bluuebunny/crossref_metadata_2025 huggingface dataset:
Existence of two nonlinear elimination mechanisms for hepatocyte growth factor in rats
Authors: Liu Ke-Xin , Kato Yukio , Kato Motohiro , Kaku Tai-Ichi , Nakamura Toshikazu , Sugiyama Yuichi
Published: December 2017

Nonlinearity in the overall elimination of hepatocyte growth factor (HGF) was examined in rats. After intravenous administration, the plasma clearance (CLplasma) of HGF exhibited a dose-dependent biphasic reduction with high- and low-affinity components. If we consider our previous finding that both receptor-mediated endocytosis (RME) and a low-affinity uptake mechanism, probably mediated by heparan sulfate proteoglycan (HSPG), in the liver are major HGF clearance mechanisms, it may be that saturation of CLplasmaat lower and higher doses represents saturation of RME and HSPG-mediated uptake, respectively. At an HGF dose (1.46 nmol/kg), which completely saturates the high-affinity component, CLplasmawas almost completely reduced when HGF was premixed with heparin. However, CLplasmawas reduced by heparin to, at most, one-fifth that after HGF alone in a dose near the linear range (3.66 pmol/kg). Saturation of CLplasmafor HGF premixed with heparin was monophasic and nonlinear only at the lowest HGF doses. In vitro, high-affinity binding of [35S]heparin to HGF was found, showing that one HGF molecule binds to the penta- or hexasaccharide unit. Because mitogenic activity of HGF has been reported in the presence of heparin, these results suggest that heparin mainly inhibits low-affinity HGF uptake by complexing with HGF, whereas its effect on RME is relatively minor.
Role of the kidney in human leptin metabolism
Authors: Meyer Christian , Robson Dave , Rackovsky Noya , Nadkarni Veena , Gerich John
Published: December 2017

To assess the role of the human kidney in leptin metabolism, we measured renal leptin net balance and urinary leptin excretion in 16 normal postabsorptive volunteers with varying degrees of obesity. Arterial leptin concentrations (11.6 ± 2.7 ng/ml) significantly exceeded renal vein concentrations (10.3 ± 2.5 ng/ml, P < 0.001). Renal leptin fractional extraction averaged 13.1 ± 1.1%, and renal leptin net balance (uptake) averaged 1,070 ± 253 ng/min. Lineweaver-Burk analysis indicated that renal leptin uptake followed saturation kinetics with an apparent Michaelis-Menten constant of 10.9 ng/ml and maximal velocity of 1,730 ng/min. Leptin was generally undetectable in urine. Using literature values for systemic leptin clearance, we calculated that renal leptin uptake could account for ∼80% of all leptin removal from plasma. These data indicate that the human kidney plays a substantial role in leptin removal from plasma by taking up and degrading the peptide.
Interleukin-1β inhibits phospholipase C and insulin secretion at sites apart from KATPchannel
Authors: Vadakekalam Jacob , Rabaglia Mary E. , Metz Stewart A.
Published: December 2017

Although interleukin-1β (IL-1β) reduces pancreatic islet content of ATP and GTP, the distal events that mediate its inhibitory effects on insulin secretion remain poorly understood. Herein, the activation of phospholipase C (PLC) was quantified during islet perifusions. An 18-h exposure to IL-1β (100 pM) totally vitiated activation of PLC induced by glucose, an effect that requires ATP and GTP and closure of the ATP-dependent K+(KATP) channel. Surprisingly, however, when islets were depolarized directly using either of two agonists, glyburide (which does not act via generation of purine nucleotides) or 40 mM K+(which acts distal to KATPchannel), PLC and insulin secretion were again obliterated by IL-1β. IL-1β also reduced the labeling of phosphoinositide substrates; however, this effect was insufficient to explain the inhibition of PLC, since the effects on substrate labeling, but not on PLC, were prevented by coprovision of guanosine or adenosine. Furthermore, when IL-1β-treated islets were exposed to 100 μM carbachol (which activates PLC partially independent of extracellular Ca2+), the effects were still obliterated by IL-1β. These data (together with the finding that IL-1β inhibited Ca2+-induced insulin release) suggest that, in addition to its effects on ATP synthesis and thereby on the KATPchannel, IL-1β has at least two undescribed, distal effects to block both PLC as well as Ca2+-induced exocytosis. The latter correlated best with IL-1β’s effect to impede phosphoinositide synthesis, since it also was reversed by guanosine or adenosine.
Effects of age on the irregularity of LH and FSH serum concentrations in women and men
Authors: Pincus Steven M. , Veldhuis Johannes D. , Mulligan Thomas , Iranmanesh Ali , Evans William S.
Published: December 2017

We evaluated an apparent distinction between follicle-stimulating hormone (FSH) and luteinizing hormone (LH) dynamics: visually, it appears that the pattern of serum concentrations of FSH is more irregular than that of LH in younger human females. We studied healthy humans, with LH and FSH serum samples obtained every 10 min for 24 h. Three groups were studied: 24 young females [8 early follicular (EFol), 8 late follicular (LFol), and 8 midluteal (MLut)]; 8 postmenopausal females; and 17 males 21–79 yr of age. To quantify serial irregularity, we utilized approximate entropy (ApEn), a scale- and model-independent statistic. For young females, FSH was consistently more irregular than LH per subject: among the younger subjects, ApEn(FSH) − ApEn(LH) = 0.342 ± 0.270; ApEn(FSH) > ApEn(LH), P < 0.00001; ApEn(FSH) > ApEn(LH) for 23 of 24 subjects. For each cycle stage, pairwise ApEn(FSH) > ApEn(LH): P < 0.005 for both LFol and MLut, P < 0.01 for EFol. Notably, for the postmenopausal women, the irregularity difference vanished: ApEn(FSH) − ApEn(LH) = 0.008 ± 0.205. Males exhibited qualitatively similar results: ApEn(FSH) − ApEn(LH) was significantly and negatively correlated with age ( r = −0.75, P = 0.0006). The capability to quantify (the extent of) differences between FSH and LH release, beyond the general 1:1 correspondence between primary LH and FSH pulses, suggests a means to assess bihormonal changes as a clinical marker of altered reproductive status in a variety of settings, e.g., a perimenopausal milieu. Mechanistically, the erosion of unequal FSH-LH regularity with age is consistent with a loss of synchrony control within the integrated hypothalamo-pituitary-gonadal axis.
Influence of thyroid status on hepatic α1-adrenoreceptor responsiveness
Authors: Daza Francisco J. , Parrilla Roberto , Martín-Requero Angeles
Published: December 2017

