bluuebunny/crossref_metadata_2025 huggingface dataset:
Endurance training does not enhance total energy expenditure in healthy elderly persons
Authors: Goran M. I. , Poehlman E. T.
Published: December 2017

Physical exercise is prescribed to older individuals to increase cardiovascular fitness and improve body composition. However, there is limited information on the effect of exercise on total energy expenditure (TEE) and its components. We therefore determined the effects of short-term endurance training in 11 elderly volunteers (56–78 years) on changes in 1) TEE, from doubly labeled water; 2) resting metabolic rate (RMR), from respiratory gas analysis, 3) the energy expenditure of physical activity (EEPA), aside from that associated with the training program, and 4) body composition from a combination of body density with total body water. Endurance training increased maximum oxygen consumption (VO2max) by 9% (2.00 +/- 0.67 to 2.17 +/- 0.64 l/min; P < 0.05) and RMR by 11% (1,596 +/- 214 to 1,763 +/- 170 kcal/day; P < 0.01). There was no significant change in TEE (2,408 +/- 478 to 2,479 +/- 497 kcal/day) before and during the last 10 days of endurance training because of a 62% reduction in EEPA (571 +/- 386 to 340 +/- 452 kcal/day; P < 0.01). There was no change in body mass, but fat masxs decreased (21.6 +/- 6.6 to 20.7 +/- 6.6 kg; P < 0.05). The increase in fat-free mass (49.5 +/- 9.0 to 50.4 +/- 9.1 kg; P < 0.05) was explained by an increase in body water (35.9 +/- 6.5 to 36.8 +/- 6.3 kg; P < 0.05). We conclude that in healthy elderly persons, endurance training enhances cardiovascular fitness, but does not increase TEE because of a compensatory decline in physical activity during the remainder of the day.
Regulation of protein synthesis by modulation of intracellular calcium in rat liver
Authors: Kimball S. R. , Jefferson L. S.
Published: December 2017

The rate of protein synthesis can be modulated in intact cells by varying the concentration and subcellular distribution of intracellular calcium. Because the biochemical reactions required for the pathway of protein synthesis occur in the cytosol of the cell, it might be expected that protein synthesis would be controlled by free cytosolic calcium rather than the sequestered cation. However, a recent report proposed that maintenance of optimal rates of protein synthesis depends on the amount of calcium sequestered in the endoplasmic reticulum rather than free cytosolic calcium (C.O. Brostrom and M. A. Brostrom, Annu. Rev. Physiol. 52: 577–590, 1990). In the present study, rat livers were perfused with buffer containing various compounds previously shown to alter intracellular calcium concentration and distribution in isolated cells. It was found that conditions designed to cause a rise in free cytosolic calcium had no effect on protein synthesis. In contrast, conditions designed to cause depletion of sequestered calcium resulted in an inhibition of protein synthesis characterized by a reduction in peptide-chain initiation relative to elongation. The inhibition of protein synthesis was further localized to a decrease in the activity of eukaryotic initiation factor (eIF) 2B as measured in extracts from perfused livers. The inhibition of eIF-2B activity was associated with a 2.4-fold increase in the proportion of the alpha-subunit of eIF-2 in the phosphorylated form. In summary, the results of the present study support a model whereby mobilization of calcium sequestered in the endoplasmic reticulum results in an inhibition of protein synthesis in rat liver.(ABSTRACT TRUNCATED AT 250 WORDS)
Splanchnic bed utilization of leucine and phenylalanine in humans
Authors: Matthews D. E. , Marano M. A. , Campbell R. G.
Published: December 2017

To study the fate of enterally delivered essential amino acids, leucine and phenylalanine, 14 healthy adults were infused in the postabsorptive state with [1-13C]leucine, [5,5,5-2H3]leucine, and [phenyl-2H5]phenylalanine for 7 h in a crossover design by intravenous and nasogastric tube routes. The amount of enterally delivered tracer that was sequestered by the splanchnic bed on the first pass was 21 +/- 1, 17 +/- 3, and 29 +/- 2 for the [13C]leucine, [2H]leucine, and [2H]phenylalanine tracers, respectively. Less than 2% of the nasogastric [1-13C]leucine tracer was oxidized on the first pass. We estimate that 40% of the nasogastric leucine tracer that was sequestered on the first pass was converted to alpha-ketoisocaproate and released, and 50% was incorporated into newly synthesized proteins. Assuming that less phenylalanine is incorporated into protein than leucine because of the lower abundance of phenylalanine in protein compared with leucine, we estimate that 80% of the extracted nasogastric phenylalanine tracer was converted to tyrosine. The study design also indicated a significant effect of duration of tracer infusion on the results, presumably due to recycling of tracer from rapidly turning over protein.
Control of electrogenic Na+ absorption in rat late distal colon by nanomolar aldosterone added in vitro
Authors: Fromm M. , Schulzke J. D. , Hegel U.
Published: December 2017

