bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention of hyperglycemia in the Zucker diabetic fatty rat by treatment with metformin or troglitazone
Authors: Sreenan S. , Sturis J. , Pugh W. , Burant C. F. , Polonsky K. S.
Published: December 2017

To determine whether metformin or troglitazone can delay the onset of diabetes in the Zucker diabetic fatty (ZDF) rat, lean control, fatty, and ZDF rats received metformin, troglitazone, or no treatment from 6 to 12 wk of age. Glucose, insulin, triglyceride (TG), and free fatty acid (FFA) levels and glucose stimulated insulin secretion by the perfused pancreas were measured. Metformin-treated rats gained significantly less weight. Both drugs prevented hyperglycemia by 12 wk in diabetic rats and significantly reduced TG and FFA levels. Insulin secretion at low glucose was elevated in untreated fatty and diabetic animals, and the increment in diabetic animals produced by glucose perfusion was attenuated compared with lean and fatty rats. Both drugs reduced basal insulin secretion in fatty and diabetic rats and improved glucose responsiveness in diabetic rats. Metformin and troglitazone delay the onset of diabetes in the ZDF rat. The significantly improved insulin secretory response of the pancreas undoubtedly contributes to the improved glucose tolerance.
Effects and fate of human IGF-binding protein-5 in rat osteoblast cultures
Authors: Schmid C. , Schlapfer I. , Gosteli-Peter M. A. , Froesch E. R. , Zapf J.
Published: December 2017

Osteoblasts prepared from calvaria of newborn rats produce insulin-like growth factors (IGF) and IGF-binding proteins (IGFBP), IGFBP-5 was discovered in bone extracts. However, we could not detect IGFBP-5 in the medium of newborn rat osteoblasts, although we found mRNA expression. To find an explanation for this discrepancy and to learn more about the physiological role of IGFBP-5 in these cells, we studied the biological activity and the fate of recombinant human (rh) IGFBP-5 in comparison to rhIGFBP-3. IGFBP-5 but not IGFBP-3 stimulated thymidine incorporation into DNA both in the absence and presence of IGF-I. However, IGFBP-5 did not enhance uridine incorporation into RNA and glucose incorporation into glycogen. 125I-rhIGFBP-5 but not 125I-rhIGFBP-3 rapidly disappeared from the culture medium consistent with the observation that endogenous (rat) IGFBP-3 but not IGFBP-5 accumulated in the medium. However, intact 125I-labeled or unlabeled rhIGFBP-5 was associated with the cell-layer matrix, whereas IGFBP-5 fragments appeared in the medium. Trapping of IGFBP-5 in the cell layer matrix may enhance local availability of IGF.
Disappearance of two major phosphatidylcholines from plasma is predominantly via LCAT and hepatic lipase
Authors: Shamburek R. D. , Zech L. A. , Cooper P. S. , Vandenbroek J. M. , Schwartz C. C.
Published: December 2017

Metabolism of 1-stearoyl-2-arachidonyl-phosphatidyl-choline (SAPC), a major phosphatidylcholine (PC) species in rat plasma, was compared with 1-palmitoyl-2-linoleoyl-PC (PLPC) metabolism. High-density lipoproteins containing SAPC and PLPC tracers labeled in the sn-2 fatty acid with 3H and 14C isotopes, respectively, were administered. The rats were depleted of endogenous bile acids and infused via the ileum with individual bile acids that ranged widely in hydrophobicity. The half-lives for SAPC and PLPC in plasma were 48 and 57 min, respectively. Most of the 3H activity that disappeared from plasma at 1 h was found in the liver in 1-palmitoyl-2-arachidonyl-PC, SAPC, and 1-oleoyl-2-arachidonyl-PC, indicating phospholipase A1 hydrolysis of plasma SAPC forming 2-arachidonyl-lysophosphatidylcholine, which was reacylated in the liver. Plasma PLPC also underwent phospholipase A1 hydrolysis, as reported previously. The fraction of 3H dose that accumulated in plasma cholesteryl arachidonate was two- to threefold higher than the fraction of 14C dose in cholesteryl linoleate. Multicompartmental models for SAPC and PLPC were developed that included lysophosphatidylcholines and cholesteryl esters. Bile acids did not influence plasma PC metabolism. Lecithin-cholesterol acyltransferase and phospholipase A1 (hepatic lipase) hydrolysis accounted for > or = 90% of the SAPC and PLPC that disappeared from plasma; SAPC and PLPC are comparable as substrates for hepatic lipase, but SAPC is preferred by lecithin-cholesterol acyltransferase.
Mechanisms of centrally administered ET-1-induced increases in systemic arterial pressure and AVP secretion
Authors: Rossi N. F. , O'Leary D. S. , Chen H.
Published: December 2017

Endothelins (ET) within the central nervous system (CNS) alter systemic cardiovascular responses and arginine vasopressin (AVP) secretion. These experiments were designed to ascertain whether the rise in systemic arterial pressure after central administration of ET-1 is mediated by enhancing sympathetic outflow and/or circulating AVP. In Long-Evans (LE/LE) rats, intracerebroventricular injection of 1-10 pmol ET-1 dose dependently increased mean arterial pressure (MAP). Peak response occurred 7-12 min after ET-1 and was inhibited by ETA receptor antagonism. Systemic vasopressin (V1) receptor blockade did not inhibit the pressor response, and rats with central diabetes insipidus (DI/DI) displayed an identical rise in MAP. Ganglionic blockade prevented ET-1-induced hemodynamic effects. Peak plasma AVP levels occurred 60 min after ET-1, as the pressor response began to wane. In sinoaortic-denervated LE/LE rats, ET-1 elicited a 10-fold increase in AVP secretion that coincided with the hemodynamic changes and was blocked by BQ-123. Thus ET-1 via ETA receptors within the CNS induced a concentration-dependent increase in systemic arterial pressure mediated by enhanced sympathetic outflow but not by circulating AVP. Reflex baroreceptor activation attenuated AVP release.
Insulin regulates liver glycogen synthase and glycogen phosphorylase activity reciprocally in rhesus monkeys
Authors: Ortmeyer H. K. , Bodkin N. L. , Hansen B. C.
Published: December 2017