The present work aimed to elucidate the influence of thyroid functional status on the α1-adrenoreceptor-induced activation of hepatic metabolic functions. The experiments were performed in either a nonrecirculating liver perfusion system featuring continuous monitoring of portal pressure,[Formula: see text], pCa, and pH, or isolated hepatocytes from euthyroid, hyperthyroid, and hypothyroid rats. Hypothyroidism decreased the α1-adrenergic stimulation of respiration, glycogen breakdown, and gluconeogenesis. These effects were accompanied by a decreased intracellular Ca2+mobilization corroborating that those processes are regulated by the Ca2+-dependent branch of the α1-adrenoreceptor signaling pathway. Moreover, in hyperthyroid rats the α1-adrenergic-induced increase in cytosolic Ca2+was enhanced, and glucose synthesis or mobilization was not altered. The thyroid status influenced neither the α1-adrenergic stimulation of vascular smooth muscle contraction nor the α1-agonist-induced intracellular alkalinization and protein kinase C (PKC) activation. Thus the distinct impairment of the Ca2+-dependent branch of the α1-adrenoreceptor signaling pathway by thyroid status provides a useful tool to investigate the role played by each signaling pathway, Ca2+or PKC, in controlling hepatic functions.
Catecholamines increase monocyte TNF receptors and inhibit TNF through β2-adrenoreceptor activation
Authors: Guirao Xavier , Kumar Ashwini , Katz Joshua , Smith Michelle , Lin Edward , Keogh Chris , Calvano Steve E. , Lowry Stephen F.
Published: December 2017

Postinjury deficits in monocyte tumor necrosis factor receptors (moTNFR) activity may alter beneficial functions during an inflammatory response. Several counter-regulatory hormones elicited during inflammation may modulate tumor necrosis factor (TNF) activity, but little is known about their influence on moTNFR. Also, catecholamines inhibit TNF production, but the adrenoreceptor mechanism of this effect has not been fully clarified. To determine the effect of catecholamines and corticosteroids on moTNFR, whole blood was coincubated for up to 8 (moTNFR) or 24 h (cytokines) in the presence of lipopolysaccharide (100 ng/ml) and 1) epinephrine (Epi, 10−6M), dexamethasone (Dex, 10−6M) or both (EpiDex, 10−6M) to assess the expression of total moTNFR, moTNFR-I, and moTNFR-II. 2) Epi and norepinephrine (EpiNE, 10−6M) and the α1+2-, β1+2-, β1-, or β2-adrenergic antagonists were used to assess the role of such adrenoreceptors on total moTNFR and TNF production, and N6,2′- O-dibutyryl adenosine 3′,5′-cyclic monophosphate (DBcAMP) alone or in combination with the phosphodiesterase inhibitor Ro-20–1724/000, to study the cAMP-dependent pathway on total moTNFR. We found that Epi upregulated total moTNFR and moTNFR-II. Dex did not significantly influence total moTNFR or moTNFR-II. Also, EpiNE increased total moTNFR and inhibited TNF by a β2-dependent mechanism. DBcAMP (10−5M) modestly enhanced total moTNFR. This suggests a common mechanism for acutely enhancing moTNFR and attenuation of soluble TNF appearance during conditions of severe stress.
Role of endothelins in regulation of vascular tone in the in situ perfused rat adrenals
Authors: Mazzocchi Giuseppina , Malendowicz Ludwik K. , Musajo Francesco G. , Gottardo Giuseppe , Markowska Anna , Nussdorfer Gastone G.
Published: December 2017

This study examined the role of endothelins (ETs) and their receptor subtypes ETAand ETB in the regulation of vascular tone in the in situ perfused rat left adrenal gland. Endothelin-1 (ET-1), which binds both ETA and ETB receptors, decreased adrenal flow rate of the perfusion medium, and its effect was reversed by the ETA antagonist BQ-123 and enhanced by the ETB antagonist BQ-788. ET-3, which preferentially binds ETB, and the selective ETB agonist BQ-3020 increased adrenal flow rate of perfusate, and their effects were annulled by BQ-788. BQ-123 magnified the effect of ET-3 and did not affect that of BQ-3020. The ETA-mediated decrease and the ETB-mediated rise in the rate of collection of perfusate were abolished by Ro-31–8220, an inhibitor of protein kinase C (PKC), and by N G-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase (NOS), respectively. Collectively, these findings suggest that ETs can regulate vascular tone in the in situ perfused rat adrenals via both PKC-coupled ETA and NOS-coupled ETB receptors, the activation of which evokes vasoconstriction and vasodilation, respectively.
Hindlimb unloading in rat decreases preosteoblast proliferation assessed in vivo with BrdU incorporation
Authors: Barou Odile , Palle Sabine , Vico Laurence , Alexandre Christian , Lafage-Proust Marie-Hélène
Published: December 2017

