bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucose transporter expression in L6 muscle cells: regulation through insulin- and stress-activated pathways
Authors: Taha C. , Tsakiridis T. , McCall A. , Klip A.
Published: December 2017

We addressed the effect of long-term treatment with insulin, 2,4-dinitrophenol (DNP; an uncoupler of oxidative phosphorylation that increases energy demand) and 300 mM mannitol (hyperosmolarity) on glucose transporter (GLUT) expression in L6 muscle cells and the signaling pathways involved. We found the following. 1) The insulin-mediated increase in GLUT-1 is 70-kDa ribosomal protein S6 kinase (p70 S6 kinase) and p38 mitogen-activated protein kinase (MAPK) dependent but extracellular signal-regulated protein kinase (ERK) and MAPK/ERK kinase (MEK) independent. The hypertonicity-stimulated elevation in GLUT-1 is p70 S6 kinase, p38 MAPK, and MEK dependent yet ERK independent. DNP also increased GLUT-1 protein but did not depend on any of the above pathways, 2) Insulin increased GLUT-3 protein in a p70 S6 kinase-independent but MEK/ERK-dependent fashion. Inhibition of p38 MAPK potentiated the effect of insulin on GLUT-3. Hypertonicity increased GLUT-3 via p70 S6 kinase- and p38 MAPK-dependent pathways. In conclusion, we have dissected the molecular mechanisms used by insulin and hypertonicity that culminate in the induction of GLUT-1 and GLUT-3. The mechanism(s) used by DNP remains unknown.
Metabolic responses from rest to steady state determine contractile function in ischemic skeletal muscle
Authors: Timmons J. A. , Poucher S. M. , Constantin-Teodosiu D. , Macdonald I. A. , Greenhaff P. L.
Published: December 2017

Skeletal muscle contraction during ischemia, such as that experienced by peripheral vascular disease patients, is characterized by rapid fatigue. Using a canine gracilis model, we tested the hypothesis that a critical factor determining force production during ischemia is the metabolic response during the transition from rest to steady state. Dichloroacetate (DCA) administration before gracilis muscle contraction increased pyruvate dehydrogenase complex activation and resulted in acetylation of 80% of the free carnitine pool to acetylcarnitine. After 1 min of contraction, phosphocreatine (PCr) degradation in the DCA group was approximately 50% lower than in the control group (P < 0.05) during conditions of identical force production. After 6 min of contraction, steady-state force production was approximately 30% higher in the DCA group (P < 0.05), and muscle ATP, PCr, and glycogen degradation and lactate accumulation were lower (P < 0.05 in all cases). It appears, therefore, that an important determinant of contractile function during ischemia is the mechanisms by which ATP regeneration occurs during the period of rest to steady-state transition.
Insulin resistance in adipocytes after downregulation of Gi subtypes
Authors: Green A. , Walters D. J. , Belt S. E.
Published: December 2017

To determine whether downregulation of Gi proteins is associated with insulin resistance, we incubated isolated adipocytes with N6-(2-phenylisopropyl)adenosine (PIA; an A1-adenosine receptor agonist; 300 nM), prostaglandin E1 (PGE1; 3 microM), or nicotinic acid (1 mM) for 4 days in primary culture. The cells were washed, and the rate of glucose transport (2-deoxy-[3H]glucose uptake) was measured after incubation with various concentrations of insulin for 45 min. Both PIA and PGE1 (which downregulate Gi) decreased the maximal responsiveness of the cells to insulin by approximately 30% and caused a rightward shift in the dose-response curve. By contrast, nicotinic acid (which does not downregulate Gi) did not alter the insulin sensitivity of the cells. Prolonged treatment of adipocytes with either PIA or PGE1 (but not nicotinic acid) rendered the cells completely resistant to the antilipolytic effect of insulin. The ability of insulin to stimulate autophosphorylation of the beta-subunit of the insulin receptor was decreased by approximately 30% in PIA-treated cells, and the dose-response curve was shifted to the right. Similarly, the ability of the receptor to phosphorylate poly(Glu4-Tyr1) was decreased by approximately 35%. This decrease in tyrosine kinase activity of the receptor may account for the decrease in insulin sensitivity of glucose transport but cannot account for the complete loss of antilipolysis. The findings suggest both a direct and indirect involvement of Gi proteins in insulin action.
Moderate exercise at energy balance does not affect 24-h leucine oxidation or nitrogen retention in healthy men
Authors: el-Khoury A. E. , Forslund A. , Olsson R. , Branth S. , Sjodin A. , Andersson A. , Atkinson A. , Selvaraj A. , Hambraeus L. , Young V. R.
Published: December 2017

Short-term metabolic experiments have revealed that physical exercise increases the oxidation of leucine, which has been interpreted to indicate an increased requirement for dietary protein in physically active subjects. Because it may be inaccurate to extrapolate measurements of amino acid oxidation made over a few hours to the entire day, we have carried out a continuous 24-h intravenous [1-13C]leucine/[15N]urea tracer study in eight healthy adult men. Their diet supplied 1 g protein.kg-1.day-1, and exercise (mean maximal O2 consumption 46%) was for 90 min during the 12-h fast and 12-h fed periods of the day. Subjects were adapted to the diet and exercise regimen for 6 days. Then, on day 7, they were dressed in the University of Uppsala energy metabolic unit's direct calorimeter suit, were connected to an open-hood indirect calorimeter, and received the tracers. Exercise increased leucine oxidation by approximately 50 and 30% over preexercise rates for fast and fed periods, respectively. This increase amounted to approximately 4-7% of daily leucine oxidation. Subjects remained in body leucine equilibrium (balance -4.6 +/- 10.5 mg.kg-1.day-1; -3.6 +/- 8.3% of intake; P = not significant from zero balance). Therefore, moderate exercise did not cause a significant deterioration in leucine homeostasis at a protein intake of 1 g.kg-1.day-1. These findings underscore the importance of carrying out precise, continuous, 24-h measurements of whole body leucine kinetics; this model should be of value in studies concerning the quantitative interactions among physical exercise, energy/protein metabolism, and diet in humans.
Simulation of IGF-I pharmacokinetics after infusion of recombinant IGF-I in human subjects
Authors: Boroujerdi M. A. , Jones R. H. , Sonksen P. H. , Russell-Jones D. L.
Published: December 2017

