bluuebunny/crossref_metadata_2025 huggingface dataset:
Epinephrine increases tricarboxylic acid cycle intermediates in human skeletal muscle
Authors: Spencer M. K. , Katz A. , Raz I.
Published: December 2017

The effects of epinephrine (E) and insulin infusions on the contents of tricarboxylic acid cycle intermediates (TCAI), adenine nucleotides and their catabolites, and amino acids in skeletal muscle have been investigated. Eight men were studied on two separate occasions: 1) during 120 min of euglycemic hyperinsulinemia (UH, approximately 5 mM; 40 mU.m-2.min-1) and 2) during UH while E was infused (UHE, 0.05 microgram.kg-1.min-1). Biopsies were taken from the quadriceps femoris muscle before and after each clamp. The sum of citrate, malate, and fumarate in muscle did not change significantly during UH (P greater than 0.05) but doubled during UHE (P less than 0.001). There were no significant changes in any of the adenine nucleotides, their catabolites (including inosine monophosphate), or aspartate during UH and UHE (P greater than 0.05); nor were there any significant changes in pyruvate or alanine contents during UH (P greater than 0.05). On the other hand, there were significant increases in pyruvate and alanine contents during UHE (P less than 0.01 and 0.05, respectively), suggesting that there was increased production of 2-oxoglutarate (a TCAI) via the alanine aminotransferase (ALT) reaction. It is concluded that E infusion increases the contents of TCAI in human skeletal muscle, and it is likely that at least part of the increase is attributable to increased flux through the ALT reaction.
Plasma Ca influences vitamin D metabolite levels as rats develop vitamin D deficiency
Authors: Kollenkirchen U. , Walters M. R. , Fox J.
Published: December 2017

The hypocalcemia that accompanies vitamin D deficiency is a major obstacle to proper interpretation of the role(s) of vitamin D metabolites in Ca-sensitive tissues. This paper describes the development and complete characterization of a dietary regimen with which normocalcemia was maintained in rats throughout the development of vitamin D deficiency. Normal weanling rats were fed diets containing 0.8% Ca, 0.5% P, and vitamin D3 (group A), or vitamin D-deficient diets containing 0.8% Ca and 0.5% P (group B); 2.0% Ca and 1.25% P (group C); or 2.0% Ca, 1.25% P, and 20% lactose (group D) for 19 wk. Group D rats were normocalcemic and normophosphatemic with normal parathyroid hormone (PTH) levels throughout the study. In contrast, from 4-19 diet wk, groups B and C were hypocalcemic with elevated PTH. Initially, plasma 25-hydroxyvitamin D3 [25(OH)D3] levels decreased most rapidly, and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels decreased least rapidly in group B rats, such that plasma 25(OH)D3 levels were reduced to 200-300 pg/ml before a decrease in 1,25(OH)2D3 levels was observed. However, vitamin D metabolite levels were similar in groups B, C, and D from 4-19 wk. Duodenal active Ca transport mirrored changes in plasma 1,25(OH)2D3 levels and was abolished after 10 wk. The results also suggested that vitamin D may not be necessary for normal bone mineralization since tibia mineral content and plasma alkaline phosphatase levels were similar in normocalcemic groups A and D throughout the study.
Demonstration of a novel feedback mechanism between FFA oxidation from intracellular and intravascular sources
Authors: Yki-Jarvinen H. , Puhakainen I. , Saloranta C. , Groop L. , Taskinen M. R.
Published: December 2017

We examined the regulation of intracellular and intravascular lipolysis in vivo. In the first series of studies, plasma free fatty acids (FFA) were elevated moderately by heparin (plus approximately 600 mumol/l) in patients with non-insulin-dependent diabetes mellitus (NIDDM) and in normal subjects. The increase in plasma FFA increased plasma FFA oxidation "submaximally" (plasma FFA oxidation less than 100% of total lipid oxidation) in a plasma FFA concentration-dependent manner. The increase in plasma FFA oxidation significantly suppressed direct intracellular oxidation of FFA. In another group of patients with NIDDM, plasma FFA was markedly increased (plus approximately 1,500 mumol/l). Plasma FFA oxidation now accounted for all lipid oxidation. Compared with substrate oxidation rates observed at submaximally elevated plasma FFAs in the same subjects at similar insulin concentrations, total lipid oxidation increased, carbohydrate oxidation decreased, and total energy production increased. These data demonstrate the existence of an FFA-dependent insulin-independent feedback mechanism between FFA oxidation from intracellular and intravascular sources. Thus the preferred response of body tissues to a change in plasma FFA oxidation is a reciprocal change in direct intracellular FFA oxidation. Substrate competition between carbohydrate and lipid, as proposed by P. J. Randle et al. (Lancet 1:785, 1963), becomes operative after the capacity for regulation within components of lipid oxidation has been utilized.
Sex differences in central adrenoreceptor-mediated vasopressin response to hemorrhage
Authors: Stone J. D. , Crofton J. T. , Share L.
Published: December 2017

Hemorrhage-induced changes in the plasma vasopressin concentration and mean arterial blood pressure (MABP) were studied in conscious rats of both sexes with and without central alpha 1-adrenoreceptor blockade. Rats were subjected to two sequential hemorrhages (H1 and H2), each 0.8% of body weight after an intracerebroventricular injection of the alpha 1-adrenoreceptor antagonist corynanthine or of vehicle. H1 stimulated vasopressin secretion more in proestrous females than in males; there were no significant sex-related differences in responses to H2. Corynanthine pretreatment attenuated the vasopressin response to H2 in males, potentiated this response in proestrous females, but had no effect in estrous females. MABP decreased after H1 in all female groups and in corynanthine-pretreated males. After H2, all groups were hypotensive to the same extent. These data indicate that central alpha 1-adrenoreceptor-mediated pathways participate in vasopressin and blood pressure responses to hemorrhage, but their role is complex and is dependent on gender and on the phase of the estrous cycle.
Insulin regulates insulin-like growth factor I mRNA in rat hepatocytes
Authors: Boni-Schnetzler M. , Schmid C. , Meier P. J. , Froesch E. R.
Published: December 2017

