bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermogenesis and mitochondrial GDP binding with age in response to the novel agonist CGP-12177A
Authors: Scarpace P. J. , Matheny M. , Borst S. E.
Published: December 2017

The ability to regulate body temperature diminishes with age in both humans and rodents. To investigate whether attenuation of sympathetically activated thermogenesis in brown adipose tissue (BAT) may account for the loss of thermoregulation with age, we assessed O2 consumption and body temperature in response to norepinephrine and the specific BAT beta-adrenergic agonist CGP-12177A in 6-, 18-, and 24-mo-old rats. In addition, the effects of this agonist on interscapular BAT mitochondrial GDP binding in young and senescent rats were determined. CGP-12177A rapidly induced an elevation in O2 consumption, which peaked at 25 min, followed by a decline over 4 h. The peak increase in O2 consumption over baseline and the cumulative 4-h response were decreased with age [P less than 0.02, analysis of variance (ANOVA)]. CGP-12177A induced an increase in body temperature that paralleled but appropriately lagged behind the increase in O2 consumption and that was decreased with age (P less than 0.02, ANOVA). The norepinephrine-induced increase in O2 consumption was also reduced with age but was not paralleled by a change in body temperature and was associated with a four- to fivefold increase in physical activity. In young rats CGP-12177A increased the number of available BAT mitochondrial GDP binding sites at 20 and 60 min post-injection, but in senescent rats GCP-12177A was unable to increase GDP binding. These data indicate that CGP-12177A is a novel agonist for BAT thermogenesis. With age there is a reduced capacity for thermogenesis that involves a failure to increase GDP binding, either due to a diminished amount of uncoupling protein with age or a failure to unmask reserve GDP binding sites.
Free fatty acids do not release lipoprotein lipase from isolated cardiac myocytes or perfused hearts
Authors: Rodrigues B. , Spooner M. , Severson D. L.
Published: December 2017

Lipoprotein lipase (LPL), located at the vascular endothelium, catalyzes the hydrolysis of plasma triacylglycerols to fatty acids and 2-monoacylglycerol. In the heart, LPL is synthesized in cardiac myocytes and then translocated to the vascular endothelium. We investigated whether lipolytic products could displace LPL from the cell surface of cardiac myocytes isolated from adult rat hearts. Incubation of myocytes with 0.15-0.9 mM oleic acid or 0.1 mM monoolein did not produce a significant increase in LPL activity in the medium. LPL on the cell surface of intact myocytes hydrolyzed exogenous [3H]triolein, but there was no associated increase in LPL activity measured in the medium. Perfusion of isolated hearts with heparin (5 U/ml) resulted in displacement of LPL from the capillary endothelium. Addition of 0.9 mM oleic acid to the perfusion medium did not increase perfusate LPL activity with perfused hearts from either control or fasted rats. Therefore lipolytic products do not release active LPL from binding sites at the surface of isolated cardiac myocytes or capillary endothelial cells in perfused hearts.
Bone mineral loss during lactation occurs in absence of parathyroid tissue
Authors: Hodnett D. W. , DeLuca H. F. , Jorgensen N. A.
Published: December 2017

The requirement of parathyroid tissue for bone mineral loss during lactation was investigated. Lactating rats parathyroidectomized (PTX) at day 2 of lactation and consuming a 2% calcium diet are hypercalcemic and hypophosphatemic at day 13 of lactation. The high-calcium diet supports normal growth of pups nursing PTX mothers. PTX lactating rats mobilize bone mineral to the same extent as euparathyroid lactating rats consuming the same diet. Non-lactating PTX rats lose no bone mineral over a similar time period, indicating lactation-specific bone mineral mobilization in the absence of parathyroid tissue. PTX rats were verified to have physiologically insignificant amounts of parathyroid tissue, as evidenced by severe hypocalcemia and/or death in each rat after a shift from a 2% calcium to a 0.02% calcium diet. These results conclusively demonstrate that lactation-associated bone mineral mobilization does not require parathyroid hormone or parathyroid tissue.
Effect of growth hormone and resistance exercise on muscle growth in young men
Authors: Yarasheski K. E. , Campbell J. A. , Smith K. , Rennie M. J. , Holloszy J. O. , Bier D. M.
Published: December 2017

The purpose of this study was to determine whether growth hormone (GH) administration enhances the muscle anabolism associated with heavy-resistance exercise. Sixteen men (21-34 yr) were assigned randomly to a resistance training plus GH group (n = 7) or to a resistance training plus placebo group (n = 9). For 12 wk, both groups trained all major muscle groups in an identical fashion while receiving 40 micrograms recombinant human GH.kg-1.day-1 or placebo. Fat-free mass (FFM) and total body water increased (P less than 0.05) in both groups but more (P less than 0.01) in the GH recipients. Whole body protein synthesis rate increased more (P less than 0.03), and whole body protein balance was greater (P = 0.01) in the GH-treated group, but quadriceps muscle protein synthesis rate, torso and limb circumferences, and muscle strength did not increase more in the GH-treated group. In the young men studied, resistance exercise with or without GH resulted in similar increments in muscle size, strength, and muscle protein synthesis, indicating that 1) the larger increase in FFM with GH treatment was probably due to an increase in lean tissue other than skeletal muscle and 2) resistance training supplemented with GH did not further enhance muscle anabolism and function.
Effects of D-beta-hydroxybutyrate and long- and medium-chain triglycerides on leucine metabolism in humans
Authors: Beaufrere B. , Chassard D. , Broussolle C. , Riou J. P. , Beylot M.
Published: December 2017