The pharmacokinetics of recombinant human insulin-like growth factor I (IGF-I) were studied in four healthy volunteers by a 3-h infusion at a rate of 20 micrograms.kg-1.h-1. A compartmental model was used to simulate the plasma “free” IGF-I and IGF-I associated with the 50- and 150-kDa plasma protein fractions. The model is based on the concept that free IGF-I and IGF binding proteins (IGFBPs) are the substrates for their own degradation and that they act as reservoirs for retention of IGF-I in the vascular compartment or inhibiting IGF-I action. The metabolic clearance rate (MCR) of free IGF-I is estimated as 2.62 +/- 0.94 ml.min-1.min-1 with a production rate of 4.75 +/- 1.74 mg/day (621.0 +/- 227.34 nmol/day). The simulation shows that higher concentrations of IGFBP-3 would increase the estimate of MCR for free IGF-I by reducing free IGF-I concentration. The model will be of value for simulation of dynamic profiles of free IGF-I and receptor-bound IGF-I in a variety of pathophysiological conditions.
Leptin receptors in the adrenal medulla of the rat
Authors: Cao G. Y. , Considine R. V. , Lynn R. B.
Published: December 2017

Leptin is the protein product of the recently cloned obesity gene. Leptin receptor mRNA is found in a number of central and peripheral locations. The hypothalamus is a presumed site of action. However, little is known about the specific locations of the receptor in peripheral organs. Epinephrine has potent anorectic effects and can cause weight loss by a variety of mechanisms. Excretion of epinephrine is reduced in the ob/ob mouse, which lacks leptin, suggesting an effect by leptin on the adrenal medulla. In the current study, the presence of the leptin receptor was identified on epinephrine-secreting cells in the adrenal medulla. Immunohistochemical studies found dense leptin receptor-like immunoreactivity in the adrenal medulla with no labeling in the adrenal cortex. Double immunofluorescent labeling confirmed that the leptin receptor was present on cells that were phenylethanolamine N-methyltransferase-like immunoreactive and therefore were epinephrine-secreting cells. Leptin receptor mRNA in the adrenal medulla was detected by reverse transcriptase-polymerase chain reaction, with the majority of the mRNA coding for the short isoform (Ob-Ra) of the receptor. Finally, autoradiography was performed using 125I-labeled leptin; specific binding was found in the adrenal medulla, with no specific binding in the adrenal cortex. These results suggest that leptin may have a direct effect on epinephrine-secreting cells in the adrenal medulla. Epinephrine may play a role in mediating the effects of leptin to reduce body weight.
Oxidant stress-induced transendothelial migration of monocytes is linked to phosphorylation of PECAM-1.
Authors: Rattan V , Sultana C , Shen Y , Kalra V K
Published: December 2017

Reactive oxygen species (ROS) are believed to cause vascular injury in the pathophysiology of atherosclerosis, diabetes, and vasoocclusion in sickle cell disease. Studies have shown that ROS causes increased adhesion of monocytes and neutrophils to the endothelium. We investigated the effects of tert-butylhydroperoxide (t-BuOOH), an inducer of oxidant stress, to determine the cellular signaling pathway leading to the transendothelial migration of polymorphonuclear leukocytes. Our studies revealed that signaling by t-BuOOH in human umbilical vein endothelial cells (HUVECs) causes a twofold increase in the transendothelial migration of monocyte-like HL-60 cells and a fivefold increase in platelet endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation. The transmigration induced by t-BuOOH was inhibited by an antibody to PECAM-1. These events were inhibited by antioxidants and inhibitors of protein kinase C, p21ras and glutathione synthesis. However, treatment of HUVECs with the phosphatase inhibitor calyculin A augmented the t-BuOOH-mediated transendothelial migration of monocytes and PECAM-1 phosphorylation. Our results suggest that oxidative stress can induce the transendothelial migration of monocytes as a result of phosphorylation of PECAM-1, a crucial event in the diapedesis of leukocytes during pathophysiology of vascular diseases.
Age-related decreases in stimulatory G protein-coupled adenylate cyclase activity in osteoblastic cells
Authors: Donahue H. J. , Zhou Z. , Li Z. , McCauley L. K.
Published: December 2017

In this study we examined parathyroid hormone (PTH)-, forskolin (FSK)-, and cholera toxin (CTX)-stimulated adenosine 3′,5′-cyclic monophosphate (cAMP) accumulation in rat osteoblastic cells (ROB) isolated from young (4 mo), mature (12 mo), and old (24–28 mo) male rats. Exposure to PTH increased cAMP accumulation in a concentration-dependent manner in all ROB cells examined. However, the maximum response in ROB from young rats was threefold greater than the maximum response in those from mature and old rats. Exposure to FSK also stimulated cAMP accumulation in a concentration-dependent manner, but there were no significant differences in responsiveness among ROB isolated from young, mature, and old rats. Exposure to CTX resulted in a dramatic concentration-dependent increase in cAMP in ROB from young rats but only a modest increase in ROB from mature and old rats. PTH binding kinetics were similar in ROB from rats in each age group. These data suggest an age-related defect in stimulatory G protein coupling to adenylate cyclase, which contributes to decreased osteoblastic responsiveness to PTH.
Effects of aging on in vivo synthesis of skeletal muscle myosin heavy-chain and sarcoplasmic protein in humans
Authors: Balagopal P. , Rooyackers Olav E. , Adey Deborah B. , Ades Philip A. , Nair K. Sreekumaran
Published: December 2017