Immobilization affects bone formation. However, the mechanisms regulating the decrease in osteoblast recruitment remain unclear. The aim of our study was to determine in vivo osteoblastic proliferation after short-term immobilization among the different bone compartments. Twelve Wistar 5-wk-old rats were assigned to two groups: six tail-suspended animals for 6 days and their six age-related controls. Osmotic minipumps, each containing 40 mg of bromodeoxyuridine (BrdU), were implanted intraperitoneally at day 4 until euthanasia. Histomorphometric measurements found a significantly lower bone volume in primary (ISP, −22%) and secondary spongiosa (IISP, −37%) in unloaded rats compared with their age-related controls. BrdU immunohistochemistry showed that the proliferation capacity of osteogenic precursors in ISP (−29%) and preosteoblasts in IISP (−80%) and in periosteum as well as bone marrow cells (−40%) was lowered by unloading. We demonstrated in vivo for the first time that 6-day tail suspension induced a significant decrease in proliferation of periosteal and trabecular preosteoblasts in ISP and IISP as well as in bone marrow cells.
Fat metabolism in formerly obese women
Authors: Ranneries Claudia , Bülow Jens , Buemann Benjamin , Christensen Niels Juel , Madsen Joop , Astrup Arne
Published: December 2017

An impaired fat oxidation has been implicated to play a role in the etiology of obesity, but it is unclear to what extent impaired fat mobilization from adipose tissue or oxidation of fat is responsible. The present study aimed to examine fat mobilization from adipose tissue and whole body fat oxidation stimulated by exercise in seven formerly obese women (FO) and eight matched controls (C). Lipolysis in the periumbilical subcutaneous adipose tissue, whole body energy expenditure (EE), and substrate oxidation rates were measured before, during, and after a 60-min bicycle exercise bout of moderate intensity. Lipolysis was assessed by glycerol release using microdialysis and blood flow measurement by 133Xe clearance technique. The FO women had lower resting EE than C (3.77 ± 1.01 vs. 4.88 ± 0.74 kJ/min, P < 0.05) but responded similarly to exercise. Adipose tissue glycerol release was twice as high in FO than in C at rest (0.455 ± 0.299 vs. 0.206 ± 0.102 μmol ⋅ 100 g−1 ⋅ min−1, P < 0.05) but increased similarly in FO and C in response to exercise. Despite higher plasma nonesterified fatty acids (NEFA) in FO ( P < 0.001), fat oxidation rates during rest and recovery were lower in FO than in C (1.32 ± 0.84 vs. 3.70 ± 0.57 kJ/min, P < 0.02) and fat oxidation for a given plasma NEFA concentration was lower at rest ( P < 0.001) and during exercise ( P = 0.01) in the formerly obese group. In conclusion, fat mobilization both at rest and during exercise is intact in FO, whereas fat oxidation is subnormal despite higher circulation NEFA levels. The lower resting EE and the failure to use fat as fuel contribute to a positive fat balance and weight gain in FO subjects.
Perfused rat hindlimb is suitable for skeletal muscle glucose transport measurements
Authors: Wojtaszewski Jørgen F. P. , Jakobsen Allan B. , Ploug Thorkil , Richter Erik A.
Published: December 2017

It has been postulated that the perfused rat hindlimb is unsuitable for measurements of muscle glucose transport [P. Hansen, E. Gulve, J. Gao, J. Schluter, M. Mueckler, and J. Holloszy. Am. J. Physiol. 268 ( Cell Physiol. 37): C30–C35, 1995]. The aim of the present study was therefore to critically evaluate the suitability of this preparation for glucose transport measurements using the extracellular marker mannitol and the glucose analogs 3- O-methyl-d-glucose or 2-deoxy-d-glucose. In all three muscle fiber types studied, the rate of 2-deoxy-d-glucose uptake during perfusion was linear from 1 to 40 min during maximal insulin stimulation and from 1 to 15 min during maximal electrical stimulation. Uptake of 2-deoxy-d-glucose was not increased by an increase in perfusate flow. Combined stimulation with a maximal insulin concentration and electrical stimulation elicited additive effects on 2-deoxy-d-glucose uptake in slow- and fast-twitch oxidative but not in fast-twitch glycolytic muscle fibers. Furthermore, in muscles having high glucose transport capacities 3- O-methyl-d-glucose is less suitable than 2-deoxy-d-glucose because of rapidly developing nonlinearity of accumulation. Our findings clearly demonstrate that the perfused hindlimb is suitable for measurements of muscle glucose transport and that the most feasible glucose analog for this purpose is 2-deoxy-d-glucose.
Increased hepatic glucose production response to glucagon in trained subjects
Authors: Drouin Réjean , Lavoie Carole , Bourque Josée , Ducros Francine , Poisson Danielle , Chiasson Jean-Louis
Published: December 2017

This study was designed to characterize the impact of endurance training on the hepatic response to glucagon. We measured the effect of glucagon on hepatic glucose production (HGP) in resting trained ( n = 8) and untrained ( n = 8) healthy male subjects (maximal rate of O2consumption: 65.9 ± 1.6 vs. 46.8 ± 0.6 ml O2⋅ kg−1⋅ min−1, respectively, P < 0.001). Endogenous insulin and glucagon were suppressed by somatostatin (somatotropin release-inhibiting hormone) infusion (450 μg/h) over 4 h. Insulin (0.15 mU ⋅ kg−1⋅ min−1) was infused throughout the study, and glucagon (1.5 ng ⋅ kg−1⋅ min−1) was infused over the last 2 h. During the latter period, plasma glucagon and insulin remained constant at 138.2 ± 3.1 vs. 145.3 ± 2.1 ng/l and at 95.5 ± 4.5 vs. 96.2 ± 1.9 pmol/l in trained and untrained subjects, respectively. Plasma glucose increased and peaked at 11.4 ± 1.1 mmol/l in trained subjects and at 8.9 ± 0.8 mmol/l in untrained subjects ( P < 0.001). During glucagon stimulation, the mean increase in HGP area under the curve was 15.8 ± 2.8 mol ⋅ kg−1⋅ min−1in trained subjects compared with 7.4 ± 1.6 mol ⋅ kg−1⋅ min−1in untrained subjects ( P < 0.01) over the first hour and declined to 6.8 ± 2.8 and 4.9 ± 1.4 mol ⋅ kg−1⋅ min−1during the second hour. In conclusion, these observations indicate that endurance training is associated with an increase in HGP in response to physiological levels of glucagon, thus suggesting an increase in hepatic glucagon sensitivity.
Regulation of fatty acid transport protein and fatty acid translocase mRNA levels by endotoxin and cytokines
Authors: Memon Riaz A. , Feingold Kenneth R. , Moser Arthur H. , Fuller John , Grunfeld Carl
Published: December 2017

