bluuebunny/crossref_metadata_2025 huggingface dataset:
Chloroquine reduces whole body proteolysis in humans
Authors: De Feo P. , Volpi E. , Lucidi P. , Cruciani G. , Santeusanio F. , Bolli G. B. , Brunetti P.
Published: December 2017

The antimalaric drug chloroquine is a well known inhibitor of lysosomal proteolysis in vitro. The present study tests the hypothesis that therapeutic doses of the drug decrease proteolysis also in vivo in humans. Leucine kinetics were determined in 20 healthy volunteers given 12 and 1.5 h before the studies 250 and 500 mg, respectively, of chloroquine phosphate (n = 10) or similar tablets of placebo (n = 10). Chloroquine reduced the rates of leucine appearance, a measure of whole body proteolysis, from 2.45 +/- 0.08 to 2.19 +/- 0.08 mumol.kg-1.min-1 (P = 0.038) and those of nonoxidative leucine disposal, an estimate of whole body protein synthesis, from 2.16 +/- 0.08 to 1.95 +/- 0.06 mumol.kg-1.min-1 (P = 0.050). The drug resulted also in a marginally significant (P = 0.051) decrement in the plasma concentrations of glucose. The effects of chloroquine on protein turnover might be potentially useful in counteracting protein wasting complicating several catabolic diseases, whereas those on glucose metabolism can explain the sporadic occurrence of severe hypoglycemic episodes in malaria patients chronically treated with this drug.
Contribution of central and peripheral adrenergic stimulation to IL-1 alpha-mediated glucoregulation
Authors: Petit F. , Jarrous A. , Dickinson R. D. , Molina P. E. , Abumrad N. N. , Lang C. H.
Published: December 2017

The present study determined the contribution of central adrenoceptors and the peripheral sympathetic nervous system in regulating the hormonal and glucose metabolic response to intracerebroventricular injection of interleukin (IL)-1 alpha. After an overnight fast, hepatic glucose production (HGP) and peripheral glucose uptake (GU) were assessed in catheterized conscious unrestrained rats using [3-3H]glucose. Intracerebroventricular injection of IL-1 alpha (100 ng) produced a hyperglycemia that resulted from an early increase in HGP (108%) that exceeded a smaller elevation (82%) in GU. Intracerebroventricular injection of the alpha- and beta-adrenergic antagonists phentolamine and propranolol before IL-1 alpha blunted the glucose metabolic response 30-50%. This attenuated response was associated with normalization of the IL-1 alpha-induced hyperglucagonemia and hyperinsulinemia and a 50-60% reduction in the incremental increase in plasma catecholamines. In contrast to central administration, systemic infusion of adrenergic blockers completely prevented the IL-1 alpha-induced increases in plasma glucose, as well as HGP and GU. In these rats, the elevated plasma levels of insulin, glucagon, and corticosterone produced by intracerebroventricular injection of IL-1 alpha were still present. The results indicate that 1) the enhanced whole body glucose metabolism seen after central administration of IL-1 alpha is mediated by increased sympathoadrenal activity and 2) the IL-1 alpha-induced increase in pancreatic insulin and glucagon secretion as well as part of the peripheral catecholamine release is mediated by central adrenoreceptors.
Hemodynamic actions of insulin
Authors: Baron A. D.
Published: December 2017

There is accumulating evidence that insulin has a physiological role to vasodilate skeletal muscle vasculature in humans. This effect occurs in a dose-dependent fashion within a half-maximal response of approximately 40 microU/ml. This vasodilating action is impaired in states of insulin resistance such as obesity, non-insulin-dependent diabetes, and elevated blood pressure. The precise physiological role of insulin-mediated vasodilation is not known. Data indicate that the degree of skeletal muscle perfusion can be an important determinant of insulin-mediated glucose uptake. Therefore, it is possible that insulin-mediated vasodilation is an integral aspect of insulin's overall action to stimulate glucose uptake; thus defective vasodilation could potentially contribute to insulin resistance. In addition, insulin-mediated vasodilation may play a role in the regulation of vascular tone. Data are provided to indicate that the pressor response to systemic norepinephrine infusions is increased in obese insulin-resistant subjects. Moreover, the normal effect of insulin to shift the norepinephrine pressor dose-response curve to the right is impaired in these patients. Therefore, impaired insulin-mediated vasodilation could further contribute to the increased prevalence of hypertension observed in states of insulin resistance. Finally, data are presented to indicate that, via a yet unknown interaction with the endothelium, insulin is able to increase nitric oxide synthesis and release and through this mechanism vasodilate. It is interesting to speculate that states of insulin resistance might also be associated with a defect in insulin's action to modulate the nitric oxide system.(ABSTRACT TRUNCATED AT 250 WORDS)
Interaction of insulin and somatotropin on body weight gain, feed intake, and body composition in rats
Authors: Roberts T. J. , Azain M. J. , Hausman G. J. , Martin R. J.
Published: December 2017

This study investigated the interaction of insulin and somatotropin on body weight gain and feed conversion in rats. Female rats (initial wt 215 g) were assigned to one of the following four treatments for a 2-wk period: 1) control; 2) 40 U protamine zinc insulin.kg-1.day-1; 3) 2 mg/day somatotropin; 4) insulin + somatotropin. Relative to the control group (gain, 1.4 g/day; intake, 16.7 g/day) insulin stimulated the rate of gain (250%), feed intake (73%), and fat pad weight (215%). Insulin caused a 270% increase in carcass fat and a 30% increase in carcass protein. Somatotropin also increased gain (178%) but did not have a significant effect on intake or fat pad weight. Somatotropin increased carcass protein 28% but had no effect on carcass fat. The greatest stimulation of body weight gain (392%) was observed with the insulin plus somatotropin combination treatment, indicating an additive effect. There were also additive effects on protein accretion and organ weights. However, feed intake and carcass fat in the combination group were intermediate between that of the control and insulin alone groups, indicating that somatotropin attenuated the ability of insulin to stimulate these parameters. These results indicate that certain effects of insulin and somatotropin, such as the promotion of lean tissue accretion, are additive, whereas other effects, such as those associated with lipid metabolism, oppose each other.
P2-purinergic stimulation of iodide efflux in FRTL-5 rat thyroid cells involves parallel activation of PLC and PLA2
Authors: Smallridge R. C. , Gist I. D.
Published: December 2017