A decline in muscle mass and contractile function are prominent features of the sarcopenia of old age. Because myosin heavy chain is an important contractile protein, it was hypothesized that synthesis of this protein decreases in sarcopenia. The fractional synthesis rate of myosin heavy chain was measured simultaneously with rates of mixed muscle and sarcoplasmic proteins from the increment of [13C]leucine in these proteins purified from serial needle biopsy samples taken from 24 subjects (age: from 20 to 92 yr) during a primed continuous infusion ofl-[1-13C]leucine. A decline in synthesis rate of mixed muscle protein ( P < 0.01) and whole body protein ( P < 0.01) was observed from young to middle age with no further change with advancing age. An age-related decline of myosin heavy-chain synthesis rate was also observed ( P < 0.01), with progressive decline occurring from young, through middle, to old age. However, sarcoplasmic protein synthesis did not decline with age. Myosin heavy-chain synthesis rate was correlated with measures of muscle strength ( P < 0.05), circulating insulin-like growth factor I ( P < 0.01), and dehydroepiandrosterone sulfate ( P < 0.05) in men and women and free testosterone levels in men ( P < 0.01). A decline in the synthesis rate of myosin heavy chain implies a decreased ability to remodel this important muscle contractile protein and likely contributes to the declining muscle mass and contractile function in the elderly.
Insulin-like growth factor (IGF)-binding protein-5-(201—218) region regulates hydroxyapatite and IGF-I binding
Authors: Campbell Phil G. , Andress Dennis L.
Published: December 2017

Insulin-like growth factor-binding protein-5 (IGFBP-5), the major bone IGFBP, modifies the biological activity of IGFs within the osteoblastic pericellular environment. Because glycosaminoglycans modulate IGFBP-5 binding to osteoblast organic extracellular matrix (ECM), we assessed whether the heparin binding domain of IGFBP-5, IGFBP-5-(102—218), modifies the interaction of IGFBP-5 with the inorganic bone ECM hydroxyapatite (HA). Synthetic IGFBP-5-(201—218) peptide increased the binding of IGFBP-5 to HA as well as the binding of IGF-I to HA-bound IGFBP-5. This action was specific for the heparin-binding domain, because IGFBP-5-(130—138), IGFBP-5-(138—152), and IGFBP-5-(1—169) were without effect. IGFBP-5-(201—218) was found to bind directly to IGFBP-5 and cause a threefold enhancement of the IGF-I binding affinity for IGFBP-5, whether IGFBP-5 was bound to HA or was in a matrix-free fluid phase. Heparin inhibited the binding of IGFBP-5 to HA and blocked the interaction of IGFBP-5 with IGFBP-5-(201—218) in the fluid phase, suggesting that the primary heparin-binding domain of IGFBP-5 specifically enhances the binding of IGFBP-5 to HA and increases IGF-I binding to IGFBP-5.
Electroretinogram in sucrose-fed diabetic rats treated with an aldose reductase inhibitor or an anticoagulant
Authors: Hotta Nigishi , Nakamura Jiro , Sakakibara Fumihiko , Hamada Yoji , Hara Tomohiro , Mori Koichi , Nakashima Eitaro , Sasaki Hiromitsu , Kasama Naoto , Inukai Shinji , Koh Naoki
Published: December 2017

To investigate the role of increased polyol pathway activity and hemodynamic deficits in the pathogenesis of diabetic retinopathy in non-insulin-dependent diabetes mellitus (NIDDM), Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of human NIDDM, were given water with or without 30% sucrose and some of them were fed laboratory chow containing 0.03% cilostazol, an anticoagulant, or 0.05% [5-(3-thienyl)tetrazol-1-yl] acetic acid monohydrate (TAT), an aldose reductase inhibitor, for 8 wk. Long-Evans Tokushima Otsuka (LETO) rats were used as nondiabetic controls. The peak latencies of oscillatory potentials of the electroretinogram in sucrose-fed OLETF rats were significantly prolonged compared with those in OLETF rats without sucrose feeding and LETO rats. There was a marked increase in platelet aggregability and a significant decrease in erythrocyte 2,3-diphosphoglycerate in sucrose-fed OLETF rats. Cilostazol significantly improved these parameters without changes in retinal levels of sorbitol and fructose. TAT, however, ameliorated all of these parameters. These findings confirm that the sucrose-fed OLETF rat is a useful animal model of retinopathy in human NIDDM and suggest that cilostazol improved diabetic retinopathy by modifying vascular factors, not by altering polyol pathway activity.
Interaction of equal increments in arterial and portal vein insulin on hepatic glucose production in the dog
Authors: Sindelar Dana K. , Chu Chang A. , Neal Doss W. , Cherrington Alan D.
Published: December 2017

We have previously shown that a selective increase of 84 pmol/l in either arterial or portal vein insulin (independent of a change in insulin in the other vessel) can suppress tracer-determined glucose production (TDGP) and net hepatic glucose output (NHGO) by ∼50%. In the present study we investigated the interaction between equal increments in arterial and portal vein insulin in the suppression of TDGP and NHGO. Isotopic ([3-3H]glucose) and arteriovenous difference methods were used in conscious overnight fasted dogs. A pancreatic clamp was used to control the endocrine pancreas. A 40-min basal period was followed by a 180-min test period, during which arterial and portal vein insulin levels were simultaneously and equally increased 102 pmol/l. Hepatic sinusoidal glucagon levels remained unchanged, and euglycemia was maintained by peripheral glucose infusion. TDGP was suppressed ∼60% by the last 30 min of the experimental period. In contrast, NHGO was suppressed 100% by that time. Coincidentally, hepatic glucose uptake (net hepatic [3H]glucose balance) increased significantly (∼4 μmol ⋅ kg−1⋅ min−1). The effects of simultaneous equal increases in peripheral and portal venous insulin were not additive in the suppression of TDGP. However, they were additive in decreasing NHGO as a result of an increase in the uptake of glucose by the liver.
Whole body leptin kinetics and renal metabolism in vivo
Authors: Zeng Jianbo , Patterson Bruce W. , Klein Samuel , Martin Daniel R. , Dagogo-Jack Samuel , Kohrt Wendy M. , Miller Steven B. , Landt Michael
Published: December 2017