Ketone bodies and/or fatty acids might play a protein-sparing role during prolonged fasting or parenteral nutrition. To assess this problem, we studied whole body leucine metabolism, using L-[1-13C]leucine in normal postabsorptive volunteers who received either long-chain triglycerides (LCT, 0.15 g.kg-1.h-1, 6 subjects), a 50-50 mixture of medium-chain triglycerides (MCT) and LCT (0.15 g.kg-1.h-1, 6 subjects), D-beta-hydroxybutyrate (540 mumol.kg-1.h-1, 6 subjects), or saline (4 subjects). Leucine concentration decreased only with MCT-LCT. Leucine flux decreased by 10-20% from basal in all groups. Leucine oxidation, which was corrected for the contribution to 13CO2 of the 13C natural abundance of the infused substrates, decreased during LCT infusion (0.31 +/- 0.02 to 0.24 +/- 0.01 mumol.kg-1.min-1, P less than 0.01), but was unaffected by MCT-LCT (despite plasma free fatty acid levels similar to those obtained with LCT), D-beta-hydroxybutyrate, or saline infusion. Therefore, 1) the effect of fatty acids on amino acid oxidation is not mediated by ketone bodies, 2) it depends on the fatty acid chain length, 3) long-chain fatty acids but not medium-chain fatty acids could play a protein-sparing role during parenteral nutrition.
Upregulation of D-myo-inositol transport in diabetic rat glomerular cells
Authors: Whiteside C. I. , Thompson J. C.
Published: December 2017

In the streptozotocin (STZ)-treated diabetic rat, reduced glomerular arteriolar resistance leads to raised intraglomerular pressure. Because vasoconstrictor hormones, such as angiotensin II, stimulate arteriolar smooth muscle and mesangial cell contraction via the D-myo-inositol (MI)-dependent transmembrane signaling pathway, in diabetes extracellular D-glucose may inhibit MI transport causing MI depletion, reduced signaling, and hypocontractility. Therefore we studied the regulation of Na-dependent MI transport in the intact cells (mesangial and endothelial) of isolated glomeruli from STZ rats after 2 wk of diabetes, with and without insulin, compared with controls. Specific [3H]MI uptake per milligram glomerular protein (10-150 min, 37 degrees C) was observed in the presence of 0, 5.5, and 30 mM D-glucose using L-[14C]glucose as a marker of nonspecific uptake. D-Glucose competitively inhibited Na-dependent MI transport (maximum velocity) into diabetic and normal glomerular cells. At 5.5 mM D-glucose, MI uptake by diabetic non-insulin-treated glomeruli was increased to 191 +/- 14% (SE) above normal glomeruli. Insulin treatment resulted in less upregulation (116 +/- 11%) of normal MI transport. High glucose concentration did not alter the rate of [3H]MI efflux from preloaded glomerular cells. To determine whether diabetes alters available substrate for transmembrane signaling, after incubation for 120 min, the incorporation of [3H]MI into cellular membrane phosphoinositides and soluble D-myo-inositol phosphates of isolated diabetic and control glomerular cells was compared. Diabetic glomerular cells displayed a significant increase (P less than 0.005) in [3H]MI incorporation into these fractions compared with controls.
Diminished muscarinic receptor-mediated cerebral blood flow response in streptozotocin-treated rats
Authors: Pelligrino D. A. , Miletich D. J. , Albrecht R. F.
Published: December 2017

Endothelium-dependent vascular relaxation in the brain may be impaired in the streptozotocin-treated chronically hyperglycemic diabetic (D) rat. To study this, we measured regional cerebral blood flow (rCBF) changes induced by intracarotid (ic) or intravenous (iv) infusions of the blood-brain permeant muscarinic receptor (MR) agonist oxotremorine (Oxo). In nondiabetic (ND) rats, both ic and iv Oxo resulted in significant (P less than 0.05) rCBF increases from values obtained during saline infusions in the regions analyzed. The maximum rCBF values measured during Oxo (expressed as percent iv or ic saline value) were 358-403% in the cortex (CX), 236-260% in the subcortex (SC), 162-186% in the brain stem (BS), and 143-158% in the cerebellum (CE). The iv or ic Oxo response in D vs. ND rats was reduced by 60-70% in the CX and SC, lost in the BS, and unchanged in the CE. The CBF response was associated with no change in cortical CMRO2 and was completely blocked during ic atropine-Oxo co-infusion or iv co-infusion of Oxo with the nitric oxide (NO) synthesis inhibitor L-nitroarginine methyl ester, demonstrating, respectively, no role for metabolic activation, the exclusive role of MR values, and the critical role for the release of the putative endothelium-dependent relaxation factor NO in mediating this effect. These findings indicate a significant, but regionally variable, impairment of the mechanism for endothelium-dependent vascular relaxation in the diabetic brain.
Circadian modulation of glucose and insulin responses to meals: relationship to cortisol rhythm
Authors: Van Cauter E. , Shapiro E. T. , Tillil H. , Polonsky K. S.
Published: December 2017

To determine whether glucose and insulin responses to a mixed meal are influenced by time of day irrespective of duration of prior fast, eight normal subjects (4 males, 4 females) were studied on two separate occasions, involving ingestion of identical meals at either 6- or 12-h intervals. The 24-h profiles of plasma glucose, serum insulin, and plasma C-peptide were obtained at 20-min intervals. Plasma cortisol levels were measured on each sample to evaluate possible relationship between diurnal variations in metabolic responses and circadian rhythm of cortisol. Rates of secretion of insulin and cortisol were mathematically derived from peripheral concentrations by deconvolution using two-compartment models for clearance kinetics. Postmeal responses of glucose, insulin, and insulin secretion rate were evaluated by calculating maximum postmeal increment, total area under curve, area under curve for 2 h after meal ingestion, and total duration of response. Postmeal cortisol responses were quantified by increment in plasma level and amount secreted in postmeal pulse. For glucose responses, irrespective of duration of prior fast, all four parameters characterizing the response were significantly greater in the evening than in the morning, with total area under curve and 2-h area under curve being approximately twofold larger in the evening than in the morning. Time of day did not significantly influence maximum postmeal increment in insulin secretion rate or duration of insulin secretory response, but total and 2-h areas under curve were 25-50% greater in the evening than in the morning. Meal ingestion was followed by a significant pulse of cortisol secretion in 37 of 40 cases.(ABSTRACT TRUNCATED AT 250 WORDS)
Carbohydrate restriction regulates the adaptive response to fasting
Authors: Klein S. , Wolfe R. R.
Published: December 2017