In skeletal muscle of both humans and monkeys, the effects of in vivo insulin during a euglycemic hyperinsulinemic clamp on the enzymes and substrates of glycogen metabolism have been well established. In liver, such effects of insulin during a clamp have not been previously studied in primates. To examine insulin action at the liver, euglycemic hyperinsulinemic clamps were performed in 10 lean young adult male rhesus monkeys. Liver biopsies were obtained at three time points: basal (fasting), that is, immediately before the onset of the clamp, and during insulin infusion at 130 and 195 min. Glycogen synthase (GS), glycogen phosphorylase (GP), glucose 6-phosphate (G-6-P), and glycogen were determined at each time point, with the greatest effects observed most frequently at 195 min. Whole body insulin-mediated glucose disposal rate was related to the change in the independent activity of GS (r = 0.63, P < 0.05). Insulin increased the GS fractional activity (P < 0.005) and decreased the activity ratio of GP (P < 0.001) compared with basal. The changes in fractional activity of GS and in activity ratio of GP were inversely related (r = - 0.68, P < 0.05), G-6-P concentration was decreased during insulin stimulation compared with basal (P = 0.01). Glycogen concentration was not significantly different between the basal and insulin-stimulated time points. We conclude that insulin during a euglycemic clamp activates liver GS while inhibiting liver GP and that insulin action on liver GS is positively related to whole body insulin-mediated glucose disposal rates in lean young adult rhesus monkeys.
Disorderly and nonstationary insulin secretion in relatives of patients with NIDDM
Authors: Schmitz O. , Porksen N. , Nyholm B. , Skjaerbaek C. , Butler P. C. , Veldhuis J. D. , Pincus S. M.
Published: December 2017

To further explore the role of the beta-cell as a pathogenic factor behind non-insulin-dependent diabetes mellitus (NIDDM), insulin secretion at modest hyperglycemia was examined in 15 healthy first-degree relatives of NIDDM patients and 13 anthropometrically and age-matched controls. The oral glucose tolerance test was normal in all, but the relatives had impaired insulin-stimulated glucose uptake (P < 0.05). During a constant intravenous glucose infusion we performed a time-series analysis of serum insulin in samples obtained at 1-min intervals for 75 min (60-135 min). The recently introduced scale- and model-independent statistic approximate entropy (ApEn) and the coefficient of variation for a 6- (9 and 15) point moving average (MA) were applied to test regularity and stationarity, respectively, of insulin secretion. Both ApEn and 6-point MA were able to significantly discern the insulin time series of the two groups (P < 0.05), demonstrating a higher degree of irregularity and nonstationarity among the offspring. Moreover, when the two complementary sets of statistics were combined into a single "index of nonpulsatility," an even more notable distinction was available (P < 0.01). No relationship was found between altered insulin secretion and insulin resistance. In conclusion, this experimental and statistical model demonstrates that the stimulated insulin secretion of glucose-tolerant relatives of NIDDM patients is characterized by disorderliness. Whether the model can predict the risk for developing a clinically important beta-cell dysfunction remains to be clarified.
Tricarboxylic acid cycle intermediates in human muscle at rest and during prolonged cycling
Authors: Gibala M. J. , Tarnopolsky M. A. , Graham T. E.
Published: December 2017

Previous studies have used the muscle concentration of citrate + malate + fumarate to estimate tricarboxylic acid (TCA) cycle pool size in humans [e.g., Am. J. Physiol. 259 (Cell Physiol. 28): C834-C841, 1990]. Our purpose was to quantify changes in individual TCA cycle intermediates (TCAI) and total pool size by measuring the concentrations of the eight TCAI in human muscle. Eight males cycled to exhaustion (Exh) at approximately 70% of their maximal oxygen uptake, and biopsies were obtained from the vastus lateralis at rest and during exercise. Succinyl-CoA was not consistently detectable, but the sum of the other seven TCAI was 1.23 +/- 0.04 mmol/kg dry wt at rest, 4.80 +/- 0.25 and 4.87 +/- 0.30 mmol/kg after 5 and 15 min of exercise, respectively, and 3.08 +/- 0.15 mmol/kg at Exh. Pool size during exercise was approximately 50% higher than that seen in rodent muscle after intense electrical stimulation (Eur. J. Biochem. 110: 371-377, 1980). Relative changes in individual TCAI were not uniform, and no one intermediate was "representative" of the changes in total pool size. We conclude that changes in specific intermediates or total pool size cannot be used as indicators of cycle flux and that the apparent species differences in total pool size may reflect differences in fiber type composition, recruitment pattern, or relative intensity of contraction.
Prolonged suppression of glucose metabolism causes insulin resistance in rat skeletal muscle
Authors: Kim J. K. , Youn J. H.
Published: December 2017

