bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical evaluation of the combined model approach for estimation of prehepatic insulin secretion
Authors: Watanabe Richard M. , Steil Garry M. , Bergman Richard N.
Published: December 2017

The combined model approach uses kinetic analysis of both plasma insulin and C-peptide dynamics to estimate prehepatic insulin secretion rates and parameters of insulin and C-peptide kinetics. The original model used single-compartment kinetics to describe both insulin and C-peptide despite knowledge that C-peptide follows two-compartment kinetics. The performance of the model under rapidly changing secretory conditions has come into question. Thus a more complex combined model is introduced, incorporating two-compartmental C-peptide disappearance. The addition of two-compartment C-peptide kinetics required a novel numerical approach to allow estimation of model parameters. This simulation study was undertaken to 1) compare the performance of the original combined model and 2) examine the numerical method used to identify parameters for the extended combined model with two-compartment C-peptide kinetics under simulated conditions of rapidly changing insulin and C-peptide. Monte Carlo simulation revealed that the original combined model does not provide accurate estimates of prehepatic insulin secretion under rapid kinetics. However, the extended combined model provides accurate reconstruction of prehepatic insulin secretory profile without separate quantification of C-peptide kinetics.
Letters to the Editor
Authors: Baggio Giovanni Gambaro Bruno
Published: December 2017

The following is an abstract of the article discussed in the subsequent letter:

Marshall, Sally M., Klavs W. Hansen, Ruth Østerby, Jan Frystyk, Hans Ørskov, and Allan Flyvbjerg. Effects of heparin on renal morphology and albuminuria in experimental diabetes. Am. J. Physiol. 271 ( Endocrinol. Metab. 34): E326–E332, 1996.—Female nondiabetic and streptozotocin diabetic Wistar rats received 200 units heparin two times daily by subcutaneous injection for 6 mo. Mesangial volume fraction was reduced in heparin-treated control (CH) compared with untreated control (C) animals (CH 0.18 ± 0.02 vs. C 0.24 ± 0.02, P < 0.05), but other histological parameters were similar. In the heparin-treated diabetic (DH) group, wet kidney weight was increased compared with the untreated diabetic (D) group (DH 1,156 ± 39 vs. D 1,050 ± 30 mg, P < 0.05), as were absolute, but not fractional, glomerular volume ( P < 0.05) and capillary volume ( P < 0.05). Basement membrane thickness (DH 193 ± 3 vs. D 231 ± 9 nm, P < 0.01) and mesangial/glomerular volume fraction ( P < 0.001) were decreased. Urinary albumin excretion was increased in the heparin-treated control animals compared with control animals [CH 980 (range 150–4,446) vs. C 221 (range 86–654) μg/24 h, P < 0.001] and in the heparin-treated diabetic animals compared with the diabetic animals [DH 12,785 (range 4,495–29,520) vs. D 899 (range 450–1,335) μg/24 h, P < 0.001]. Thus the possibly deleterious increases in glomerular capillary volume and albumin excretion may negate the beneficial effects of heparin on mesangial and basement membrane structures.
Amylin influences insulin-stimulated glucose metabolism by two independent mechanisms
Authors: Castle Arthur L. , Kuo Chia-Hua , Ivy John L.
Published: December 2017

The effects of amylin on fiber type-specific muscle glucose metabolism under hyperglycemic (10 mmol/l) and hyperinsulinemic (2.1 nmol/l) conditions were investigated using a rat hindlimb perfusion system. Amylin concentration ranged from 1 to 100 nM. Efficacy for inhibition of glucose uptake traced with 2-deoxyglucose by amylin was demonstrated in all three fiber types. The incorporation of 2-deoxy-[3H]glucose tracer decreased from control values by 41% in fast oxidative (FO), 36% in fast glycolytic (FG), and 37% in slow oxidative (SO) muscle with 100 nM amylin. Amylin increased intracellular glucose 6-phosphate (G-6- P), and G-6- P was negatively correlated with 2-deoxyglucose uptake in both FO ( r = −0.65; P < 0.01) and FG ( r = −0.53; P < 0.01) muscle. Muscle glycogen concentration increased under control conditions and decreased in the presence of 100 nM amylin. Lactate arteriovenous efflux across the hindlimb increased significantly above control with 100 nM amylin (5.03 ± 0.81 to 11.28 ± 0.94 μmol ⋅ g−1⋅ h−1). Adenosine 3′,5′cyclic monophosphate (cAMP) increased in FO and FG muscle with amylin. Salmon calcitonin-(8—32), an amylin antagonist, ameliorated the effect of amylin on all responses other than 2-deoxyglucose uptake and G-6- Pconcentration. These results suggest that amylin may work through at least two independent mechanisms, a cAMP-mediated effect on glycogen metabolism and a non-cAMP-mediated inhibition of glycolysis.
Effects of ovarian steroid hormones and thyroxine on calcitonin secretion in pregnant rats
Authors: Lu Chien-Chen , Tsai Shiow-Chwen , Wang Shyi-Wu , Tsai Ching-Lin , Lau Chin-Pang , Shih Hsi-Chang , Chen Yen-Hao , Chiao Yu-Chung , Liaw Charlie , Wang Paulus S.
Published: December 2017

In the present study, the roles of ovarian steroid hormones and thyroxine (T4) in regulating the secretion of calcitonin (CT) in pregnant rats were examined. The levels of plasma progesterone, pre- and post-CaCl2plasma CT, and recovery time of plasma CT and calcium after calcium challenge were greatest in midterm pregnant rats. The levels of basal plasma progesterone, CT, calcium, and recovery time of plasma CT after calcium challenge were less in late pregnant rats, but basal plasma estradiol was highest in late pregnancy. The concentrations of plasma T4 were gradually decreased in rats during pregnancy. Regardless of the presence of estradiol, administration of progesterone in ovariectomized (Ovx) rats resulted in an increase of plasma T4 as well as the basal and calcium-induced secretion of CT. Administration of estradiol alone did not alter the CaCl2-induced levels but decreased the post-CaCl2 levels of plasma calcium in Ovx rats. The basal levels of plasma CT were decreased in Ovx rats treated with T4. These results suggest that the hypercalcitoninemia in midterm pregnant rats is due to an increased secretion of progesterone. Hypocalcitoninemia in late pregnant rats, however, is due in part to lower plasma calcium.
Analysis of insulin-stimulated skeletal muscle glucose uptake in conscious rat using isotopic glucose analogs
Authors: O’Doherty Robert M. , Halseth Amy E. , Granner Daryl K. , Bracy Deanna P. , Wasserman David H.
Published: December 2017

