bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of [3-3H]glucose and [6-14C]glucose to measure glucose turnover and glucose metabolism in humans
Authors: Katz H. , Homan M. , Butler P. , Rizza R.
Published: December 2017

[3-3H]glucose is frequently used to measure glucose turnover in humans. If fructose 6-phosphate-fructose 1,6-diphosphate cycling (Fpc) is negligible in both liver and muscle, then [3-3H]- and [6-14C]glucose (corrected for Cori cycle activity) should provide equivalent measures of glucose turnover. In addition, if glycogenolysis is fully suppressed, then [14C]lactate specific activity should equal that of [6-14C]glucose from which it was derived, and oxidation of [6-14C]glucose, as measured by rate of generation of 14CO2, should equal total glucose oxidation (i.e., that derived from intra- and extracellular pools) as measured by indirect calorimetry. To address these questions, glucose turnover was measured simultaneously with [3-3H]- and [6-14C]glucose in the basal state and in presence of low (approximately 200 pM) and high (approximately 750 pM) insulin concentrations. Glucose turnover rates measured with [3-3H]- and [6-14C]glucose were equivalent at all insulin concentrations, indicating that Fpc had no detectable effect on measurement of glucose appearance. [14C]lactate specific activity was lower (P less than 0.01) than that of [6-14C]glucose in the basal state but not during either low- or high-dose insulin infusion, implying that all lactate was derived from extracellular glucose. On the other hand, glucose oxidation as measured by rate of generation of 14CO2 was lower (P less than 0.05) than glucose oxidation as measured by indirect calorimetry during both insulin infusions, implying either that suppression of glycogenolysis was not complete in all tissues or that one or both of these techniques do not accurately measure glucose oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)
Anabolic effects of clenbuterol on skeletal muscle are mediated by beta 2-adrenoceptor activation
Authors: Choo J. J. , Horan M. A. , Little R. A. , Rothwell N. J.
Published: December 2017

The potent anabolic effects of the beta 2-adrenoceptor agonist clenbuterol on skeletal muscle have been reported to be independent of actions on beta-adrenoceptors. In the present study clenbuterol, presented to rats in the diet (4 mg/kg), caused significant increases in gastrocnemius muscle mass, protein, and RNA content and a decrease in epididymal fat pad mass. These effects were not mimicked by oral administration of the beta 2-adrenoceptor agonist salbutamol even at high dose (52 mg/kg diet), and the effects of clenbuterol were not inhibited by addition of DL-propranolol (200 mg/kg diet). However, the selective beta 2-antagonist ICI-118,551 (200 mg/kg diet) reversed the anabolic effects of clenbuterol, and a high dose of DL-propranolol (1,000 mg/kg diet) also inhibited these actions of clenbuterol. Furthermore, continuous infusion of salbutamol (1.15 mg.kg body wt-1.day-1) via miniosmotic pumps did cause significant increases in muscle mass, protein, and RNA content. These results indicate that the anabolic effects of clenbuterol are dependent on interaction with the beta 2-adrenoceptor. However, a long duration of action appears to be required to induce the anabolic effects of beta 2-agonists.
Chronic stress enhances vasopressin but not corticotropin-releasing factor secretion during hypoglycemia
Authors: De Goeij D. C. , Binnekade R. , Tilders F. J.
Published: December 2017

Quantitative immunocytochemistry was used to investigate the effect of chronic intermittent stress on the storage and release of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) in the zona externa of the median eminence (ZEME). Wistar rats were subjected to repeated once daily insulin stress and studied 24 h after the last episode of hypoglycemia. Chronic intermittent hypoglycemia differentially affected CRF immuno-staining (CRFi) and AVPi stores in the ZEME, characterized by a transitory fall in CRFi (7 days) and a gradual increase in AVPi (11 days). The acute hypothalamic response to stress was studied by measuring insulin-induced depletion of CRFi and AVPi in the ZEME after blockade of fast axonal transport with colchicine (5 micrograms/rat ic). Three hours after insulin, CRFi was reduced by 24 and 28% in naive and repeatedly (11 times) stressed animals, respectively. In contrast, insulin did not affect CRFi in rats exposed to hypoglycemia for 7 days. In addition, hypoglycemia reduced AVPi in the ZEME by 37, 42, and 54% in naive and repeatedly (7 and 11 times) stressed rats, respectively. We conclude that chronic intermittent hypoglycemia induces a shift in hypothalamic signals for adrenocorticotropic hormone release in favor of AVP. This may result in altered sensitivity of the corticotrophs for hypophysiotropic factors and corticosteroids that are of physiological importance for the pituitary response to subsequent stressors.
Functional changes in salivary glands of autoimmune disease-prone NOD mice
Authors: Hu Y. , Nakagawa Y. , Purushotham K. R. , Humphreys-Beher M. G.
Published: December 2017

Lymphocytic infiltration of the salivary glands in autoimmune diseases results in the human condition known as xerostomia. To date, an animal model for the autoimmune development of salivary gland dysfunction has yet to be described. With the autoimmune diabetes-prone nonobese diabetic (NOD) mouse strain, salivary flow rates and total saliva protein concentration in both male and female mice showed a progressive decline in the nondiabetic and diabetic states. Submandibular gland weight decreased from control mice with the progression to onset of diabetes in both sexes, whereas the weight of the parotid gland remained unchanged. The level of saliva amylase activity, when measured relative to unit volume, decreased in nondiabetic males but increased upon onset of diabetes to control values. When expressed relative to protein concentration in saliva, amylase activity was depressed for both sets of NOD mice but was higher upon diabetes onset than in the nondiabetic animals. In females a similar pattern was observed except that amylase activity expressed relative to unit volume was not significantly depressed in either set of NOD mice. The same observations were made for glandular amylase activity. The level of epidermal growth factor (a product of the ductal cells of the submandibular gland) was reduced over 500- and 18-fold for male and female diabetic mice, respectively. Sodium dodecyl sulfate polyacrylamide gels of total saliva showed changes in mobility as well as concentration of several proteins in the NOD mice.(ABSTRACT TRUNCATED AT 250 WORDS)
Sepsis-induced insulin resistance in rats is mediated by a beta-adrenergic mechanism
Authors: Lang C. H.
Published: December 2017