It has been possible to obtain in a mammalian epithelium of dietetically and surgically untreated animals a dose response of in vitro-added aldosterone (Aldo, 10(-10) to 10(-5) M) on electrogenic Na+ absorption (JeNa). JeNa was measured in the Ussing chamber on stripped rat late distal colon 8 h after in vitro addition of Aldo. Submaximal effects were obtained at 3 nM Aldo; after a lag time of 2 h, short-circuit current (Isc) increased to a maximum of 234 +/- 15 microA/cm2 and dropped after 0.1 mM amiloride to -18 +/- 3 microA/cm2, resulting in JeNa of 9.4 +/- 0.6 mumol.h-1 x cm-1. Net Na+ tracer fluxes and Isc exhibited parallel time courses, so that electroneutral Na+ transport was not induced in late distal colon by acute Aldo. A plot of JeNa vs. Na conductance revealed an electromotive force (ENa) of 126 +/- 1 mV for all Aldo concentrations tested. Kinetic data were as follows: Michaelis constant 1.2 nM, maximal velocity (Vmax) 10.5 mumol.h-1 x cm-2, and Hill coefficient 2.1. In contrast to the large effect in late distal colon, 3 nM Aldo caused JeNa of < 1 mumol.h-1 x cm-2 in early distal colon, proximal colon, and cecum. Antimineralocorticoid sensitivity and ENa did not vary with Aldo concentration or time of the experiment, consistent with a unique mechanism during the early and late response up to 8 h, as well as at mineralocorticoid and glucocorticoid Aldo concentrations. Acute Aldo in a range of 0.1–10 nM fully controls JeNa between zero and Vmax in late distal colon.(ABSTRACT TRUNCATED AT 250 WORDS)
Lactate transport studied in sarcolemmal giant vesicles from rats: effect of training
Authors: Pilegaard H. , Juel C. , Wibrand F.
Published: December 2017

The effect of training on lactate transport capacity was studied in giant vesicles obtained with collagenase treatment of rat skeletal muscles. Marker enzyme analyses demonstrated that these vesicles are predominantly of sarcolemmal origin. Treadmill training induced significant adaptations in the capacity of rat skeletal muscles to transport lactate but swimming [low-intensity training, approximately 50% of maximal oxygen consumption (VO2 max)] did not. After 7 wk of moderate (90% of VO2max)- and high-intensity (112% of VO2max) interval treadmill training the carrier-mediated equilibrium exchange flux with 30 mM lactate was increased by 58 and 76%, respectively. During 5 wk of detraining the capacity to transport lactate decreased to near control level. It is concluded that physical training can increase the capacity to transport lactate in rat skeletal muscles and that the training intensity is of great importance. The adaptation appears to include both an increased number of transport proteins and a higher affinity of the individual transporters.
Activation of central alpha 1-adrenoceptors in humans stimulates secretion of prolactin and TSH, as well as ACTH
Authors: al-Damluji S. , Francis D.
Published: December 2017

In normal male volunteers, intravenous infusions of the alpha 1-adrenergic agonist methoxamine stimulated the secretion of prolactin, thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH), and the effects were abolished by pretreatment with the alpha 1-antagonist prazosin. To investigate the site of action of methoxamine, its effects were compared with those of equipotent doses of norepinephrine, an alpha 1-agonist that reaches the pituitary gland and the median eminence after an intravenous infusion but, unlike methoxamine, does not cross the blood-brain barrier. Norepinephrine did not stimulate secretion of prolactin, TSH, or ACTH, suggesting that the stimulant alpha 1-adrenoceptors are located in the central nervous system and not directly on the pituitary gland or in the periphery. The alpha 2- and beta-adrenoceptor agonist properties of norepinephrine could not account for the differences from methoxamine, as pretreatment with prazosin did not modify hormone concentrations after norepinephrine. Methoxamine had no behavioral stimulant effects, as judged by visual analog scales that were sensitive to physiological changes in behavioral arousal. In four patients with hypothalamic dysfunction but responsive pituitary corticotrophs, methoxamine had no stimulant effect on the secretion of ACTH, confirming that the alpha 1-adrenoceptors that stimulate ACTH secretion are not located directly on the pituitary. None of the drugs had an effect on the secretion of growth hormone or the gonadotrophins.
Expression of GLUT-4 glucose transporter in unweighted soleus muscle of normal and STZ-induced diabetic rats
Authors: Ishihara H. , Asano T. , Katagiri H. , Lin J. L. , Tsukuda K. , Inukai K. , Yazaki Y. , Oka Y.
Published: December 2017

Effects of 6 days of hindlimb suspension on expression of glucose transporters were studied in the skeletal muscle of nondiabetic and streptozotocin-induced diabetic rats. Although total membrane protein recovered from soleus muscles tended to decrease with suspension, GLUT-4 protein concentration (amount per gram membrane protein) was increased by 66 and 91% compared with weight-bearing control in nondiabetic and diabetic rats, respectively. Therefore, the amount of GLUT-4 protein in whole soleus muscle did not decrease with the hindlimb suspension in normal and diabetic rats. In contrast, hindlimb suspension decreased GLUT-4 mRNA amount in whole soleus muscle by 47 and 27% in nondiabetic and diabetic rats, respectively. Thus the GLUT-4 protein-to-GLUT-4 mRNA ratio was increased 2.1-fold in nondiabetic and 1.4-fold in diabetic rats. The extensor digitorum longus muscle, which generally shows little response to unweighting, exhibited no such changes. These results suggest that the amount of GLUT-4 glucose transporter in the unweighted soleus muscle was maintained via a translational and/or posttranslational mechanism in nondiabetic rats as well as in streptozotocin-induced diabetic rats under the condition of reduced weight-bearing activity.
Glucose uptake and glycogen synthesis in normal and chronically active muscles
Authors: Talmadge R. J. , Silverman H.
Published: December 2017

