bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of cell density on in vitro glucose metabolism by isolated adipocytes
Authors: Digirolamo M. , Thacker S. V. , Fried S. K.
Published: December 2017

We studied the effect of variable isolated fat cell concentrations (from 0.17 to 1.25 x 10(6) cells/ml) on rate and pattern of basal and insulin-stimulated glucose metabolism by rat epididymal fat cells. Cell concentration did not affect total glucose utilization, but high cell concentrations increased the absolute and relative conversion of glucose to CO2 and glyceride-fatty acids by two- to threefold and decreased the conversion to lactate, pyruvate, and glyceride-glycerol when compared with values observed at low cell concentration. When effects of adenosine deaminase (ADA) and N-6(2-phenylisopropyl)adenosine (PIA) were examined, addition of ADA to incubated cells produced no significant changes in the rate or pattern of adipocyte glucose metabolism; PIA had a slight and uniform effect on the conversion of glucose to its metabolic products and minimal effect on insulin-stimulated glucose metabolism. Medium free fatty acid concentration did not change during the incubation at various cell density, but intracellular free fatty acids were found to be inversely related to fat cell density in the medium. Thus a variable fat cell density influences the pattern of adipocyte glucose metabolism in vitro. This effect may be due to variable rates of lipolysis and resulting changes in intracellular fatty acid concentration rather than to adenosine per se. This work has practical implications in the need to define cell density when carrying out in vitro measurements of adipocyte glucose conversion to products.
Local bone injections of LPS and M-CSF increase bone resorption by different pathways in vivo in rats
Authors: Orcel P. , Feuga M. , Bielakoff J. , De Vernejoul M. C.
Published: December 2017

We investigated the local in vivo action of lipopolysaccharide (LPS), a potent monocyte activator, and of macrophage colony-stimulating factor (M-CSF), a hemopoietic growth factor influencing monocyte differentiation, on bone resorption in normal female 8-wk-old rats. LPS (2 injections of 0.5 microgram), M-CSF (2 injections of either 12.5, 25, 100, or 500 ng), or vehicle was injected into bone marrow space through a thin catheter implanted, under hydrochloride anesthesia, in the distal end of the right femur. Histomorphometry was performed after staining of the tartrate-resistant acid phosphatase (TRAP). The number of osteoclasts and of TRAP-positive marrow cells (considered as osteoclast precursors) were counted in the secondary spongiosa. LPS caused a 3-fold increase in osteoclast surface, a 4.5-fold increase in the number of osteoclasts, but no change in the number of TRAP-positive marrow cells. M-CSF induced a striking dose-dependent biphasic effect on the number of TRAP-positive marrow cells and on bone resorption (no change with the lowest or with the highest concentrations, although the two intermediate doses significantly increased resorption surfaces and the number of osteoclasts). Our results demonstrate a local in vivo effect of LPS and of M-CSF on bone resorption and suggest that these substances act at different stages of osteoclast development and function.
Absence of glucocorticoid negative feedback to moderate hemorrhage in conscious rats
Authors: Thrivikraman K. V. , Plotsky P. M.
Published: December 2017

Hypothalamic-pituitary-adrenal (HPA) axis responses to stressors elicit and are modulated by glucocorticoids. In the present study, pituitary-adrenal responses to repeated 14 ml/kg (approximately 20%) blood losses separated by 90 min were evaluated in chronically cannulated male rats. Plasma adrenocorticotropin (ACTH) and corticosterone (Cort) levels peaked by 9 and 18 min after hemorrhage, respectively. ACTH returned toward prestimulus values upon retransfusion, whereas Cort remained elevated. Repeated hemorrhage was associated with significantly larger pituitary-adrenal secretory responses, as compared with the initial hemorrhage. These responses were characterized by a more rapid rate of rise in plasma ACTH and delayed Cort secretion. Treatment of rats with intravenous Cort in place of the initial hemorrhage was without effect on the magnitude of pituitary-adrenal responses to a hemorrhage 90 min later. From these observations, it is suggested that 1) the physical stressor of hemorrhage elicits reproducible activation of the HPA axis in rats, 2) HPA axis activation after hemorrhage appears to be mediated via glucocorticoid-independent pathways, and 3) responsiveness to repeated hemorrhage is modestly amplified by some aspect of the initial stimulus.
Lowering plasma free fatty acid levels improves insulin action in conscious pregnant rabbits
Authors: Gilbert M. , Basile S. , Baudelin A. , Pere M. C.
Published: December 2017

Acute elevation in plasma free fatty acid (FFA) levels in nonpregnant rabbits simulates some aspects of insulin resistance observed in late pregnancy. The aim of this study was therefore to evaluate whether lowered FFA induced by nicotinic acid (NA) infusion can improve insulin action in pregnant rabbits. To assess insulin sensitivity we applied euglycemic hyperinsulinemic clamp without (control study) or with concomitant NA infusion (NA study; infusion started 150 min before the glucose clamp) in conscious virgin and pregnant rabbits after an 18-h fast. A primed constant infusion of [3-3H]glucose was used to measure total glucose disposal and hepatic glucose production. Hyperinsulinemia, in association with NA infusion (NA study) brings about a significantly greater stimulation of total glucose disposal in both pregnant (approximately 30%) and nonpregnant (approximately 35%) rabbits compared with the control study. A more pronounced inhibition of hepatic glucose production occurred in NA study in pregnant rabbits (approximately 30 vs. approximately 10%) but it did not reach a statistical significance, whereas there was a total inhibition in nonpregnant rabbits. We conclude that acute decrease in plasma FFA levels mainly improves insulin action at the site of glucose utilization. These results therefore suggest that elevated FFA would contribute to the peripheral insulin resistance in late pregnancy.
Radioactively iodinated cyclo(His-Pro) crosses the blood-brain barrier and reverses ethanol-induced narcosis
Authors: Banks W. A. , Kastin A. J. , Akerstrom V. , Jaspan J. B.
Published: December 2017

