bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxytocin-mediated recruitment of slowly cycling cross bridges and isometric force in rat myometrium
Authors: Ruzycky A. L. , Ameredes B. T.
Published: December 2017

The relationship between cross-bridge cycling rate and isometric stress was investigated in rat myometrium. Stress production by myometrial strips was measured under resting, K+ depolarization, and oxytocin-stimulated conditions. Cross-bridge cycling rates were determined from measurements of maximal unloaded shortening velocity, using the quick-release method. Force redevelopment after the quick release was used as an index of cross-bridge attachment. With maximal K+ stimulation, stress increased with increased cross-bridge cycling (+76%; P < 0.05) and attached cross bridges (+112%; P < 0.05). Addition of oxytocin during K+ stimulation further increased stress (+30%; P < 0.05). With this force component, the cross-bridge cycling rate decreased (-60%; P < 0.05) similar to that under resting conditions. Attached cross-bridges did not increase with this additional stress. The results suggest two distinct mechanisms mediating myometrial contractions. One requires elevated intracellular calcium and rapidly cycling cross bridges. The other mechanism may be independent of calcium and appears to be mediated by slowly cycling cross bridges, supporting greater unit stress.
Age-related changes in the diurnal rhythm of CRH gene expression in the paraventricular nuclei
Authors: Cai A. , Wise P. M.
Published: December 2017

A circadian rhythm secretion of corticotropin-releasing hormone (CRH) is thought to regulate the circadian pattern of secretion of adrenocorticotropic hormone and corticosterone. We have previously reported that the amplitude of the diurnal rhythm of serum corticosterone concentrations decreases in 17- to 20-mo-old rats. In the present experiment, we tested whether an age-related alteration in the daily rhythm and/or level of CRH mRNA in the paraventricular nuclei (PVN) occurs during middle age. Groups of young and middle-aged animals were killed at several times of day. We assessed the level of CRH mRNA in the PVN and dorsal medial subdivision of the PVN using in situ hybridization. In young rats, CRH mRNA expression exhibited a diurnal rhythm in the dorsal medial PVN. The same trend was observed in the entire medial PVN. In middle-aged rats, no rhythm was detected in either region. The overall average level of CRH mRNA was not different between these two age groups. These findings suggest that changes in the suprachiasmatic nucleus or in its ability to entrain neuroendocrine outputs occur relatively early during the aging process.
Influences of dietary energy and protein on leucine kinetics during feeding in healthy adults
Authors: Gibson N. R. , Fereday A. , Cox M. , Halliday D. , Pacy P. J. , Millward D. J.
Published: December 2017

Ten adult men were infused with L-[1-13C]leucine for 9 h commencing in the postabsorptive state (PA, 0-3 h), during the half-hourly feeding of low-protein meals (LP, protein = 2% calories, 3-6 h), and during feeding isoenergetic high-protein meals (HP, protein = 14% calories, 6-9 h). Leucine oxidation and turnover (protein synthesis and degradation) were determined from plasma alpha-[1-13C]ketoisocaproate enrichment and expired 13CO2 excretion measured during the third hour of each 3-h period. Plasma insulin increased markedly with feeding to a level that was maintained with both diets. The negative postabsorptive leucine balance became less negative during the LP meals (P < 0.01) and was positive with the HP meals (P < 0.01). The significant responses to feeding (all P < 0.01) were for oxidation -13% (PA-LP), +50% (LP-HP), and +29% (PA-HP); for degradation -24% (PA-LP), -30% (LP-HP), and -47% (PA-HP); and for synthesis -14% (PA-LP), +29% (LP-HP), and +11% (PA-HP). These data support a feeding mechanism involving both an insulin-mediated, protein-conserving influence of dietary energy that inhibits degradation, lowers amino acid levels, and reduces oxidation, and amino acid-mediated augmentation of the inhibition of degradation, a stimulation of synthesis, and an increase in oxidation when leucine dietary supply exceeds the capacity for its net deposition.
Postmarathon paradox: insulin resistance in the face of glycogen depletion
Authors: Tuominen J. A. , Ebeling P. , Bourey R. , Koranyi L. , Lamminen A. , Rapola J. , Sane T. , Vuorinen-Markkola H. , Koivisto V. A.
Published: December 2017

Acute physical exercise enhances insulin sensitivity in healthy subjects. We examined the effect of a 42-km marathon run on insulin sensitivity and lipid oxidation in 19 male runners. In the morning after the marathon run, basal serum free fatty acid concentration was 2.2-fold higher, muscle glycogen content 37% lower (P < 0.01), glycogen synthase fractional activity 56% greater (P < 0.01), and glucose oxidation reduced by 43% (P < 0.01), whereas lipid oxidation was increased by 55% (P < 0.02) compared with the control study. During euglycemic-hyperinsulinemic clamp, whole body glucose disposal was decreased by 12% (P < 0.01) because of a 36% lower glucose oxidation rate (P < 0.05), whereas the rate of lipid oxidation was 10-fold greater (P < 0.02) than in the control study. After the marathon, muscle glycogen content correlated positively with lipid oxidation (r = 0.60, P < 0.05) and maximal aerobic power (Vo2peak; r = 0.61, P < 0.05). Vo2peak correlated positively with basal lipid oxidation (r = 0.57, P < 0.05). In conclusion, 1) after the marathon run, probably because of increased lipid oxidation, the insulin-stimulated glucose disposal is decreased despite muscle glycogen depletion and the activation of glycogen synthase; 2) the contribution of lipid oxidation in energy expenditure is increased in proportion to physical fitness; 3) these adaptations of fuel homeostasis may contribute to the maintenance of physical performance after prolonged exercise.
kappa-Opioid agonist inhibition of osmotically induced AVP release: preferential action at hypothalamic sites
Authors: Rossi N. F. , Brooks D. P.
Published: December 2017