Extracellular ATP increases inositol phosphates, cytosolic Ca2+ concentration ([Ca2+]i), arachidonic acid (AA) release, and iodide efflux in FRTL-5 cells. To examine the sequence of events in P2-purinergic receptor activation by ATP, a phospholipase C (PLC) inhibitor (U-73122) and a phospholipase A2 (PLA2) inhibitor (U-26384), as well as 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid (BAPTA) and downregulation of protein kinase C (PKC) were used. ATP increased inositol trisphosphate (IP3), [Ca2+]i, AA release, and 125I efflux dose dependently. U-73122 inhibited the IP3 and calcium increase but not AA; U-26384 prevented AA release but not the increase in calcium. Both agents inhibited iodide efflux. BAPTA prevented any ATP-induced increase in [Ca2+]i without affecting AA release or 125I efflux. PKC downregulation had no effect on ATP-stimulated AA release, but reduced 125I efflux. We conclude that ATP-induced iodide efflux involves parallel, not sequential, activation of PLC and PLA2. No increase in [Ca2+]i or PKC activity is required for PLA2 activation. In contrast, an increase in 125I efflux depends on PKC and PLA2 activities, but not an increase in [Ca2+]i.
Simplified measurement of norepinephrine kinetics: application to studies of aging and exercise training
Authors: Marker J. C. , Cryer P. E. , Clutter W. E.
Published: December 2017

We assessed simplified approaches to measurement of steady-state norepinephrine (NE) kinetics (short, nonprimed infusions of [3H]NE or of unlabeled NE and arterialized venous sampling), then reexamined the kinetic mechanism(s) of the age-associated increase in plasma NE, and tested the hypothesis that the latter is the result of a sedentary lifestyle. We studied 17 young (21-28 yr) and 21 elderly (60-76 yr) subjects and a subset (n = 8) of the latter again after 1 yr of physical training. NE appearance rates (Ra) and NE metabolic clearance rates (MCRs), calculated from arterialized venous data, were not significantly different from those calculated from arterial data, whereas those calculated from venous data were substantially (approximately 50%) higher. NE Ra and NE MCR, determined from infusions of unlabeled NE were approximately 20% higher than those determined with [3H]NE, a finding plausibly attributed to approximately 20% suppression of endogenous NE appearance. Arterialized venous plasma NE concentrations were significantly higher in the elderly as a result of significantly higher NE Ra and lower NE MCR. However, arterial NE Ra was not increased, and venous NE MCR was not decreased significantly in the elderly. In the subset of elderly subjects, 1 yr of physical training, which increased peak O2 consumption by 24%, did not decrease plasma NE or NE Ra or increase NE MCR. Therefore, 1) arterial sampling provides no practical advantage over arterialized venous sampling in the measurement of NE kinetics. 2) The use of unlabeled NE infusions to determine NE kinetics overestimates NE Ra and NE MCR by approximately 20%.(ABSTRACT TRUNCATED AT 250 WORDS)
Protein synthesis and breakdown in skin and muscle: a leg model of amino acid kinetics
Authors: Biolo G. , Gastaldelli A. , Zhang X. J. , Wolfe R. R.
Published: December 2017

In the postabsorptive state, amino acids are released from the periphery to provide precursors for protein synthesis in the splanchnic organs. To evaluate the differential role of the most important peripheral tissues, i.e., skin and muscle, in the interorgan amino acid exchange, we have developed a model to simultaneously measure the rates of protein synthesis and degradation in these tissues. Anesthetized dogs were studied using the arteriovenous catheterization of the leg in combination with muscle and skin biopsies. L-[alpha-15N]lysine and L-[ring-2H5]phenylalanine were infused as independent markers of both skin and muscle protein kinetics. Model structure described leg skin and muscle as tissues arranged in parallel and accounted for blood flow distribution. Lysine data show that, in the postabsorptive state, the fractional rate (%/h) of skin protein synthesis (0.543 +/- 0.218) was comparable to the fractional rate of degradation (0.507 +/- 0.157), whereas, in muscle, degradation (0.454 +/- 0.116) was greater (P < 0.05) than synthesis (0.318 +/- 0.109). Similar conclusions were apparent from the phenylalanine data. Skin protein synthesis and degradation accounted for approximately 10-15% of the total leg protein kinetics.
Loss of fatty acid control of gluconeogenesis and PDH complex flux in adrenalectomized rats
Authors: Cipres G. , Urcelay E. , Butta N. , Ayuso M. S. , Parrilla R. , Martin-Requero A.
Published: December 2017