The importance of either carbohydrate or energy restriction in initiating the metabolic response to fasting was studied in five normal volunteers. The subjects participated in two study protocols in a randomized crossover fashion. In one study the subjects fasted for 84 h (control study), and in the other a lipid emulsion was infused daily to meet resting energy requirements during the 84-h oral fast (lipid study). Glycerol and palmitic acid rates of appearance in plasma were determined by infusing [2H5]glycerol and [1-13C]palmitic acid, respectively, after 12 and 84 h of oral fasting. Changes in plasma glucose, free fatty acids, ketone bodies, insulin, and epinephrine concentrations during fasting were the same in both the control and lipid studies. Glycerol and palmitic acid rates of appearance increased by 1.63 +/- 0.42 and 1.41 +/- 0.46 mumol.kg-1.min-1, respectively, during fasting in the control study and by 1.35 +/- 0.41 and 1.43 +/- 0.44 mumol.kg-1.min-1, respectively, in the lipid study. These results demonstrate that restriction of dietary carbohydrate, not the general absence of energy intake itself, is responsible for initiating the metabolic response to short-term fasting.
ATP depletion stimulates calcium-dependent protein breakdown in chick skeletal muscle
Authors: Fagan J. M. , Wajnberg E. F. , Culbert L. , Waxman L.
Published: December 2017

The contribution of metabolic energy to the degradation of intracellular proteins in skeletal muscle was investigated. Isolated chick skeletal muscles deprived of oxygen and muscles incubated in buffer under nonphysiological conditions containing inhibitors of glycolysis and mitochondrial respiration had lower concentrations or undetectable levels of ATP and faster rates of proteolysis. Both total protein breakdown and the breakdown of myofibrillar proteins were stimulated 35-124% in ATP-depleted tissues. However, ATP-depleted muscles incubated in buffer to which no Ca2+ was added showed slower rates of total protein breakdown and no significant change in myofibrillar proteolysis compared with control muscles. Trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane (E-64), a compound that inhibits the calpains and the lysosomal cysteine proteases, completely blocked the Ca(2+)-stimulated breakdown of nonmyofibrillar and myofibrillar proteins in ATP-depleted muscles. However, Ca(2+)-stimulated proteolysis was not inhibited in ATP-depleted muscles incubated with weak bases to prevent lysosome function. These data suggest that intracellular proteins can be degraded in skeletal muscle in the absence of metabolic energy and that the calpains play a major role in the enhanced proteolysis in skeletal muscles depleted of ATP.
Lipoprotein lipase release from cardiac myocytes is increased by decavanadate but not insulin
Authors: Braun J. E. , Severson D. L.
Published: December 2017

Streptozotocin-induced diabetes reduced cellular lipoprotein lipase (LPL) activity in cardiac myocytes from rat hearts and decreased the heparin-induced release of LPL into the medium. This effect of diabetes was rapidly reversed by in vivo treatment with insulin (5 U iv for 1 h); administration of insulin in vivo to control rats also increased heparin-releasable LPL activity. In contrast, in vitro addition of insulin to control and diabetic myocytes did not alter either cellular or heparin-releasable LPL activities. Insulin stimulated glucose oxidation and protein synthesis in control and diabetic myocytes. Decavanadate (0.05-1 mM) or vanadyl ion (0.5 mM) enhanced the release of LPL into the medium. Heparin- and decavanadate-induced release of LPL was not additive, and heparin pretreatment reduced the subsequent release of LPL by decavanadate. Decavanadate displaced LPL bound to heparin-Sepharose and increased LPL release into the perfusate of hearts. Therefore, decavanadate can mimic heparin in its effect on LPL. The absence of a direct in vitro effect of insulin on LPL in cardiac myocytes suggests that insulin may require some other in vivo factor or that diabetes-induced changes in LPL activity are secondary to some other metabolic factor.
Role of hepatic nerves in response of liver to intraportal glucose delivery in dogs
Authors: Adkins-Marshall B. , Pagliassotti M. J. , Asher J. R. , Connolly C. C. , Neal D. W. , Williams P. E. , Myers S. R. , Hendrick G. K. , Adkins R. B. , Cherrington A. D.
Published: December 2017

Net hepatic glucose uptake (NHGU) is much greater during oral or intraportal glucose loading than during peripheral intravenous glucose delivery even when similar glucose loads and hormone levels reaching the liver are maintained. To determine whether this difference is influenced by the hepatic nerves, nine conscious 42-h-fasted dogs in which a surgical denervation of the liver (liver norepinephrine levels postdenervation averaged 2.4% of normal) had been performed were subjected to a 40-min control period and two randomized 90-min test periods during which somatostatin (0.8 microgram.kg-1.min-1), intraportal insulin (1.2 mU.kg-1.min-1), and intraportal glucagon (0.5 ng.kg-1.min-1) were infused. The glucose load to the liver was increased twofold by infusing glucose into a peripheral vein (Pe) or the portal vein (Po). Arterial insulin and glucagon concentrations were 39 +/- 2 and 39 +/- 3 microU/ml and 55 +/- 5 and 54 +/- 7 pg/ml during Pe and Po, respectively. The hepatic glucose loads were 50.3 +/- 4.4 and 51.4 +/- 5.8 mg.kg-1.min-1 while NHGU was 2.1 +/- 0.5 and 2.2 +/- 0.7 mg.kg-1.min-1 during Pe and Po, respectively. Similar hormone levels and glucose loads reaching the liver in dogs with intact hepatic nerve supplies were previously shown to be associated with NHGU of 1.4 +/- 0.7 and 3.5 +/- 0.8 mg.kg-1.min-1 in the presence of peripheral and portal glucose delivery, respectively. In conclusion, an intact nerve supply to the liver appears to be vital for the normal response of the liver to intraportal glucose delivery.
Binding of thyroxine and 3,5,3'-triiodothyronine to trout plasma lipoproteins
Authors: Babin P. J.
Published: December 2017

