) than in lean (44.2 ± 6.6 and 137.4 ± 30.4 μmol/min, respectively; P < 0.05) women. The percent increase in glycerol Racorrelated closely with the percent decline in plasma insulin in both groups ( r2 = 0.85; P < 0.05). Whole body NE spillover declined in lean ( P < 0.05) but not obese subjects with continued fasting, whereas regional adipose tissue NE spillover did not change in either group. We conclude that, compared with lean women, in UBO women 1) basal adipose tissue lipolysis is lower, but whole body lipid kinetics is higher because of their greater fat mass; 2) the increase in lipolysis during fasting is blunted because of an attenuated decline in circulating insulin; and 3) downregulation of whole body sympathetic nervous system activity is impaired during fasting.
Control of adrenal cell proliferation by AT1 receptors in response to angiotensin II and low-sodium diet
Authors: McEwan Pauline E. , Vinson Gavin P. , Kenyon Christopher J.
Published: December 2017

The effects of angiotensin II (ANG II), the angiotensin type 1 (AT1) receptor antagonist losartan, and low-sodium diet on rat adrenal cell proliferation were studied in vivo with immunocytochemistry. Both ANG II and low-sodium diet increased proliferation of endothelial cells of the zona glomerulosa. Losartan prevented ANG II-induced hyperplasia of glomerulosa cells but not the effects of a low-sodium diet. Glomerulosa cells after ANG II + losartan treatment appeared hypertrophied compared with those of controls. Proliferative effects of ANG II and low-sodium diet in the reticularis were blocked by losartan. No changes were seen in the fasciculata. Proliferation in the medulla was increased with losartan, was decreased by ANG II, but was unaffected by low-sodium diet. In conclusion, 1) cell hypertrophy and proliferation of glomerulosa cells are mediated by AT1 receptor-dependent and -independent processes, 2) proliferation of reticularis cells is controlled by AT1 receptors, and 3) reciprocal control of chromaffin cell proliferation by ANG II may involve indirect AT1-dependent processes.
Muscular long-chain fatty acid content during graded exercise in humans
Authors: Kiens Bente , Roemen Theo H. M. , van der Vusse Ger J.
Published: December 2017

We measured the content of long-chain fatty acids (LCFA) in biopsies obtained from the vastus lateralis muscle in humans at rest and after different exercise intensities. Nine volunteers exercised at 65% of maximal oxygen uptake (V˙o2 max) for 40 min and at 90% of V˙o2 maxfor another 15 min on a Krogh bicycle ergometer. LCFA measured in muscle tissue averaged 76 ± 5 nmol/g wet wt at rest, decreased significantly after exercise at 65% V˙o2 maxto 48 ± 4 nmol/g wet wt, and increased to 68 ± 5 nmol/g wet wt ( P < 0.05) after high-intensity exercise. The calculated myocyte LCFA content at rest amounted to 69 ± 5 nmol/g wet wt, decreased by 43% ( P < 0.05) after exercise at 65% ofV˙o2 max, and subsequently increased by 54% after exercise at 90% ofV˙o2 max( P < 0.05) compared with the values obtained at the lower workload. The blood plasma LCFA concentration during the low-intensity exercise (366 ± 23 nmol/ml) was similar to the values obtained at rest (372 ± 31 nmol/ml) but decreased significantly during the high-intensity workload (249 ± 49 nmol/ml). From these data it is proposed that 1) in human skeletal muscle, metabolism rather than cellular availability of LCFA governs the rate of LCFA utilization at rest and during exercise, and 2) consequently reduction in muscle LCFA oxidation during high-intensity exercise (e.g., 90%V˙o2 max) is due primarily to a decrease in mitochondrial LCFA oxidation rate rather than an insufficient cellular availability of LCFA.
High-resistance training and muscle metabolism during prolonged exercise
Authors: Goreham C. , Green H. J. , Ball-Burnett M. , Ranney D.
Published: December 2017

To investigate the hypothesis that changes in muscle submaximal exercise metabolism would occur as a result of fiber hypertrophy, induced by high-resistance training (HRT), active but untrained males (age 20 ± 0.7 yr; mean ± SE) performed lower-limb weight training 3 days/wk for 12 wk using three sets of 6–8 repetitions maximal (RM)/day. Muscle metabolism was examined at different stages of training (4, 7, and 12 wk) using a two-stage continuous cycle test performed at the same absolute power output and duration (56.4 ± 2.9 min) and representing 57 and 72% of pretraining peak aerobic power (V˙o 2 peak). Compared with pretraining, at the end of exercise, HRT resulted in a higher ( P < 0.05) phosphocreatine (PCr; 27.4 ± 6.7 vs. 38.0 ± 1.9 mmol/kg dry wt), a lower lactate (38.9 ± 8.5 vs. 24.4 ± 6.1 mmol/kg dry wt), and a higher ( P < 0.05) glycogen content (132 ± 11 vs. 181 ± 7.5 mmol glucosyl units/kg dry wt). The percent change from rest before and after training was 63 and 50% for PCr, 676 and 410% for lactate, and 60 and 43% for glycogen, respectively. These adaptations, which were observed only at 72%V˙o 2 peak, occurred by 4 wk of training in the case of PCr and glycogen and before any changes in fiber cross-sectional area, capillarization, or oxidative potential. Fiber hypertrophy, observed at 7 and 12 wk of training, failed to potentiate the metabolic response. No effect of HRT was found onV˙o 2 peak with training (41.2 ± 2.9 vs. 41.0 ± 2.1 ml ⋅ kg−1 ⋅ min−1) or on the steady-state, submaximal exercise rate of oxygen consumption. It is concluded that the HRT results in muscle metabolic adaptations that occur independently of fiber hypertrophy.
Kinetics of dodecanedioic acid triglyceride in rats
Authors: de Gaetano A. , Mingrone G. , Castagneto M. , Benedetti G. , Greco A. V. , Gasbarrini G.
Published: December 2017