An isotopic method was used in conscious rats to determine the roles of glucose transport and the transsarcolemmal glucose gradient (TSGG) in control of basal and insulin-stimulated muscle glucose uptake. Rats received an intravenous 3- O-[3H]methylglucose (3- O-[3H]MG) infusion from −100 to 40 min and a 2-deoxy-[3H]glucose infusion from 0 to 40 min to calculate a glucose metabolic index (Rg). Insulin was infused from −100 to 40 min at rates of 0.0, 0.6, 1.0, and 4.0 mU ⋅ kg−1⋅ min−1, and glucose was clamped at basal concentrations. The ratios of soleus intracellular to extracellular 3- O-[3H]MG concentration and soleus glucose concentrations were used to estimate the TSGG using principles of glucose countertransport. Tissue glucose concentrations were compared in well-perfused, slow-twitch muscle (soleus) and poorly perfused, fast-twitch muscle (vastus lateralis, gastrocnemius). Data show that 1) small increases in insulin increase soleus Rgwithout decreasing TSGG, suggesting that muscle glucose delivery and phosphorylation can accommodate the increased flux; 2) due to a limitation in soleus glucose phosphorylation and possibly delivery, insulin at high physiological levels decreases TSGG, and at supraphysiological insulin levels the TSGG is not significantly different from 0; 3) maximum Rgis maintained even though TSGG decreases with increasing insulin levels, indicating that glucose transport continues to increase and is not rate limiting for maximal insulin-stimulated glucose uptake; and 4) muscle consisting of fast-twitch fibers that are poorly perfused exhibits a 35–45% fall in tissue glucose with insulin, suggesting that glucose delivery is a major limitation in sustaining the TSGG. In conclusion, control of glucose uptake is distributed between glucose transport and factors that determine the TSGG. Insulin stimulation of glucose transport increases the demands on the factors that maintain glucose delivery to the muscle membrane and glucose phosphorylation inside the muscle.
High-protein meals do not enhance myofibrillar synthesis after resistance exercise in 62- to 75-yr-old men and women
Authors: Welle Stephen , Thornton Charles A.
Published: December 2017

This study tested the hypothesis that increasing the protein content of isocaloric meals increases the rate of myofibrillar synthesis in muscle of healthy subjects over 60 yr old and enhances the stimulation of myofibrillar synthesis induced by resistance exercise. Myofibrillar synthesis of sedentary and exercised quadriceps muscle was determined by incorporation ofl-[1-13C]leucine. During the tracer infusion, subjects consumed meals with a low (7% of energy, n = 6)-, normal (14%, n = 6)-, or high (28%, n = 6)-protein content. In sedentary muscle, the mean (± SE) myofibrillar synthesis was 1.56 ± 0.13%/day in the low-protein group, 1.73 ± 0.11 %/day in the normal-protein group, and 1.76 ± 0.10%/day in the high-protein group ( P = 0.42). Myofibrillar synthesis was faster in exercised muscle (mean 27%, P < 10−6) in all groups (2.10 ± 0.14 %/day in low protein; 2.18 ± 0.10 %/day in normal protein; 2.11 ± 0.09 %/day in high protein; P = 0.84). The stimulation of myofibrillar synthesis by exercise was not significantly different among low-protein [0.54 ± 0.12 %/day (37 ± 9%)], normal-protein [0.46 ± 0.08 %/day (28 ± 5%)], and high-protein groups [0.34 ± 0.04 %/day (20 ± 3%); P = 0.31]. We conclude that high-protein meals do not enhance the stimulation of myofibrillar protein synthesis induced by resistance exercise.
Signaling and sites of interaction for RX-871024 and sulfonylurea in the stimulation of insulin release
Authors: Efanov Alexandre M. , Zaitsev Sergei V. , Efanova Ioulia B. , Zhu Shunsheng , Östenson Claes-Göran , Berggren Per-Olof , Efendić Suad
Published: December 2017

The objective of this study was to compare effects of RX-871024, a compound with imidazoline structure, and the sulfonylurea glibenclamide, representatives of two groups of ATP-dependent potassium channel (KATP) blockers, on insulin secretion and cytoplasmic free calcium concentration ([Ca2+]i). Furthermore, we studied the interaction of the compounds on these two parameters. The experiments were performed in the perfused rat pancreas, isolated rat pancreatic islets, and dispersed β-cells. At maximal effective concentrations of the compounds, RX-871024 had a more pronounced insulinotropic effect than glibenclamide, but the increase in [Ca2+]iwas similar. Glibenclamide enhanced the insulinotropic effect of suboptimal concentrations of RX-871024 at 3.3 and 16.7 mM glucose. Notably, glibenclamide and RX-871024 also stimulated insulin secretion under Ca2+-clamped conditions, i.e., during plasma membrane depolarization with KCl and glucose or in permeabilized islets. The magnitudes of insulin stimulation under the latter types of conditions were similar for both compounds. It is concluded that RX-871024 and the sulfonylurea glibenclamide promote insulin secretion by two mechanisms, namely closure of KATP channels and a direct stimulation of exocytosis. At a similar increase in [Ca2+]i, the maximal stimulatory effect of RX-871024 on insulin secretion was stronger than that of glibenclamide, implying that RX-871024 also affects insulin secretion by a signal transduction pathway that is not activated by glibenclamide.
Skeletal muscle malonyl-CoA content at the onset of exercise at varying power outputs in humans
Authors: Odland L. Maureen , Howlett Richard A. , Heigenhauser George J. F. , Hultman Eric , Spriet Lawrence L.
Published: December 2017