To evaluate the regulatory role of growth hormone (GH) and insulin on insulin-like growth factor I (IGF-I) mRNA levels, we employed primary rat hepatocytes. Cells were incubated for 16 h with 10 nM insulin, 10 nM GH, or a combination thereof, and IGF-I mRNA levels were analyzed by Northern blotting. Insulin results in 2.5-fold and GH in 3.8-fold higher IGF-I mRNA levels than hormone-free controls, and a combination of insulin and GH had an additive effect (6.7-fold). The effect of 10 nM insulin was constant at variable GH concentrations. Therefore, GH and insulin affect IGF-I mRNA levels independently of each other. The half-maximal effective dose of insulin was 4.7 X 10(-10) M, and, in kinetic experiments, insulin was effective within 2 h. These findings demonstrate that insulin modulates hepatic IGF-I production by a direct regulation of the transcript levels of IGF-I.
Cytosolic calcium responses of single rMTC 44-2 cells to stimulation with external calcium and potassium
Authors: Fajtova V. T. , Quinn S. J. , Brown E. M.
Published: December 2017

Few endocrine tissues can detect changes in the extracellular Ca2+ concentration within the physiological range and modify their hormone secretion accordingly. A rat cell line of C-cell origin (rMTC 44-2) secretes calcitonin and neurotensin in response to small increases in external Ca2+. To better understand the mechanism of extracellular Ca2+ sensing in this cell type, we studied single fura-2-loaded rMTC 44-2 cells perfused with increasing concentrations of Ca2+ and K+. In the basal state (Ca2+ = 0.5 mM), cytosolic Ca2+ levels were 53 nM, with 27% of the cells having spikes or oscillations. With elevation of the external Ca2+ to between 0.5 and 4 mM, 84% of the cells showed a rapid (less than 5 s) rise in cytosolic Ca2+ to values 2- to 10-fold higher than basal levels. Most of the responding cells exhibited complex patterns of cytosolic Ca2+ fluctuations, including oscillations with frequencies varying from less than 1/min to as many as 6/min. When averaged over time, the cytosolic Ca2+ of individual cells showed a dose-dependent response with changes in external Ca2+, resembling the relationship between extracellular Ca2+ and calcitonin secretion. With continued or repeated stimulation, the spike amplitude often declined. These cytosolic Ca2+ responses were attenuated in the presence of the Ca(2+)-channel blockers cadmium and nifedipine. Cytosolic Ca2+ responses to perfusion with elevated K+ (20 mM) were similar in waveform to those seen with Ca2+ stimulation. Most cells displayed cytosolic Ca2+ changes in response to both ionic secretagogues when stimulated with external Ca2+ or K+.(ABSTRACT TRUNCATED AT 250 WORDS)
Free-living energy expenditure measured by two independent techniques in pregnant and nonpregnant Gambian women
Authors: Heini A. , Schutz Y. , Diaz E. , Prentice A. M. , Whitehead R. G. , Jequier E.
Published: December 2017

Free-living energy expenditure (EE) was assessed in 37 young pregnant Gambian women at the 12th (n = 11, 53.5 +/- 1.7 kg), 24th (n = 14, 54.7 +/- 2.1 kg), and 36th (n = 12, 65.0 +/- 2.6 kg) wk of pregnancy and was compared with nonpregnant nonlactating (NPNL) control women (n = 12, 50.3 +/- 1.6 kg). The following two methods were used to assess EE: 1) the heart rate (HR) method using individual regression lines (HR vs EE) established at different activity levels in a respiration chamber and 2) the doubly labeled water (2H2(18)O) method in a subgroup of 25 pregnant and 7 control women. With the HR method the EE during the agricultural rainy season was found to be 2,408 +/- 87, 2,293 +/- 122, and 2,782 +/- 130 kcal/day at 12, 24, and 36 wk of gestation and were not significantly different from the control group (2,502 +/- 133 kcal/day). These findings were confirmed by the 2H2(18)O measurements, which failed to show any effect of pregnancy on EE. Expressed per unit body weight, the free-living EE was found to be lower (P less than 0.01 with 2H2(18)O method) at 36 wk of gestation than in the NPNL group. It is concluded that, in these Gambian women, energy-sparing mechanisms that contribute to meet the additional energy stress of gestation are operating during pregnancy (e.g., diminished spontaneous physical activity).
Vasoconstrictor-induced secretion of ANP in fetal sheep
Authors: Rosenfeld C. R. , Samson W. K. , Roy T. A. , Faucher D. J. , Magness R. R.
Published: December 2017

Fetal secretion of atrial natriuretic peptide (ANP) increases during volume expansion and hypoxia. It is unknown whether this is associated with alterations in right atrial pressure (RAP) or distension and whether increases in ANP secretion reflect effects of specific vasopressors. To address this we studied fetal sheep (n = 13) at 125-140 days gestation, infusing either angiotensin II (ANG II; 0.023-5.73 micrograms/min) or the alpha-agonist phenylephrine (Phen; 0.031-7.64 micrograms/min) while monitoring mean arterial pressure (MAP), RAP, heart rate, and amniotic sac pressure. Arterial blood was obtained before and at 5 min of infusion to measure ANP, blood gases, and pH; umbilical venous blood was collected to determine placental clearance of ANP. ANG II caused dose-dependent increases in MAP and plasma ANP (P less than 0.05), whereas Phen caused dose-dependent increases in MAP, but ANP rose only with the highest dose (40 +/- 12%). delta MAP and delta RAP were highly correlated for Phen (r = 0.74, P = 0.002) and ANG II (r = 0.90, P less than 0.001), but for both agents the increase in delta RAP was proportionately greater than delta MAP, and increases in plasma ANP were greater per millimeter mercury rise in RAP than that observed with MAP. Increases in ANP were associated with a dose-dependent rise in hematocrit, suggesting decreases in intravascular volume. There was no fetal placental clearance of ANP. As in adults, ANG II- and alpha-agonist-induced fetal ANP secretion appears to primarily reflect increases in RAP and thus right atrial distension.
Alterations in levels of Na(+)-K(+)-ATPase isoforms in heart, skeletal muscle, and kidney of diabetic rats
Authors: Ng Y. C. , Tolerico P. H. , Book C. B.
Published: December 2017