Although several studies indicate that kappa-opioid agonists induce a water diuresis by inhibiting vasopressin (AVP) secretion, the locus of the kappa-receptors (neurohypophysial vs. hypothalamic) responsible for this effect remains unclear. We have ascertained the effect of the selective kappa-agonist BRL-52656 (BRL) on AVP secretion by using compartmentalized rat hypothalamoneurohypophysial explants in culture. When applied to the hypothalamus, nanomolar concentrations of BRL inhibited osmotically stimulated AVP secretion. This response was blocked by the highly selective kappa-opioid antagonist nor-binaltorphimine (BNI). However, osmotically stimulated AVP release was suppressed at the neurohypophysial site only by 100 nM BRL and was not reversed by BNI but only by naloxone. This dose of BRL, administered to the posterior pituitary compartment, did not appear to act by the agonist gaining access to hypothalamic kappa-opiate receptors, because BNI added to the hypothalamus failed to prevent the inhibition of AVP secretion. The data demonstrate that BRL is a potent inhibitor of osmotically stimulated AVP secretion via activation of kappa-opiate receptors within the hypothalamus, but that higher concentrations of the drug may also stimulate non-kappa-neurohypophysial opiate receptors that suppress AVP release.
Progesterone binding to mineralocorticoid receptors: in vitro and in vivo studies
Authors: Myles K. , Funder J. W.
Published: December 2017

In previous studies using expressed recombinant human mineralocorticoid receptors (MR), progesterone was reported to have widely divergent affinity, from approximately 10 nM to < 10 pM. In the present studies, cytosol preparations of colon or hippocampus were incubated with [3H]aldosterone or [3H]progesterone, alone or with excess RU-486, and the ability of each steroid to compete for MR was determined. In guinea pigs, progesterone has equivalent affinity to aldosterone for MR in vitro, and in rats three times of that aldosterone, with no differences between tissues. In vivo, in both epithelial (kidney, colon) and nonepithelial tissues (heart, hippocampus), progesterone was 10- to 100-fold less potent a competitor than aldosterone for MR, both in the absence of transcortin (8-day-old rats) and in adult mice. Bolus injection of [3H]progesterone was not specifically bound in any of the four tissues. Whether progesterone at steady state may bid for MR occupancy under conditions of high circulating free levels (in utero, luteal phase, pregnancy), presumably to act as an antagonist to cortisol/corticosterone in unprotected nonepithelial receptors, thus remains to be determined.
Norepinephrine and serotonin vasoconstriction in rat hindlimb control different vascular flow routes
Authors: Newman J. M. , Dora K. A. , Rattigan S. , Edwards S. J. , Colquhoun E. Q. , Clark M. G.
Published: December 2017

The vasoconstrictors, norepinephrine at low dose ( < or = 0.1 microM; LDNE) and serotonin (5-HT), produce opposing metabolic effects in the constant-flow perfused rat hindlimb characterized by increased and decreased oxygen uptake, respectively. In the present study, the effects of each vasoconstrictor are compared in the red blood cell-free buffer-perfused hindlimb on postequilibration endogenous red blood cell efflux, vascular entrapment of fluorescein-labeled dextran (Fx), and vascular corrosion casting by use of 30-micron spheres of methyl methacrylate (MM). A marked transient washout of red blood cells occurred immediately in association with vasoconstriction induced by LDNE that was not apparent when a similar extent of vasoconstriction was induced by 5-HT. Fx perfusions indicated that LDNE recruited a new vascular space that was reaccessed by a second exposure to the vasoconstrictor. 5-HT closed off a previously perfused vascular space that was reaccessed when the vasoconstrictor was removed. Corrosion casting of the arterial tree with MM showed no increase in cast weight, but more vessels filled because of LDNE. Higher doses of NE (2.5 microM) or 5-HT caused a marked decrease in cast weight with fewer vessels filled. The data suggest that LDNE and 5-HT, in association with vasoconstriction at different sites, control different capillary flow routes in the hindlimb that in turn may influence metabolism by increasing or decreasing nutrient access, respectively.
Role of fat-derived substrates in the regulation of gluconeogenesis during fasting
Authors: Fery F. , Plat L. , Melot C. , Balasse E. O.
Published: December 2017

To determine the role of fat-derived substrates in the regulation of glucose metabolism during fasting, glucose turnover, urea nitrogen production, alanine conversion to glucose, and substrate oxidation rates were measured in 34 normal 4-day-fasted volunteers treated with the antilipolytic drug acipimox or placebo for 8 h. The approximately 50% inhibition of lipolysis induced by acipimox increased glucose concentration and production, respectively, by approximately 35 and approximately 30%, whereas the protein breakdown and the amount of alanine converted to glucose were increased, respectively, by approximately 70 and approximately 85%. Insulin levels were reduced by approximately 40%, cortisol levels doubled, and growth hormone concentration increased sevenfold. The relative contribution of free fatty acid (FFA) and ketone body lowering to the observed response was evaluated in nine acipimox-treated subjects in whom ketone body concentration was clamped with an intravenous beta-hydroxybutyrate infusion. The results of these experiments suggest that, during fasting, both FFA and ketone bodies tend to suppress gluconceogenesis and to protect the protein stores. FFA seem to exert their effects mainly through their ability to modulate the hormonal milieu (especially insulin), whereas ketone bodies seem to act mainly by other mechanisms. Thus the widespread view according to which FFA exert a stimulatory role on gluconeogenesis does not apply to the fasting state in vivo.
Properties of AT1a and AT1b angiotensin receptors expressed in adrenocortical Y-1 cells
Authors: Tian Y. , Baukal A. J. , Sandberg K. , Bernstein K. E. , Balla T. , Catt K. J.
Published: December 2017