Bacterial infection decreases insulin-mediated glucose uptake (IMGU) by skeletal muscle and produces whole body insulin resistance. Because circulating catecholamines are elevated by the septic insult, the present study was performed to determine the potential role of the beta-adrenergic system in eliciting these changes. Before induction of sepsis, an infusion containing saline, propranolol, or atenolol was started and continued throughout the experimental protocol. Sepsis increased the basal rate of glucose production and utilization and impaired IMGU by peripheral tissues. The peripheral insulin resistance in septic rats was manifested by an increase in the dose producing 50% of maximal response and a decrease in the maximal responsiveness. Infusion of propranolol, a nonselective beta-adrenergic antagonist, attenuated the sepsis-induced increase in basal glucose turnover by 70% and completely prevented the decrease in IMGU by the whole body. In contrast, atenolol, a selective beta 1-antagonist, did not alter the glucose metabolic response to infection. Under basal conditions, propranolol prevented or attenuated the increase in glucose uptake by the gastrocnemius, diaphragm, skin, liver, lung, spleen, and ileum normally observed in septic rats. In addition, propranolol prevented the decrease in IMGU by various muscles and skin in septic animals. These results suggest that adrenergic stimulation, probably mediated by a beta 2-adrenergic mechanism, is partially responsible for the sepsis-induced increases in basal whole body glucose turnover and plays a prominent role in the development of peripheral insulin resistance in this condition.
Concomitant interindividual variation in body temperature and metabolic rate
Authors: Rising R. , Keys A. , Ravussin E. , Bogardus C.
Published: December 2017

There is significant variation in metabolic rate in humans, independent of differences in body size, body composition, age, and gender. Although it has been generally held that the normal human "set-point" body temperature is 37 degrees C, these interindividual variations in metabolic rate also suggest possible variations in body temperature. To examine the possibility of correlations between metabolic rate and body temperature, triplicate measurements of oral temperatures were made before and after measurement of 24-h energy expenditure in a respiratory chamber in 23 Pima Indian men. Fasting oral temperatures varied more between individuals than can be attributed to methodological errors or intraindividual variation. Oral temperatures correlated with sleeping (r = 0.80, P < 0.0001), and 24-h (r = 0.48, P < 0.02) metabolic rates adjusted for differences in body size, body composition, and age. Similarly, in the 32 Caucasian men of the Minnesota Semi-Starvation Study, oral temperature correlated with adjusted metabolic rate, and the interindividual differences in body temperature were maintained throughout semistarvation and refeeding. These results suggest that a low body temperature and a low metabolic rate might be two signs of an obesity-prone syndrome in humans.
Ammonium chloride-induced acidosis increases protein breakdown and amino acid oxidation in humans
Authors: Reaich D. , Channon S. M. , Scrimgeour C. M. , Goodship T. H.
Published: December 2017

The effect of acidosis on whole body protein turnover was determined from the kinetics of infused L-[1-13C]leucine. Seven healthy subjects were studied before (basal) and after (acid) the induction of acidosis with 5 days oral ammonium chloride (basal pH 7.42 +/- 0.01, acid pH 7.35 +/- 0.03). Bicarbonate recovery, measured from the kinetics of infused NaH13CO3, was increased in the acidotic state (basal 72.9 +/- 1.2 vs. acid 77.6 +/- 1.6%; P = 0.06). Leucine appearance from body protein (PD), leucine disappearance into body protein (PS), and leucine oxidation (O) increased significantly (PD: basal 120.5 +/- 5.6 vs. acid 153.9 +/- 6.2, P < 0.01; PS: basal 98.8 +/- 5.6 vs. acid 127.0 +/- 4.7, P < 0.01; O: basal 21.6 +/- 1.1 vs. acid 26.9 +/- 2.3 mumol.kg-1.h-1, P < 0.01). Plasma levels of the amino acids threonine, serine, asparagine, citrulline, valine, leucine, ornithine, lysine, histidine, arginine, and hydroxyproline increased significantly with the induction of acidosis. These results confirm that acidosis in humans is a catabolic factor stimulating protein degradation and amino acid oxidation.
K+ channels in adrenal zona glomerulosa cells. I. Characterization of distinct channel types
Authors: Vassilev P. M. , Kanazirska M. V. , Quinn S. J. , Tillotson D. L. , Williams G. H.
Published: December 2017

Four distinct types of K+ channels were identified in rat and bovine adrenal zona glomerulosa (ZG) cells and characterized using single-channel recording techniques. Inward rectifier channels were the most frequently observed K+ channel types in the membrane patches of both rat and bovine ZG cells. The slope conductance of the inward current was 42 pS with an extracellular K+ concentration of 150 mM. The probability of the open state of these channels increased with depolarization. With the use of inside-out membrane patches with symmetric 150 mM K+ solutions, the rectifying behavior was found to require Mg2+ on the intracellular side of the membrane. Delayed rectifier K+ channels with conductances of 27 and 48 pS were found with rat ZG cells. These channels persisted with prolonged positive voltage steps and showed long mean open times with increasing depolarization. Transient outward currents with a conductance of 28 pS were observed only in bovine ZG cells. These channels showed substantial inactivation during positive voltage steps of 250 ms duration. Ca(2+)-activated K+ channels with a large conductance (228 pS) were identified in rat and bovine ZG cells. These different classes of K+ channels may be important for the control of resting membrane potential and the generation of action potentials, thus participating in the regulation of Ca2+ influx and aldosterone secretion in ZG cells.
Muscle glucose transport, GLUT-4 content, and degree of exercise training in obese Zucker rats
Authors: Banks E. A. , Brozinick J. T. , Yaspelkis B. B. , Kang H. Y. , Ivy J. L.
Published: December 2017