In streptozotocin (STZ)-induced diabetic rats, activities of Na(+)-K(+)-ATPase and the Na pump have been shown to be altered. Cellular mechanisms underlying such changes remain unclear. The present studies examined by immunoblotting the levels of Na(+)-K(+)-ATPase subunit isoforms in heart, skeletal muscle, and kidney of diabetic rats. Effects of insulin treatment on these levels were also studied. In cardiac muscle, STZ-induced diabetes caused a marked decrease in alpha 2-levels, a moderate decrease in beta 1-levels, and no significant change in alpha 1-levels. Corresponding to these changes, Na(+)-K(+)-ATPase activity, estimated by K(+)-dependent p-nitrophenylphosphatase activity, also decreased. By contrast, there were significant increases in alpha 1- and alpha 2-levels in skeletal muscle and in alpha 1- and beta 1-levels in kidneys of diabetic rats. There was also a detectable, but not significant, increase in beta 1-levels in diabetic skeletal muscle. In kidney, the increase in subunit levels was associated with significantly increased Na(+)-K(+)-ATPase activity, whereas, in skeletal muscle, no increase in enzyme activity was observed. In diabetic rats, 7 days of insulin treatment (10 U/kg sc) partially reversed the decreased alpha 2- and beta 1-levels in diabetic cardiac muscle, without significant effect on alpha 1-levels. In skeletal muscle, insulin treatment also partially reversed the elevated alpha 1- and alpha 2-levels but was without significant effect on beta 1-levels. It is concluded that STZ-induced diabetes exerted isoform- and tissue-specific regulation of the Na(+)-K(+)-ATPase subunit isoforms.(ABSTRACT TRUNCATED AT 250 WORDS)
Characterization of osteogenic response to mechanical stimulation in cancellous bone of rat caudal vertebrae
Authors: Chow J. W. , Jagger C. J. , Chambers T. J.
Published: December 2017

We have recently developed an experimental model in which pins, inserted into the 7th and 9th caudal vertebrae of 13-wk-old rats, are used to load the 8th caudal vertebra in compression. We have now applied this model to assess the responsiveness of rat cancellous bone to mechanical stimulation. We found that daily exposure to loads that induce strains similar to those observed in bone during relatively gentle physical activity, for 30 cycles/day, increased the rate of lamellar bone formation on cancellous surfaces by up to 140-fold. Bone formation rate showed a highly significant (P < 0.0001) correlation with the number of days for which the bones were loaded and with the size of the load. A single loading episode of 300 cycles, representing a 10-min period of loading, increased bone formation to 24 times that in nonloaded controls. Indexes of bone resorption were essentially the inverse of the bone formation parameters. These experiments show that rat cancellous bone is exquisitely sensitive to mechanical stimulation and suggest that the mechanical environment is a major determinant of the physiological behavior of mammalian cancellous bone.
Long-term effects on pancreatic function of feeding a HC formula to rats during the preweaning period
Authors: Vadlamudi S. , Hiremagalur B. K. , Tao L. , Kalhan S. C. , Kalaria R. N. , Kaung H. L. , Patel M. S.
Published: December 2017

We have investigated pancreatic changes associated with hyperinsulinemia and an insulin secretory response to an oral glucose load in a new rat model for obesity. Male Sprague-Dawley pups were reared on a high-carbohydrate (HC) or high-fat (HF) formula by gastrostomy during the suckling period and were weaned onto a stock diet. These animals remained either nutritionally unchallenged or challenged with a high-sucrose diet during the postweaning period. The HC formula-fed animals showed increased insulin concentrations in the plasma and pancreas and also showed impaired insulin secretory response compared with mother-fed control or HF animals in adult life. Immunocytochemical and morphometric studies revealed that hyperinsulinemia in the HC animals during the preweaning period and also in adult life was associated with hypertrophy of beta-cells in the pancreas. The results show that consumption of a HC formula during the suckling period influences pancreatic islet morphology resulting in hyperinsulinemia which eventually leads to the development of obesity later in adult life.
Lack of effect of hyperglycemia on lipolysis in humans
Authors: Cersosimo E. , Coppack S. , Jensen M.
Published: December 2017

To examine whether hyperglycemia is an independent regulator of adipose tissue lipolysis, we measured palmitate flux ([3H]palmitate) on two occasions in eight volunteers with insulin-dependent diabetes. On one. occasion, euglycemia was maintained for 4 h continuously; on a different occasion, hyperglycemia (plasma glucose, 12 mmol/l) was induced after 2 h of euglycemia. Palmitate flux decreased from 1.39 +/- 0.22 to 1.25 +/- 0.18 mumol.kg-1 x min-1 during sustained euglycemia and from 1.43 +/- 0.24 to 1.13 +/- 0.19 mumol.kg-1 x min-1 during the transition from the euglycemic to the hyperglycemic study intervals. There were no significant differences between the changes in palmitate flux from the first to the second study interval on the control (euglycemia-euglycemia) and experimental (euglycemia-hyperglycemia) study days and no difference between palmitate flux on different study days. Thus, in the face of euinsulinemia, euglucagonemia, and the absence of somatostatin, no effect of hyperglycemia on free fatty acid metabolism could be detected in humans.
Role of angiotensin II in brown adipose thermogenesis during cold acclimation
Authors: Cassis L. A.
Published: December 2017

