bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of amino acid arteriovenous differences across the liver and placenta of the fetal lamb
Authors: Marconi A. M. , Battaglia F. C. , Meschia G. , Sparks J. W.
Published: December 2017

Amino acid and ammonia concentrations as well as oxygen content were measured in either the right or left hepatic vein, the umbilical vein, and the umbilical artery in 13 fetal lambs in late gestation. There was an uptake of all of the essential and most of the nonessential amino acids by both lobes of the fetal liver. The umbilical venous-hepatic venous amino acid concentration differences were similar in the two hepatic lobes. While glutamine and glycine were taken up by both hepatic lobes, their metabolically related amino acids, glutamate and serine, were released by the fetal liver into the systemic circulation. There was a reciprocal net placental uptake from the umbilical circulation of glutamate and serine and a net fetal of glutamine and glycine, suggestive of interorgan cycling of these amino acids between the placenta and fetal liver. Total fetal umbilical nitrogen uptake was 0.91 g N.kg-1.day-1. The umbilical venous-hepatic venous differences of ammonia were positive and not significantly different in the two lobes. There was a significant umbilical uptake of ammonia (12.8 +/- 1.8 microM; 0.0078 microM NH3/microM O2). However, 0 the ratios of NH3 to O2 were much higher in each lobe (right, 0.060; left, 0.079; each P less than 0.01) than in the umbilical circulation.
Indirect calorimetry: methodological and interpretative problems
Authors: Simonson D. C. , DeFronzo R. A.
Published: December 2017

The technique of indirect calorimetry is now widely used to examine rates of energy production and substrate oxidation in humans. Although the basic principles of indirect calorimetry are well established, it is important to recognize that there are several potential pitfalls in the methodology and data interpretation that must be appreciated to properly understand and apply the results derived from this technique. In particular, one must recognize that the fundamental measurement provided by indirect calorimetry is the net disappearance rate of a substrate regardless of the metabolic interconversions that the substrate may undergo before its disappearance from its metabolic pool. Under most circumstances, direct oxidation represents the major route by which a substrate disappears from its metabolic pool, and the two terms are often used interchangeably. However, under conditions when rates of gluconeogenesis, ketogenesis, or lipogenesis are elevated, the presumed equivalence between oxidation and disappearance may no longer apply, even though the actual measurements derived from indirect calorimetry remain valid. When indirect calorimetry is combined with other in vivo metabolic techniques (e.g., the insulin clamp or radioisotope turnover methods) it can provide a powerful tool for noninvasively examining complex metabolic processes.
Influence of cell heterogeneity on skeletal muscle lactate kinetics
Authors: Pagliassotti M. J. , Donovan C. M.
Published: December 2017

Lactate and [14C]lactate kinetics were studied in three rabbit skeletal muscle preparations with distinct fiber type profiles, glycolytic (99.1 +/- 0.2% type IIb fibers), oxidative (97.5 +/- 0.6% type I fibers), and mixed (type I, IIa, and IIb fibers). Single-pass perfusions were carried out for 2 h in the presence of lactate (1 mM), glucose (5 mM), [6-3H]glucose, and [U-14C]lactate. All preparations displayed net lactate release, [14C]lactate removal, and 14CO2 release. Net lactate release was greatest in the glycolytic preparation, 9.7 +/- 0.5 mumol.100 g-1.min-1, and least in the oxidative preparation, 3.7 +/- 0.2 mumol.100 g-1.min-1. [14C]lactate arteriovenous difference was greatest in the mixed preparation, 1,688 +/- 58 (disintegrations/min)/ml (dpm/ml), and least in the glycolytic preparation, 505 +/- 10.3 dpm/ml. Steady-state incorporation of [14C]lactate was observed in CO2, amino acids, and pyruvate. Tissue lactate specific activity (LSA) in all preparations was significantly lower than arterial LSA, but not significantly different from venous LSA. Estimates of lactate removal based on venous LSA were not significantly different from net glycolytic flux. In conclusion, 1) under basal, resting conditions net lactate release and [14C]lactate removal are properties of all fiber types, and 2) tracer estimates of lactate turnover in skeletal muscle reflect net glycolytic flux through pyruvate.
Role of cell type in net lactate removal by skeletal muscle
Authors: Pagliassotti M. J. , Donovan C. M.
Published: December 2017

Net lactate uptake and subsequent pathways for removal were studied in three rabbit skeletal muscle preparations of distinct fiber type composition, i.e., glycolytic (99.1 +/- 0.2% type IIb fibers), oxidative (97.5 +/- 0.6% type I fibers), and mixed (type I, IIa, and IIb fibers). Single-pass perfusions were carried out for 3 h in the presence of glucose, lactate, and [U-14C]lactate. Lactate levels, initially set at either 1 mM (n = 4/prep) or 2 mM (n = 4/prep), were elevated twice during the perfusion at 60 and 120 min. Net lactate uptake (mumol.100 g-1.min-1) was first observed in the oxidative preparation, 1.4 +/- 0.2, at an arterial lactate concentration of approximately 2.5 mM, whereas net lactate uptake in the glycolytic, 0.7 +/- 0.2, and mixed preparations, 7.0 +/- 0.5, was first observed at 4 mM. Net lactate balance, [14C]lactate removal, and 14CO2 release demonstrated strong linear correlations (r = 0.94-0.98) with arterial lactate concentration. To quantify the fate of [14C]lactate, preparations were perfused at a single elevated lactate concentration (approximately 8 mM) for 2 h. Oxidation was the primary means of disposal in the oxidative and mixed preparations, whereas glyconeogenesis dominated removal in the glycolytic preparation. The arterial lactate concentration at which a given muscle switches from net production to net removal, the rate of removal, and subsequent pathway(s) for disposal are a function of that muscle's fiber type composition.
In vivo somatostatin, vasopressin, and oxytocin synthesis in diabetic rat hypothalamus
Authors: Fernstrom J. D. , Fernstrom M. H. , Kwok R. P.
Published: December 2017