The cloning of two novel fatty acid (FA) transport proteins, FA transport protein (FATP) and FA translocase (FAT), has recently been reported; however, little is known about their in vivo regulation. Endotoxin [lipopolysaccharide (LPS)], tumor necrosis factor (TNF), and interleukin-1 (IL-1) stimulate adipose tissue lipolysis and enhance hepatic lipogenesis and reesterification while suppressing FA oxidation in multiple tissues. Hence, in this study we examined their effects on FATP and FAT mRNA levels in Syrian hamsters. Our results demonstrate that LPS decreased FATP and FAT mRNA expression in adipose tissue, heart, skeletal muscle, brain, spleen, and kidney, tissues in which FA uptake and/or oxidation is decreased during sepsis. In the liver, where FA oxidation is decreased during sepsis but the uptake of peripherally derived FA is increased to support reesterifiation, LPS decreased FATP mRNA expression by 70–80% but increased FAT mRNA levels by four- to fivefold. The effects of LPS on FATP and FAT mRNA levels in liver were observed as early as 4 h after administration and were maximal by 16 h. TNF and IL-1 mimicked the effect of LPS on FATP and FAT mRNA levels in both liver and adipose tissue. These results indicate that the mRNAs for both transport proteins are downregulated by LPS in tissues in which FA uptake and/or oxidation are decreased during sepsis. On the other hand, differential regulation of FATP and FAT mRNA in liver raises the possibility that these proteins may be involved in transporting FA to different locations inside the cell. FATP may transport FA toward mitochondria for oxidation, which is decreased in sepsis, whereas FAT may transport FA to cytosol for reesterification, which is enhanced in sepsis.
Reduced glucose clearance as the major determinant of postabsorptive hyperglycemia in diabetic rats
Authors: Wi Jae K. , Kim Jason K. , Youn Jang H.
Published: December 2017

The relationships between postabsorptive glucose concentration and hepatic glucose output (HGO) and glucose clearance were studied in rats one day after treatment with various doses of streptozotocin (STZ; 0, 15, 30, 40, 50, or 75 mg/kg; n = 6 per dose; study 1). Glucose fluxes were estimated using a prolonged (6-h) infusion of [3-3H]glucose to ensure complete tracer equilibration at hyperglycemia. Postabsorptive glucose was significantly increased at the high doses of STZ (50 and 75 mg/kg; P < 0.01) and was strongly correlated with glucose clearance across all doses ( r = −0.85, P < 0.001) but less strongly with HGO ( r = 0.46, P < 0.01). In the group treated with 50 mg/kg STZ, postabsorptive glucose was increased twofold compared with the control (i.e., zero dose) group, with no change in HGO and a 45% decrease in glucose clearance, indicating that the hyperglycemia was due to a decrease in glucose clearance. To understand the cellular mechanisms of decreased glucose clearance in STZ diabetic rats, skeletal muscle glucose clearance and intracellular glucose and glucose 6-phosphate (G-6- P) concentrations were determined in normal and STZ (50 mg/kg) diabetic rats at their postabsorptive glucose levels as well as at matched hyperglycemia (12 mM; study 2). Glucose clearance was significantly decreased in soleus ( P< 0.05) muscles of the diabetic rats, and this was associated with significantly decreased intracellular glucose and G-6- P levels at matched hyperglycemia ( P < 0.05), suggestive of decreased glucose transport. In conclusion, postabsorptive hyperglycemia in STZ diabetic rats was largely due to decreased glucose clearance, although increased HGO may also have been a contributing factor at the highest STZ dose. The decrease in postabsorptive glucose clearance in STZ diabetic rats appeared to be associated with an impairment of glucose transport in soleus (type I) muscles.
Nutritional state regulates insulin receptor and IRS-1 phosphorylation and expression in chicken
Authors: Dupont Joëlle , Derouet Michel , Simon Jean , Taouis Mohammed
Published: December 2017

After insulin binding, insulin receptors (IR) phosphorylate the insulin receptor substrate 1 (IRS-1) on specific motifs and thereby initiate insulin action. The interaction between IR and IRS-1 and their expression were studied in vivo in two target tissues (muscle and liver) in chickens, a species that is insulin resistant. To induce extreme changes in plasma insulin levels, chickens were subjected to three different nutritional states (ad libitum fed, fasted for 48 h, and refed for 30 min after 48-h fast). Liver membrane IR number was significantly increased in fasted compared with fed chickens. This upregulation of IR number was concomitant with the an enhanced expression of IR mRNA as determined by reverse transcription-polymerase chain reaction. In leg muscle, IR mRNA was not altered by the nutritional state. Using specific antibodies directed toward human IR, anti-phosphotyrosines, or mouse IRS-1, we demonstrated that IR and IRS-1 are associated in vivo in liver and muscles. Tyrosine phosphorylation of liver IR and IRS-1 were significantly decreased by prolonged fasting and restored by 30-min refeeding. These alterations were not observed in muscle. Fasting increased IRS-1 mRNA expression in liver but not in muscle. These results are the first evidence showing that chicken liver and muscle express IRS-1. Therefore, the chicken insulin resistance is not accounted for by the lack of IRS-1. The differences observed for the regulation of IR and IRS-1 messengers and phosphorylation between liver and muscle in response to alterations of the nutritional state remain to be explained.
Role of human liver lipogenesis and reesterification in triglycerides secretion and in FFA reesterification
Authors: Diraison Frederique , Beylot Michel
Published: December 2017