Adrenocortical Y-1 cells were stably transfected with the AT1a and AT1b subtypes of the rat angiotensin (ANG)IIAT1 receptor cDNA to study the pharmacological and functional properties of the two receptors. Selected clones of transfected cells expressing the AT1a or AT1b receptor subtypes bound the native ligand ANG II and the peptide antagonist [Sar1,Ile8]ANG II with similar affinities, but they differed in their relative affinities for the nonpeptide antagonist losartan (half-maximal inhibitory concentration 9.7 and 4.7 nM), ANG III (126 and 33 nM), and the peptide antagonist [Sar1,Gly8]ANG II (6.2 and 1.2 nM). Photoaffinity labeling of the expressed receptors revealed a single component of 65 kDa for both receptor subtypes, suggesting that both receptors were glycosylated in a similar manner. The sensitivity of 125I-ANG II binding to AT1a and AT1b receptors to guanine nucleotides was unaffected by pertussis toxin treatment. ANG II stimulated the formation of inositol phosphates and increased the level of cytoplasmic Ca2+ in both At1a- and AT1b-transfected Y-1 cells. However, ANG II had little effect on forskolin-induced adenosine 3',5'-cyclic monophosphate accumulation, causing only minor inhibition in AT1a-transfected cells and slight enhancement in AT1b-transfected cells. These data indicate that AT1a and AT1b receptors show small but significant differences in their binding pharmacology and, upon activation, are coupled through Gq/G11 to the phosphoinositide-Ca2+ signaling pathway. However, neither AT1a nor AT1b receptors exhibit coupling to Gi and inhibition of adenylate cyclase when expressed in murine adrenal tumor cells.
TNF directly stimulates glucose uptake and leucine oxidation and inhibits FFA flux in conscious dogs
Authors: Sakurai Y. , Zhang X. J. , Wolfe R. R.
Published: December 2017

We tested the hypothesis that the metabolic changes in glucose, lipid, and protein metabolism seen during tumor necrosis factor (TNF) infusion were due to the increase in plasma glucagon concentration rather than to the direct effects of TNF. We employed a pancreatic clamp technique to keep plasma insulin and glucagon concentrations constant throughout a 4-h isotope infusion. Glucose, lipid, and protein kinetics were measured by means of the primed, constant infusion of [6,6-2H]glucose, [2H5]glycerol, [2H2]palmitic acid, and [1-13C]leucine. After a 2-h baseline period (period 1), TNF was infused as a primed, constant infusion (prime, 2.5 micrograms/kg; constant infusion, 62.5 ng.kg-1.min-1) for 2 h (period 2). Whereas plasma glucose concentration dropped significantly during TNF infusion, endogenous glucose production did not change. The decrease in glucose concentrations was due to a stimulation of glucose clearance (P < 0.05). The rate of lipolysis did not decrease significantly, but free fatty acid (FFA) flux and plasma FFA concentration significantly decreased during TNF infusion (P < 0.05). The rate of appearance of leucine was not affected by TNF infusion, but TNF caused a significant increase in 13CO2 excretion (P < 0.05) and leucine oxidation (P < 0.05). The calculated rates of whole body protein synthesis decreased. We concluded that TNF did not directly affect glucose production. Furthermore, changes in protein and lipid kinetics during TNF infusion were not mediated by changes in insulin or glucagon and may have reflected direct effects of TNF.
Glutamine interferes with glucocorticoid-induced expression of glutamine synthetase in skeletal muscle
Authors: Hickson R. C. , Wegrzyn L. E. , Osborne D. F. , Karl I. E.
Published: December 2017

Skeletal muscle atrophy from glucocorticoids is prevented by glutamine infusion. Because the gene-encoding glutamine synthetase (GS) is glucocorticoid inducible, it represented an appropriate model for resting whether glucocorticoids and glutamine exert opposing actions on the expression of specific genes related to atrophy in muscle tissue. Rats were administered hydrocortisone 21-acetate or the dosing vehicle (carboxymethyl cellulose) and were infused with saline (Sal) or glutamine (Gln, 240 mM, 0.75 ml/h) for 7 days. Hormone treatment did not significantly lower glutamine levels in fast-twitch white or red regions of the quadriceps. Despite higher serum glutamine concentrations with amino acid infusion [1.52 +/- 0.03 (Gln) vs. 1.20 +/- 0.04 (Sal) mumol/ml], muscle glutamine concentrations were not markedly increased in these fiber types. In saline-infused animals, glucocorticoid treatment produced 200-300% increases in plantaris, fast-twitch white, and fast-twitch red muscle GS enzyme activity and mRNA. Moreover, in all muscle types studied, glutamine infusion diminished glucocorticoid effects on GS enzyme activity to 131-159% and on GS mRNA to 110-200% of the values in saline-treated controls. These data demonstrate that glutamine infusion results in inhibiting GS expression, but the absence of changes in muscle glutamine concentration suggests the interplay of additional regulators of the GS gene.
GHRH activates a nonselective cation current in human GH-secreting adenoma cells
Authors: Takano K. , Takei T. , Teramoto A. , Yamashita N.
Published: December 2017

Electrophysiological responses induced by human (h) growth hormone-releasing hormone (GHRH) were analyzed using the perforated whole cell clamp technique in human growth hormone (GH)-secreting adenoma cells. Application of hGHRH depolarized the membrane by increasing Na+ conductance. The reversal potential of the hGHRH-induced current was -20 to 0 mV. The channel was permeable to Na+, Li+ and K+ but not to TMA+. These properties were compatible with those of nonselective cation channels. Similar nonselective cation current was activated by 8-bromoadenosine 3',5'-cyclic monophosphate and forskolin, and the activation of the hGHRH-induced current was inhibited by protein kinase A (PKA) inhibitors, (R)-p-adenosine 3',5'-cyclic monophosphate and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoleinsulfonamide, and PKA inhibitor peptide PKI-(5-24), indicating that hGHRH-induced current was activated by PKA. Cholera toxin pretreatment eliminated the hGHRH-induced current, suggesting that Gs is involved in the activation of this current. This current became irreversible when the cells were pretreated with okadaic acid, suggesting that the recovery of the hGHRH-induced current was mediated by a serine/threonine protein phosphatase. GHRH-induced GH secretion was inhibited in Na+-free medium, suggesting the importance of the nonselective cation current on hGHRH-induced GH secretion. In human GH-secreting nonadenoma cells, hGHRH increased Na+ conductance, as was the case in GH-secreting adenoma cells.
Acute effect of epinephrine on muscle proteolysis in perfused rat hindquarters
Authors: Kadowaki M. , Kamata T. , Noguchi T.
Published: December 2017