The kinetics of the triglyceride of dodecanedioic acid (TGDA) has been investigated in 30 male Wistar rats after a rapid intravenous bolus injection. TGDA and its product of hydrolysis, nonesterified dodecanedioic acid (NEDA), were measured in plasma samples taken at different times using an improved high-performance liquid chromatographic method. The 24-h urinary excretion of TGDA was 1.54 ± 0.37 μmol, corresponding to ∼0.67% of the administered amount. Several kinetics models were considered, including central and peripheral compartments for the triglyceride and the free forms and expressing transports between compartments with combinations of linear, carrier-limited, or time-varying mechanisms. The parameter estimates of the kinetics of TGDA and of NEDA were finally obtained using a three-compartment model in which the transfer of TGDA to NEDA was assumed to be linear, through a peripheral compartment, and the tissue uptake of NEDA was assumed to be carrier limited. TGDA had a large volume of distribution (∼0.5 l/kg body wt) with a fast disappearance rate from plasma (0.42 min−1), whereas NEDA had a very small volume of distribution (∼0.04 l/kg body wt) and a tissue uptake with maximal transport rate of 0.636 mM/min. In conclusion, this first study on the triglyceride form of dodecanedioic acid indicates that it is rapidly hydrolyzed and that both triglyceride and nonesterified forms are excreted in the urine to a very low extent. The tissue uptake rate of NEDA is consistent with the possibility of achieving substantial energy delivery, should it be added to parenteral nutrition formulations. Furthermore, the amount of sodium administered with the triglyceride form is one-half of that necessary with the free diacid.
Sympathetic nervous system activity and α-adrenergic responsiveness in older hypertensive humans
Authors: Supiano Mark A. , Hogikyan Robert V. , Sidani Mohamad A. , Galecki Andrzej T. , Krueger Jodi L.
Published: December 2017

We have previously demonstrated in normotensive humans an age-associated increase in sympathetic nervous system (SNS) activity combined with appropriate downregulation of α-adrenergic responsiveness. Impaired downregulation of α-adrenergic responsiveness, despite a comparable level of SNS activity, could contribute to higher blood pressure in older hypertensive humans. We measured arterial plasma norepinephrine (NE) levels and the extravascular NE release rate (NE2) derived from [3H]NE kinetics (to assess systemic SNS activity), and platelet and forearm arterial adrenergic responsiveness in 20 normotensive (N) and in 24 hypertensive (H), otherwise healthy, older subjects (60–75 yr). Although plasma NE levels were similar (N 357 ± 27 vs. H 322 ± 22 pg/ml; P = 0.37), NE2tended to be greater in the hypertensive group (H 2.23 ± 0.21 vs. N 1.64 ± 0.20 μg ⋅ min−1⋅ m−2; P = 0.11), and the NE metabolic clearance rate was greater (H 1,100 ± 30 vs. N 900 ± 50 ml/m2; P = 0.004). In the hypertensive group, there was a greater α-agonist-mediated inhibition of platelet membrane adenylyl cyclase activity and a NE- but not ANG II-mediated decrease in forearm blood flow. Compared with normotensive subjects, in older hypertensive subjects 1) NE metabolic clearance rate is increased, 2) systemic SNS activity tends to be increased, and 3) arterial and platelet α-adrenergic responsiveness is enhanced. These results suggest that heightened SNS activity coupled with enhanced α-adrenergic responsiveness may contribute to elevated blood pressure in older hypertensive humans.
TNF-binding protein ameliorates inhibition of skeletal muscle protein synthesis during sepsis
Authors: Cooney Robert , Kimball Scot R. , Eckman Rebecca , Maish George , Shumate Margaret , Vary Thomas C.
Published: December 2017

We examined the effects of TNF-binding protein (TNFBP) on regulatory mechanisms of muscle protein synthesis during sepsis in four groups of rats: Control; Control+TNFBP; Septic; and Septic+TNFBP. Saline (1.0 ml) or TNFBP (1 mg/kg, 1.0 ml) was injected daily starting 4 h before the induction of sepsis. The effect of TNFBP on gastrocnemius weight, protein content, and the rate of protein synthesis was examined 5 days later. Sepsis reduced the rate of protein synthesis by 35% relative to controls by depressing translational efficiency. Decreases in protein synthesis were accompanied by similar reductions in protein content and muscle weight. Treatment of septic animals with TNFBP for 5 days prevented the sepsis-induced inhibition of protein synthesis and restored translational efficiency to control values. TNFBP treatment of Control rats for 5 days was without effect on muscle protein content or protein synthesis. We also assessed potential mechanisms regulating translational efficiency. The phosphorylation state of p70S6 kinase was not altered by sepsis. Sepsis reduced the gastrocnemius content of eukaryotic initiation factor 2Bε (eIF2Bε), but not eIF2α. The decrease in eIF2Bε content was prevented by treatment of septic rats with TNFBP. TNFBP ameliorates the sepsis-induced changes in protein metabolism in gastrocnemius, indicating a role for TNF in the septic process. The data suggest that TNF may impair muscle protein synthesis by reducing expression of specific initiation factors during sepsis.
Depression of liver protein synthesis during surgery is prevented by growth hormone
Authors: Barle Hans , Essén Pia , Nyberg Björn , Olivecrona Hans , Tally Michael , McNurlan Margaret A. , Wernerman Jan , Garlick Peter J.
Published: December 2017