To measure 1) the contribution of hepatic de novo lipogenesis (DNL) and plasma free fatty acid (FFA) reesterification to plasma triglyceride (TG) secretion, and 2) the role of oxidation and hepatic and extrahepatic reesterification in FFA utilization, five normal subjects drank deuterated water and were infused (postabsorptive state) with [1-13C]palmitate and [1,2,3-2H5]glycerol. Total lipid oxidation (Lox) was measured by indirect calorimetry. FFA oxidation (2.76 ± 0.65 μmol ⋅ kg−1⋅ min−1) accounted for 45% of FFA turnover rate (Rt) (1.04 μmol ⋅ kg−1⋅ min−1) and 91% of Lox; FFA reesterification was 3.27 ± 0.54 μmol ⋅ kg−1⋅ min−1. Fractional and absolute TG Rtwere 0.21 ± 0.02 h−1and 0.11 ± 0.05 μmol ⋅ kg−1⋅ min−1. DNL accounted for 3.9 ± 0.9% of TG secretion, and hepatic FFA reesterification accounted for 49.4 ± 5.7%; this last process represented a utilization of FFA of 0.16 ± 0.02 μmol ⋅ kg−1⋅ min−1. We conclude that, in the postabsorptive state, 1) DNL and FFA reesterification account for only 50–55% of TG secretion, the remaining presumably being provided by stored lipids or lipoproteins taken up by liver, 2) most reesterification occurs in extrahepatic tissues, and 3) oxidation and reesterification each contribute about one-half to FFA utilization; FFA oxidation accounts for almost all Lox.
Physiological plasma levels of androgens reduce bone loss in the ovariectomized rat
Authors: Lea C. K. , Flanagan A. M.
Published: December 2017

The effect of androstenedione (ADIONE) slow-release pellets on cancellous bone volume (BV/TV) at the tibial metaphysis was investigated in ovariectomized (OVX) rats at various times from 21 to 180 days. Plasma levels of ADIONE and testosterone (T) in OVX rats were significantly reduced at 21 days and were restored close to levels in the sham rats with the 1.5-mg ADIONE pellet. OVX animals with and without ADIONE pellets resulted in close to a 50% reduction in BV/TV by day 21. By day 180, OVX rats had only ∼5% BV/TV, whereas that in ADIONE-treated OVX rats was significantly greater at ∼12%. The reduced BV/TV was associated with increased bone resorption and formation. In a separate 90-day experiment, we found that the antiandrogen, Casodex, abrogated the ADIONE-induced skeletal-protective effect in OVX rats, whereas the antiaromatase, Arimidex, had no effect. This provides evidence that ADIONE protects against the development of osteopenia in the estrogen-deficient rat and mediates its effect through androgens and not estrogens.
Muscle acetyl group availability is a major determinant of oxygen deficit in humans during submaximal exercise
Authors: Timmons James A. , Gustafsson Thomas , Sundberg Carl Johan , Jansson Eva , Greenhaff Paul L.
Published: December 2017

The delay in skeletal muscle mitochondrial ATP production at the onset of exercise is thought to be a function of a limited oxygen supply. The delay, termed the oxygen deficit, can be quantified by assessing the above baseline oxygen consumption during the first few minutes of recovery from exercise. During submaximal exercise, the oxygen deficit is reflected by the extent of muscle phosphocreatine (PCr) breakdown. In the present study, nine male subjects performed 8 min of submaximal, single leg knee extension exercise after saline (Control) and dichloroacetate (DCA) infusion on two separate occasions. Administration of DCA increased resting skeletal muscle pyruvate dehydrogenase complex activation status threefold (Control = 0.4 ± 0.1 vs. DCA = 1.3 ± 0.1 mmol acetyl-CoA ⋅ min−1⋅ kg wet muscle−1at 37°C, P < 0.01) and elevated acetylcarnitine concentration fivefold (Control = 2.2 ± 0.5 vs. DCA = 10.9 ± 1.2 mmol/kg dry mass, P < 0.01). During exercise, PCr degradation was reduced by ∼50% after DCA (Control = 33.2 ± 7.1 vs. DCA = 18.4 ± 7.1 mmol/kg dry mass, P < 0.05). It would appear, therefore, that in humans acetyl group availability is a major determinant of the rate of increase in mitochondrial respiration at the onset of exercise and hence the oxygen deficit.
Contraction duration affects metabolic energy cost and fatigue in skeletal muscle
Authors: Hogan Michael C. , Ingham Erica , Kurdak S. Sadi
Published: December 2017

It has been suggested that during a skeletal muscle contraction the metabolic energy cost at the onset may be greater than the energy cost related to holding steady-state force. The purpose of the present study was to investigate the effect of contraction duration on the metabolic energy cost and fatigue process in fully perfused contracting muscle in situ. Canine gastrocnemius muscle ( n = 6) was isolated, and two contractile periods (3 min of isometric, tetanic contractions with 45-min rest between) were conducted by each muscle in a balanced order design. The two contractile periods had stimulation patterns that resulted in a 1:3 contraction-to-rest ratio, with the difference in the two contractile periods being in the duration of each contraction: short duration 0.25-s stimulation/0.75-s rest vs. long duration 1-s stimulation/3-s rest. These stimulation patterns resulted in the same total time of stimulation, number of stimulation pulses, and total time in contraction for each 3-min period. Muscle O2uptake, the fall in developed force (fatigue), the O2cost of developed force, and the estimated total energy cost (ATP utilization) of developed force were significantly greater ( P < 0.05) with contractions of short duration. Lactate efflux from the working muscle and muscle lactate concentration were significantly greater with contractions of short duration, such that the calculated energy derived from glycolysis was three times greater in this condition. These results demonstrate that contraction duration can significantly affect both the aerobic and anaerobic metabolic energy cost and fatigue in contracting muscle. In addition, it is likely that the greater rate of fatigue with more rapid contractions was a result of elevated glycolytic production of lactic acid.
Food restriction alters pregnancy-associated changes in IGF and IGFBP in the guinea pig
Authors: Sohlström A. , Katsman A. , Kind K. L. , Roberts C. T. , Owens P. C. , Robinson J. S. , Owens J. A.
Published: December 2017