To investigate the regulation of intramuscular fuel selection, we measured the malonyl-CoA (M-CoA) content in human skeletal muscle at three exercise power outputs [35, 65, and 90% maximal rate of O2consumption (V˙o2 max)]. Four males and four females cycled for 10 min at one power output on three separate occasions with muscle biopsies sampled at rest and at 1 and 10 min. The respiratory exchange ratio was 0.84 ± 0.03, 0.92 ± 0.02, and >1.0 at 35, 65 and 90%V˙o2 max, respectively. Muscle lactate content increased and phosphocreatine content decreased as a function of power output. Pyruvate dehydrogenase a activity increased from 0.40–0.64 mmol ⋅ kg wet muscle−1⋅ min−1at rest to 1.57 ± 0.28, 2.80 ± 0.41, and 3.28 ± 0.27 mmol ⋅ kg wet muscle−1⋅ min−1after 1 min of cycling at the three power outputs, respectively. Mean resting M-CoA contents were similar at all power outputs (1.85–1.98 μmol/kg dry muscle). During exercise at 35%V˙o2 max, M-CoA decreased from rest at 1 min (1.85 ± 0.29 to 1.20 ± 0.12 μmol/kg dry muscle) but returned to rest level by 10 min (1.86 ± 0.25 μmol/kg dry muscle). M-CoA content did not decrease during cycling at 65%V˙o2 max. At 90%V˙o2 max, M-CoA did not increase despite significant acetyl-CoA accumulation (the substrate for M-CoA synthesis). The data suggest that a decrease in M-CoA content is not required for the increase in free fatty acid uptake and oxidation that occurs during exercise at 35 and 65%V˙o2 max. Furthermore, M-CoA content does not increase during exercise at 90%V˙o2 maxand does not contribute to the lower rate of fat oxidation at this power output.
Remodeling of the HDL in NIDDM: a fundamental role for cholesteryl ester transfer protein
Authors: Castle Christine K. , Kuiper Susan L. , Blake William L. , Paigen Beverly , Marotti Keith R. , Melchior George W.
Published: December 2017

When the Aygene is expressed in KK mice, the yellow offspring (KKAymice) become obese, insulin resistant, hyperglycemic, and severely hypertriglyceridemic, yet they maintain extraordinarily high plasma high-density lipoprotein (HDL) levels. Mice lack the ability to redistribute neutral lipids among circulating lipoproteins, a process catalyzed in humans by cholesteryl ester transfer protein (CETP). To test the hypothesis that it is the absence of CETP that allows these hypertriglyceridemic mice to maintain high plasma HDL levels, simian CETP was expressed in the KKAymouse. The KKAy-CETP mice retained the principal characteristics of KKAymice except that their plasma HDL levels were reduced (from 159 ± 25 to 25 ± 6 mg/dl) and their free apolipoprotein A-I concentrations increased (from 7 ± 3 to 22 ± 6 mg/dl). These changes appeared to result from a CETP-induced enrichment of the HDL with triglyceride (from 6 ± 2 to 60 ± 18 mol of triglyceride/mol of HDL), an alteration that renders HDL susceptible to destruction by lipases. These data support the premise that CETP-mediated remodeling of the HDL is responsible for the low levels of that lipoprotein that accompany hypertriglyceridemic non-insulin-dependent diabetes mellitus.
Preferential utilization of newly synthesized cholesterol for brain growth in neonatal lambs
Authors: Turley Stephen D. , Burns Dennis K. , Dietschy John M.
Published: December 2017

These studies used the suckling lamb as a model to determine the sources of cholesterol that are utilized for development of the central nervous system in the neonate. Lambs were studied at 1.3 and 16.4 days after birth. Over this 15-day interval, 14 g of new brain tissue were formed. About 9–10 mg of cholesterol were utilized daily for this new tissue growth. To determine the source of this cholesterol, the absolute rates of low-density lipoprotein clearance and cholesterol synthesis were measured in vivo in nine separate regions of the central nervous system. Low-density lipoprotein clearance throughout the brain was very low and at most could have contributed only 0.3–0.4 mg cholesterol daily for new brain growth. In contrast, the brain synthesized 7–8 mg of cholesterol/day. There were pronounced regional differences in the concentration of cholesterol throughout the brain, and these correlated closely with the rate of sterol synthesis ( r = 0.95) in these same regions. We conclude that the principal source of sterol for brain growth in suckling lambs is de novo synthesis.
A negative arterial-portal venous glucose gradient decreases skeletal muscle glucose uptake
Authors: Galassetti Pietro , Shiota Masakazu , Zinker Brad A. , Wasserman David H. , Cherrington Alan D.
Published: December 2017

