bluuebunny/crossref_metadata_2025 huggingface dataset:
Interferon-alpha downregulates expression of the oxytocin receptor in cultured human myometrial cells
Authors: Maggi M. , Peri A. , Baldi E. , Mancina R. , Granchi S. , Fantoni G. , Finetti G. , Forti G. , Raggi C. C. , Serio M.
Published: December 2017

Previous studies in the endometrium of ruminants showed that type I interferon (IFN) prevents oxytocin receptor (OTR) formation. We studied the effect of IFN-alpha on human myometrial cells in culture expressing a high density of biologically active OTR. We found that IFN-alpha induced a 35-50% decrease in OTR mRNA and protein and that this inhibition was time and dose dependent. Maximal inhibition of OTR mRNA was obtained after 2-3 days, whereas 1-(beta-mercapto-beta, beta-cyclopentamethyl-enepropionic acid,2-O-Me-Tyr,Thr4,Orn8,Tyr9-amide)-[125I]vasotocin ([125I]OTA) binding reached a nadir after 3-4 days, with half-maximal inhibitory concentration (IC50) = 1,100 U/ml. Mathematical analysis of multiple homologous competition curves for [125I]OTA indicated that IFN-alpha treatment (5,000 U/ml x 3 days) reduced just the binding capacity (Bmax) without changing the binding affinity. Accordingly, the same treatment with IFN-alpha did not affect the half-maximally effective concentration (EC50) for the oxytocin-induced increase in intracellular calcium but significantly decreased maximal responsiveness (Emax) of myometrial cells to OT stimulation. In conclusion, our data demonstrate, for the first time, a negative regulation by IFN-alpha of the steady-state expression of OTR mRNA in cultured human myometrial cells obtained from nonpregnant uteri. This inhibition was followed by a parallel decrease in both the Bmax for [125I]OTA and Emax for oxytocin, suggesting a decreased OTR protein availability.
Islet amyloid polypeptide and insulin gene expression are regulated in parallel by glucose in vivo in rats
Authors: Mulder H. , Ahren B. , Sundler F.
Published: December 2017

Islet amyloid polypeptide (IAPP) is a novel amyloid-forming beta-cell hormone with putative roles in glucose metabolism and non-insulin-dependent diabetes mellitus (NIDDM) pathogenesis. To study how IAPP and insulin expression are regulated by glucose, rats were fasted for 48h followed by administration of glucose at repeated 4-h intervals; IAPP and insulin mRNA levels were determined by quantitative in situ hybridization. Fasting markedly reduced IAPP and insulin mRNA levels. Two (6 h) and four (14 h) glucose injections dose dependently increased both mRNA levels; the effects were matched by similar changes in plasma glucose levels. Actinomycin D blocked the glucose-induced increase in IAPP expression. IAPP and insulin mRNA levels were significantly correlated over the range of glucose levels. The parallel regulation of IAPP and insulin gene expression by glucose is consistent with a role for IAPP in glucose homeostasis. Thus, under hyperglycemic conditions such as NIDDM, IAPP gene expression is likely to increase. Hence, IAPP could, by elevated local concentrations, contribute to amyloid formation and/or affect metabolism unfavorably by inhibition of insulin release and action.
Reversal of portacaval shunting normalizes brain energy consumption in most brain structures
Authors: Hawkins P. A. , DeJoseph M. R. , Hawkins R. A.
Published: December 2017

The cerebral metabolic rate of glucose consumption (CMRGlc) was measured throughout brains of rats with 1) portacaval shunts created for 2 wk, followed by restoration of normal blood circulation for 2 wk; 2) portacaval shunts created for 2 wk, followed by a sham operation and 2 wk of recovery; 3) two sham operations, each with 2 wk of recovery times. Portacaval-shunted rats had diminished CMRGlc (decreases of 7-23%) throughout the brain in agreement with previous studies. After restoration of normal liver blood flow, the CMRGlc of most structures returned to near-normal values, although a few structures, notably the hippocampus, remained 11-13% lower. These data suggest that the consequences of portacaval shunting to brain energy metabolism can be markedly improved, if not completely reversed, by restoring the normal pattern of blood flow to an otherwise healthy liver. Other metabolic and physical data collected (liver weight, liver-to-body weight, plasma ammonia) returned to normal except plasma glucose concentrations, which remained lower by 11%, suggesting a persistent, albeit mild, defect in glucose homeostasis.
Effect of perfusion rate on the time course of insulin-mediated skeletal muscle glucose uptake
Authors: Baron A. D. , Brechtel-Hook G. , Johnson A. , Cronin J. , Leaming R. , Steinberg H. O.
Published: December 2017

To better define the time course of skeletal muscle glucose uptake and its modulation by changes in perfusion, we performed systemic euglycemic-hyperinsulinemic clamps (40 mU.m-2.min-1) for a 90-min period in a group of lean, insulin-sensitive subjects (n = 9) on two occasions (approximately 4 wk apart) with insulin-mediated vasodilation intact or inhibited. Insulin-mediated vasodilation was inhibited by an intrafemoral artery infusion of NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of nitric oxide synthase. During the study, leg blood flow (LBF) and arteriovenous glucose difference (AVG delta) were measured every 10 min; leg glucose uptake (LGU) was calculated as LGU = LBF x AVG delta. The systemic insulin infusion caused a time-dependent increase in LBF from 0.194 +/- 0.024 to 0.349 +/- 0.046 l/min (P < 0.01). The intrafemoral artery infusion of L-NMMA completely inhibited this increase in LBF. AVG delta, LGU, and whole body glucose disposal rates increased in a time-dependent manner in both studies. The maximum AVG delta was lower with insulin-mediated vasodilation intact than when inhibited (25.9 +/- 2.5 vs. 35.0 +/- 1.6 mg/dl, P < 0.001). The time to achieve half-maximal (T1/2) AVG delta was somewhat longer with insulin-mediated vasodilation intact compared with inhibited (35.6 +/- 4.1 vs. 29.7 +/- 1.6 min, P < 0.01). Maximal LGU was 93.9 +/- 26.8 and 57.2 +/- 11.6 mg/min (P < 0.005), and the T1/2 LGU was 50.2 +/- 16.0 and 36.3 +/- 8.8 min (P = 0.1) during intact and inhibited insulin-mediated vasodilation, respectively. Thus insulin-mediated vasodilation has a modest effect in slowing the time course at which insulin stimulates glucose uptake but has a marked effect in augmenting the maximal rate of insulin-stimulated glucose uptake in skeletal muscle. Impaired insulin-mediated vasodilation, as observed in patients with essential hypertension, may explain, at least in part, the insulin resistance observed in these patients.
Skeletal muscle myosin heavy-chain synthesis rate in healthy humans
Authors: Balagopal P. , Ljungqvist O. , Nair K. S.
Published: December 2017