The role of angiotensin II (ANG II) in increased sympathetic neuroeffector mechanisms observed in cold-induced thermogenesis of brown adipose tissue (BAT) was examined. Cold exposure (4 degrees C) for 7 days resulted in an increase in interscapular fat (ISF) ANG II content expressed per gram wet weight or per lobe of ISF, without concomitant changes in plasma components of the renin-angiotensin system. Additionally, in ISF slices preloaded with [3H]norepinephrine (NE), ANG II (10 nM) resulted in an increase (3-fold) in evoked 3H overflow from ISF slices from cold-exposed rats compared with ambient temperature controls. However, although basal 3H outflow was increased (2-fold) in ISF slices from cold-exposed rats, evoked 3H overflow was not different between ISF slices from cold-exposed and control rats. Specific neuronal uptake of [3H]NE in ISF slices from cold-exposed rats was decreased by 64%. Administration of the non-peptide AT1-receptor antagonist losartan to cold-exposed rats resulted in complete inhibition of ANG II-mediated presynaptic facilitation of evoked 3H overflow from ISF slices. However, losartan administration had no effect on cold-induced increases in ANG II content, protein content, and decreases in neuronal [3H]NE uptake in ISF. Results from these studies suggest that cold-induced thermogenesis of BAT results in alterations in presynaptic ANG II facilitation of NE release and defects in removal of NE from the synaptic cleft (neuronal uptake), both of which would enhance sympathetic nervous system-mediated thermogenesis. Furthermore, these results demonstrate a role for ANG II in enhanced sympathetic activity of cold-induced thermogenesis in BAT.
Effects of endotoxin on pigs prefed omega-3 vs. omega-6 fatty acid-enriched diets
Authors: Murray M. J. , Svingen B. A. , Yaksh T. L. , Holman R. T.
Published: December 2017

We investigated in a porcine model whether omega-3 fatty acids modify the physiological response to sepsis. For 8 days, 16 male pigs were fed a diet containing 18% fat by weight enriched with either omega-3 or omega-6 fatty acids (FA). A group of six pigs receiving their regular diet served as controls. The omega-3 FA-supplemented pigs had elevated levels of omega-3 FA in their serum-free FA, serum phospholipid (PL), and platelet PL levels compared with either of the other groups. On the ninth day, the unanesthetized pigs were injected with 0.3 mg/kg of endotoxin (Escherichia coli) intravenously. The animals had a significant decrease in their arterial O2 pressure (PaO2) [from 84.4 +/- 6.8 (SD) to 64 +/- 9.4, and from 83.1 +/- 7.2 to 55.9 +/- 6.3 mmHg in the omega-6 FA and regular diet groups, respectively]. The PaO2 did not decrease in the omega-3 FA pigs. The omega-3 FA group had significantly lower pulmonary vascular resistance (541 +/- 205 dyn.s.cm-5) 20 min after endotoxin compared with either the omega-6 FA or regular diet groups (797 +/- 233 and 1,102 +/- 552 dyn.s.cm-5, respectively) and more normal blood pressure compared with the other two groups. Plasma thromboxane (Tx) B2 and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) levels were lowest in the omega-3 FA diet group and highest in the regular diet group.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of glutamine deprivation on glutamine transport and synthesis in primary culture of rat skeletal muscle
Authors: Tadros L. B. , Willhoft N. M. , Taylor P. M. , Rennie M. J.
Published: December 2017

The effects of deprivation and supplementation of exogenous glutamine (0.06 and 2.2 mM in the culture medium, respectively) were studied in mononucleated myoblasts and in multinucleated myotubes. Myoblasts cultured in glutamine-deprived medium showed reductions in plating efficiency and myotube fusion index. Myotubes grown in glutamine-supplemented cultures had higher intracellular glutamine concentrations than those grown in glutamine-deprived medium (67 +/- 4.2 vs. 46 +/- 3.6 nmol/mg cell protein, respectively) and glutamine-supplemented myotubes utilized glutamine, whereas glutamine-deprived myotubes released it. Glutamine deprivation for 12 h caused a significant, cycloheximide-blockable increase in the capacity for glutamine uptake via system Nm in both myoblasts and myotubes (maximum velocity increases of 23 +/- 5.3 and 35 +/- 4.2%, respectively), which was reversed by glutamine replenishment. Depriving myotubes of glutamine did not alter the kinetics of uptake of amino acid transport systems A, ASC, or L. Glutamine deprivation resulted in a threefold increase in glutamine synthetase activity, whereas glutaminase activity remained unchanged. System Nm and glutamine synthetase appear to undergo adaptive upregulation in glutamine-deprived muscle cells to compensate for the reduced exogenous glutamine supply.
Effect of growth hormone administration and treadmill exercise on serum and skeletal IGF-I in rats
Authors: Yeh J. K. , Aloia J. F. , Chen M. , Ling N. , Koo H. C. , Millard W. J.
Published: December 2017