The effect of a negative arterial-portal venous (a-pv) glucose gradient on skeletal muscle and whole body nonhepatic glucose uptake was studied in 12 42-h-fasted conscious dogs. Each study consisted of a 110-min equilibration period, a 30-min baseline period, and two 120-min hyperglycemic (2-fold basal) periods (either peripheral or intraportal glucose infusion). Somatostatin was infused along with insulin (3 × basal) and glucagon (basal). Catheters were inserted 17 days before studies in the external iliac artery and hepatic, portal and common iliac veins. Blood flow was measured in liver and hindlimb using Doppler flow probes. The arterial blood glucose, arterial plasma insulin, arterial plasma glucagon, and hindlimb glucose loads were similar during peripheral and intraportal glucose infusions. The a-pv glucose gradient (in mg/dl) was 5 ± 1 during peripheral and −18 ± 3 during intraportal glucose infusion. The net hindlimb glucose uptakes (in mg/min) were 5.0 ± 1.2, 20.4 ± 4.5, and 14.8 ± 3.2 during baseline, peripheral, and intraportal glucose infusion periods, respectively ( P < 0.01, peripheral vs. intraportal); the hindlimb glucose fractional extractions (in %) were 2.8 ± 0.4, 4.7 ± 0.8, and 3.9 ± 0.5 during baseline, peripheral, and intraportal glucose infusions, respectively ( P < 0.05, peripheral vs. intraportal). The net whole body nonhepatic glucose uptakes (in mg ⋅ kg−1⋅ min−1) were 1.6 ± 0.1, 7.9 ± 1.3, and 5.4 ± 1.1 during baseline, peripheral, and intraportal glucose infusion, respectively ( P < 0.05, peripheral vs. intraportal). In the liver, net glucose uptake was 70% greater during intraportal than during peripheral glucose infusion (5.8 ± 0.7 vs. 3.4 ± 0.4 mg ⋅ kg−1⋅ min−1). In conclusion, despite comparable glucose loads and insulin levels, hindlimb and whole body net nonhepatic glucose uptake decreased significantly during portal venous glucose infusion, suggesting that a negative a-pv glucose gradient leads to an inhibitory signal in nonhepatic tissues, among which skeletal muscle appears to be the most important.
Effects of daytime melatonin infusion in young adults
Authors: Van Den Heuvel Cameron J. , Kennaway David J. , Dawson Drew
Published: December 2017

Daytime oral melatonin typically exerts soporific and thermoregulatory effects; however, it is not clear whether these effects reflect the normal physiological response to endogenous nocturnal melatonin production. We infused melatonin at doses that produced physiological and supraphysiological steady-state levels in 24 young adults during two daytime bed rest protocols. From 1000 to 1630, subjects were infused intravenously with saline or melatonin in counterbalanced order. Each group of eight subjects received melatonin (and saline) infusions at one dose rate: 0.04 μg ⋅ h−1⋅ kg body wt−1(low), 0.08 μg ⋅ h−1⋅ kg−1(medium), or 8.0 μg ⋅ h−1⋅ kg−1(high). Low and medium melatonin infusions produced plasma and saliva levels within the normal nocturnal range observed in young adults. These levels were not associated with any changes in rectal, hand, forehead, or tympanic temperatures or with subjective sleepiness. High melatonin produced supraphysiological plasma and saliva levels and was associated with a significant attenuation in the daytime increase in rectal temperature, significantly increased hand temperature, and greater sleepiness. It is not yet clear whether the thermoregulatory and soporific effects of daytime supraphysiological melatonin administration are equivalent to the physiological responses to endogenous melatonin.
Plasma growth hormone secretion is impaired in obesity-prone rats before onset of diet-induced obesity
Authors: Lauterio Thomas J. , Barkan Ariel , DeAngelo Mark , DeMott-Friberg Roberta , Ramirez Ray
Published: December 2017

Sprague-Dawley rats, which become obese (obesity prone) when fed a moderately high-fat (MHF; 32.5% of kcal as fat) diet, have decreased growth hormone (GH) concentrations compared with obesity-resistant rats fed the same diet. To determine whether plasma GH concentrations are different in obesity-prone rats compared with obesity-resistant rats before diet-induced obesity occurs, total integrated GH concentrations were determined in male Sprague-Dawley rats before exposure to the MHF diet. After initial blood sampling, rats were fed an MHF diet for 15 wk, over which time the animals were separated into two discrete populations based on body weight gain. Analysis of GH in episodic blood samples showed that the obesity-prone group had a GH secretion deficit before the onset of obesity (115.2 ± 12.9 ng ⋅ ml−1 ⋅ 200 min−1) compared with obesity-resistant rats (237.2 ± 47.1 ng ⋅ ml−1 ⋅ 200 min−1). The GH concentration difference was due to a decrease in mean GH peak height in rats that later became obese (34.8 ng/ml) compared with rats that remained lean (74.2 ng/ml). The results suggest that GH secretion impairment exists before dietary challenge or onset of obesity and may contribute to the susceptibility to obesity observed in these animals.
Effects of flooding amino acids on incorporation of labeled amino acids into human muscle protein
Authors: Smith Kenneth , Reynolds Nigel , Downie Shaun , Patel Ayyub , Rennie Michael J.
Published: December 2017

We investigated the effects of the nature of the flooding amino acid on the rate of incorporation of tracer leucine into human skeletal muscle sampled by biopsy. Twenty-three healthy young men (24.5 ± 5.0 yr, 76.2 ± 8.3 kg) were studied in groups of four or five. First, the effects of flooding with phenylalanine, threonine, or arginine (all at 0.05 g/kg body wt) on the incorporation of tracer [13C]leucine were studied. Then the effects of flooding with labeled [13C]glycine [0.1 g/kg body wt, 20 atoms percent excess (APE)] and [13C]serine (0.05 g/kg body wt, 15 APE) on the incorporation of simultaneously infused [13C]leucine were investigated. When a large dose of phenylalanine or threonine was administered, incorporation of the tracer leucine was significantly increased (from 0.036 to 0.067 %/h and 0.037 to 0.070 %/h, respectively; each P < 0.01). However, when arginine, glycine, or serine was administered as a flooding dose, no stimulation of tracer leucine incorporation could be observed. These results, together with those previously obtained, suggest that large doses of individual essential, but not nonessential, amino acids are able to stimulate incorporation of constantly infused tracer amino acids into human muscle protein.
Angiotensin II induces acrosomal exocytosis in bovine spermatozoa
Authors: Gur Yael , Breitbart Haim , Lax Yehudit , Rubinstein Sara , Zamir Nadav
Published: December 2017