Mixed muscle protein synthetic rate has been measured in humans. These measurements represent the average of synthetic rates of all muscle proteins with variable rates. We determined to what extent the synthesis rate of mixed muscle protein in humans reflects that of myosin heavy chain (MHC), the main contractile protein responsible for the conversion of ATP to mechanical energy as muscle contraction. Fractional synthetic rates of MHC and mixed muscle protein were measured from the increment of [13C]leucine in these proteins in vastus lateralis biopsy samples taken at 5 and 10 h during a primed continuous infusion of L-[1-13C]leucine in 10 young healthy subjects. Calculations were done by use of plasma [13C]ketoisocaproate (KIC) and muscle tissue fluid [13C]leucine as surrogate measures of leucyl-tRNA. Fractional synthetic rate of MHC with plasma KIC (0.0299 +/- 0.0043%/h) and tissue fluid leucine (0.0443 +/- 0.0056%/h) were only 72 +/- 3% of that of mixed muscle protein (0.0408 +/- 0.0032 and 0.0603 +/- 0.0059%/h, respectively, with KIC and tissue fluid leucine). Contribution of MHC (7 +/- 1 mg.kg-1.h-1) to synthetic rates of whole body mixed muscle protein (36 +/- 5 mg.kg-1.h-1) and whole body protein (127 +/- 4 mg.kg-1.h-1) is only 18 +/- 1 and 5 +/- 1%, respectively. This relatively low contribution of MHC to whole body and mixed muscle protein synthesis warrants direct measurement of synthesis rate of MHC in conditions involving abnormalities of muscle contractile function.
Metabolic adaptation to protein restriction in insulin-dependent diabetes mellitus
Authors: Hoffer L. J. , Taveroff A. , Schiffrin A.
Published: December 2017

Eight normal subjects, four subjects with intensively treated insulin-dependent diabetes mellitus (IDDM), and six subjects with conventionally treated IDDM consumed a test meal of 0.5 g protein and 10 kcal per kg body weight, first while adapted to a conventional diet high in protein, and then again after 5 days of dietary protein restriction. Metabolic N balance (N consumed minus urea production) and net protein utilization were measured over the 9 h after consumption of the test meal, as was recovery in urea of 15N from a tracer dose of [15N]alanine included in each test meal. After the first test meal, N balance and net protein utilization were similar and close to zero for all groups. After the second test meal, N balance and net protein utilization became positive for all groups (P < 0.05) but significantly less so (P < 0.05) for the conventionally treated than for the normal and intensively treated diabetic subjects. 15N recovery in urea was reduced for all groups after the second test meal (P < 0.05) but probably less effectively (P < 0.09) for the conventionally treated diabetic subjects. Metabolic adaptation to protein restriction may be less effective than normal in conventionally treated IDDM.
Effect of in vivo injection of cholera and pertussis toxin on glucose transport in rat skeletal muscle
Authors: Ploug T. , Han X. , Petersen L. N. , Galbo H.
Published: December 2017

Cholera toxin (CTX) and pertussis toxin (PTX) were examined for their ability to inhibit glucose transport in perfused skeletal muscle. Twenty-five hours after an intravenous injection of CTX, basal transport was decreased approximately 30%, and insulin- and contraction-stimulated transport was reduced at least 86 and 49%, respectively, in both the soleus and red and white gastrocnemius muscles. In contrast, PTX treatment was much less efficient. Impairment of glucose transport appeared to develop 10-15 h after CTX administration, which coincided with development of hyperglycemia despite hyperinsulinimia, increased plasma free fatty acid levels, increased adenosine 3',5'-cyclic monophosphate (cAMP) concentrations in muscle, but no difference in plasma catecholamines. Twenty-five hours after CTX treatment, GLUT-4 protein in both soleus and red gastrocnemius muscles was decreased, whereas no change in GLUT-1 protein content was found. In contrast, GLUT-4 mRNA was unchanged, but transcripts for GLUT-1 were increased > or = 150% in all three muscles from CTX-treated rats. The findings suggest that CTX via increased cAMP impairs basal as well as insulin- and contraction-stimulated muscle glucose transport, at least in part from a decrease in intramuscular GLUT-4 protein.
Effect of rhGH and rhIGF-I treatment on protein utilization in elderly women
Authors: Butterfield G. E. , Thompson J. , Rennie M. J. , Marcus R. , Hintz R. L. , Hoffman A. R.
Published: December 2017