This study was undertaken to elucidate the specific effects of growth hormone (GH) on liver protein metabolism in humans during surgery. Otherwise healthy patients scheduled for elective laparoscopic cholecystectomy were randomized into controls ( n = 9) or pretreatment with 12 units of GH for 1 day (GH 1, n = 9) or daily for 5 days (GH 5, n = 10). The fractional synthesis rate of liver proteins, as assessed by flooding with [2H5]phenylalanine, was higher in the GH 5 group (22.0 ± 6.9%/day, mean ± SD, P < 0.05) than in the control (16.1 ± 3.1%/day) and GH 1 (16.5 ± 5.5%/day) groups. During surgery, the fraction of polyribosomes in the liver, as assessed by ribosome analysis, decreased in the control group by ∼12% ( P < 0.01) but did not decrease in the GH-treated groups. In addition, the concentrations of the essential amino acids and aspartate in the liver decreased in response to GH treatment. In conclusion, GH pretreatment decreases hepatic free amino acid concentrations and preserves liver protein synthesis during surgery.
Cyclic stretch regulates autocrine IGF-I in vascular smooth muscle cells: implications in vascular hyperplasia
Authors: Standley Paul R. , Obards Tamar J. , Martina Cherie L.
Published: December 2017

Vascular smooth muscle cells (VSMC) subjected to acute or chronic stretch display enhanced growth rates in vitro and in vivo. Clinical examples of vascular hyperplasia (e.g., systolic hypertension and postinjury restenosis) suggest that local insulin-like growth factor I (IGF-I) expression is enhanced. Therefore, we investigated the role of in vitro cyclic stretch on rat VSMC IGF-I secretion and cellular growth. In serum-free medium, cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated thymidine incorporation ∼40% above that seen in nonstretched cells. Graded stretch magnitude (100–125% resting length) yielded graded increases in VSMC growth. Exogenous IGF-I increased growth of serum-starved, nonstretched VSMC in a dose-dependent manner, with maximal growth seen with 10−7M. IGF-I secretion from stretched cells was 20- to 30-fold greater than from those cells cultured in a static environment. Stretch-induced increases in growth were completely blocked on addition of anti-IGF-I and partially blocked with platelet-derived growth factor (PDGF) antibodies and with a tyrosine kinase inhibitor (tyrphostin-1). Finally, blockade of stretch-activated cation channels with GdCl3profoundly inhibited stretch-induced growth. We conclude that stretch increases VSMC IGF-I secretion and that such autocrine IGF-I is required for stretch-induced growth. PDGF and stretch-sensitive cation channels are likely additional components of a complex pathway that regulates stretch-induced VSMC seen in systolic hypertension and postinjury restenosis.
Insulin action on heart and skeletal muscle glucose uptake in weight lifters and endurance athletes
Authors: Takala Teemu O. , Nuutila Pirjo , Knuuti Juhani , Luotolahti Matti , Yki-Järvinen Hannele
Published: December 2017

There are no studies comparing myocardial metabolism between endurance- and resistance-trained athletes. We used 2-deoxy-2-[18F]fluoro-d-glucose and positron emission tomography combined with the euglycemic hyperinsulinemic clamp technique to compare the ability of insulin to stimulate myocardial, skeletal muscle, and whole body glucose uptake between weight lifters ( n = 8), endurance athletes ( n = 8), and sedentary men ( n = 9). Maximal aerobic power (ml ⋅ kg− 1⋅ min− 1) was higher in the endurance athletes (71 ± 2, P < 0.001) than the weight lifters (42 ± 2) and the sedentary men (42 ± 2). Skeletal muscle glucose uptake (μmol ⋅ kg muscle− 1⋅ min− 1) was enhanced in the endurance athletes (125 ± 16, P < 0.01) but was similar in weight lifters (59 ± 12) and sedentary (63 ± 7) men. The rate of glucose uptake per unit mass of myocardium (μmol ⋅ kg− 1⋅ min− 1) was similarly decreased in endurance athletes (544 ± 50) and weight lifters (651 ± 45) compared with sedentary men (1,041 ± 78, P < 0.001 vs. endurance athletes and weight lifters). Both groups of athletes had increased left ventricular mass. Consequently, total left ventricular glucose uptake was comparable in all groups. These data demonstrate that aerobic but not resistance training is associated with enhanced insulin sensitivity in skeletal muscle. Despite this, cardiac changes are remarkably similar in weight lifters and endurance athletes and are characterized by an increase in left ventricular mass and diminished insulin-stimulated glucose uptake per heart mass.
Distribution of the lactate/H+ transporter isoforms MCT1 and MCT4 in human skeletal muscle
Authors: Pilegaard Henriette , Terzis Gerasimos , Halestrap Andrew , Juel Carsten
Published: December 2017

The profiles of the lactate/H+ transporter isoforms [monocarboxylate transporter isoforms (MCT)] MCT1 and MCT4 (formerly MCT3 of Price, N. T., V. N. Jackson, and A. P. Halestrap. Biochem. J. 329: 321–328, 1998) were studied in the soleus, triceps brachii, and vastus lateralis muscles of six male subjects. The fiber-type compositions of the muscles were evaluated from the occurrence of the myosin heavy chain isoforms, and the fibers were classified as type I, IIA, or IIX. The total content of MCT1 and MCT4 was determined in muscle homogenates by Western blotting, and MCT1 and MCT4 were visualized on cross-sectional muscle sections by immunofluorescence microscopy. The Western blotting revealed a positive, linear relationship between the MCT1 content and the occurrence of type I fibers in the muscle, but no significant relation was found between MCT4 content and fiber type. Moreover, the interindividual variation in MCT4 content was much larger than the interindividual variation in MCT1 content in homogenate samples. The immunofluorescence microscopy showed that within a given muscle section, the MCT4 isoform was clearly more abundant in type II fibers than in type I fibers, whereas only minor differences existed in the occurrence of the MCT1 isoform between type I and II fibers. Together the present results indicate that the content of MCT1 in a muscle varies between different muscles, whereas fiber-type differences in MCT1 content are minor within a given muscle section. In contrast, the content of MCT4 is clearly fiber-type specific but apparently quite similar in various muscles.
Differential regulation of MAP kinase, p70S6K, and Akt by contraction and insulin in rat skeletal muscle
Authors: Sherwood Daniel J. , Dufresne Scott D. , Markuns Jeffrey F. , Cheatham Bentley , Moller David E. , Aronson Doron , Goodyear Laurie J.
Published: December 2017