An acute and direct effect of epinephrine (Epi) on muscle proteolysis was investigated using a single-pass mode of rat hindquarter perfusion. The rate of tyrosine (Tyr) release at > 30 min with cycloheximide was regarded as the muscle proteolytic rate. Infusion of Epi (500 nM) to the hindquarters of fed rats led to a sharp decrease in the Tyr release to 50% within 5 min, accompanied by an increase in perfusion pressure and edema around the perfused tissues. To clarify the mechanism, alpha- and beta-antagonists were used together with Epi. A mixture of 10 microM prazosin and 10 microM yohimbine (alpha-adrenergic blockade) before or after Epi infusion completely prevented the edema development and resulted in a new steady state to 80% of the initial rate. On the contrary, 100 microM propranolol (a beta-antagonist) with Epi did not abolish the edema and caused fluctuation in Tyr release. Whether the above results are affected by changes in Tyr transport at the plasma membrane was tested by measuring Tyr efflux from the perfused muscle. Only a beta-adrenergic blockade significantly reduced the rate constant of Tyr efflux from the intracellular pool by 13%. These results suggested that the suppression of Tyr release by alpha-adrenergic activity was mainly due to the effect on Tyr efflux, whereas that by beta-adrenergic activity was not at the Tyr transport level but at the proteolysis level, demonstrating that Epi directly inhibits proteolysis of skeletal muscle via the beta-adrenoceptor.
Acid-base homeostasis parallels anabolism in surgically stressed rats treated with GH and IGF-I
Authors: Evans S. J. , Lo H. C. , Ney D. M. , Welbourne T. C.
Published: December 2017

The effect of a standard surgical stress and subsequent total parenteral nutrition (TPN) treatment on systemic acid-base balance was assessed in four groups of rats: TPN controls, TPN coinfused with recombinant human insulin-like growth factor I (rhIGF-I, 800 micrograms/day), TPN with recombinant human growth hormone (rhGH, 800 micrograms in two divided daily sc doses), and combined rhGH plus rhIGF-I (800 + 800 micrograms/day). After the 6-day time course, TPN controls exhibited a systemic metabolic acidosis (HCO3- = 20.4 +/- 0.4 mM) and lost 7 g body wt/6 days. Either growth factor ameliorated the acidosis (rhGH = 22.6 +/- 0.6 and IGF-I = 22.0 +/- 0.5 mM) and promoted weight gain (11 +/- 2 and 10 +/- 3 g/6 days, respectively). Combined growth factor treatment, rhGH+rhIGF-I, restored acid-base balance (HCO3- = 24.7 +/- 0.6 mM) and exhibited an additive effect on weight gain (25 +/- 3 g/6 days). Ammonium and sulfate excretion as indexes of renal acid excretion and systemic sulfuric acid production, respectively, were highest in the TPN control, Growth factors alone reduced sulfuric acid production, whereas combined growth factor treatment reduced acid production and eliminated acid excretion despite elevated renal glutaminase activity. However, renal cortical glutamate content was elevated in the combined growth factor treatment (10.6 +/- 0.7 vs. 7.3 +/- 0.5 rhGH+rhIGF-1 vs. TPN, P < 0.05), consistent with repression of the elevated glutaminase activity. These findings point to an important role for acid-base homeostasis in the anabolic response and are consonant with an additive effect of growth factors, rhGH+rhIGF-I, in correcting the metabolic acidosis associated with surgical stress.
Precursor pool for hepatic protein synthesis in humans: effects of tracer route infusion and dietary proteins
Authors: Cayol M. , Boirie Y. , Prugnaud J. , Gachon P. , Beaufrere B. , Obled C.
Published: December 2017

The estimation of the hepatic protein synthesis precursor pool was investigated through the measurement of very low-density lipoprotein (VLDL) apolipoprotein (apo)B100 labeling in healthy volunteers. L-[1-13C]leucine and L-[5,5,5-2H3]leucine were administered intravenously and intragastrically, respectively. Subjects were continuously fed with isoenergetic meals providing either 16% protein or no protein. The labeling of leucine incorporated into VLDL apoB100 (leucine-apoB) was lower than plasma leucine or alpha-ketoisocaproate (KIC) enrichments with the intravenous tracer. By contrast, with the oral tracer, leucine-apoB enrichment was higher than either plasma free leucine or KIC labeling. The KIC and leucine-apoB enrichments relative to plasma leucine enrichment were not affected by protein intake. Albumin or fibrinogen synthesis rates were similar whatever the administration route of the tracer when leucine-apoB was used to indicate the precursor, which was not the case for plasma leucine or KIC. The present data suggest that leucine-apoB enrichment represents a reliable indicator of the hepatic precursor pool for protein synthesis. The effect of dietary protein on the calculated rates of albumin and fibrinogen synthesis is also reported in relation to the choice of the precursor.
Role of nitric oxide resistance in erythropoietin-induced hypertension in rats with chronic renal failure
Authors: Vaziri N. D. , Zhou X. J. , Naqvi F. , Smith J. , Oveisi F. , Wang Z. Q. , Purdy R. E.
Published: December 2017