Ejaculated mammalian spermatozoa must reside in the female genital tract for some time before gaining the ability to fertilize the egg. During this time, spermatozoa undergo some physiological changes that collectively are called capacitation. Capacitation of mammalian spermatozoa is a prerequisite for acrosome reaction, which is an exocytotic event occurring before fertilization. The specific biophysical and biochemical changes that accompany sperm capacitation and the agonists inducing acrosome reaction are not fully understood. Using SDS-gel electrophoresis and immunoblotting, we demonstrate the existence of a class of angiotensin receptors (AT1) in bovine spermatozoa. In capacitated sperm, we show that angiotensin II (ANG II) AT1receptors are localized in the head and tail, whereas in noncapacitated cells the receptors are localized in the tail only. We find that ANG II markedly stimulates acrosomal exocytosis of capacitated bovine spermatozoa in vitro in a concentration range of 0.1–10 nM. No effect of ANG II was found in noncapacitated cells. The ability of ANG II to stimulate the acrosome reaction depends on the presence of calcium ions in the incubation medium. The ANG II-induced acrosome reaction was markedly inhibited by a selective AT1receptor antagonist, losartan (DUP 753). PD-123319, a selective antagonist of the ANG II AT2receptor, had no effect on the ANG II-induced acrosome reaction. Thus ANG II via activation of AT1receptors may play a regulatory role in the induction of the acrosome reaction.
Insulin-like growth factors sustain insulin-like growth factor-binding protein-5 expression in osteoblasts
Authors: Gabbitas Bari , Canalis Ernesto
Published: December 2017

Insulin-like growth factors (IGFs) I and II are considered to be autocrine regulators of bone cell function. Recently, we demonstrated that IGF-I induces IGF-binding protein-5 (IGFBP-5) expression in cultures of osteoblast-enriched cells from 22-day fetal rat calvariae (Ob cells). In the present study, we postulated that IGFs play an autocrine role in the maintenance of IGFBP-5 basal expression in Ob cells. IGFBP-2 and -3, at concentrations that bind endogenous IGFs, decreased IGFBP-5 mRNA levels, as determined by Northern blot analysis, and protein levels, as determined by Western immunoblots of extracellular matrix extracts of Ob cells. IGFBP-2 and -3 in excess inhibited IGFBP-5 heterogeneous nuclear RNA levels, as determined by RT-PCR, and did not alter the half-life of IGFBP-5 mRNA in transcriptionally arrested Ob cells. In conclusion, blocking endogenous IGFs in Ob cells represses IGFBP-5 expression, suggesting that IGFs are autocrine inducers of IGFBP-5 synthesis in osteoblasts.
Advancing age and insulin resistance: role of plasma tumor necrosis factor-α
Authors: Paolisso Giuseppe , Rizzo Maria Rosaria , Mazziotti Gherardo , Tagliamonte Maria Rosaria , Gambardella Antonio , Rotondi Mario , Carella Carlo , Giugliano Dario , Varricchio Michele , D’Onofrio Felice
Published: December 2017

In 70 healthy subjects with a large age range, the relationships between plasma tumor necrosis factor-α (TNF-α) and body composition, insulin action, and substrate oxidation were investigated. In the cross-sectional study ( n = 70), advancing age correlated with plasma TNF-α concentration ( r = 0.64, P < 0.001) and whole body glucose disposal (WBGD; r= −0.38, P < 0.01). The correlation between plasma TNF-α and age was independent of sex and body fat (BF; r = 0.31, P < 0.01). Independent of age and sex, a significant relationship between plasma TNF-α and leptin concentration ( r = 0.29, P < 0.02) was also found. After control for age, sex, BF, and waist-to-hip ratio (WHR), plasma TNF-α was still correlated with WBGD ( r = −0.33, P < 0.007). Further correction for plasma free fatty acid (FFA) concentration made the latter correlation no more significant. In a multivariate analysis, a model made by age, sex, BF, fat- free mass, WHR, and plasma TNF-α concentrations explained 69% of WBGD variability with age ( P < 0.009), BF ( P < 0.006), fat-free mass ( P < 0.005), and plasma TNF-α ( P < 0.05) significantly and independently associated with WBGD. In the longitudinal study, made with subjects at the highest tertiles of plasma TNF-α concentration ( n = 50), plasma TNF-α concentration predicted a decline in WBGD independent of age, sex, BF, WHR [relative risk (RR) = 2.0; 95% confidence intervals (CI) = 1.2–2.4]. After further adjustment for plasma fasting FFA concentration, the predictive role of fasting plasma TNF-α concentration on WBGD (RR = 1.2; CI = 0.8–1.5) was no more significant. In conclusion, our study demonstrates that plasma TNF-α concentration is significantly associated with advancing age and that it predicts the impairment in insulin action with advancing age.
Effects of FFA on insulin-stimulated glucose fluxes and muscle glycogen synthase activity in rats
Authors: Park Joong-Yeol , Kim Chul-Hee , Hong Sung K. , Suh Kyo I. , Lee Ki-Up
Published: December 2017

To examine effects of free fatty acids (FFA) on insulin-stimulated glucose fluxes, euglycemic hyperinsulinemic (86 pmol ⋅ kg−1⋅ min−1) clamps were performed for 5 h in conscious rats with ( n = 8) or without ( n = 8) lipid-heparin infusion. Glucose infusion rate required to maintain euglycemia was not different between the two groups during the first 2 h of clamps but became significantly lower with lipid-heparin infusion in the 3rd h and thereafter. To investigate changes in intracellular glucose metabolism during lipid-heparin infusion, additional clamps ( n = 8 each) were performed for 1, 2, 3, or 5 h with an infusion of [3-3H]glucose. Insulin-stimulated whole body glucose utilization (Rd), glycolysis, and glycogen synthesis were estimated on the basis of tracer concentrations in plasma during the final 40 min of each clamp. Similar to changes in glucose infusion rate, Rdwas not different between the two groups in the 1st and 2nd h but was significantly lower with lipid-heparin infusion in the 3rd h and thereafter. Whole body glycolysis was significantly lower with lipid-heparin infusion in all time periods, i.e., 1st, 2nd, 3rd, and 5th h of clamps. In contrast, whole body glycogen synthesis was higher with lipid-heparin infusion in the 1st and 2nd h but lower in the 5th h. Similarly, accumulation of [3H]glycogen radioactivity in muscle glycogen was significantly higher with lipid-heparin during the 1st and 2nd h but lower during the 3rd and 5th h. Glucose 6-phosphate (G-6- P) concentrations in gastrocnemius muscles were significantly higher with lipid-heparin infusion throughout the clamps. Muscle glycogen synthase (GS) activity was not altered with lipid-heparin infusion at 1, 2, and 3 h but was significantly lower at 5 h. Thus increased availability of FFA significantly reduced whole body glycolysis, but compensatory increase in skeletal muscle glycogen synthesis in association with accumulation of G-6- P masked this effect, and Rdwas not affected in the early phase (within 2 h) of lipid-heparin infusion. Rdwas reduced in the later phase (>2 h) of lipid-heparin infusion, when glycogen synthesis was reduced in association with reduced skeletal muscle GS activity.
Skeletal muscle insulin resistance after trauma: insulin signaling and glucose transport
Authors: Strömmer Lisa , Permert Johan , Arnelo Urban , Koehler Camilla , Isaksson Bengt , Larsson Jörgen , Lundkvist Inger , Björnholm Marie , Kawano Yuichi , Wallberg-Henriksson Harriet , Zierath Juleen R.
Published: December 2017