The plasma vectors of thyroid hormones (TH) in trout have been characterized. Plasma components were separated by density gradient ultracentrifugation after first labeling binding sites with trace levels of radioactive hormones, both in vivo and in vitro. Lipoproteins play only a minor role in humans but are major carriers of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) in trout plasma. More than 67% of T4 and 89% of T3 were bound to lipoproteins (density less than 1.210 g/ml), predominantly to high-density lipoproteins (HDL), regardless of the nutritional status of the animals. The percentage of hormone bound to very-low-density lipoproteins, on the other hand, was proportional to their concentration and thus to nutritional status. T3 and T4 could also bind to vitellogenin, a very-high-density lipoprotein, which could transfer TH to the yolk of oocytes. Homologous ligand displacement indicated that T3 could bind to at least two classes of saturable sites in the plasma. In addition, plasma HDL were the major binding sites with low affinity (1.7 +/- 0.4 x 10(5) M-1) but with high capacity (3.1 +/- 0.3 x 10(-5) M). In conclusion, these results show that lipoproteins are the principal binding sites of TH in trout plasma.
Quantification of hormone pulsatility via an approximate entropy algorithm
Authors: Pincus S. M. , Keefe D. L.
Published: December 2017

Approximate entropy (ApEn) is a recently developed formula to quantify the amount of regularity in data. We examine the potential applicability of ApEn to clinical endocrinology to quantify pulsatility in hormone secretion data. We evaluate the role of ApEn as a complementary statistic to widely employed pulse-detection algorithms, represented herein by ULTRA, via the analysis of two different classes of models that generate episodic data. We conclude that ApEn is able to discern subtle system changes and to provide insights separate from those given by ULTRA. ApEn evaluates subordinate as well as peak behavior and often provides a direct measure of feedback between subsystems. ApEn generally can distinguish systems given 180 data points and an intra-assay coefficient of variation of 8%. This suggests ApEn as applicable to clinical hormone secretion data within the foreseeable future. Additionally, the models analyzed and extant clinical data are both consistent with episodic, not periodic, normative physiology.
Ontogeny of prolyl endopeptidase, pyroglutamyl peptidase I, TRH, and its metabolites in rat pancreas
Authors: Salers P. , Ouafik L. H. , Giraud P. , Maltese J. Y. , Dutour A. , Oliver C.
Published: December 2017

We demonstrate that two enzymes, soluble unspecific pyroglutamyl peptidase I and prolyl endopeptidase, able to degrade thyrotropin-releasing hormone (TRH) in vitro were present in pancreas at the early stage of rat development. Specific particulate pyroglutamyl peptidase II remained undetectable during ontogenesis. Pyroglutamyl peptidase I specific activity increased until day 3 and decreased after day 5. Furthermore, prolyl endopeptidase specific activity rose slightly to a peak on postnatal day 20. A good correlation between immunoreactive TRH and deaminated TRH (TRH-OH) was found in the 1st wk after birth. However, His-Pro diketopiperazine (DKP) levels were stable and low during development. We show that hot acidic extraction conditions could artefactually generate His-Pro DKP. In vivo, active site-directed inhibitors of pyroglutamyl peptidase I and prolyl endopeptidase enzymes do not show any TRH-deamidating and/or pyroglutamyl peptidase I pathways in neonatal rat pancreas. The data suggest that these two enzymes are not involved in intra- or extracellular control of TRH levels in neonatal rat pancreas and that pancreatic TRH content appears to be principally regulated by biosynthetic steps. Nevertheless, low levels of endogenous His-Pro DKP and TRH-OH identified in neonatal rat pancreas suggest that TRH or TRH-like peptides may be metabolized in this tissue in intact rats, albeit at low rates.
Roles of paraventricular catecholamines in feeding-associated corticosterone rhythm in rats
Authors: Honma K. , Noe Y. , Honma S. , Katsuno Y. , Hiroshige T.
Published: December 2017

Effects of local destruction of the brain catecholaminergic neurons were examined on the light- and feeding-associated circadian rhythms in plasma corticosterone in rats. 6-Hydroxydopamine (6-OHDA), a selective and long-lasting neurotoxin of the catecholaminergic neurons, was microinjected into the following discrete areas of the brain: the paraventricular nucleus (PVN), median eminence (ME), suprachiasmatic nucleus (SCN), ventromedial hypothalamic nucleus (VMH), lateral hypothalamic nucleus (LH), and the ascending bundle of noradrenergic neurons (NAB). And the feeding-associated as well as the light-associated circadian rhythms in plasma corticosterone were determined. The light-associated circadian rhythm was assayed under a 24-h light-dark cycle with free access to food, whereas the feeding-associated circadian rhythm was measured under restricted daily feeding in which rats had free access to food at a fixed time of day. 6-OHDA reduced the norepinephrine concentrations in respective regions to 10-30% of the control value, except for the LH. The light-associated circadian rhythm was not affected by 6-OHDA into the SCN or PVN. By contrast, 6-OHDA into the PVN or ventral NAB suppressed the feeding-associated circadian peak. 6-OHDA into the VMH and LH showed some effects on plasma corticosterone level but not on the feeding-associated circadian rhythm. 6-OHDA had no systematic effect on plasma corticosterone level when injected into the SCN, ME, and dorsal NAB. These findings indicate that the catecholaminergic neurons projecting to the PVN are involved in the feeding-associated but not in the light-associated circadian rhythms.
Erectile and copulatory dysfunction in chronically diabetic BB/WOR rats
Authors: Murray F. T. , Johnson R. D. , Sciadini M. , Katovich M. J. , Rountree J. , Jewett H.
Published: December 2017