We studied the mechanism of erythropoietin (EPO)-induced hypertension (HTN) in rats with chronic renal failure (CRF). After partial nephrectomy, rats were randomized into four groups. Group A received EPO, 150 U/kg, two times weekly for 6 wk to prevent anemia; group B received placebo injections and became anemic; group C received EPO but was kept anemic by dietary iron deficiency; and group D received placebo and regular transfusions to match hematocrit (Hct) in group A. Blood pressure (BP), Hct, platelet cytosolic calcium ([Ca2+]i) and magnesium concentration, and pressor and vasodilatory responses were determined. By design, Hct in groups A and D were comparable and significantly greater (P < 0.01) than in groups B and C. Despite divergent Hct values, the EPO-treated groups A and C showed a significant rise in BP compared with the placebo-treated groups B and D. HTN occurred whether EPO therapy was begun immediately or 4 wk after nephrectomy. EPO therapy augmented the elevation of basal [Ca2+]i and restored the defective thrombin-mediated rise of platelet [Ca2+]i in CRF animals. EPO therapy did not alter caudal artery contraction in response to either 68 mM K(+)-induced depolarization, angiotensin II or alpha 1-agonist, methoxamine in vitro, or the pressor response to angiotensin II in vivo. However, EPO therapy impaired the hypotensive response to nitric oxide (NO) donors, sodium nitroprusside and S-nitroso-N-acetyl-D,L-penicillamine, and reversed the CRF-induced upregulation of guanosine 3',5'-cyclic monophosphate production by thoracic aorta in vitro. Thus EPO-induced HTN in CRF rats is Hct independent and is associated with and perhaps causally related to increased basal and stimulated [Ca2+]i and impaired vasodilatory response to NO.
Role of the lactate transporter (MCT1) in skeletal muscles
Authors: McCullagh K. J. , Poole R. C. , Halestrap A. P. , O'Brien M. , Bonen A.
Published: December 2017

We used an antibody, constructed against the monocarboxylate transporter 1 (MCT1) protein (L. Carpenter, R. C. Poole, and A. P. Halestrap. Biochim. Biophys. Acta 1279: 157-165, 1996), to study the expression and role of MCT1 in rat skeletal muscles. MCT1 was higher in red than in white muscles (P < 0.05) and was highly correlated with the oxidative fiber content (%slow-twitch oxidative + %fast-twitch oxidative glycolytic) of skeletal muscles (r = 0.91). MCT1 was highly related to lactate uptake in skeletal muscles (r = 0.90). Total lactate dehydrogenase (LDH) activity, an index of glycolysis, was negatively correlated with MCT1 in rat muscles (r = -0.80). MCT1 was also strongly correlated with the heart-type forms of LDH (LDH-1 vs. MCT1, r = 0.83; LDH-2 vs. MCT1, r = 0.89). There was no relationship between MCT1 and the muscle form of LDH (LDH-5; P > 0.05). MCT1 was highly correlated with citrate synthase activity, a marker of the oxidative capacity of muscle (r = 0.82). Therefore, MCT1 may have kinetics that favor the uptake of L-lactate into the muscle cell for oxidative metabolism, and MCT1 may be coordinately expressed with the heart forms of LDH and enzymes of oxidative metabolism.
T3 potentiates the adrenergic stimulation of type II 5'-deiodinase activity in cultured rat brown adipocytes
Authors: Hernandez A. , Obregon M. J.
Published: December 2017

Iodothyronine type II 5'-deiodinase (5'D-II) activities were studied in cultures of rat brown adipocytes. In the presence of serum, the adrenergically stimulated 5'D-II activities were very low. In the absence of serum, adenosine 3',5'-cyclic monophosphate (cAMP) analogues stimulated 5'D-II activity. Thyroxine (T4) inhibited these increases. Norepinephrine slightly increased 5'D-II activity in hypothyroid conditions, but 3,5,3'-triiodothyronine (T3) strongly potentiated the adrenergic stimulation of 5'D-II (20-fold). T3 amplification of the adrenergic stimulation was via beta-adrenergic receptors, specifically mimicked by beta3-agonists, but it was not observed using cAMP analogues. The stimulatory effect of T3 predominated over the inhibitory action of T4, increased with exposure to T3, and required de novo protein synthesis. The half-life of 5'D-II was 30 min, suggesting that stabilization of 5'D-II did not occur. The effect was only observed in differentiated adipocytes. Retinoic acid has similar although smaller effects than T3. In conclusion, the presence of T3 is required and strongly potentiates the noradrenergic stimulation of 5'D-II activity in rat brown adipocytes.
Lack of effect of an acute ileal perfusion of short-chain fatty acids on glucose metabolism in healthy men
Authors: Alamowitch C. , Boillot J. , Boussairi A. , Ruskone-Fourmestraux A. , Chevalier A. , Rizkalla S. W. , Guyon F. , Bornet F. R. , Slama G.
Published: December 2017

Dietary fiber intake is associated with several beneficial effects on carbohydrate metabolism. Some authors have speculated that this improvement may be due to short-chain fatty acids (SCFA) produced by the colonic fermentation of dietary fibers. To test this hypothesis, six healthy men aged 26 +/- 2 (SE) yr with a body mass index of 20.9 +/- 0.7 received on three occasions an 18-h ileal perfusion infused at a flow rate of 3.3 ml/min, containing either 90 mmol/l of SCFA (60% acetate, 25% propionate, and 15% butyrate) (A), SCFA during the first 12 h and then a saline solution (A/S), or a saline solution (S). Basal hepatic glucose production (BHGP), insulin sensitivity (3-step euglycemic-hyperinsulinic clamp), and erythrocyte insulin binding (EIB) were studied 12 h after the beginning of the ileal perfusion. There was no change in BHGP or insulin sensitivity. However, maximal EIB was significantly different: 7.1 +/- 0.1 (A), 6.8 +/- 0.1 (A/S), vs. 6.5 +/- 0.1% (S) (P = 0.03). We conclude that acute administration of SCFA does not significantly alter glucose metabolism in healthy subjects.
Adipose tissue stearoyl-CoA desaturase mRNA is increased by obesity and decreased by polyunsaturated fatty acids
Authors: Jones B. H. , Maher M. A. , Banz W. J. , Zemel M. B. , Whelan J. , Smith P. J. , Moustaid N.
Published: December 2017