To determine whether an impairment of intracellular glucose metabolism causes insulin resistance, we examined the effects of suppression of glycolysis or glycogen synthesis on whole body and skeletal muscle insulin-stimulated glucose uptake during 450-min hyperinsulinemic euglycemic clamps in conscious rats. After the initial 150 min to attain steady-state insulin action, animals received an additional infusion of saline, Intralipid and heparin (to suppress glycolysis), or amylin (to suppress glycogen synthesis) for up to 300 min. Insulin-stimulated whole body glucose fluxes were constant with saline infusion (n = 7). In contrast, Intralipid infusion (n = 7) suppressed glycolysis by approximately 32%, and amylin infusion (n = 7) suppressed glycogen synthesis by approximately 45% within 30 min after the start of the infusions (P < 0.05). The suppression of metabolic fluxes increased muscle glucose 6-phosphate levels (P < 0.05), but this did not immediately affect insulin-stimulated glucose uptake due to compensatory increases in other metabolic fluxes. Insulin-stimulated whole body glucose uptake started to decrease at approximately 60 min and was significantly decreased by approximately 30% at the end of clamps (P < 0.05). Similar patterns of changes in insulin-stimulated glucose fluxes were observed in individual skeletal muscles. Thus the suppression of intracellular glucose metabolism caused decreases in insulin-stimulated glucose uptake through a cellular adaptive mechanism in response to a prolonged elevation of glucose 6-phosphate rather than the classic mechanism involving glucose 6-phosphate inhibition of hexokinase.
Glucagon enhances the direct suppressive effect of insulin on hepatic glucose production in humans
Authors: Lewis G. F. , Vranic M. , Giacca A.
Published: December 2017

The present study examines the role of glucagon in modulating the hepatic and extrahepatic effects of insulin on hepatic glucose production (HGP). We infused glucagon at a constant rate (0.65 ng x kg(-1) x min(-1)) during equimolar portal and peripheral insulin delivery in seven healthy males by our previously published tolbutamide infusion method. In contrast to our previous study, in which glucagon fell by approximately 30% during hyperinsulinemia and suppression of HGP was significantly greater with equimolar peripheral than with portal insulin delivery, HGP was actually suppressed to a lesser extent with peripheral insulin delivery (69 +/- 10%) than when insulin was delivered portally (76 +/- 5%, P < 0.05). To further examine whether glucagon was enhancing the effect of portal insulin, in four additional individuals HGP was suppressed to a greater extent during a tolbutamide infusion when glucagon was administered continuously throughout the basal and hyperinsulinemic periods than when glucagon was infused during the basal period only; HGP suppressed by 63 +/- 3 vs. 52 +/- 3%, respectively, P = 0.02). Tolbutamide had no effect on HGP when infused into three C-peptide-negative individuals with type I diabetes during a low-dose insulin and glucagon infusion. These data suggest that glucagon levels are an important determinant of the balance between insulin's direct and indirect effects on HGP, with glucagon likely potentiating the direct hepatic effect of insulin.
Influence of protein intake on whole body and splanchnic leucine kinetics in humans
Authors: Cayol M. , Boirie Y. , Rambourdin F. , Prugnaud J. , Gachon P. , Beaufrere B. , Obled C.
Published: December 2017

The influence of the protein content of the meal on protein turnover was investigated in the splanchnic bed and in the remaining parts of the body in humans. Two groups of five subjects consumed every 20 min a liquid formula providing either 1.5 g protein x kg(-1) x day(-1) (P) or no protein (PF). L-[1-(13)C]leucine and L-[5,5,5-(2)H3]leucine were administered by vein and gut, respectively. An open two-pool model was developed to calculate leucine kinetics in both compartments, with the assumption that the enrichment of the tracers incorporated into very low density lipoprotein apolipoprotein B100 at isotopic steady state could reflect the leucine labeling in the splanchnic region. Nonsplanchnic uptake and release of leucine were not significantly different in the two groups. Within the splanchnic area, leucine uptake was 2.1 times higher in the P than in the PF group (P < 0.01), whereas leucine release was reduced but not significantly (-19%) in the P group compared with the PF group. Moreover, data derived from this model showed that protein intake induced an increase in whole body protein synthesis and no change in whole body protein breakdown. Albumin synthesis, as well as its contribution to whole body protein synthesis, was significantly enhanced by protein intake.
Insulin stimulates cell surface aminopeptidase activity toward vasopressin in adipocytes
Authors: Herbst J. J. , Ross S. A. , Scott H. M. , Bobin S. A. , Morris N. J. , Lienhard G. E. , Keller S. R.
Published: December 2017

We previously discovered that insulin stimulates the marked translocation of a novel membrane aminopeptidase, designated vp165 for vesicle protein of 165 kDa, to the cell surface in adipocytes. To examine the hypothesis that this enzyme acts on peptide hormones, we assessed the relative affinity of the enzyme for 22 peptide hormones by measuring the inhibitory effect of each on the hydrolysis of a fluorogenic substrate, and we directly assayed the cleavage of four of these. Angiotensin III, angiotensin IV, and Lys-bradykinin bound to the enzyme with half-saturation constants between 20 and 600 nM and were cleaved by vp165. Vasopressin bound with lower affinity but at saturation was cleaved more rapidly. Subsequently, the effect of insulin on the rates of cleavage of 125I-labeled vasopressin by intact 3T3-L1 and rat adipocytes was determined. With both cell types, vasopressin cleavage was stimulated approximately threefold. These findings indicate that a physiological role for vp165 may be the processing of peptide hormones and that insulin could enhance the cleavage of extracellular substrates by eliciting the translocation of vp165 to the cell surface.
Clenbuterol, a beta2-adrenoceptor agonist, reduces scoliosis due to partial transection of rat spinal cord
Authors: Zeman R. J. , Zhang Y. , Etlinger J. D.
Published: December 2017