The hindlimb muscles of the C57Bl6J dy2J/dy2J (dy2J) mouse suffer from a chronic neural stimulation (pseudomyotonia), resulting in increased contractile activity. In response to the increased contractile activity, these muscles store increased amounts of glycogen. In this study, glucose uptake and glycogenesis (glycogen synthesis from glucose) were analyzed in chronically active and normal muscles. In vivo experiments demonstrate increased 3-O-methylglucose (3-MG) uptake rates and glycogenesis by chronically active dy2J gastrocnemius muscles (Gast) vs. normal control Gast. The chronically active diaphragm muscle (Dia) showed the highest rates of 3-MG uptake, as well as glycogenesis in vivo when compared with other skeletal muscles. No differences were observed between dy2J and control Dia. The levels of blood glucose were similar between dy2J and control animals. In vitro experiments demonstrated an increased sensitivity and responsiveness to insulin for glucose uptake in the dy2J soleus muscle (Sol). Glycogenesis by dy2J Sol was elevated only at the highest insulin concentration tested (10,000 microU/ml). In contrast, the dy2J extensor digitorum longus muscle had an increased sensitivity and responsiveness to insulin for both glucose uptake and glycogenesis. This study demonstrates that chronically active muscles have elevated capacities for glucose uptake and glycogenesis and may help to explain the elevated glycogen levels in the dy2J hindlimb muscles.
Major role of dihydropyridine-sensitive Ca2+ channels in Ca(2+)-induced calcitonin secretion
Authors: Scherubl H. , Kleppisch T. , Zink A. , Raue F. , Krautwurst D. , Hescheler J.
Published: December 2017

Endocrine cells are known to possess multiple types of Ca2+ channels. In neurons, omega-conotoxin-sensitive N-type Ca2+ channels have been shown to play a dominant role in neurotransmitter release, but uncertainty remains about the types of Ca2+ channels involved in stimulus-secretion coupling in endocrine cells. We investigated the relative contribution of 1,4-dihydropyridine-sensitive and omega-conotoxin-sensitive Ca2+ channels to Ca(2+)-induced calcitonin release in parafollicular cells of the thyroid (C cells). In whole cell voltage-clamp experiments, both 1,4-dihydropyridine-sensitive and omega-conotoxin-sensitive Ca2+ channel currents were identified. The dihydropyridine isradipine (1 microM) but not omega-conotoxin (1 microM) inhibited the steady-state Ca2+ influx at physiological membrane potentials, the spontaneous electrical activity, and calcitonin secretion (at 2-h incubations). Moreover, suppression of the spontaneous electrical activity by the Na+ channel blocker tetrodotoxin did not affect calcitonin release. We conclude that 1,4-dihydropyridine-sensitive Ca2+ channels play a major role in Ca(2+)-dependent calcitonin release and that calcitonin secretion due to Ca2+ influx proceeds even in the absence of action potentials.
Exercise training and clenbuterol reduce insulin resistance of obese Zucker rats
Authors: Torgan C. E. , Brozinick J. T. , Banks E. A. , Cortez M. Y. , Wilcox R. E. , Ivy J. L.
Published: December 2017

This study compared the effects of aerobic exercise training and chronic administration of the selective beta 2-adrenergic agonist clenbuterol on whole body and skeletal muscle insulin resistance in obese (fa/fa) Zucker rats. Obese rats were randomly assigned to training, clenbuterol, or sedentary control groups. Lean littermates served as a second control group. After 4-5 wk of treatment, an oral glucose tolerance test was performed, followed 1 wk later by hindlimb perfusion, during which time the rates of glucose uptake and 3-O-methyl-D-glucose (3-MG) transport were assessed in the presence of a submaximal (500 microU/ml) insulin concentration. Training resulted in a significant increase in citrate synthase and cytochrome oxidase activity in the recruited muscles. Clenbuterol induced a large increase in muscle mass but provoked a significant decrease in oxidative enzyme activity and beta-adrenergic receptor density. Both treatments increased glucose tolerance and reduced the postglucose insulin response, with the improvements being more pronounced in the clenbuterol group. However, only exercise training improved insulin-stimulated hindlimb muscle glucose uptake (11.37 +/- 0.65, 8.73 +/- 0.77, and 8.27 +/- 0.41 mumol.g-1.h-1 for trained, clenbuterol, and sedentary control groups, respectively) and 3-MG transport. These results suggest that aerobic exercise training attenuated the insulin-resistant condition in the obese Zucker rat by a mechanism other than or in addition to beta 2-adrenergic receptor activation.
Acute effects of ethanol on hepatic endocytosis and processing of insulin in perfused rat liver
Authors: Fawcett J. , Hammond B. , Smith G. D.
Published: December 2017

This study utilizes the perfused rat liver combined with subcellular fractionation and compartmental analysis to investigate the effects of ethanol on hepatic uptake, endocytosis, and processing of insulin. At 4 min after the start of a 2-min pulse of radiolabeled insulin, increasing ethanol concentrations progressively inhibited insulin uptake by the liver (57% at 50 mM ethanol). Subcellular fractionation of the perfused livers showed a progressive shift in distribution from a predominantly endosomal location (control) to a bimodal distribution between endosomes and plasma membrane. This could be largely accounted for by a specific reduction in the endosome-associated insulin. Binding studies showed no changes in the binding properties of the plasma membrane insulin receptor. Compartmental analysis of the perfusate efflux curves confirmed the lack of effect of ethanol on the binding constants but showed a significant decrease in the endocytic rate constant (50%) together with an increase in the retroendocytic rate constant (33%). Simulation studies with the compartmental model showed that these changes could account for the observed decrease in uptake by the liver. No changes were found in the subsequent endocytic degradation of insulin.
Determinants of decline in resting metabolic rate in aging females
Authors: Poehlman E. T. , Goran M. I. , Gardner A. W. , Ades P. A. , Arciero P. J. , Katzman-Rooks S. M. , Montgomery S. M. , Toth M. J. , Sutherland P. T.
Published: December 2017