The pituitary-testicular axis, penile reflexes, and copulatory behavior were studied in male BB diabetic rats from 10 to 40 wk of diabetes. Serum testosterone was diminished from 18 to 28 wk of diabetes, and the responses to human chorionic gonadotropin stimulation were blunted. Serum luteinizing hormone (LH) in diabetic rats did not differ from that of the control rats before or after LH-releasing hormone stimulation. Serum follicle-stimulating hormone and prolactin levels were also similar to controls. After 26 wk of diabetes, androgen-sensitive reproductive accessory organs were significantly reduced in size. This also was true for the androgen-sensitive bulbocavernosus and ischiocavernosus muscles. Penile reflexes in these animals from 20 to 32 wk of diabetes were consistently reduced in number and demonstrated prolonged latency. Copulatory behavior was evaluated in these animals at 25 and 28 wk of diabetes and revealed a reduced number of BB diabetic rats showing normal behavior at 25 wk of diabetes. At 28 wk of diabetes, mount latency, intromission latency, ejaculatory latency, and the postejaculatory interval were all prolonged compared with controls. In addition, the number of diabetic animals showing normal behavior was reduced compared with controls. These studies demonstrate that chronically BB diabetic rats develop diminished testosterone and erectile dysfunction that precedes ejaculatory dysfunction in a similar fashion as impotence in diabetic men. We suggest that further studies in this animal model may be critical to the better understanding and treatment of impotence in diabetic men.
Endothelin in rabbit uterus during pregnancy
Authors: Peri A. , Vannelli G. B. , Fantoni G. , Giannini S. , Barni T. , Orlando C. , Serio M. , Maggi M.
Published: December 2017

Specific immunostaining for endothelin-1 (ET-1) was observed in the uterine mucosa of pregnant and nonpregnant rabbits. During gestation, giant cells immunopositive for ET-1 were identified in either endometrium or myometrium. In the latter, they were located in close proximity to the muscular fibers. High-affinity (dissociation constant = 0.25 nM) high-capacity [maximal binding (Bmax) = 7 pmol/mg protein] receptors for ET-1 were present in myometrial membranes of estrous rabbits. During pregnancy the concentration of ET-1 receptors progressively decreased (Bmax on day 29 = 4 pmol/mg protein), rising again at the time of spontaneous delivery. Conversely, ET-1 receptors in the aorta did not change during pregnancy and parturition. The presence of giant cells immunopositive for ET-1 in close proximity to the myometrial cells, together with the evidence of an increase in ET-1 receptors in myometrium of parturient rabbits, suggests a paracrine role for endometrial ET-1 during delivery. Because we previously demonstrated that oxytocin releases ET-1 from endometrial cells in primary culture and that endometrial and myometrial oxytocin receptors abruptly rise at the time of parturition, we propose that ET-1 might participate in the complex cell-to-cell interactions that occur during labor.
Corelease of galanin and NE from pancreatic sympathetic nerves during severe hypoglycemia in dogs
Authors: Havel P. J. , Mundinger T. O. , Veith R. C. , Dunning B. E. , Taborsky G. J.
Published: December 2017

To determine whether norepinephrine (NE) and galanin are coreleased during reflex activation of the sympathetic nervous system by hypoglycemia, we administered insulin to halothane-anesthetized (0.8%) dogs and measured the spillover of NE and galanin-like immunoreactivity (GLIR) into pancreatic venous plasma. Insulin injection produced hypoglycemia [plasma glucose (PG) = 34 +/- 3 mg/dl] but did not activate pancreatic noradrenergic (delta pancreatic NE output = +20 +/- 130 pg/min) or galaninergic nerves (delta GLIR output = +40 +/- 50 fmol/min). To determine whether more severe hypoglycemia would activate these nerves, insulin was administered to dogs infused with somatostatin (SS; 2.5 micrograms/min) to block the counterregulatory increase of glucagon secretion. SS reduced the glucagon response to hypoglycemia by greater than 90%, which allowed PG to decrease to 14 +/- 1 mg/dl. Pancreatic NE output increased by 470 +/- 140 pg/min (P less than 0.005); however, pancreatic GLIR output did not increase significantly (delta = +70 +/- 50 fmol/min). When SS was discontinued, pancreatic NE output increased by 490 +/- 200 pg/min (P less than 0.025), and GLIR output increased by an additional +160 +/- 70 fmol/min (P less than 0.025; total delta from baseline = +230 +/- 90 fmol/min, P less than 0.025), suggesting that SS may restrain pancreatic NE and galanin release. Pancreatic NE and GLIR spillover were also increased during severe hypoglycemia when ganglionic neurotransmission was partially impaired with hexamethonium but not when the neural pathway was interrupted by spinal cord transection. We conclude that NE and galanin are coreleased from pancreatic sympathetic nerves when these nerves are centrally activated during severe hypoglycemia in halothane-anesthetized dogs.
Electrical pacing induces adenylyl cyclase in skeletal muscle independent of the beta-adrenergic receptor
Authors: Kraus W. E. , Longabaugh J. P. , Liggett S. B.
Published: December 2017