This work aimed to determine the role played by the adrenal gland in the fatty acid control of gluconeogenesis in isolated perfused rat livers. The gluconeogenic substrate concentration responses were not altered in adrenalectomized (ADX) rats. This observation indicates that glucocorticoids are not essential to maintain normal basal gluconeogenic rates. In contrast, fatty acid failed to stimulate gluconeogenesis from lactate and elicited attenuated stimulation with pyruvate as substrate in livers from ADX rats. Fatty acid-induced stimulation of respiration and ketone body production were similar in control and ADX rats. Thus the diminished responsiveness of the gluconeogenic pathway to fatty acid cannot be the result of different rates of energy production and/or generation of reducing power. Fatty acids did not inhibit pyruvate decarboxylation in livers from ADX rats. Even though mitochondria isolated from livers of ADX rats showed normal basal rates of pyruvate metabolism, fatty acids failed to inhibit pyruvate decarboxylation and the activity of the pyruvate dehydrogenase complex. This novel observation of the glucocorticoid effect in controlling the pyruvate dehydrogenase complex responsiveness indicates that the mitochondrial partitioning of pyruvate between carboxylation and decarboxylation reactions may be altered in livers from ADX rats. We propose that the diminished effect of fatty acid in stimulating gluconeogenesis in livers from ADX rats is the result of a limited pyruvate availability for the carboxylase reaction due to a lack of inhibition of flux through the pyruvate dehydrogenase complex.
Plasma and platelet catecholamine and catecholamine sulfate response to various exercise tests
Authors: Strobel G. , Friedmann B. , Jost J. , Bartsch P.
Published: December 2017

We tested the hypothesis that platelet and plasma catecholamine sulfates (CA-S) and platelet catecholamines (CA) reflect the overall sympathoadrenergic activation by exercise of 1 h duration. Ten well-trained subjects performed a low-intensity [62% maximum O2 consumption (VO2max); LI] and a high-intensity exercise test (77% VO2max; HI) and two tests at a similar average power output that consisted of 20 min at 77% VO2max and 40 min at 62% VO2max (HI/LI) and vice versa (LI/HI). Plasma norepinephrine sulfate (NE-S) increased to higher levels after HI than after LI exercise (15.5 +/- 2.1 vs. 8.9 +/- 0.7 nmol/l). Immediately after HI/LI and LI/HI plasma NE-S was similarly increased (9.59 +/- 1.1 vs. 9.96 +/- 1.3 nmol/l), whereas norepinephrine was higher after LI/HI than after HI/LI (23.0 +/- 3.2 vs. 15.7 +/- 2.3 nmol/l). Platelet CA and CA-S were increased only after HI. In conclusion, the plasma NE-S response to exercise parallels the overall sympathetic activation. These results support the hypothesis that plasma NE-S measured immediately after exercise reflects the overall sympathoadrenergic activity over prolonged periods of exercise. Platelet CA and CA-S poorly reflect sympathoadrenergic activation.
Evidence for an abnormal postprandial response to a high-fat meal in women predisposed to obesity
Authors: Raben A. , Andersen H. B. , Christensen N. J. , Madsen J. , Holst J. J. , Astrup A.
Published: December 2017

The present study was undertaken to investigate fat metabolism after a high-fat meal [50 energy percent (E%) fat] in formerly obese subjects with a familial history of obesity. Twelve normal-weight postobese women (PO) and 12 closely matched controls were given the test meal after a 2-day carbohydrate-rich weight-maintenance diet (58 E% carbohydrate). Whereas the thermic effect of the meals was similar in the two groups, postprandial fat oxidation was 2.5 times more suppressed in PO compared with controls (P < 0.05). A similarly enhanced suppression of arterialized plasma concentrations of nonesterified fatty acids was seen postprandially in PO (P < 0.05), possibly due to a more marked suppression of epinephrine and a reduced glucagon response in PO than in controls. Moreover, the postprandial plasma triglyceride response was attenuated and only amounted to 43% of that in controls (P < 0.05). This may be explained by a more pronounced increase in gastric inhibitory polypeptide in PO, giving rise to a higher adipose tissue lipoprotein lipase activity. No other differences were found in plasma substrates and hormones or in subjective appetite scores. In conclusion, a metabolic and hormonal pattern favoring lipid storage was observed in postobese subjects after a high-fat meal.
Stochastic modeling of the hypothalamic pulse generator activity
Authors: Camproux A. C. , Thalabard J. C. , Thomas G.
Published: December 2017

Luteinizing hormone (LH) is released by the pituitary in discrete pulses. In the monkey, the appearance of LH pulses in the plasma is invariably associated with sharp increases (i.e, volleys) in the frequency of the hypothalamic pulse generator electrical activity, so that continuous monitoring of this activity by telemetry provides a unique means to study the temporal structure of the mechanism generating the pulses. To assess whether the times of occurrence and durations of previous volleys exert significant influence on the timing of the next volley, we used a class of periodic counting process models that specify the stochastic intensity of the process as the product of two factors: 1) a periodic baseline intensity and 2) a stochastic regression function with covariates representing the influence of the past. This approach allows the characterization of circadian modulation and memory range of the process underlying hypothalamic pulse generator activity, as illustrated by fitting the model to experimental data from two ovariectomized rhesus monkeys.
Calcium uptake by chorioallantoic membrane: effects of vitamins D and K
Authors: Elaroussi M. A. , DeLuca H. F.
Published: December 2017

The chorioallantoic membrane (CAM) of birds is an epithelial tissue that actively transports large amounts of Ca during embryonic development. In this study the effect of vitamins D and K on Ca uptake by the CAM was studied. Four dietary treatments were used to produce eggs that are the following: deficient in vitamins D and K (-D/-K), sufficient in both (+D/+K), or deficient in one and sufficient in the other (-D/+K or +D/-K). Vitamin D-deficient (-D) Japanese quail embryos (from hens fed 1,25-dihydroxyvitamin D3) do not hatch because of severe Ca deficiency resulting from their inability to obtain Ca from shell, whereas vitamin K deficiency results in only 14% reduction in hatchability. The results demonstrate that Ca uptake by CAM is vitamin D dependent and only slightly vitamin K dependent. Ca-binding activity of CAM extracts was unchanged by vitamin K deficiency, and only a small increase was provided by vitamin D treatment. Vitamin D stimulated both Ca entry and exist from the chorion cells as indicated by the increased accumulated 45Ca in +D embryos. We conclude that vitamin D is essential for the utilization of eggshell Ca by the developing embryo and hence its survival, suggesting that Ca transport across the CAM is largely a vitamin D-dependent process.
Codominant effects of the fatty (fa) gene during early development of obesity
Authors: Truett G. E. , Tempelman R. J. , Walker J. A.
Published: December 2017