Leptin metabolism was investigated in male Sprague-Dawley rats by use of125I-labeled leptin plasma kinetic and arteriovenous balance studies. When conscious rats received bolus venous injections of 125I-leptin, intact (precipitable) leptin quickly disappeared from circulation in a biexponential manner during the 2-h experimental period. After substantial delay, most of the injected radioactivity appeared in the urine. The data were described by a two-compartment model, which postulated that plasma leptin exchanged with a nonplasma pool and that all of the tracer cleared from plasma appeared in urine or in a degraded form in plasma. The half-life of leptin was 9.4 ± 3.0 min, and the leptin production rate was 3.6 ± 1.2 ng ⋅ 100 g fat−1 ⋅ min−1. The left kidney extracted 21 ± 1.5% of intact arterial125I-leptin 5 min after femoral venous injection. Endogenous arterial leptin was reduced 21 ± 8 and 18 ± 12%, respectively, in simultaneously sampled left and right renal veins. Renal elimination appears to be the major elimination mechanism for leptin in normal rats, and the kinetic studies suggest that uptake of leptin by renal tissue rather than glomerular filtration is the predominant elimination mechanism.
AICA riboside increases AMP-activated protein kinase, fatty acid oxidation, and glucose uptake in rat muscle
Authors: Merrill G. F. , Kurth E. J. , Hardie D. G. , Winder W. W.
Published: December 2017

5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) has previously been reported to be taken up into cells and phosphorylated to form ZMP, an analog of 5′-AMP. This study was designed to determine whether AICAR can activate AMP-activated protein kinase (AMPK) in skeletal muscle with consequent phosphorylation of acetyl-CoA carboxylase (ACC), decrease in malonyl-CoA, and increase in fatty acid oxidation. Rat hindlimbs were perfused with Krebs-Henseleit bicarbonate containing 4% bovine serum albumin, washed bovine red blood cells, 200 μU/ml insulin, and 10 mM glucose with or without AICAR (0.5–2.0 mM). Perfusion with medium containing AICAR was found to activate AMPK in skeletal muscle, inactivate ACC, and decrease malonyl-CoA. Hindlimbs perfused with 2 mM AICAR for 45 min exhibited a 2.8-fold increase in fatty acid oxidation and a significant increase in glucose uptake. No difference was observed in oxygen uptake in AICAR vs. control hindlimb. These results provide evidence that decreases in muscle content of malonyl-CoA can increase the rate of fatty acid oxidation.
Influence of muscle glycogen content on metabolic regulation
Authors: Weltan Sandra M. , Bosch Andrew N. , Dennis Steven C. , Noakes Timothy D.
Published: December 2017

Euglycemia was maintained in 13 subjects with low muscle glycogen [low glycogen, euglycemic (LGE), n = 8; low glycogen, euglycemic, hyperinsulinemic (LGEI), n = 5] and 6 subjects with normal muscle glycogen (NGE), whereas hyperglycemia was maintained in 8 low muscle glycogen subjects (LGH). All subjects cycled for 145 min at 70% of maximal oxygen uptake during the infusions. Insulin was infused in LGEI at 0.2 mU ⋅ kg−1 ⋅ min−1. During exercise, respiratory exchange ratio (RER) was lower and norepinephrine higher in LGE than in NGE. In LGEI and LGH, RER at the start of exercise was the same as in LGE but did not decrease as in LGE. Free fatty acids (FFA) were higher and plasma insulin concentrations lower in LGE than NGE, LGEI, or LGH over the first 45 min of exercise. Rate of glucose infusion (Ri) and rate of glucose oxidation (Rox) were higher in LGH and LGEI than in NGE or LGE, and Ri matched Rox in all groups except LGH, in which Ri was greater than Rox. Muscle glycogen disappearance was greater in NGE than LGE, LGEI, or LGH, but the latter three groups did not differ. In conclusion, this study showed that low muscle glycogen content results in a decrease in RER, an increase in FFA, fat oxidation, and norepinephrine both at rest and during exercise, and does not affect Rox when euglycemia is maintained by infusion of glucose alone. Rox was increased only during insulin and hyperglycemia.
Synthetic flavonoids cross the placenta in the rat and are found in fetal brain
Authors: Elst J. P. Schröder-Van Der , Van Der Heide D. , Rokos H. , De Escobar G. Morreale , Köhrle J.
Published: December 2017

The synthetic flavonoid EMD-49209 is a potent inhibitor of the in vivo and in vitro binding of thyroxine (T4) to transthyretin (TTR). We studied the distribution of125I-labeled EMD-49209 in maternal tissues, intestinal contents, and fetal tissues in rats that were 20 days pregnant (from 1 to 24 h after intravenous injection). The percent dose of EMD decreased quickly with time. In maternal brain no radioactive flavonoid could be detected. EMD was excreted very rapidly from the intestines. In the fetal compartment the percent dose of EMD increased with time; after 24 h it contained 17% of the EMD. The flavonoid was found in all fetal tissues investigated and also in the fetal brain. Because TTR concentrations are high in the fetal rat, especially in the brain, the transfer of flavonoid to the fetal brain might be linked to TTR expression. The presence of flavonoid in the fetal brain raises the possibility of an essential interference of flavonoids with the availablity of T4 in the fetal compartment.
A disrupted cholecystokinin A receptor gene induces diabetes in obese rats synergistically with ODB1 gene
Authors: Takiguchi Soichi , Takata Yutaka , Takahashi Nobuhiko , Kataoka Kazuhiro , Hirashima Tsukasa , Kawano Kazuya , Miyasaka Kyoko , Funakoshi Akihiro , Kono Akira
Published: December 2017