To assess the effect of recombinant human growth hormone (rhGH) and recombinant human insulin-like growth factor I (rhIGF-I) on protein utilization, 14 women, age 66-82 yr, were invited to participate in studies of nitrogen balance (n = 14), whole body protein turnover (n = 14), and muscle protein synthesis (n = 8). They were studied both 1 wk before and during the last week of a 1-mo regimen, to which they had been randomly assigned, of either 0.025 mg rhGH/kg once daily or rhIGF-I at 0.015 (low), 0.03 (mid), or 0.06 (high) mg/kg twice daily. Nitrogen balance increased significantly after 1 wk of treatment in all groups (P < 0.05). After 1 mo, the magnitude of this effect had diminished by 50% in the rhGH group but remained elevated throughout the treatment period with all doses of rhIGF-I. Both protein synthesis and breakdown, measured by a primed constant infusion of [15N]glycine, were significantly increased with rhGH (9% and 8%, respectively), low-dose rhIGF-I (4.5% and 4%), and high-dose rhIGF-I (18% and 17%). Net synthesis was significantly increased with rhGH (48%) and high- and mid-dose rhIGF-I (27% and 196%, respectively). Muscle protein synthesis as measured by incorporation of [1-13C]leucine increased significantly with rhGH (50%) and the mid (67%) and high (57%) doses of rhIGF-I. These data show that whole body and muscle protein synthesis are responsive to growth factor stimulation in elderly women.
Induction of human skeletal muscle lipoprotein lipase gene expression by short-term exercise is transient
Authors: Seip R. L. , Mair K. , Cole T. G. , Semenkovich C. F.
Published: December 2017

Exercise increases skeletal muscle lipoprotein lipase (LPL) expression, but the time course of this response is not known. In the present study, we examined the time course of the LPL response to both short-term and acute exercise and measured circulating levels of putative regulators of muscle LPL. Nine adults underwent short-term exercise training (60-90 min of stationary cycling at 55-70% of leg ergometer peak oxygen uptake on 5 consecutive days). Five vastus lateralis biopsies were performed: before training, 20 h after the fourth bout (immediately before the 5th bout), and 0.2, 4, and 8 h after the fifth bout. After four bouts of exercise in 4 days, there was no increase in LPL mass or LPL mRNA exactly 20 h after the fourth bout. However, when tissues were sampled closer to the exercise bout on the 5th day, transient increases were seen. On day 5, LPL mRNA increased by 127% (P < 0.05) at 4 h postexercise and was followed by an increase in LPL mass of 93% (P < 0.05) at 8 h postexercise. Serum triglycerides decreased by 23% (P < 0.05) during the protocol. Two nonexercising subjects showed no consistent change in LPL mRNA or mass. Acute exercise transiently increased levels of norepinephrine (9-fold) and epinephrine (5-fold) and reduced insulin levels. Acute exercise preceded by four daily bouts of exercise induces a transient rise in LPL mRNA followed by rise in LPL mass, suggesting that these responses are temporally related. This induction of LPL gene expression may result from dynamic changes in serum catecholamines, plasma insulin, or events intrinsic to muscle contraction itself.
Electrical stimulation inactivates muscle acetyl-CoA carboxylase and increases AMP-activated protein kinase
Authors: Hutber C. A. , Hardie D. G. , Winder W. W.
Published: December 2017

Muscle malonyl-CoA decreases during exercise or electrical stimulation, the exercise-induced decline being accompanied by changes in the kinetic properties [maximal velocity (Vmax), activation constant (Ka), and citrate concentration required to produce 50% Vmax (K0.5)] of acetyl-CoAcarboxylase (ACC) and by an increase in the AMP-activated protein kinase activity (AMPK). This study was designed to ascertain whether the exercise-induced changes are contraction mediated and, if so, to follow the time course of these changes. The left sciatic nerve of rats was stimulated at 1 Hz for 0, 2, 5, 10, 20, or 30 min, and the gastrocnemius-plantaris muscle group was then excised, frozen in liquid nitrogen, and later analyzed for malonyl-CoA and other metabolites. ACC and AMPK activities were quantitated in ammonium sulfate precipitates from homogenates prepared from the frozen muscles. The Vmax and Ka of ACC for citrate decreased and increased, respectively, over the first 10 min of stimulation, but significantly increased AMPK activity was not observed until 10 to 20 min of stimulation (P < 0.05). Stimulation increased estimated free AMP (P < 0.05). Thus exercise-induced changes in functional properties of ACC appear to be contraction mediated and are accompanied by increased AMPK activity and an increase in the estimated free AMP.
Mechanisms of host wasting induced by administration of cytokines in rats
Authors: Ling P. R. , Schwartz J. H. , Bistrian B. R.
Published: December 2017

This study determined the effects of chronic administration of the two principal proximate cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF), on host wasting in rats. The effects were compared with those observed in a matched pair-fed group to distinguish the contribution from anorexia. Both TNF and IL-1 produced weight loss, net nitrogen loss, and skeletal muscle catabolism and increased liver weight. Such effects were independent from and additive to those resulting from semistarvation. However, under equivalent nutritional conditions, TNF infusion led to a greater effect on muscle protein catabolism and liver weight and caused liver protein anabolism, whereas only the group receiving IL-1 had altered glucose metabolism in the postabsorptive state. Tachyphylaxis was seen in the response of food intake over time after administration of IL-1. These actions define the two principal mechanisms for the development of protein calorie malnutrition that occur because of cytokine action, anorexia producing semistarvation and an increased net protein catabolic rate reducing anabolic efficiency.
Transient upregulation of IGF-I gene expression in brown adipose tissue of cold-exposed rats
Authors: Duchamp C. , Burton K. A. , Geloen A. , Dauncey M. J.
Published: December 2017