Growth factors may be mediators of local and systemic factors that enhance bone formation. This study examined the effect of treadmill exercise and ovine growth hormone administration on levels of insulin-like growth factor I (IGF-I) in serum (ng/ml), long bone, and vertebrae and on bone formation rate. Forty female rats were divided into four groups: control; exercise (17 m/min, 1 h/day); growth hormone (0.05 mg.100 g-1.day-1); growth hormone plus exercise. After 9 wk of study, the serum levels of IGF-I were higher in the intervention groups than in the control group; however, the IGF-I concentration and the periosteal bone formation rate in the long bone were significantly higher only in the exercised rats. The IGF-I concentration and the cancellous bone formation rate in the vertebrae did not differ among the experimental groups. The vertebral and long bone formation rate were correlated with bone concentrations of IGF-I. Serum levels of IGF-I were also correlated with serum osteocalcin and the long bone formation but not with the vertebral bone formation. The association of bone formation with serum and bone IGF-I supports the suggestion that IGF-I is one of the growth factors that regulate bone formation, in particular as a mediator of the response of bone to exercise.
Acute noradrenergic activation induces insulin resistance in human skeletal muscle
Authors: Lembo G. , Capaldo B. , Rendina V. , Iaccarino G. , Napoli R. , Guida R. , Trimarco B. , Sacca L.
Published: December 2017

We assessed in normal subjects the effects of an acute increase in forearm norepinephrine (NE) release, evoked by -20 mmHg lower body negative pressure (LBNP), on insulin-mediated muscle glucose uptake. Seven normal subjects underwent the following two insulin euglycemic clamps in random sequence: one during application of LBNP and the other without LBNP (control study). In the control study, hyperinsulinemia (approximately 60 microU/ml) produced a significant increment in forearm NE release, measured by using the forearm perfusion technique combined with infusion of tritiated NE (from 4.91 +/- 1 to 7.94 +/- 1.33 ng.l-1.min-1; P < 0.05). Forearm glucose uptake rose from 0.97 +/- 0.13 to 5.2 +/- 0.2 mg.l-1.min-1 in response to insulin infusion. When the insulin clamp was performed during LBNP, forearm NE release rose to significantly higher values than those of the control study (from 4.33 +/- 0.52 to 12.7 +/- 1.46 ng.l-1.min-1; P < 0.01 vs. control). Under these conditions, the stimulatory effect of insulin on forearm glucose uptake was markedly reduced (from 0.78 +/- 0.10 to 3.2 +/- 0.7 mg.l-1.min-1; P < 0.02 vs. control). Forearm blood flow and plasma epinephrine and free fatty acid concentrations were comparable in the two study sessions. These data demonstrate that an acute activation of endogenous NE release antagonizes insulin-mediated glucose uptake in forearm skeletal muscle, probably accounted for by a direct metabolic effect of NE.
Effect of chronic energy deprivation on cardiac thyroid hormone receptor and myosin isoform expression
Authors: Swoap S. J. , Haddad F. , Bodell P. , Baldwin K. M.
Published: December 2017

Thyroid hormone (3,5,3'-triiodothyronine; T3) and its receptor (TR) play an important regulatory role for in vivo and in vitro cardiac myosin heavy chain (MHC) isoform gene expression by activating the alpha- and inhibiting the beta-MHC genes. Previous studies have shown that chronic energy deprivation (CED; 50% of normal caloric intake) in the rat impacts cardiac MHC protein expression and hemodynamic parameters in a pattern typically seen with hypothyroidism; yet, unlike hypothyroidism, circulating T3 levels are not depressed. Therefore, the goal of this study was to determine if the altered MHC isoform expression observed in CED is associated with altered TR expression, both at the mRNA and protein levels. Female rats weighing approximately 250 g were allocated into two groups, designated as normal control (NC) and CED. After 5 wk, the relative content of alpha-MHC protein and mRNA levels decreased in CED ventricles by 20% (P < 0.05). In contrast, the relative content of both beta-MHC protein and mRNA levels increased five- to sixfold in CED (P < 0.05). Although there were no changes in TR mRNA levels relative to 18S rRNA in CED, the total number of nuclear TRs decreased 3.5-fold in the CED group (P < 0.05), from a maximum binding capacity of 840 +/- 130 fmol/mg DNA in NC to 241 +/- 118 fmol/mg DNA in CED, with no change in the affinity of the receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of porcine insulin-like growth factor I and growth hormone receptor mRNA expression by energy status
Authors: Weller P. A. , Dauncey M. J. , Bates P. C. , Brameld J. M. , Buttery P. J. , Gilmour R. S.
Published: December 2017

Regulation of insulin-like growth factor I (IGF-I) and growth hormone (GH) receptor mRNA in liver and muscle by energy status was assessed in 2-mo-old pigs by altering thermoregulatory demand and energy intake over a 5-wk period to produce a range of plasma IGF-I concentrations from 3.5 +/- 0.7 to 28.9 +/- 6.2 nmol/l. These values were related directly to growth rates (0.06 +/- 0.02 to 0.44 +/- 0.01 kg/day) and total hepatic IGF-I mRNA levels. Increased growth rates were accompanied by an increase in hepatic class 1 and class 2 IGF-I mRNA levels and an increase in the ratio of class 2 to class 1 IGF-I mRNA in liver, suggesting a distinct role for class 2 expression in the endocrine growth response. High levels of class 1 transcripts and a virtual absence of class 2 transcripts characterized all muscle tissues examined, and there was no correlation with plasma IGF-I levels. This suggests that growth promotion in response to increased energy status is regulated via endocrine hepatic IGF-I rather than via a paracrine response. The levels of GH receptor mRNA were positively correlated with overall growth rate (P < 0.005) in liver and negatively correlated (P < 0.05) in muscle, indicating distinct tissue-specific effects of energy status.
Thapsigargin inhibits the glucose-induced decrease of intracellular Ca2+ in mouse islets of Langerhans
Authors: Roe M. W. , Mertz R. J. , Lancaster M. E. , Worley J. F. , Dukes I. D.
Published: December 2017