Otsuka Long-Evans Tokushima fatty (OLETF) rats develop hyperglycemia, hyperinsulinemia, and mild obesity, which are characteristic of human non-insulin-dependent diabetes mellitus. We have shown that two recessive genes, ODB1 mapped on the X chromosome and ODB2 mapped on chromosome 14, are involved in the induction of the diabetes in OLETF rats. Recently we found that OLETF rats are the naturally occurring cholecystokinin type A receptor (CCKAR) gene knockout rats. In this study, we focused on the genotype of CCKAR gene and the ODB1 gene in regulation of glucose homeostasis in the F2 cross of the OLETF rats. Relatively high plasma glucose levels were observed in the F2 offspring with the homozygously disrupted CCKAR gene. A synergistic effect for increasing plasma glucose levels in F2 rats between disrupted CCKAR gene and the ODB1 gene was shown. The CCKAR gene was found to map very close to ODB2 by a linkage analysis using microsatellite markers. These results suggest that CCKAR gene maintains normoglycemia in rats.
Insulin acutely suppresses glucose production by both peripheral and hepatic effects in normal dogs
Authors: McCall Richard H. , Wiesenthal Stephanie R. , Shi Z. Qing , Polonsky Kenneth , Giacca Adria
Published: December 2017

To determine whether the predominant effect of insulin in suppressing tracer-determined glucose production (Ra) is hepatic or peripheral, we infused insulin peripherally (PER) and portally (POR) at both low (0.75 pmol ⋅ kg−1⋅ min−1) and high physiological rates (2.7 pmol ⋅ kg−1⋅ min−1) during euglycemic clamps in normal dogs. We also infused insulin peripherally at one-half these rates (1/2 PER) to match the peripheral insulin levels in POR and thus obtain a selective POR vs. 1/2 PER difference in hepatic insulin levels. At the high-rate insulin infusion, peripheral insulin levels were greatest with PER (PER = 212 ± 10 pM, n = 5; POR = 119 ± 5 pM, n = 6; 1/2 PER = 122 ± 5 pM, n = 6). Calculated hepatic insulin levels were greatest with POR (POR = 227 ± 13 pM, PER = 206 ± 19 pM, 1/2 PER = 123 ± 8 pM). High-dose PER yielded a greater suppression of Rathan POR (79 ± 18 vs. 56 ± 6%, P < .001). Rawas only suppressed by 45 ± 6% with 1/2 PER ( P< 0.01 vs. POR on 6 paired experiments). Free fatty acid (FFA) was suppressed by 57 ± 8% with PER and only by 33 ± 5 and 37 ± 2% with POR and 1/2 PER, respectively. The low-dose PER and POR yielded an equal Rasuppression (PER = 46 ± 9%, POR = 43 ± 4%). Only 1/2 PER was associated with a lower suppression of Ra(36 ± 8, P < 0.05 vs. POR). FFA showed similar suppression in all three groups (∼25%). Using both insulin infusion rates, the percent Rasuppression per unit difference in peripheral insulin was approximately twofold greater than that per unit difference in hepatic insulin. These results suggest that, during euglycemic clamps without somatostatin in normal dogs, Rasuppression is mediated by both peripheral and hepatic effects of insulin and that peripheral insulin, at least at high physiological infusion rates, is more potent than hepatic insulin in suppressing Ra.
Cortisol infusion depresses the ratio of bioactive to immunoreactive ACTH in adrenalectomized sheep fetuses
Authors: Zehnder Timothy J. , Valego Nancy K. , Schwartz Jeffrey , Green Jennifer , Rose James C.
Published: December 2017

We examined the effects of exogenous cortisol on plasma immunoreactive adrenocorticotropic hormone (iACTH), bioactive ACTH (bACTH), and ACTH-(1—39) in nine adrenalectomized fetuses at 126–130 and 136–140 days of gestation. Fetuses received 4 h of cortisol (2 μg ⋅ kg−1 ⋅ min−1) or saline infusions on consecutive days. Blood was obtained before and at intervals during infusions. Arterial blood gases and hematocrits were normal and did not change with age. Plasma cortisol did not change during saline infusions but increased significantly (range 30–70 ng/ml) during cortisol infusions. Basal plasma iACTH, bACTH, ACTH-(1—39), and bACTH-to-iACTH and ACTH-(1—39)-to-iACTH ratios were significantly higher in the older fetuses. Cortisol infusions decreased plasma iACTH, bACTH, and ACTH-(1—39) in both groups, and the suppression as a percent of the baseline was similar. The bACTH-to-iACTH ratio declined to the same level at 126–130 (0.201 ± 0.040 to 0.051 ± 0.002) and 136–140 (0.389 ± 0.088 to 0.046 ± 0.002) days of gestation. These data suggest that physiological concentrations of cortisol selectively inhibit bACTH secretion, and the ACTH response to cortisol inhibition is not different between 126 and 140 days of gestation in adrenalectomized sheep fetuses.
Divergent changes in plasma ACTH and pituitary POMC mRNA after cortisol administration to late-gestation ovine fetus
Authors: Jeffray T. M. , Matthews S. G. , Hammond G. L. , Challis J. R. G.
Published: December 2017