Injury to the spinal cord often results in abnormal lateral curvature of the spine, or scoliosis, that is associated with neuromuscular weakness. The lateral curvature of the spine is thought to be a consequence of insufficient or asymmetrical loading of the vertebrae. To study neuromuscular scoliosis, an animal model of spinal cord injury was used in which the spinal cord was partially (3/4) transected, with the left lateral columns left intact. Partial transection of the spinal cord in the rat caused scoliosis that was maximal four to five vertebrae distal to the lesion site. As in previous experiments involving unilateral spinal cord lesions, the scoliotic curves were convex on the weakened side. Subtotal transection at T5 or T11 resulted in lateral displacement of vertebrae T9-T12 or L2-L5, respectively, of up to 11 mm. Interestingly, this vertebral displacement is greatly reduced by clenbuterol, a beta2-adrenoceptor agonist that has been found to retard loss of muscle contractility and bone mineralization due to denervation. Together these results suggest that stimulation of beta2-receptors opposes vertebral unloading due to neuromuscular weakness and thereby acts as a countermeasure to scoliosis.
Renal assimilation of oligopeptides: physiological mechanisms and metabolic importance
Authors: Adibi S. A.
Published: December 2017

Assimilation of systemic oligopeptides (di- and tripeptides) is largely a function of kidneys. The most specific and unique mechanism utilized for the performance of this renal function is transport, followed by intracellular hydrolysis and then release of constituent amino acids to the systemic circulation. Among tissues examined (liver, kidney, intestine, and muscle), kidney is the only tissue capable of accumulating dipeptides in concentrations that are greater than their plasma concentrations. Kidney also is the tissue with the highest cytoplasmic dipeptidase activity. Intracellular accumulation is mediated by two transporters (Pept-1 and Pept-2), both of which have been recently cloned. These transporters use dipeptides and tripeptides as substrates and rely on protons and membrane potential for their driving force. Pept-1 is a low-affinity, high-capacity transporter, and Pept-2 is a high-affinity, low-capacity transporter. The nutritional and metabolic regulation of renal assimilation of oligopeptides is suggested by the selective decrease in dipeptide balance across the kidneys of starved human subjects and by the insulin stimulation of dipeptide transport by a renal cell line. Peptiduria has been observed in a variety of diseases, but the mechanism, except in genetic diseases affecting hydrolysis of oligopeptides, is not known. Finally, the capacity for active transport of oligopeptides and peptidomimetic drugs enables kidneys to play major roles in nutritional and pharmacological therapies.
Role of the kidney in plasma glucose regulation during hyperglycemia
Authors: Cersosimo E. , Ajmal M. , Naukam R. J. , Molina P. E. , Abumrad N. N.
Published: December 2017

Little is known about the role of the kidney in plasma glucose regulation during hyperglycemia. We studied 12 overnight-fasted conscious dogs after either intrarenal (IR, n = 6) or peripheral (PH, n = 6) dextrose infusion to maintain hyperglycemia without glycosuria. Systemic and renal glucose kinetics were measured with [6-3H]glucose, lactate balance was measured by arteriovenous difference, and glycogen content was assayed in the kidneys. Plasma glucose (approximately 5.5 vs. approximately 6.3 mM), insulin (approximately 70 vs. approximately 110 pM), and glucose appearance (approximately 14 vs. approximately 16 mumol.kg-1.min-1 increased comparably in both groups (P < 0.05). In IR, fractional extraction of glucose (FEGlc) increased from 4.1 +/- 0.2 to 16.1 +/- 0.5% (P < 0.001) and lactate balance reversed to renal output (+1.3 +/- 0.2 vs. -0.9 +/- 0.2 mumol.kg-1.min-1, P < 0.01). Glycogen content was twofold higher in the left (127 +/- 33 micrograms/g tissue) than in the right kidney (56 +/- 11 micrograms/g tissue, P < 0.01). In PH, FEGlc decreased from 4.9 +/- 0.6 to 2.2 +/- 0.3% (P < 0.05), renal glucose utilization did not change (approximately 1.3 mumol.kg-1.min-1); and glycogen content was equal in both kidneys (approximately 45 micrograms/g tissue). We conclude that, although the kidney plays a minor role in plasma glucose disposal in physiological hyperglycemia, increased glucose uptake, glycogen storage, and lactate formation precede glycosuria and may represent important mechanisms by which the kidney contributes to normalization of plasma glucose in diabetes.
Adenosine exerts a glycogen-sparing action in contracting rat skeletal muscle
Authors: Vergauwen L. , Richter E. A. , Hespel P.
Published: December 2017

The role of adenosine in regulating glycogen breakdown during electrically induced muscle contractions was investigated in isolated rat hindquarters perfused with a standard medium either lacking or containing 100 microU/ml insulin and/or 1.67 nM isoprenaline. Nonselective A1/A2-adenosine receptor antagonism via caffeine enhanced (P < 0.05) glycogen breakdown in contracting fast-oxidative (FO) fibers by 40%, provided they were exposed to both insulin and isoprenaline. Combined A1/A2-receptor antagonism by 8-cyclopentyl-1,3-dipropylxanthine (CPDPX) plus 3,7-dimethyl-1-proparglyxanthine (DMPX) fully reproduced (P < 0.05) this stimulatory effect. Furthermore, CPDPX plus DMPX also enhanced (P < 0.05) glycogenolysis during contractions in soleus but not in white gastrocnemius muscle. In contrast, CPDPX or DMPX alone did not affect glycogenolysis in either fiber type. Muscle adenosine 3',5'-cyclic monophosphate concentration during contractions was increased (P < 0.05) by CPDPX plus DMPX in both fiber types, whereas glycogen synthase fractional activity was depressed (P < 0.05). Phosphorylase activity was not changed by CPDPX plus DMPX. It is concluded that adenosine exerts a glycogen-sparing action in oxidative skeletal muscle exposed to both insulin and beta-adrenergic stimulation during contraction, presumably via stimulation of glycogen synthase activity.
Changes in cytokine production and T cell subpopulations in experimentally induced zinc-deficient humans
Authors: Beck F. W. , Prasad A. S. , Kaplan J. , Fitzgerald J. T. , Brewer G. J.
Published: December 2017