The effect of moderate food restriction on pregnancy-associated changes in weight gain, body composition, and circulating insulin-like growth factors (IGF) I and II and IGF-binding proteins (IGFBP)-1 through -4 and their relationship was determined in the guinea pig. Pregnancy did not stimulate weight gain but reduced fat deposition in ad libitum-fed animals and increased weight gain and fat deposition in food-restricted animals relative to their respective virginal group. Pregnancy increased the abundance of circulating IGF-I regardless of food intake and increased that of IGF-II in food-restricted animals only. Pregnancy also increased circulating IGFBP-1 and -2 in ad libitum-fed and food-restricted animals and IGFBP-4 in ad libitum-fed animals. Multiple regression analysis showed that maternal weight gain was negatively associated with circulating IGF-II and IGFBP-2. Fetal weight was positively associated with maternal circulating IGF-II and negatively associated with maternal circulating IGFBP-1 and -2. Significant interactions indicate, however, that the role of IGF-II and IGFBP-1 on fetal growth is dependent on the nutritional status of the mother.
Diurnal rhythm returns to normal after elimination of portacaval shunting
Authors: Hawkins Paul A. , Dejoseph Mary R. , Hawkins Richard A.
Published: December 2017

Previous studies showed that portacaval shunting causes metabolic and behavioral changes in rats. Most metabolic changes reversed within 1–2 wk after restoration of normal circulation. However, the rate of cerebral glucose metabolism (CMRGlc) remained depressed in some areas. The question arose whether complete recovery was possible. Therefore, a long-term behavioral study was undertaken to determine the time course of recovery. Diurnal activity was monitored for 48 h each week over a period of 14 wk: 2 wk before shunting, 6 wk after shunting, and 6 wk after restoration of normal hepatic circulation. Nighttime activity was depressed within 1 wk of shunting and did not change. Normal circulation to the liver was reestablished after 6 wk. The diurnal cycle was normal 3 wk later. Thus, although recovery of the diurnal rhythm is possible, the relatively long period necessary suggests the correction of a significant structural or chemical abnormality. A study of CMRGlcwas made using the behavioral study as an index of the time necessary for recovery. CMRGlcreturned to normal throughout the brain 6 wk after cessation of shunting except in the hippocampus and amygdala (7–8% decrease).
Ovariectomy augments B lymphopoiesis and generation of monocyte-macrophage precursors in rat bone marrow
Authors: Erben Reinhold G. , Raith Sylvia , Eberle Johannes , Stangassinger Manfred
Published: December 2017

To investigate the effects of estrogen depletion on hematopoiesis and bone turnover, female rats were either ovariectomized (OVX) or sham operated and killed at 1, 2, 3, and 4 wk postsurgery. Flow cytometric analysis of bone marrow cells (BMC) revealed that, in close temporal association with the rise in bone turnover as measured by bone histomorphometry, the number of Thy 1.1+and KiB1R+BMC increased two- to threefold in OVX rats relative to sham controls. The Thy 1.1+BMC were further characterized as Thy 1.1+/KiB1R+and Thy 1.1+/HIS24+double-positive cells of the B cell lineage. A transient rise in ED1+myeloid cells expressing a lysosomal antigen specific for the monocyte-macrophage and osteoclast lineage coincided with the upregulation of osteoclast numbers in OVX rats at 2 wk postsurgery, but the number of ED8+myelomonocytic BMC remained unchanged. Administration of estradiol prevented the rise in Thy 1.1+, KiB1R+, and ED1+BMC in OVX animals. Our study indicates that ovariectomy upregulates B lymphopoiesis in rat bone marrow and increases myeloid cell differentiation into the monocyte-macrophage and possibly also the osteoclast lineage.
Glucose stimulates transcription of fatty acid synthase and malic enzyme in avian hepatocytes
Authors: Hillgartner F. Bradley , Charron Tina
Published: December 2017

Transcription of fatty acid synthase (FAS) and malic enzyme (ME) in avian liver is low during starvation or feeding a low-carbohydrate, high-fat diet and high during feeding a high-carbohydrate, low-fat diet. The role of glucose in the nutritional control of FAS and ME was investigated by determining the effects of this metabolic fuel on expression of FAS and ME in primary cultures of chick embryo hepatocytes. In the presence of triiodothyronine, glucose (25 mM) stimulated an increase in the activity and mRNA abundance of FAS and ME. These effects required the phosphorylation of glucose to glucose 6-phosphate but not further metabolism downstream of the aldolase step of the glycolytic pathway. Xylitol mimicked the effects of glucose on FAS and ME expression, suggesting that an intermediate of the pentose phosphate pathway may be involved in mediating this response. The effects of glucose on the mRNA abundance of FAS and ME were accompanied by similar changes in transcription of FAS and ME. These data support the hypothesis that glucose plays a role in mediating the effects of nutritional manipulation on transcription of FAS and ME in liver.
Insulin sensitivity and glucose effectiveness: minimal model analysis of regular and insulin-modified FSIGT
Authors: Pacini Giovanni , Tonolo Giancarlo , Sambataro Maria , Maioli Mario , Ciccarese Milco , Brocco Enrico , Avogaro Angelo , Nosadini Romano
Published: December 2017