Expression of a single copy of the rat obesity fatty (fa) gene may affect energy balance. To test this hypothesis, the effects of zero, one, and two copies of fa on early growth were evaluated, using a molecular genetic method for counting fa alleles inherited by 7- and 14-day-old F2 offspring of a BN/Crl x Crl:ZUC-fa F1 intercross. Litter and sex effects were controlled by multiple-regression analysis, allowing genotype effects on the weights of body, inguinal adipose pads, interscapular brown adipose tissue, and liver to be isolated. At 7 days of age, the fa copy number had linear effects on body and inguinal adipose pads weight. At 14 days of age, the fa copy number had linear effects on body, inguinal adipose pads, and interscapular brown adipose tissue weights and an additional quadratic effect on inguinal adipose pads weight. Thus fa has codominant effects on growth during the first week of life. The recessive effects of fa on growth appear during the second week of life.
In vitro and in vivo analysis of murine lipoprotein lipase gene promoter: tissue-specific expression
Authors: Gimble J. M. , Hua X. , Wanker F. , Morgan C. , Robinson C. , Hill M. R. , Nadon N.
Published: December 2017

Lipoprotein lipase, an enzyme of central importance to lipid metabolism, is most abundant in adipose tissues, cardiac and skeletal muscle, and portions of the brain. The current work examined the murine lipoprotein lipase promoter using transient transfection, gel-retention analyses, and transgenic mice. Maximum expression of the luciferase reporter gene in transfected cells was observed with -101 bp of the promoter. Nuclear extracts from tissues expressing lipoprotein lipase contained DNA binding proteins that recognize the CCAAT box (-64 bp) and an octamer motif (-46 bp); this combination of factors was absent in nonexpressing tissues. Transgenic mice from three of five founders prepared with -1,824-bp promoter constructs expressed the luciferase reporter gene at highest levels in brown adipose tissue and brain. These findings suggest that the -1,824-bp promoter region contains sequence elements responsible for the tissue-specific transcription of lipoprotein lipase in vivo.
Differential effects of interleukin-1 receptor antagonist in cytokine- and endotoxin-treated rats
Authors: Ling P. R. , Istfan N. W. , Colon E. , Bistrian B. R.
Published: December 2017

Previous studies have demonstrated that the administration of the cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF)(20 micrograms/kg) to rats in a fasting state can produce many and perhaps most of the metabolic alterations found in patients with sepsis and injury. The purposes of the present study were 1) to define the metabolic effects of IL-1 and TNF during a fed state provided by continuous intravenous feeding for 20 h and 2) to characterize the unique effects of IL-1 among the overall response to cytokines by using IL-1 receptor antagonist (IL-1RA; 5 mg/kg). The effects were also explored during the endotoxemic condition induced by infusion of 200 micrograms/kg of endotoxin into rats. The results showed that during feeding IL-1 is responsible for the increase in glucose flux and plasma insulin, the development of insulin resistance, and plasma zinc depression during condition mimicking sepsis and injury, similar to effects observed in the fasting state. The changes in energy expenditure have a more complex mechanism. The results also suggested that certain host responses to cytokines or endotoxin, particularly related to protein metabolism, differed between the fed and fasting states. These data may have a special clinical relevance for the insulin-resistant state that develops during severe infection, since using IL-1RA in conjunction with nutritional therapy may offer additional advantages in the treatment of these severe metabolic disorders.
Metabolism of alpha-ketoisocaproic acid in isolated perfused liver of cirrhotic rats
Authors: Blonde-Cynober F. , Plassart F. , de Bandt J. P. , Rey C. , Lim S. K. , Moukarbel N. , Ballet F. , Poupon R. , Giboudeau J. , Cynober L.
Published: December 2017

To determine the hepatic fate of alpha-ketoisocaproate (KIC) in cirrhosis, six groups of isolated rat livers were perfused with 0, 0.5, 1 (with or without alpha-[1-14C]KIC), 2, and 5 mM KIC; control livers from healthy rats were studied in parallel under similar conditions. KIC was rapidly removed by the normal livers, whereas uptake was lower in the cirrhotic livers at all concentrations tested (at 2 mM, 4.04 +/- 0.33 vs. 6.32 +/- 0.58 mumol/min; P < or = 0.05). The transamination pathway, evaluated by leucine exchanges, was more important in the cirrhotic livers (25.4 vs. 6.8% in controls at 2 mM). The incorporation of alpha-[1-14C]KIC in proteins of cirrhotic liver was increased compared with controls (0.25 +/- 0.04% of alpha-[1-14C]KIC was incorporated in proteins excreted in perfusate vs. 0.20 +/- 0.04 in controls; P < or = 0.05). In addition, a line of evidence suggests that glutamine rather than glutamate is the N donor for leucine synthesis from KIC. The decarboxylation pathway evaluated by beta-hydroxybutyrate production and by 14CO2 release from alpha-[1-14C]KIC was reduced, respectively, by 40-85% (according to KIC dose) and by 24% at 90 min in cirrhotic livers compared with healthy livers. These results indicate a dramatic modification of KIC metabolism in the cirrhotic liver; its uptake by the liver is decreased and its incorporation into proteins is increased via an enhancement of transamination to leucine, probably as a consequence of an inhibition of branched-chain keto acid dehydrogenase.
Regulation of mineral homeostasis in osteopetrotic (op) rats
Authors: Hermey D. C. , Ireland R. A. , Zerwekh J. E. , Popoff S. N.
Published: December 2017