The possible involvement of locally produced insulin-like growth factor I (IGF-I) in the cold-induced hyperplasia of interscapular brown adipose tissue (BAT) was investigated in 2-, 4-, and 7-day cold-exposed (CE, 4 degrees C) rats by measuring BAT IGF-I expression at a time when extensive BAT cell proliferation occurs. By comparison with thermoneutral (25 degrees C) controls, plasma IGF-I decreased in CE rats despite an increased food intake, whereas BAT IGF-I peptide increased markedly to peak after 4 days at 4 degrees C. The ratio of class 1 to class 2 IGF-I mRNA was much higher in BAT than in liver. BAT IGF-I mRNA levels per unit weight total RNA doubled after 2 days at 4 degrees C but decreased thereafter to the level in controls. Upregulation of BAT IGF-I mRNA also occurred in CE rats with a food intake restricted to the level of controls. The transient cold-induced upregulation of BAT IGF-I (per unit weight total RNA) suggests that IGF-I plays a role in the early cold-induced BAT hyperplasia that occurs in vivo.
Daily energy expenditure in free-living heart failure patients
Authors: Toth M. J. , Gottlieb S. S. , Goran M. I. , Fisher M. L. , Poehlman E. T.
Published: December 2017

We examined the hypothesis that weight loss in heart failure patients is associated with elevated daily energy expenditure. Twelve cachectic patients [age = 73 +/- 6 yr; weight loss = 15 +/- 6 kg; body mass index (BMI) = 21 +/- 5 kg/m2], 13 noncachectic patients (age = 67 +/- 5 yr; BMI = 27 +/- 5 kg/m2), and 50 healthy elderly controls (age = 69 +/- 6 yr; BMI = 26 +/- 4 kg/m2) were studied. Daily energy expenditure and it components were measured using doubly labeled water and indirect calorimetry and body composition by dual-energy X-ray absorptiometry. Fat mass and fat-free mass were lower (P < 0.05) in cachectic patients compared with noncachectic patients and healthy controls. Daily energy expenditure was lower (P < 0.05) in cachectic patients (1,870 +/- 347 kcal/day) compared with noncachectic patients (2,349 +/- 545 kcal/day) and healthy controls (2,543 +/- 449 kcal/day). Differences in daily energy expenditure were primarily due to lower (P < 0.05) physical activity energy expenditure in cachectic (269 +/- 307 kcal/day) and noncachectic patients (416 +/- 361 kcal/day) compared with healthy controls (728 +/- 374 kcal/day). A lower (P < 0.05) resting energy expenditure was also noted in cachectic patients (1,414 +/- 210 kcal/day) compared with noncachectic patients (1,698 +/- 252 kcal/day) and healthy controls (1,561 +/- 223 kcal/day). These findings show that daily energy expenditure is not higher, but significantly lower, in cachectic heart failure patients due to lower physical activity and resting energy expenditure. These results argue against the hypothesis that an abnormally elevated daily energy expenditure is associated with weight loss in heart failure.
Insulin secretion in adult rats that had experienced different underfeeding patterns during their development
Authors: Martin M. A. , Alvarez C. , Goya L. , Portha B. , Pascual-Leone A. M.
Published: December 2017

Four populations of 70-day-old undernourished rats were studied. All rats were submitted to a 65% restriction of food intake as follows: 1) undernutrition of the mother from day 14 of gestation until birth only (fetal period, group F), 2) undernourished during fetal and suckling periods only (group FS), 3) undernourished from day 14 of gestation until day 70 of life (group FSA), and 4) undernourished from day 28 of life until day 70 (group A). Body weight, plasma glucose, glucose tolerance, basal plasma insulin, in vivo glucose-induced insulin secretion, pancreatic insulin content, and in vitro response of isolated islets to glucose and amino acids were investigated. Islet insulin content decreased in all four groups studied, and islet mass was found reduced in group FSA. Glucose tolerance was decreased in group A, and in vitro response of islets decreased in both groups FSA and A. We conclude that two different adaptive processes should be considered: the possible long-term consequences of impaired pancreas development due to inadequate perinatal nutrition and the functional alteration of insulin secretion to undernutrition in adulthood.
Density of fat-free body mass: relationship with race, age, and level of body fatness
Authors: Visser M. , Gallagher D. , Deurenberg P. , Wang J. , Pierson R. N. , Heymsfield S. B.
Published: December 2017

The two-compartment body composition method assumes that fat-free body mass (FFM) has a density of 1.100 kg/l. This study tested the hypothesis that FFM density is independent of race, age, and body fatness. Subjects were 703 black and white subjects, ages 20-94 yr, with body mass index (BMI) 17-35 kg/m2. Body composition was assessed using a four-compartment model based on tritium dilution volume, body density by underwater weighing, bone mineral by dual-energy X-ray absorptiometry, and body weight. No relationship was observed between FFM density and race or BMI. A tendency was observed for a lower FFM density only in older white women. The difference in percent body fat (delta fat) between the four-compartment model and underwater weighing was < 2% for all groups. Race, age, and BMI explained only 2.3 (women) and 1.4% (men) of the variance in delta fat, whereas the total body water fraction of FFM explained 77%. In contrast to current thinking, these results show that the assumption of constant FFM density is valid in black, elderly, and obese subjects.
Determination of protein synthesis in human rectal cancer in situ by continuous [1-13C]leucine infusion
Authors: Hartl W. H. , Demmelmair H. , Jauch K. W. , Schmidt H. L. , Koletzko B. , Schildberg F. W.
Published: December 2017