Stearoyl-CoA desaturase (SCD) is a key regulatory enzyme in the synthesis of unsaturated fatty acids. Although regulation of hepatic SCD by obesity and polyunsaturated fatty acids (PUFA) has been well investigated, no studies have addressed whether similar regulation occurs in adipose tissue. We addressed these questions by feeding control (12% corn oil) and high-PUFA (48% corn oil) diets to lean and obese Zucker rats and analyzing SCD mRNA levels in adipose tissue and liver. We report that SCD mRNA content was dramatically elevated in adipose tissue of obese vs. lean rats on both diets and was significantly decreased by PUFA in both genotypes. Interestingly, we demonstrate that SCD expression was directly downregulated in a dose dependent manner by PUFA in 3T3-L1 adipocytes. We conclude that 1) obese Zucker rats overexpress the SCD gene in both liver and adipose tissue and 2) PUFA directly suppress SCD expression in adipocytes. Further studies will elucidate the mechanisms responsible for obesity- and PUFA-mediated regulation of SCD in adipose cells.
Role for GTP in glucose-induced phospholipase C activation in pancreatic islets
Authors: Vadakekalam J. , Rabaglia M. E. , Chen Q. H. , Metz S. A.
Published: December 2017

We have previously demonstrated a permissive role for GTP in insulin secretion; in the current studies, we examined the effect of GTP on phospholipase C (PLC) activation to explore one possible mechanism for that observation. In rat islets preexposed to the GTP synthesis inhibitors mycophenolic acid (MPA) or mizoribine (MZ), PLC activation induced by 16.7 mM glucose (or by 20 mM alpha-ketoisocaproic acid) was inhibited 63% without altering the labeling of phosphoinositide substrates. Provision of guanine, which normalizes islet GTP content and insulin release, prevented the inhibition of PLC by MPA. Glucose-induced phosphoinositide hydrolysis was blocked by removal of extracellular Ca2+ or by diazoxide. PLC induced directly by Ca2+ influx (i.e., 40 mM K+) was reduced 42% in MPA-pretreated islets but without inhibition of the concomitant insulin release. These data indicate that glucose-induced PLC activation largely reflects Ca2+ entry and demonstrate (for the first time in intact cells) that adequate GTP is necessary for glucose (and Ca(2+)-)-induced PLC activation but not for maximal Ca(2+)-induced exocytosis.
Effects of refeeding of undernourished and insulin treatment of diabetic neonatal rats on IGF and IGFBP
Authors: Goya L. , Rivero F. , Martin M. A. , Arahuetes R. , Hernandez E. R. , Pascual-Leone A. M.
Published: December 2017

The effect of refeeding and insulin treatment of undernourished and diabetic neonatal rats, respectively, on the regulation of insulin-like growth factor (IGF) and insulin-like growth factor binding protein (IGFBP) was investigated. The changes in body weight, insulinemia, glycemia, serum IGF-I, and growth hormone (GH) as well as the increase of the 30-kDa IGFBP in undernourished and diabetic neonatal rats previously shown elsewhere were reversed by refeeding and insulin treatment, respectively. Also, changes in liver mRNA expression of IGF-I and-II and IGFBP-1 and -2 were restored in refed undernourished and IGF-I and IGFBP-1 levels recovered in insulin-treated diabetic rats. However, serum GH was still below normal after rehabilitation in both situations. Thus the present results support the idea of a GH-independent IGF/ IGFBP regulation mediated by a balance of insulin and nutrients as has already been suggested in previous neonatal studies.
Effects of heparin on renal morphology and albuminuria in experimental diabetes
Authors: Marshall S. M. , Hansen K. W. , Osterby R. , Frystyk J. , Orskov H. , Flyvbjerg A.
Published: December 2017

Female nondiabetic and streptozotocin diabetic Wistar rats received 200 units heparin two times daily by subcutaneous injection for 6 mo. Mesangial volume fraction was reduced in heparin-treated control (CH) compared with untreated control (C) animals (CH 0.18 +/- 0.02 vs. C 0.24 +/- 0.02, P < 0.05), but other histological parameters were similar. In the heparin-treated diabetic (DH) group, wet kidney weight was increased compared with the untreated diabetic (D) group (DH 1,156 +/- 39 vs. D 1,050 +/- 30 mg, P < 0.05), as were absolute, but not fractional, glomerular volume (P < 0.05) and capillary volume (P < 0.05). Basement membrane thickness (DH 193 +/- 3 vs. D 231 +/- 9 nm, P < 0.01) and mesangial/glomerular volume fraction (P < 0.001) were decreased. Urinary albumin excretion was increased in the heparin-treated control animals compared with control animals [CH 980 (range 150-4,448) vs. C 221 (range 86-654) micrograms/24 h, P < 0.001] and in the heparin-treated diabetic animals compared with the diabetic animals [DH 12,785 (range 4,495-29,520) vs. D 899 (range 450-1,335) micrograms/24 h, P < 0.001]. Thus the possibly deleterious increases in glomerular capillary volume and albumin excretion may negate the beneficial effects of heparin on mesangial and basement membrane structures.
Regulation of obese gene expression in KK mice and congenic lethal yellow obese KKAy mice
Authors: Hayase M. , Ogawa Y. , Katsuura G. , Shintaku H. , Hosoda K. , Nakao K.
Published: December 2017