The effects of high (HI)- and low (LI)-intensity exercise training were examined on insulin-stimulated 3-O-methyl-d-glucose (3-MG) transport and concentration of insulin-regulatable glucose transporter protein (GLUT-4) in the red (fast-twitch oxidative) and white (fast-twitch glycolytic) quadriceps of the obese Zucker rat. Sedentary obese (SED) and lean (LN) Zucker rats were used as controls. 3-MG transport was determined during hindlimb perfusion in the presence of 8 mM 3-MG, 2 mM mannitol, 0.3 mM pyruvate, and 0.5 mU/ml insulin. HI and LI rats displayed greater rates of red quadriceps 3-MG transport and GLUT-4 concentrations than SED rats. No significant differences in rates of 3-MG transport or GLUT-4 concentrations were observed in the red quadriceps of HI and LI rats. There were no differences found in the rates of 3-MG transport in the white quadriceps of HI, LI, and SED rats although the difference between the HI and SED rats approached significance (P < 0.07). The GLUT-4 concentration and citrate synthase activity of HI rats were significantly greater than SED rats. The 3-MG transport rates of LN rats were twofold greater than SED rats regardless of fiber type, but a difference in GLUT-4 content between the LN and SED rats was observed only in the white quadriceps. GLUT-4 content of the obese rats was significantly correlated with citrate synthase activity (r = 0.93) and 3-MG transport (r = 0.82). The results suggest that the improvement in muscle insulin resistance of the obese Zucker rat after exercise training is due in part to an increased GLUT-4 concentration, which is related with the degree to which the muscle is trained.

glucose transporter; insulin; insulin resistance; diabetes, muscle fiber type

Submitted on May 21, 1992

Accepted on July 31, 1992
Thermogenic response to epinephrine in the forearm and abdominal subcutaneous adipose tissue
Authors: Simonsen L. , Bulow J. , Madsen J. , Christensen N. J.
Published: December 2017

Whole body energy expenditure, thermogenic and metabolic changes in the forearm, and intercellular glucose concentrations in subcutaneous adipose tissue on the abdomen determined by microdialysis were measured during epinephrine infusion in healthy subjects. After a control period, epinephrine was infused at rates of 0.2 and 0.4 nmol.kg-1 x min-1. Whole body resting energy expenditure was 4.36 +/- 0.56 (SD) kJ/min. Energy expenditure increased to 5.14 +/- 0.74 and 5.46 +/- 0.79 kJ/min, respectively (P < 0.001), during the epinephrine infusions. Respiratory exchange ratio was 0.80 +/- 0.04 in the resting state and did not change. Local forearm oxygen uptake was 3.9 +/- 1.3 mumol.100 g-1 x min-1 in the basal period. During epinephrine infusion, it increased to 5.8 +/- 2.1 (P < 0.03) and 7.5 +/- 2.3 mumol.100 g-1 x min-1 (P < 0.001). Local forearm glucose uptake was 0.160 +/- 0.105 mumol.100 g-1 x min-1 and increased to 0.586 +/- 0.445 and 0.760 +/- 0.534 mumol.100 g-1 x min-1 (P < 0.025). The intercellular glucose concentration in the subcutaneous adipose tissue on the abdomen was equal to the arterial concentration in the basal period but did not increase as much during infusion of epinephrine, indicating glucose uptake in adipose tissue in this condition. If it is assumed that forearm skeletal muscle is representative for the average skeletal muscle, it can be calculated that on average 40% of the enhanced whole body oxygen uptake induced by infusion of epinephrine is taking place in skeletal muscle. It is proposed that adipose tissue may contribute to epinephrine-induced thermogenesis.
Pharmacokinetics of ANF and urodilatin during cANF receptor blockade and neutral endopeptidase inhibition
Authors: Abassi Z. A. , Tate J. , Hunsberger S. , Klein H. , Trachewsky D. , Keiser H. R.
Published: December 2017

Urodilatin is a new member of the family of natriuretic peptides. It is of renal origin. Previous reports indicate that urodilatin is natriuretic in lower doses than atrial natriuretic factor (ANF)-(99–126) and that it might be more effective than ANF in the treatment of cardiovascular edema. The present study was designed to compare the pharmacokinetics of the hydrolysis and clearance of 125I-labeled urodilatin and 125I-ANF. In control rats, the volume of distribution (Vss), metabolic clearance rate (MCR), and distribution half-life (distribution t1/2) of urodilatin in plasma were not significantly different from those of ANF. Infusion of clearance (c)ANF-(4–23), a specific ligand for receptors that clear ANF in excess amounts (i.e., a bolus injection of 100 micrograms/kg followed by a continuous infusion of 10 micrograms.kg-1 x min-1), increased the amount of intact peptide in the plasma to the same extent for both urodilatin and ANF. In addition, cANF-(4–23) decreased the Vss and the MCR and increased the distribution t1/2 of both peptides to about the same degree. Prior treatment of rats with SQ-28,603, a specific neutral endopeptidase (NEP; EN 3.4.24.11) inhibitor, was without significant effect on the metabolic clearance of urodilatin, whereas it decreased the clearance of ANF by 65%. Furthermore, an infusion of SQ-28,603 suppressed the appearance of the hydrolytic products of ANF in blood but not of urodilatin. Moreover, the inhibitor increased the total amount of ANF recovered in the kidneys to five times the control values, whereas it did not alter the renal uptake of urodilatin.(ABSTRACT TRUNCATED AT 250 WORDS)
Studies on mechanisms of hepatic insulin resistance in cafeteria-fed rats
Authors: Davidson M. B. , Garvey D.
Published: December 2017