We considered the association of several metabolic and lifestyle variables as modulators of the decline in resting metabolic rate (RMR) and fat-free weight (FFW) in 183 healthy females (18-81 yr). RMR showed a curvilinear decline with age, which was significant in women aged 51-81 yr but not in women aged 18-50 yr. FFW showed a curvilinear decline with age, which was significant (P < 0.01) in women 48-81 yr but not in women 18-47 yr. The decline in RMR was primarily associated with the loss of FFW (r2 = 72%), whereas the decline in FFW was explained primarily by differences in maximal O2 consumption (VO2max), age, leisure time physical activity, and dietary protein intake (total r2 = 46%). We conclude that RMR and FFW showed a curvilinear decline with age which was accelerated beyond the middle-age years. Second, the age-related decline in RMR was primarily associated with the loss of FFW. Third, the loss of FFW was partially related to a decrement in VO2max and nutritional factors. Therapeutic interventions designed to increase VO2max by elevating physical activity may preserve fat-free weight and thus offset the decline of RMR in aging women.
Time of day of birth and absence of endocrine and uterine contractile activity rhythms in sheep
Authors: Apostolakis E. M. , Rice K. E. , Longo L. D. , Seron-Ferre M. , Yellon S. M.
Published: December 2017

To determine whether 24-h rhythms characterize hormone secretion and uterine activity in the pregnant sheep, blood samples were drawn every 1-4 h for 48 h from ewes and fetuses from day 120 of gestation to term. Repetitive 24-h rhythms were absent for cortisol, progesterone, and prolactin in maternal and fetal circulation and for hourly mean uterine contraction rate and amplitude. To test whether photoperiod or pineal melatonin contributes to the absence of rhythms, pineal-intact and pinealectomized ewes and their fetuses were studied in reverse photoperiod. Again, there was little evidence to suggest 24-h endocrine rhythms except for prolactin in two fetuses by cosinor analyses. Prolactin concentrations were increased in pinealectomized ewes and their fetuses. In the apparent absence of rhythms, 20 of 21 pineal-intact ewes gave birth at night; however, 6 out of 7 pinealectomized ewes gave birth during the day. Thus photoperiod and the maternal pineal gland profoundly influenced the time of day of birth in the absence of circadian endocrine or uterine activity rhythms.
Effect of amino acids alone or with insulin on muscle and liver protein synthesis in adult and old rats
Authors: Mosoni L. , Houlier M. L. , Mirand P. P. , Bayle G. , Grizard J.
Published: December 2017

This study was carried out to analyze age-related changes on amino acid and insulin effects on muscle and liver protein synthesis. Conscious male rats, aged 12 (adult) and 24 (old) mo, were infused for 90 min with either saline, amino acids, or amino acids with insulin and glucose. Protein synthesis was measured during the last 15 min of infusion (flooding dose of valine with L-[2,3,4-3H]valine). Gastrocnemius protein mass was 29% lower in old rats than in adults. However, basal muscle absolute synthesis rates were unchanged with age, and fractional synthesis rates (FSR) were increased. Amino acids significantly stimulated muscle FSR to a similar extent (18-20%) in adult (P < 0.01) and old rats (P = 0.03 when variability introduced by muscle atrophy was taken into account by a variance-covariance analysis). Insulin did not elicit any additional effect. Liver protein synthesis did not change with age or in response to infusions. We conclude that, despite an age-related loss of muscle proteins, capacity of muscle protein synthesis to be stimulated is preserved with age.
Shift from alpha- to beta-type adrenergic receptor-mediated responses in chronically endotoxemic rats
Authors: Pittner R. A. , Spitzer J. A.
Published: December 2017

Hepatocytes from chronically endotoxemic rats, or appropriate saline controls, were maintained in primary culture for 3 or 20 h. The ability of a variety of hormones to stimulate glycogen phosphorylase a was examined. At 3 h in culture, hepatocytes from endotoxemic rats had lower basal activities and exhibited impaired response to vasopressin, angiotensin II, and, to a lesser extent, norepinephrine and glucagon. The norepinephrine response was predominantly of the alpha-type in the saline rats but mixed alpha- and beta-type in the endotoxic cells. After 20 h in culture, vasopressin and angiotensin II responses were still impaired, while norepinephrine and glucagon responses were similar to those seen in the saline cells. The response to norepinephrine was predominantly of the beta-type in the endotoxic cells but still of the alpha-type in the saline cells. The results show that multiple mechanisms are involved in endotoxin-mediated inhibition of glycogen phosphorylase a activity and that alterations in intracellular calcium homeostasis play more of a significant role than adenosine 3',5'-cyclic monophosphate-mediated processes in diminished responsiveness of the liver seen in endotoxemia.
Lactate is essential for maintenance of euglycemia in iron-deficient rats at rest and during exercise
Authors: Linderman J. K. , Dallman P. R. , Rodriguez R. E. , Brooks G. A.
Published: December 2017

To evaluate the hypothesis that lactate supply is essential to maintain euglycemia during iron deficiency, female Sprague-Dawley rats were assigned to iron-sufficient (50 mg Fe2+/kg diet, +Fe), or iron-deficient (15 mg Fe2+/kg diet, -Fe) dietary groups and were injected with a specific beta 2-adrenergic inhibitor, ICI 118,551 (1.0 mg/kg body wt). Rats were studied at rest or after 30 min of running at 13.4 m/min 0% grade. Dietary iron deficiency decreased hemoglobin concentration 38%, but resting arterial concentrations of glucose ([Glc]), lactate ([La]), or alanine ([Ala]) were unaffected. Administration of ICI 118,551 (beta 2-blockade) decreased [La] and [Glc] 52 and 32% in resting -Fe rats, respectively. beta 2-Blockade attenuated the exercise-induced rise in [La] and decreased [Glc] 31% in exercising -Fe rats. [Ala] were unaffected by iron deficiency or exercise but decreased 24 and 18% because of beta 2-blockade in resting and exercising +Fe rats. Iron deficiency depleted resting liver glycogen concentration 45%, with no additional effect of exercise or beta 2-blockade. beta-Blockade decreased arterial insulin and increased arterial glucagon concentrations in resting -Fe and +Fe rats. During exercise glucagon concentration increased significantly more in -Fe than +Fe rats. Decreased arterial [La] with a corresponding decrease in arterial [Glc] in response to beta 2-blockade support the contention that lactate supply is critical to maintenance of euglycemia in -Fe rats at rest and during exercise.
Zinc metabolism and metallothionein expression in bone marrow during erythropoiesis
Authors: Huber K. L. , Cousins R. J.
Published: December 2017