The in vivo labeling of somatostatin-14, somatostatin-28, arginine vasopressin, and oxytocin was studied in rat hypothalamus after third ventricular administration of [35S]cysteine to streptozotocin-diabetic and normal rats. Immunoreactive somatostatin levels in hypothalamus were unaffected by diabetes, as was the incorporation of [35S]cysteine into hypothalamic somatostatin-14 and somatostatin-28. In contrast, immunoreactive vasopressin levels in hypothalamus and posterior pituitary (and oxytocin levels in posterior pituitary) were below normal in diabetic rats. Moreover, [35S]cysteine incorporation into hypothalamic vasopressin and oxytocin (probably mainly in the paraventricular nucleus because of its proximity to the third ventricular site of label injection) was significantly above normal. The increments in vasopressin and oxytocin labeling were reversed by insulin administration. In vivo cysteine specific activity and the labeling of acid-precipitable protein did not differ between normal and diabetic animals; effects of diabetes on vasopressin and oxytocin labeling were therefore not caused by simple differences in cysteine specific activity. These results suggest that diabetes 1) does not influence the production of somatostatin peptides in hypothalamus but 2) stimulates the synthesis of vasopressin and oxytocin. For vasopressin at least, the increase in synthesis may be a compensatory response to the known increase in its secretion that occurs in uncontrolled diabetes.
Triglyceride kinetics, tissue lipoprotein lipase, and liver lipogenesis in septic rats
Authors: Lanza-Jacoby S. , Tabares A.
Published: December 2017

The mechanism for the development of hypertriglyceridemia during gram-negative sepsis was studied by examining liver production and clearance of very-low-density lipoprotein (VLDL) triglyceride (TG). To assess liver output and peripheral clearance the kinetics of VLDL-TG were determined by a constant iv infusion of [2-3H]glycerol-labeled VLDL. Clearance of VLDL-TG was also evaluated by measuring activities of lipoprotein lipase (LPL) in heart, soleus muscle, and adipose tissue from fasted control, fasted E. coli-treated, fed control, and fed E. coli-treated rats. Lewis inbred rats, 275-300 g, were made septic with 8 x 10(7) live E. coli colonies per 100 g body wt. Twenty-four hours after E. coli injection, serum TG, free fatty acids (FFA), and cholesterol of fasted E. coli-treated rats were elevated by 170, 76, and 16%, respectively. The elevation of serum TG may be attributed to the 67% decrease in clearance rate of VLDL-TG in fasted E. coli-treated rats compared with their fasted controls. The suppressed activities of LPL in adipose tissue, skeletal muscle, and heart were consistent with reduced clearance of TG. Secretion of VLDL-TG declined by 31% in livers of fasted E. coli-treated rats, which was accompanied by a twofold increase in the composition of liver TG. Rates of in vivo TG synthesis in livers of the fasted E. coli-treated rats were twofold higher than in those of fasted control rats. Decreased rate of TG appearance along with the increase in liver synthesis of TG contributed to the elevation of liver lipids in the fasted E. coli-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Glycogenesis and glyconeogenesis in skeletal muscle: effects of pH and hormones
Authors: Bonen A. , McDermott J. C. , Tan M. H.
Published: December 2017

We examined the effects of selected hormones and pH on the rates of glyconeogenesis (L-[U-14C]-lactate----glycogen) and glycogenesis (D-[U-14C]glucose----glycogen) in mouse fast-twitch (FT) and slow-twitch muscles incubated in vitro (37 degrees C). Glyconeogenesis and glycogenesis increased linearly with increasing concentrations of lactate (5-20 mM) and glucose (2.5-10 mM), respectively, in both muscles. Glyconeogenesis was approximately three- to fourfold greater in the extensor digitorum longus (EDL) than in the soleus, whereas basal glycogenesis was twofold greater in the soleus muscle than in the EDL. Lactate accounted for up to 5% of the glycogen formed in the soleus and up to 32% in the EDL relative to the rates of glycogenesis (i.e., 5 mM glucose + 10 nM insulin) in each muscle. Corticosterone (10(-12)-10(-6) M) failed to alter glyconeogenesis, whereas this hormone reduced glycogenesis. Insulin (10 nM) markedly stimulated glycogenesis but failed to stimulate glyconeogenesis. The rates of both glycogenesis and glyconeogenesis were pH sensitive, with optimal rates at pH 6.5-7.0 in both muscles. Glyconeogenesis increased by 49% in the soleus and by 39% EDL at pH 6.5 compared with pH 7.4. Glycogenesis increased in the soleus (SOL) and EDL in the absence (SOL: +22%; EDL: +52%) and presence of insulin (SOL: +22%; EDL: +51%) at pH 6.5 when compared with pH 7.4. In additional experiments with the perfused rat hindquarter, rates of glyconeogenesis were shown to be highly correlated with proportion of FT muscle fibers in a muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
Evolution of dexamethasone-induced insulin resistance in rats
Authors: Stojanovska L. , Rosella G. , Proietto J.
Published: December 2017