Whether hyperinsulinemia causes insulin resistance or vice versa is controversial. The development of hyperinsulinemia and insulin resistance was tracked in the cafeteria-fed rat to determine which occurred first. After 3 days of cafeteria feeding the rats were obese, manifested a small but significant decrease in fasting glucose levels, and showed no change in fasting insulin levels, basal hepatic glucose production (HGP), insulin binding to hepatic membranes, and glucose utilization during a euglycemic hyperinsulinemic clamp, but the rats did demonstrate an increased glucose disappearance rate associated with an enhanced insulin response to intra-arterial glucose and hepatic insulin resistance during the clamp. After 7 days of cafeteria feeding, the results were similar except that fasting hyperglycemia and hyperinsulinemia, an enhanced basal HGP, and decreased insulin binding developed. After 6 wk of cafeteria feeding, both hepatic and peripheral insulin resistances were present. After 7 days of cafeteria feeding in rats given streptozotocin or etomoxir, an inhibitor of free fatty acid (FFA) oxidation, hepatic insulin resistance persisted despite elimination of hyperinsulinemia and reduction of FFA oxidation. These data do not support a causal role for either hyperinsulinemia or enhanced lipolysis of hypertrophied fat stores and subsequent FFA oxidation in the liver in the development of hepatic insulin resistance in this animal model of obesity.
Stepwise degradation of NT in pars convoluta and recta of rabbit proximal tubules: evidence of axial heterogeneity
Authors: Bjerke T. , Nielsen S. , Sheikh M. I. , Christensen E. I.
Published: December 2017

Reabsorption and degradation of the neuropeptide neurotensin (NT) in rabbit proximal pars convoluta (PC) and pars recta (PR) nephron segments were characterized. Brush-border membrane vesicle fractions (PC or PR) were incubated with [3H]NT, and the extent and pattern of peptide hydrolysis were determined by reversed-phase high-pressure liquid chromatography (rHPLC). Furthermore, isolated rabbit PC and PR segments were perfused with [3H]NT, reabsorption of [3H]NT was quantified, and the collected perfusate was analyzed by HPLC. Metabolites were characterized. Finally, rabbit proximal tubules were microinfused in vivo with [3H]NT to follow the tubular uptake by electron microscope autoradiography. Degradation increased with time in both vesicle fractions. The main difference was an extensive cleavage of NT in PR, as revealed by a higher proportion of end metabolites. This was also visualized as a higher proportion of the large degradation product in rHPLC fraction 39 [NT-(1–11)] in PC as compared with PR after 30 min of incubation. The isolated perfused proximal tubular segments processed NT with large efficiency. PC segments processed 90% of the perfused amount, and PR processed 88%. Only 13% in PC and 10% in PR of the processed NT were found in the bath and the tubule. The main part of processed NT was in the collected perfusate, and rHLPC profiles revealed that NT-(1–11) was the only metabolite in both PC and PR. Electron microscope autoradiography demonstrated autoradiographic grains over invaginations and over the apical part of the proximal tubule cell in endocytic vesicles and vacuoles 10 min after microinfusion of [3H]NT.(ABSTRACT TRUNCATED AT 250 WORDS)
Thyroxine and triiodothyronine distribution and metabolism in thyroxine-replaced athyreotic dogs and normal humans
Authors: Kaptein E. M. , Moore G. E. , Ferguson D. C. , Hoenig M.
Published: December 2017

Reported parenteral L-thyroxine (T4) replacement doses (10–20 micrograms.kg-1 x day-1) are larger than T4 production rates (2.5 micrograms.kg-1 x day-1) in athyreotic dogs but not humans. Furthermore, initial volumes of 3,5,3'-triiodothyronine (T3) tracer distribution exceed those for T4 in both species. To evaluate these discrepancies, serum T4 and T3 tracer kinetic studies from T4-replaced athyreotic dogs (5 micrograms.kg-1 x day-1 sc) and euthyroid humans were analyzed in a three-pool model (rapidly and slowly equilibrating pools with serum). Dogs had lower total T4 (41%) and T3 (31%) and higher free fractions of T4 (432%) and T3 (456%) than humans. Initial T3 distribution volumes were 454% those for T4 in dogs and 149% in humans, 498% of predicted plasma volumes in dogs and 121–138% in humans. Thus plasma volumes were used as time 0 estimates for T3 data analysis. Dogs had higher fractional T4 and T3 transfer rates from serum to the rapid pools (440–451%), total T4 clearance (353%) and production rates (147%), similar total T3 clearance, but lower free T3 clearance (32%) and production rates (45%) than humans. These findings suggest: 1) higher fractional transfer rates of T4 and T3 from serum to tissues and total serum T4 clearance rates in dogs than humans relate to lower canine serum T4 and T3 binding, and 2) parenteral L-T4 replacement doses required to achieve upper-normal serum total T4 concentrations in athyreotic dogs (5 micrograms.kg-1 x day-1) correspond to T4 production rates (6.8 micrograms.kg-1 x day-1).
Effect of prolonged exercise on muscle citrate concentration before and after endurance training in men
Authors: Coggan A. R. , Spina R. J. , Kohrt W. M. , Holloszy J. O.
Published: December 2017