Continuous electrical pacing (EP) at 10 Hz of the peroneal nerve innervating fast-twitch muscles of the hindlimb in adult rabbits increases skeletal muscle concentrations of adenosine 3',5'-cyclic monophosphate (cAMP) by 3.1-fold at 10 days and increases beta-adrenergic receptor (beta-AR) density by 2.0-fold at 21 days. To determine whether beta-AR, the alpha-subunit of guanine nucleotide proteins (Gs alpha), or adenylyl cyclase is primarily responsible for pacing-induced increases in muscle cAMP, we measured adenylyl cyclase activity (ACA) in muscles that were electrically paced for 3 (n = 4), 10 (n = 8), and 21 (n = 8) days. EP resulted in a time-dependent increase in ACA that was 2.2 +/- 0.3-fold (P less than 0.005) at 21 days. EP significantly increased GTP-, 5'-guanylylimidodiphosphate-, isoproterenol-, NaF-, and forskolin-stimulated ACA, and propranolol administration to rabbits during EP did not alter pacing-induced changes in ACA. There were no changes in protein concentration, Na(+)-K(+)-adenosinetriphosphatase activity, or Gs alpha with EP. Based on these studies, we conclude that EP appears to increase cAMP through mechanisms independent of the beta-AR and through mechanisms that may involve alterations at the level of adenylyl cyclase.
Spontaneous physical activity and obesity: cross-sectional and longitudinal studies in Pima Indians
Authors: Zurlo F. , Ferraro R. T. , Fontvielle A. M. , Rising R. , Bogardus C. , Ravussin E.
Published: December 2017

Healthy, nondiabetic Pima Indians [103 males, 77 females; 27 +/- 6 (SD) yr, 97 +/- 25 kg, 33 +/- 9% body fat] were studied in a respiratory chamber in which spontaneous physical activity (SPA) was measured by two microwave sensors. SPA, defined as the percentage of time the subjects were active, varied widely from 4.4 to 17.5%. It was higher in males (9.3 +/- 2.0%) than in females (8.6 +/- 2.3%; P less than 0.05) and was not related to body fatness in either sex. However, SPA accounted for a significant portion of the daily energy expenditure (24-h EE) in males (1,389 +/- 423 kJ/day) and females (1,163 +/- 351 kJ/day) and correlated positively with 24-h EE adjusted for differences in fat-free mass, fat mass, age, and sex (r = 0.42, P less than 0.0001). In 88 siblings, family membership accounted for 57% of the variance in SPA (r(i) = 0.57, P less than 0.02). Body composition was reassessed in a subgroup of 123 subjects (65 males, 58 females) 33 +/- 14 mo later. In males only, SPA correlated inversely to the rate of subsequent body weight change (r = -0.25, P less than 0.05) and the rate of fat-mass change (r = -0.35, P less than 0.005). We conclude that spontaneous physical activity is a familial trait that may play a role in the pathogenesis of obesity.
Soluble and particulate phenylethanolamine N-methyltransferase in hypothalamus of diabetic rats
Authors: Chappell J. E. , Stewart J. K.
Published: December 2017

Experimental diabetes increases total phenylethanolamine N-methyltransferase (PNMT) activity in the medulla-pons but not in the hypothalamus. In this study diabetes was induced with streptozotocin (65 mg/kg) in male Sprague-Dawley rats. Twenty-eight days after treatment there were no differences in soluble PNMT activity in the hypothalamus of diabetics and controls, but PNMT activity in a membrane-associated (particulate) fraction of hypothalamus was evaluated approximately twofold in tissues of diabetic animals compared with controls. A specific PNMT inhibitor, incubated with tissue extracts of control rats, abolished greater than 90% of particulate PNMT activity in the hypothalamus but reduced soluble PNMT activity in the hypothalamus by only 47%. These findings indicate that membrane-associated PNMT activity in rat hypothalamus differs from soluble hypothalamic PNMT in the in vitro response to an inhibitor and the in vivo response to diabetes and suggest the importance of separating subcellular hypothalamic fractions prior to assay of PNMT.
Estimation of the rate of appearance in the non-steady state with a two-compartment model
Authors: Mari A.
Published: December 2017

A simple tracer-based method for calculating the rate of appearance of endogenous substances in the non-steady state, free from the inconsistencies of Steele's equation, is still lacking. This paper presents a method based on a two-compartment model by which the rate of appearance can be calculated with only a modest increase in complexity over Steele's approach. An equation is developed where the rate of appearance is expressed as a sum of three terms: a steady-state term, a term for the first compartment, and a term for the second compartment. The formula employs three parameters and makes the relationship between rate of appearance and specific activity changes explicit. An equation is also provided for estimating the error of the method in each individual run. The algorithm can be implemented with a spreadsheet on a personal computer. Simulated and experimental data obtained by the hyperinsulinemic euglycemic glucose clamp technique were used as a test. The accuracy with which the time course of glucose production could be reconstructed was clearly better than that using Steele's equation. Marked negative values for endogenous glucose output were calculated with Steele's equation but not with the new method. The characteristics of generality, simplicity, and accuracy and the availability of an error estimate make this new method suitable for routine application to non-steady-state tracer analysis.
Effects of ovarian hormones on brain opioid binding sites in castrated female rats
Authors: Dondi D. , Limonta P. , Maggi R. , Piva F.
Published: December 2017