We have utilized an experimental model of human zinc deficiency for study of cytokines production by TH1 and TH2 cells. Additionally, we determined ratios of CD4+ to CD8+ and CD4+ CD45RA+ to CD4+CD45RO+ cells and percentages of CD73+ T cytolytic cells in the CD8+ subset. The data were collected during baseline, at the end of the zinc-restricted period, and following zinc repletion. Our results showed that functions of TH1 cells, as evidenced by production of interferon-gamma, interleukin-2 (IL-2), and tumor necrosis factor-alpha, were decreased, whereas functions of TH2 cells (production of IL-4, IL-6, and IL-10) were unaffected by zinc deficiency. Thus an imbalance between TH1 and TH2 cells resulted because of zinc deficiency in humans. Our studies also showed that zinc may be required for regeneration of new CD4+ T lymphocytes and maintenance of T cytolytic cells. We conclude that an imbalance between TH1 and TH2 cells, decreased recruitment of T naive cells, and decreased percentage of T cytolytic cells may account for decreased cell-mediated immune functions in zinc-deficient subjects.
Increased expression of nitric oxide synthase in the myometrium of the pregnant rat uterus
Authors: Riemer R. K. , Buscher C. , Bansal R. K. , Black S. M. , He Y. , Natuzzi E. S.
Published: December 2017

Nitric oxide (NO) relaxes uterine smooth muscle and is produced by the pregnant uterus. Our previous studies revealed an increase in rat uterine NO synthase (NOS) activity in pregnancy and a decline at term. In the present study, we have examined the distribution of NOS isoform expression to determine whether their regulation is consistent with a role in the inhibition of uterine contractions before term. At day 17-18 of pregnancy, NOS immunohistochemistry revealed expression of two isoforms: endothelial constitutive form of NOS (ecNOS) in vascular endothelium and inducible form of NOS (iNOS) in myometrial and vascular smooth muscle and in decidual epithelium. Immunoblotting revealed that expression of iNOS declined nearly fivefold, whereas ecNOS declined twofold in laboring rats at term. We conclude that iNOS is expressed in myometrium of pregnant rat uterus but not the virgin rat and that iNOS expression declines at term when labor is present. The pattern of changes in myometrial iNOS expression with advancing gestation suggests that NO could act in an autocrine and/or paracrine manner to inhibit uterine contractions before term.
Glucose production and gluconeogenesis in adults with uncomplicated falciparum malaria
Authors: Dekker E. , Romijn J. A. , Ekberg K. , Wahren J. , Van Thien H. , Ackermans M. T. , Thuy L. T. , Chandramouli V. , Kager P. A. , Landau B. R. , Sauerwein H. P.
Published: December 2017

Although glucose production is increased in severe malaria, the influence of uncomplicated malaria on glucose production is unknown. Therefore, we measured in eight adult Vietnamese patients with uncomplicated falciparum malaria and eight healthy Vietnamese controls glucose production (by infusion of [6,6-2H2]glucose) and the fractional contribution of gluconeogenesis (by oral ingestion of 2H2O); glycogenolysis was calculated as the difference between the two. After 20 h of fasting, plasma glucose was 4.7 +/- 0.2 mmol/l in the patients and 4.3 +/- 0.2 mmol/l in the controls (not significant). Glucose production was approximately 25% higher in the patients (16.9 +/- 1.3 vs. 13.4 +/- 0.3 mumol.kg-1.min-1, P = 0.01). Fractional and absolute gluconeogenesis were increased in the patients (approximately 87 vs. approximately 59%, P < 0.001; and 14.6 +/- 1.3 vs. 7.9 +/- 0.2 mumol.kg-1.min-1, P < 0.001, respectively). The contribution of glycogenolysis to total glucose production was decreased in the patients: 2.3 +/- 0.5 vs. 5.5 +/- 0.4 mumol.kg-1.min-1 (P < 0.002). In conclusion, in adult patients with uncomplicated falciparum malaria, glucose production is increased by approximately 25% due to an increased rate of gluconeogenesis, whereas glycogenolysis is decreased. The mechanism by which these changes occur is uncertain. However, counterregulatory hormone and cytokine concentrations were increased in the patients.
Increased activity of the hexosamine synthesis pathway in muscles of insulin-resistant ob/ob mice
Authors: Buse M. G. , Robinson K. A. , Gettys T. W. , McMahon E. G. , Gulve E. A.
Published: December 2017

Enhanced glucose flux via the hexosamine biosynthetic pathway has been implicated in insulin resistance. We measured products of this pathway, UDP-N-acetyl hexosamines (UDP-HexNAc), and activity of the rate-limiting enzyme L-glutamine:D-fructose-6-phosphate amidotransferase (GFAT) in tissues of ob/ob mice and lean controls. Ob/ob mice were obese, hyperglycemic, and hyperinsulinemic. Resistance to the effect of insulin on glucose transport was demonstrated in isolated soleus muscles, although total GLUT-4 concentration was mildly increased in muscles from ob/ob mice. UDP-HexNAc concentrations in hindlimb muscles decreased between 8 and 17 wk but were always higher in ob/ob vs. controls (P < 0.001, mean increase 67%). Concentrations of UDP-hexoses and GDP-mannose were similar in ob/ob and control muscles. Muscle GFAT activity declined with age but was increased in ob/ob vs. controls at each age examined (P < 0.001, mean increase 108%). UDP-HexNAc concentrations and GFAT activity were similar in livers of ob/ob and controls. These data suggest that glucose flux via the hexosamine pathway is selectively increased in muscle but not liver of ob/ob mice and may contribute to muscle insulin resistance in this model of non-insulin-dependent diabetes mellitus.
Oxidative metabolism in insulin-treated gestational diabetes mellitus
Authors: Hsu H. W. , Butte N. F. , Wong W. W. , Moon J. K. , Ellis K. J. , Klein P. D. , Moise K. J.
Published: December 2017