To elucidate the regulation of obese (ob) gene expression in obesity and diabetes, we examined ob gene expression in KK mice and congenic lethal yellow obese KKAy mice. Northern blot analysis revealed that the ob mRNA levels are roughly equivalent in each of the epididymal, mesenteric, and subcutaneous white adipose tissue (WAT) from KK and KKAy mice at 4 wk of age, when the obese phenotype of KKAy mice was not apparent. Expression of the ob gene was augmented in the mesenteric and subcutaneous WAT but was unchanged in the epididymal WAT in KKAy mice at 12 wk of age, when KKAy mice developed marked obesity with hyperglycemia, hyperlipidemia, and hyperinsulinemia. The ob gene expression was also examined during fasting in 12-wk-old KK and KKAy mice. After 24 or 72 h of fasting in both mouse strains, ob gene expression was downregulated in the epididymal and mesenteric WAT but was unchanged in the subcutaneous WAT. The present study demonstrates that adipose tissue expression of the ob gene is regulated depending on the nutritional status in KK and KKAy mice.
Decreased glucose-induced cAMP and insulin release in islets of diabetic rats: reversal by IBMX, glucagon, GIP
Authors: Dachicourt N. , Serradas P. , Giroix M. H. , Gangnerau M. N. , Portha B.
Published: December 2017

The first aim of the study was to investigate the possibility that a defect on the islet adenosine 3',5'-cyclic monophosphate (cAMP) production could be involved in the failure of the glucose-induced insulin secretion in the neonatal streptozotocin diabetic rats. Exposure to glucose concentration that induced a rise of the cAMP content in the control islets did not elicit any significant increase in cAMP in diabetic islets. Forskolin, isobutyl methylxanthine (IBMX), glucagon, or pertussis toxin amplified the cAMP accumulation and the insulin release to the same extent in both types of islets. Somatostatin, prostaglandin E2, UK-14304, or galanin inhibited cAMP accumulation and insulin release to the same extent in both types of islets. Our second purpose was to investigate whether the use of activators of adenylate cyclase could restore the beta-cell competence to glucose in diabetic rats. The addition of IBMX, glucagon, or gastric inhibitory polypeptide (GIP) to perifused islets of diabetic rats amplified their insulin response to glucose, and a clear biphasic pattern of the release was regained. In conclusion, although there is no major alteration of the functionality of the adenylate cyclase in the beta-cells of the diabetic rats, we have identified a defective glucose-induced cAMP generation that could be explained by a block in the step(s) linking glucose metabolism and activation of adenylate cyclase.
Application of probability-generating functions in evaluation of some isotopomer distributions
Authors: Kotz S.
Published: December 2017

A method for calculating probability functions and moments of a distribution of isotopomers, constructed by Kelleher and Masterson (2), is described. The method involves the use of the so-called probability-generating functions, a mathematical device especially convenient for the purpose of calculation of probabilistic quantities in discrete models of the Kelleher-Masterson type.
Altered metabolism and superoxide generation in neural tissue of rat embryos exposed to high glucose
Authors: Yang X. , Borg L. A. , Eriksson U. J.
Published: December 2017

Oxygen uptake and glucose utilization of embryonic and fetal neural tissue of normal and diabetic rat pregnancy were studied. Exposure to 50 mM glucose inhibited oxygen uptake of embryonic neural tissue of normal rats by 28% at gestational day 9 (P < 0.001) and 20% at days 10-12 and 15 (P < 0.001) and stimulated glucose utilization by 132% at day 9 (P < 0.001), 50% at days 10 and 11 (P < 0.01), 168% at day 12 (P < 0.001), and 338% at day 15 (P < 0.001), indicating a Crabtree effect. The glucose-altered metabolism led to production of superoxide by the tissue, which was 1.8 to 2.4 nmol.h-1.microgram DNA-1 at days 9-12 and 1.2 nmol.h-1.microgram DNA-1 at day 15. The embryonic neural tissue of diabetic rats showed a diminished metabolic sensitivity to high glucose exposure, suggesting an impaired mitochondrial function. Consequently, the glucose-induced superoxide production was not detected in the tissue of embryos of diabetic rats. The data suggest that high concentration of glucose alters embryonic and fetal metabolism and causes generation of superoxide. Prolonged duration of the glucose-induced metabolic changes may impair cellular function and lead to embryonic dysmorphogenesis.
Retinol is specifically required during midgestation for neonatal survival
Authors: Wellik D. M. , Norback D. H. , DeLuca H. F.
Published: December 2017

Previous work has demonstrated that vitamin A-deficient, retinoic acid-supplemented pregnant rats cannot complete gestation without the administration of retinol. As little as 2 micrograms administered on day 10 of gestation is sufficient to prevent the characteristic fetal resorption that begins at day 15 of gestation. This single dose of retinol supports continued development through day 20 of gestation. However, if gestation is allowed to proceed to parturition, the newborn pups die within a few minutes of being severed from the umbilical cord. The pups are born with a pink and healthy skin tone, but within seconds of umbilical separation, they begin to gasp for air, become cyanotic in appearance, and die within several minutes from an apparent inability to obtain oxygen. Histological examination of these neonates demonstrates delayed pulmonary development. Branching and scalloping of ducts and saccule and subsaccule formation are decreased. This phenotype is consistent with that observed in respiratory distress syndrome seen in some premature human infants.
Use of labeling pattern of liver glutamate to calculate rates of citric acid cycle and gluconeogenesis
Authors: Large V. , Brunengraber H. , Odeon M. , Beylot M.
Published: December 2017