To study the effects of contractile activity on mitogen-activated protein kinase (MAP kinase), p70 S6 kinase (p70S6K), and Akt kinase signaling in rat skeletal muscle, hindlimb muscles were contracted by electrical stimulation of the sciatic nerve for periods of 15 s to 60 min. Contraction resulted in a rapid and transient activation of Raf-1 and MAP kinase kinase 1, a rapid and more sustained activation of MAP kinase and the 90-kDa ribosomal S6 kinase 2, and a dramatic increase in c- fos mRNA expression. Contraction also resulted in an apparent increase in the association of Raf-1 with p21Ras, although stimulation of MAP kinase signaling occurred independent of Shc, IRS1, and IRS2 tyrosine phosphorylation or the formation of Shc/Grb2 or IRS1/Grb2 complexes. Insulin was considerably less effective than contraction in stimulating the MAP kinase pathway. However, insulin, but not contraction, increased p70S6Kand Akt activities in the muscle. These results demonstrate that contraction-induced activation of the MAP kinase pathway is independent of proximal steps in insulin and/or growth factor-mediated signaling, and that contraction and insulin have discordant effects with respect to the activation of the MAP kinase pathway vs. p70S6Kand Akt. Of the numerous stimulators of MAP kinase in skeletal muscle, contractile activity emerges as a potent and physiologically relevant activator of MAP kinase signaling, and thus activation of this pathway is likely to be an important molecular mechanism by which skeletal muscle cells transduce mechanical and/or biochemical signals into downstream biological responses.
Leptin opposes insulin’s effects on fatty acid partitioning in muscles isolated from obese ob/obmice
Authors: Muoio Deborah M. , Dohm G. Lynis , Tapscott Edward B. , Coleman Rosalind A.
Published: December 2017

Because muscle triacylglycerol (TAG) accumulation might contribute to insulin resistance in leptin-deficient ob/obmice, we studied the acute (60- to 90-min) effects of leptin and insulin on [14C]glucose and [14C]oleate metabolism in muscles isolated from lean and obese ob/ob mice. In ob/ob soleus, leptin decreased glycogen synthesis 36–46% ( P < 0.05), increased oleate oxidation 26% ( P < 0.05), decreased oleate incorporation into TAG 32% ( P < 0.05), and decreased the oleate partitioning ratio (oleate partitioned into TAG/CO2) 44% ( P < 0.05). Insulin decreased oleate oxidation 31% ( P < 0.05), increased oleate incorporation into TAG 46% ( P< 0.05), and increased the partitioning ratio 125% ( P < 0.01). Adding leptin diminished insulin’s antioxidative, lipogenic effects. In soleus from lean mice, insulin increased the partitioning ratio 142%, whereas leptin decreased it 51%, as previously reported (Muoio, D. M., G. L. Dohm, F. T. Fiedorek, E. B. Tapscott, and R. A. Coleman. Diabetes 46: 1360–1363, 1997). The phosphatidylinositol 3-kinase inhibitor wortmannin blocked insulin’s effects on lipid metabolism but only attenuated leptin’s effects. Increasing glucose concentration from 5 to 10 mM did not affect TAG synthesis, suggesting that insulin-induced lipogenesis is independent of increased glucose uptake. These data indicate that leptin opposes insulin’s promotion of TAG accumulation in lean and ob/ob muscles. Because acute leptin exposure does not correct insulin resistance in ob/ob muscles, in vivo improvements in glucose homeostasis appear to require other long-term factors, possibly TAG depletion.
Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo
Authors: Szczepaniak Lidia S. , Babcock Evelyn E. , Schick Fritz , Dobbins Robert L. , Garg Abhimanyu , Burns Dennis K. , McGarry J. Denis , Stein Daniel T.
Published: December 2017

We validate the use of1H magnetic resonance spectroscopy (MRS) to quantitatively differentiate between adipocyte and intracellular triglyceride (TG) stores by monitoring the TG methylene proton signals at 1.6 and 1.4 ppm, respectively. In two animal models of intracellular TG accumulation, intrahepatic and intramyocellular TG accumulation was confirmed histologically. Consistent with the histological changes, the methylene signal intensity at 1.4 ppm increased in both liver and muscle, whereas the signal at 1.6 ppm was unchanged. In response to induced fat accumulation, the TG concentration in liver derived from1H MRS increased from 0 to 44.9 ± 13.2 μmol/g, and this was matched by increases measured biochemically (2.1 ± 1.1 to 46.1 ± 10.9 μmol/g). Supportive evidence that the methylene signal at 1.6 ppm in muscle is derived from investing interfascial adipose tissue was the finding that, in four subjects with generalized lipodystrophy, a disease characterized by absence of interfacial fat, no signal was detected at 1.6 ppm; however, a strong signal was seen at 1.4 ppm. An identical methylene chemical shift at 1.4 ppm was obtained in human subjects with fatty liver where the fat is located exclusively within hepatocytes. In experimental animals, there was a close correlation between hepatic TG content measured in vivo by1H MRS and chemically by liver biopsy [ R = 0.934; P < .0001; slope 0.98, confidence interval (CI) 0.70–1.17; y-intercept 0.26, CI −0.28 to 0.70]. When applied to human calf muscle, the coefficient of variation of the technique in measuring intramyocellular TG content was 11.8% in nonobese subjects and 7.9% in obese subjects and of extramyocellular (adipocyte) fat was 22.6 and 52.5%, respectively. This study demonstrates for the first time that noninvasive in vivo1H MRS measurement of intracellular TG, including that within myocytes, is feasible at 1.5-T field strengths and is comparable in accuracy to biochemical measurement. In addition, in mixed tissue such as muscle, the method is clearly advantageous in differentiating between TG from contaminating adipose tissue compared with intramyocellular lipids.
Dose-response study of GH effects on circulating IGF-I and IGFBP-3 levels in healthy young men and women
Authors: Ghigo E. , Aimaretti G. , Maccario M. , Fanciulli G. , Arvat E. , Minuto F. , Giordano G. , Delitala G. , Camanni F.
Published: December 2017