Cyclo(His-Pro) (cHP) is a peptide widely distributed in the central nervous system (CNS) and peripheral tissues that can affect brain function after either peripheral or CNS administration. This suggests that cHP may be a neuromodulator capable of crossing the blood-brain barrier (BBB). We, therefore, studied the ability of radioactively labeled cHP (I-cHP) to cross the BBB. We found that I-cHP can cross the BBB in either the direction of blood to brain or brain to blood by nonsaturable mechanisms. The rate of entry of I-cHP into the CNS was low in comparison with other peptides, especially considering its relatively low molecular weight and high lipid solubility. However, this slow entry was offset by a long half-life in blood and extreme enzymatic resistance, allowing cHP to accumulate in the CNS. This accumulation was sufficient to allow intravenous cHP to reverse ethanol-induced narcosis, an effect mediated through the CNS. The rate of entry of I-cHP was resistant to conditions that alter the passage of some other substances across the BBB or that have been shown to affect cHP metabolism such as aging, diabetes, and pretreatment with aluminum. Entry of cHP into the brain was not retarded by binding to serum proteins. Significant amounts of I-cHP entered the serum, brain, and other tissues after intraperitoneal administration, the route used in many studies of cHP. Taken together, these results show that cHP is a highly stable peptide that, after intravenous injection, slowly enters the brain by a nonsaturable mechanism in amounts large enough to affect such aspects of the CNS as ethanol-induced narcosis.
Triiodothyronine receptor complex in developing rat brain and pituitary
Authors: Rodriguez M. , Jolin T.
Published: December 2017

In vitro saturation analysis combined with nuclear 3,5,3'-triiodothyronine (T3) quantification was used to examine the changes in T3 binding parameters in rat pituitary and cerebrocortical nuclei from fetal day 14 to postnatal day 20. T3 receptors were first detectable in neuronal, glial, and pituitary nuclei on fetal days 14, 17, and 18, respectively. Thereafter T3 receptor concentrations in neuronal, glial, and pituitary nuclei increased throughout the developmental period studied, reaching maximal levels during neonatal life (1,129, 1,025, and 635 fmol/mg DNA, respectively). T3 levels in pituitary, neuronal, and glial nuclei also increased during development there being a 35-, 34-, and 120-fold rise between fetal days 16–18 and the 20th postnatal day. Endogenous T3 receptor occupancy throughout the experimental period increased six- to ninefold in the three types of nuclei. The presence of T3 receptor complex in the pituitary and cerebrocortical nuclei during perinatal development lends further support to the hypothesis that T3 may be an important factor in determining the differentiation and development of these cells.
Effect of spaceflight on human protein metabolism
Authors: Stein T. P. , Leskiw M. J. , Schluter M. D.
Published: December 2017

Nitrogen balance and the whole body protein synthesis rate were measured before, during, and after a 9.5-day spaceflight mission on the space shuttle Columbia. Protein synthesis was measured by the single-pulse [15N]glycine method. Determinations were made 56, 26, and 18 days preflight, on flight days 2 and 8, and on days 0, 6, 14, and 45 postflight. We conclude that nitrogen balance was decreased during spaceflight. The decrease in nitrogen balance was greatest on the 1st day when food intake was reduced and again toward the end of the mission. An approximately 30% increase in protein synthesis above the preflight baseline was found for flight day 8 for all 6 subjects (P < 0.05), indicating that the astronauts showed a stress response to spaceflight.
Exercise increases muscle GLUT-4 levels and insulin action in subjects with impaired glucose tolerance
Authors: Hughes V. A. , Fiatarone M. A. , Fielding R. A. , Kahn B. B. , Ferrara C. M. , Shepherd P. , Fisher E. C. , Wolfe R. R. , Elahi D. , Evans W. J.
Published: December 2017

A decline in insulin sensitivity is associated with aging, inactivity, and obesity. The effects of exercise training on glucose homeostasis independent of weight loss in older glucose-intolerant individuals are not well established. We examined the effects of exercise training on oral glucose tolerance, insulin action, and concentration of the GLUT-4 glucose transporters in skeletal muscle. Exercise training at 50 and 75% of heart rate reserve was performed for 12 wk in 18 individuals (age = 64 +/- 2, body fat = 37.0 +/- 1.5%). Peripheral insulin action was determined 96 h after the last exercise bout using a two-step hyperinsulinemic-euglycemic glucose clamp (insulin = 192 and 708 pmol/l). Percent body fat and fat-free mass (FFM) were unchanged with training. Diet composition, assessed by diet record, did not change over the 12 wk. Improved oral glucose tolerance was observed, as exhibited by lower plasma glucose concentrations after training (P < 0.05), whereas plasma insulin response remained unchanged. The rate of glucose disposal was unchanged during the low insulin concentration but increased 11.0% at the high insulin concentration (P < 0.05) after training (54.4 +/- 4.4 vs. 60.4 +/- 5.5 mumol.kg FFM-1.min-1). Skeletal muscle glycogen and GLUT-4 concentration increased 24 and 60%, respectively, with training. There was no direct relationship between the change in GLUT-4 protein and the change in glucose disposal rate. These findings demonstrate that chronic exercise training without changes in body composition improves peripheral insulin action in subjects with impaired glucose tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)
Hormonal regulation of malic enzyme and glucose-6-phosphate dehydrogenase in brown adipose tissue
Authors: Carvalho S. D. , Negrao N. , Bianco A. C.
Published: December 2017