It has been hypothesized that endurance training reduces carbohydrate utilization during exercise via citrate-mediated inhibition of phosphofructokinase (PFK). To test this hypothesis, vastus lateralis muscle biopsy samples were obtained from eight men before and immediately (approximately 10 s) after 2 h of cycle ergometer exercise at 60% of pretraining peak O2 uptake, both before and after 12 wk of endurance exercise training (3 days/wk running, 3 days/wk interval cycling). Training increased muscle citrate synthase (CS) activity from 3.69 +/- 0.48 (SE) to 5.30 +/- 0.42 mol.h-1.kg protein-1 and decreased the mean respiratory exchange ratio during exercise from 0.92 +/- 0.01 to 0.88 +/- 0.01 (both P < 0.001). Muscle citrate concentration at the end of exercise correlated significantly with CS activity (r = 0.70; P < 0.005) and was slightly but not significantly higher after training (0.80 +/- 0.19 vs. 0.54 +/- 0.19 mmol/kg dry wt; P = 0.16). Muscle glucose 6-phosphate (G-6-P) concentration at the end of exercise, however, was 31% lower in the trained state (1.17 +/- 0.10 vs. 1.66 +/- 0.27 mmol/kg dry wt; P < 0.05), in keeping with a 36% decrease in the amount of muscle glycogen utilized (133 +/- 22 vs. 209 +/- 19 mmol.kg dry wt-1.2 h-1; P < 0.01). The lower G-6-P concentration after training suggests that the training-induced reduction in carbohydrate utilization results from attenuation of flux before the PFK step in glycolysis and is not due to citrate-mediated inhibition of PFK.
Similar effects of NPY on energy metabolism and on plasma insulin in adrenalectomized ob/ob and lean mice
Authors: Walker H. C. , Romsos D. R.
Published: December 2017

A single intracerebroventricular (icv) injection of dexamethasone (250 ng) lowers brown adipose tissue (BAT) thermogenesis and whole body metabolic rates and raises plasma insulin concentrations within 30 min in adrenalectomized ob/ob mice with minimal effects in adrenalectomized lean mice. The present study was conducted to determine if intracerebroventricular neuropeptide Y (NPY), a neuropeptide regulated in part by glucocorticoids, would mimic effects of dexamethasone in these mice. NPY lowered BAT metabolism and whole body oxygen consumption and raised plasma insulin concentrations within 30 min in adrenalectomized ob/ob mice similarly to dexamethasone; but, unlike dexamethasone, NPY was as effective in modulating these metabolic responses in adrenalectomized lean mice as in ob/ob mice. Further, intracerebroventricular NPY increased food intake equally in both ob/ob and lean mice, whereas dexamethasone did not alter food intake during the 30 min postinjection period. These data are consistent with the hypothesis that NPY mediates some of the effects of intracerebroventricular dexamethasone action in ob/ob mice and that the divergence between ob/ob and lean mice lies in glucocorticoid control of NPY release/synthesis rather than in NPY action mechanisms.
Glucose transport and transporters in muscle giant vesicles: differential effects of insulin and contractions
Authors: Ploug T. , Wojtaszewski J. , Kristiansen S. , Hespel P. , Galbo H. , Richter E. A.
Published: December 2017

Collagenase treatment of skeletal muscle results in the formation of large spheres of membranes (3–30 microns diam). A procedure is described for purification and concentration of these giant membrane vesicles prepared from rat muscle. Morphological observations, marker enzyme analysis, and immunoblotting demonstrate that the vesicles are of plasma membrane origin and that sarcoplasmic reticulum, T-tubules, and mitochondrial inner membranes are absent from the preparation. Western blots demonstrate that the vesicles contain GLUT-4 glucose transporters, whereas GLUT-1 could not be detected. Vesicles prepared from control muscle display specific transport of D-glucose with a maximum velocity (Vmax) for glucose influx of approximately 2,500 pmol.mg plasma membrane protein-1.s-1 and an apparent Michaelis constant (Km) of 16 mM measured at zero-trans conditions at room temperature. Muscle contractions in vivo doubled the Vmax of vesicle glucose transport and membrane GLUT-4 content but did not change Km. In contrast, in vivo administration of insulin did not affect vesicle glucose transport or membrane GLUT-4 content. The combination of insulin and contractions caused similar changes as did contractions alone. It is concluded that the present vesicle population contains membrane components almost exclusively derived from the plasma membrane and contains very little if any GLUT-1 but substantial amounts of GLUT-4. Thus the preparation allows the study of transport kinetics of pure GLUT-4 transporters. The procedure for preparing vesicles probably results in activation of the glucose transport system similar to the activation by insulin but not by contractions.(ABSTRACT TRUNCATED AT 250 WORDS)
Hepatic glucose production and insulin sensitivity and responsiveness in iron-deficient anemic rats
Authors: Borel M. J. , Beard J. L. , Farrell P. A.
Published: December 2017

We performed euglycemic hyperinsulinemic glucose clamps at insulin infusion rates of 1.9, 4.0, 9.3, and 19.3 mU.kg-1 x min-1 in rats with varying severities of iron deficiency anemia (IDA; mean hemoglobin concentrations of 59, 79, 107, and 137 g/l) to assess the effect of IDA on insulin sensitivity and responsiveness. Glucose appearance and disappearance (Rd) rates were determined using a primed continuous infusion of [3-3H]glucose. Basal plasma glucose and insulin concentrations were similar between the IDA and control rats. Basal hepatic glucose production was significantly (P = 0.0001) elevated in the two most anemic groups (13.6 +/- 2.4 and 12.6 +/- 3.1 vs. 10.6 +/- 2.2 and 10.2 +/- 2.0 mg.kg-1 x min-1). A significant upward shift in the insulin dose-response curves for Rd indicated an increase in peripheral insulin responsiveness in the two most anemic groups while a slight leftward shift was suggestive of an increase in insulin sensitivity in all three anemic groups. Hepatic insulin sensitivity and responsiveness were unaffected by IDA. We conclude that increased glucose utilization rates in IDA rats are due primarily to an increase in peripheral insulin responsiveness.
Ouabain is secreted by the adrenal gland in awake dogs
Authors: Boulanger B. R. , Lilly M. P. , Hamlyn J. M. , Laredo J. , Shurtleff D. , Gann D. S.
Published: December 2017

