bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupling of external to cellular respiration during exercise: the wisdom of the body revisited
Authors: Wasserman K.
Published: December 2017

The changes in cellular respiration needed to increase energy output during exercise are intimately and predictably linked to external respiration through the circulation. This review addresses the mechanisms by which lactate accumulation might influence O2 uptake (VO2) and CO2 output (VCO2) kinetics. Respiratory homeostasis (a steady state with respect to VO2 and VCO2) is achieved by 3-4 min for work rates not associated with an increase in arterial lactate. When blood lactate increases significantly above rest for constant work rate exercise, VO2 characteristically increases past 3 min (slow component) at a rate proportional to the lactate concentration increase. The development of a similar slow component in VCO2 is not evident. The divergence of VCO2 from VO2 increase can be accounted for by extra CO2 release from the cell as HCO3- buffers lactic acid. Thus the slow component of aerobic CO2 production (parallel to VO2) is masked by the increase in buffer VCO2. This CO2, and the consumption of extracellular HCO3- by the lactate-producing cells, shifts the oxyhemoglobin dissociation curve rightward (Bohr effect). The exercise lactic acidosis has been observed to occur after the minimal capillary PO2 is reached. Thus the lactic acidosis serves to facilitate oxyhemoglobin dissociation and O2 transport to the muscle cells without a further decrease in end-capillary PO2. From these observations, it is hypothesized that simultaneously measured dynamic changes in VO2 and VCO2 might be useful to infer the aerobic and anaerobic contributions to exercise bioenergetics for a specific work task.
Regulation of metallothionein concentrations in rat brain: effect of glucocorticoids, zinc, copper, and endotoxin
Authors: Gasull T. , Giralt M. , Hernandez J. , Martinez P. , Bremner I. , Hidalgo J.
Published: December 2017

The effects of known inducers of liver metallothionein (MT) synthesis on MT concentrations in the rat brain have been determined using antibodies that are specific for MT I and II and do not cross-react with MT III. There were substantial differences in the MT concentrations in different areas of the brain. Dexamethasone increased MT levels after 24 h in the frontal cortex, cortex, medulla oblongata plus pons, midbrain, striatum, hippocampus, and cerebellum but not in the hypothalamus. Corticosterone produced similar results except in the hippocampus. Long-lasting adrenocorticotropic hormone increased MT concentrations after 12 h in midbrain and striatum but not in the liver. Adrenalectomy decreased MT concentrations after 6 days in the medulla oblongata plus pons, striatum, hippocampus, and hypothalamus but increased concentrations in the liver and kidneys; these effects were reversed by corticosterone. The role of glucocorticoids in the regulation of MT levels therefore differs between tissues and within specific areas of the brain. Injection of zinc or copper intracerebroventricularly and the use of a zinc-deficient diet increased and decreased MT levels, respectively, in some but not all brain areas. Endotoxin increased liver MT but not brain MT I levels after 8 h.
Adrenal responses to the peptide PACAP in conscious functionally hypophysectomized calves
Authors: Edwards A. V. , Jones C. T.
Published: December 2017

Intra-aortic infusions of pituitary adenylate cyclase-activating peptide-(1-38) (PACAP) produced a dose-related fall in aortic blood pressure over the range of 4-40 pmol.min-1.kg-1 in the presence of exogenous adrenocorticotropic hormone-(1-24) (ACTH, 2 ng.min-1.kg-1 i.v.; P < 0.01). At the higher dose there was a significant fall in adrenal vascular resistance in the absence, but not in the presence, of ACTH. PACAP also produced a dose-related increase in right adrenal cortisol output over the same range, which was significantly greater in the absence of exogenous ACTH (P < 0.01). At the higher dose, PACAP produced small but significant increases in adrenal epinephrine and norepinephrine output (P < 0.01) both in the presence and the absence of ACTH. There was also a small rise in Met5-enkephalin output, and corticotrophin-releasing factor (CRF) was released in the presence, but not in the absence, of ACTH. It is concluded that PACAP is capable of exerting potent steroidogenic and vasodilator effects in the adrenal gland in the normal conscious calf and of releasing significant amounts of catecholamines, enkephalins, and CRF from the adrenal medulla. These findings identify PACAP as a candidate neuromodulator in the adrenal gland in this species.
Isolation of rat Leydig cells and precursor forms after administration of ethane dimethane sulfonate
Authors: Risbridger G. P. , Davies A.
Published: December 2017

The cytotoxic drug ethane dimethane sulfonate (EDS) has been extensively used as a means of studying the regeneration of Leydig cells in the adult rat testis. This study used the EDS-treated rat testis as a source of material for the isolation of regenerating Leydig cells and their precursors and describes the procedures required for the isolation of these cell preparations. As early as 13-15 days after EDS, cells in the precursor fraction can bind low, but detectable, levels of iodinated purified human chorionic gonadotropin. However, no luteinizing hormone (LH) response was detected in terms of steroid production. The precursor fraction of cells isolated from the EDS-treated rat testis 17-19 days after the administration of EDS was heterogeneous in light-microscopic appearance, but identifiable Leydig-like cells were present. The cells in this fraction were the first to exhibit the ability to respond to LH with the production of detectable levels of the reduced androgen, 5 alpha-androstane-3 alpha,17 beta-diol. The amount of androgen produced by both the Leydig cell and precursor fractions had increased by 21 days after EDS and reached the levels produced by immature adultlike Leydig cells, which can be isolated from the 20-day-old rat testes. These studies demonstrate that steroidogenically responsive precursor forms of Leydig cells can be isolated from the EDS-treated testes 17-19 days after depletion of the adult Leydig cell population.
Dexamethasone potentiates IGF-I actions in porcine granulosa cells
Authors: Urban R. J. , Bodenburg Y. H. , Nagamani M. , Peirce J.
Published: December 2017

