bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of ruminal dosing of mechanical stimulating brush on carcass characteristics and fatty acid composition of dressed carcass fat in fattening Holstein steers fed with high‐concentrate diets
Authors: HORIGUCHI Ken‐ichi , TAKAHASHI Toshiyoshi
Published: March 2003

This experiment was undertaken to examine the effect of dosing of a mechanical stimulating brush (RF) in the rumen on dressed carcass characteristics and on the fatty acid composition of dressed carcass fat in fattening beef cattle. The fattening trial was carried out with high‐concentrate diets (organic cell wall contents: 27.5% on a dry mater basis) in eight Holstein steers (12 months of age). Four of the experimental animals were orally dosed with three RF/head (RF group); the other four animals without RF dosing were allotted as the control group. Grass hay was fed to the animals (0.2 kg/head/day) until 19 months of age. Concentrate diet was given ad libitum during the experiment. There were no statistical differences between the RF group and the control group in yield score and meat quality score of dressed carcass characteristics. Regarding fatty acid composition of dressed carcass fat, the proportion of C18 : 2 fatty acids in subcutaneous fat in the RF group was greater (P < 0.05) than that in the control group. C16 : 0 fatty acids in kidney fat in the RF group was lower (P < 0.05), and C18 : 2 fatty acids and total unsaturated fatty acids of 18 carbon number in kidney fat in the RF group were higher (P < 0.05) compared with the control group. The proportion of C18 : 2 fatty acids in rib eye fat in the RF group was greater (P < 0.05) than that in the control group. C18 : 1 fatty acids, C18 : 2 fatty acids and total unsaturated fatty acids of 18 carbon number in rib fat in the RF group were greater (P < 0.05) than those in the control group. The results suggest that in fattening Holstein steers fed with high‐concentrate diets, the effect of ruminal RF dosing on dressed carcass characteristics is not significant, but the proportion of unsaturated fatty acid of carcass fat is increased.
Parvovirus‐mediated gene transfer for the haemophilias
Authors: Walsh C. E. , Chao H.
Published: March 2003

Summary.  Gene therapy may revolutionize the treatment of haemophilia. Effective gene therapy requires sustained therapeutic levels of factors IX (FIX) and VIII. Adeno‐associated virus (AAV) is a member of the parvovirus family, is a nonpathogenic virus with a broad host cell range, and does not provoke a significant immune response upon infection. These favourable characteristics make AAV a suitable gene transfer vector for factor deficient patients. A new understanding of AAV biology coupled with novel AAV vector designs suggest that the goal of effective gene transfer is within reach. We review here recent advances in AAV vectors used for gene transfer of the haemophilias.
The role of land plants, phosphorus weathering and fire in the rise and regulation of atmospheric oxygen
Authors: Lenton Timothy M.
Published: March 2003

The evolution of vascular plants and their spread across the land surface, beginning ∼420 Ma, progressively increased the rate of weathering of phosphorus from rocks. This phosphorus supply promoted terrestrial and marine productivity and the burial of organic carbon, which has been the major source of O2 over geological timescales. Hence, it is predicted that the rise of plants led to an increase in the O2 content of the atmosphere from ∼12 vol %, 570–400 Ma to its present level of ∼21 vol % by ∼340 Ma. Previous modelling studies suggest that O2 then rose to ∼35 vol % ∼300 Ma. Such high concentrations are difficult to reconcile with the known persistence of forests, because rising O2 increases the frequency and intensity of vegetation fires, tending to decrease biomass and cause ecological shifts toward faster regenerating ecosystems. Rising O2 also directly inhibits C3 photosynthetic carbon assimilation and increases the production of toxic reactive oxygen species in cells. These effects suppress plant‐induced phosphorus weathering and hence organic carbon burial, providing a sensitive negative feedback on O2. A revised model predicts that this mechanism could have regulated atmospheric O2 within the range 15–25 vol % for the last 350 million years.
Isolation and characterization of a new nucleolar protein, Nrap, that is conserved from yeast to humans
Authors: Utama Budi , Kennedy Derek , Ru Kelin , Mattick John S.
Published: March 2003

Background: The nucleolus is the site of rRNA synthesis and processing in eukaryotic cells, but its composition remains poorly understood.