Glucocorticoids are known to cause insulin resistance and glucose intolerance. Although there have been many studies investigating the mechanism of this effect, several aspects remain to be clarified. The aim of this study was to investigate the evolution and sites of insulin resistance in dexamethasone-treated rats. To achieve this, chronically catheterized nonstressed rats had glucose kinetics measured during an oral glucose tolerance test by means of a double isotope technique. Studies were performed after 6, 48, or 96 h of dexamethasone administration (10 micrograms.rat-1.day-1) and were compared with control rats not treated with the steroid. Total hepatic glucose production (HGP) was increased in the 6-h (166 +/- 8.3, P less than 0.05) and 48-h (198 +/- 21, P less than 0.03) treated groups but not in the 96-h treated rats (140 +/- 8, P = 0.99) compared with the controls (141 +/- 8 mg/55 min). This increased HGP was despite the presence of higher insulin levels in the steroid-treated rats (1,220 +/- 115, P less than 0.09; 1,732 +/- 197, P less than 0.005; 1,567 +/- 107, P less than 0.001 in 6-, 48-, and 96-h treated rats, respectively, compared with 937 +/- 99 mU.l-1 x 55 min-1 in control rats). The metabolic clearance rate of glucose was higher in the dexamethasone-treated rats (200 +/- 14, P less than 0.07; 227 +/- 18, P less than 0.01; 227 +/- 17, P less than 0.01 in 6-, 48-, and 96-h groups, respectively, compared with 165 +/- 10 ml/55 min in control rats).(ABSTRACT TRUNCATED AT 250 WORDS)
Whole body and plasma protein synthesis in exercise and recovery in human subjects
Authors: Carraro F. , Hartl W. H. , Stuart C. A. , Layman D. K. , Jahoor F. , Wolfe R. R.
Published: December 2017

The effect of 4 h of exercise at 40% of maximal oxygen consumption (VO2 max) on protein metabolism was assessed in normal volunteers maintained on a diet containing 42 kcal.kg-1.day-1 and either 0.9 or 2.5 g protein.kg-1.day-1. Primed constant infusions of [1,2-13C]-leucine and [15N]glycine enabled the quantitation of whole body protein turnover and also the fractional synthetic rates (FSR) of albumin, fibrinogen, and fibronectin. In subjects who did not exercise, the fractional synthetic rates (%/day) on normal and high-protein intakes, respectively, were as follows: albumin, 10 +/- 1 and 9 +/- 1; fibrinogen, 21 +/- 3 and 18 +/- 1; and fibronectin, 31 +/- 3 and 34 +/- 3. Neither exercise nor recovery had an effect of whole body protein turnover or on albumin FSR, but the FSR of fibronectin was significantly elevated at the end of exercise, and fibrinogen was significantly elevated in recovery. Dietary protein intake had no major effect on the response to exercise. Thus, in response to exercise, there is a stimulation of the synthesis of some acute phase proteins, which may be a mechanism whereby nitrogen resulting from muscle protein breakdown is spared.
Placental growth hormone as a potential regulator of maternal IGF-I during human pregnancy
Authors: Caufriez A. , Frankenne F. , Englert Y. , Golstein J. , Cantraine F. , Hennen G. , Copinschi G.
Published: December 2017

Ninety-three healthy women were investigated during normal pregnancy, and 177 blood samples were obtained at various gestational stages. In 8 of the women, serial measurements were obtained over a period of 16-34 wk from 8 to 40 wk of gestation. In 13 women, daily blood samples were obtained from day 0 to day 6 after delivery. Insulin-like growth factor I (IGF-I) and human placental lactogen (hPL) were measured by radioimmunoassays. Growth hormone (GH) was estimated by two monoclonal antibody-based radioimmunoassays insensitive to physiological concentrations of hPL: the K24 assay, which recognizes only pituitary hGH, and the 5B4 assay, which reacts with all the known pituitary as well as placental GH variants. Placental GH was distinguished from the main pituitary variant through its specific immunoreactivity pattern. Mean plasma levels of IGF-I were relatively stable until 29-30 wk gestation, then increased progressively to reach a maximum at 35-36 wk. Regardless of gestational age, individual IGF-I values exhibited a highly significant positive correlation with placental GH, reflected by 5B4 immunoreactivity, whereas the correlation between IGF-I and hPL was not statistically significant. Considering each 2-wk gestational period separately, we found a positive correlation between IGF-I and 5B4 hGH at 31-32 wk. Conversely, no evidence of correlation was found between IGF-I and hPL at any period. After delivery, IGF-I evolution exhibited a biphasic pattern, with an initial decrease to low values followed by a progressive return toward levels found in nonpregnant healthy women. These results strengthen our previous hypothesis that placental growth hormone is involved in the control mechanism of serum IGF-I levels in normal pregnant women.
Direct effect of parathyroid hormone on insulin secretion from pancreatic islets
Authors: Fadda G. Z. , Akmal M. , Lipson L. G. , Massry S. G.
Published: December 2017

Indirect evidence indicates that parathyroid hormone (PTH) interacts with pancreatic islets and modulates their insulin secretion. This property of PTH has been implicated in the genesis of impaired insulin release in chronic renal failure. We examined the direct effect of PTH-(1-84) and PTH-(1-34) on insulin release using in vitro static incubation and dynamic perifusion of pancreatic islets from normal rats. Both moieties of the hormone stimulated in a dose-dependent manner glucose-induced insulin release but higher doses inhibited glucose-induced insulin release. This action of PTH was modulated by the calcium concentration in the media. The stimulatory effect of PTH was abolished by its inactivation and blocked by its antagonist [Tyr-34]bPTH-(7-34)NH2. PTH also augmented phorbol ester (TPA)-induced insulin release, stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation by pancreatic islets, and significantly increased (+50 +/- 2.7%, P less than 0.01) their cytosolic calcium. Verapamil inhibited the stimulatory effect of PTH on insulin release. The data show that 1) pancreatic islets are a PTH target and may have PTH receptors, 2) stimulation of glucose-induced insulin release by PTH is mediated by a rise in cytosolic calcium, 3) stimulation of cAMP production by PTH and a potential indirect activation of protein kinase C by PTH may also contribute to the stimulatory effect on glucose-induced insulin release, and 4) this action of PTH requires calcium in incubation or perifusion media.
Ketone bodies and islet function: 86Rb handling and metabolic data
Authors: Malaisse W. J. , Lebrun P. , Rasschaert J. , Blachier F. , Yilmaz T. , Sener A.
Published: December 2017