The osteopetrotic (op) rat is a lethal mutation characterized by severe skeletal sclerosis resulting from reduced bone resorption. Although the skeletal manifestations have been studied extensively, little is known about mineral homeostasis in this mutation. This paucity of data prompted us to undertake this study quantitating circulating levels of calcium, phosphorus, 1,25-dihydroxyvitamin D [1,25(OH)2D] and parathyroid hormone (PTH) in op mutants and normal rats between 2 and 8 wk of age. Calcium and phosphorus levels were significantly lower in op mutants at younger ages; both parameters normalized by 6 wk. Serum levels of 1,25(OH)2D were markedly elevated in op rats at all ages and showed no signs of normalization. Serum PTH levels were also elevated at most ages, with the greatest increase occurring when op mutants were severely hypocalcemic. These results demonstrate that, in op mutants, changes in circulating PTH and calcium levels were interdependent; however, levels of 1,25(OH)2D did not change despite normalization of serum calcium and phosphorus. The latter deserves further investigation and supports the hypothesis of a localized (skeletal) resistance to 1,25(OH)2D.
Altered response of protein synthesis to nutritional state and endurance training in old rats
Authors: Mosoni L. , Valluy M. C. , Serrurier B. , Prugnaud J. , Obled C. , Guezennec C. Y. , Mirand P. P.
Published: December 2017

This study was undertaken to determine whether the loss of muscle protein mass during aging could be explained by a reduced sensitivity of muscle protein synthesis to feeding and exercise. Male Wistar rats aged 12 and 24 mo were exercised by treadmill running for 4 mo. Protein synthesis was measured by the flooding dose method in tibialis anterior, soleus, and liver of conscious rested, trained rats and age-matched controls in the postprandial or in the postabsorptive state. No marked change with age could be detected in basal muscle protein synthesis. In contrast, protein synthesis was stimulated in adult but not in old rats by feeding in tibialis anterior and by exercise in soleus. In liver, protein synthesis was not modified by age but was stimulated by feeding and by exercise, which improved the response to feeding. We conclude that the impact of nutrition on muscle protein synthesis is blunted in old age, which could contribute to the age-related loss of nutrition-sensitive muscle proteins.
Insulinopenia and hyperglycemia influence the in vivo partitioning of GE and SI
Authors: Christopher M. J. , Rantzau C. , Ward G. M. , Alford F. P.
Published: December 2017

We determined the impact of variable insulinemia and glycemia on the in vivo partitioning of glucose effectiveness (GE) and insulin sensitivity (SI) and the in vitro intracellular processing of glucose metabolism. Six somatostatin- and [3-3H]glucose-infused dogs underwent euglycemic and hyperglycemic clamps at four physiological insulin (Ins) levels before a muscle biopsy. From the rates of glucose infusion (GINF), total glucose disposal (Rd), total glycolysis (GF), and glucose storage (GS), plots of delta GINF, delta Rd, delta GS vs. delta log Ins concentration were found to be linear for each dog, allowing calculation of the partitioning of GE and SI into their major in vivo sites (periphery vs. liver) and intracellular metabolic pathways (GS vs. GF). Insulinopenia induced a significant reduction in total GE. From insulinopenia to high insulinemia, the 2.3-fold increase in total GE was due to the increased peripheral glucose responsiveness of the GS pathway. Hyperglycemia induced a significant reduction in total SI, with approximately one-half of this reduction due to the decreased peripheral insulin responsiveness of the GF pathway. In skeletal muscle, both glycogen content and glycogen synthase fractional activity were positively correlated with log Ins concentration, Rd, and GS but negatively correlated with glucose 6-phosphate concentration. Moreover, both Rd and GS were negatively correlated with lactate concentration. We conclude that 1) the inhibition of GE and SI induced by insulinopenia and hyperglycemia, respectively, is due mainly to the reduced peripheral responsiveness of contrasting intracellular metabolic pathways; and 2) hyperinsulinemia and/or hyperglycemia stimulates glycogen synthesis and GF but not nonoxidative glycolysis.
Paradoxical insulin-induced increase in gluconeogenesis in response to prolonged hypoglycemia in conscious dogs
Authors: Davis S. N. , Dobbins R. , Tarumi C. , Jacobs J. , Neal D. , Cherrington A. D.
Published: December 2017