To understand better interactions between glucocorticoids and insulin-like growth factor I (IGF-I) in the ovary, we studied the effects of dexamethasone on IGF-I stimulation of P-450 cholesterol side-chain cleavage enzyme (P-450scc) mRNA concentrations in porcine granulosa cells. Dexamethasone potentiated IGF-I-stimulated P-450scc mRNA concentrations and progesterone production in granulosa cell cultures. Time-course and dose-response studies showed that maximal enhancement occurred at a 1-microM dexamethasone concentration after 48 h of treatment. This potentiation was prevented by the glucocorticoid receptor antagonist RU-38486, 17 beta-hydroxy-11 beta-[-4-dimethyl-aminophenyl]estra-4,9,-dien-3-one (RU-486). We investigated mechanisms for this potentiation by performing IGF-I binding studies in porcine granulosa cells. Dexamethasone increased IGF-I binding, and Scatchard analysis showed this enhanced binding was caused by an increase in receptor concentration. Northern blot hybridization using a rat type I IGF-I receptor gene riboprobe showed that although dexamethasone alone did not increase IGF-I receptor mRNA concentrations, it did prevent a decrease in receptor mRNA concentrations caused by IGF-I. In addition, we used synthetic primers from conserved regions of the rat type I IGF-I receptor gene with total RNA from porcine granulosa cells and polymerase chain reaction to isolate a 615-base pair porcine type I IGF-I receptor cDNA clone. Ribonuclease protection assay results were similar to those found with the rat IGF-I receptor riboprobe. We conclude that dexamethasone potentiates IGF-I actions on steroidogenesis in the porcine ovary.
Pi transport regulation by chicken growth plate chondrocytes
Authors: Montessuit C. , Bonjour J. P. , Caverzasio J.
Published: December 2017

Inorganic phosphate (Pi) is a key element for the growth and mineralization of the epiphyseal cartilage. In this study, the characteristics of the transport of Pi in growth plate chondrocytes have been determined using primary cultures of chicken growth plate cartilage cells. The uptake of Pi was significantly increased in the presence of extracellular sodium. The kinetic parameters of the saturable sodium-dependent Pi transport (NaPiT) were determined. The Michaelis constant for Pi was 0.443 +/- 0.095 mM, and the concentration of sodium with which half-maximal Pi transport was observed was 48.0 +/- 8.7 mM. Stoichiometric analysis suggested that more than one sodium ion was cotransported with each Pi molecule. NaPiT was sensitive to inhibition by Pi analogues such as phosphonoformic acid and arsenate. These data strongly suggest that Pi uptake by chicken growth plate chondrocytes is a carrier-mediated process driven by the transmembrane electrochemical gradient of sodium. Two important regulators of biosynthetic activities of growth plate chondrocytes, insulin-like growth factor I (IGF-I) and parathyroid hormone (PTH), selectively regulated Pi transport. With IGF-I, maximal stimulation (117 +/- 7% above control) was observed at doses > 5 nM, with an half-maximal effective concentration of 0.46 +/- 0.18 nM. A significant effect was observed after 1 h of exposure and was maintained for up to 24 h. PTH increased Pi transport with a biphasic dose-response curve. The change in NaPiT was transient, being maximally observed after 8 h (58 +/- 8%) and unexpressed after 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Hypoglycemia counterregulation in elderly humans: relationship to glucose levels
Authors: Ortiz-Alonso F. J. , Galecki A. , Herman W. H. , Smith M. J. , Jacquez J. A. , Halter J. B.
Published: December 2017

This study was designed to define the effect of human aging on hypoglycemia counterregulatory mechanisms. A hyperinsulinemic (2 mU.kg-1.min-1) glucose clamp procedure was used to control glucose and insulin levels during stepwise lowering of plasma glucose. Counterregulatory hormones, hepatic glucose production (HGP), glucose utilization, and symptoms of hypoglycemia were studied in 13 healthy young [age 24 +/- 1 (SE) yr] and 11 healthy old (age 65 +/- 1 yr) nondiabetic volunteers on two occasions: 1) at matched euglycemia and 70 and 60 mg/dl (study 1) and 2) at matched euglycemia and 60 and 50 mg/dl (study 2). The old had consistently lower epinephrine (P < 0.005), glucagon (P < 0.02), cortisol (P < 0.05), and pancreatic polypeptide (P < 0.02) responses at the 60-mg/dl glucose step in study 1. However, these differences were no longer detectable at the more severe hypoglycemic stimulus of 50 mg/dl in study 2. A consistent increase in HGP occurred in both groups only at the 50-mg/dl glucose step (study 2) and was not different between young and old. There were also no differences in symptom responses between young and old. In summary, we found that elderly individuals have a subtle impairment of the glucose counterregulatory response during moderate hypoglycemia, but this impairment is no longer detectable during more severe hypoglycemia.
Molecular pathophysiology of glucagon-SV40 T antigen transgenic mice
Authors: Drucker D. J.
Published: December 2017

The gene encoding proglucagon is expressed in the pancreas, intestine, and brain. The molecular determinants of proglucagon gene expression and the biological activities of the proglucagon-derived peptides (PGDPs) have been examined using transgenic mice harboring a glucagon-SV40 large T antigen (GLUTag) transgene. These experiments have delineated DNA sequences important for intestinal-specific proglucagon gene transcription. GLUTag mice develop neuroendocrine tumors of the pancreas and large bowel, leading to elevated plasma levels of the PGDPs and suppression of endogenous proglucagon gene expression. Transplantation of the large bowel tumors subcutaneously into nude mice provides additional evidence for inhibition of endogenous pancreatic proglucagon gene expression by one or more of the tumor-derived PGDPs. The large bowel GLUTag tumors exhibit abnormalities in the posttranslational processing of proglucagon. GLUTag tumors may be passaged in vivo and in vitro and have been used to generate stable cell lines that express the proglucagon gene at high levels. Taken together, these studies highlight the utility of transgenic systems for the physiological analysis of hormone action and the molecular determinants of peptide hormone gene expression.
Dynorphin binds to neuropeptide Y and peptide YY receptors in human neuroblastoma cell lines
Authors: Miura M. , Inui A. , Sano K. , Ueno N. , Teranishi A. , Hirosue Y. , Nakajima M. , Okita M. , Togami J. , Koshiya K. , et al.
Published: December 2017