The metabolism of ketone bodies was investigated in rat pancreatic islets incubated in the absence or presence of D-glucose. The generation of 14CO2 from 3-14C-labeled ketone bodies, the interconversion of D-(-)-beta-hydroxybutyrate and acetoacetate (AcAc), the reciprocal effects of ketone bodies and D-glucose on their respective catabolism, and the influence of these exogenous nutrients on the output of 14CO2 from islets preincubated with either L-[U-14C]glutamine or [U-14C]palmitate provided an estimation of the nutrient-induced changes in O2 uptake that was in fair agreement with the observed modifications of islet respiration. There was a close correlation between such changes and the corresponding values for insulin output. Because the stimulation of insulin release by ketone bodies also coincided with a decrease in 86Rb outflow from prelabeled islets, these findings suggest that the insulinotropic action of ketone bodies is causally linked to their catabolism through an increase in ATP generation rate and a subsequent decrease in K+ conductance. A complementary participation of changes in mitochondrial redox state to stimulus-secretion coupling is considered, however, in the light of comparisons between the effects of D-(-)-beta-hydroxybutyrate and AcAc, respectively, on mitochondrial NADH generation, 45Ca net uptake, and D-[6-14C]glucose oxidation.
Distinction of NPY receptors in vitro and in vivo. I. NPY-(18-36) discriminates NPY receptor subtypes in vitro
Authors: Michel M. C. , Schlicker E. , Fink K. , Boublik J. H. , Gothert M. , Willette R. N. , Daly R. N. , Hieble J. P. , Rivier J. E. , Motulsky H. J.
Published: December 2017

We studied the possibility of multiple neuropeptide Y (NPY) receptor subtypes. NPY-stimulated Ca2+ mobilization in human erythroleukemia (HEL) cells was used to screen a number of NPY analogues. The potencies of three of these analogues [peptide YY (PYY), [D-Tyr-36]NPY, and NPY-(18-36)] were compared with that of NPY in the following model systems: Ca2+ mobilization and inhibition of adenosine 3',5'-cyclic monophosphate accumulation in HEL cells, potentiation of vasoconstriction in the isolated rabbit ear artery, reduction of cutaneous microvascular perfusion in the rat digit, and inhibition of [3H]serotonin release in rat brain. In each of the five models, PYY was a full agonist that exhibited a similar or slightly higher potency than NPY, whereas [D-Tyr-36]NPY and NPY-(18-36) were partial agonists with lower potencies: NPY-(18-36) had a lower potency and efficacy than [D-Tyr-36]NPY in HEL cells and the rabbit ear artery, but was more effective than [D-Tyr-36]NPY for constricting cutaneous microvasculature and inhibiting serotonin release. Because of its weak partial agonism, we also tested NPY-(18-36) as an antagonist of NPY-stimulated Ca2+ mobilization in HEL cells. NPY-(18-36) shifted the NPY concentration-response curve to the right with a KB affinity value of 297 nM. In summary, [D-Tyr-36]NPY and NPY-(18-36) are partial agonists, the relative potency of which varies between systems. These data demonstrate the presence of multiple NPY receptor subtypes. We propose a modified classification scheme of NPY receptor subtypes.
Lighting conditions affect serum and pituitary TSH in male rats
Authors: Laakso M. L. , Porkka-Heiskanen T. , Stenberg D. , Johansson G. , Mannisto P. T.
Published: December 2017

It has been reported that periodicity of lighting plays a role in the regulation of the function of the hypothalamus-anterior pituitary-thyroid axis in the rat. We studied whether other properties of lighting influence the levels of pituitary and serum thyrotropin (TSH) in adult male rats. The animals were reared 7 days under various lighting conditions, then trunk blood and adenohypophyses were collected at different times of the day, and TSH was measured radioimmunologically. In natural lighting conditions the diurnal variation of plasma and pituitary TSH levels was abolished, and the overall levels of plasma TSH were higher and those of pituitary TSH lower than in ordinary laboratory lighting conditions. The intensity of lighting affected the serum TSH levels; daytime serum TSH decreased in the rats under low daytime illuminances and in those under nighttime twilight instead of darkness. Changing the rate of the lighting transition at dawn and dusk had no influence on the TSH patterns. We conclude that, in addition to periodicity, other features of lighting affect the daily secretion patterns of TSH.
Time course of exercise-induced decline in malonyl-CoA in different muscle types
Authors: Winder W. W. , Arogyasami J. , Elayan I. M. , Cartmill D.
Published: December 2017

Malonyl-CoA is a potent inhibitor of carnitine palmitoyltransferase I (CPT-I), the rate-limiting enzyme for fatty acid oxidation in mitochondria from liver of fed rats. Malonyl-CoA has also been demonstrated to inhibit skeletal muscle CPT-I. This study was designed to determine the rate of decline in malonyl-CoA in muscle during the course of a prolonged exercise bout. Adult male rats were anesthetized (pentobarbital sodium, intravenously) at rest or after running for 5, 10, 20, 30, 60, or 120 min on a treadmill (21 m/min, 15% grade). Malonyl-CoA was then quantitated in the soleus (type I fibers) and in the superficial white (type IIB) and deep red (type IIA) regions of the quadriceps. Malonyl-CoA decreased in red quadriceps from 2.8 +/- 0.2 to 1.4 +/- 0.2 pmol/mg after 5 min and to 0.9 +/- 0.1 pmol/mg after 20 min of exercise. The concentration of malonyl-CoA remained at this level for the duration of the exercise bout (120 min). In white quadriceps, resting values of malonyl-CoA were lower than in red quadriceps, and a significant decline was not observed until 30 min of exercise. A significant decrease in the soleus was observed after 20 min of exercise. This decline in muscle malonyl-CoA may be an important signal for allowing increased fatty acid oxidation during long-term exercise.
Fetoplacental deamination and decarboxylation of leucine
Authors: Loy G. L. , Quick A. N. , Hay W. W. , Meschia G. , Battaglia F. C. , Fennessey P. V.
Published: December 2017