The activities of malic enzyme (ME) and glucose-6-phosphate dehydrogenase (G-6-PDH), two NADPH-generating lipogenic enzymes, were measured in brown adipose tissue (BAT) of rats undergoing various neurohormonal manipulations. Methimazole-induced hypothyroidism doubled the activity of these two enzymes but, surprisingly, triiodothyronine (T3) given to hypothyroid rats caused a time- and dose-dependent stimulation of up to three- to fourfold. Unilateral BAT denervation modestly reduced the activity of these enzymes (approximately 30%) and failed to prevent the stimulation induced by hypothyroidism, whereas growth hormone (GH) successfully blocked this effect of hypothyroidism. Insulin stimulated both enzymes regardless of the thyroid status but failed to abolish the inhibitory effect of GH. In intact rats, cold exposure caused a time-dependent increase in the activity of both ME and G-6-PDH, which reached 5.2- and 3-fold, respectively, after 96 h. This cold-induced stimulation was not observed in hypothyroid rats, but it was restored by physiological doses of thyroxine (800 ng.100 g body wt-1.24 h-1). Replacement with T3 (300 ng.100 g body wt-1.24 h-1), in contrast, did not have this effect. In hypothyroid rats with hemidenervation of BAT, norepinephrine (NE) modestly increased ME and G-6-PDH activities in the denervated side, with little or no effect in the intact side. Receptor-saturating doses of T3 (50 micrograms.100 g body wt-1.day-1 over 48 h) stimulated two- and threefold both enzymes in both sides, reducing or obliterating the effect of denervation. The data suggest a complex neurohormonal regulation of the activity of ME and G-6-PDH in BAT.(ABSTRACT TRUNCATED AT 250 WORDS)
Exercise training increases GLUT-4 protein concentration in previously sedentary middle-aged men
Authors: Houmard J. A. , Shinebarger M. H. , Dolan P. L. , Leggett-Frazier N. , Bruner R. K. , McCammon M. R. , Israel R. G. , Dohm G. L.
Published: December 2017

The purpose of this study was to determine if 14 wk of exercise training would increase insulin-sensitive glucose transporter protein (GLUT-4) concentration in skeletal muscle of previously sedentary middle-aged men (47.2 +/- 1.3 yr; n = 13). Muscle samples (lateral gastrocnemius) and insulin action [insulin sensitivity index (ISI), minimal model] were obtained in the sedentary condition and 48 h after the final training bout. GLUT-4 protein concentration increased (P < 0.001, 2,629 +/- 331 to 4,140 +/- 391 absorbance units/100 micrograms protein) with exercise training by 1.8-fold. ISI increased by twofold (P < 0.05, 2.1 +/- 0.5 to 3.4 +/- 0.7 SI x 10(5) min/pM) with training. The percentage of GLUT-4 rich type IIa muscle fibers increased by approximately 10% (P < 0.01), which may have contributed to the elevation in transporter protein. GLUT-4 concentration and citrate synthase activity (1.7-fold, P < 0.001) also increased by similar increments. These findings indicate that GLUT-4 protein concentration is elevated in middle-aged individuals with exercise training.
Salmon calcitonin reduces vertebral bone loss in glucocorticoid-treated beagles
Authors: Lyles K. W. , Jackson T. W. , Nesbitt T. , Quarles L. D.
Published: December 2017

Glucocorticoids induce bone loss by increasing bone resorption and decreasing bone formation. In this study we have investigated the potential of salmon calcitonin to attenuate glucocorticoid-induced bone loss in a dog model. Male beagles were divided into three groups: 1) untreated controls, 2) prednisone-treated dogs (1 mg.kg-1.day-1 orally), and 3) prednisone-calcitonin-treated dogs (1.5 U.kg-1.day-1 calcitonin subcutaneously and 1 mg.kg-1.day-1 prednisone orally). Assessment of bone mass by dual energy X-ray absorptiometry demonstrated that bone density remained stable in controls throughout 48 wk. Prednisone-treated dogs lost 13.2% of their initial bone mass by 48 wk. Concomitant calcitonin treatment attenuated prednisone-induced bone loss to only 3.2% at 48 wk. Bone histomorphometry of the spine showed reduced trabecular bone volume in prednisone-treated dogs, whereas control and prednisone-calcitonin-treated animals maintained normal trabecular bone volume. Both prednisone- and prednisone-calcitonin-treated dogs acquired a defect in osteoblastic function as evidenced by a reduction in mean wall thickness and trabecular thickness. Thus calcitonin attenuates the early bone loss induced by glucocorticoids. However, calcitonin failed to prevent glucocorticoid-induced osteoblast dysfunction.
Expression of growth hormone-responsive serpin mRNAs in perinatal rat liver
Authors: Berry S. A. , Bergad P. L. , Bundy M. V.
Published: December 2017

Hormonal mechanisms controlling growth of the fetus are poorly understood, and generally growth hormone (GH) is not thought to influence perinatal growth. To examine the influence of GH in the expression of genes in perinatal rat liver, we measured RNA levels of several GH responsive and growth axis genes. Spi 2.1, Spi 2.2, Spi 2.3, insulin-like growth factors (IGF) I and II, and GH receptor mRNAs were measured in rat liver total RNA from gestational days 19, 20, 21, and postnatal day 2. Spi 2.1 and 2.3 genes were faintly expressed on day 20, 6% and 13 +/- 1% of adult levels on gestation day 21, and 6% and 31 +/- 6% of adult levels on day 2. Deoxyribonuclease I (DNase I)-hypersensitive sites in the 5' flanking region of the Spi 2.1 gene, which are concordant with GH response, were not present in DNA extracted from livers at gestation day 19 but were present at days 20, 21, and 2, suggesting the gene is transcriptionally competent after day 19 and that the areas of chromatin vulnerable to DNase I digestion are the same in pre- and postnatal life. Low levels of GH receptor mRNAs (approximately 10% of adult) were present on all measured days. IGF-I mRNA was below quantitatable levels in day 19 or 20 fetal samples and was only 2.7 +/- 0.1% of adult levels on day 21. Levels on day 2 were 9.6 +/- 1.9% of adult. IGF-II mRNA was essentially constant throughout this period, with a minimal increase at day 21 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)
Plasma catecholamines do not respond to insulin-induced hypoglycemia in a teleost, Anguilla rostrata
Authors: Navarro I. , Epple A.
Published: December 2017