The aim of this study was to determine the effects of differing insulin concentrations on the gluconeogenic response to equivalent prolonged hypoglycemia. Insulin was infused intraportally, for 3 h, into normal 18-h fasted conscious dogs at 2 (lower, n = 6) or 8 mU.kg-1.min-1 (high, n = 7) on separate occasions. This resulted in steady-state arterial insulin levels of 80 +/- 8 and 610 +/- 55 microU/ml, respectively. Glucose was infused during high dose to maintain the hypoglycemic plateau (50 +/- 1 mg/dl) equivalent to lower. Epinephrine (806 +/- 180 vs. 2,589 +/- 260 pg/ml), norepinephrine (303 +/- 55 vs. 535 +/- 60 pg/ml), cortisol (5.8 +/- 1.2 vs. 12.1 +/- 1.5 micrograms/dl), and pancreatic polypeptide (598 +/- 250 vs. 1,198 +/- 150 pg/ml) were all increased (P < 0.05) in the presence of high-dose insulin. Net hepatic glucose production increased significantly from 2.2 +/- 0.3 to 3.8 +/- 0.5 mg.kg-1.min-1 (P < 0.05) during high-dose infusion but remained at basal levels (2.3 +/- 0.4 mg.kg-1.min-1) during lower-dose insulin. During the 3rd h of hypoglycemia, gluconeogenesis accounted for between 42 and 100% of glucose production during high-dose infusion but only 22-52% during lower-dose insulin. Intrahepatic gluconeogenic efficiency, however, increased similarly during both protocols. Lipolysis, as indicated by arterial blood glycerol levels, increased by a greater amount during high- compared with lower-dose insulin infusion. Six hyperinsulinemic euglycemic control experiments (2 or 8 mU.kg-1.min-1, n = 3 in each) provided baseline data. Gluconeogenesis remained similar to basal levels, but lipolysis was significantly suppressed during both series of hyperinsulinemic euglycemic studies. In summary, these data suggest that 1) the important counterregulatory processes of gluconeogenesis and lipolysis can be significantly increased during prolonged hypoglycemia despite an eightfold increase in circulating insulin levels and 2) the amplified gluconeogenic rate present during the hypoglycemic high-dose insulin infusions was caused by enhanced substrate delivery to the liver rather than an increase in intrahepatic gluconeogenic efficiency.
Dietary fat and adiposity: a dose-response relationship in adult male rats fed isocalorically
Authors: Boozer C. N. , Schoenbach G. , Atkinson R. L.
Published: December 2017

This study examined the effects of increasing levels of dietary fat fed isocalorically on body weight, body composition, and adipose distribution. Adult male rats were weight matched into four groups. One group that was fed a low-fat diet (12%) served as reference controls. The other three groups were fed diets of 24, 36, or 48% fat in amounts to equal the energy intake of the control group. After 6 wk, body weights of the four groups were not significantly different. Intrascapular brown fat did not differ between groups. Total body fat and adipose depot weights, however, increased in proportion to the level of fat in the diet. Total body fat and retroperitoneal and mesenteric depot weights of the 48% fat group were greater than controls (P < 0.05). Mesenteric fat in this group was also significantly increased over all other groups (P < 0.05). These results show that high-fat diets fed to adult animals cause increased body fat in the absence of significant changes in body weight and that mesenteric fat is increased disproportionately.
Orchidectomy and NMDA increase GnRH secretion as measured by push-pull perfusion of rat anterior pituitary
Authors: Grattan D. R. , Park S. K. , Selmanoff M.
Published: December 2017

Using push-pull perfusion to measure concentrations of gonadotropin-releasing hormone (GnRH) in the extracellular fluid of the anterior pituitary gland of the male rat, we have measured GnRH release at specific times before and after castration and in response to acute administration of N-methyl-D-aspartate (NMDA). After castration (7 days), mean GnRH levels were substantially increased (4.3-fold) compared with intact controls (0.94 +/- 0.16 vs. 0.22 +/- 0.08 pg/10 min, respectively, P < 0.05) due to an increase in both the frequency and amplitude of GnRH pulses. Testosterone partially reduced GnRH release (0.62 +/- 0.10 pg/10 min). NMDA induced a rapid increase in plasma luteinizing hormone (LH) in both intact and castrated rats and increased GnRH concentrations in the perfusion samples (P < 0.05). There was no change in LH release induced by two doses of injected GnRH (5 and 25 ng/100 g body wt) 2 days after castration, but by 6 days after castration the response to both doses was significantly increased. These results demonstrate that GnRH release in the male rat is acutely increased by NMDA and is chronically increased after orchidectomy. Increased pituitary sensitivity to GnRH also contributes to the hypersecretion of LH after castration, particularly at longer times after removal of testosterone negative feedback.
Stimulation of muscle glucose disposal by insulin in humans is a function of the preexisting plasma insulin level
Authors: Vogt C. , Petrides A. S.
Published: December 2017

To examine whether tissue sensitivity to insulin is dependent upon the prevailing plasma insulin concentration, the ability of acute hyperinsulinemia to stimulate glucose disposal was investigated in six normal subjects before and after prolonged reduction of the plasma insulin concentration. Glucose turnover ([6,6-2H2]glucose), whole body glucose oxidation and nonoxidative glucose disposal (indirect calorimetry), and glycogen synthase activity in muscle were determined in the postabsorptive and in the insulin-stimulated states (euglycemic hyperinsulinemic clamp: 3 mU.kg-1.min-1) before and after a 4-day subcutaneous infusion of the somatostatin analogue octreotide (200 micrograms/24 h). Constant octreotide infusion 1) decreased postabsorptive and meal-stimulated plasma insulin levels by approximately 30-40% but did not significantly alter overall glucose tolerance, free fatty acid, growth hormone, and glucagon levels and 2) was associated with significant increases in insulin-mediated whole body glucose disposal (pre-drug: 10.29 +/- 0.49 vs. postdrug: 11.42 +/- 0.72 mg.kg-1.min-1, P < 0.04), nonoxidative glucose disposal (6.82 +/- 0.57 vs. 7.68 +/- 0.62, P < 0.03), and fractional glycogen synthase activity (0.14 +/- 0.03 vs. 0.20 +/- 0.04 mU/mg protein, P < 0.02). In contrast, infusion of saline instead of octreotide for 4 days to control subjects did not alter any of the metabolic parameters. We conclude that lowering the plasma insulin concentration over a prolonged period of time increases insulin sensitivity. The effects of insulin to stimulate whole body glucose utilization, nonoxidative glucose disposal, and glycogen synthase activity in muscle are therefore functions of the preexisting plasma insulin concentration.
Beta-adrenergic blockade heightens the exercise-induced increase in leucine oxidation
Authors: Lamont L. S. , McCullough A. J. , Kalhan S. C.
Published: December 2017