Fetal and placental metabolism of leucine (Leu) and ketoisocaproic acid (KIC) were studied in seven fetal lambs at 132 +/- 1.3-days gestation. Fetal infusions of [1-13C]Leu, [1-14C]Leu, and antipyrine were carried out for 4 h. Uterine and umbilical blood flows were measured using the antipyrine steady-state diffusion technique. Leu and KIC concentrations, [14C]Leu-specific activities, 14CO2, [13C]Leu, and [13C]KIC enrichment (mole percent enrichment) were measured in the maternal artery, uterine vein, and umbilical artery and vein to calculate net fluxes of tracee and tracer molecules between fetus and placenta and between the uteroplacenta and the maternal circulation. There were net Leu and KIC fluxes into the fetus from the placenta with the KIC flux equal to approximately 19% of the combined Leu plus KIC flux. In addition, there was a net KIC flux into the uterine circulation. The fraction of infused tracer Leu escaping the placenta into the mother was small (approximately 6%). By contrast, there was a rapid exchange of tracer Leu carbon between placenta and fetus resulting in a significant flux of labeled KIC from placenta to fetus. Approximately 20% of the infused tracer carbon was converted to CO2 within the fetus. This rate of conversion was greater than 80% of the total fetoplacental conversion rate and significantly higher than the flux of KIC tracer carbon from placenta to fetus. Fetal KIC decarboxylation rate, calculated from the fetal KIC enrichment data, was 2.83 +/- 0.40 mumol.min-1.kg fetus-1 and approximately 60% of the combined net Leu and KIC flux into the fetus from the placenta.(ABSTRACT TRUNCATED AT 250 WORDS)
Insulin binding to individual rat skeletal muscles
Authors: Koerker D. J. , Sweet I. R. , Baskin D. G.
Published: December 2017

Studies of insulin binding to skeletal muscle, performed using sarcolemmal membrane preparations or whole muscle incubations of mixed muscle or typical red (soleus, psoas) or white [extensor digitorum longus (EDL), gastrocnemius] muscle, have suggested that red muscle binds more insulin than white muscle. We have evaluated this hypothesis using cryostat sections of unfixed tissue to measure insulin binding in a broad range of skeletal muscles; many were of similar fiber-type profiles. Insulin binding per square millimeter of skeletal muscle slice was measured by autoradiography and computer-assisted densitometry. We found a 4.5-fold range in specific insulin tracer binding, with heart and predominantly slow-twitch oxidative muscles (SO) at the high end and the predominantly fast-twitch glycolytic (FG) muscles at the low end of the range. This pattern reflects insulin sensitivity. Evaluation of displacement curves for insulin binding yielded linear Scatchard plots. The dissociation constants varied over a ninefold range (0.26-2.06 nM). Binding capacity varied from 12.2 to 82.7 fmol/mm2. Neither binding parameter was correlated with fiber type or insulin sensitivity; e.g., among three muscles of similar fiber-type profile, the EDL had high numbers of low-affinity binding sites, whereas the quadriceps had low numbers of high-affinity sites. In summary, considerable heterogeneity in insulin binding was found among hindlimb muscles of the rat, which can be attributed to heterogeneity in binding affinities and the numbers of binding sites. It can be concluded that a given fiber type is not uniquely associated with a set of insulin binding parameters that result in high or low binding.
Lack of effect of hyperglycemia on lipolysis in humans
Authors: Caruso M. , Divertie G. D. , Jensen M. D. , Miles J. M.
Published: December 2017

Controversy exists regarding whether plasma glucose concentrations are independently involved in the regulation of adipose tissue lipolysis. In the present study, six subjects with insulin-dependent diabetes and six nondiabetic volunteers were studied during infusion of somatostatin, growth hormone, and insulin at rates designed to maintain basal rates of lipolysis, which was traced using a constant infusion of [1-14C]palmitate. A euglycemic (approximately 5 mmol/l) clamp was performed for 3 h, followed by 3 h of hyperglycemia (approximately 9 and approximately 11 mmol/l in nondiabetic and diabetic subjects, respectively). Ten nondiabetic subjects were studied during 6 h of euglycemia to exclude time-dependent changes in lipolysis. The results showed that palmitate concentrations did not change between euglycemia and hyperglycemia in either group [118 +/- 10 vs. 132 +/- 14 mumol/l and 145 +/- 21 vs. 134 +/- 15 mumol/l in nondiabetic and diabetic subjects, respectively; both P = not significant (NS)]. Similarly, palmitate rate of appearance (Ra) did not change during hyperglycemia (1.0 +/- 0.1 and 1.7 +/- 0.4 mumol.kg-1.min-1 in nondiabetic and diabetic subjects, respectively) compared with euglycemia (1.0 +/- 0.1 and 1.6 +/- 0.4 mumol.kg-1.min-1 in nondiabetic and diabetic subjects, respectively; P = NS). Palmitate concentrations and Ra did not change during 6 h of euglycemia in nondiabetic volunteers. Thus hyperglycemia per se has no effect on free fatty acid turnover. Changes in lipolysis that occur coincident with hyperglycemia are probably due to changes in other circulating substrates or hormones known to affect lipolysis.
Different responses of trabecular and cortical bone to 1,25(OH)2D3 infusion
Authors: Bikle D. D. , Halloran B. P. , McGalliard-Cone C. , Morey-Holton E.
Published: December 2017