The importance of epinephrine as a counterregulatory hormone in hypoglycemia is still debated. In the American eel (Anguilla rostrata), a species particularly sensitive to the hyperglycemic effect of exogenous epinephrine, insulin-induced hypoglycemia does not provoke an increase of plasma catecholamines; nor does a 35-fold rise of endogenous epinephrine within 5 min cause a statistically significant hyperglycemia. Together with findings in several other species of greatly varying phylogenetic position, these observations suggest that in vertebrates plasma epinephrine does not have significant, if any, glucoregulatory functions.
Aldose reductase gene expression and osmotic dysregulation in cultured human retinal pigment epithelial cells
Authors: Stevens M. J. , Henry D. N. , Thomas T. P. , Killen P. D. , Greene D. A.
Published: December 2017

A "compatible osmolyte hypothesis" proposes that intracellular nonionic organic osmolytes such as sorbitol, myo-inositol, taurine, betaine, and glycerophosphorylcholine respond coordinately to changes in external osmolality, thereby maintaining the intracellular ionic milieu. Osmoregulation may be the primary physiological function of aldose reductase, which catalyzes the conversion of glucose to sorbitol. Glucose-induced sorbitol accumulation in isosmotic hyperglycemic states is associated with compensatory depletion of myo-inositol and taurine. Because such depletion may predispose to chronic diabetic complications, the relationship between osmolyte shifts and aldose reductase gene expression was studied in two human retinal pigment epithelial cell lines, one exhibiting osmoregulated and the other high basal aldose reductase gene expression. High basal expression of the aldose reductase gene was associated with rapid sorbitol accumulation and myo-inositol depletion in response to hyperglycemic (20 mM) concentrations of glucose. Myo-inositol and sorbitol behaved as compensating intracellular osmolytes by accumulating markedly in response to hyperosmolality (300 mM mannitol). Thus the pattern of response of myo-inositol to hyperglycemic and hyperosmotic levels of glucose and mannitol was related to the degree of basal aldose reductase gene expression, which may therefore influence the development of diabetic complications.
Metabolic and thermogenic effects of lactate infusion in humans
Authors: Ferrannini E. , Natali A. , Brandi L. S. , Bonadonna R. , De Kreutzemberg S. V. , DelPrato S. , Santoro D.
Published: December 2017

Lactate has been suggested to interfere with intermediary metabolism by restricting both lipolysis and glucose utilization. To test this hypothesis, in paired studies in healthy volunteers, sodium lactate (25 mumol.min-1 x kg-1) or saline was infused for 1 h in the fasting state and during 2 h of euglycemic (4.75 mM) hyperinsulinemia (approximately 400 pmol/l). Hyperlactatemia (approximately 2 mM) had no inhibitory effect on fasting free fatty acid or glycerol levels nor did it alter the suppressive action of insulin on these substrates. Likewise, sodium lactate infusion did not influence hepatic glucose production ([3-3H]glucose technique) or its suppression by insulin. During the clamp, hyperlactatemia was associated with a small increase in whole body glucose disposal (34.9 +/- 4.1 vs. 30.3 +/- 3.7 mumol.min-1 x kg-1, P < 0.05) with no major change in the pattern of substrate (carbohydrate vs. lipid) oxidation. By simultaneously measuring arteriovenous gradients across the deep tissues of the forearm (forearm technique), it was found that hyperlactatemia did not impede insulin-mediated glucose uptake; furthermore, it could be estimated that muscle tissues were responsible for the disposal of roughly one-fifth of the lactate load. Whole body energy expenditure was stimulated above the level achieved with hyperinsulinemia when lactate was also infused. Thus, under the present experimental conditions, physiological hyperlactatemia did not interfere with lipolysis, hepatic glucose production, or whole body or forearm muscle glucose utilization, or with insulin action on these processes, and was accompanied by a strong thermogenic effect.
Differential regulation of intracellular glucose metabolism by glucose and insulin in human muscle
Authors: Mandarino L. J. , Consoli A. , Jain A. , Kelley D. E.
Published: December 2017