To investigate whether protein, carbohydrate, and fat metabolism was normalized in insulin-treated gestational diabetes mellitus (GDM), eight Hispanic women with GDM and eight healthy controls were studied at 32-36 wk of gestation and 6 wk postpartum. Net substrate utilization was measured using room respiration calorimetry. Exogenous substrate oxidation was determined by 13C recovered in breath CO2 from 13C-labeled leucine, glucose, and Hiolein. Women with GDM had higher 24-h oxygen consumption, carbon dioxide production, total energy expenditure, and basal metabolic rates than controls due to larger body mass. Adjusted for weight or fat-free mass, total energy expenditure, basal metabolic rate, and basal and 24-h whole body net protein, carbohydrate, and fat utilization did not differ between insulin-treated GDM subjects and controls in pregnancy or postpartum. Oxidation of [13C]leucine and [13C]glucose did not differ by group or pregnancy status. Recovery of exogenously administered [13C]Hiolein, a biosynthetic triglyceride, as breath 13CO2 was significantly lower in the GDM group antepartum and postpartum (P = 0.02), indicating lower oxidation of exogenous triglycerides in GDM.
Increased sciatic nerve blood flow in diabetic rats: assessment by "molecular" vs. particulate microspheres
Authors: Chang K. , Ido Y. , LeJeune W. , Williamson J. R. , Tilton R. G.
Published: December 2017

Sciatic nerve blood flow in diabetic rats in typically increased or unchanged when assessed by the reference sample microsphere method in our laboratory. In contrast, blood flow is generally reported to be decreased approximately 50% when assessed with laser Doppler flowmetry or hydrogen clearance polarography. To address concerns that increased blood flow observed with microspheres might be anomalous because of their particulate nature and/or because insufficient numbers of microspheres are captured in the nerve, a plasma-soluble "molecular microsphere" ([3H]desmethylimipramine, mol wt = 266) and 11.3-micron 153Gd-labeled microspheres were injected sequentially to assess blood flow in rats with streptozotocin diabetes of 2-4 wk duration. Nerve blood flows in diabetic rats were increased 1.5- to 2-fold (vs. control rats) with both tracers; these increases were prevented by tolrestat, an inhibitor of aldose reductase. These observations indicate that blood flow in sciatic nerve (like that in retina and kidney) is increased early after the onset of diabetes and is 1) demonstrable with a plasma-soluble tracer as well as with particulate microspheres and 2) linked to increased metabolism of glucose via the sorbitol pathway.
Diabetes impairs sciatic nerve hyperemia induced by surgical trauma: implications for diabetic neuropathy
Authors: Ido Y. , Chang K. , LeJeune W. , Tilton R. G. , Monafo W. W. , Williamson J. R.
Published: December 2017

The most widely used methods to assess nerve blood flow in diabetics rats are hydrogen clearance polarography and laser Doppler flowmetry, techniques requiring surgical exposure of the nerve. In these experiments, we examined the hypothesis that the trauma of surgical exposure introduces an important and hitherto largely unrecognized variable that could account for discordant reports on nerve blood flow changes induced by diabetes. We used the noninvasive (for sciatic nerve) reference sample microsphere method to quantify sciatic nerve blood flow in unexposed va. surgically exposed nerves in rats with streptozotocin-induced diabetes (at different temperatures and after curarization) and in unexposed vs. surgically exposed nerves in galactose-fed rats. Baseline resting blood flow in unexposed nerves in both animal models of diabetes was either normal or increased (but was decreased in diabetic rats given d-tubocurarine). Furthermore, the normal brisk hyperemic nerve blood flow response to the minimal trauma associated with surgical exposure of the nerve was markedly impaired in diabetic and in galactose-fed rats. Normalization of the blood flow response to trauma in galactose-fed rats by an aldose reductase inhibitor suggests that the impairment is linked to increased polyol pathway metabolism. These findings 1) confirm our previous findings that sciatic nerve blood flow in diabetic rats is increased or unchanged in unexposed nerves, while also confirming reports that in surgically exposed nerves blood flow is higher in control than in diabetic rats, and 2) indicate that blood flows in surgically exposed nerves are largely a measure of vascular responses to injury rather than (patho)physiological blood flow in undisturbed nerves.
Differential effects of lipoic acid stereoisomers on glucose metabolism in insulin-resistant skeletal muscle
Authors: Streeper R. S. , Henriksen E. J. , Jacob S. , Hokama J. Y. , Fogt D. L. , Tritschler H. J.
Published: December 2017