Ouabain has been identified in the plasma and adrenal glands of several mammals, including humans. To investigate possible adrenal secretion of ouabain in vivo, at rest, and in response to acute blood volume changes, we prepared trained adult dogs (n = 10) with splenectomy and unilateral adrenal venous (AV) cannulation. Two days later, after an overnight fast, dogs had either 1) 20% hemorrhage (hem) or 2) 20% blood volume expansion (exp; 6% Dextran 70, 0.9% NaCl) in random order. In AV and arterial plasma (ART), ouabain was measured by a ouabain-specific immunoassay, and cortisol and aldosterone were measured by radioimmunoassay. ART and AV ouabain concentration did not change after hem or exp [P = not significant (NS)]. In 94 of 97 paired samples, the concentration of ouabain in AV was greater than that in ART (Wilcoxon, P < 0.001), and the mean ouabain concentration was greater in AV (756.4 +/- 85.7 pmol/l) than ART (235.4 +/- 18.5 pmol/l; P < 0.001). The mean AV-to-ART ouabain concentration ratio was 5.7 +/- 1.29. Adrenal secretion of ouabain was not influenced by hem or exp (analysis of variance, P = NS). Adrenal secretion of cortisol and aldosterone increased after hem (P < 0.05) and was unaltered by exp (P = NS). This study demonstrates that ouabain is secreted by the adrenal gland in the awake dog. However, adrenal ouabain secretion and arterial blood ouabain are not altered by acute hem or exp.
Glucocorticoid regulation of splanchnic glutamine, alanine, glutamate, ammonia, and glutathione fluxes
Authors: Tamarappoo B. K. , Nam M. , Kilberg M. S. , Welbourne T. C.
Published: December 2017

Interorgan glutamine and associated metabolite fluxes were measured across the gut and liver to delineate splanchnic bed fluxes secondary to enhanced arterial loads mobilized in the periphery by glucocorticoid. Experiments were performed on adrenalectomized rats since adrenalectomy doubled the hepatic glucocorticoid receptor population compared with intact animals. Under these conditions, triamcinolone supplement (40 micrograms.day-1.100 g body wt-1) enhanced the combined net glutamine uptake by gut and liver eightfold, whereas combined gut and liver unidirectional breakdown and synthesis fluxes both increased (3.4- and 7.4-fold, respectively). Triamcinolone supplement also altered the pattern of metabolite released; gut released predominantly ammonium and some alanine, whereas the liver removed more alanine along with glutamine and released more urea, glutamate, and glutathione. Mechanistically, enhanced cellular glutamine uptake could be attributed to a three- to fourfold acceleration of glutamine transport associated with a rise in intracellular glutamine content. However, uptake by isolated membrane vesicles revealed only a small (27%) increase in System N activity, whereas extraction and reconstitution of the transporter into proteoliposomes failed to demonstrate increased transporter activity. Similarly, activity of phosphate-dependent glutaminase and glutamate dehydrogenase increased in crude homogenates (2-fold), but the former disappears in completely disrupted preparations. Furthermore, whereas messenger RNA and assayable enzymic activity for glutamate dehydrogenase clearly increased with glucocorticoid, glutaminase message was less significantly increased. Thus glucocorticoid appears directly capable of accelerating hepatic glutamine extraction primarily by modulating transporter activity that is closely coupled to glutamine utilization.
Methods for assessment of the rate of onset and offset of insulin action during nonsteady state in humans
Authors: Butler P. C. , Caumo A. , Zerman A. , O'Brien P. C. , Cobelli C. , Rizza R. A.
Published: December 2017

Measurement of glucose turnover under non-steady-state conditions has proven problematic. When the mass of the glucose pool is not changing (i.e., glucose concentrations are constant) non-steady-state error can be minimized if all glucose entering the circulation has the same specific activity as plasma [radioactive infused glucose (hot-GINF) method]. Alternatively, a second tracer can be used to measure the effective volume of glucose [variable-pV method of Issekutz (T. Issekutz, R. Issekutz, and D. Elahi. (Can. J. Physiol. 52:215-224, 1974)]. To determine whether these techniques provide concordant assessments of insulin action under non-steady-state conditions, glucose turnover was measured in six subjects. After initiation of insulin (0.6 mU.kg-1 x min-1), both methods indicated similar rates of suppression of hepatic glucose release, which was complete by approximately 100-120 min. In contrast, the traditional fixed-pV method of Steele (R. Steele, J. Wall, R. DeBodo, and N. Altszuler. Am. J. Physiol. 187:15-24 1956) underestimated turnover (P < 0.01) resulting in apparent complete suppression of glucose release within approximately 40 min (P < 0.01 vs. other methods). The hot-GINF and variable-pV methods also yielded similar estimates of turnover after discontinuation of insulin. Both indicated that resumption of hepatic glucose release was slower (P < 0.01) and fall of glucose uptake faster (P < 0.01) than suggested by the fixed-pV method. Thus both the hot-GINF and variable-pV methods avoid non-steady-state error introduced by the fixed-pV method and provide concordant assessments of the rate of onset and offset of insulin action.
Converting enzyme inhibition modulates sympathetic neurotransmission in vivo via multiple mechanisms
Authors: Schwieler J. H. , Kahan T. , Nussberger J. , Hjemdahl P.
Published: December 2017