Previous studies regarding the effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on bone have suggested that 1,25(OH)2D3 increases bone mass and calcium. Many of these studies have focused on trabecular or total bone without examining cortical bone per se. To determine whether the response of trabecular bone to 1,25(OH)2D3 differed from the response of cortical bone, we infused 1,25(OH)2D3 into rats and examined bone mass, 45Ca accumulation, and the density distribution of bone particles (as a measure of bone maturation) in both the proximal tibia and shaft. In the proximal tibia 1,25(OH)2D3 decreased 45Ca accumulation, yet increased bone mass and shifted the particle distribution to more mineralized fractions. In the shaft there was a redistribution of bone to less mineralized fractions that was not accompanied by a change in total bone mass or a decrease in 45Ca accumulation. Thus 1,25(OH)2D3 may retard bone maturation and mineralization throughout the tibia, but this effect in the proximal tibia appears to be overshadowed by a reduction in bone resorption resulting in an accumulation of well-mineralized bone in that region. Bone resorption, however, was not measured directly. The net result is an increase in bone mass and density of trabecular bone not seen in cortical bone.
Measurement of albumin synthesis in humans: a new approach employing stable isotopes
Authors: Ballmer P. E. , McNurlan M. A. , Milne E. , Heys S. D. , Buchan V. , Calder A. G. , Garlick P. J.
Published: December 2017

A new method for measuring albumin synthesis in humans with stable isotopes is presented. This can readily be applied in most clinical conditions, even when albumin losses are occurring or when repeated assessment is required. After rapid intravenous injection of a large dose of [13C]leucine (57 mg/kg body wt, 19.4 atoms%), plasma samples were taken at intervals up to 90 min. The enrichment of free leucine in plasma measured by gas chromatography-mass spectrometry rose to a peak at 10 min and then fell slowly, whereas that in liver biopsies (from surgical patients) ranged from 101.5 to 80.5% of the plasma value between 10 and 90 min after injection. The fractional synthesis rate (FSR) was calculated by dividing the increase in enrichment of leucine in albumin, measured by gas isotope ratio mass spectrometry, by the area under the plasma free leucine enrichment vs. time curve after allowing for the period between synthesis of the protein and its secretion into the plasma. The FSR in healthy postabsorptive males was 7.2 +/- 1.3%/day, and the absolute synthesis rate was 157 +/- 39 mg.kg body wt-1.day-1. These rates are comparable to those obtained by other methods.
Adipocyte lactate production remains elevated during refeeding after fasting
Authors: Newby F. D. , Wilson L. K. , Thacker S. V. , DiGirolamo M.
Published: December 2017

The metabolic state occurring with refeeding after fasting is characterized by the rapid restoration of hepatic glycogen. Recent evidence suggests that a main substrate for glycogenesis is lactate. Because adipose tissue is an active site of lactate production that increases with fasting, we examined the magnitude and duration of lactate production by isolated adipocytes from three adipose depots of rats fasted for 48 h and then refed for up to 96 h. The data show that 48 h of fasting results in a markedly elevated rate of adipocyte lactate production, which increased from 3-9% of total glucose metabolized in the fed state to 49-60% in the fasted state. During the refeeding period, lactate production remained elevated for 12-24 h and then declined. Mesenteric adipocytes had a higher rate and more prolonged elevation in lactate production than cells from the other two depots. We conclude that, with refeeding after a fast, adipocyte glucose conversion to lactate remains elevated during the time of hepatic glycogen restoration. This suggests that adipose tissue may actively produce lactate for glycogenesis during refeeding.
Sustained hyperglycemia results in testicular dysfunction and reduced fertility potential in BBWOR diabetic rats
Authors: Cameron D. F. , Rountree J. , Schultz R. E. , Repetta D. , Murray F. T.
Published: December 2017

Rats with short-term diabetes show a greater than 50% reduction of serum testosterone and increased lipid in Leydig cells but normal testicular structure. The purpose of this study was to determine the extent of testicular pathology (morphology index), integrity of the blood-testis barrier, daily sperm production (DSP), number of Leydig cells per testis (LC/T), and total trunk testosterone (TTT) in diabetic rats (BBWORdp) with long-term hyperglycemia (300-350 mg/dl for greater than 180 days) and to evaluate its effects on fertility potential. Results were compared with similarly aged normoglycemic rats (BBWORdr) and normal control Wistar rats. After 6 mo of diabetes, testis weights, DSPs, TTTs, and the morphology index were significantly reduced. The LC/T was not different from BBWORdr rats. The blood-testis barrier appeared intact, although structural abnormalities were noted in Sertoli-Sertoli junction complexes. There was a significant reduction in the number of pregnancies per rat and implantations per pregnancy in matings utilizing the diabetic BBWORdp rat and control Wistar female rats. Results indicate that long-term diabetes with sustained hyperglycemia leads to significant testicular dysfunction associated with decreased fertility potential.
Effect of training on response to a glucose load adjusted for daily carbohydrate intake
Authors: Dela F. , Mikines K. J. , Von Linstow M. , Galbo H.
Published: December 2017