Plasma concentrations of cortisol and adrenocorticotropic hormone (ACTH) rise in the late-gestation sheep fetus at approximately the same time as there is an increase in the plasma levels of corticosteroid- binding globulin (CBG). We hypothesized that intrafetal cortisol infusion during late pregnancy would stimulate an increase in fetal plasma CBG, which in turn would bind cortisol and diminish glucocorticoid negative-feedback regulation of the fetal pituitary, leading to an increase in plasma ACTH concentrations. Cortisol was infused into chronically catheterized fetal sheep beginning at 126.1 ± 0.5 days of gestation and continued for 96 h. Control fetuses were infused with saline. In cortisol-infused fetuses, the plasma cortisol concentrations rose significantly from control levels (4.4 ± 0.6 ng/ml) to 19.3 ± 3.1 ng/ml within 24 h and remained significantly elevated throughout the infusion period. Plasma immunoreactive (ir) ACTH concentrations were significantly elevated in cortisol-infused fetuses within 24–48 h and remained significantly higher than in controls throughout the 96-h experimental period. Plasma free cortisol concentrations increased 10-fold and remained significantly elevated in cortisol-infused animals, despite a rise in plasma corticosteroid-binding capacity. Levels of pituitary proopiomelanocortin (POMC) mRNA in the fetal pars distalis and pars intermedia were 96 and 38% lower, respectively, after 96 h of cortisol infusion. Therefore physiological elevations of plasma cortisol, in the late-gestation ovine fetus, lead to increases in mean plasma irACTH concentrations, but this is not associated with increases in fetal pituitary POMC mRNA levels.
Angiotensin II-induced Ca2+mobilization and prolactin release in normal and hyperplastic pituitary cells
Authors: Díaz-Torga Graciela , Iglesias Arturo González , Achával-Zaia Rita , Libertun Carlos , Becú-Villalobos Damasia
Published: December 2017

We evaluated the effects of angiotensin II (ANG II) and its antagonists on prolactin release, intracellular calcium ([Ca2+]i) mobilization, and [3H]thymidine uptake in cells from normal rat pituitaries and from estrogen-induced pituitary tumors. ANG II (10−7to 10−9M) increased prolactin release significantly in control and not in tumoral cells. In control cells, ANG II (10−6to 10−9M) produced an immediate spike of [Ca2+]ifollowed by a plateau. Spike levels rose significantly between 10−10and 10−8M ANG II, whereas the onset of the spike was retarded with decreasing concentrations. In tumoral cells, ANG II did not produce a spike phase even at 10−6M. ANG II-induced prolactin release and calcium mobilization were blocked by losartan (AT1receptor antagonist) and not by PD-123319 (AT2antagonist). Finally, [3H]thymidine uptake was not modified by ANG II (10−7to 10−10M) or its antagonists in either group. Our results suggest that chronic in vivo estrogenic treatment alters in vitro pituitary response to ANG II. Alterations might function to limit excessive prolactin secretion of hypersecreting tumors. Besides, ANG II does not modify DNA synthesis in vitro of cells from normal or tumor-derived hypophyses.
Ca2+-induced loss of Ca2+/calmodulin-dependent protein kinase II activity in pancreatic β-cells
Authors: Jones Peter M. , Persaud Shanta J.
Published: December 2017

Elevations in intracellular Ca2+in electrically permeabilized islets of Langerhans produced rapid insulin secretory responses from β-cells, but the Ca2+-induced secretion was not maintained and was irrespective of the pattern of administration of elevated Ca2+. Ca2+-insensitive β-cells responded normally to activators of protein kinase C or cAMP-dependent kinase with increased insulin secretion. The loss of secretory responsiveness to Ca2+was paralleled by a reduction in Ca2+-induced protein phosphorylation. This was caused by a reduction in Ca2+/calmodulin-dependent protein kinase II (CaMK II) activity in the desensitized cells, as assessed by measuring the phosphorylation of a CaMK II-specific exogenous substrate, autocamtide-2. The Ca2+-induced reductions in kinase activity and protein phosphorylation were not dependent on the activation of Ca2+-dependent protein kinases and were not caused by the activation of phosphoprotein phosphatases or of Ca2+-activated proteases. The concomitant reductions in CaMK II activity and Ca2+-induced insulin secretion suggest that the activation of CaMK II is required for normal insulin secretory responses to increased intracellular Ca2+concentrations.
Dual-energy X-ray absorptiometry: fat estimation errors due to variation in soft tissue hydration
Authors: Pietrobelli Angelo , Wang Zimian , Formica Carmelo , Heymsfield Steven B.
Published: December 2017

Dual-energy X-ray absorptiometry (DXA) is rapidly gaining acceptance as a reference method for analyzing body composition. An important and unresolved concern is whether and to what extent variation in soft tissue hydration causes errors in DXA fat estimates. The present study aim was to develop and validate a DXA physical hydration model and then to apply this model by simulating errors arising from hypothetical overhydration states. The DXA physical hydration model was developed by first linking biological substance elemental content with photon attenuation. The validated physical model was next extended to describe photon attenuation changes anticipated when predefined amounts of two known composition components are mixed, as would occur when overhydration develops. Two overhydration models were developed in the last phase of study, formulated on validated physical models, and error was simulated for fluid surfeit states. Results indicate that systematic errors in DXA percent fat arise with added fluids when fractional masses are varied as a percentage of combined fluid + soft tissue mass. Three independent determinants of error magnitude were established: elemental content of overhydration fluid, fraction of combined fluid + soft tissue as overhydration fluid, and initial soft tissue composition. Small but systematic and predictable errors in DXA soft tissue composition analysis thus can arise with fluid balance changes.
Hepatic glucose disposition during concomitant portal glucose and amino acid infusions in the dog
Authors: Moore Mary Courtney , Flakoll Paul J. , Hsieh Po-Shiuan , Pagliassotti Michael J. , Neal Doss W. , Monohan Michael T. , Venable Carol , Cherrington Alan D.
Published: December 2017