The aim of our study was to define the dose-response effect of a short-term treatment with different recombinant human growth hormone (rhGH) doses (1.25, 2.5, 5.0, 10.0, and 20.0 μg ⋅ kg−1 ⋅ day−1for 4 days) on insulin-like growth factor I (IGF-I) and insulin-like growth factor-binding protein (IGFBP)-3 levels in 21 normal young adults of both sexes. The dose of 1.25 μg/kg rhGH did not modify IGF-I levels. The dose of 2.5 μg/kg rhGH significantly increased IGF-I levels in men ( P < 0.05) but not in women, whereas the higher doses increased IGF-I levels in both sexes ( P < 0.002). IGFBP-3 levels were not modified by 1.25 or 2.5 μg/kg rhGH in either sex. On the other hand, 5.0 μg/kg increased IGFBP-3 levels in men ( P < 0.05) but not in women, whereas the higher doses increased IGFBP-3 levels similarly in both sexes ( P < 0.02). In conclusion, our results demonstrate that IGF-I and IGFBP-3 responses to rhGH are dose and sex dependent. However, IGFBP-3 is less sensitive than IGF-I to rhGH stimulation.
A negative arterial-portal venous glucose gradient increases net hepatic glucose uptake in euglycemic dogs
Authors: Galassetti Pietro , Chu Chang An , Neal Doss W. , Reed George W. , Wasserman David H. , Cherrington Alan D.
Published: December 2017

We investigated whether a negative arterial-portal venous (a-pv) glucose gradient, or “portal signal,” can increase net hepatic glucose uptake (NHGU) and decrease muscle glucose uptake at euglycemia as it does at hyperglycemia. Twenty 42-h fasted dogs were studied during a basal and two 120-min euglycemic periods ( period I and period II). Glucagon was maintained at basal levels, and insulin was raised 3-fold (3×Ins, n = 10) or 15-fold (15×Ins, n = 10). During period I, dogs received glucose only peripherally. During period II, one-half of the dogs continued the peripheral infusion; the other one-half received glucose intraportally (4 mg ⋅ kg−1⋅ min−1and reduced peripheral glucose infusion). A negative a-pv glucose gradient was present during intraportal glucose infusion. All 3×Ins and 15×Ins dogs had similar NHGU in period I. In period II, it was 2.1 ± 0.3 (3×Ins) and 2.5 (15×Ins) mg ⋅ kg−1⋅ min−1greater in the presence than in the absence of the portal signal ( P < 0.001). The net glucose fractional extraction data paralleled NHGU. In 3×Ins, but not in 15×Ins, whole body nonhepatic glucose uptake was lower in the presence of the portal signal than in its absence. In conclusion, in hyperinsulinemic, but not hyperglycemic conditions, the portal signal is effective in activating NHGU. The inhibition of nonhepatic glucose uptake, on the other hand, is minimal under euglycemic as opposed to hyperglycemic conditions.
Stimulation of both aerobic glycolysis and Na+-K+-ATPase activity in skeletal muscle by epinephrine or amylin
Authors: James J. Howard , Wagner Kenneth R. , King Jy-Kung , Leffler Rebecca E. , Upputuri Radha Krishna , Balasubramaniam Ambikaipakan , Friend Lou Ann , Shelly Daniel A. , Paul Richard J. , Fischer Josef E.
Published: December 2017

Epinephrine and amylin stimulate glycogenolysis, glycolysis, and Na+-K+-ATPase activity in skeletal muscle. However, it is not known whether these hormones stimulate glycolytic ATP production that is specifically coupled to ATP consumption by the Na+-K+pump. These studies correlated glycolysis with Na+-K+-ATPase activity in resting rat extensor digitorum longus and soleus muscles incubated at 30°C in well-oxygenated medium. Lactate production rose three- to fourfold, and the intracellular Na+-to-K+ratio (Na+/K+) fell with increasing concentrations of epinephrine or amylin. In muscles exposed to epinephrine at high concentrations (5 × 10−7and 5 × 10−6M), ouabain significantly inhibited glycolysis by ∼70% in either muscle and inhibited glycogenolysis by ∼40 and ∼75% in extensor digitorum longus and soleus, respectively. In the absence of ouabain, but not in its presence, statistically significant inverse correlations were observed between lactate production and intracellular Na+/K+for each hormone. Epinephrine had no significant effect on oxygen consumption or ATP content in either muscle. These results suggest for the first time that stimulation of glycolysis and glycogenolysis in resting skeletal muscle by epinephrine or amylin is closely linked to stimulation of active Na+-K+transport.
Initial aerobic power does not alter muscle metabolic adaptations to short-term training
Authors: Green H. , Grant S. , Bombardier E. , Ranney D.
Published: December 2017

To investigate the hypothesis that training-induced increases in muscle mitochondrial potential are not obligatory to metabolic adaptations observed during submaximal exercise, regardless of peak aerobic power (V˙o2 peak) of the subjects, a short-term training study was utilized. Two groups of untrained male subjects ( n = 7/group), one with a high (HI) and the other with a low (LO)V˙o2 peak(means ± SE; 51.4 ± 0.90 vs. 41.0 ± 1.3 ml ⋅ kg−1⋅ min−1; P< 0.05), cycled for 2 h/day at 66–69% ofV˙o2 peakfor 6 days. Muscle tissue was extracted from vastus lateralis at 0, 3, and 30 min of standardized cycle exercise before training (0 days) and after 3 and 6 days of training and analyzed for metabolic and enzymatic changes. During exercise after 3 days of training in the combined HI + LO group, higher ( P < 0.05) concentrations (mmol/kg dry wt) of phosphocreatine (40.5 ± 3.4 vs. 52.2 ± 4.2) and lower ( P < 0.05) concentrations of Pi(61.5 ± 4.4 vs. 53.3 ± 4.4), inosine monophosphate (0.520 ± 0.19 vs. 0.151 ± 0.05), and lactate (37.9 ± 5.5 vs. 22.8 ± 4.8) were observed. These changes were also accompanied by reduced levels of calculated free ADP, AMP, and Pi. All adaptations were fully expressed by 3 min of exercise and by 3 days of training and were independent of initialV˙o2 peaklevels. Moreover, maximal activity of citrate synthase, a measure of mitochondrial capacity, was only increased with 6 days of training (5.71 ± 0.29 vs. 7.18 ± 0.37 mol ⋅ kg protein−1⋅ h−1; P < 0.05). These results demonstrate that metabolic adaptations to prolonged exercise occur within the first 3 days of training and during the non-steady-state period. Moreover, neither time course nor magnitude of metabolic adaptations appears to depend on increases in mitochondrial potential or on initial aerobic power.
Muscle net glucose uptake and glucose kinetics after endurance training in men
Authors: Bergman B. C. , Butterfield G. E. , Wolfel E. E. , Lopaschuk G. D. , Casazza G. A. , Horning M. A. , Brooks G. A.
Published: December 2017