From responses to identical absolute glucose loads in trained (T) and untrained (UT) subjects, it has been inferred that training promotes health by reducing glucose levels and insulin secretion. To mimic daily living conditions, we studied responses to oral glucose loads making up identical fractions of daily carbohydrate intake (i.e., same relative glucose load) in seven T and eight UT males [maximal O2 uptake (VO2max) 76 +/- 2 vs. 48 +/- 1 (SE) ml.min-1.kg-1; age 24 +/- 1 vs. 25 +/- 1 yr]. Daily energy intake was higher in T than in UT subjects (18,607 +/- 835 vs. 12,493 +/- 720 kJ/day, P less than 0.05), reflecting a 2.3 times higher carbohydrate intake (678 +/- 34 vs. 294 +/- 18 g/day, P less than 0.05). After 1 g/kg body wt glucose, C-peptide and insulin responses were lower in T than in UT subjects (P less than 0.05). However, after identical relative glucose loads [high: 2.3 +/- 0.2 (T) vs. 1 (UT) g/kg; low: 1 (T) vs. 0.4 +/- 0.03 (UT) g/kg], glucose [incremental areas 300 +/- 56 (T) vs. 304 +/- 35 (UT) mM.180 min and 148 +/- 30 (T) vs. 124 +/- 22 (UT)] and C-peptide [181 +/- 18 (T) vs. 171 +/- 27 (UT) nM.180 min, and 100 +/- 13 (T) vs. 71 +/- 12 (UT)] responses did not differ between groups, while insulin responses were lower in T [at low relative load 15 +/- 4 (T) vs. 20 +/- 2 (UT) nM.180 min, P less than 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of intravenous infusion of 17 amino acids on the secretion of GH, glucagon, and insulin in sheep
Authors: Kuhara T. , Ikeda S. , Ohneda A. , Sasaki Y.
Published: December 2017

The effects of intravenous infusion of 17 amino acids, each at a dose of 3 mmol/kg over 30 min, on the secretion of insulin, glucagon, and growth hormone (GH) were studied in 6 castrated male sheep. Insulin-like growth factor I (IGF-I) secretion was also studied using eight of the amino acids. Plasma alpha-amino nitrogen reached a peak at 30 min followed by a gradual decrease thereafter. The greatest increase was obtained using aspartic acid and the smallest with methionine, responses to the remaining amino acids lying between these two. Leucine was the most effective amino acid in stimulating insulin secretion but did not produce any increase in glucagon and GH secretion. Alanine, glycine, and serine induced a greater enhancement of both glucagon and insulin secretion than other amino acids. No amino acid was able to specifically stimulate glucagon secretion without also increasing insulin or GH secretion. With regard to insulin and glucagon secretion, amino acids could be divided into groups according to their R groups. Neutral straight-chain amino acids stimulated both insulin and glucagon secretion, with a greater secretory response to shorter C-chain amino acids. Branched-chain amino acids tended to enhance insulin and suppress glucagon secretion. Acidic amino acids caused an increase in GH secretion. Aspartic acid caused the strongest stimulation of GH secretion, exceeding that induced by arginine. No changes in plasma IGF-I were brought about by any of the amino acids tested.
Interaction of exercise and insulin action in humans
Authors: Wasserman D. H. , Geer R. J. , Rice D. E. , Bracy D. , Flakoll P. J. , Brown L. L. , Hill J. O. , Abumrad N. N.
Published: December 2017

To assess the interaction of exercise and insulin action, healthy males were studied with saline infusion (n = 5) or with a hyperinsulinemic euglycemic clamp (0.5, 1.0, 2.0, or 15.0 mU.kg-1.min-1; n = 5 at each dose) during rest (40 min), moderate-intensity cycle exercise (100 min), and recovery (100 min). Metabolism was assessed using isotopic methods and indirect calorimetry. During rest, exercise, and recovery with saline infusion, plasma glucose was unchanged, total glucose utilization (Rd) was 2.4 +/- 0.4, 4.9 +/- 0.2, and 2.6 +/- 0.2 mg.kg-1.min-1, and carbohydrate (CHO) oxidation (OX) was 1.4 +/- 0.3, 10.6 +/- 1.1, and 0.5 +/- 0.2 mg.kg-1.min-1. The glucose infusion, insulin-dependent Rd, and CHO OX increased synergistically when exercise and insulin clamps were combined. Exercise decreased (P less than 0.05) the half-maximal doses (ED50) and increased the maximal responses (Vmax) for insulin-dependent Rd and CHO OX. Estimates of insulin-independent Rd were 1.3 +/- 0.7, 4.1 +/- 1.3, and 1.9 +/- 0.7 mg.kg-1.min-1 and insulin-independent CHO OX were 1.2 +/- 0.9, 10.4 +/- 1.3, and 0.6 +/- 0.3 mg.kg-1.min-1 during rest, exercise, and recovery. Estimates during exercise were greater than those at rest (P less than 0.05). The total suppression of free fatty acids (FFA) and fat OX by insulin were elevated by exercise (P less than 0.05). In summary, exercise and insulin interact synergistically in stimulating Rd and CHO OX.(ABSTRACT TRUNCATED AT 250 WORDS)
Hierarchy of glycemic thresholds for counterregulatory hormone secretion, symptoms, and cerebral dysfunction
Authors: Mitrakou A. , Ryan C. , Veneman T. , Mokan M. , Jenssen T. , Kiss I. , Durrant J. , Cryer P. , Gerich J.
Published: December 2017

To define glycemic thresholds for activation of counterregulatory hormone secretion, initiation of symptoms (autonomic and neuroglycopenic), and onset of deterioration of cognitive function, we measured indexes of these responses during glycemic plateaus of 90, 78, 66, 54, and 42 mg/dl in 10 normal volunteers, with the use of the hyperinsulinemic glucose clamp technique. Activation of glucagon, epinephrine, norepinephrine, and growth hormone secretion began at arterialized venous plasma glucose concentrations of 68 +/- 1, 68 +/- 1, 65 +/- 1, and 67 +/- 2 (SE) mg/dl, respectively. Autonomic symptoms (anxiety, palpitations, sweating, irritability, and tremor) began at 58 +/- 2 mg/dl, which was significantly (P = 0.0001) lower. Neuroglycopenic symptoms (hunger, dizziness, tingling, blurred vision, difficulty thinking, and faintness) and deterioration in cognitive function tests began at 51 +/- 3 and 49 +/- 2 mg/dl, respectively, values that were both significantly (P = 0.018 and 0.004, respectively) lower than that for initiation of autonomic symptoms. We therefore conclude that there is a distinct hierarchy of responses to decrements in plasma glucose, such that the threshold for activation of counterregulatory hormone secretion occurs at higher plasma glucose levels than that for initiation of autonomic warning symptoms, which in turn occurs at higher plasma glucose levels than that for onset of neuroglycopenic symptoms and deterioration in cerebral function. Such a hierarchy would maximize the opportunity to avoid incapacitating hypoglycemia.
Decreased thermogenic response to food with intragastric vs. oral feeding
Authors: De Jonge L. , Agoues I. , Garrel D. R.
Published: December 2017