Previous studies on human colorectal tumor protein synthesis in situ relied on techniques that required intra- or perioperative sampling to obtain a sufficient biopsy size. The purpose of the present study was to develop a new technique by use of new mass spectrometry equipment [capillary gas chromatography (GC)-combustion isotope ratio mass spectrometry (IRMS)], which allows reduction of the necessary sampling size. Thereby, tumor sampling could be done via conventional rectosigmoidoscopy, excluding the need for further disturbing invasive measures. Fifteen postabsorptive patients with localized rectal cancer received a primed-constant infusion of [1-13C]leucine (0.16 mumol.kg-1.min-1 constant, 9.6 mumol/kg prime). Forceps biopsies were taken after 3 and 6 h. In five subjects, tumor tissue and normal mucosa were studied simultaneously. Determination of protein-bound leucine enrichment was done by GC-IRMS, and GC-quadrupole MS was used to determine tracer-to-tracee ratios (tracer/tracee) for free intracellular leucine. GC-MS data demonstrated achievement of a steady state in the precursor pool enrichment after 3 h of isotope infusion (tracer/tracee at 3 h: 6.34 +/- 0.46%, at 6 h: 6.58 +/- 0.38%). Calculation of tumor protein synthesis yielded a fractional synthetic rate (FSR) of 1.06 +/- 0.11%/h or 25.5 +/- 2.6%/day (range 12.0-37.1%/day). At any time, protein-bound leucine enrichment was significantly higher in tumor tissue than in normal mucosa of the same subject. However, protein synthetic rates were comparable (tumor: 1.09 +/- 0.20%/h, mucosa: 1.29 +/- 0.28%/h). Thus combined GC-combustion IRMS and GC-/quadrupole MS provide a simple, reliable, and minimally invasive method to determine tumor FSR in situ, thereby excluding interferences common to previous methods. Tumor and mucosa tissues are similar with respect to protein synthesis, but they apparently differ with respect to leucine extraction from the arterial blood.
Adenylyl cyclase inhibitory pathway is differentially modified in rat white and brown fat by high-energy diets
Authors: Kenan Y. , Levinson M. , Pines M. , Naim M.
Published: December 2017

Incubation of white adipose tissue (WAT) adipocytes from rats fed a high-energy diet (Exp group) with antilipolytic Gi-coupled adenylyl cyclase inhibitory agonists, nicotinic acid (Nic) and N8-(L-2-phenylisopropyl)adenosine (PIA), resulted in lower cellular adenosine 3',5'-cyclic monophosphate (cAMP) levels than in stimulated adipocytes from rats fed a nutritionally balanced diet (Con group). In contrast to WAT, incubation of brown adipose tissue (BAT) adipocytes with Nic yielded higher cAMP levels in the Exp vs. Con rats. In both WAT and BAT adipocytes, pertussis toxin treatment abolished the differences in Nic- and PIA-inhibited cAMP formation between Exp and Con animals. Immunoblotting of adipocyte membranes indicated a lower content of Gi alpha but not Gs alpha in BAT membranes of Exp vs. Con animals after 6 and 10 wk of feeding. No such differences were found in the Gs alpha or Gi alpha contents of WAT membranes. Thus the inhibitory pathway of adenylyl cyclase is proposed to be sensitized in WAT and desensitized in BAT of rats fed high-energy diets. These modifications in sensitivity are in line with reduced cAMP and lipolysis in WAT and increased cAMP and thermogenesis in BAT during obesity.
Hepatic fatty acid synthase gene transcription is induced by a dietary copper deficiency
Authors: Wilson J. , Kim S. , Allen K. G. , Baillie R. , Clarke S. D.
Published: December 2017

A dietary copper (Cu) deficiency is associated with a twofold increase in hepatic fatty acid biosynthesis. We hypothesized that the induction of hepatic lipogenesis associated with a dietary Cu deficiency reflected an enhanced expression of genes encoding lipogenic enzymes, i.e., fatty acid synthase (FAS). Male weanling rats were pair-meal fed for 42 days a high-sucrose diet that was Cu deficient (CuD; 0.7 microgram Cu/g) or Cu adequate (CuA; 5.0 micrograms Cu/g). The CuD diet increased FAS enzymatic activity twofold (P < 0.05). This rise in enzymatic activity was accompanied by a threefold increase in FAS mRNA and a 2.5-fold increase in FAS gene transcription (P < 0.05). Neither the mRNA abundance nor the rate of gene transcription for phosphoenolpyruvate carboxykinase or beta-actin was affected by the CuD diet. The induction of FAS gene transcription was associated with a 65-85% increase in hepatic reduced glutathione (GSH; P < 0.05). When hepatic GSH synthesis was suppressed by treating CuD rats with L-buthionine sulfoximine, the induction of FAS expression was completely prevented. Similarly, feeding N-acetylcysteine to CuA rats increased hepatic GSH levels 2.5-fold, and this was accompanied by a significant induction in FAS expression. These data indicate that the increase in hepatic lipogenesis associated with a Cu deficiency reflects an induction in hepatic lipogenic gene transcription (i.e., FAS) and that the rate of gene transcription may be dependent on hepatic thiol redox.
Nociceptin, a novel endogenous ligand for the ORL1 receptor, has potent erectile activity in the cat
Authors: Champion H. C. , Wang R. , Hellstrom W. J. , Kadowitz P. J.
Published: December 2017

The heptadecapeptide nociceptin, also known as orphanin FQ, is a newly discovered endogenous ligand for the opioid-like G protein-coupled receptor ORL1. The present study was undertaken to investigate the effects of intracavernosal injections of nociceptin on penile erection in anesthetized cats. Responses to nociception were compared with erectile responses elicited by intracavernosal injection of vasoactive intestinal polypeptide (VIP), adrenomedullin (ADM), the novel nitric oxide donor diethylaminenitric oxide complex sodium (DEA/NO), and the control triple-drug combination (papaverine, phentolamine, and prostaglandin E1). The order of potency was VIP > ADM > nociceptin > DEA/NO. Intracavernosal injections of nociceptin in doses of 0.3-30 nmol elicited dose-related increases in cavernosal pressure and penile length that were comparable to those induced by the triple-drug combination, which is used in the treatment of erectile dysfunction. The response to nociceptin was rapid in onset, and the duration of the peak pressure increase and total response was significantly shorter than the response to the control triple-drug combination but longer in duration than responses to VIP and ADM. Intracavernosal injection of the triple-drug combination resulted in a greater decrease in mean systemic arterial blood pressure than did nociceptin. These data demonstrate that intracavernosal injection of this novel endogenous ligand for the ORL1 receptor induces a potent and relatively long-lasting erectile response in the cat.
Exercise-stimulated glucose transport in skeletal muscle is nitric oxide dependent
Authors: Roberts C. K. , Barnard R. J. , Scheck S. H. , Balon T. W.
Published: December 2017