Zinc metabolism and metallothionein induction in rat bone marrow were investigated during induced erythropoiesis. Redistribution of body zinc was measured with 65Zn after acute blood loss in rats fed zinc-restricted or zinc-adequate diets. Uptake of 65Zn by bone marrow was related to time after blood loss, metallothionein induction, and dietary zinc status. Increased 65Zn uptake by marrow of zinc-restricted rats suggests a minimal amount of zinc is necessary to support expansion of the erythrocytic compartment. Zinc induction of marrow metallothionein also occurred in rats in which anemia was produced using phenylhydrazine. Anemic rats which were administered zinc had higher concentrations of marrow metallothionein compared with control rats. Induction of marrow metallothionein by zinc in nonanemic rats required prior treatment with erythropoietin. Percoll fractionation showed marrow metallothionein was most abundant in erythroblasts. These experiments suggest metallothionein synthesis occurs in erythropoietin-sensitive precursor cells in the marrow in response to increased zinc accessibility.
Splanchnic bed utilization of glutamine and glutamic acid in humans
Authors: Matthews D. E. , Marano M. A. , Campbell R. G.
Published: December 2017

To study the fate of enterally delivered nonessential amino acids, glutamine and glutamate, 14 healthy adults were infused in the postabsorptive state with [2-15N]glutamine and [15N]glutamate for 7 h by intravenous (iv) and nasogastric (ng) tube routes. The amount of enterally delivered tracer that was sequestered by the splanchnic bed on the first pass was 54 +/- 4 and 88 +/- 2% for the [2-15N]glutamine and [15N]glutamate tracers, respectively. Only 46 and 12% of the ng glutamine and glutamate tracers entered systemic blood, respectively. The relative amount of 15N transferred from glutamate to glutamine, the transaminating amino acids leucine, isoleucine, valine, and alanine, and to proline was significantly higher when the [15N]glutamate was infused by the ng vs. iv route. The same was also true for [2-15N]glutamine, which presumably transferred 15N after it was converted to glutamate. Thus we conclude that the splanchnic bed sequesters over one-half of the glutamine and almost all of the glutamate delivered to it in the postabsorptive state. There is production of transaminating amino acids in the splanchnic bed, and the splanchnic bed produces simultaneously both glutamine from glutamate and glutamate from glutamine.
Requirement for transmembrane sodium flux in maintenance of cytosolic calcium levels in rat Sertoli cells
Authors: Gorczynska E. , Handelsman D. J.
Published: December 2017

The prompt rise in cytosolic calcium induced by follicle-stimulating hormone (FSH) in rat Sertoli cells suggests a role for calcium in FSH signal transduction. To evaluate the requirement for sodium in transmembrane calcium fluxes in Sertoli cells, we measured intracellular calcium concentration under sodium-free conditions and during stimulation by monensin and veratridine, used to elevate cytosolic sodium. Cytosolic calcium levels were measured by dual-wavelength spectrofluorimetry using freshly isolated cells loaded with fura-2 acetoxymethyl ester. Whereas, removal of extracellular sodium lowered cytosolic calcium in unstimulated cells from 89 +/- 4 to 75 +/- 8 nM, treatment with monensin and veratridine increased cytosolic calcium to 142 +/- 19 and 126 +/- 13 nM, respectively. Without extracellular calcium, monensin still produced 47% of the rise in cytosolic calcium observed in the presence of extracellular calcium, indicating approximately equal contributions of calcium from intracellular and extracellular sources. Blockade of voltage-sensitive or/and voltage-insensitive calcium channels by verapamil and ruthenium red was unable to completely prevent the monensin-induced elevation of cytosolic calcium. In addition tetrodotoxin failed to block the FSH-induced rise in cytosolic calcium. These observations, together with the considerable reduction in monensin-induced rise in cytosolic calcium under extracellular sodium-free condition, support the hypothesis that sodium-calcium exchange rather than the specific calcium or sodium channels regulate basal and monensin-induced transmembrane sodium and calcium fluxes in Sertoli cells.
Okadaic acid stimulates IGF-II receptor translocation and inhibits insulin action in adipocytes
Authors: Tanti J. F. , Gremeaux T. , Cormont M. , Van Obberghen E. , Le Marchand-Brustel Y.
Published: December 2017