The effect of concomitant intraportal infusion of glucose and gluconeogenic amino acids (AA) on net hepatic glucose uptake (NHGU) and glycogen synthesis was examined in 42-h-fasted dogs. After a basal period, there was a 240-min experimental period during which somatostatin was infused continuously into a peripheral vein and insulin and glucagon (at 3-fold basal and basal rates, respectively) and glucose (18.3 μmol ⋅ kg−1⋅ min−1) were infused intraportally. One group (PoAA, n = 7) received an AA mixture intraportally at 7.6 μmol ⋅ kg−1⋅ min−1, whereas the other group (NoAA, n = 6) did not receive AA. Arterial blood glucose concentrations and hepatic glucose loads were the same in the two groups. NHGU averaged 4.8 ± 2.0 (PoAA) and 9.4 ± 2.0 (NoAA) μmol ⋅ kg−1⋅ min−1( P < 0.05), and tracer-determined hepatic glucose uptake was 4.6 ± 1.6 (PoAA) and 10.0 ± 1.7 (NoAA) μmol ⋅ kg−1⋅ min−1( P < 0.05). AA data for PoAA and NoAA, respectively, were as follows: arterial blood concentrations, 1,578 ± 133 vs. 1,147 ± 86 μM ( P < 0.01); hepatic loads, 56 ± 3 vs. 32 ± 4 μmol ⋅ kg−1⋅ min−1( P < 0.01); and net hepatic uptakes, 14.1 ± 1.4 vs. 5.6 ± 0.4 μmol ⋅ kg−1⋅ min−1( P < 0.01). The rate of net hepatic glycogen synthesis was 7.5 ± 1.9 (PoAA) vs. 10.7 ± 2.3 (NoAA) μmol ⋅ kg−1⋅ min−1( P = 0.1). In a net sense, intraportal gluconeogenic amino acid delivery directed glucose carbon away from the liver. Despite this, net hepatic carbon uptake was equivalent in the presence and absence of amino acid infusion.
Genetic and environmental influences on prolactin secretion during wake and during sleep
Authors: Linkowski Paul , Spiegel Karine , Kerkhofs Myriam , L’Hermite-Balériaux Mireille , Van Onderbergen Anne , Leproult Rachel , Mendlewicz Julien , Van Cauter Eve
Published: December 2017

To delineate the contributions of genetic and environmental factors in the regulation of human prolactin (PRL) secretion, the 24-h profile of plasma PRL was obtained at 15-min intervals in 10 pairs of monozygotic and 10 pairs of dizygotic twins. Sleep was monitored polygraphically. PRL secretory rates were derived from plasma concentrations by deconvolution. Diurnal (24-h) variations were quantified by a regression curve to define nadir, acrophase, and amplitude. Pulses of PRL secretion were identified using a computerized algorithm. A procedure specifically developed for twin studies was used to partition the variance into genetic and environmental contributions. Significant genetic effects were identified for daytime PRL concentrations, rhythm amplitude, and overall waveshape of the daily PRL profile. In contrast, environmental effects were dominant for mean concentrations during sleep, total secretory output during sleep, overall 24-h concentrations, and total 24-h secretion. However, when interindividual variations in sleep fragmentation were taken into account, the estimates of genetic variance for PRL concentrations and secretion during sleep approached statistical significance. Significant genetic influences were identified for slow-wave sleep (SWS). Because SWS is associated with increased nocturnal PRL secretion, it is possible that genetic effects on PRL secretion during sleep reflect genetic influences on SWS. In conclusion, genetic factors determine partially both the basal daytime concentrations of PRL and the temporal organization of PRL secretion over the 24-h cycle in normal young men.
Effect of growth hormone treatment on postprandial protein metabolism in growth hormone-deficient adults
Authors: Russell-Jones D. L. , Bowes S. B. , Rees S. E. , Jackson N. C. , Weissberger A. J. , Hovorka R. , Sonksen P. H. , Umpleby A. M.
Published: December 2017

Growth hormone (GH) treatment of GH-deficient adults increases lean body mass. To investigate this anabolic effect of GH, body composition and postabsorptive and postprandial protein metabolism were measured in 12 GH-deficient adults randomized to placebo or GH treatment. Protein metabolism was measured after an infusion of [1-13C]leucine before and after a standard meal at 0 and 2 mo. After 2 mo, there was an increase in lean body mass in the GH group ( P < 0.05) but no change in the placebo group. In the postabsorptive state, there was increased nonoxidative leucine disappearance (NOLD; a measure of protein synthesis) and leucine metabolic clearance rate and decreased leucine oxidation in the GH group ( P < 0.05) but no change in the placebo group. After the meal, there was an increase in NOLD and oxidation in all studies ( P < 0.05), but the increase in NOLD, measured as area under the curve, was greater in the GH group ( P < 0.05). This study clearly demonstrates for the first time that the increase in protein synthesis in the postabsorptive state after GH treatment of GH-deficient adults is maintained in the postprandial state.
Short-term culture of ovine embryos modifies fetal myogenesis
Authors: Maxfield E. K. , Sinclair K. D. , Broadbent P. J. , McEvoy T. G. , Robinson J. J. , Maltin C. A.
Published: December 2017

Certain reproductive techniques culture embryos in vitro; however, little is known about the impact of culture on fetal growth. Coculture of day 1ovine zygotes on a bovine granulosa cell layer to blastocysts followed by transfer to synchronous recipients increased fetal weight by 11 and 40% at days 61 and 125, respectively, compared with the transfer of in vivo-produced blastocysts. Plantaris muscle weights were increased by 40% in cultured fetuses at day 125. Examination of myogenesis in plantaris muscle showed that primary fiber number was unchanged at day 61 by culture but that primary fiber area was increased significantly by 15 and 25% at days 61 and 125, respectively; secondary fiber area was increased by 40% at day 125 by culture, and the ratio of secondary to primary fiber numbers was 18–20% greater in the cultured groups compared with the controls at days 61 and 125. The results show that coculture of preimplantation embryos may alter myogenic programming. These changes may contribute to the abnormally large muscles observed in oversize fetuses.
Short-chain fatty acids regulate IGF-binding protein secretion by intestinal epithelial cells
Authors: Nishimura Akiyoshi , Fujimoto Mika , Oguchi Satoshi , Fusunyan Robert D. , MacDermott Richard P. , Sanderson Ian R.
Published: December 2017