The modulation of neuropeptide Y (NPY) and peptide YY (PYY) receptors by dynorphin, luteinizing hormone-releasing hormone (LHRH), corticotropin-releasing factor (CRF), and cholecystokinin octapeptide has been studied in human neuroblastoma cell lines SK-N-MC and SMS-MSN, which express Y1 and Y2 receptors for NPY/PYY. Dynorphin A and LHRH inhibited the binding of NPY/PYY to SK-N-MC cell membranes at concentrations ranging from 10(-7) to 10(-5) M, whereas dynorphin A and CRF were effective in SMS-MSN cells. The inhibitory effect of dynorphin A on NPY/PYY binding was observed in the presence of guanosine 5'-O-(3-thiotriphosphate), a nonhydrolyzable GTP analogue, as well as H-7 and H-8, novel inhibitors of protein kinases C and A. However, U-50488, the most potent kappa-selective compound did not mimic the dynorphin action. Dynorphin A showed neither effect on the dissociation of NPY/PYY from their receptors nor inhibition on the basal as well as forskolin-stimulated adenosine 3',5'-cyclic monophosphate response. These results indicate that the interaction of dynorphin A with Y1 and Y2 receptors is not mediated by changes in receptor-G protein interaction, receptor phosphorylation, and allosteric binding to NPY/PYY receptors but that dynorphin A binds to NPY/PYY receptors at high concentrations, probably in an antagonistic manner.
Characterization, expression, and hormonal control of a thymic beta 2-adrenergic receptor
Authors: Marchetti B. , Morale M. C. , Paradis P. , Bouvier M.
Published: December 2017

In the present study, we have characterized the beta 2-adrenergic receptor (beta 2-AR)-adenosine 3',5'-cyclic monophosphate (cAMP) system of the rat thymus gland and examined the hormonal regulation of the thymic beta 2-AR gene expression under physiological or pharmacological conditions accompanied by marked alterations of the sex steroid hormone milieu. We report here that membrane preparations of female rat thymic tissue contain iodocyanopindolol binding sites that exhibit pharmacological properties typical of a beta-AR. Detailed analysis by computer modeling of the binding potencies of a large series of beta 1- and beta 2-adrenergic agonists and antagonists revealed predominantly the beta 2-AR subtype (78%) in rat thymus. This inference from radioligand binding studies was corroborated functionally by the rank order of potencies of a series of adrenergic agonists to stimulate the production of cAMP. Northern blot analysis, using a human beta 2-AR cDNA as a probe, revealed the presence of a mRNA of 2.3 kb, which is consistent with the size of the beta 2-AR mRNA found in other rat tissues. Physiological regulation of specific beta 2-AR in the rat thymus was indicated by significant increases in both receptor concentration and steady-state levels of beta 2-AR mRNA during the diestrous 2 and proestrous phases of the rat estrous cycle and pregnancy, whereas castration sharply reduced beta 2-AR numbers and transcript levels within the thymus. The modulation of the thymic beta 2-AR-cAMP signaling system by the preexisting sex steroid milieu, coupled with the sex-dependent adrenergic modulation of thymic cell-mediated immune response, may contribute to the various sex-related alterations in immune responsiveness and could play a role in sexually related immune disorders.
5 alpha-Dihydrotestosterone partially restores cancellous bone volume in osteopenic ovariectomized rats
Authors: Tobias J. H. , Gallagher A. , Chambers T. J.
Published: December 2017

Although androgens are thought to be important for skeletal maintenance in females and males, little is known about the mechanisms involved. To investigate this question further, we examined the effects of administering 0.01, 0.1, or 1.0 mg/kg 5 alpha-dihydrotestosterone (DHT) for 60 days on the skeleton of ovariectomized rats. Treatment was delayed until 90 days after ovariectomy to enable bone loss to stabilize. We found that ovariectomy markedly reduced cancellous bone volume of the proximal tibial metaphysis due to a combination of loss and thinning of trabeculae. Cancellous bone volume was partially restored by all doses of DHT, with trabecular thickness, but not number, returning to that of sham-operated animals. DHT also stimulated longitudinal bone growth and endosteal and periosteal bone formation and suppressed histomorphometric indexes of cancellous bone resorption. This suggests that DHT influences skeletal metabolism in osteopenic ovariectomized rats both by stimulating bone formation and suppressing resorption, although it is unclear which, if any, of these actions predominate at cancellous sites.
Role of interleukin-6 and prostaglandins in the effect of monocyte-conditioned medium on osteoclast formation
Authors: Kanatani M. , Sugimoto T. , Fukase M. , Chihara K.
Published: December 2017