Stimulation of pancreatic islets of Langerhans with glucose results in changes in intracellular Ca2+ concentration ([Ca2+]i). With the use of mouse islets loaded with fura 2, the earliest glucose-induced alteration of [Ca2+]i was a pronounced decline in [Ca2+]i. This effect (phase 0) was evident 1 min after increasing extracellular glucose from 2 to 12 mM and was sustained for 3-5 min. Phase 0 was also observed when glucose was increased from 5 to 12 mM, indicating that it was not an experimental artifact resulting from substrate depletion. The [Ca2+]i-lowering effect of glucose was mimicked by D-glyceraldehyde but not by 2-deoxyglucose, pyruvate, glyburide, or 30 mM extracellular KCl. Mannoheptulose inhibited phase 0, whereas diazoxide, sodium azide, calmidazolium, or increasing extracellular [Ca2+] to 10 mM were all without effect. After the elevation of islet [Ca2+]i with 5 microM glyburide, 12 mM glucose caused a considerable transient decrease in [Ca2+]i. Under similar conditions, 5 mM caffeine attenuated phase 0, whereas 1 microM thapsigargin, a specific inhibitor of the sarcoplasmic and endoplasmic reticulum family of Ca(2+)-adenosinetriphosphatases (SERCA), almost completely inhibited any glucose-induced reduction of [Ca2+]i. These observations suggest that glucose causes an elevation of beta-cell SERCA activity triggered by factors generated during the cytosolic stages of glycolysis.
Fasting and postprandial phenylalanine and leucine kinetics in liver cirrhosis
Authors: Tessari P. , Inchiostro S. , Barazzoni R. , Zanetti M. , Orlando R. , Biolo G. , Sergi G. , Pino A. , Tiengo A.
Published: December 2017

To investigate body protein turnover and the pathogenesis of increased concentration of plasma phenylalanine in liver cirrhosis, we have studied phenylalanine and leucine kinetics in cirrhotic (diabetic and nondiabetic) patients, and in normal subjects, both in the postabsorptive state and during a mixed meal, using combined intravenous and oral isotope infusions. Postabsorptive phenylalanine concentration and whole body rate of appearance (Ra) were approximately 40% greater (P < 0.05) in patients than in controls. Leucine concentrations were comparable, but intracellular leucine Ra was also increased (P < 0.05), suggesting increased whole body protein breakdown. Postprandial phenylalanine Ra was also greater (P < 0.05) in the patients. This difference was due to a diminished fractional splanchnic uptake of the dietary phenylalanine (approximately 40% lower in the cirrhotics vs. controls, P < or = 0.05). Postprandial leucine Ra was also increased in the patients, but splanchnic uptake of dietary leucine was normal. Thus both increased body protein breakdown and decreased splanchnic extraction of dietary phenylalanine can account for the increased phenylalanine concentrations in liver cirrhosis.
Measurement of pyruvate and lactate kinetics across the hindlimb and gut of anesthetized dogs
Authors: Chinkes D. L. , Zhang X. J. , Romijn J. A. , Sakurai Y. , Wolfe R. R.
Published: December 2017

We have developed a new model to quantify regional pyruvate and lactate transmembrane transport, shunting, exchange, production, and oxidation in vivo. The method is based on the systemic continuous infusion of pyruvate or lactate stable isotopic carbon tracers and the measurement of pyruvate and lactate enrichment and concentration in the artery and vein of that region (e.g., leg or gut), the pyruvate and lactate enrichment of intracellular free water in the tissue as measured by biopsy, and the rate of blood flow through the tissue. The purpose of the experiment was to measure the pyruvate and lactate kinetics in leg muscle and gut in anesthetized dogs (n = 6). The transmembrane transport and degree of shunting of pyruvate and lactate were comparable in muscle and gut. When modified for substrate inflow, interconversion between pyruvate and lactate took place at a rate twice as fast in muscle as in the gut, and production and oxidation of pyruvate was approximately 50% greater in muscle than in the gut. Thus our new model enables quantitation of many aspects of lactate and pyruvate kinetics. We conclude that in anesthetized animals the muscle is the tissue most responsible for whole body peripheral pyruvate and lactate kinetics.
Lesions of hypothalamic paraventricular nuclei do not prevent the effect of estradiol on energy and fat balance
Authors: Dagnault A. , Richard D.
Published: December 2017

The chronic effects of estradiol (E2) on energy balance have been investigated in ovariectomized rats with hypothalamic paraventricular nuclei (PVH) lesions. Body weight and food intake were monitored throughout the E2 treatment, which lasted 26 days. At the end of this treatment, rats were decapitated, and their carcasses were processed to determine the body contents in energy, fat, and protein. Plasma adrenocorticotropic hormone (ACTH) and corticosterone were determined by radioimmunoassay and protein-binding assay at the end of the study. Regardless of whether they were sham- or PVH-lesioned, E2-treated rats ate, expended, and gained significantly less energy than untreated animals. In addition, E2-treated rats deposited less fat and protein than the rats not receiving E2. In contrast to the E2 treatment, PVH lesions accelerated the gains in energy and fat regardless of whether the rats were treated with E2 or with a placebo. There were no interaction effects of PVH lesions and the E2 treatment on energy or fat gains. Plasma levels of corticosterone and ACTH were higher in E2-treated rats than in animals receiving the placebo treatment. The present results provide evidence that the hypothalamic PVH is not an essential neuroanatomical structure in the effects of E2 on energy and fat balances.
[Ca2+]i signaling in pregnant human myometrium
Authors: Szal S. E. , Repke J. T. , Seely E. W. , Graves S. W. , Parker C. A. , Morgan K. G.
Published: December 2017