Insulin and glucose stimulate glucose uptake in human muscle by different mechanisms. Insulin has well-known effects on glucose transport, glycogen synthesis, and glucose oxidation, but the effects of hyperglycemia on the intracellular routing of glucose are less well characterized. We used euglycemic and hyperglycemic clamps with leg balance measurements to determine how hyperglycemia affects skeletal muscle glucose storage, glycolysis, and glucose oxidation in normal human subjects. Glycogen synthase (GS) and pyruvate dehydrogenase complex (PDHC) activities were determined using muscle biopsies. During basal insulin replacement, hyperglycemia (11.6 +/- 0.31 mM) increased leg muscle glucose uptake (0.522 +/- 0.129 vs. 0.261 +/- 0.071 mumol.min-1 x 100 ml leg tissue-1, P < 0.05), storage (0.159 +/- 0.082 vs. -0.061 +/- 0.055, P < 0.05), and oxidation (0.409 +/- 0.080 vs. 0.243 +/- 0.085, P < 0.05) compared with euglycemia (6.63 +/- 0.33 mM). The increase in basal glucose oxidation due to hyperglycemia was associated with increased muscle PDHC activity (0.499 +/- 0.087 vs. 0.276 +/- 0.049, P < 0.05). However, the increase in leg glucose storage was not accompanied by an increase in muscle GS activity. During hyperinsulinemia, hyperglycemia (11.9 +/- 0.49 mM) also caused an additional increase in leg glucose uptake over euglycemia (6.14 +/- 0.42 mM) alone (5.75 +/- 1.25 vs. 3.75 +/- 0.58 mumol.min-1 x 100 ml leg-1, P < 0.05). In this case the major intracellular effect of hyperglycemia was to increase glucose storage (5.03 +/- 1.16 vs. 2.39 +/- 0.37, P < 0.05). At hyperinsulinemia, hyperglycemia had no effect on muscle GS or PDHC activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino acid uptake by the fetal ovine hindlimb under normal and euglycemic hyperinsulinemic states
Authors: Wilkening R. B. , Boyle D. W. , Teng C. , Meschia G. , Battaglia F. C.
Published: December 2017

As part of an effort to establish the contribution of different fetal organs to fetal amino acid metabolism, we measured in nine sheep fetuses the uptake of 27 amino acids by the hindlimb under normal conditions and conditions by euglycemic hyperinsulinemia. The fetal hindlimb is representative of nonvisceral tissues, which in the mature fetus account for approximately 70% of fetal weight and 30% of fetal O2 consumption. In the normal condition, there was a significant uptake of 21 amino acids for a net total nitrogen uptake of 132 +/- 21 mg N.day-1 x 100 g-1. The amino acids taken up by the fetal limb included alanine and glutamine. In addition, the fetal limb had significant glutamate and serine uptakes. Because glutamate flows from fetus to placenta and there is no fetal uptake of maternal serine, this indicates production and interorgan transport of these amino acids within the fetus. Insulin infusion significantly decreased the arterial concentration of every amino acid with the exception of cystathionine and significantly increased limb blood flow and glucose uptake. It significantly increased the limb uptake of alanine, asparagine, glycine, isoleucine, methionine, and tyrosine, decreased the uptake of aspartate, and produced no significant change in the net total nitrogen uptake, which remained similar to control (137 +/- 16 mg N.day-1 x 100 g-1).
Insulin selectively attenuates breakdown of nonmyofibrillar proteins in peripheral tissues of normal men
Authors: Moller-Loswick A. C. , Zachrisson H. , Hyltander A. , Korner U. , Matthews D. E. , Lundholm K.
Published: December 2017

The role of insulin to control protein synthesis and degradation in the human leg and forearm was investigated in eight healthy individuals. The glucose clamp technique with simultaneous infusion of crystalline amino acids were used to create hyperinsulinemia (100–120 mU/l) in combination with euglycemia and elevated plasma concentrations of amino acids (> 4 mmol/l). A primed constant infusion with L-[U-14C]tyrosine and L-[phenyl-2H5]phenylalanine was used for simultaneous measurements of the disposal (protein synthesis) and the release (protein degradation) of tyrosine and phenylalanine, respectively, across the leg and forearm before and during hyperinsulinemia. The balance of 3-methylhistidine was also determined as a measure of muscle breakdown. Insulin stimulated tissue glucose and net amino acid uptake across the arm and leg tissues, whereas the disposal of both tyrosine and phenylalanine (protein synthesis) was not stimulated across the arm and the leg during hyperinsulinemia. The release of tyrosine and phenylalanine was significantly decreased from both leg and arm tissues (protein degradation) in response to insulin. However, the release of 3-methylhistidine from skeletal muscles was totally unaffected by hyperinsulinemia. We conclude that it is unlikely that insulin contributes to the normal stimulation of protein synthesis during feeding in humans and that insulin has no effect on breakdown of the large myofibrillar protein pool in skeletal muscles in unstressed individuals.
Immunization against vasoactive intestinal peptide does not affect thyroid hormone secretion or thyroid blood flow
Authors: Michalkiewicz M. , Huffman L. J. , Dey M. , Hedge G. A.
Published: December 2017

Vasoactive intestinal peptide (VIP) is present in thyroid parasympathetic nerves. To assess the involvement of endogenous VIP in the regulation of thyroid function, blood levels of thyroid hormones and thyroid blood flows (TBF) were measured after systemic immunization against VIP or after transection of the superior laryngeal nerves in male rats, which reduced the thyroid content of VIP but did not affect blood levels of thyroid hormones or TBF. Anti-VIP monoclonal antibody or anti-VIP serum was used for immunization against VIP in normal rats. In addition, VIP antibody was given to rats fed an iodine-deficient diet for 5 days to examine the involvement of this peptide in iodine deficiency-induced increases in TBF. Effects were measured at different times (90 s, 30 min, 1 h, and 5 days) after immunoneutralization, but none of these treatments changed blood levels of thyroid hormones or TBF in normal or iodine-deficient rats. However, passive immunization against VIP was associated with a high binding capacity of rat plasma to VIP, and this treatment reduced blood levels of prolactin as well as blood flows to the duodenum, stomach, and lung. These findings suggest that the VIP present in thyroid nerves is not involved in maintaining basal thyroid hormone secretion or TBF and that this neuropeptide does not mediate thyroid vascular adjustments to dietary iodine deficiency.
Insulin-like growth factor I exerts growth hormone- and insulin-like actions on human muscle protein metabolism
Authors: Fryburg D. A.
Published: December 2017