Okadaic acid, an inhibitor of protein phosphatases 2A and 1, stimulates glucose transport in muscle and fat cells, suggesting that serine/threonine phosphorylation steps are involved in the translocation of glucose transporters. Here we have investigated whether such phosphorylation events could also participate in another membrane-associated insulin-stimulated process: insulin-like growth factor II (IGF-II) receptor translocation in adipocytes. Maximally effective concentrations of insulin and okadaic acid stimulated deoxyglucose uptake by 5.5- and 2.5-fold, respectively, whereas IGF-II binding was increased 3.5-fold and 1.5-fold. Subcellular fractionation indicated that the okadaic acid-induced stimulation of IGF-II binding resulted from an increase in the number of IGF-II receptors in the plasma membrane with a concomitant disappearance from the low-density microsomal fraction. These changes occurred in parallel to those observed for the glucose transporter GLUT-4. Both insulin-stimulated glucose transport and IGF-II binding were prevented when cells were pretreated with okadaic acid. To understand the mechanism of this inhibitory effect, insulin receptor autophosphorylation and the tyrosine phosphorylation of endogenous proteins were studied. Insulin induced the tyrosine phosphorylation of its receptor beta-subunit and of proteins at 120 and 185 kDa, whereas okadaic acid alone had no effect. When okadaic acid and insulin were added together, the beta-subunit autophosphorylation was similar to that observed with insulin alone, but the tyrosine phosphorylation of substrates was prevented. Taken together, our data suggest that, in adipocytes, serine/threonine phosphorylation events mimicked by okadaic acid are required for the translocation of IGF-II receptors and glucose transporters.(ABSTRACT TRUNCATED AT 250 WORDS)
Exercise training increases GLUT-4 protein in rat adipose cells
Authors: Hirshman M. F. , Goodyear L. J. , Horton E. D. , Wardzala L. J. , Horton E. S.
Published: December 2017

The relative abundance and subcellular distribution of the GLUT-1 and GLUT-4 glucose transporter isoforms were determined in basal and insulin-stimulated adipose cells from wheel cage exercise-trained rats and compared with both age-matched sedentary controls and young cell size-matched sedentary controls. Exercise training increased total estimated GLUT-4 by 67 and 54% compared with age-matched and young controls, respectively. Total estimated GLUT-1 per cell was not significantly different among the three groups. Expressed per cell, plasma membrane GLUT-4 protein in basal adipose cells from exercise-trained and age-matched control rats was 2.5-fold greater than in young controls (P < 0.05) and was associated with higher basal rates of glucose transport in these cells (P < 0.02). In insulin-stimulated cells, plasma membrane GLUT-4 was 67% greater in the exercise-trained animals than young controls (P < 0.01), and 31% greater than in age-matched controls. Rates of glucose transport were correspondingly higher. In basal cells, low-density microsomal GLUT-4 from exercise-trained rats was approximately twofold greater than from age-matched controls and young controls. With insulin stimulation, GLUT-4 in low-density microsomes decreased to similar levels in all groups. We conclude that the total amount of GLUT-4 protein, but not GLUT-1, is increased in adipose cells by exercise training and that this increase in GLUT-4 is due primarily to an increase in intracellular GLUT-4.(ABSTRACT TRUNCATED AT 250 WORDS)
Acute effects of resistance exercise on muscle protein synthesis rate in young and elderly men and women
Authors: Yarasheski K. E. , Zachwieja J. J. , Bier D. M.
Published: December 2017

Muscle mass and function are improved in the elderly during resistance exercise training. These improvements must result from alterations in the rates of muscle protein synthesis and breakdown. We determined the rate of quadriceps muscle protein synthesis using the in vivo rate of incorporation of intravenously infused [13C]leucine into mixed-muscle protein in both young (24 yr) and elderly (63-66 yr) men and women before and at the end of 2 wk of resistance exercise training. Before training, the fractional rate of muscle protein synthesis was lower in the elderly than in the young (0.030 +/- 0.003 vs. 0.049 +/- 0.004%/h; P = 0.004) but increased (P < 0.03) to a comparable rate of muscle protein synthesis in both young (0.075 +/- 0.009%/h) and elderly subjects (0.076 +/- 0.011%/h) after 2 wk of exercise. In the elderly, muscle mass, 24-h urinary 3-methylhistidine and creatinine excretion, and whole body protein breakdown rate determined during the [13C]leucine infusion were not changed after 2 wk of exercise. These findings demonstrate that, during the initial phase of a resistance exercise training program, a marked increase in quadriceps muscle protein synthesis rate occurs in elderly and young adults without an increase in the rate of whole body protein breakdown. In the elderly, this was not accompanied by an increase in urinary 3-methylhistidine excretion, an index of myofibrillar protein breakdown.
Onset of excess fat deposition in Zucker rats with and without decreased thermogenesis
Authors: Markewicz B. , Kuhmichel G. , Schmidt I.
Published: December 2017

To study the first stages of excess fat deposition in Zucker rats, we artificially fed littermates with identical amounts of milk from 4 to 15-16 days of age while continuously recording oxygen consumption (VO2) and deep body temperature. Under intermittent cold loads simulating the periodic thermoregulatory stimulation experienced in the nest, differences between the amounts of body fat deposited by artificially reared fatty (fa/fa) and lean (Fa/-) pups were as large as those seen in mother-reared pups. The decreased VO2 of the cold-reared fatty pups could account for 90-100% of their extra fat deposition. At thermoneutrality, 16-day-old littermates reared with low feeding rates showed small but significant genotype differences in body fat that were not energetically accounted for by differences in VO2 or lean body mass. Slightly but significantly lower fecal energy losses indicated that differences in resorption might account for the positive energy balance of thermoneutrally reared fa/fa pups. Reduced energy expenditure thus efficiently fuels excess fat deposition but is not essential for the onset of excess fat deposition in fa/fa pups. Other factors than reduced sympathetic activation of brown adipose tissue must be considered as a primary cause for the development of fa/fa obesity.
5'- and 5-deiodinase activities in adult rat cecum and large bowel contents inhibited by intestinal microflora
Authors: Nguyen T. T. , DiStefano J. J. , Huang L. M. , Yamada H. , Cahnmann H. J.
Published: December 2017