Surgical trauma induces peripheral insulin resistance; however, the cellular mechanism has not been fully elucidated. We examined the effects of surgical trauma on insulin receptor signaling and glucose transport in skeletal muscle, a tissue that plays a predominant role in maintaining glucose homeostasis. Surgical trauma was induced by intestinal resection in the rat. Receptor phosphorylation was not altered with surgical trauma. Phosphotyrosine-associated phosphatidylinositol (PI) 3-kinase association was increased by 60 and 82% compared with fasted and fed controls, respectively ( P < 0.05). Similar results were observed for insulin receptor substrate-1-associated PI 3-kinase activity. Insulin-stimulated protein kinase B (Akt kinase) phosphorylation was increased by 2.2-fold after surgical trauma ( P < 0.05). The hyperphosphorylation of Akt is likely to reflect amplification of PI 3-kinase after insulin stimulation. Submaximal rates of insulin-stimulated 3- O-methylglucose transport were reduced in trauma vs. fasted rats by 51 and 38% for 100 and 200 μU/ml of insulin, respectively ( P< 0.05). In conclusion, insulin resistance in skeletal muscle after surgical trauma is associated with reduced glucose transport but not with impaired insulin signaling to PI 3-kinase or its downstream target, Akt. The surgical trauma model presented in this report provides a useful tool to further elucidate the molecular mechanism(s) underlying the development of insulin resistance after surgical trauma.
Surgical trauma decreases glutathione synthetic capacity in human skeletal muscle tissue
Authors: Luo Jia-Li , Hammarqvist Folke , Andersson Kerstin , Wernerman Jan
Published: December 2017

To gain insight into cellular metabolism underlying the glutathione (GSH) alterations induced by surgical trauma, we assessed postoperative skeletal muscle GSH metabolism and its redox status in 10 patients undergoing elective abdominal surgery. Muscle biopsy specimens were taken from the quadriceps femoris muscle before and at 24 and 72 h after surgery. GSH concentrations decreased by 40% at 24 h postoperatively compared with the paired preoperative values ( P < 0.001) and remained low at 72 h ( P < 0.01). The concentration of GSH disulfide (GSSG) did not significantly change throughout the study period, whereas the total GSH (as GSH equivalent) concentration decreased after surgery. Of the GSH constituent amino acids, the concentration of cysteine remained unchanged throughout the study period (from 28.2 ± 10.1 preoperatively to 29.4 ± 13.9 at 24 h postoperatively and to 28.3 ± 15.6 μmol/kg wet wt at 72 h postoperatively). Despite a reduction in glutamate concentration by 40% 24 h after surgery, no correlation was established between GSH and glutamate concentrations postoperatively. Activity of γ-glutamylcysteine synthetase did not change significantly after surgery, whereas GSH synthetase activity decreased postoperatively (from 66.4 ± 19.1 preoperatively to 41.0 ± 10.5 24 h postoperatively, P < 0.01, and to 46.0 ± 11.7 μU/mg protein 72 h postoperatively, P < 0.05). The decrease of GSH was correlated to the reduced GSH synthetase activity seen at 24 h postoperatively. These results indicate that the skeletal muscle GSH pool is diminished in patients after surgical trauma. The depletion of the GSH pool is associated with a decreased activity of GSH synthetase, indicating a decreased GSH synthetic capacity in skeletal muscle tissue.
Blockage of gonadotropin-induced first ovulation caused by thyroidectomy and its possible mechanisms in rats
Authors: Tamura Kazuhiro , Hatsuta Minoru , Watanabe Gen , Taya Kazuyoshi , Kogo Hiroshi
Published: December 2017

To determine the role of the thyroid gland on the ovarian functions during the initiation process of puberty, we examined the effects and its mechanisms of hypothyroidism on the first ovulation induced by equine chorionic gonadotropin (eCG) in immature female rats. Animals were thyroidectomized on day 22 and were injected with 5 IU of eCG on day 26 to induce the first ovulation on day 29. The number of antral follicles that secrete inhibin and the ovarian weight were significantly increased in thyroidectomized rats (Tx rats) 48 h after eCG treatment compared with those in non-Tx rats. However, thyroidectomy (Tx) significantly suppressed the rates of ovulating animals on day 29. The blockage of ovulation in Tx rats was recovered by administration of human chorionic gonadotropin or luteinizing hormone (LH)-releasing hormone (LHRH) on day 28. Inhibition of serum LH (not follicle-stimulating hormone) levels induced by Tx was almost restored to control levels by injection of LHRH. A significant increment in prolactin levels in Tx rats was also observed on day 28. The present data indicate that Tx before puberty in female rats causes the blockage of the first ovulation and that the inhibitory effects on ovulation are mainly due to the reduction in the preovulatory LH surge, which is partially mediated through an inhibition of LHRH action on the secretion of LH.
Monocarboxylate transporter expression in mouse brain
Authors: Koehler-Stec E. M. , Simpson I. A. , Vannucci S. J. , Landschulz K. T. , Landschulz W. H.
Published: December 2017