There is evidence suggesting some role of mononuclear cells at the resorptive site in bone remodeling. The possibility was therefore postulated that these cells might provide some signal for osteoclast formation. We examined the effects of human monocyte-conditioned medium (CM) on the formation of osteoclast-like cells from hemopoietic blast cells in the absence of stromal cells and unfractionated bone cells in the presence of stromal cells. In both culture systems, the osteoclast-like cell formation induced by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] or human parathyroid hormone (PTH)-(1–34) was significantly inhibited by adding 20% CM. The effects of monocyte-derived local regulators of bone turnover on osteoclast-like cell formation induced by 1,25(OH)2D3 or PTH were determined. Interleukin-6 (IL-6) inhibited osteoclast-like cell formation in both culture systems, whereas prostaglandin (PG) E2 significantly inhibited the formation only in the hemopoietic blast cell culture. The inhibitory effect of CM on osteoclast-like cell formation from hemopoietic blast cells was not observed when CM was prepared from monocytes pretreated with indomethacin. The inhibitory effect of CM and IL-6 on osteoclast-like cell formation in both culture systems was blocked by adding neutralizing IL-6 antibody. The present study demonstrated that CM inhibited osteoclast-like cell formation induced by 1,25(OH)2D3 and PTH presumably through the action of local regulators of bone turnover, such as IL-6 and PG. Our findings thus provide additional evidence that mononuclear cells play an important role at the resorptive site in bone remodeling.
Modulation of growth factor incorporation into ECM of human osteoblast-like cells in vitro by 17 beta-estradiol
Authors: Slater M. , Patava J. , Kingham K. , Mason R. S.
Published: December 2017

Human fetal osteoblast-like cells formed a regular multilayered structure in vitro with an extensive collagen-based extracellular matrix. With colloidal gold immunocytochemistry, labels for alkaline phosphatase and osteocalcin were distributed in a relatively diffuse pattern, in contrast to the bone growth factors, insulin-like growth factors I and II (IGF-I and IGF-II), transforming growth factor-beta 1 (TGF-beta 1), and basic fibroblast growth factor, which were colocalized in the collagenous matrix of the multilayer. The inclusion of 17 beta-estradiol (10(-11) to 10(-9) M) in the culture medium increased multilayer depths, increased labeling for IGF-I, IGF-II, and TGF-beta 1, and resulted in earlier detection of TGF-beta 1 label. In contrast, the increase in multilayer depth resulting from treatment with human platelets, an exogenous source of growth factors, was not accompanied by an increase in matrix IGF-I, IGF-II, or TGF-beta 1 label, suggesting a particular effect of estradiol to facilitate this process. Because growth factors in bone matrix may act as coupling agents when released during resorption, reduced growth factor incorporation in the presence of reduced sex steroid concentrations may lead to uncoupling of resorption and subsequent formation.
Amazing pancreas: specific regulation of pancreatic secretion of individual digestive enzymes in rats
Authors: Maouyo D. , Morisset J.
Published: December 2017

We investigated the effects of somatostatin (SMS)-201-995, atropine, and MK-329 on the role of cholinergic- and cholecystokinin-related systems and on the secretory relationship between five pancreatic digestive enzymes in rats. Animals kept in restraint cages and provided with pancreatic, biliary, duodenal, and jugular vein cannulas were treated as follows: 1) 0.25 micrograms.kg-1.h-1 caerulein alone, 2) both 0.25 micrograms.kg-1.h-1 caerulein and 100 micrograms.kg-1.h-1 atropine, 3) both caerulein and 5 micrograms.kg-1.h-1 SMS, 4) 91.3 micrograms.kg-1.h-1 carbachol alone, 5) both carbachol and 0.5 mg.kg-1.h-1 MK-329, and 6) both carbachol and 5 micrograms.kg-1.h-1 SMS, respectively. Food, but not water, was denied rats starting 10 h before the experiment and throughout the 6-h experimental period. The secretory patterns over the 6-h experimental period showed noticeably independent regulation of pancreatic secretion of individual digestive enzymes. The relationship between paired enzymes significantly varied according to the treatment. The correlation between chymotrypsinogen and the other enzymes was markedly modulated by MK-329. Our results suggest that SMS is a major "gate-keeper" in the regulation of exocrine pancreatic secretion and that the secretion of each digestive enzyme is individually regulated. Furthermore, they suggest that cholecystokinin and acetylcholine and their respective agonists are essentially initiators of secretory processes of the pancreas. Therefore, the paradigms of the regulation of pancreatic secretion heretofore accepted should be reexamined.
Phosphatase inhibitors potentiate adrenergic-stimulated cAMP and cGMP production in rat pinealocytes
Authors: Ho A. K. , Chik C. L.
Published: December 2017

The role of phosphoprotein phosphatase in the regulation of adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) accumulation in rat pinealocytes was investigated using the three phosphatase inhibitors calyculin A, tautomycin, and okadaic acid. Calyculin A (0.1 microM) was found to enhance the isoproterenol- and norepinephrine-stimulated cAMP accumulation six- and threefold, respectively, whereas tautomycin and okadaic acid were less effective. The effect of calyculin A was rapid (within 5 min) and persisted in the presence of phosphodiesterase inhibition. However, in contrast to protein kinase C activation or intracellular calcium elevation, the phosphatase inhibitors were less effective in potentiating the cAMP response stimulated by forskolin or cholera toxin, and their effects were not blocked by calphostin C or N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. The adrenergic-stimulated cGMP response was also less sensitive to the phosphatase inhibition. Therefore, our results suggest that 1) the adrenergic-stimulated cAMP signal is subjected to the tonic inhibition by phosphoprotein phosphatase; 2) phosphatase inhibitors enhance cAMP synthesis through their actions at the receptor level; and 3) the cAMP signal is more sensitive to the regulation by phosphorylation than cGMP in rat pinealocytes.
Bovine fast-twitch myosin light chain 1: cloning and mRNA amount in muscle of cattle treated with clenbuterol
Authors: Smith S. B. , Davis S. K. , Wilson J. J. , Stone R. T. , Wu F. Y. , Garcia D. K. , Lunt D. K. , Schiavetta A. M.
Published: December 2017