Results: We have identified a novel nucleolar RNA‐associated protein (Nrap) which is highly conserved from yeast (Saccharomyces cerevisiae) to human, with homologues in mouse, Drosophila melanogaster, Caenorhabditis elegans, Arabidopsis thaliana, Schizosaccharomyces pombe, and other species. In the mouse, we have found that Nrap is ubiquitously expressed and is specifically localized in the nucleolus. We have also identified splice variants in human and mouse, and defined the intron‐exon structure of the human Nrap gene. Nrap is inherited into daughter nuclei by associating with the condensed chromosomes during mitosis. RNase treatment of permeabilized cells indicated that the nucleolar localization of Nrap is RNA dependent. The effects of actinomycin D, cycloheximide and 5,6‐dichloro‐β‐d‐ribofuranosyl‐benzimidazole on Nrap expression and distribution in cultured cells suggest that Nrap is associated with the pre‐rRNA transcript.

Conclusions: Nrap is a large nucleolar protein (of more than 1000 amino acids), and is a new class of protein with new structural and functional motifs. Nrap appears to be associated with ribosome biogenesis by interacting with pre‐rRNA primary transcript.
Effects of noradrenaline and flow on lactate uptake in the perfused rat hindlimb
Authors: Ye J.‐M. , Steen J.T. , Matthias A. , Clark M.G. , Colquhoun E.Q.
Published: March 2003

Skeletal muscle can release or take up lactate depending on the lactate concentration gradient across the cell membrane. In the perfused rat hindlimb without arterial lactate, both noradrenaline (NA) infusion and increased flow promote lactate release and oxygen consumption (VO2). However, it is unclear whether NA or increased flow rate have similar effects on lactate uptake. The present study compares these effects in the rat hindlimb perfused at a basal flow rate of 0.33 mL min−1 g−1 and 25 °C in the presence of added arterial lactate. When 10 mmol L−1 L‐(+)‐lactate was added to the arterial perfusate, lactate was taken up (16 ± 1.0 μmol g−1 h−1, n = 13) by the hindlimb with a 35% higher VO2 than that without added lactate. Doubling perfusion flow rate enhanced lactate uptake and VO2 by 120% and 40%, respectively. Glucose uptake was also increased (by 253%) with increased flow. Infusion of NA increased perfusion pressure, VO2 and glucose uptake similarly to those induced by increased flow rate. However, lactate uptake was inhibited by NA. This inhibition was not altered by the β‐adrenergic antagonist propranolol. Vasopressin also showed similar effects to NA to decrease lactate uptake associated with increased VO2 and vasoconstriction. These data indicate that in the presence of a high arterial lactate concentration, NA has opposite effects from increased flow rate on skeletal muscle lactate uptake although both have similar effects on lactate release in the absence of arterial lactate. Inhibition of lactate uptake may relate to the vasoconstrictive action of NA.
Microsphere infusion reverses vasoconstrictor‐mediated change in hindlimb oxygen uptake and energy status
Authors: VINCENT  , RATTIGAN  , CLARK
Published: March 2003

The vasoconstrictors, angiotensin II (AII) and serotonin (5‐HT) produce opposing metabolic effects and appear to control different flow routes in the constant‐flow perfused rat hindlimb. In the present study the association between vascular flow route recruitment and metabolism was assessed by selective microsphere embolism of either route. Microspheres (MS, 11.9 ± 0.1 μm, mean  ± SE diameter) were injected during AII, 5‐HT or vehicle infusions (basal conditions) and the effects on hindlimb (4.7 ± 0.1 g muscle) oxygen uptake (V˙O2) and indices of energy status CrP/Cr, CrP/ATP and energy charge (EC) of the calf muscle group assessed. MS (1.5 × 106) injected during vehicle, or 5‐HT infusion increased V˙O2 (P < 0.05) but did not affect energy status. During AII, MS decreased V˙O2. Change in V˙O2 correlated positively with CrP/Cr (r = 0.68, P < 0.0001) and CrP/ATP (r = 0.51, P < 0.001) but not EC (r = 0.08, P = 0.59). MS (1.5 × 106) increased pressure but did not affect the flow rate. The metabolic changes resulting from 1.5 × 106 microspheres were intensified by a second injection of 1.5 × 106 microspheres but further injection (>3.0 × 106 microspheres) began to inhibit flow. It is concluded that a finite number (≤3.0 × 106) of microspheres of 11.9 μm diameter has opposite effects on V˙O2 depending on the vasoconstrictor present and that these effects result from the occlusion of the different vascular route accessed by each vasoconstrictor. The data support the proposal that hindlimb metabolism can be controlled by vasoconstrictors as a result of selective vascular recruitment.
Contrasting effects of platelet‐derived growth factor (PDGF) isomers on mitogenesis, contraction and intracellular calcium concentration in human vascular smooth muscle
Authors: HAFIZI  , NOBIN  , ALLEN  , CHESTER  , YACOUB
Published: March 2003