Although glucose is the major metabolic fuel needed for normal brain function, monocarboxylic acids, i.e., lactate, pyruvate, and ketone bodies, can also be utilized by the brain as alternative energy substrates. In most mammalian cells, these substrates are transported either into or out of the cell by a family of monocarboxylate transporters (MCTs), first cloned and sequenced in the hamster. We have recently cloned two MCT isoforms (MCT1 and MCT2) from a mouse kidney cDNA library. Northern blot analysis revealed that MCT1 mRNA is ubiquitous and can be detected in most tissues at a relatively constant level. MCT2 expression is more limited, with high levels of expression confined to testes, kidney, stomach, and liver and lower levels in lung, brain, and epididymal fat. Both MCT1 mRNA and MCT2 mRNA are detected in mouse brain using antisense riboprobes and in situ hybridization. MCT1 mRNA is found throughout the cortex, with higher levels of hybridization in hippocampus and cerebellum. MCT2 mRNA was detected in the same areas, but the pattern of expression was more specific. In addition, MCT1 mRNA, but not MCT2, is localized to the choroid plexus, ependyma, microvessels, and white matter structures such as the corpus callosum. These results suggest a differential expression of the two MCTs at the cellular level.
Amylin-mediated inhibition of insulin-stimulated glucose transport in skeletal muscle
Authors: Castle Arthur L. , Kuo Chia-Hua , Han Dong-Ho , Ivy John L.
Published: December 2017

We examined the effects of amylin on 3- O-methyl-d-glucose (3- O-MG) transport in perfused rat hindlimb muscle under hyperinsulinemic (350 μU/ml, 2,100 pmol/l) conditions. Amylin at 100 nmol/l concentration inhibited 3- O-MG transport relative to control in all three basic muscle fiber types. Transport decreased in slow-twitch oxidative (from 5.65 ± 1.13 to 3.46 ± 0.71 μmol ⋅ g−1⋅ h−1), fast-twitch oxidative (from 6.84 ± 0.90 to 4.84 ± 0.76 μmol ⋅ g−1⋅ h−1), and fast-twitch glycolytic (from 1.27 ± 0.20 to 0.60 ± 0.05 μmol ⋅ g−1⋅ h−1) muscle. Amylin inhibition of insulin-stimulated glucose transport in skeletal muscle was accompanied by a 433 ± 72% increase in intracellular glucose 6-phosphate (G-6- P) despite the absence of extracellular glucose. The source of hexose units for the formation and maintenance of G-6- P was likely glycogen. Amylin increased glycogenolysis, increased lactate formation, and decreased glycogen synthase activity. Furthermore, the kinetics of glycogen synthase suggest that this enzyme may control intracellular G-6- P concentration. Despite the large increase in G-6- P, no detectable increase in uridine diphosphate- N-acetylhexosamines occurred, suggesting that the proposed glucosamine pathway may not be involved in transport inhibition. However, decreases in uridine diphosphate hexoses were detected. Therefore, uridine or hexosamine-based metabolites may be involved in amylin action.
Temporal activation of p70 S6 kinase and Akt1 by insulin: PI 3-kinase-dependent and -independent mechanisms
Authors: Somwar Romel , Sumitani Satoru , Taha Celia , Sweeney Gary , Klip Amira
Published: December 2017

Several studies have suggested that activation of p70 ribosomal S6 kinase (p70 S6 kinase) by insulin may be mediated by the phosphatidylinositol 3-kinase (PI 3-kinase)-Akt pathway. However, by temporal analysis of the activation of each kinase in L6 muscle cells, we report that the activation of the two serine/threonine kinases (Akt and p70 S6 kinase) can be dissociated. Insulin stimulated p70 S6 kinase in intact cells in two phases. The first phase (5 min) of stimulation was fully inhibited by wortmannin (IC50= 20 nM) and LY-294002 (full inhibition at 5 μM). After this early inhibition, p70 S6 kinase was gradually stimulated by insulin in the presence of 100 nM wortmannin. After 30 min, the stimulation was 65% of the maximum attained in the absence of wortmannin. The IC50of wortmannin for inhibition of this second phase was ∼150 nM. In contrast, activation of Akt1 by insulin was completely inhibited by 100 nM wortmannin at all time points investigated. Inhibition of mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase with PD-098059 (10 μM) or treatment with the protein kinase C inhibitor bisindolylmaleimide (10 μM) had no effect on the late phase of insulin stimulation of p70 S6 kinase. We have previously shown that GLUT-1 protein synthesis in these cells is stimulated by insulin via the mTOR-p70 S6 kinase pathway, based on its sensitivity to rapamycin. We therefore investigated whether the signals leading to GLUT-1 synthesis correlated with the early or late phase of stimulation of p70 S6 kinase. GLUT-1 synthesis was not inhibited by wortmannin (100 nM). In summary, insulin activates p70 ribosomal S6 kinase in L6 muscle cells by two mechanisms, one dependent on and one independent of the activation of PI 3-kinase. In addition, activation of Akt1 is fully inhibited by wortmannin, suggesting that Akt1 does not participate in the late activation of p70 S6 kinase. Wortmannin-sensitive PI 3-kinases and Akt1 are not required for insulin stimulation of GLUT-1 protein biosynthesis.
Age-related differences in the secretion of calcitonin in female rats
Authors: Lu Chien-Chen , Tsai Shiow-Chwen , Wang Shyi-Wu , Huang William J. S. , Wang Paulus S.
Published: December 2017