The cDNA clone encoding the fast-twitch isoform of myosin light chain 1 (MLC-1f) was isolated from bovine longissimus dorsi muscle and sequenced in M13 and pUC8. An 0.8-kb subclone, produced by digestion of the cDNA with EcoRI, contained the portion of the molecule common to MLC-1f and MLC-3f. The cDNA in pUC8 contained an additional 81 bp upstream of the EcoR I digestion site, which was unique to MLC-1f. The cDNA clone was used to measure MLC-1f mRNA in longissimus dorsi muscle of cattle chronically administered the beta-adrenergic agonist clenbuterol. Treatment with clenbuterol for 50 days increased succinic dehydrogenase negative (type IIB) and positive (types I and IIA) myofiber cross-sectional areas by 25%. After the 50-day treatment period, the amount of MLC-1f mRNA was 90% greater in longissimus dorsi muscle of treated animals than in the initial group. This effect was lost when clenbuterol treatment was withdrawn for a 78-day period, during which time muscle growth in the treated animals stopped completely. We conclude that we have cloned the bovine cDNA for MLC-1f, which has provided additional evidence that beta-adrenergic agonists increase myofibrillar gene expression.
Energy expenditure in children of lean and obese parents
Authors: Goran M. I. , Carpenter W. H. , McGloin A. , Johnson R. , Hardin J. M. , Weinsier R. L.
Published: December 2017

We evaluated whether children of obese parents have defects in energy expenditure in a study of 73 children (5 +/- 0.9 yr of age) of lean and obese parents. Total energy expenditure (TEE) was measured over 14 days by use of doubly labeled water and physical activity energy expenditure (AEE) derived by subtracting resting energy expenditure (REE) under postprandial conditions. Fat and fat-free mass (FFM) were measured in children and parents with use of bioelectrical resistance. There were no significant correlations between TEE, REE, or AEE in children (after adjustment for FFM) and body fat in children or body fat in mothers or fathers. In three-way analysis of covariance (ANCOVA, with FFM as a covariate), there were no significant effects of gender in children, obesity in mothers, or obesity in fathers on TEE or AEE in children. There was a significant effect of gender and a significant interaction between obesity in mothers and obesity in fathers on REE; relative to children with two nonobese or two obese parents, REE was approximately 6% lower in children when mothers only or fathers only were obese. In conclusion, our data do not support the hypothesis that children of obese parents have major defects in energy expenditure.
Effect of immobilization on glucose transport and glucose transporter expression in rat skeletal muscle
Authors: Ploug T. , Ohkuwa T. , Handberg A. , Vissing J. , Galbo H.
Published: December 2017

The effect of 42-48 h of immobilization by casting on maximal velocity of 3-O-methylglucose (3-MG) transport in skeletal muscle was studied in the perfused rat hindquarter. Immobilization resulted in a decrease of approximately 42% for maximum insulin-stimulated 3-MG transport in fast-twitch red fibers and a decrease of approximately 42% for contraction-stimulated transport in slow-twitch red fibers compared with nonimmobilized control muscle. No effect of immobilization on 3-MG transport was found in fast-twitch white muscle. Combination of insulin and muscle contractions always resulted in glucose transport that was identical in immobilized and control muscle. Western blot did not detect a decrease in GLUT-1 or GLUT-4 protein with immobilization. Furthermore, in fast-twitch red fibers, insulin receptor number and receptor kinase activity did not differ between immobilized and control muscle. It is concluded that during short-term immobilization a resistance of muscle glucose transport to stimulation develops that is fiber type specific and selective for insulin or contractions. The resistance can be overcome by the combined action of insulin and contractions and reflect factors other than glucose transporter number and insulin receptor binding and receptor kinase activity.
1,25(OH)2D3 suppresses expression and secretion of atrial natriuretic peptide from cardiac myocytes
Authors: Wu J. , Garami M. , Cao L. , Li Q. , Gardner D. G.
Published: December 2017

We have examined the effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the expression of the rat atrial natriuretic peptide (ANP) gene and the secretion of the encoded protein product in neonatal rat cardiac myocyte cultures. 1,25(OH)2D3 effected a dose- and time-dependent inhibition of agonist-stimulated ANP secretion, which was accompanied by a reduction in the levels of the ANP mRNA transcript. The latter effect appeared to derive, at least in part, from suppression of ANP gene transcription. Of interest, both the reduction in mRNA levels and the inhibition of transcriptional activity were amplified by simultaneous treatment with retinoic acid, suggesting that heterodimerization of liganded 1,25(OH)2D3 receptor and retinoic acid receptor (likely retinoid X receptor) may underlie the inhibitory mechanism in the cardiac myocyte. Neither the secretory effect nor the effect on transcription proved to be calcium dependent. 22-Oxacalcitriol, a nonhypercalcemic analogue of 1,25(OH)2D3, was equally effective in suppressing ANP mRNA levels and transcription of the gene. These findings add to a growing body of data that imply an important role for 1,25(OH)2D3 in the regulation of cardiovascular function.
Effects of glucagon with or without insulin administration on liver glycogen metabolism
Authors: Ercan N. , Gannon M. C. , Nuttall F. Q.
Published: December 2017

Rats fed ad libitum were given insulin alone (4 U/kg), glucagon alone (25 micrograms/kg), or insulin and glucagon sequentially. Phosphorylase a and synthase R activities, hepatic glycogen, uridine diphosphoglucose, inorganic phosphate (Pi), and plasma glucose, lactate, glucagon, and insulin concentrations were determined over the subsequent 40 min. In separate animals, muscle extraction of 2-deoxy-D-[3H]glucose also was determined. After glucagon administration, glycogen phosphorylase a and plasma glucose were increased within 5 min. However, the glycogen concentration did not decrease for 20 min. Glucagon administration to rats pretreated with insulin stimulated a similar increase in phosphorylase a activity. Again, glycogen was not degraded for 20 min. After insulin only, glycogen concentration remained unchanged. Plasma glucose decreased as expected. In each group, muscle extraction of 2-deoxy-D-[3H]glucose increased compared with the controls (P < 0.05). In summary, glucagon and/or insulin administration did not stimulate significant glycogen degradation for 20 min, even though phosphorylase was activated. The mechanism remains to be determined.
Uteroplacental carbon substrate metabolism and O2 consumption after long-term hypoglycemia in pregnant sheep
Authors: Carver T. D. , Hay W. W.
Published: December 2017