We evaluated the hypotheses that alterations in glucose disposal rate (Rd) due to endurance training are the result of changed net glucose uptake by active muscle and that blood glucose is shunted to working muscle during exercise requiring high relative power output. We studied leg net glucose uptake during 1 h of cycle ergometry at two intensities before training [45 and 65% of peak rate of oxygen consumption (V˙o 2 peak)] and after training [65% pretrainingV˙o 2 peak, same absolute workload (ABT), and 65% posttrainingV˙o 2 peak, same relative workload (RLT)]. Nine male subjects (178.1 ± 2.5 cm, 81.8 ± 3.3 kg, 27.4 ± 2.0 yr) were tested before and after 9 wk of cycle ergometer training, five times a week at 75%V˙o 2 peak. The power output that elicited 66.0 ± 1.1% ofV˙o 2 peak before training elicited 54.0 ± 1.7% after training. Whole body glucose Rd decreased posttraining at ABT (5.45 ± 0.31 mg ⋅ kg−1 ⋅ min−1at 65% pretraining to 4.36 ± 0.44 mg ⋅ kg−1 ⋅ min−1) but not at RLT (5.94 ± 0.47 mg ⋅ kg−1 ⋅ min−1). Net glucose uptake was attenuated posttraining at ABT (1.87 ± 0.42 mmol/min at 65% pretraining and 0.54 ± 0.33 mmol/min) but not at RLT (2.25 ± 0.81 mmol/min). The decrease in leg net glucose uptake at ABT was of similar magnitude as the drop in glucose Rd and thus could explain dampened glucose flux after training. Glycogen degradation also decreased posttraining at ABT but not RLT. Leg net glucose uptake accounted for 61% of blood glucose flux before training and 81% after training at the same relative (65%V˙o 2 peak) workload and only 38% after training at ABT. We conclude that 1) alterations in active muscle glucose uptake with training determine changes in whole body glucose kinetics; 2) muscle glucose uptake decreases for a given, moderate intensity task after training; and 3) hard exercise (65%V˙o 2 peak) promotes a glucose shunt from inactive tissues to active muscle.
Measurement of gluconeogenesis and mass isotopomer analysis based on [U-13C]glucose
Authors: Radziuk Jerry , Lee W.-N. Paul
Published: December 2017

Two methods of measuring rates of gluconeogenesis based on label redistribution after the introduction of [U-13C]glucose into the whole body are examined. These methods are compared with methods previously derived for carbon-14 tracers. It is shown that the three approaches (stoichiometric, dilution, and combinatorial) are equivalent, provided the same set of assumptions are used. Barring a factor of two [see Am. J. Physiol. 270 ( Endocrinol. Metab. 33): E709–E717, 1996], the differences (∼10–15%) in the carbon-based dilutional and the molecule-based estimates of the rate of gluconeogenesis from published isotopomer data likely arise from small differences in the assumptions that concern the relative rate of label loss from the different isotopomers. The production of unlabeled substrate for glucose synthesis (phospho enolpyruvate) from the different isotopomers of lactate is shown to be a potential source of error in these methods. This error is estimated using models of the interaction of the gluconeogenetic pathway and the tricarboxylic acid (TCA) cycle and is shown to vary from negligible to 30% depending on the relative flux of the two pathways through the oxaloacetate pool. Because the estimates obtained by both methods considered are lower than is physiologically expected, some of the assumptions made may not hold. Future work will exploit the rich information content of isotopomer data to yield improved estimates.
Proline ameliorates arginine deficiency during enteral but not parenteral feeding in neonatal piglets
Authors: Brunton Janet A. , Bertolo Robert F. P. , Pencharz Paul B. , Ball Ronald O.
Published: December 2017

The indispensability of arginine has not been conclusively established in newborns. Because parenteral feeding bypasses the gut (where de novo synthesis of arginine occurs from proline), a dietary supply of arginine that is sufficient to maintain urea cycle function may be of greater importance during intravenous compared with enteral feeding. Two-day-old piglets ( n = 12) were fed nutritionally complete diets for 5 days via either a central vein catheter (IV pigs, n = 6) or a gastric catheter (IG pigs, n = 6). Subsequently, each piglet received three incomplete test diets [arginine free (−ARG/+PRO), proline free (−PRO/+ARG), or arginine and proline free (−ARG/−PRO)] in a randomized crossover design. Plasma ammonia was assayed every 30 min for 8 h or until hyperammonemia was observed. Ammonia increased rapidly in IV pigs receiving −ARG/+PRO and −ARG/−PRO (84 ± 36 and 74 ± 37 μmol ⋅ l−1 ⋅ h−1, respectively), requiring early diet cessation. A rapid increase was also exhibited by IG pigs receiving the −ARG/−PRO, but not the −ARG/+PRO diet (31 ± 15 vs. 11 ± 7 μmol ⋅ l−1 ⋅ h−1, respectively, P < 0.05). Plasma arginine and proline were indicative of deficiency (IG and IV groups) when deplete diets were infused. Arginine is indispensable in parenteral and enteral nutrition, independent of dietary proline.
Arterial KIC as marker of liver and muscle intracellular leucine pools in healthy and type 1 diabetic humans
Authors: Barazzoni R. , Meek S. E. , Ekberg K. , Wahren J. , Nair K. S.
Published: December 2017