The mechanism that causes hypercalcitonemia in female rats and is associated with aging was investigated. Young (3 mo), adult (8 mo), middle-aged (12 mo), and old (21 mo) rats were infused with CaCl2 and were bled from a jugular catheter after a CaCl2 challenge. To mimic some of the hormonal changes caused by aging, the anterior pituitary (AP)-grafted ovariectomized rats with hyperprolactinemic syndrome were used to mimic the physiological status of aging. The rat thyroid gland was incubated with or without ovine prolactin (oPRL; 40 or 80 ng/ml) at 37°C for 30 min. Old rats possessed the lowest levels of plasma estradiol and progesterone yet had the highest levels of plasma prolactin and calcitonin (CT) compared with young, adult, and middle-aged rats. The basal release of thyroid CT in vitro in thyroid glands gradually increased with age. Compared with cortex (CX)-grafted rats, the AP-grafted rats possessed higher levels of plasma PRL, basal and CaCl2-induced levels of plasma CT, and the release of thyroid CT in thyroid glands. After stimulation with oPRL, the in vitro release of thyroid CT increased in both CX- and AP-grafted rats. These results suggest that the hypersecretion of CT in old rats is due at least in part to hyperprolactinemia.
Effects of β-adrenergic blockade on hepatic and renal glucose production during hypoglycemia in conscious dogs
Authors: Cersosimo Eugenio , Zaitseva Irina N. , Ajmal Mohamed
Published: December 2017

To investigate the role of β-adrenergic mechanisms in the counterregulatory response of the liver and kidney to hypoglycemia, we studied 10 dogs before and after a 2-h constant infusion of insulin (4 mU ⋅ kg−1⋅ min−1) either without ( n = 4) or with (8 μg/min, n = 6) propranolol and variable dextrose to maintain hypoglycemia, 7 days after surgical placement of sampling catheters in left renal and hepatic veins and femoral artery. Systemic glucose appearance (Ra) and endogenous (EGP), hepatic (HGP), and renal (RGP) glucose production were measured by a combination of arteriovenous difference and peripheral infusion of [6-3H]glucose, renal blood flow with a flow probe, and hepatic plasma flow by indocyanine green clearance. Without β-adrenergic blockade, arterial glucose decreased from 5.12 ± 0.02 to 2.53 ± 0.07 mmol/l, glucose Raincreased from 17.8 ± 0.7 to 30.5 ± 2.5 ( P< 0.01) when EGP was 22.2 ± 0.5, HGP from 13.5 ± 1.1 to 19.3 ± 1.3, and RGP from 2.4 ± 1.0 to 8.6 ± 0.9 μmol ⋅ kg−1⋅ min−1(all P < 0.05). When propranolol was infused, glucose decreased from 5.97 ± 0.02 to 2.71 ± 0.03 mmol/l, glucose Raincreased from 16.3 ± 1.0 to 25.1 ± 1.6 when EGP was 9.9 ± 0.4, HGP decreased from 14.4 ± 0.7 to 10.4 ± 0.6, and RGP decreased from 3.8 ± 1.3 to 1.1 ± 0.8 μmol ⋅ kg−1⋅ min−1(all P < 0.05). Our data indicate that β-adrenergic blockade impairs glucose recovery during sustained hypoglycemia, in part, by preventing the simultaneous compensatory increase in HGP and RGP.
Hyperglycemia-induced inhibition of splanchnic fatty acid oxidation increases hepatic triacylglycerol secretion
Authors: Sidossis Labros S. , Mittendorfer Bettina , Walser Eric , Chinkes David , Wolfe Robert R.
Published: December 2017

The effect of hyperglycemia (∼8 mmol/l) on splanchnic fatty acid oxidation and triacylglycerol (TG) secretion rates was investigated in five healthy men. U-13C-labeled fatty acids were infused to estimate fatty acid kinetics and oxidation across the splanchnic region, and in vivo labeled very low density lipoprotein (VLDL)-TG was infused to estimate TG secretion rate. Plasma fatty acid carbon enrichment and concentration were maintained constant by infusion of lipids and heparin in the hyperglycemia experiments. Fatty acid uptake by the splanchnic region was 1.4 ± 0.2 and 2.2 ± 0.9 μmol ⋅ kg−1⋅ min−1in the basal and clamp experiments, respectively, whereas fatty acid oxidation decreased from 0.4 ± 0.04 to 0.2 ± 0.05 μmol ⋅ kg−1⋅ min−1( P < 0.05). Hepatic TG secretion increased from 0.35 ± 0.07 μmol ⋅ kg−1⋅ min−1in the basal state to 0.53 ± 0.11 μmol ⋅ kg−1⋅ min−1after 15 h of hyperglycemia ( P< 0.05). Similarly, plasma VLDL-TG concentration increased from 0.28 ± 0.06 to 0.43 ± 0.05 mmol/l during the clamp ( P < 0.05). In summary, hyperglycemia attenuates fatty acid oxidation in the splanchnic region in human volunteers, even when fatty acid availability is constant. This adaptation results in a significant increase in the VLDL-TG secretion rate and concentration in plasma.
Kinetics of dexamethasone-induced alterations of glucose metabolism in healthy humans
Authors: Schneiter P. , Tappy L.
Published: December 2017

Six healthy human subjects were studied during three 75-g oral, [13C]glucose tolerance tests to assess the kinetics of dexamethasone-induced impairment of glucose tolerance. On one occasion, they received dexamethasone (4 × 0.5 mg/day) during the previous 2 days. On another occasion, they received a single dose (0.5 mg) of dexamethasone 150 min before ingestion of the glucose load. On the third occasion, they received a placebo. Postload plasma glucose was significantly increased after both 2 days dexamethasone and single dose dexamethasone compared with control ( P < 0.05). This corresponded to a 20–23% decrease in the metabolic clearance rate of glucose, whereas total glucose turnover ([6,6-2H]glucose), total (indirect calorimetry) and exogenous glucose oxidation (13CO2production), and suppression of endogenous glucose production were unaffected by dexamethasone. Plasma insulin concentrations were increased after 2 days of dexamethasone but not after a single dose of dexamethasone. In a second set of experiments, the effect of a single dose of dexamethasone on insulin sensitivity was assessed in six healthy humans during a 2-h euglycemic hyperinsulinemic clamp. Dexamethasone did not significantly alter insulin sensitivity. It is concluded that acute administration of dexamethasone impairs oral glucose tolerance without significantly decreasing insulin sensitivity.