These experiments were performed to analyze whether treatments of ovariectomized female rats with ovarian steroid regimens able to induce either an increase (positive feedback effect) or a decrease (negative feedback effect) of serum levels of luteinizing hormone (LH) have some impact on the characteristics of mu-opioid binding sites in circumscribed areas of the brain. The increase of serum levels of LH elicited by a treatment with estradiol benzoate (EB) plus progesterone (P; positive feedback effect) was accompanied by a significant decrease in the number of mu-binding sites in the hypothalamus and in the corpus striatum. The decrease in serum levels of LH induced by a treatment with EB alone (negative feedback effect) brought about a significant increase of the number of mu-binding sites in the thalamus and in the hippocampus. These results seem to suggest that the release of LH induced by EB plus P may involve a decrease of hypothalamic mu-binding sites. Apparently, the inhibitory effect on LH release exerted by EB alone does not involve any change of the density of these binding sites in the hypothalamus.
Effect of a high-fat diet on the incorporation of stored triacylglycerol into hepatic VLDL
Authors: Francone O. L. , Griffaton G. , Kalopissis A. D.
Published: December 2017

Triacylglycerol (TG) stored in cytoplasmic lipid droplets of hepatocytes was labeled by in vivo [1-(14)C]oleic acid injection to study the effect of a high-fat diet on its incorporation into very-low-density lipoproteins (VLDL). Compared with the control diet, hepatocytes of fat-fed rats 1) contained 7.6 times more cytoplasmic (floating fat) TG and 1.9 times more endoplasmic reticulum (microsomal) TG; 2) had 8 and 6 times lower TG specific activities in cytoplasm and endoplasmic reticulum, respectively; 3) incorporated 22% less 14C label into hepatocyte esterified lipids (TG, cholesterol, phospholipid); 4) secreted 48 and 33% less radioactive and total VLDL-TG, respectively; 5) oxidized more cytoplasmic TG-fatty acid (FA); and 6) showed a 50% decreased total utilization of stored TG-FA. With both diets, the lysosomal inhibitor chloroquine concomitantly decreased productions of labeled VLDL-TG, CO2, and acid-soluble oxidation products. The decreased incorporation of stored TG into VLDL-TG appreciably contributes to the overall inhibition of hepatic VLDL secretion by fat feeding. It appears to be related to the decreased mobilization rate of stored TG and its increased channelling toward oxidation.
Glucocorticoid increases glucose cycling and inhibits insulin release in pancreatic islets of ob/ob mice
Authors: Khan A. , Ostenson C. G. , Berggren P. O. , Efendic S.
Published: December 2017

Normoglycemic ob/ob mice were treated for 24 or 48 h with either 25 micrograms/day of dexamethasone or saline. After an overnight fast, the animals were killed and pancreatic islets were incubated with 3H2O or [U-14C]glucose or [5-3H]glucose at 5.5 and 16.7 mM glucose. Incorporation of 3H from 3H2O into carbon 2 of medium glucose and the yield of 14CO2 from [U-14C]glucose and 3H2O from [5-3H]glucose were measured. Dexamethasone treatment for 48 h significantly increased the rate of dephosphorylation of glucose in islets both at 5.5 mM (24 vs. 16%) and 16.7 mM (56 vs. 36%) glucose, whereas glucose oxidation and utilization were unaffected. Dexamethasone treatment also inhibited insulin release by approximately 60% at 5.5 and 16.7 mM glucose, either in the presence or absence of 10 mM arginine, but had no effect when insulin release was stimulated by 1 mM 3-isobutyl-1-methylxanthine. Moreover, 24-h treatment with dexamethasone significantly increased glucose cycling at low and high glucose concentrations in the medium and inhibited insulin responsiveness to glucose and arginine. In conclusion, short-term dexamethasone treatment increases glucose flux through glucose-6-phosphatase in islets from ob/ob mice. This effect may contribute to the decreased insulin response to glucose and arginine found in animals treated with dexamethasone.
In vivo estimation of lactose hydrolysis in premature infants using a dual stable tracer technique
Authors: Kien C. L. , Ault K. , McClead R. E.
Published: December 2017

To investigate their putative capacity for lactose digestion, primed continuous orogastric infusions of [1-13C]glucose and D-[1-13C]lactose were administered on consecutive days to five premature infants (30–31 wk gestation, 15–32 days of age), who were fed by orogastric infusions of human milk or formula. By monitoring the plateau isotopic enrichment of plasma glucose using isotopomers containing the entire derivatized glucose molecule or C-2 through C-6, we were able to distinguish label appearing in the peripheral circulation deriving from unmetabolized glucose from that arising from recycled or fermented glucose (or lactose). Isotopic enrichment of the C-1 of glucose, corrected for recycling, was then calculated during each tracer infusion, and the fraction of dietary lactose subjected to in vivo hydrolysis was estimated from these values and the respective tracer infusion rates, assuming similar absorptive and metabolic fates of labeled glucose arising from either tracer. This fraction averaged 1.02 +/- 0.16 (SD), suggesting that lactose digestion is efficient by 34-wk postconceptional age.
Selective expression of an arachidonate 12-lipoxygenase by pancreatic islet beta-cells
Authors: Shannon V. R. , Ramanadham S. , Turk J. , Holtzman M. J.
Published: December 2017

The immunohistochemical distribution of arachidonate lipoxygenases in rat pancreas was characterized with specific polyclonal anti-5-lipoxygenase and anti-12-lipoxygenase antibodies. Immunohistochemical analysis of formaldehyde-fixed paraffin-embedded rat pancreas using anti-12-lipoxygenase antibody and biotin-avidin-peroxidase detection demonstrated specific staining of islets and no staining of pancreatic exocrine tissue. Less intense staining of pancreatic vascular myocytes and endothelial cells was also observed. Immunoblotting of isolated pancreatic islet extracts with the anti-12-lipoxygenase antibody demonstrated immunoperoxidase staining of a single protein band which comigrated with purified 12-lipoxygenase (relative molecular weight = 72,000) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Dispersed cells prepared from isolated islets and then subjected to fluorescence-activated cell sorting and immunostaining exhibited 12-lipoxygenase antigen in beta-cell populations but not in non-beta-cell (predominantly alpha-cell) populations. Assays of enzymatic activity confirmed that the 12-lipoxygenase-catalyzed conversion of arachidonic acid to 12-hydroxyeicosatetraenoic acid methyl ester occurred only with purified beta-cells and not with islet non-beta-cells. No evidence of 5-lipoxygenase antigen or enzymatic activity was found in purified beta-cells or in islet non-beta-cells. We conclude that rat pancreatic islet beta-cells contain an arachidonate 12-lipoxygenase which shares antigenic epitopes with the homologous enzyme contained in tissues from other species. In addition, the selective localization of the 12-lipoxygenase to pancreatic beta-cells and its absence in pancreatic acinar cells and in islet non-beta-cells support observations suggesting that 12-lipoxygenase products may participate in glucose-induced insulin secretion from beta-cells.
Glucose-induced insulin release in islets of young rats: time-dependent potentiation and effects of 2-bromostearate
Authors: Bliss C. R. , Sharp G. W.
Published: December 2017