In human protein turnover studies with isotopically labeled leucine (Leu) as a tracer, plasma ketoisocaproate (KIC) enrichment is extensively used as a surrogate measure of intracellular leucine enrichment. To test how accurately arterial ketoisocaproate (A-KIC) represents leucine isotopic enrichment in the hepatic (HV) and femoral veins (FV), which drain liver and muscle beds, we measured Leu and KIC enrichments in samples collected from HV, FV, and femoral artery (A) in 24 control and 6 type I diabetic subjects after a primed, continuous infusion ofl-[1-13C,15N]-Leu. Studies were performed during insulin deprivation or insulin replacement in the diabetic group, whereas the effect of normal saline or three different doses of insulin infusion (0.25, 0.50, and 1 mU ⋅ kg−1⋅ min−1) were assessed in healthy controls. The ratios of baseline isotopic enrichments of A-KIC to HV Leu and FV Leu were 0.93 ± 0.01 and 0.94 ± 0.02, respectively, in normal subjects and 1.07 ± 0.04 and 1.05 ± 0.03, respectively, in diabetic subjects ( P < 0.01, diabetic vs. normal subjects). Insulin did not change A-KIC-to-HV Leu ratios in either group, but the A-KIC-to-FV Leu ratio decreased during insulin infusion in normal subjects ( P < 0.05). In conclusion, A-KIC represents a reliable surrogate measure of HV Leu enrichment at different levels of circulating insulin in humans. The present data support the use of A-KIC as a surrogate precursor pool for hepatic protein synthesis.
In vivo regulation of protein-serine kinases by insulin in skeletal muscle of fructose-hypertensive rats
Authors: Bhanot Sanjay , Salh Baljinder S. , Verma Subodh , McNeill John H. , Pelech Steven L.
Published: December 2017

The effects of tail-vein insulin injection (2 U/kg) on the regulation of protein-serine kinases in hindlimb skeletal muscle were investigated in hyperinsulinemic hypertensive fructose-fed (FF) animals that had been fasted overnight. Basal protein kinase B (PKB) activity was elevated about twofold in FF rats and was not further stimulated by insulin. Phosphatidylinositol 3-kinase (PI3K), which lies upstream of PKB, was increased ∼3.5-fold within 2–5 min by insulin in control rats. Basal and insulin-activated PI3K activities were further enhanced up to 2-fold and 1.3-fold, respectively, in FF rats. The 70-kDa S6 kinase (S6K) was stimulated about twofold by insulin in control rats. Both basal and insulin-stimulated S6K activity was further enhanced up to 1.5-fold and 3.5-fold, respectively, in FF rats. In control rats, insulin caused a 40–50% reduction of the phosphotransferase activity of the β-isoform of glycogen synthase kinase 3 (GSK-3β), which is a PKB target in vitro. Basal GSK-3β activity was decreased by ∼40% in FF rats and remained unchanged after insulin treatment. In summary, 1) the PI3K → PKB → S6K pathway was upregulated under basal conditions, and 2) insulin stimulation of PI3K and S6K activities was enhanced, but both PKB and GSK-3 were refractory to the effects of insulin in FF rats.
A new model of cancer cachexia: contribution of the ubiquitin-proteasome pathway
Authors: Lazarus Douglas D. , Destree Antonia T. , Mazzola Laureen M. , McCormack Teresa A. , Dick Lawrence R. , Xu Bi , Huang Jian Q. , Pierce Jacqueline W. , Read Margaret A. , Coggins Michael B. , Solomon Vered , Goldberg Alfred L. , Brand Stephen J. , Elliott Peter J.
Published: December 2017

A new model of cachexia is described in which muscle protein metabolism related to the ubiquitin-proteasome pathway was investigated. Cloning of the colon-26 tumor produced a cell line, termed R-1, which induced cytokine (noninterleukin-1β, interleukin-6 and tumor necrosis factor-α)-independent cachexia. Implantation of R-1 cells in mice elicited significant (20–30%) weight loss and decreased blood glucose by 70%, and adipose tissue levels declined by 95% and muscle weights decreased by 20–25%. Food intake was unaffected. The decrease in muscle weight reflected a decline in insoluble, but not soluble, muscle protein that was associated with a significant increase in net protein degradation. The rate of ubiquitin conjugation of proteins was significantly elevated in muscles of cachectic mice. Furthermore, the proteasome inhibitor lactacystin blocked the increase in protein breakdown but had no significant effect on proteolysis. Several markers of the ubiquitin-proteasome pathway, E214kmRNA and E214kprotein and ubiquitin-protein conjugates, were not elevated. Future investigations with this new model should gain further insights into the mechanisms of cachexia and provide a background to evaluate novel and more efficacious therapies.
Leptin has acute effects on glucose and lipid metabolism in both lean and gold thioglucose-obese mice
Authors: Bryson Janet M. , Phuyal Jenny L. , Swan Verity , Caterson Ian D.
Published: December 2017

Leptin is reported to have effects in peripheral tissues that are independent of its central effects on food intake and body weight. In this study, the acute effects of a single dose of recombinant mouse leptin on lipid and glucose metabolism in lean and gold thioglucose-injected obese mice were examined. Changes were measured 2 h after leptin injection. In lean mice, liver and white adipose tissue (WAT) lipogenesis was inhibited. The activity of the pyruvate dehydrogenase complex (PDHCa), the rate-determining step for glucose oxidation, was reduced in heart, liver, quadriceps muscle, and both brown and white adipose tissues. Muscle and liver glycogen and liver triglyceride (TG) content was unchanged, but muscle TG was decreased. In obese mice, liver and WAT lipogenesis was inhibited and PDHCa reduced in heart and quadriceps muscle. Muscle and liver glycogen was decreased but not TG. Serum insulin was reduced in obese but not lean mice. These results are consistent with a role for leptin in the maintenance of steady-state energy stores by decreasing lipid synthesis and increasing fat mobilization, with decreased glucose oxidation occurring as a result of increased fatty acid oxidation.
Enhanced triglyceride clearance with intraperitoneal human acylation stimulating protein in C57BL/6 mice
Authors: Murray Ian , Sniderman Allan D. , Cianflone Katherine
Published: December 2017