The present study was aimed at characterizing the responses of human vascular smooth muscle to all three dimeric isomers of platelet‐derived growth factor (PDGF‐AA, ‐AB and –BB) in terms of mitogenesis, contraction and intracellular calcium concentration. The potential of interaction between PDGF and endothelin‐1 (ET‐1) was also investigated. All three PDGF isoforms (0.1–20 ng mL−1) stimulated DNA synthesis in cultured human coronary artery and saphenous vein vascular smooth muscle cells (VSMC), measured by [3H]thymidine incorporation. PDGF‐AB and ‐BB elicited comparable large increases in DNA synthesis of maximum 595 ± 149% (P = 0.001, n = 9) and 576 ± 17% (P < 0.001, n = 5), respectively, whereas PDGF‐AA was only weakly mitogenic (61 ± 16% increase; P < 0.05, n = 3). At a threshold concentration, PDGF acted in synergy with ET‐1 to enhance DNA synthesis (816 ± 337% increase; P < 0.05, n = 7). In contrast to mitogenesis, none of the three PDGF isomers had any effect on contraction of human saphenous veins in vitro, nor did they affect the contractile response to ET‐1, 5‐HT or the thromboxane mimetic U46619. The effects of the three PDGF isomers on intracellular calcium ([Ca2+]i) rises in cultured human VSMC were heterogeneous, with PDGF‐BB inducing the largest increase in [Ca2+]i (442 ± 53 nmol L−1) vs. PDGF‐AB (290 ± 28 nmol L−1), whilst PDGF‐AA had no effect. Both the responses to PDGF‐AB and ‐BB relied upon intracellular calcium release, whilst only PDGF‐AB showed additional dependence on influx of extracellular calcium. In summary, PDGF is strongly mitogenic and comitogenic with ET‐1, despite not being a vasoconstrictor, for human VSMC. Also, human VSMC showed heterogeneous responses to the three PDGF isoforms. These results implicate PDGF, and in particular the PDGF receptor‐β, as important role players in the development of vascular smooth muscle‐mediated intimal thickening in humans.
Molecular mechanics of two smooth muscle heavy meromyosin constructs that differ by an insert in the motor domain
Authors: LAUZON  , TRYBUS  , WARSHAW
Published: March 2003

Phasic and tonic smooth muscles express two myosin heavy chain isoforms that differ by only a seven amino acid insert in a flexible surface loop located near the nucleotide‐binding site. The inserted isoform found predominantly in phasic muscle has two times the actin‐activated ATPase activity and in vitro actin filament velocity as the non‐insert isoform found mainly in tonic muscle (Kelley, C.A., Takahashi, M., Yu, J.H. & Adelstein, R.S. 1993. J Biol Chem268, 12848, Rovner, A.S., Freyzon, Y. & Trybus, K.M. 1997. J Musc Res Cell Motil18, 103). We used a laser trap to characterize the molecular mechanics of the inserted isoform [(+)insert] and of a mutant lacking the insert [(−)insert], which is analogous to the isoform found in tonic muscles. The constructs were expressed in the baculovirus/insect cell system. Unitary displacements (Duni) were similar for both the constructs (≈10 nm) but the attachment time (ton) for the (−)insert was two times that of the (+)insert. These data suggest that the insert in the nucleotide‐binding loop does not affect the inherent mechanics of the myosin molecule but rather the kinetics of the cross‐bridge cycle.
Severe haemorrhage partially reverses moderate haemorrhage‐induced decrease in intestinal vascular capacitance
Authors: WANG  , WELT  , RUTLEN
Published: March 2003