The effect of a 6-h intra-arterial infusion of recombinant human (rh) insulin-like growth factor I (IGF-I) on forearm muscle metabolism was studied in 19 postabsorptive subjects. Forearm glucose, lactate, and phenylalanine (Phe) balances, as well as estimates of protein degradation (Phe Ra) and synthesis (Phe Rd) were measured before and at 3 and 6 h into an infusion of rhIGF-I at a dose of 1.8 (n = 6), 6.0 (n = 8), or 10.0 (n = 5) micrograms.kg-1.h-1. In response to intra-arterial IGF-I, deep venous IGF-I rose by 55, 141, and 315%, respectively (all P < 0.01), and forearm blood flow accelerated by 75 (1.8 microgram), 213 (6.0 micrograms), and 159% (10.0 micrograms; all P < 0.02). No change in forearm glucose uptake was observed at the lowest dose, whereas four- to sixfold increases were observed at both the 6 and 10 micrograms.kg-1.h-1 doses (both P < 0.02). Forearm Phe balance shifted positively at all three doses by 27 +/- 6, 48 +/- 7, and 51 +/- 9 nmol.min-1 x 100 ml-1, respectively (all P < 0.01). At all three doses, Phe Rd increased comparably by 49-74% (all P < 0.05). At the 6.0 and 10.0 but not the 1.8 microgram.kg-1.h-1 dose, Phe Ra decreased by approximately 45% (P < 0.02). Forearm muscle metabolism was also studied in the contralateral non-IGF-infused arm at these three doses. Despite increases in deep venous IGF-I up to 517 ng/ml due to recirculating IGF-I (10.0 micrograms.kg-1.h-1 dose), contralateral forearm muscle glucose, lactate, or Phe handling did not change. In conclusion, intra-arterial IGF-I exhibits growth hormone-like effects at all doses tested, whereas the insulin-like effects are observed at higher doses; these effects appear dependent on the route of administration.
Effect of needle biopsy from the vastus lateralis muscle on insulin-stimulated glucose metabolism in humans
Authors: Holck P. , Porksen N. , Nielsen M. F. , Nyholm B. , Bak J. F. , Andreasen F. , Moller N. , Schmitz O.
Published: December 2017

To examine the cellular mechanisms behind conditions characterized by insulin resistance, the clamp technique is often combined with muscle biopsies. To test whether the trauma of a needle biopsy from the vastus lateralis muscle per se may influence insulin-stimulated glucose uptake, eight healthy subjects underwent two randomly sequenced hyperinsulinemic (insulin infusion rate: 0.6 mU.kg-1.min-1 for 150 min) euglycemic clamps with an interval of 4-6 wk. In one study (study B) a muscle biopsy (approximately 250 mg, i.e., larger than normal standard) was taken in the basal state just before the clamp procedure, whereas the other was a control study (study C). Insulin-stimulated glucose uptake was significantly reduced in study B (5.36 +/- 0.96 mg.kg-1.min-1) compared with study C (6.06 +/- 0.68 mg.kg-1.min-1; P < 0.05). Nonoxidative glucose disposal (indirect calorimetry) was decreased (2.81 +/- 1.08 vs. 3.64 +/- 1.34 mg.kg-1.min-1; P < 0.05), whereas glucose oxidation was unaltered. Likewise, endogenous glucose output ([3-3H]glucose) was identically suppressed during hyperinsulinemia. Circulating levels of epinephrine, glucagon, and growth hormone did not differ significantly in studies B and C. In contrast, plasma norepinephrine, serum cortisol, and free fatty acid rose after biopsy (P < 0.05). In conclusion, performance of a muscle biopsy may diminish insulin sensitivity by affecting nonoxidative glucose metabolism. This should be considered when assessing whole body insulin sensitivity after a percutaneous needle muscle biopsy.
Effect of ouabain on pressor responsiveness in normal man
Authors: Pidgeon G. B. , Richards A. M. , Nicholls M. G. , Bailey R. R. , Lynn K. L. , Lewis L. K. , Yandle T. G.
Published: December 2017

To assess the effects of ouabain on pressor and vasoactive hormone responsiveness, 10 healthy volunteers were pretreated with ouabain (0.5 mg i.v. 42 and 18 h before study) or placebo before pressor challenge with angiotensin II (ANG II; 2, 4, and 8 ng.kg-1.min-1 for 30 min/dose) and norepinephrine (NE; 5, 15, and 45 ng.kg-1.min-1 for 15 min/dose). There were no differences at baseline between the two study days regarding mean arterial pressure (MAP) or heart rate. Baseline pulse pressure, however, was significantly greater after ouabain (47 +/- 3 vs. 41 +/- 1 mmHg; P < 0.05). The mean maximum increments in MAP during ANG II and NE infusions were 17.5 +/- 1.1 and 10.5 +/- 1.3 (SE) mmHg, respectively, after ouabain and 19.2 +/- 1.3 and 10.4 +/- 1.5 mmHg after placebo (not significant). The mean heart rate was lower during both infusion periods on the ouabain study day compared with control (P < 0.05). Baseline plasma levels of ANG II, aldosterone, plasma renin activity, atrial and brain natriuretic peptide, guanosine 3',5'-cyclic monophosphate, NE, and epinephrine and achieved levels during the two infusions were similar on the two study days. We conclude that short-term ouabain administration does not alter pressor responsiveness or plasma levels of vasoactive hormones in healthy volunteers.
Roles of uptake1 and catechol-O-methyltransferase in removal of circulating catecholamines in the rabbit
Authors: Friedgen B. , Halbrugge T. , Graefe K. H.
Published: December 2017