Enzymatic mechanisms for deiodination of 3,5,3'-triiodothyronine or thyroxine in the phenolic ring (5'-deiodinase) or tyrosyl ring (5-deiodinase) are found in cells of many organs, including the intestinal wall. Deiodinases are highly active in intestinal tissue of developing rat fetuses and relatively inactive in adult intestinal cells, but little is known about these systems in the luminal contents of intestines. We have found both 5- and 5'-deiodinase activities in adult rat intestinal contents and have shown that their expression is inhibited by resident intestinal microflora, which are normally present in the adult but not in the fetus, possibly because they are bound by intestinal bacteria in the adult.
Effects of recombinant human IGF-I on glucose and leucine kinetics in men
Authors: Elahi D. , McAloon-Dyke M. , Fukagawa N. K. , Sclater A. L. , Wong G. A. , Shannon R. P. , Minaker K. L. , Miles J. M. , Rubenstein A. H. , Vandepol C. J. , et al.
Published: December 2017

To examine the effects of recombinant human (rh) insulin-like growth factor I (IGF-I), insulin, and saline on metabolic parameters, we studied 20 young nonobese healthy men. Euglycemic clamps with 240-min IGF-I infusions at two doses (49 and 33 pmol.kg-1 x min-1, n = 8 and 12 subjects) were performed and compared with hyperinsulinemic-euglycemic clamps (2.25 pmol.kg-1 x min-1, n = 9). Leucine and glucose kinetics were examined with L-[1-13C]leucine and [3-3H]glucose. Glucose rate of appearance (Ra) declined equivalently in the 49 pmol.kg-1.min-1 IGF-I and insulin clamps but remained at basal levels during the 33 pmol.kg-1 x min-1 IGF-I infusions. In contrast, Rd of glucose was increased by 176% in the 49 pmol.kg-1 x min-1 IGF-I and 78% in the 33 pmol.kg-1 x min-1 IGF-I infusions. Furthermore, to prevent hypoglycemia after the termination of both rhIGF-I infusions, it was necessary to infuse glucose for an additional 2-20 h. Ra of leucine was suppressed significantly by both IGF-I and insulin, whereas leucine oxidation was not affected by either hormone. Therefore, the rate of disappearance of leucine expressed as the difference between Ra and oxidation rates was significantly reduced in all clamps. In addition, IGF-I significantly suppressed beta-cell secretion without affecting the other glucoregulatory hormones. In contrast to insulin, IGF-I had no apparent effect on lipolysis, as measured by changes in nonesterified fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)
Continuous on-line hydrogen ion monitoring to study flow dynamics of perifusion systems and cellular metabolism
Authors: Brand R. M. , Ghazzi M. N. , Rolfes-Curl A. , Cantor H. C. , Midgley A. R.
Published: December 2017

Time-dependent concentration profiles of input signals and feedback of metabolic products can strongly influence cellular responsiveness. To study these parameters, we developed a perifusion system that can deliver biological signals to cells with minimal dispersion, monitor real time responses, and remove waste products continuously. By monitoring pH with miniature hydrogen ion-selective electrodes at intervals of 1 s, effects of dispersion, flow rate, pumping system, and changes in cellular metabolism were demonstrated. Dynamic responses of a human cell line to a series of 10-min pulses of the metabolic uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) were monitored. A rapid 1-min increase in acid release occurred on exposure to CCCP, followed by a decrease in acidification and then a gradual return to a baseline slightly more acidic than before administration of CCCP. These observations demonstrate that this perifusion system can reveal small changes in pH (+/- 0.0005 units) induced by metabolic perturbations and has the potential to reveal the dynamics of cellular responsiveness to a wide range of hormonal, metabolic, and other chemical signals.
Increased rates of muscle protein turnover and amino acid transport after resistance exercise in humans
Authors: Biolo G. , Maggi S. P. , Williams B. D. , Tipton K. D. , Wolfe R. R.
Published: December 2017

The rates of protein synthesis and degradation and of amino acid transport were determined in the leg muscle of untrained postabsorptive normal volunteers at rest and approximately 3 h after a resistance exercise routine. The methodology involved use of stable isotopic tracers of amino acids, arteriovenous catheterization of the femoral vessels, and biopsy of the vastus lateralis muscle. During postexercise recovery, the rate of intramuscular phenylalanine utilization for protein synthesis increased above the basal value by 108 +/- 18%, whereas the rate of release from proteolysis increased by 51 +/- 17%. Muscle protein balance improved (P < 0.05) after exercise but did not become positive (from -15 +/- 12 to -6 +/- 3 nmol phenylalanine.min-1.100 ml leg volume-1). After exercise, rates of inward transport of leucine, lysine, and alanine increased (P < 0.05) above the basal state from 132 +/- 16 to 208 +/- 29, from 122 +/- 8 to 260 +/- 8, and from 384 +/- 71 to 602 +/- 89 nmol.min-1.100 ml leg-1, respectively. Transport of phenylalanine did not change significantly. These results indicate that, during recovery after resistance exercise, muscle protein turnover is increased because of an acceleration of synthesis and degradation. A postexercise acceleration of amino acid transport may contribute to the relatively greater stimulation of protein synthesis.
Effects of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-I-(7-36) on insulin secretion
Authors: Jia X. , Brown J. C. , Ma P. , Pederson R. A. , McIntosh C. H.
Published: December 2017