Chronic maternal hypoglycemia leads to fetal growth restriction, but the effects on placental metabolism and its contribution to reduced fetal growth have not been determined. To study these factors, experiments were conducted in seven normal control (C) and six chronically insulin-infused hypoglycemic (H) pregnant sheep over the second half of gestation to measure effects of maternal and fetal hypoglycemia [maternal: 2.0 +/- 0.2 (H) vs. 3.6 +/- 0.1 mM (C); fetal: 0.7 +/- 0.1 (H) vs. 1.1 +/- 0.1 mM (C)] on placental metabolism of glucose, other carbon substrates, and O2. Placental and fetal weight were proportionately reduced in the H group [placental wt: 258 +/- 18 (H) vs. 376 +/- 18 g (C), -31%; fetal wt: 2,540 +/- 190 (H) vs. 3,558 +/- 230 g (C), -29%]. Glucose uptake by the uterus was reduced in the H group [0.10 +/- 0.01 (H) vs. 0.19 +/- 0.02 mmol/min (C)]; it was partitioned more to uteroplacental consumption (UPGC) and less to transfer to the fetus (PGT) [UPGC-to-PGT ratio: 20.0 +/- 2.1 (H) and 13.5 +/- 1.2 (C), P < 0.05 for both]. Metabolism of glucose by nonoxidative and oxidative pathways (as estimated by uteroplacental lactate production-to-UPGC ratio and normal rates of placental O2 consumption) was not significantly changed in the H group. Acetoacetate and beta-hydroxybutyrate net uptake and fructose production rates were significantly reduced in the H group, and there was no change in free fatty acid or amino acid uptake rates. With acute return of maternal and fetal glucose concentrations to normal, UPGC and PGT exceeded normal rates by approximately 25%. Thus chronic reduced glucose supply to the uteroplacenta produces a smaller placenta that uses glucose normally and in preference to transfer to the fetus, demonstrating placental metabolic autonomy at the expense of the fetus.
Effects of a continuous lipid infusion on glucose metabolism in critically ill patients
Authors: Tissot S. , Normand S. , Khalfallah Y. , Delafosse B. , Viale J. P. , Annat G. , Motin J. , Riou J. P.
Published: December 2017

The effects of lipid administration on carbohydrate oxidation rate remain controversial, particularly in critically ill patients. The aim of this study was to determine the effects of these patients of a continuous lipid infusion on glucose metabolism using indirect calorimetry and stable isotopes. We studied seven patients, mechanically ventilated, during two consecutive 24-h periods. Throughout the first period they received a continuous infusion of glucose (2 mg.kg-1.min-1) and amino acids. During the second period, in addition to the glucose, they received a continuous infusion of 1 mg.kg-1.min-1 of long-chain triglycerides emulsion. Substrate oxidation rates were calculated from pulmonary gas exchange and nitrogen excretion measurements. Glucose kinetic parameters were measured using primed constant infusions of [6,6-2H2]glucose and [1-13C]glucose. The lipid infusion did not modify the glucose metabolism parameters; 45% of the lipid supply was stored.
Route of nutrient delivery affects insulin sensitivity and liver glucose transporter expression in rat
Authors: Colomb V. , Leturque A. , Guihot G. , Loizeau M. , Lavie S. , Colomer S. , Ricour C. , Girard J.
Published: December 2017

To optimize artificial nutrition (AN) techniques for patients suffering from malnutrition or reduced intestinal absorption, utilization of energy fuels, especially glucose, requires better understanding. Because the liver plays a key role in glucose homeostasis, the aim of this study was to assess the effects of continuous intragastric and intravenous nutrition on insulin secretion and several markers of liver glucose metabolism, especially glucose transporter GLUT-2. Wistar male rats underwent catheterization of either stomach (intragastric) or vena cava (intravenous) and received 24 h/day the same all-in-one formula over 7 to 14 days. The metabolic parameters from intragastrically fed rats did not differ significantly from those from orally fed control rats. Intravenous nutrition induced insulin resistance (marked hyperinsulinemia and/or mild hyperglycemia) and reduced liver GLUT-2 protein and mRNA levels. The decrease in liver GLUT-2 gene expression might be mediated either by an inhibitory role of hyperinsulinemia or by the decrease in gut or portal factors. These results suggest that the route of nutrient delivery influences their utilization by the liver.
Contribution of fructose and lactate produced in placenta to calculation of fetal glucose oxidation rate
Authors: McGowan J. E. , Aldoretta P. W. , Hay W. W.
Published: December 2017

We examined the rate of production of [14C]fructose and [14C]lactate from [U-14C]glucose by the placenta and the contribution of 14CO2 from fetal oxidation of these metabolic products to the calculation of glucose oxidation rate in fetal sheep. During fetal tracer infusions (n = 16), oxidation of fructose contributed 16 +/- 3% of total fetal CO2 production; oxidation of lactate accounted for 3.3 +/- 0.1%. Thus 80% of total fetal CO2 production resulted from direct oxidation of carbon atoms in glucose; the "direct" glucose oxidation fraction was 0.46 +/- 0.04. During maternal tracer infusion (n = 15), CO2 production from fructose was 21 +/- 3, 20 +/- 3, and 30 +/- 4% and from lactate was 16 +/- 3, 13 +/- 3, and 11 +/- 4% in hypo-, normo-, and hyperglycemic animals, respectively; the direct glucose oxidation fraction was 0.40 +/- 0.04, not different from the fraction obtained with the fetal tracer infusion. Fetal oxidation of substrates derived from glucose metabolism in the placenta contributes significantly to fetal CO2 production. Fetal oxidation of placental products of a metabolic substrate tracer should be considered in studies of fetal oxidative metabolism.
Human GLUT-2 overexpression does not affect glucose-stimulated insulin secretion in MIN6 cells
Authors: Ishihara H. , Asano T. , Tsukuda K. , Katagiri H. , Inukai K. , Anai M. , Yazaki Y. , Miyazaki J. , Kikuchi M. , Oka Y.
Published: December 2017