Anesthetized rabbits were simultaneously infused with [3H]norepinephrine (NE), [3H]epinephrine (Epi), [3H]dopamine (DA), and [3H]isoproterenol (Iso), and their plasma clearances and fractional extractions across the systemic (ERS), as well as pulmonary (ERP), circulation were determined before and after blockade of uptake1 by desipramine (2 mg/kg). Desipramine reduced the clearance of NE, Epi, and DA by 39, 13, and 14%, respectively, but did not affect Iso clearance. Similar results were obtained with respect to the effects of desipramine on ERS. By contrast, desipramine reduced ERP of NE and DA (which for both amines was markedly lower than ERS) by > 70%; its effect on the very low ERP of Epi was not determinable. Comparison of the desipramine-sensitive components of ERS and ERP indicated that for uptake1 NE was the preferred substrate in the systemic circulation and DA was preferred in the pulmonary circulation. In the absence and presence of desipramine, catechol-O-methyltransferase inhibition had no effect on the clearance of NE, Epi, and DA and decreased Iso clearance by 25%. Hence the contribution by uptake1 to the removal of circulating catecholamines depends on the type of amine and on whether the systemic or pulmonary circulation is considered. Moreover catechol-O-methyltransferase does not appear to contribute to the clearance of NE, Epi, and DA but plays a definite role in the removal of circulating Iso.
Endothelin-1 modulates renin and prolactin release from human decidua by different mechanisms
Authors: Chao H. S. , Poisner A. M. , Poisner R. , Handwerger S.
Published: December 2017

Endothelin (ET)-1 stimulates the synthesis and release of renin and inhibits the expression of prolactin (PRL) from term human decidual cells. To examine the mechanisms by which ET-1 exerts its differential effects on renin and PRL expression, we have studied total renin and PRL release from term human decidual cells in response to pharmacological agents that affect calcium- and protein kinase C-dependent mechanisms. Calcium ionophore A-23187 stimulated basal renin release and potentiated ET-1-stimulated renin release but had no effect on basal or ET-inhibited PRL release. The calcium channel blocker nifedipine inhibited ET-1-stimulated renin release but had no effect on PRL release. The protein kinase C agonist phorbol 12-myristate 13-acetate (PMA) stimulated basal renin release and potentiated the effect of ET-1 on renin release. However, PMA inhibited basal PRL release and also enhanced the inhibitory effect of ET-1. The PKC inhibitor staurosporine increased basal PRL release and completely reversed the inhibitory effect of ET on PRL release. These results indicate that the effects of ET-1 on both decidual renin and PRL release are dependent on the activation of protein kinase C. However, the effect of ET-1 on renin release appears to be dependent on extracellular calcium, whereas the effect on PRL is not influenced by extracellular calcium.
Sulfation pathway of thyroid hormone metabolism in selenium-deficient male rats
Authors: Wu S. Y. , Huang W. S. , Chopra I. J. , Jordan M. , Alvarez D. , Santini F.
Published: December 2017

Male Sprague-Dawley rats were fed a selenium-deficient yeast-based laboratory diet or a control diet for 6 wk. The tissue type I 5'-monodeiodinase (5'-MDI) activity and the immunoassayable 5'-MDI were significantly (P < 0.05) reduced in the liver and the kidney but not in the thyroid of selenium-deficient rats. The mean serum concentrations of thyroxine sulfate (T4S), 3,3',5'-triiodothyronine sulfate (T3S), and reverse T3 sulfate (rT3S) (ng/dl) were significantly increased in selenium-deficient rats (15.7, 59.4, and 22.8, respectively, n = 12) compared with control rats (< 1.0, 18.5, and 9.1, respectively, n = 12, P < 0.01). Kinetic studies were carried out during a constant infusion of unlabeled sulfated iodothyronines (T4S, T3S, or rT3S, n = 5-6/group) at a rate of 1 microgram/h by Alzet minipump for 48 h. The data showed that elevated serum concentrations of T4S or T3S in the selenium-deficient rat are due both to reduced metabolic clearance rate (MCR, mean, l.kg-1.day-1, 7.4 for T4S and 4.5 for T3S in selenium deficiency vs. 12 and 9.2, respectively in controls, P < 0.05) and increased production rate (mean, microgram.kg-1.day-1, 1.2 for T4S, and 2.7 for T3S in selenium deficiency vs. 0.12 and 1.7, respectively, in the controls, P < 0.05). However, the increased serum rT3S concentration in selenium-deficient rats is due mainly to reduced MCR (mean, l.kg-1.day-1, 34 vs. 67 in controls, P < 0.05) and its daily production rate remained unchanged in selenium deficiency (mean, microgram.kg-1.day-1, 7.6 vs. 6.1 in the control group, P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Fasting glucose homeostasis in the adaptation to chronic nutritional deprivation in rats
Authors: Rao R. H.
Published: December 2017

The hormonal basis for the metabolic paradox of relative hypoglycemia despite insulinopenia and insulin resistance in chronic nutritional deprivation was studied in weanling rats restricted to 60% of ad libitum intake over 8 wk (n = 12 each). Lower insulin and glucagon levels were observed in both peripheral and portal blood (P = 0.0016) in the malnourished rats on multivariate analysis of variance, indicating decreased islet secretion. Peripheral and portal hormone levels were proportionately similar, indicating that hepatic extraction was not altered. Despite relative hypoglycemia, glucose turnover rate, total glucose mass, and volume of distribution of glucose were not altered. This indicates that the sum total of the effects of malnutrition on the various hormonal influences controlling glucose turnover had resulted in the establishment of a new dynamic equilibrium associated with lower plasma glucose levels. It is concluded that fasting glucose levels are sustained at a lower level in chronic malnutrition by an adaptive process that includes insulin resistance and insulinopenia, counterbalanced not only by glucagon resistance, as shown earlier, but also by decreased glucagon secretion.
Red cell velocity during functional hyperemia: implications for rheology and oxygen transport
Authors: Hester R. L. , Duling B. R.
Published: December 2017