To examine the effects of sensory stimulations associated with eating on postprandial energy expenditure, thermogenic response to food (TRF) was measured in nine subjects after ingestion of a test meal and after intragastric injection of the same pureed meal through a nasogastric tube. A third measure was made after ingestion of water and a fourth after chewing the meal without deglutition. Each measurement lasted 6 h. Intragastric injection of the meal elicited a lower TRF than oral ingestion in every subject, and this difference was seen whether TRF was calculated from the pretest energy expenditure (PTEE) or from energy expenditure measured after water ingestion (EEW) (175 +/- 57 vs. 83 +/- 32 and 209 +/- 68 vs. 106 +/- 45 kJ for PTEE and EEW, respectively; P less than 0.05 for each test). In both tests, changes in respiratory quotient, plasma glucose, and insulin were similar. Sensory stimulation by the meal without deglutition did not induce a significant change in energy expenditure. These results suggest that TRF has two components in humans, one of which is dependent on preabsorptive sensory stimulations. Lack of change in substrate oxidations between oral and intragastric feeding suggests that TRF related to preabsorptive stimulations does not depend on the preferential use of fatty acids or glucose as a source of fuel.
Growth hormone, cortisol, or both are involved in defense against, but are not critical to recovery from, hypoglycemia
Authors: Boyle P. J. , Cryer P. E.
Published: December 2017

We tested the hypotheses that growth hormone, cortisol, or both are involved in defense against but are not critical to recovery from prolonged hypoglycemia and that the putative roles of these hormones in defense against prolonged hypoglycemia are permissive rather than direct. To do so we studied control subjects (n = 10) and patients with growth hormone and cortisol deficiencies resulting from hypopituitarism both in the untreated state (n = 7) and with prestudy and basal intrastudy growth hormone and cortisol replacement (n = 6). Postabsorptive plasma glucose, insulin, glucagon, and epinephrine concentrations were no different in the untreated patients and controls. Twelve-hour insulin infusions, in low doses adjusted over the 1st 2 h to produce plasma glucose concentrations of 3.6 mmol/l (65 mg/dl) and then fixed at that dose, resulted in significantly (P less than 0.0001) lower late plasma glucose concentrations in the patients, without and with replacement. The 12-h plasma glucose concentrations were 2.9 +/- 0.1 mmol/l (53 +/- 1 mg/dl) in the control subjects, 2.4 +/- 0.1 mmol/l (43 +/- 2 mg/dl; P less than 0.001 vs. control) in the deficient patients, and 2.5 +/- 0.1 mmol/l (45 +/- 2 mg/dl; P less than 0.01 vs. control) in the replaced patients. Rates of glucose recovery from hypoglycemia after discontinuation of insulin were identical in all three studies. Thus growth hormone, cortisol, or probably both play a demonstrable role in defense against prolonged, in contrast to short-term, hypoglycemia in humans. This does not appear to be the result of permissive actions of the hormones and is therefore best attributed to their increments during hypoglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)
Epinephrine inhibits insulin-mediated glycogenesis but enhances glycolysis in human skeletal muscle
Authors: Raz I. , Katz A. , Spencer M. K.
Published: December 2017

The effect of epinephrine (E) infusion on insulin-mediated glucose metabolism in humans has been studied. Eight glucose-tolerant men were studied on two separate occasions: 1) during 120 min of euglycemic hyperinsulinemia (UH, approximately 5 mM; 40 mU.m-2.min-1); and 2) during UH while E was infused (UHE, 0.05 microgram.kg-1.min-1). Biopsies were taken from the quadriceps femoris muscle before and after each clamp. Glucose disposal, correcting for endogenous glucose production, was 36 +/- 3 and 18 +/- 2 (SE) mumol.kg fat-free mass (FFM)-1.min-1 during the last 40 min of UH and UHE, respectively (P less than 0.001). Nonoxidative glucose disposal (presumably glycogenesis) averaged 23.0 +/- 3.0 and 4.0 +/- 1.1 (P less than 0.001), whereas carbohydrate oxidation (which is proportional to glycolysis) averaged 13.1 +/- 1.4 and 15.3 +/- 1.1 mumol.kg FFM-1.min-1 (P less than 0.05) during UH and UHE, respectively. UHE resulted in significantly higher contents of UDP-glucose, hexose monophosphates, postphosphofructokinase intermediates, and glucose 1,6-bisphosphate (G-1,6-P2) in muscle (P less than 0.05-0.001), but there were no significant differences in high-energy phosphates or fructose 2,6-bisphosphate (F-2,6-P2) between treatments. Fractional activities of phosphorylase increased (P less than 0.01), and glycogen synthase decreased (P less than 0.001) during UHE. It is concluded that E inhibits insulin-mediated glycogenesis because of an inactivation of glycogen synthase and an activation of glycogenolysis. E also appears to inhibit insulin-mediated glucose utilization, at least partly, because of an increase in G-6-phosphate (which inhibits hexokinase) and enhances glycolysis by G-1,6-P2-, fructose 6-phosphate-, and F-1,6-P2-mediated activation of PFK.