The purpose of this study was to assess the interaction between beta-blockade and exercise on amino acid kinetics. This was a three-way crossover experiment using beta 1-blockade, beta 1,beta 2-blockade, and a placebo control. Three 6-h L-[1-13C]leucine and L-[alpha-15N]lysine infusions were performed. The first 3 h established an isotopic steady state, and 1 h of exercise (approximately 50% of maximal O2 consumption) and 2 h of recovery followed. Plasma glucose decreased with exercise during all trials (P < 0.0001). During beta 1- and beta 1,beta 2-blockade, plasma free fatty acids were reduced during rest and exercise (P < 0.001). Leucine and lysine rates of appearance were unaffected by beta-blockade during rest but were decreased with placebo exercise. Leucine oxidation increased with beta-blockade (P < 0.01) and exercise (P < 0.001). There was a statistical interaction between both treatments (P < 0.004). In conclusion, leucine oxidation increased with exercise, further increased with beta 1-blockade, and was additionally heightened with beta 1,beta 2-blockade. This cumulative response indicates that leucine oxidation was regulated through beta 1- and beta 2-receptors.
Transgenic GLUT-4 overexpression in fat enhances glucose metabolism: preferential effect on fatty acid synthesis
Authors: Tozzo E. , Shepherd P. R. , Gnudi L. , Kahn B. B.
Published: December 2017

GLUT-4 expression varies widely among normal humans and those with obesity and diabetes. Using the alpha P2 promoter/enhancer ligated to the human GLUT-4 gene, we created transgenic mice to study the impact of alterations in GLUT-4 expression selectively in adipocytes on glucose homeostasis and body composition. Here we investigated molecular mechanisms for enhanced glucose tolerance and obesity in these mice. [U-14C]glucose incorporation into triglycerides, glyceride-glycerol, glyceride-fatty acids, CO2, and lactate was measured in adipocytes incubated at 3, 0.5, and 3 microM glucose with or without maximally stimulating insulin. In nontransgenic and transgenic mice, the major pathway for glucose metabolism shifts from lipogenesis at tracer glucose concentration to glycolysis at physiological glucose concentration. In transgenic adipocytes incubated at 3 microM glucose, metabolism via all major pathways is enhanced by 8.6- to 38-fold in the absence of insulin and 3- to 13-fold in the presence of insulin. At physiological glucose concentration, constitutive metabolism to triglycerides, CO2, and lactate is two- to threefold greater in transgenic than in nontransgenic adipocytes. De novo fatty acid synthesis is preferentially increased: 31-fold for basal and 21-fold for insulin-stimulated compared with nontransgenic adipocytes. Thus overexpression of GLUT-4 in adipocytes of transgenic mice results in increased glucose metabolism in all major pathways, with differential regulation of the pathways involved in lipogenesis.
Plasminogen activator inhibitor-1 rises after hemorrhage in rats
Authors: Yamashita M. , Darlington D. N. , Weeks E. J. , Jones R. O. , Gann D. S.
Published: December 2017

Large hemorrhage leads to hypercoagulability, a phenomenon that has never been well explained. Because an elevation of plasminogen activator inhibitor (PAI)-1 increases procoagulant activity, we have determined whether plasma PAI activity and tissue PAI-1 mRNA are elevated after hemorrhage. Sprague-Dawley rats were bled (20 or 15 ml/kg) 4 days after cannulation. Plasma PAI activity was determined by the capacity of plasma to inhibit tissue-type plasminogen activator activity. Changes of PAI-1 mRNA in various tissues were detected by high-performance liquid chromatography after reverse transcription and polymerase chain reaction. Hemorrhage (20 ml/kg) significantly elevated plasma PAI activity at 0.5, 1, 2, 4, 6, and 8 h after hemorrhage and PAI-1 mRNA in liver at 1, 2, 4, and 6 h after hemorrhage. The PAI-1 message was also significantly elevated in lung, heart, and kidney at 4 h after hemorrhage. The increases of PAI-1 mRNA after 20 ml/kg hemorrhage were significantly greater than those after 15 ml/kg hemorrhage. These findings indicate that large hemorrhage can induce the increases in PAI activity and PAI-1 message and suggest that induction of PAI-1 may be involved in the thrombogenic responses observed after large hemorrhage.
The nucleus raphe obscurus controls pancreatic hormone secretion in the rat
Authors: Krowicki Z. K. , Hornby P. J.
Published: December 2017

Until recently, the dorsal vagal complex (DVC) was considered as the only brain stem regulatory center for the vagal control of the endocrine pancreas. Because the nucleus raphe obscurus (NRO) maintains anatomic connections via the DVC to the pancreas, a functional significance of these findings was investigated in the present study. Kainic acid and vehicle were microinjected into the right DVC and the NRO of alpha-chloralose-anesthetized rats, and plasma concentrations of rat insulin, glucagon, and glucose were determined before and 5, 15, 30, and 60 min after injections. Chemical stimulation of neurons in the DVC by kainic acid at a dose of 200 pmol evoked increases in concentrations of insulin, with a peak at 15 min, and glucagon, with a peak at 30 min. Microinjection of kainic acid into the NRO at a dose of 200 pmol, but not at a dose of 20 pmol, produced increases in plasma concentrations of insulin, with a peak at 30 min, and glucagon, with a peak at 60 min. Plasma glucose levels on microinjection of kainic acid into the NRO at a dose of 20 pmol were decreased, whereas no changes on microinjection of kainic acid at a dose of 200 pmol were observed. The effects of kainic acid on insulin and glucagon secretion in the NRO were abolished by bilateral vagotomy. The study demonstrates for the first time that the NRO can contribute to vagal control of pancreatic endocrine function, although the exact circuitry and neurotransmitters involved in this response remain unknown.
Contribution of pancreatic hormone responses to the elevation in carbohydrate metabolism with reduced PaO2
Authors: Zinker B. A. , Wilson R. , Wasserman D. H.
Published: December 2017