The purpose of the present study was to determine the changes in intracellular ionized calcium concentration ([Ca2+]i) or [Ca2+]i sensitivity accompanying spontaneous and agonist-induced contraction of human myometrium at term pregnancy, as well as to quantify the response to three prototypical agonists: 1) oxytocin, 2) vasopressin, and 3) phenylephrine. Uterine biopsies were obtained at the time of cesarean section from patients who delivered at or near full-term gestation. These preparations were used to measure isometric force development and [Ca2+]i levels with the luminescent calcium indicator aequorin. Concentration-response relationships were determined with respect to isometric force development in the presence of the agonist. [Ca2+]i-force relationships were determined with respect to spontaneous phasic contractions, as well as agonist-induced phasic and tonic contractions. The results provide evidence that the phasic nature of term human myometrium is due to 1) the resting [Ca2+]i level being less than the calcium threshold for contractions and 2) the inability of the tissue to maintain high [Ca2+]i levels for prolonged periods of time. In addition, calcium-independent mechanisms of regulation were suggested by the relatively minor calcium sensitizing action of oxytocin and the observation that relaxation of tonic contractions preceded the fall in [Ca2+]i levels.
Impaired cardiac performance in GH-deficient adults and its improvement after GH replacement
Authors: Cittadini A. , Cuocolo A. , Merola B. , Fazio S. , Sabatini D. , Nicolai E. , Colao A. , Longobardi S. , Lombardi G. , Sacca L.
Published: December 2017

Cardiac performance was investigated by radionuclide angiography in 11 patients with childhood-onset growth hormone (GH) deficiency and in 12 control subjects. Both at rest and during maximal physical exercise, systolic function was markedly depressed in GH-deficient patients. Ejection fraction rose from 66 +/- 6 to 76 +/- 7% during exercise in control subjects, whereas in GH-deficient patients it remained unchanged or even decreased (55 +/- 6 and 54 +/- 9% at rest and after exercise, respectively; P < 0.01 vs. controls). Cardiac index was significantly lower in GH-deficient patients than in controls, both at rest (2.7 +/- 0.6 vs. 3.7 +/- 0.5 l.min-1.m-2; P < 0.001) and during exercise (8 +/- 1.2 vs. 10 +/- 1.5 l.min-1.m-2; P < 0.01). Five GH-deficient patients were treated with recombinant human (rh) GH for 6 mo at a dose of 0.05 IU.kg-1.day-1. Cardiac index at rest improved from 2.8 +/- 0.6 to 3.3 +/- 0.8 l.min-1.m-2 (P < 0.01) after rhGH. Also, cardiac index response to exercise improved markedly and became similar to that of controls (7.5 +/- 1.2 and 10.1 +/- 1.1 l.min-1.m-2 before and after rhGH, respectively; P < 0.005). Exercise tolerance was impaired in GH-deficient patients and was restored by rhGH treatment. The data support the hypothesis that GH plays an important role in the maintenance of a normal cardiac performance in humans.
Growth hormone and parathyroid hormone stimulate IGFBP-3 in rat osteoblasts
Authors: Schmid C. , Schlapfer I. , Peter M. , Boni-Schnetzler M. , Schwander J. , Zapf J. , Froesch E. R.
Published: December 2017

Osteoblast-like cells prepared from calvaria of newborn rats produce insulin-like growth factor (IGF) I and several insulin-like growth factor binding proteins (IGFBPs) in vitro. Among the IGFBPs found in conditioned cell culture medium, IGFBP-3 is the most abundant. Intact IGFBP-3, as assessed by 125I-labeled IGF-II ligand blot analysis, is more abundant in culture media of cells exposed to growth hormone (GH) or to parathyroid hormone (PTH), both at 5 x 10(-9) mol/l, for 24 h. At the same time, concentrations of IGF-I are increased in media of cells exposed to PTH but not to GH, compared with hormone-free control cultures. IGFBP-3 mRNA is increased in osteoblasts exposed to PTH or to GH but not in response to 5 x 10(-9) mol/l IGF-I. PTH exerts a rapid (within 2 h) stimulatory effect on IGF-I and IGFBP-3 production, both at the message and peptide levels, whereas GH increases only IGFBP-3, both at the message and peptide levels (after 24 h). We conclude that IGF-I does not mediate increased IGFBP-3 production by rat osteoblasts in response to GH and PTH.
Stimulus-secretion coupling in parathyroid cells deficient in protein kinase C activity
Authors: Racke F. K. , Nemeth E. F.
Published: December 2017

The role of protein kinase C (PKC) in regulating cytosolic Ca2+ concentrations ([Ca2+]i) and parathyroid hormone (PTH) secretion was studied in bovine parathyroid cells rendered deficient in PKC activity by incubation with phorbol 12-myristate 13-acetate (PMA). Pretreatment with PMA caused a time- and concentration-dependent loss of functional PKC activity as assessed by the failure of [Ca2+]i and PTH secretion to respond to the subsequent addition of PKC activators or the inhibitor staurosporine. Pretreatment for 24 h with 1 microM PMA caused a loss of 85% of the total and 98% of the cytosolic PKC activity. Cells so pretreated were considered to be "PKC downregulated." Increasing the concentration of extracellular Ca2+ or Mg2+ caused corresponding increases in [Ca2+]i that were similar in control and in PKC-downregulated cells. PTH secretion regulated by extracellular Ca2+ or Mg2+ was likewise similar in control and PKC-downregulated cells. Stimulus-secretion coupling is thus unimpaired in parathyroid cells deficient in PKC activity. Cytosolic Ca2+ responses remained depressed in cells incubated for 24 h with low concentrations of PMA (30 or 100 nM). However, under these conditions, extracellular Ca2+ still suppressed PTH secretion similarly to control cells. These results reveal a dissociation between cytosolic Ca2+ and PTH secretion and suggest that signals other than cytosolic Ca2+ are involved in the regulation of PTH secretion.
Cortisol feedback regulation of pulsatile ACTH secretion in fetal sheep during late gestation
Authors: Apostolakis E. M. , Longo L. D. , Yellon S. M.
Published: December 2017