The minimal model is widely used to evaluate insulin action on glucose disappearance from frequently sampled intravenous glucose tolerance tests (FSIGT). The common protocols are a regular (rFSIGT, single injection of 0.3 g/kg of glucose) and an insulin-modified test (mFSIGT, with an additional insulin administration at 20 min). This study compared the insulin sensitivity index (SI) and glucose effectiveness (SG) obtained in the same individual (16 normal subjects) with the two tests. SI was 7.11 ± 0.80 10−4 ⋅ min−1 ⋅ μU−1 ⋅ ml in rFSIGT and 6.96 ± 0.83 in mFSIGT ( P = 0.656), regression r = 0.92, P < 0.0001; SG was 0.0260 ± 0.0028 min−1 and 0.0357 ± 0.0052, respectively, statistically different ( P = 0.013) but still with a good regression ( r = 0.66, P = 0.0051). SG and insulin amount during the early period correlated ( r = 0.6, P = 0.015 in rFSIGT and r = 0.76, P = 0.0006 in mFSIGT). In summary, both FSIGTs with minimal model analysis provide the same SI, which is a very robust index. SG was different by 28% due probably to the relationship between SG and the amount of circulating insulin. In studies comparing groups, the simpler rFSIGT can still be used with the advantage of accounting for endogenous insulin, thus offering the possibility of direct inferences on the β-cell activity.
On the mechanism of lactational anovulation in the rhesus monkey
Authors: Ördög Tamás , Chen Ming-Dao , O’Byrne Kevin T. , Goldsmith Jason R. , Connaughton Martin A. , Hotchkiss Julane , Knobil Ernst
Published: December 2017

The relative roles of infant suckling and of maternal prolactin (PRL) secretion in lactational anovulation were studied in ovary-intact and ovariectomized rhesus monkeys nursing young that had been removed from their natural mothers. Hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator activity was monitored electrophysiologically in freely behaving animals by radiotelemetry. Serum luteinizing hormone, PRL, estradiol, and progesterone were also measured. Suckling inhibited GnRH pulse generator activity and ovarian cyclicity in all ovary-intact females but had no such effect on the pulse generator in long-term ovariectomized animals. When PRL secretion was suppressed by daily bromocriptine administration, GnRH pulse generator activity remained significantly inhibited and ovulation was prevented in four monkeys (6 trials), whereas in two females (6 trials) a rapid increase in pulse generator frequency and the resumption of ovarian cyclicity were observed although suckling activity was maintained. One monkey displayed both response types. Although these results indicate that suckling per se is able to restrain GnRH pulse generator activity in the absence of PRL, they also suggest that the relative importance of these determinants is variable depending on factors that remain to be determined. The present study also confirms the permissive role of the ovary in the lactational suppression of GnRH pulse generator activity.
Epinephrine translocates GLUT-4 but inhibits insulin-stimulated glucose transport in rat muscle
Authors: Han Xiao-Xia , Bonen Arend
Published: December 2017

We examined the effects of epinephrine (25, 50, and 150 nM) on 1) basal and insulin-stimulated 3- O-methylglucose (3-MG) transport in perfused rat muscles and 2) GLUT-4 in skeletal muscle plasma membranes. Insulin increased glucose transport 330–600% in three types of skeletal muscle [white (WG) and red (RG) gastrocnemius and soleus (SOL)]. Glucose transport was also increased by epinephrine (22–48%) in these muscles ( P < 0.05). In contrast, the insulin-stimulated 3-MG transport was reduced by epinephrine in all three types of muscles; maximal reductions were observed at 25 nM epinephrine in WG (−25%) and RG (−32.5%). A dose-dependent decrease occurred in SOL (−27% at 25 nM; −55% at 150 nM, P < 0.05). Insulin (20 mU/ml) and epinephrine (150 nM) each translocated GLUT-4 to the plasma membrane, and no differences in translocation were observed between insulin and epinephrine ( P > 0.05). In addition, epinephrine did not inhibit insulin-stimulated GLUT-4 translocation, and the combined epinephrine and insulin effects on GLUT-4 translocation were not additive. The increase in surface GLUT-4 was associated with increases in muscle cAMP concentrations, but only when epinephrine alone was present. No relationship was evident between muscle cAMP concentrations and surface GLUT-4 in the combined epinephrine and insulin-stimulated muscles. These studies indicate that epinephrine can translocate GLUT-4 while at the same time increasing glucose transport when insulin is absent, or can inhibit glucose transport when insulin is present.
Effect of insulin on glycerol production in obese adolescents
Authors: Robinson Childsy , Tamborlane William V. , Maggs David G. , Enoksson Staffan , Sherwin Robert S. , Silver David , Shulman Gerald I. , Caprio Sonia
Published: December 2017

Impaired stimulation of glucose metabolism and reduced suppression of lipolytic activity have both been suggested as important defects related to the insulin resistance of adolescent obesity. To further explore the relationship between these abnormalities, we studied seven obese [body mass index (BMI) 35 ± 2 kg/m2] and seven lean (BMI 21 ± 1 kg/m2) adolescents aged 13–15 yr and compared them with nine lean adults (aged 21–27 yr, BMI 23 ± 1 kg/m2) during a two-step euglycemic-hyperinsulinemic clamp in combination with 1) a constant [2H5]glycerol (1.2 mg ⋅ m−2⋅ min−1) infusion to quantify glycerol turnover and 2) indirect calorimetry to estimate glucose and net lipid oxidation rates. In absolute terms, basal glycerol turnover was increased and suppression by insulin was impaired in obese adolescents compared with both groups of lean subjects ( P < 0.01). However, when the rates of glycerol turnover were adjusted for differences in body fat mass, the rates were similar in all three groups. Basal plasma free fatty acid (FFA) concentrations were significantly elevated, and the suppression by physiological increments in plasma insulin was impaired in obese adolescents compared with lean adults ( P < 0.05). In parallel with the high circulating FFA levels, net lipid oxidation in the basal state and during the clamp was also elevated in the obese group compared with lean adults. Net lipid oxidation was inversely correlated with glucose oxidation ( r = −0.50, P < 0.01). In conclusion, these data suggest that lipolysis is increased in obese adolescents (vs. lean adolescents and adults) as a consequence of an enlarged adipose mass rather than altered sensitivity of adipocytes to the suppressing action of insulin.
Insulin inhibits vascular smooth muscle contraction at a site distal to intracellular Ca2+concentration
Authors: Kahn Andrew M. , Husid Annat , Odebunmi Timothy , Allen Julius C. , Seidel Charles L. , Song Tom
Published: December 2017