Accumulated evidence suggests that GLUT-2, in addition to its role in glucose transport, may also have other functions in glucose-stimulated insulin secretion. As a first step in addressing this possibility, we have engineered MIN6 cells overexpressing human GLUT-2 by transfection with human GLUT-2 cDNA. Stable transformants harboring human GLUT-2 cDNA exhibited an approximately twofold increase in 3-O-methyl-D-glucose uptake at 0.5 and 15 mM. Glucokinase activity or glucose utilization measured by conversion of [5-3H]glucose to [3H]H2O was not, however, altered in the MIN6 cells overexpressing human GLUT-2. Furthermore, glucose-stimulated insulin secretion was not affected by over-expression of human GLUT-2. An abundance of GLUT-2, therefore, does not correlate with the glucose responsiveness of cells in which glycolysis is regulated at the glucose phosphorylating step. These data suggest that GLUT-2 by itself does not have significant functions other than its role in glucose transport in glucose sensing by MIN6 cells.
Constant-pressure perfusion of rat hindlimb shows alpha- and beta-adrenergic stimulation of oxygen consumption
Authors: Ye J. M. , Clark M. G. , Colquhoun E. Q.
Published: December 2017

Isolated rat hindlimbs were perfused at 37 degrees C and constant physiological pressure (80 +/- 0.5 mmHg) while the flow rate that was allowed to freely self-adjust was monitored. Under these conditions, evidence was obtained for both alpha- and beta-adrenergic stimulation of oxygen consumption (VO2) in contrast to constant-flow perfusion, which has only convincingly shown alpha-adrenergic stimulation of VO2 in response to adrenergic agents. Addition of norepinephrine (NE; 1-33 nM) led to an increase in VO2 with a maximum of 29% above the basal value at 3.3 nM, even though the flow rate decreased. Phenylephrine (3.3-33 nM) and vasopressin (10-100 pM) also showed similar, but lesser in magnitude, vasoconstriction-associated stimulatory effects on VO2. Prazosin (an alpha 1-antagonist) completely reversed the NE-mediated decrease in flow rate and significantly blocked the increased VO2. In contrast, isoproterenol (10-1,000 nM) increased both flow rate (30%) and VO2 (32%). The isoproterenol-stimulated VO2 was not blocked by the beta 1-, beta 2-antagonist propranolol (10 microM), although the increased flow was reversed. In the presence of propranolol (1 or 10 microM), BRL-35135A (a beta 3-agonist) also stimulated VO2 (18%) without significant change in flow rate. These results lend further support to the role of the alpha 1-adrenoceptor in muscle VO2. In addition there is evidence for the presence of a functional beta 3-adrenoceptor as an additional subtype responsible for NE-mediated thermogenesis in the rat hindlimb.
Effect of blood flow on muscle lactate release studied in perfused rat hindlimb
Authors: Pilegaard H. , Bangsbo J. , Henningsen P. , Juel C. , Richter E. A.
Published: December 2017

The influence of blood flow on muscle lactate and H+ release as well as muscle glyconeogenesis was studied in the perfused rat hindlimb. After 2 min of supramaximal stimulation the perfusate flow rate was 7 (F7), 12 (F12), or 18 (F18) ml/min for 30 min. Perfusate samples were drawn frequently and muscle samples were obtained before stimulation, immediately after stimulation, and at 3, 10, and 30 min of recovery from soleus, white gastrocnemius (WG) and red gastrocnemius. During the first 5 min of recovery lactate release was 35-39% lower (P < 0.05) in F7 than in F12 and F18 but with no differences in total release during recovery. In F7 the concentration of lactate was higher (P < 0.05) in soleus after 10 min (18-20%) and in WG after 30 min (63-67%) than in F12 and F18. During the first 2 min of recovery H+ release was 23-34% lower (P < 0.05) in F7 than in F12 and F18. The difference between H+ and lactate release was larger (P < 0.05) in F7 than in F12 and F18 from 3 to 10 min and from 5 to 10 min of recovery, respectively. Muscle glycogen concentrations after 30 min of recovery were independent of flow in each of the muscles. The present data suggest that 1) in the range of blood flow rates from 0.61 to 0.92 ml.min-1.g-1, lactate and H+ release are independent of the flow rate, whereas at a lower flow rate (0.36 ml.min-1.g-1) release of these substances is decreased; 2) low blood flow influences lactate efflux more than H+ release; and 3) muscle glyconeogenesis from lactate is of minor importance.
Regulation of glucose transport and GLUT-1 expression by iron chelators in muscle cells in culture
Authors: Potashnik R. , Kozlovsky N. , Ben-Ezra S. , Rudich A. , Bashan N.
Published: December 2017