The racemic mixture of the antioxidant alpha-lipoic acid (ALA) enhances insulin-stimulated glucose metabolism in insulin-resistant humans and animals. We determined the individual effects of the pure R-(+) and S-(-) enantiomers of ALA on glucose metabolism in skeletal muscle of an animal model of insulin resistance, hyperinsulinemia, and dyslipidemia: the obese Zucker (fa/fa) rat. Obese rats were treated intraperitoneally acutely (100 mg/kg body wt for 1 h) or chronically [10 days with 30 mg/kg of R-(+)-ALA or 50 mg/kg of S-(-)-ALA]. Glucose transport [2-deoxyglucose (2-DG) uptake], glycogen synthesis, and glucose oxidation were determined in the epitrochlearis muscles in the absence or presence of insulin (13.3 nM). Acutely, R-(+)-ALA increased insulin-mediated 2-DG-uptake by 64% (P < 0.05), whereas S-(-)-ALA had no significant effect. Although chronic R-(+)-ALA treatment significantly reduced plasma insulin (17%) and free fatty acids (FFA; 35%) relative to vehicle-treated obese animals, S-(-)-ALA treatment further increased insulin (15%) and had no effect on FFA. Insulin-stimulated 2-DG uptake was increased by 65% by chronic R-(+)-ALA treatment, whereas S-(-)-ALA administration resulted in only a 29% improvement. Chronic R-(+)-ALA treatment elicited a 26% increase in insulin-stimulated glycogen synthesis and a 33% enhancement of insulin-stimulated glucose oxidation. No significant increase in these parameters was observed after S-(-)-ALA treatment. Glucose transporter (GLUT-4) protein was unchanged after chronic R-(+)-ALA treatment but was reduced to 81 +/- 6% of obese control with S-(-)-ALA treatment. Therefore, chronic parenteral treatment with the antioxidant ALA enhances insulin-stimulated glucose transport and non-oxidative and oxidative glucose metabolism in insulin-resistant rat skeletal muscle, with the R-(+) enantiomer being much more effective than the S-(-) enantiomer.
Leptin increases uncoupling protein expression and energy expenditure
Authors: Scarpace P. J. , Matheny M. , Pollock B. H. , Tumer N.
Published: December 2017

In ob/ob mice, leptin increases energy expenditure and sympathetic outflow to brown adipose tissue (BAT). To test whether the mechanism of increased energy expenditure may involve increased thermogenesis in BAT, we acclimated normal rats to thermoneutrality for 2 wk followed by leptin administration for 1 wk. Some rats were food restricted for 1 wk to the level of food consumption in the leptin-treated ad libitum-fed rats, and the same rats were both food restricted and administered leptin for a second week. We examined oxygen consumption and uncoupling protein (UCP) expression in BAT. Leptin increased oxygen consumption after the 5th and 6th days in ad libitum-fed rats and after the 4th, 5th, and 6th days in food-restricted rats. Leptin increased BAT UCP mRNA levels greater than twofold in both ad libitum-fed and food-restricted rats. These data demonstrate a leptin-induced increase in energy expenditure in nonmutant rodents and suggest that one mechanism by which leptin increases energy expenditure is through increased thermogenesis in BAT, including increased expression of UCP.
Intestinal growth-promoting properties of glucagon-like peptide-2 in mice
Authors: Tsai C. H. , Hill M. , Asa S. L. , Brubaker P. L. , Drucker D. J.
Published: December 2017

Glucagon-like peptide-2 (GLP-2) has been shown to promote intestinal epithelial proliferation. We studied crypt cell proliferation, enterocyte cell death, and feeding behavior in GLP-2-treated mice. GLP-2 had no effect on food consumption [7.7 +/- 0.3 vs. 8.0 +/- 0.4 g/day, saline (control) vs. GLP-2-treated mice, P = not significant]; however, GLP-2 increased the crypt cell proliferation rate (46.0 +/- 1 vs. 57 +/- 5%, control vs. GLP-2, P < 0.01) and decreased the enterocyte apoptotic rate (5.9 +/- 0.7 vs. 2.8 +/- 0.2% apoptotic cells, control vs. GLP-2, P < 0.05) in small bowel (SB) epithelium. GLP-2 induced a significant increase in SB weight (1.3- to 1.75-fold increase over control, P < 0.05 to P < 0.001) in mice 1-24 mo of age. Increased SB weight was maintained after daily administration of GLP-2 to mice for 12 wk, and cessation of GLP-2 administration in older mice led to regression of (increased) SB weight and mucosal height. These observations suggest that GLP-2 regulates both cell proliferation and apoptosis and promotes intestinal growth after both short- and long-term administration in vivo.
Lactic acid potentiates bradykinin- and low-pH-induced release of CGRP from rat spinal cord slices
Authors: Wang X. , Fiscus R. R.
Published: December 2017

Previous data from our laboratory have shown that calcitonin gene-related peptide (CGRP) is released into the circulation during pathogenesis of endotoxic, hemorrhagic, and septic shock and appears to mediate in part the vascular problems of shock. Elevations in the levels of bradykinin (BK) and lactic acid and lowering of tissue pH also occur during shock and could be involved in CGRP release. In the present study, we have tested whether lactic acid, alone or in combination with BK or low pH, triggers release of CGRP-like immunoreactivity (CGRP-LI) from sensory nerves, using rat spinal cord slices as a tissue model. Lowering media pH from 7.4 to < or = 6.0 increased the release of CGRP-LI. Lactic acid (5 and 10 mM) by itself elevated CGRP-LI release from a control of 6.89 +/- 0.95 to 57.2 +/- 8.2 and 116 +/- 13 pg/mg protein, respectively. The combination of pH 6.0 and lactic acid (5 or 10 mM) caused more than additive stimulation of CGRP-LI release. BK (50 or 100 microM) elevated CGRP-LI release, which was greatly enhanced by lactic acid (2.5 or 5 mM). The data indicate that lactic acid potentiates BK- and low-pH-induced release of CGRP from sensory nerves in spinal cord. Similar mechanisms may occur at peripheral ends of sensory nerves, contributing to CGRP release during septic shock and other conditions with elevated lactic acid levels (e.g., strenuous exercise and tissue ischemia).
Mixed muscle protein synthesis and breakdown after resistance exercise in humans
Authors: Phillips S. M. , Tipton K. D. , Aarsland A. , Wolf S. E. , Wolfe R. R.
Published: December 2017