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (GLP)-I-(7-36) are probably the most important "incretins," but there is controversy as to their relative insulinotropic activities. The effects of natural (np) and synthetic porcine (sp) GIP, synthetic human (sh) GIP, and GLP-I-(7-36) on insulin secretion from the perfused rat pancreas were compared using gradient perfusion. Insulin secretion was increased by both spGIP and GLP-I-(7-36) at concentrations of approximately 16 pM. Maximal responses to GLP-I-(7-36) in the presence of 16.7 mM glucose were slightly greater than with npGIP or spGIP, but with 10 mM glucose spGIP and GLP-I-(7-36) exerted equivalent effects. Responses to shGIP were greatly reduced compared with spGIP. In the presence of 50 pM spGIP or GLP-I-(7-36) the glucose threshold was 4.5 +/- 0.11 mM. The data indicate that GLP-I-(7-36) and porcine GIP are equally insulinotropic and share the same glucose threshold for activity, whereas shGIP is less active. At the concentrations found postprandially, however, GIP is likely to be the more important incretin.
A simulation model for glucose kinetics and estimates of glucose utilization rate in type 1 diabetic patients
Authors: Boroujerdi M. A. , Umpleby A. M. , Jones R. H. , Sonksen P. H.
Published: December 2017

A glucose kinetic model is described that contains insulin-independent and insulin-dependent pathways of glucose uptake and includes a saturating flux term for glucose transport into the cells by the glucose transporters. The rate of glucose utilization was estimated in control subjects and diabetic patients by use of a bolus of [3-3H]glucose. Diabetic patients were studied after three regimens of insulin therapy: 1) after 24 h of insulin withdrawal, 2) after conventional insulin therapy, and 3) after an overnight insulin infusion such that plasma glucose was maintained between 4 and 6 mmol/l. In addition, the model was used to simulate published results from glucose clamp experiments with a range of glycemic levels and insulin concentrations. Estimates of glucose utilization flux in diabetic patients and model simulation suggest that high plasma glucose concentrations in uncontrolled diabetic patients can be attributed to a high glucose production rate by the liver associated with a reduction in glucose metabolic clearance rate due to relative saturation of the available pool of glucose transporters.
Influence of dehydration on locally mediated hindlimb vasodilation in baboons
Authors: Thornton R. M. , Proppe D. W.
Published: December 2017

Previous studies indicate that the heat stress-induced cutaneous vasodilation in baboons is attenuated during dehydration by mechanisms other than the well-known neurohumoral vasoconstrictor mechanisms. Therefore, this study sought to determine whether dehydration also attenuates locally mediated maximum hindlimb blood flow and vascular conductance in baboons. Five baboons were chronically instrumented to measure arterial blood pressure and mean external iliac artery blood flow (MIBF). Hindlimb vasodilation was induced by occlusions of the external iliac artery for 2.5, 5.0, 7.5, and 10.0 min and by close-arterial injections of acetylcholine (ACh) and sodium nitroprusside (NP) in graded doses. These vasodilatory stimuli were applied in euhydrated and dehydrated states, the latter being produced by water deprivation for 64-68 h. Maximum MIBF and iliac vascular conductance (IVC) after arterial occlusion were reduced by 67–70% during dehydration. Also, maximum MIBF and IVC produced by ACh in the dehydrated state were 46–;52% lower than in the euhydrated state. A similar reduction in the responses to NP occurred during dehydration. It is concluded that the maximum hindlimb blood flow and vascular conductance produced by local, nonneurohumoral mechanisms are attenuated in the baboon during dehydration.
Pulmonary vascular reactivity to biogenic amines during acute hypoxia
Authors: Porcelli R. J. , Cutaia M. V.
Published: December 2017

The effects of acute hypoxia on the pressor responses to five biogenic amines were studied in isolated blood-perfused cat lungs. Hypoxia (Po2 = 46 +/- 2 Torr) reduced the pressor responses to phenylephrine while changing the pressor responses to epinephrine and norepinephrine to vasodilation. Hypoxia reduced the pressor responses to histamine, and these reductions were preceded by small but significant vasodilations. Hypoxia had no effect on the pressor responses to serotonin. These changes in pulmonary vasoactivity were reversed on reoxygenation, independent of changes in base-line tone and not correlated with circulating catecholamines. We also examined the effects of hypoxia on the pressor responses to norepinephrine during beta-blockade with propranolol and then alpha-blockade with dibenzyline. The vasodilation produced during hypoxia by norepinephrine was blocked by propranolol, and vasoconstriction reappeared. When alpha-blockade was then established, vasodilation to norepinephrine reemerged during hypoxia. These results demonstrate that hypoxia produces changes in pulmonary vascular responsiveness that are acute in nature and reversible. Although the cellular nature of these changes is unknown, the data suggest that hypoxia produces acute shifts in antagonistic adrenergic receptor activity by either 1) reducing alpha- or increasing beta-receptor activity or 2) acutely changing adrenergic receptor conformation, affinity, or efficacy, such that beta-activity prevails.
Enhanced release of endothelium-derived factor(s) by chronic increases in blood flow
Authors: Miller V. M. , Vanhoutte P. M.
Published: December 2017

Chronic increases in blood flow caused by an arteriovenous fistula augment endothelium-dependent relaxations to acetylcholine. To determine whether endothelial muscarinic receptors are altered, concentration-response curves to acetylcholine were obtained in the presence of pirenzepine in fistula- and sham-operated canine femoral arteries. Pirenzepine inhibited the response to acetylcholine in both arteries. The pA2 (log Kb) for the antagonist was the same. A bioassay system was used to assess release of endothelium-derived relaxing factor. Rings of femoral artery (without endothelium) from unoperated dogs relaxed more when superfused with perfusate derived from endothelium of fistula-operated arteries during acetylcholine stimulation. Rings without endothelium of sham- and fistula-operated arteries relaxed to the same extent when superfused with perfusate derived from the endothelium of unoperated femoral arteries. These results suggest that augmented relaxations to acetylcholine in canine arteries where blood flow is chronically elevated do not result from changes in the subtype of endothelial muscarinic receptors or in the sensitivity of the underlying smooth muscle to endothelium-derived relaxing factor(s). They are likely due to increased release of endothelium-derived relaxing factor(s) on muscarinic activation.