Acylation stimulating protein (ASP), a novel adipocyte-derived autocrine protein, stimulates triglyceride synthesis and glucose transport in vitro in human and murine adipocytes. In vitro, chylomicrons increase ASP and precursor complement C3 production in adipocytes. Furthermore, in vivo, ASP production from human adipose tissue correlates positively with triglyceride clearance postprandially. The aim of the present study was to determine if intraperitoneally injected ASP accelerated triglyceride clearance in vivo after a fat load in C57Bl/6 mice. ASP increased the triglyceride clearance with a reduction of the triglyceride area under the curve over 6 h (AUC0–6) from 102.6 ± 30.0 to 61.0 ± 14.5 mg ⋅ dl−1⋅ h−1( P < 0.05), especially in the latter postprandial period (AUC3–6; 56.2 ± 18.0 vs. 24.9 ± 8.9 mg ⋅ dl−1⋅ h−1, P < 0.025). ASP also reduced plasma glucose both in the mice with accelerated plasma triglyceride clearance and in those with relatively delayed triglyceride clearance ( P < 0.025). Therefore, ASP alters postprandial triglyceride and glucose metabolism.
Triiodothyronine induces collagenase-3 and gelatinase B expression in murine osteoblasts
Authors: Pereira Renata C. , Jorgetti Vanda , Canalis Ernesto
Published: December 2017

Triiodothyronine (T3) increases bone resorption, but its effects on matrix metalloprotease (MMP) expression in bone are unknown. We tested the effects of T3on collagenase-3 and gelatinase A and B expression in MC3T3 osteoblastic cells. T3at 1 nM to 1 μM for 24–72 h increased collagenase-3 and gelatinase B mRNA levels, but it did not increase gelatinase A transcripts. In addition, T3increased immunoreactive collagenase and gelatinase activity. Cycloheximide prevented the stimulatory effect of T3on collagenase-3 but not on gelatinase B transcripts. Indomethacin did not prevent the effect of T3on either MMP. T3did not alter the decay of collagenase-3 or gelatinase B mRNA in transcriptionally arrested MC3T3 cells, and it increased the rate of collagenase-3 and gelatinase B gene transcription. Although T3enhanced the expression of the tissue inhibitor of metalloproteinase-1 in MC3T3 cells, it increased collagen degradation in cultured intact rat calvariae. In conclusion, T3increases collagenase-3 and gelatinase B synthesis in osteoblasts by transcriptional mechanisms. This effect may contribute to the actions of T3on bone matrix remodeling.
Glucose and amino acid kinetic response to graded infusion of rhIGF-I in the late gestation ovine fetus
Authors: Liechty Edward A. , Boyle David W. , Moorehead Helen , Lee Wei-Hua , Yang Xian-Lin , Denne Scott C.
Published: December 2017

Insulin-like growth factor I (IGF-I) has anabolic effects and is thought to be important in fetal development. The present study was designed to determine the dose response of recombinant human (rh) IGF-I on ovine fetal glucose and amino acid kinetics. Chronically catheterized fetal lambs were studied at 122–127 days gestation. The kinetics of leucine, phenylalanine, and glucose were measured before and during the infusion of rhIGF-I. rhIGF-I was infused into the fetal inferior vena cava at low, medium, or high rates (9.9, 20.1, or 40.2 nmol/h, respectively). A stepwise increase in serum IGF-I was achieved (164 ± 3, 222 ± 7, and 275 ± 5 ng/ml). Insulin concentrations were decreased at the medium and high rhIGF doses. The rate of appearance (Ra) of leucine and phenylalanine and leucine oxidation decreased. Phenylalanine appearance from protein breakdown was decreased, with a maximal suppression of 30% observed at the highest rate of infusion. Glucose Ra was increased at the medium and high doses; other aspects of glucose metabolism were unchanged. The change in both glucose Ra and suppression of proteolysis was significantly correlated to the rhIGF-I infusion rate. It is concluded that rhIGF-I exerts dose-related effects in the ovine fetus, increasing fetoplacental glucose turnover and causing significant suppression of both proteolysis and amino acid oxidation.
Potassium control of extrarenal renin secretion in transgenic (mRen-2)27 and normal rats
Authors: Rong Pei , Wilkinson-Berka Jennifer L. , Skinner Sandford L.
Published: December 2017

Plasma active renin and prorenin were followed for 12 h after bilateral, unilateral, and sham nephrectomy (BNx, UNx, and SNx) in anesthetized transgenic (mRen-2)27 rats to compare them with Sprague-Dawley and spontaneously hypertensive rats (SDR and SHR). In Ren-2 rats, active renin and prorenin increased with plasma potassium post-BNx and were augmented by potassium infusion. The increase in prorenin but not active renin was abolished by bilateral adrenalectomy (BADRx). However, this did not reduce prorenin below normal, indicating that the high plasma prorenin Ren-2 phenotype is not only of adrenal origin. SNx and UNx also raised plasma active renin and prorenin in Ren-2 rats, with positive correlations to plasma potassium. In SDR and SHR, active renin fell below prorenin post-BNx, and adrenal ablation and potassium loading (in SDR) modified the decreasing active renin profile consistent with low levels of regulated extrarenal secretion. In Ren-2 rats, adrenal but not extra-adrenal prorenin secretion is potassium sensitive and stress related. The unidentified source of active renin in BNx+BADRx Ren-2 rats is also potassium and stress related.