The development of glucose-stimulated insulin release and time-dependent potentiation (TDP) has been studied in isolated islets from 7-, 14-, and 21-day-old and 3-mo-old rats. Responses were small at 7 days and changed little at 14 days. At 21 days the amount of insulin released in response to glucose was two times that at 14 days but was still less than one-half that released by 3-mo islets. Glucose-induced TDP was absent at 7 days but was present at 21 days. The second phase response to glucose decreased with perifusion time in 7-, 14-, and 21-day islets. In 7- and 21-day islets, high glucose in the presence of 2-bromostearate, an inhibitor of fatty acid oxidation, prevented the time-dependent decrease in responses; in addition, it induced TDP and enhanced TDP in the 7-day and 21-day islets, respectively. The data suggest that, in the young islet, glucose metabolism fails to inhibit fatty acid oxidation as it does in the mature islet and that this leads to a diminished signal for stimulus-secretion coupling.
Regulation of eukaryotic initiation factor-2B activity in muscle of diabetic rats
Authors: Karinch A. M. , Kimball S. R. , Vary T. C. , Jefferson L. S.
Published: December 2017

Peptide-chain initiation is inhibited in fast-twitch skeletal muscle, but not heart, of diabetic rats. We have investigated mechanisms that might maintain eukaryotic initiation factor (eIF)-2B activity, preventing loss of efficiency of protein synthesis in heart of diabetic rats but not in fast-twitch skeletal muscle. There was no change in the amount or phosphorylation state of eIF-2 in skeletal or cardiac muscle during diabetes. In contrast, eIF-2B activity was decreased in fast-twitch but not slow-twitch muscle from diabetic animals. NADP+ inhibited partially purified eIF-2B in vitro, but addition of equimolar NADPH reversed the inhibition. The NADPH-to-NADP+ ratio was unchanged in fast-twitch muscle after induction of diabetes but was increased in heart of diabetic rats, suggesting that NADPH also prevents inhibition of eIF-2B in vivo. The activity of casein kinase II, which can phosphorylate and activate eIF-2B in vitro, was significantly lower in extracts of fast-twitch, but not cardiac muscle, of diabetic rats compared with controls. The results presented here demonstrate that changes in eIF-2 alpha phosphorylation are not responsible for the effect of diabetes on eIF-2B activity in fast-twitch skeletal muscle. Modulation of casein kinase II activity may be a factor in the regulation of protein synthesis in muscle during acute diabetes. The activity of eIF-2B in heart might be maintained by the increased NADPH/NADP+.
Effects of glucocorticoids on lymphocyte metabolism
Authors: Serrano M. A. , Curi R. , Parry-Billings M. , Williams J. F. , Newsholme E. A.
Published: December 2017

The immunosuppressive effect of glucocorticoids has been widely reported; however, the mechanism of action of these hormones on the immune system has not been fully established. In the present study, the effect of glucocorticoids on glucose, glutamine, and pyruvate metabolism in lymph node lymphocytes was investigated. Addition of dexamethasone to the incubation medium did not alter glucose and glutamine metabolism but inhibited pyruvate utilization by 40%. This latter effect took 1 h to occur and remained for up to 6 h, even after removal of dexamethasone from the culture medium. Measurements of the activity of pyruvate dehydrogenase in lymphocytes and the rate of [1–14C]-pyruvate conversion into 14CO2 in incubated lymphocyte mitochondria demonstrated that glucocorticoids decrease pyruvate utilization by inhibiting the activity of this key regulatory enzyme. The effect of such an inhibition of pyruvate utilization on the function of cells of the immune system remains to be clarified.
Twin study of the 24-h cortisol profile: evidence for genetic control of the human circadian clock
Authors: Linkowski P. , Van Onderbergen A. , Kerkhofs M. , Bosson D. , Mendlewicz J. , Van Cauter E.
Published: December 2017

To determine whether genetic factors control the expression of human circadian rhythmicity, we analyzed the 24-h profile of plasma cortisol in 11 monozygotic and 10 dizygotic pairs of normal male twins. Blood was sampled every 15 min, and sleep was monitored. Circadian rhythmicity was characterized by measures of amplitude, phase, and overall waveshape. Pulsatility was quantified by pulse frequency, pulse amplitude, and relative contribution of pulsatile vs. circadian variations. Data were analyzed by a procedure specifically developed for twin studies. Genetic control was demonstrated for the timing of the nocturnal nadir and for the proportion of overall temporal variability associated with pulsatility. Environmental effects were detected for the 24-h mean and the timing of the morning acrophase. The timing of the cortisol nadir is a robust marker of human circadian phase and is dependent, under entrained conditions, on the length of the endogenous period. Animal studies have shown that the endogenous period and the pattern of entrainment to exogenous 24-h periodicities are genetically controlled. Our results indicate that, despite the increased impact of social inputs, genetic factors also control human circadian rhythmicity.