It has been suggested that there are separate insulin-stimulated and contraction-stimulated glucose transport pathways in skeletal muscle. This study examined the effects of nitric oxide on glucose transport in rat skeletal muscle by use of an isolated sarcolemmal membrane preparation and the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME), administered in the drinking water (1 mg/ml). Female Sprague-Dawley rats were divided into five groups: control, acute exercise, acute exercise+L-NAME, insulin stimulated, and insulin stimulated+L-NAME. Exercise (45 min of exhaustive treadmill running) increased glucose transport (37 +/- 2 to 76 +/- 5 pmol.mg-1.15 s-1) and this increase was completely inhibited by L-NAME (40 +/- 4 pmol.mg-1.15 s-1). A maximum dose of insulin increased glucose transport (87 +/- 10 pmol.mg-1.15 s-1), and adding L-NAME had no effect (87 +/- 11 pmol.mg-1.15 s-1). In addition, exercise, but not exercise+L-NAME, increased sarcolemma GLUT-4 content. This study confirms that there are separate pathways for contraction- and insulin-stimulated glucose transport. More importantly, although exercise and insulin both significantly increased glucose transport, L-NAME had no effect on insulin-stimulated glucose transport but blocked the exercise-stimulated transport. We conclude that nitric oxide is involved in the signal transduction mechanism to increase glucose transport during exercise.
Decreased muscle insulin receptor kinase correlates with insulin resistance in normoglycemic Pima Indians
Authors: Youngren J. F. , Goldfine I. D. , Pratley R. E.
Published: December 2017

Defects in insulin receptor tyrosine kinase activity are present in insulin-resistant non-insulin-dependent diabetes mellitus patients and certain nondiabetic individuals, both lean and obese. However, the relationship between insulin receptor function, insulin action, and obesity is unclear. To address this issue, we have employed a new and highly sensitive enzyme-linked immunosorbent assay to measure in vitro insulin-stimulated autophosphorylation of immunocaptured muscle insulin receptors in a group of 25 normoglycemic Pima Indians. Insulin action, determined during two-step euglycemic insulin clamps, varied widely in these subjects. Maximal in vitro insulin stimulation of insulin receptor autophosphorylation strongly correlated with both low (Mlow)- and high (Mhigh)-dose insulin-stimulated glucose disposal (r = 0.62 and 0.51, P < 0.002 and 0.011, respectively). Insulin receptor autophosphorylation was inversely related to percent body fat (r = -0.52, P < 0.009). After control for percent body fat, receptor autophosphorylation remained correlated with Mlow (partial r = 0.49, P < 0.025). These data therefore suggest that defects in insulin receptor function are major contributors to insulin resistance in both lean and obese normoglycemic Pima Indians.
Effects of dexamethasone on hepatic glucose production and fructose metabolism in healthy humans
Authors: Tounian P. , Schneiter P. , Henry S. , Delarue J. , Tappy L.
Published: December 2017

This study was designed to determine whether glucocorticoids alter autoregulation of glucose production and fructose metabolism. Two protocols with either dexamethasone (DEX) or placebo (Placebo) were performed in six healthy men during hourly ingestion of[13C]fructose (1.33 mmol.kg-1.h-1) for 3 h. In both protocols, endogenous glucose production (EGP) increased by 8 (Placebo) and 7% (DEX) after fructose, whereas gluconeogenesis from fructose represented 82 (Placebo) and 72% (DEX) of EGP. Fructose oxidation measured from breath 13CO2 was similar in both protocols [9.3 +/- 0.7 (Placebo) and 9.6 +/- 0.5 mumol.kg-1.min-1 (DEX)]. Nonoxidative carbohydrate disposal, calculated as fructose administration rate minus net carbohydrate oxidation rate after fructose ingestion measured by indirect calorimetry, was also similar in both protocols [5.8 +/- 0.8 (Placebo) and 5.9 +/- 2.0 mumol.kg-1.min-1 (DEX)]. We concluded that dexamethasone 1) does not alter the autoregulatory process that prevents a fructose-induced increase in gluconeogenesis from increasing total glucose production and 2) does not affect oxidative and nonoxidative pathways of fructose. This indicates that the insulin-regulated enzymes involved in these pathways are not affected in a major way by dexamethasone.
Ovine fetal metabolism during norepinephrine infusion
Authors: Milley J. R.
Published: December 2017

Although stress in fetal life not only increases fetal catecholamine concentration but also decreases fetal growth, there have been few studies that define the specific role of catecholamines in mediating the fetal response to stress. None, however, have investigated effects on fetal amino acid or protein metabolism, processes that should be affected during aberrant fetal growth. Therefore, hormone concentrations as well as oxygen, glucose, lactate, and amino nitrogen, leucine, and protein metabolism were measured with and without norepinephrine infusion in fetuses of eight pregnant ewes (118-125 days of gestation). Transumbilical uptake of oxygen increased during norepinephrine infusion, whereas uptake of glucose remained constant and that of lactate and amino acids fell. The proportion of fetal oxidative metabolism that could be supported by transplacental uptake of exogenous substrates was < 1, indicating that endogenous substrates were used to maintain fetal oxidative metabolism and therefore that fetal growth was diminished. Both fetal leucine uptake and oxidation decreased during norepinephrine infusion, as did fetal protein synthesis and proteolysis. Fetal protein synthesis fell more than proteolysis, however. Consequently, fetal protein accretion, a variable closely related to fetal growth, also fell. Thus the effects of norepinephrine infusion in fetuses suggest that fetal catecholamines play an important role not only in altering fetal metabolism but also in regulating fetal growth.
Mechanisms of homologous and heterologous desensitization of PTH/PTHrP receptor signaling in LLC-PK1 cells
Authors: Guo J. , Liu B. Y. , Bringhurst F. R.
Published: December 2017