Gastrointestinal epithelial cells secrete insulin-like growth factor (IGF)-binding proteins (IGFBPs), which modulate the actions of IGFs on cell proliferation and differentiation. Short-chain fatty acids are bacterial metabolites from unabsorbed carbohydrate (including fiber). We hypothesized that they may alter the pattern of IGFBPs secreted by epithelial cells as part of a wider phenomenon by which luminal molecules regulate gastrointestinal epithelial cell signaling. The intestinal epithelial cell line, Caco-2, predominantly secretes IGFBP-3; however, butyrate increased the secretion of IGFBP-2 in a dose-dependent and reversible manner. Butyrate decreased the secretion of IGFBP-3. Butyrate altered only the synthesis and not the cell sorting of IGFBPs because 1) the secretion of IGFBPs remained polarized despite changes in their rates of production, and 2) IGFBP secretion corresponded to mRNA accumulation. The ability of short-chain fatty acids or the fungicide trichostatin A to stimulate IGFBP-2 correlated with their actions on histone acetylation. In conclusion, intestinal epithelial cells respond to short-chain fatty acids by altering secretion of IGFBPs.
Alterations in myocardial lipid metabolism during lactation in the rat
Authors: Wang Xin , Hole David G. , Da Costa Teresa H. M. , Evans Rhys D.
Published: December 2017

Metabolism of nonesterified fatty acid (palmitate, 1.1 mM) and triacylglycerol (TAG; triolein, 0.4 mM in the form of both rat chylomicrons and very low density lipoproteins) was studied in isolated perfused working hearts from fed nulliparous, lactating, and weaned rats. Hearts from virgin rats oxidized palmitate readily, but optimal cardiac mechanical performance occurred during perfusion with chylomicrons. In hearts from lactating dams, there was a significant increase in palmitate oxidation and a marked decrease in TAG oxidation from both chylomicrons and very low density lipoproteins compared with hearts from nulliparous animals. There was a concomitant decrease in lipoprotein lipase activity in hearts from lactating animals, and TAG in the absence of palmitate could not support optimal cardiac mechanical function. After litter removal, the changes in fatty acid and TAG metabolism observed in lactation returned to nulliparous values within 96 h. These results suggest that, during lactation, both exogenous and endogenous TAGs are directed away from heart and toward the lactating mammary gland; the heart, therefore, has to rely to a greater extent on nonesterified fatty acid for energy provision under these conditions.
Dehydroepiandrosterone attenuates preadipocyte growth in primary cultures of stromal-vascular cells
Authors: McIntosh M. , Hausman D. , Martin R. , Hausman G.
Published: December 2017

The purpose of this study was to determine whether the antiobesity actions of dehydroepiandrosterone (DHEA) are due to an influence on preadipocyte proliferation and/or differentiation in primary cultures of pig and rat stromal-vascular (SV) cells. Pig SV cells were isolated from dorsal subcutaneous adipose tissue of 7-day-old pigs. For the proliferation assays, pig SV cells were grown for 4 days in plating medium containing DHEA at 0, 15, 50, or 150 μM. For the differentiation assays, pig SV cells were grown in plating medium for 3 days and then switched to a serum-free medium containing DHEA at 0, 15, 50, or 150 μM for the next 6 days. Rat SV cells were isolated from inguinal fat pads of 5-wk-old male rats. Rat SV cells were exposed to DHEA at 0, 5, 25, or 75 μM during proliferation. For the differentiation assays, rat SV cells were grown for 8 days in a serum-free medium containing DHEA at 0, 5, 25, or 75 μM. Preadipocyte differentiation [lipid staining, glycerol-3-phosphate dehydrogenase (GPDH) activity] and proliferation (preadipocyte-specific antigen staining) decreased with increasing levels of DHEA in cultures of pig SV cells. In cultures of rat SV cells, preadipocyte differentiation (lipid staining, GPDH activity) and proliferation ([3H]thymidine incorporation) were decreased in the 25 and 75 μM DHEA groups compared with the control and 5 μM DHEA groups. The level of expression of CCAAT enhancer binding protein-α, a master regulator of adipogenesis, in cultures of pig SV cells treated with 150 μM DHEA was 38% of control cultures. These data support the hypothesis that DHEA directly attenuates adipogenesis via attenuation of preadipocyte proliferation and differentiation.
Effects of epinephrine on lipid metabolism in resting skeletal muscle
Authors: Peters Sandra J. , Dyck David J. , Bonen Arend , Spriet Lawrence L.
Published: December 2017

The effects of physiological (0, 0.1, 2.5, and 10 nM) and pharmacological (200 nM) epinephrine concentrations on resting skeletal muscle lipid metabolism were investigated with the use of incubated rat epitrochlearis (EPT), flexor digitorum brevis (FDB), and soleus (SOL) muscles. Muscles were chosen to reflect a range of oxidative capacities: SOL > EPT > FDB. The muscles were pulsed with [1-14C]palmitate and chased with [9,10-3H]palmitate. Incorporation and loss of the labeled palmitate from the triacylglycerol pool (as well as mono- and diacylglycerol, phospholipid, and fatty acid pools) permitted the simultaneous estimation of lipid hydrolysis and synthesis. Endogenous and exogenous fat oxidation was quantified by14CO2and3H2O production, respectively. Triacylglycerol breakdown was elevated above control at all epinephrine concentrations in the oxidative SOL muscle, at 2.5 and 200 nM (at 10 nM, P= 0.066) in the FDB, and only at 200 nM epinephrine in the EPT. Epinephrine stimulated glycogen breakdown in the EPT at all concentrations but only at 10 and 200 nM in the FDB and had no effect in the SOL. We further characterized muscle lipid hydrolysis potential and measured total hormone-sensitive lipase content by Western blotting (SOL > FDB > EPT). This study demonstrated that physiological levels of epinephrine cause measurable increases in triacylglycerol hydrolysis at rest in oxidative but not in glycolytic muscle, with no change in the rate of lipid synthesis or oxidation. Furthermore, epinephrine caused differential stimulation of carbohydrate and fat metabolism in glycolytic vs. oxidative muscle. Epinephrine preferentially stimulated glycogen breakdown over triacylglycerol hydrolysis in the glycolytic EPT muscle. Conversely, in the oxidative SOL muscle, epinephrine caused an increase in endogenous lipid hydrolysis over glycogen breakdown.