Possible association between the degree of iron load and glucose metabolism has been postulated by both in vivo and in vitro studies. Because skeletal muscle plays a major role in whole body glucose utilization, we evaluated the effect of iron chelators deferoxamine (DFO) and bipyridyl (Bip) on glucose metabolism and transport in cultured L6 muscle cells. Bip (0.1 mM) or DFO (0.5 mM) added for 24 h to the culture medium increased glucose consumption, lactate production, and [14C]glucose incorporation into glycogen by approximately twofold. 2-Deoxy-glucose uptake by L6 myotubes increased time dependently, reaching a 5-fold and 2.5-fold increase after 12 h for Bip and DFO, respectively. Insulin induced a 2.5-fold increase in glucose uptake in untreated cells, which was additive to the chelator's effect. Iron chelator-induced glucose transport stimulation was inhibited by cycloheximide (2.5 micrograms/ml), indicating dependence on de novo protein synthesis. Increases in GLUT-1 protein and mRNA concentration, without changes in GLUT-4, were found to be responsible for iron chelator effects. We conclude that L6 cells adapt to reduction in iron availability by increasing glucose utilization through an enhanced expression of GLUT-1, without losing their physiological response to insulin.
NIDDM is associated with loss of pancreatic beta-cell L-type Ca2+ channel activity
Authors: Roe M. W. , Worley J. F. , Tokuyama Y. , Philipson L. H. , Sturis J. , Tang J. , Dukes I. D. , Bell G. I. , Polonsky K. S.
Published: December 2017

Development of non-insulin-dependent diabetes mellitus (NIDDM) is associated with defects in glucose-stimulated insulin secretion. We have investigated Zucker diabetic fatty rats (ZDF), an animal model of NIDDM, and found that, compared with control islets, the expression of mRNA encoding C- and D-isoforms of alpha 1-subunits of beta-cell L-type voltage-dependent Ca2+ channels (VDCC) was significantly reduced in islets isolated from ZDF rats. This correlated with a substantial reduction of L-type Ca2+ currents (ICa) in ZDF beta-cells. Intracellular Ca2+ concentration responses in ZDF islets after glucose, KCI, or BAY K 8644 stimulation were markedly attenuated, whereas responses evoked by carbachol were unimpaired, consistent with a specific decrease in ICa in the diabetic islets. This reduction was accompanied by loss of pulsatile insulin secretion from ZDF islets treated with oscillatory increases of external glucose concentration. Our findings suggest that the attenuation of ICa in diabetic islets may contribute to the abnormal glucose-dependent insulin secretory responses associated with NIDDM and indicate that this defect is caused by decreased expression of genes encoding beta-cell VDCC alpha 1-subunits.
A model to measure insulin effects on glucose transport and phosphorylation in muscle: a three-tracer study
Authors: Saccomani M. P. , Bonadonna R. C. , Bier D. M. , DeFronzo R. A. , Cobelli C.
Published: December 2017

We studied five healthy subjects with perfused forearm and euglycemic clamp techniques in combination with a three-tracer (D-[12C]mannitol, not transportable; 3-O-[14C]methyl-D-glucose, transportable but not metabolizable; D-[3-3H]glucose, transportable and metabolizable) intra-arterial pulse injection to assess transmembrane transport and intracellular phosphorylation of glucose in vivo in human muscle. The washout curves of the three tracers were analyzed with a multicompartmental model. A priori identifiability analysis of the tracer model shows that the rate constants of glucose transport into and out of the cells and of glucose phosphorylation are uniquely identifiable. Tracer model parameters were estimated by a nonlinear least-squares parameter estimation technique. We then solved for the tracee model and estimated bidirectional transmembrane transport glucose fluxes, glucose intracellular phosphorylation, extracellular and intracellular volumes of glucose distribution, and extracellular and intracellular glucose concentrations. Physiological hyperinsulinemia (473 +/- 22 pM) caused 2.7-fold (63.1 +/- 7.2 vs. 23.4 +/- 6.1 mumol.min-1.kg-1, P < 0.01) and 5.1-fold (42.5 +/- 5.8 vs. 8.4 +/- 2.2 mumol.min-1.kg-1, P < 0.01) increases in transmembrane influx and intracellular phosphorylation of glucose, respectively. Extracellular distribution volume and concentration of glucose were unchanged, whereas intracellular distribution volume of glucose was increased (approximately 2-fold) and intracellular glucose concentration was almost halved by hyperinsulinemia. In summary, 1) a multicompartment model of three-tracer kinetic data can quantify transmembrane glucose fluxes and intracellular glucose phosphorylation in human muscle; and 2) physiological hyperinsulinemia stimulates both transport and phosphorylation of glucose and, in doing so, amplifies the role of glucose transport as a rate-determining step of muscle glucose uptake.
Gut proteolysis contributes essential amino acids during exercise
Authors: Williams B. D. , Wolfe R. R. , Bracy D. P. , Wasserman D. H.
Published: December 2017

Arteriovenous difference and tracer dilution techniques were utilized to determine the effect of exercise on whole body, gut, liver, and splanchnic leucine kinetics. Five postabsorptive dogs were infused with [1-13C]leucine and studied during rest, 90 min of moderate-intensity treadmill exercise (1st 45 min, early; last 45 min, late exercise), and 90 min of recovery. The whole body leucine rate of appearance (Rai; mumol.min 1.kg-1) increased from rest (3.33 +/- 0.11) during early (3.68 +/- 0.14) and late (4.24 +/- 0.27, P < 0.05) exercise and was 3.41 +/- 0.19 during recovery. Gut Ra increased from rest (0.64 +/- 0.08) during early (0.92 +/- 0.12) and late (1.30 +/- 0.20, P < 0.05) exercise and was 0.77 +/- 0.16 during recovery. Liver leucine Ra did not significantly change (P > 0.05). The whole body leucine rate of disappearance (Rd) paralleled whole body leucine Ra throughout. Leucine Rd across the gut, liver, and splanchnic bed, however, did not significantly change (P > 0.05), indicating an increase in leucine uptake outside of these regions. Because active skeletal muscle is likely the principal consumer of these amino acids, the data suggest that gut protein-derived amino acids are utilized for the attenuation of net muscle protein catabolism during and immediately following exercise.