Parathyroid hormone (PTH) activates multiple intracellular effectors, including adenylyl cyclase (AC) and phospholipase C (PLC), via a single receptor [PTH/parathyroid hormone-related protein receptor (PTHR)] expressed in bone and kidney. Homologous desensitization of PTHR signaling occurs, but the relative importance of reduced receptor expression vs. impaired receptor-effector coupling in this process remains unclear. It also is not known if AC and PLC responses to PTH are desensitized independently or interdependently. In LLC-PK1 cells that expressed transfected wild-type PTHRs, PTH caused dose- and time-dependent desensitization of both the AC and PLC-responses to PTH without altering PTHR expression. Desensitization of AC was blocked in mutant cells resistant to adenosine 3',5'-cyclic monophosphate but not when cells expressed mutant PTHRs with defective PLC coupling. Desensitization of PLC was unaffected by PKA blockade, partially mimicked by phorbol ester, and not reproduced by agents that selectively activated AC. The finding that homologous PTHR desensitization in LLC-PK1 cells is signal specific suggests that prior exposure of other cells to PTH also may induce discordant regulation of subsequent PTHR signaling, altering the character as well as the intensity of the hormonal response.
Roles of intensity and duration of nocturnal exercise in causing phase delays of human circadian rhythms.
Authors: Buxton O M , Frank S A , L'Hermite-Balériaux M , Leproult R , Turek F W , Van Cauter E
Published: December 2017

To determine the roles of intensity and duration of nocturnal physical activity in causing rapid phase shifts of human circadian rhythms, eight healthy men were studied three times under constant conditions with no exercise, a 3-h bout of moderate-intensity exercise, or a 1-h bout of high-intensity exercise. Exercise stimulus was centered at 0100. Circadian phase was estimated from the onsets of the nocturnal elevation of plasma thyrotropin (TSH) and melatonin. Mean phase shifts of TSH onsets were -18 +/- 8 (baseline), -78 +/- 10 (low-intensity exercise, P < 0.01), and -95 +/- 19 min (high-intensity exercise, P < 0.01). Mean phase delays of melatonin onsets were -23 +/- 10 (baseline), -63 +/- 8 (low-intensity exercise, P < 0.04), and -55 +/- 15 min (high-intensity exercise, P < 0.12). Taken together with our previous findings, this study indicates that nocturnal physical activity may phase delay human circadian rhythms and demonstrates that phase-shifting effects may be determined with exercise durations and intensities compatible with the demands of a real-life setting.
Fructose transport and GLUT-5 protein in human sarcolemmal vesicles.
Authors: Kristiansen S , Darakhshan F , Richter E A , Hundal H S
Published: December 2017

Sarcolemmal vesicles were produced from human skeletal muscle biopsy material obtained at rest and immediately after maximal dynamic exercise (100% maximal O2 uptake) for analysis of fructose transport and hexose transporter (GLUT-5) protein concentration. Human sarcolemmal vesicles displayed a time-dependent uptake of D-fructose that displayed saturable Michaelis-Menten type kinetics (maximal transport 477 +/- 37 pmol.min-1.mg protein-1; half-maximal concentration constant 8.3 +/- 1.2 mM). At a hexose concentration of 5 mM, vesicle transport rate was eight times faster for glucose than for fructose. Preincubation of human muscle vesicles with 35 microM cytochalasin B before the uptake assay resulted in > 95% inhibition in D-glucose uptake, whereas transport of D-fructose was unaffected. Sarcolemmal vesicles prepared from exercised human muscle showed a significant increase (49%) in vesicle GLUT-4 content (P < 0.03, n = 10), which accounts for the increase in vesicle glucose transport that we have recently reported [S. Kristiansen, M. Hargreaves, and E.A. Richter. Am. J. Physiol. 270 (Endocrinol. Metab. 33): E197-E201, 1996]. In contrast, exercise did not increase the vesicle GLUT-5 protein content or induce changes in vesicle fructose transport activity. In conclusion, we propose that fructose transport into human skeletal muscle occurs via a mechanism distinct from that utilized by glucose on the basis of differences in sensitivity to cytochalasin B and responsiveness to exercise. Furthermore, our findings signify that uptake of fructose in human skeletal muscle is mediated by the GLUT-5 transporter.
Growth hormone-binding protein enhances growth hormone activity in vivo.
Authors: Turyn D , Dominici F P , Sotelo A I , Bartke A
Published: December 2017

The decay curve of labeled growth hormone (GH) in the plasma followed a three-compartment model and could be described by the equation: concentration = Ae-alpha t + Be-beta t + Ce-gamma t, where A, B, and C are y-intercepts and alpha, beta, and gamma are compartments. When 125I-labeled ovine prolactin (oPRL) was injected, the decay curve could be described by the equation: concentration = Ae-alpha t + Ce-gamma t. Formation of 125I-labeled bovine-GH-binding protein (GHBP) complexes with somatogenic characteristics was demonstrated in the serum of both normal and GH transgenic mice. In contrast, 125I-oPRL was unable to form complexes of this type in any of the mice studied. Receptor-mediated liver uptake was found to be faster for PRL than for GH (5-6 min vs. 15-20 min). Liver uptake of radioactivity was significantly lower for PRL than for GH [liver to blood ratio (L/B) of 1.7 +/- 0.3 at 6 min vs. L/B of 3.7 +/- 0.6 at 20 min, respectively]. The presence of binding proteins for GH substantially reduces the clearance of this hormone and consequently increases the liver uptake of GH (mediated by GH receptors). This suggests that GHBPs act to increase the biological activity of GH in vivo.
1,25 (OH)2D3 enhances PTH-induced Ca2+ transients in preosteoblasts by activating L-type Ca2+ channels.
Authors: Li W , Duncan R L , Karin N J , Farach-Carson M C
Published: December 2017