In fetal sheep, plasma cortisol and adrenocorticotropic hormone (ACTH) concentrations increase during late gestation to surge within 72 h of birth (approximately 146 days gestation). To determine the feedback role of cortisol in control of pulsatile ACTH secretion, six chronically catheterized fetuses were treated with cortisol (1 microgram/h i.v.) for 96 h at 133 days gestation. Before (133 days), during (134 and 137 days), and after (142 days) cortisol treatment (5-min sampling for 2 h), ACTH pulses were evident in each fetus. At 134 days, ACTH pulse peak, nadir, and estimated secretory rate were significantly increased while frequency, amplitude, mean concentrations, and cortisol binding capacity (CBC) were unchanged. At 137 days, most characteristics of pulsatile ACTH secretion remained enhanced compared with pretreatment controls. At 142 days (96 h postinfusion), ACTH secretion parameters returned to pretreatment levels, but cortisol concentrations remained elevated. Cortisol infusion was then reinitiated at 142 days and, 22–24 h later, parameters of ACTH secretion increased except for amplitude, secretory rate, and CBC activity. The data indicate an absence of cortisol negative feedback regulation of pulsatile ACTH secretion. Rather, the ACTH rise that accompanied cortisol infusion suggests that cortisol exerts a positive feedforward influence on ACTH secretion in the ovine fetus near term.
VLDL production is decreased to a similar extent by acute portal vs. peripheral venous insulin
Authors: Lewis G. F. , Zinman B. , Uffelman K. D. , Szeto L. , Weller B. , Steiner G.
Published: December 2017

Acute changes in very low-density lipoprotein (VLDL) triglyceride (TG) and VLDL apolipoprotein (apo) B production were examined in 11 healthy young males in response to insulin delivered either by the peripheral venous route or secreted directly by the pancreas. Steady rates of pancreatic insulin secretion were achieved for 5 h by a programmed intravenous tolbutamide infusion, while euglycemia was maintained with a dextrose infusion. Insulin secretory rate was calculated from peripheral C-peptide levels by deconvolution, and, in a subsequent study, exogenous insulin was infused peripherally to match this pancreatic insulin secretory rate in each subject. Changes in VLDL TG and VLDL apo B production were determined semiquantitatively on each occasion by examining the change in slope of the specific activity (SA) of 3H-labeled triglyceride glycerol ([3H]TGG) and 131I-VLDL apo B vs. time curves, respectively, occurring with acute hyperinsulinemia. Plasma-free fatty acids (FFA), TG, apo B, and VLDL TG/VLDL apo B ratio decreased to a similar extent in both studies after the onset of hyperinsulinemia. VLDL TG production decreased significantly in both the tolbutamide (-47.1 +/- 7.3%, P < 0.002) and the exogenous insulin infusion study (-52.8 +/- 12.4%, P < 0.005). VLDL apo B production also decreased significantly in both studies (-58.9 +/- 7.5%, P = 0.0007 and -52.1 +/- 6.8%, P < 0.006, respectively), and there were no significant differences between studies. Tolbutamide was shown to have no independent effect on VLDL TG or VLDL apo B production in four insulin-deficient diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal oxygen consumption, thermogenesis, and amino acid utilization during i.v. infusion of amino acids in man
Authors: Brundin T. , Wahren J.
Published: December 2017

The renal contribution to the amino acid-induced whole body thermogenesis was examined. Using indirect calorimetry and catheter techniques, pulmonary and renal oxygen uptake and blood flow, blood temperatures, and net renal exchange of amino acids, glucose and lactate were measured in eight healthy men before and during 3 h of intravenous infusion of 720 kJ of an amino acid solution. During the infusion, the pulmonary oxygen uptake increased from 252 +/- 12 to 310 +/- 8 ml/min, cardiac output increased from 5.9 +/- 0.3 to 6.8 +/- 0.3 l/min, and the arterial blood temperature increased from 36.34 +/- 0.04 to 36.68 +/- 0.07 degrees C. Renal oxygen consumption, heat production, blood flow, and net glucose exchange remained unchanged during the infusion. The net renal uptake of amino acid energy from the blood rose from 2 +/- 2 to 11 +/- 4 W. The total renal energy expenditure was 9-10 W throughout the study period. It is concluded that intravenous amino acid infusion greatly augments the uptake and utilization of amino acids in the kidneys but does not stimulate the renal oxygen consumption, heat production, blood flow, or glucose release.
Induction of secretogranin II mRNA by protein synthesis inhibitors in GH4C1 cells
Authors: Scammell J. G. , Valentine D. L.
Published: December 2017

The effect of cycloheximide (CHX) on the expression of secretogranin II (SgII), a member of the granin family of secretory proteins, was investigated in rat pituitary GH4C1 (GH) cells. The administration of CHX resulted in a dose- and time-dependent increase in SgII mRNA expression, the greatest effect (3.8-fold above control) being achieved with 1 microgram/ml CHX, which resulted in > 90% inhibition of protein synthesis. Emetine (1 microgram/ml), pactamycin (0.6 microgram/ml), anisomycin (2.5 micrograms/ml), and puromycin (100 micrograms/ml), protein synthesis inhibitors structurally and mechanistically unrelated to CHX, also increased the level of SgII mRNA expression. Treatment with forskolin (10 microM) alone had no effect on SgII mRNA levels but potentiated the effect of CHX. Neither 100 nM phorbol 12-myristate 13-acetate nor 45 mM KCl affected SgII mRNA levels in the absence or presence of 1 microgram/ml CHX. The effect of CHX was blocked by the transcription inhibitors actinomycin D (5 micrograms/ml) and 5,6-dichlorobenzimidazole riboside (20 micrograms/ml) but not by the coadministration of the polysome destabilizer pactamycin (0.6 microgram/ml), suggesting that the effect of CHX was transcriptional. These studies show that the expression of SgII mRNA is induced by protein synthesis inhibitors in GH cells, suggesting the presence of a labile repressor, which not only controls the basal expression of the SgII gene but also completely inhibits the stimulatory effect of forskolin.