The use of the labeling pattern of hepatic glutamate during infusion of L-[3-13C]- or [3-14C]lactate to calculate rates of citric acid cycle activity and gluconeogenesis has been proposed. We tested the validity of this approach by perfusing isolated rat livers (48 h starved) with pyruvate and lactate (10% enriched with [3-13C]lactate) without (control) or with infusion of glucagon (to inhibit pyruvate kinase), mercaptopicolinate (to inhibit phosphoenolpyruvate carboxykinase), or dichloroacetate (to stimulate pyruvate dehydrogenase). Compared with control experiments, glucagon increased glucose output (P < 0.05) and decreased the calculated flux through pyruvate kinase (P < 0.05). Mercaptopicolinate almost totally suppressed glucose production and dramatically reduced the calculated gluconeogenic rate and flux through phosphoenolpyruvate carboxykinase (P < 0.001). Dichloroacetate moderately increased the calculated flux through pyruvate dehydrogenase (P < 0.05). In experiments with perfused livers from fed rats, the calculated gluconeogenic rate and flux through phosphoenolpyruvate carboxykinase were very low compared with control experiments (P < 0.001), whereas the pyruvate dehydrogenase flux was increased (P < 0.05). Therefore, the expected modifications of the citric acid cycle activity and gluconeogenic rate were clearly detected using the labeling pattern of glutamate to calculate these metabolic rates. Except for the perfusions with mercaptopicolinate, the dilution by isotopic exchange in the oxaloacetate pool calculated from the model agreed with the actual dilution of enrichment between liver pyruvate and phosphoenolpyruvate. The present results support the validity of this approach to trace liver metabolism.
Thyroid hormone stimulates renin synthesis in rats without involving the sympathetic nervous system
Authors: Kobori H. , Ichihara A. , Suzuki H. , Miyashita Y. , Hayashi M. , Saruta T.
Published: December 2017

The present study was performed to examine whether renal expression of the renin gene is regulated by thyroid hormone. Thirty male Sprague-Dawley rats were divided into hypothyroid, control, and hyperthyroid groups by use of daily intraperitoneal administration of methimazole, saline vehicle, or thyroxine, respectively. Each group was further subdivided into sympathetic innervated and sympathetic denervated subgroups by use of intraperitoneal administration of saline vehicle or 6-hydroxydopamine. Plasma renin activity and renal levels of renin were measured by radioimmunoassays after 8 wk. Renal expression of renin mRNA was evaluated by a semiquantitative reverse transcriptase-polymerase chain reaction. Compared with control animals, plasma renin activity, renal level of renin, and renal expression of renin mRNA were reduced (82, 94, and 71%, respectively) in hypothyroid animals and elevated (155, 1,182, and 152%, respectively) in hyperthyroid animals. Sympathetic denervation had no independent effect on these renin values. Our results indicate that thyroid hormone stimulates renin synthesis without involving the sympathetic nervous system.
Negative energy balance with exercise in identical twins: plasma glucose and insulin responses
Authors: Oppert J. M. , Nadeau A. , Tremblay A. , Despres J. P. , Theriault G. , Bouchard C.
Published: December 2017

The effects of long-term (93 days) negative energy balance on plasma glucose and insulin were investigated by means of exercise with constant energy intake in seven pairs of young sedentary male identical twins. Results showed a significant decrease in fasting (-24%, P < 0.02) and postprandial insulin (-16%, P < 0.05). Fasting and postprandial plasma glucose and glucagon were not modified. Mean glucose disposal rate measured during a euglycemic-hyperinsulinemic clamp performed in five twin pairs was increased by 34% (P = 0.13). No significant intrapair similarity was found for the responses of fasting and postprandial insulin levels and of glucose disposal rate. Changes in glucose disposal rate were significantly greater in high compared with low losers for computerized tomography-measured abdominal visceral fat (3.0 +/- 1.1 vs. 0.3 +/- 0.5 mg x kg(-1) x min(-1), P < 0.05) despite similar losses in total body fat. We conclude that 1) a long-term negative energy balance generated by exercise training significantly reduces plasma insulin levels, whereas insulin sensitivity tends to be improved; 2) training-induced changes in insulin sensitivity are associated with changes in abdominal visceral fat; and 3) data from this experiment conducted with a small number of twin pairs suggest that the genotype does not seem to be a major determinant of the changes in insulin levels and sensitivity brought about by negative energy balance with exercise.
Effects of exercise training on glucose transport and cell surface GLUT-4 in isolated rat epitrochlearis muscle
Authors: Reynolds T. H. , Brozinick J. T. , Rogers M. A. , Cushman S. W.
Published: December 2017

The effects of exercise training on maximal glucose transport activity and cell surface GLUT-4 were examined in rat epitrochlearis muscle. Five days of swim training (2 x 3 h/day) produce a significant increase in citrate synthase activity (24.5 +/- 0.6 vs. 20.1 +/- 0.7 micromol x min(-1) x g(-1)), GLUT-4 content (22.9 +/- 0.8 vs. 17.4 +/- 0.4% GLUT-4 standard), and glycogen levels (54.3 +/- 9.4 vs. 28.6 +/- 9.4 micromol/g). Maximally, insulin-stimulated glucose transport activity and cell surface GLUT-4 are increased by 55 (1.50 +/- 0.11 vs. 0.97 +/- 0.10 micromol x ml(-1) x 20 min(-1)) and 48% [12.0 +/- 0.8 vs. 8.1 +/- 0.9 disintegrations x min(-1) (dpm) x mg(-1)], respectively, in exercise-trained epitrochlearis muscles. In contrast, hypoxia-stimulated glucose transport activity and cell surface GLUT-4 are reduced by 38 (0.78 +/- 0.08 vs.1.25 +/- 0.14 micromol x ml(-1) x 20 min(-1)) and 40% (5.7 +/- 0.9 vs. 9.4 +/- 1.2 dpm/mg), respectively, in exercise-trained epitrochlearis muscles. These results demonstrate that changes in insulin- and hypoxia-stimulated glucose transport activity after exercise training are fully accounted for by the appearance of cell surface GLUT-4 and support the concept of two intracellular pools of GLUT-4. Finally, we propose that high levels of muscle glycogen with exercise training may contribute to the decrease in hypoxia-stimulated glucose transport activity.