Several hypertensive states are associated with resistance to insulin-induced glucose disposal and insulin-induced vasodilation. Insulin can inhibit vascular smooth muscle (VSM) contraction at the level of the VSM cell, and resistance to insulin’s inhibition of VSM cell contraction may be of pathophysiological importance. To understand the VSM cellular mechanisms by which insulin resistance leads to increased VSM contraction, we sought to determine how insulin inhibits contraction of normal VSM. It has been shown that insulin lowers the contractile agonist-stimulated intracellular Ca2+([Formula: see text]) transient in VSM cells. In this study, our goal was to see whether insulin inhibits VSM cell contraction at steps distal to [Formula: see text] and, if so, to determine whether the mechanism is dependent on nitric oxide synthase (NOS) and cGMP. Primary cultured VSM cells from canine femoral artery were bathed in a physiological concentration of extracellular Ca2+and permeabilized to Ca2+with a Ca2+ionophore, either ionomycin or A-23187. The resultant increase in[Formula: see text] contracted individual cells, as measured by photomicroscopy. Preincubating cells with 1 nM insulin for 30 min did not affect basal [Formula: see text] or the ionomycin-induced increase in [Formula: see text], as determined by fura 2 fluorescence measurements, but it did inhibit ionomycin- and A-23187-induced contractions by 47 and 51%, respectively (both P < 0.05). In the presence of 1.0 μM ionized Ca2+, ionomycin-induced contractions were inhibited by insulin in a dose-dependent manner. In the presence of ionomycin, insulin increased cGMP production by 43% ( P < 0.05). 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 μM), a selective inhibitor of guanylate cyclase that blocked cGMP production in these cells, completely blocked the inhibition by insulin of ionomycin-induced contraction. It was found that the cells expressed the inducible isoform of NOS. NG-monomethyl-l-arginine or NG-nitro-l-arginine methyl ester (0.1 mM), inhibitors of NOS, did not affect ionomycin-induced contraction but prevented insulin from inhibiting contraction. We conclude that insulin stimulates cGMP production and inhibits VSM contraction in the presence of elevated[Formula: see text]. This inhibition by insulin of VSM contraction at sites where [Formula: see text] could not be rate limiting is dependent on NOS and cGMP.
Intracellular Mg2+regulates ADP phosphorylation and adenine nucleotide synthesis in human erythrocytes
Authors: Page Sarah , Salem Michael , Laughlin Maren R.
Published: December 2017

13C- and31P-NMR were used in methylene blue-treated human erythrocytes to determine the dependence on intracellular Mg2+concentration ([Mg2+]i) of the pentose phosphate pathway (PPP), the glycolytic pathway, and adenine nucleotide synthesis. The PPP flux had an [Mg2+]iat half-maximal velocity ([Mg2+]i,0.5) of 0.02 mM, well below the physiological range (0.2–0.7 mM). Flux through the PPP was reduced at higher [Mg2+]ias flux through phosphofructokinase was increased ([Mg2+]i,0.5= 0.16 mM). [Mg2+]i,0.5of phosphoglycerate kinase flux, which equals net ADP phosphorylation rate, was 0.27 mM, well within the physiological [Mg2+]irange. The rate of adenine nucleotide synthesis from [2-13C]glucose-derived ribose 5-phosphate and exogenous adenine also exhibited dependence on [Mg2+]ibut was not saturable up to 1.6 mM. Therefore, net flux through the PPP and glycolytic pathways in erythrocytes is not strongly dependent on [Mg2+]iat physiological ion concentrations, but both ADP phosphorylation and adenine nucleotide synthesis are likely to be regulated by normal fluctuations in [Mg2+]i.
Effects of hyperthyroidism on vascular contractile and relaxation responses
Authors: McAllister Richard M. , Grossenburg Vance D. , Delp Michael D. , Laughlin M. Harold
Published: December 2017

Previous research has shown that skeletal muscle blood flow, at rest and during muscular contractions, is elevated in the hyperthyroid state. We hypothesized that reduced vascular contractile and enhanced endothelium-dependent relaxation responses contribute to these observations. To test these hypotheses, male rats were administered triiodothyronine (Hyper, n = 27; 300 μg/kg) for 6–12 wk. Compared with euthyroid control rats (Eut, n = 27), Hyper exhibited left ventricular hypertrophy (Eut, 2.01 ± 0.04 mg/g body wt; Hyper, 2.70 ± 0.06; P < 0.0005) and greater oxidative enzyme activity in several skeletal muscles (all P < 0.0005). Vascular rings, 2–3 mm in axial length, were prepared from abdominal aortas, and responses to vasoactive agents were determined in vitro. Compared with Eut, vascular rings with intact endothelium from Hyper exhibited reductions in contractile responses to norepinephrine (NE) across a range of NE concentrations ( P < 0.05). Maximal tension developed in response to NE was reduced ∼30% in hyperthyroidism (Eut, 3.8 ± 0.2 g; Hyper, 2.6 ± 0.4; P < 0.01). Contractile responses to NE were not different between Eut and Hyper in rings denuded of endothelium. Maximal vasorelaxation responses to acetylcholine (ACh), after precontraction with NE (10−7 M), were enhanced in the hyperthyroid state (Eut, 65.1 ± 4.8%; Hyper, 84.0 ± 7.1; P < 0.05). Enhanced vasorelaxation to ACh was also observed when precontraction was induced by prostaglandin F2α. These findings indicate that vascular contractile and relaxation responses are altered in male hyperthyroid rats.