We investigated the mechanism(s) by which angiotensin-converting enzyme (ACE) inhibition influences peripheral sympathetic neurotransmission. Thus effects of the angiotensin II (ANG II) receptor antagonist losartan (Du Pont 753) were compared with those of the ACE inhibitor benazeprilat on sympathetic neurotransmission in canine gracilis muscle in situ, with alpha-adrenoceptors either intact or irreversibly blocked by phenoxybenzamine. Furthermore, effects of the bradykinin receptor antagonist HOE 140 and the prostaglandin synthesis inhibitor diclofenac were studied after ACE inhibition. Losartan reduced the vasoconstrictor response to exogenous ANG II by 76 +/- 4% at the dose used and lowered muscle perfusion pressures. ACE inhibition by benazeprilat reduced plasma ANG-(1-8) octapeptide levels (from 8 +/- 2 to 2 +/- 1 pM), mean arterial pressure, and muscle perfusion pressures. After ACE inhibition, both HOE 140 (at a dose that reduced the vasodilatory response to exogenous bradykinin by 80 +/- 3%) and diclofenac elevated basal perfusion pressures. Losartan reduced the nerve stimulation-evoked overflow of endogenous norepinephrine (NE) (-14 +/- 6%) and vasoconstrictor responses (alpha-adrenoceptors intact). ACE inhibition increased NE overflow when alpha-adrenoceptors were intact (+12 +/- 5%) and tended to reduce it when alpha-adrenoceptors were blocked (-12 +/- 4%). During ACE inhibition, HOE 140 reduced and diclofenac enhanced the evoked NE overflow. In the absence of ACE inhibition, neither HOE 140 nor diclofenac influenced NE overflow. Our findings indicate that ACE inhibition influences sympathetic neurotransmission via reduced ANG II formation and enhanced bradykinin and prostaglandin accumulation. The effects of ANG II on sympathetic neurotransmission are, however, small under these in vivo conditions.
Alterations in hypothalamic NPY and CRF in anorexic tumor-bearing rats
Authors: McCarthy H. D. , McKibbin P. E. , Perkins A. V. , Linton E. A. , Williams G.
Published: December 2017

Regional hypothalamic concentrations of neuropeptide Y (NPY) and corticotropin-releasing factor (CRF), respectively a stimulant and an inhibitor of feeding behavior, were investigated in hypothalamic nuclei in rats carrying the Yoshida sarcoma. Tumor-bearing rats (n = 10), non-tumor-bearing controls (n = 10), and food-restricted rats (n = 10), which did not carry tumors but were pair-fed to match the reduced food intake of the tumor-bearing group, were studied after 10 days. NPY concentrations in the arcuate nucleus (ARC, the main site of NPY synthesis) were significantly increased above controls (P < 0.01) in both tumor-bearing and food-restricted groups. However, NPY concentrations in the paraventricular nucleus (PVN, an NPY-sensitive site of NPY release) showed opposing changes, with a 25% decrease (P = 0.052) in the tumor-bearing but a 48% increase (P < 0.01) in the food-restricted group. CRF concentrations in both the PVN and the ARC were significantly reduced (P < 0.01) in the food-restricted group, but remained close to control values in the tumor-bearing group (P not significant). Changes in hypothalamic appetite-regulating neuropeptides in cancer anorexia, which may result from the action of cytokines produced by a host defense response or the tumor itself, may account for reduced feeding. Such changes may include impaired activity of NPY or failure of CRF activity to be suppressed after underfeeding and weight loss.
Effect of sodium intake on insulin sensitivity
Authors: Donovan D. S. , Solomon C. G. , Seely E. W. , Williams G. H. , Simonson D. C.
Published: December 2017

To examine the effects of sodium intake on insulin sensitivity, we performed euglycemic insulin clamp studies (40 mU.m-2.min-1) in eight healthy normotensive nondiabetic white males (age = 36 +/- 5 yr; wt = 66 +/- 3 kg) after 5 days on high (200 meq/day)- and low (10 meq/day)-sodium diets administered in random order. High sodium intake was associated with significantly greater urinary sodium excretion (160 +/- 7 vs. 8 +/- 2 meq/day; P < 0.0001), suppression of plasma aldosterone (7 +/- 3 vs. 38 +/- 6 ng/dl; P < 0.001) and renin (1.5 +/- 0.2 vs. 6.0 +/- 0.9 ng.ml-1.h-1; P < 0.005) levels, but no change in blood pressure (116 +/- 3/63 +/- 2 vs. 114 +/- 3/64 +/- 2 mmHg; P = not significant). The rate of glucose infusion during the clamp was significantly reduced during the high- vs. low-sodium diet (279 +/- 19 vs. 334 +/- 24 mg.m-2.min-1; P < 0.01). This impairment in insulin sensitivity was not related to changes in serum potassium, epinephrine, norepinephrine, cortisol, or growth hormone but was highly correlated with an increment in circulating free fatty acid levels during high sodium intake (r = 0.82, P < 0.05). These data suggest that 1) high sodium intake may exacerbate insulin resistance by increasing circulating free fatty acids, and 2) differences in sodium intake may influence measures of insulin sensitivity in other disease states.
Quantitation of measurement error with Optimal Segments: basis for adaptive time course smoothing
Authors: Bradley D. C. , Steil G. M. , Bergman R. N.
Published: December 2017

We introduce a novel technique for estimating measurement error in time courses and other continuous curves. This error estimate is used to reconstruct the original (error-free) curve. The measurement error of the data is initially assumed, and the data are smoothed with "Optimal Segments" such that the smooth curve misses the data points by an average amount consistent with the assumed measurement error. Thus the differences between the smooth curve and the data points (the residuals) are tentatively assumed to represent the measurement error. This assumption is checked by testing the residuals for randomness. If the residuals are nonrandom, it is concluded that they do not resemble measurement error, and a new measurement error is assumed. This process continues reiteratively until a satisfactory (i.e., random) group of residuals is obtained. In this case the corresponding smooth curve is taken to represent the original curve. Monte Carlo simulations of selected typical situations demonstrated that this new method ("OOPSEG") estimates measurement error accurately and consistently in 30- and 15-point time courses (r = 0.91 and 0.78, respectively). Moreover, smooth curves calculated by OOPSEG were shown to accurately recreate (predict) original, error-free curves for a wide range of measurement errors (2-20%). We suggest that the ability to calculate measurement error and reconstruct the error-free shape of data curves has wide applicability in data analysis and experimental design.
Revised equations for calculating CO2 production from doubly labeled water in humans
Authors: Speakman J. R. , Nair K. S. , Goran M. I.
Published: December 2017