Muscle blood flow increases during work. Any associated change in blood velocity that occurs during functional hyperemia can have profound effects on wall shear rate and arteriolar hemoglobin saturations. We measured arteriolar red cell velocity and cross-sectional area during muscle contraction to determine the physiological significance of any of these changes in calculations of wall shear rate and the in situ spectrophotometric measurement of hemoglobin oxygen saturation. Calculated cremaster muscle blood flow increased 64–236% during twitch and tetanic stimulation, respectively, which was due entirely to an increase in cross-sectional area, with muscle work producing little change in either the red cell velocity or the calculated wall shear rate. Small changes ranging from a 3% increase to a 4% decrease in hemoglobin saturation were evident in second- and third-order arterioles, which apparently reflects offsetting effects of the increase in metabolic rate and the increase in arteriolar blood volume. A simple model explaining the microcirculatory adjustments made during muscle work requires dilation of both feed arteries and arterioles if red cell velocity is to remain constant during hyperemia.
Effect of sodium intake on gene expression and plasma levels of ANF in rats
Authors: Lattion A. L. , Aubert J. F. , Fluckiger J. P. , Nussberger J. , Waeber B. , Brunner H. R.
Published: December 2017

The effect of short- and long-term sodium loading and sodium restriction on the gene expression as well as on circulating plasma levels of atrial natriuretic factor (ANF) was evaluated in normotensive Wistar rats. These rats were fed either a low-, a regular-, or a high-sodium diet (regular diet and 1% saline as drinking fluid) and studied after 1 and 3 wk. The ANF mRNA was determined in pooled atria and ventricles of the different groups of rats, using the dot-blot technique. Plasma ANF levels were measured with a radioimmunoassay. After 1 wk on the high-sodium diet, ANF mRNA was increased in right atria and ventricles together with circulating ANF levels when compared with animals maintained for the same period on a low-sodium diet. After 3 wk on the various diets, the differences in cardiac ANF mRNA and in plasma ANF levels had disappeared. Gene expression of ANF was also looked for in different areas of the brain, lung, thyroid, adrenals, and the kidney; no hybridization was detected in any of these organs. These data suggest that in rats, the transcription of the ANF gene and peptide release in enhanced only during short-term adaptation to dietary sodium loading.
Efficiency and capacity of protein synthesis are increased in pressure overload cardiac hypertrophy
Authors: Nagai R. , Low R. B. , Stirewalt W. S. , Alpert N. R. , Litten R. Z.
Published: December 2017

We measured the rate of protein synthesis and total RNA content in the right ventricle (RV) at day 2 and day 4 after pulmonary artery constriction to determine the contributions of changes in capacity and efficiency of in vivo protein synthesis to pressure overload (PO) cardiac hypertrophy. A significant increase in the proportion of RV weight to total heart weight was observed at day 2 and day 4 when compared with untreated controls. The rate of protein synthesis was significantly higher at day 2 post-PO (0.31 +/- 0.06 day-1 or 30 +/- 5 mg.g RV-1.day-1, means +/- SD, P less than 0.05) as well as at day 4 (0.25 +/- 0.05 day-1 or 28 +/- 9 mg.g RV-1.day-1, P less than 0.05) than for untreated rabbits (0.15 +/- 0.03 day-1 or 17 +/- 4 mg.g RV-1.day-1). RNA content was significantly higher at day 2 (1.47 +/- 0.17 mg/g RV, P less than 0.05) than in controls (1.16 +/- 0.14 mg/g RV), whereas there was a slight but nonsignificant increase at day 4 (1.36 +/- 0.21 mg/g RV, P less than 0.1). The efficiency of protein synthesis (synthesis/RNA) per gram RV was significantly increased both at day 2 (20.5 +/- 2.2 g protein.g RNA-1.day-1, P less than 0.05) and day 4 (19.8 +/- 3.5 g protein.g RNA-1.day-1, P less than 0.05) compared with control (14.6 +/- 2.3 g protein.g RNA-1.day-1). The increase in efficiency appeared to be caused by pressure overload itself based on a comparison of 0-4 day data vs. data obtained from sham animals (P less than 0.05).
Relation between cytosolic free calcium and respiratory rates in cardiac myocytes
Authors: Moreno-Sanchez R. , Hansford R. G.
Published: December 2017

Rates of O2 uptake of isolated rat cardiac myocytes were determined as a function of cytosolic free Ca2+ concentration ([Ca2+]c) that was estimated from intracellular quin2 fluorescence. [Ca2+]c was increased by depolarization with K+ or veratridine. In each case, there was a correlation between increase in [Ca2+]c and stimulation of O2 uptake. Apparent exception seen on raising K+ were resolved on the of an effect of osmolality on O2 uptake rates. Increase in O2 uptake and [Ca2+]c by veratridine was sensitive to variation of extracellular Na+, Ca2+, and pH in a way that suggests a major involvement of the Na+-Ca2+ exchange: partial inhibition by 2.7 microM verapamil and total inhibition by 30 microM 3',4'-dichlorobenzamil were consistent with this conclusion. Attempts were made to assess the quantitative significance of direct activation of respiration by Ca2+ at the level of mitochondrial dehydrogenases vs. an indirect mechanism involving increased ADP generation. Ruthenium red, which blocks the former process but not the latter, gave a small decrease in O2 uptake rates. However, activation of oxidative phosphorylation by ADP was predominant under these conditions of profound and sustained depolarization, based on a lowered mitochondrial NADH content in response to veratridine.