Mixed muscle protein fractional synthesis rate (FSR) and fractional breakdown rate (FBR) were examined after an isolated bout of either concentric or eccentric resistance exercise. Subjects were eight untrained volunteers (4 males, 4 females). Mixed muscle protein FSR and FBR were determined using primed constant infusions of [2H5]phenylalanine and 15N-phenylalanine, respectively. Subjects were studied in the fasted state on four occasions: at rest and 3, 24, and 48 h after a resistance exercise bout. Exercise was eight sets of eight concentric or eccentric repetitions at 80% of each subject's concentric 1 repetition maximum. There was no significant difference between contraction types for either FSR, FBR, or net balance (FSR minus FBR). Exercise resulted in significant increases above rest in muscle FSR at all times: 3 h = 112%, 24 h = 65%, 48 h = 34% (P < 0.01). Muscle FBR was also increased by exercise at 3 h (31%; P < 0.05) and 24 h (18%; P < 0.05) postexercise but returned to resting levels by 48 h. Muscle net balance was significantly increased after exercise at all time points [(in %/h) rest = -0.0573 +/- 0.003 (SE), 3 h = -0.0298 +/- 0.003, 24 h = -0.0413 +/- 0.004, and 48 h = -0.0440 +/- 0.005], and was significantly different from zero at all time points (P < 0.05). There was also a significant correlation between FSR and FBR (r = 0.88, P < 0.001). We conclude that exercise resulted in an increase in muscle net protein balance that persisted for up to 48 h after the exercise bout and was unrelated to the type of muscle contraction performed.
Effect of acute plasma volume expansion on substrate turnover during prolonged low-intensity exercise
Authors: Phillips S. M. , Green H. J. , Grant S. M. , MacDonald M. J. , Sutton J. R. , Hill R. E. , Tarnopolsky M. A.
Published: December 2017

We investigated the effect of acute, graded increases in plasma volume (PV) by use of dextran on substrate turnover and oxidation during exercise. Eight untrained males [peak aerobic power (VO2peak) = 45.2 +/- 2.2 (SE) ml.kg-1.min-1] performed 2 h of cycle ergometry at 46 +/- 4% of VO2peak on three occasions in a randomized order: 0% PV expansion (CON) and after 14% (LOW) and 21% (HIGH) PV expansion. Glucose and glycerol turnover were measured using primed continuous infusions of [6,6-2H2]glucose and [2H5]glycerol, respectively. Glycerol rate of appearance (Ra) was taken as a relative index of whole body lipolysis. Increases in PV had no effect on glucose Ra or disappearance (Rd) either at rest or during exercise. At the onset of exercise, both glucose Ra and Rd increased approximately 100% (P < 0.01). Glucose Ra and Rd continued to increase with exercise duration (P < 0.05) so that, at 120 min of exercise, they were > 330% higher than at rest (P < 0.01). Glycerol Ra also increased with exercise duration (P < 0.05). Total lipolysis during exercise, calculated as the area under the glycerol Ra vs. time curve, was reduced during LOW vs. CON (P < 0.01). Further expansion of PV (HIGH) had no additional effect on whole body lipolysis. No effect of hypervolemia was observed on whole body fat or carbohydrate oxidation. These results indicate that acute PV expansion can alter whole body lipolysis, possibly via a reduction in catecholamine secretion.
Superoxide dismutase reduces islet microvascular injury induced by streptozotocin in the rat
Authors: Enghofer M. , Usadel K. H. , Beck O. , Kusterer K.
Published: December 2017

Intravenous administration of streptozotocin (STZ) leads to permanent diabetes mellitus in rats. We investigated the possible role of islet microcirculatory changes and free radical formation in this animal model. In vivo fluorescence microscopy was performed for 4 h after administration of STZ. Vascular permeability, capillary blood flow, and endothelial leukocyte adhesion were measured in endocrine and exocrine pancreatic tissue. The earliest microcirculatory event was an increase in vascular permeability in pancreatic islets, with a peak 1 h after STZ administration. The difference between islet and exocrine tissue light intensity was +15.8 +/- 5.6% at t = 60 min. Islet blood flow velocity significantly decreased after 3 h, whereas blood flow in the exocrine pancreas was not affected. Complete stasis of islet blood flow was observed only in rats receiving STZ. Neither increased leukocyte adhesion to islet vascular endothelium nor ischemia-reperfusion phenomena were observed. Prophylactic administration of the radical scavenger superoxide dismutase prevented STZ-induced damage to the islet microcirculation in the initial phase of this model. We conclude that STZ leads to severe microcirculatory disturbances within pancreatic islets in rats. Apparently, these changes are mediated at least in part by free oxygen radicals.
Glutamate transport regulation of renal glutaminase flux in vivo.
Authors: Carter P , Welbourne T
Published: December 2017

We proposed that glutamate transport into cultured kidney cells represses cellular glutaminase activity and hence regulates glutamine utilization. To test this putative regulatory mechanism in vivo, glutamine uptake and conversion to glutamate as well as ammonium production were measured in the intact functioning rat kidney. Glutamine uptake was determined as net removal, arteriovenous concentration difference times renal plasma flow, and also as unidirectional uptake from the fractional extraction of tracer L-[14C]glutamine. Ammonium production was measured as that released into the renal vein plus that excreted, and intracellular glutamine conversion to glutamate was assessed from the rise in cortical glutamate radiolabel specific activity. Cellular glutamate content was reduced 50-60% by infusing D-aspartate (a high-affinity glutamate transporter inhibitor) over 30 min, consistent with interdiction of glutamate uptake. This reduction in the glutaminase repressor was associated with a three- to fivefold increase in glutamine uptake and intracellular conversion to glutamate and ammonium. These results are consistent with and predictable from our previous in vitro model and point to an important role for this regulatory mechanism in the intact functioning organ.