The Schoeller model for calculating rate of CO2 production (rCO2) from doubly labeled water (DLW) relies on the assumption that deuterium and oxygen-18 overestimate body water by 4 and 1%, respectively. However, the deuterium-to-oxygen-18 dilution space ratio (DSR) varies considerably, and it is unknown whether this is due to analytical or biological sources. From 161 published values in adult humans, we derived a mean DSR of 1.0427 +/- 0.0218. Propagation of error suggests that analytical uncertainty accounts for 20-50% of the observed variation in the DSR, whereas reliability testing in vivo and in vitro demonstrate that 70-100% of observed interindividual variation in the DSR can be attributed to analytical uncertainty. The discrepancy between propagated error and experimental reliability suggest that it is unwise to rely on propagation of error when evaluating sources of error in DLW. The new constant of 1.0427 was used to revise existing equations for calculating rCO2 from DLW. Compared with the existing equation, the revised equation improved the accuracy (-0.38 vs. +10.3%) and the precision (9.3 vs 10.7%) of rCO2 calculations in previously published validation studies. We conclude that 1) variation in the oxygen-18-to-deuterium DSR is primarily influenced by analytical noise and warrants use of a fixed ratio, 2) existing equations should be revised because the original DSR may have been underestimated, and 3) the modified equations improve the accuracy and precision of rCO2 calculated from DLW.
Do nonesterified fatty acids regulate skeletal muscle protein turnover in humans?
Authors: Walker M. , Shmueli E. , Daley S. E. , Cooper B. G. , Alberti K. G.
Published: December 2017

We examined whether elevated plasma nonesterified fatty acid (NEFA) levels exert a direct effect on protein metabolism by measuring [2H5]phenylalanine skeletal muscle exchange and whole body turnover. [2H5]phenylalanine was infused (0.5 mg.kg-1 x h-1) for 300 min in seven healthy subjects on two occasions. Intralipid (10%; 30 ml/h) or 0.154 mol/l NaCl was infused in random order from 120 min. Measurements were taken during basal (90-120 min) and infusion (270-300 min) periods. Intralipid infusion increased plasma NEFA levels [1.31 +/- 0.13 vs. 0.49 +/- 0.05 (SE) mmol/l; P < 0.05] and forearm NEFA uptake [45 +/- 76 vs. -51 +/- 44 nmol . 100 ml forearm-1 x min-1; P < 0.05]. Serum insulin and blood ketone body levels were similar with the two treatments. Elevated plasma NEFA levels were associated with a comparable decrease in forearm phenylalanine uptake (11 +/- 2 vs. 17 +/- 2 nmol x 100 ml forearm-1 x min-1; lipid vs. control, P < 0.05) and release (20 +/- 2 vs. 26 +/- 3 nmol x 100 ml forearm-1 x min-1; lipid vs. control, P < 0.05). However, there were no significant changes in net forearm phenylalanine exchange and whole body phenylalanine turnover. Therefore, elevated plasma NEFA levels were associated with a comparable decrease in the rates of skeletal muscle protein synthesis and breakdown but did not appear to influence overall protein balance, as assessed using [2H5]phenylalanine.
Osmotic stimulation of the supraoptic nucleus: central and peripheral vasopressin release and blood pressure
Authors: Ludwig M. , Horn T. , Callahan M. F. , Grosche A. , Morris M. , Landgraf R.
Published: December 2017

Experiments were performed to determine the effect of direct osmotic stimulation of the supraoptic nucleus (SON) on central and peripheral vasopressin (AVP) release and arterial pressure. A microdialysis method was used to deliver hyperosmotic NaCl, mannitol or urea bilaterally into the SON and to sample SON extracellular fluid and blood. Simultaneous brain and blood microdialysis showed that hyperosmotic NaCl increased central and peripheral AVP release and increased mean arterial pressure (MAP). The pressor response was not blocked by intravenous injection of a V1-receptor antagonist, D(CH2)5Tyr(Me)AVP, suggesting that circulating AVP was not involved in that response. Hyperosmotic mannitol or urea caused an increase in central peptide release, but failed to affect MAP or peripheral AVP release. The results suggest that central AVP release within the SON may be due to osmoreceptor stimulation while the peripheral effects on AVP release and MAP are specific for sodium. The results also demonstrate the utility of brain and blood microdialysis for the delivery of stimuli into specific brain regions with simultaneous monitoring of central and peripheral peptide release.
Islet amyloid polypeptide inhibits insulin secretion in conscious rats
Authors: Furnsinn C. , Leuvenink H. , Roden M. , Nowotny P. , Schneider B. , Rohac M. , Pieber T. , Clodi M. , Waldhausl W.
Published: December 2017

To investigate the effect of islet amyloid polypeptide (IAPP, amylin) exposure on insulin secretion in vivo, the plasma glucose level of conscious rats was clamped at 11.1 mmol/l (hyperglycemic clamp) during the last 2 h of a 24-h infusion study. Group parameters were A, 24-h saline; B and C, 22-h saline followed by 2-h IAPP (B, 8.5 pmol/min; C, 85 pmol/min), and D, 24-h IAPP (85 pmol/min). Induced hyperglycemia increased plasma insulin concentration by 426 +/- 34 pmol/l in control rats (group A). This effect on plasma insulin was reduced by 31% and 53% during short-term IAPP infusion (group B, 8.5 pmol/min, 294 +/- 41 pmol/l; C, 85 pmol/min, 202 +/- 25 pmol/l; short-term effect, P < 0.0001), whereas insulin levels tended to increase after 24 h of continuous IAPP exposure (group D, 682 +/- 120 pmol/l; P < 0.05 vs. group A). Glucose infusion rate required to maintain constant hyperglycemia fell dose dependently during short-term but not during long-term IAPP infusion (mumol.kg-1.min-1: group A, 203 +/- 11; B, 154 +/- 7; C, 119 +/- 7; D, 212 +/- 9; short-term effect, P < 0.0001). In parallel, muscle glycogen content was dose dependently reduced by short-term IAPP exposure. We conclude that IAPP inhibits glucose-stimulated insulin secretion and decreases muscle glycogen storage in conscious rats in vivo.