Reduced O2 availability, as might occur under some physiological and pathological conditions, stimulates insulin and glucagon release and increases glucose fluxes and muscle carbohydrate metabolism. The aim of this study was to determine the role of reduced PO2, independent of changes in glucagon and insulin. In six dogs, in paired studies separated by 2 wk, glucagon and insulin levels were fixed throughout by infusion of somatostatin with basal intraportal glucagon and insulin replacement. A control period was followed by 90 min of breathing 21% (NO) or 8% (LO) O2. Isotopic and arteriovenous methods were used to assess carbohydrate metabolism. Measured variables were constant over time in NO. Arterial PO2 (Pao2) was approximately 100 mmHg in NO and approximately 30 mmHg in LO, resulting in a 50% fall in O2 content. Insulin, glucagon, and catecholamine levels were similar in NO and LO. Cortisol was significantly increased in LO. Arterial glucose was unchanged in both groups. In the last 45 min of the experimental period in LO, 1) glucose production (14 +/- 1 to 18 +/- 1 mumol.kg-1.min-1), glucose disappearance (15 +/- 1 to 17 +/- 1 mumol.kg-1.min-1), and net hepatic glucose output (11 +/- 1 to 15 +/- 1 mumol.kg-1.min-1) rose, 2) limb pyruvate oxidation (11 +/- 2 to 24 +/- 5 mumol/min) and estimated glycogenolysis (9 +/- 3 to 42 +/- 9 mumol/min) increased, 3) percentages of CO2 from limb pyruvate and glucose increased, and percentage of lactate from blood glucose decreased, and 4) arterial blood lactate was approximately 100% more, although net limb and hepatic lactate balances were unaltered, which suggests that neither liver nor muscle is the source of increased blood lactate. Comparison of these results with our previous study [Zinker et al. Am. J. Physiol. 266 (Endocrinol. Metab. 29): E921-E929, 1994] shows that the response to reduced PaO2, although present, is reduced when glucagon and insulin levels are fixed at basal. The majority of stimulation of glucose production by decreased PaO2 is still present when pancreatic hormones are clamped at basal, while the response by the hindlimb tissues is greatly reduced.
Differential regulation by TGF-beta 1 and insulin of insulin-like growth factor binding protein-2 in IEC-6 cells
Authors: Guo Y. S. , Townsend C. M. , Jin G. F. , Beauchamp R. D. , Thompson J. C.
Published: December 2017

The purposes of this study were to determine the regulation of insulin-like growth factor binding protein-2 (IGFBP-2) in IEC-6 cells by transforming growth factor-beta 1 (TGF-beta 1) and insulin and to determine whether IGFBP-2 mediated the growth-inhibitory action on the cells. Utilizing Western ligand blot analysis, we found that TGF-beta 1 at concentrations of 0.5, 1.0, and 2 ng/ml significantly increased levels of 32-kDa IGFBP in the conditioned medium (CM) of IEC-6 cells in a dose-dependent fashion and that low doses of insulin (1.0 and 5.0 microgram/ml) also increased IGFBP levels in the CM of IEC-6 cells, but a high dose of insulin (10 micrograms/ml) depressed IGFBP release in the CM. Immunoblotting has shown that the IGFBP of 32 kDa was IGFBP-2 and further confirmed the above results. IGFBP-2 mRNA levels were stimulated by TGF-beta 1 (2.0 ng/ml) and suppressed by insulin (5.0 micrograms/ml). In addition, des (1–3) IGF-I (50 ng/ml) and insulin stimulated the proliferation of IEC-6 cells. Anti-IGFBP-2 antibodies partially blocked the inhibitory role in IEC-6 cell growth evoked by des (1–3) IGF-I. These findings suggest that the upregulation of IGFBP-2 by TGF-beta 1 occurs, at least in part, at the level of mRNA, whereas the regulation by insulin appears to be at a posttranslational level, and that the TGF-beta 1-stimulated production of IGFBP may contribute to the growth-inhibitory action in intestinal epithelial cells.x
Cortisol feedback in adrenalectomized adult sheep
Authors: McFarlane A. , Coghlan J. , Tresham J. , Wintour E. M.
Published: December 2017

These experiments tested the sensitivity of cortisol feedback on adrenocorticotropic hormone (ACTH) secretion in adult sheep. In series I, five bilaterally adrenalectomized (ADX) adult sheep were maintained on "low" (125 micrograms/h) or "high" (500 micrograms/h) intravenous cortisol replacement, and dose-response curves were obtained with corticotropin-releasing factor (CRF) and arginine vasopressin (AVP). CRF caused incremental increases in plasma ACTH at the low but not the high dose of cortisol. AVP was similarly ineffective in stimulating ACTH at the high dose of cortisol. However, in series II, where ADX animals were again maintained on low or high cortisol infusions, a combined infusion of CRF and AVP was able to stimulate a robust ACTH response during both steroid replacement regimens. These studies demonstrate that the pituitary represents a major site of steroid feedback in the sheep, with a relatively small increase in the concentration of cortisol, within the normal unstressed physiological range, being able to inhibit ACTH secretion in response to exogenous CRF and AVP. However, under these conditions, inhibition of ACTH release can be overcome by the combined action of CRF and AVP. Further studies in series III, concerned with the nature of glucocorticoid inhibition of AVP release, demonstrate that whereas exposure to maximal cortisol levels (5,000 micrograms/h) completely abolishes the ACTH response to severe hemorrhage (15 ml/kg over 15 min), AVP release is maintained, suggesting that the system controlling AVP release during hemorrhagic stress is less sensitive to the negative influences of glucocorticoids than is the system controlling ACTH release.