We previously demonstrated electrophysiologically that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] shifts the activation threshold of L-type Ca2+ channels in osteoblasts toward the resting potential and prolongs mean open time. Presently, we used single-cell Ca2+ imaging to study the combined effects of 1,25(OH)2D3 and parathyroid hormone (PTH) during generation of Ca2+ transients in fura 2-loaded MC3T3-E1 cells. Pretreatment with 1,25(OH)2D3 concentrations, which alone did not produce Ca2+ transients, consistently enhanced Ca2+ responses to PTH. Enhancement was dose dependent over the range of 1 to 10 nM and was blocked by pretreatment with 5 microM nitrendipine during pretreatment. A 1,25(OH)2D3 analog that activates L-type channels and shifts their activation threshold also enhanced PTH responses. In contrast, an analog devoid of membrane Ca2+ effects did not enhance PTH-induced Ca2+ transients. The PTH-induced Ca2+ transient involved activation of a dihydropyridine-insensitive cation channel that was inhibited by Gd3+. Together, these data suggest that 1,25(OH)2D3 increases osteoblast responsiveness to PTH through rapid modification of L-type Ca2+ channel gating properties, whose activation enhances Ca2+ entry through other channels such as the PTH-responsive, Gd(3+)-sensitive cation channel.
L-arginine for testing endothelium-dependent vascular functions in health and disease.
Authors: Giugliano D , Marfella R , Verrazzo G , Acampora R , Nappo F , Ziccardi P , Coppola L , D'Onofrio F
Published: December 2017

The objective of this study was to assess the role of L-arginine, the natural precursor of nitric oxide, for testing endothelial function in physiological and pathophysiological conditions. In an initial study of 20 healthy subjects, mean blood pressure decreases in response to increasing doses of L-arginine (1, 2, 3, and 5 g) were 1.1 +/- 1.3, 2.6 +/- 1.5, 7.6 +/- 1.3, and 7.7 +/- 2 mmHg, respectively, P < 0.01. The enantiomer D-arginine (3 g) did not produce any change in mean blood pressure and platelet aggregation (n = 10), whereas the infusion of the L-arginine analog NG-monomethyl-L-arginine (6 mg/min) reduced by 70% the vascular effects of L-arginine. In the whole population of 52 healthy subjects, there was an inverse correlation between age and blood pressure or platelet aggregation changes after L-arginine. Compared with matched controls (n = 20), the changes in mean blood pressure and platelet aggregation after L-arginine were significantly lower in non-insulin-dependent diabetic (n = 20) and hypercholesterolemic (n = 16), but not in hypertensive (n = 20), subjects. Changes in blood viscosity were significantly lower only in hypercholesterolemic subjects. Our findings suggest that an intravenous bolus of 3 g L-arginine may be a simple and useful tool to assess the endothelial control of blood pressure and platelet activity in health and disease.
Rat adipose tissue amino acid metabolism in vivo as assessed by microdialysis and arteriovenous techniques.
Authors: Kowalski T J , Wu G , Watford M
Published: December 2017

In fed, anesthetized rats, microdialysis demonstrated a net release of glycerol, glutamine, serine, tyrosine, and taurine and a net uptake of glutamate, aspartate, glycine, and arginine across the inguinal adipose depot. However, the results also indicated excessive proteolysis associated with implantation of the microdialysis probe, and a novel arteriovenous difference technique was developed. Arteriovenous difference across the inguinal fat pat demonstrated a net uptake of glucose and a net release of lactate and glycerol. Starvation (48 h) resulted in higher rates of glycerol and lactate release with lower rates of glucose uptake. A net uptake of triacylglycerol was seen in starved-refed animals. Net glutamine, tyrosine, and taurine release was seen in fed and starved animals, but in starved-refed animals taurine and serine were the only amino acids showing significant release. No significant net uptake or release of ammonia, pyruvate, or alanine was observed. These experiments confirm that adipose tissue is a site of glutamine synthesis and suggest that the principal substrates are derived from intracellular proteolysis. The results also demonstrate the viability of an arteriovenous difference technique for the study of adipose tissue in the rat.
Insulin is degraded extracellularly in wounds by insulin-degrading enzyme (EC 3.4.24.56)
Authors: Shearer Jeffry D. , Coulter Cynthia F. , Engeland William C. , Roth Richard A. , Caldwell Michael D.
Published: December 2017

The exact mechanism by which insulin reverses impaired wound healing is unknown. Previous investigators have shown that insulin is degraded in experimental wounds, suggesting that the action of insulin may be locally modified. The following study corroborates these findings and identifies the major proteinase responsible for insulin degradation in wound fluid (WF). Adult male Fisher rats were wounded by subcutaneous implantation of polyvinyl alcohol sponges while under pentobarbital sodium anesthesia. WF and serum were collected on 1, 5, 10, and 14 days postinjury. Decreased insulin concentration in late WF correlated with an increased insulin-degrading activity. Multiple proteinases appear to participate in the overall degradation of insulin in WF. However, the primary enzyme responsible for insulin degradation in WF was characterized by immunoprecipitation and immunoblotting and identified as the neutral thiol-dependent metalloproteinase, insulin-degrading enzyme (EC 3.4.24.56 ). Exogenous steroid administration caused a decrease in WF insulin-degrading activity. Glucagon and adrenocorticotrophin degradation was also observed, whereas minimal degradation of insulin-like growth factors I and II and epidermal growth factor was detected in WF. The ability to extracellularly degrade insulin may represent a unique mechanism for the regulation of this hormone’s role in healing wounds.