The purpose of the present study was to compare the effect of severe haemorrhage with moderate haemorrhage on intestinal vascular capacitance. In 12 chloralose‐anaesthetized pigs, moderate and subsequent severe haemorrhage was induced by removal of 15 and 25% of blood volume, respectively. Six of the animals were vagotomized prior to induction of haemorrhage. The portal vein pressure/intestinal blood volume (P–V) relationship was measured by using blood pool scintigraphy and varying portal vein pressure. Moderate haemorrhage resulted in a leftward shift of the P–V relationship towards the pressure axis with decreases in cardiac output, portal blood flow and arterial pressure, and an increase in heart rate. Severe haemorrhage shifted the P–V relationship back towards the volume axis compared with moderate haemorrhage, with further decreases in cardiac output, portal blood flow and arterial pressure. While moderate haemorrhage reduced intestinal blood volume at a portal vein pressure of 7 mmHg (Vp7) to 81 ± 3% of the control value (P < 0.01), severe haemorrhage increased Vp7 to 88 ± 1% of the control value (P < 0.05 compared with moderate haemorrhage). After vagotomy, moderate haemorrhage decreased Vp7 to 84 ± 4% of the control value (P < 0.01), whereas Vp7 did not change significantly after severe haemorrhage (Vp7 increased to 86 ± 1% of the control value). Thus, severe haemorrhage is associated with an increase in intestinal vascular capacity compared with moderate haemorrhage. This increase is mediated in part via the cardiac vagal reflex. The attenuation of intestinal venoconstriction during severe haemorrhage probably contributes to further decreases in cardiac output and arterial pressure by redistribution of blood to the peripheral circulation.
Stratification does not limit O2 uptake in rabbit lungs
Authors: HELLER  , SCHUSTER
Published: March 2003

This study was performed to assess the role of stratification, i.e. axial gas mixing deficit within alveolar space, in limiting alveolar gas exchange for oxygen. The single‐breath method for varying breath‐holding time with oxygen‐labelled carbon dioxide, C18O2, was applied to 10 anaesthetized, paralysed and artificially ventilated rabbits. Alveolar partial pressure of C18O2 was analysed using respiratory mass spectrometry. Starting from residual volume, the lungs were rapidly inflated using 40 mL of indicator gas mixture (1% C18O2 in nitrogen). After executing breath‐holding, the lungs were rapidly deflated. Pulmonary diffusing capacity of carbon monoxide was determined in the same way. On the basis of a serial compartment model, the lower limit of the stratificational conductance of oxygen was estimated, using the rate constant of C18O2 removal from alveolar space (4 s−1) and Graham's law. We found that the stratificational conductance in rabbits amounts to at least 13.5 mL mmHg−1 min−1. The pulmonary diffusing capacity of oxygen was calculated by multiplying the carbon monoxide diffusing capacity of rabbit lungs by a factor of 1.2, yielding a value of 0.77 mL mmHg−1 min−1. These results show that stratificational conductance is at least 17.5 times higher than pulmonary oxygen diffusing capacity, indicating that stratification does not limit oxygen uptake in rabbit lungs.
Nervous control of alkaline secretion in the duodenum as studied by the use of cholera toxin in the anaesthetized rat
Authors: JAUP  , PEREGRIN A. TIMAR , JODAL  , LUNDGREN
Published: March 2003

There is experimental evidence for an axon reflex control of alkaline secretion in the rat duodenum. We have investigated if there is also an intramural reflex control of alkaline secretion similar to that demonstrated with regard to the control of the fluid transport in the rat jejunum. Alkaline secretion in the duodenum of an anesthetized rat was continuously monitored using anin situtitration technique. The segment was extrinsically denervated. Exposing the duodenal segment to 80 μg cholera toxin markedly increased alkaline secretion. This response was abolished by hexamethonium (28 μmol (10 mg) kg−1body wt), a nicotinic receptor blocker, lidocaine (0.5 mL of a 1% solution on the serosal surface), a local anaesthetic, and nifedipine (5.75 μmol (2 mg) kg−1body wt i.v.), a calcium channel blocker. The response to cholera toxin was partially abolished by granisetron (0.11 μmol (40 μg) kg−1body wt i.v.), a 5‐HT3receptor blocker. Atropine (1.7 μmol (0.5 mg) kg−1body wt i.v.), a muscarinic receptor blocker, had no effect. We therefore conclude that the alkaline secretion in the rat jejunum evoked by cholera toxin exhibits the same pharmacological properties as the fluid secretion caused by the toxin in the jejunum. This suggests that the alkaline secretion in the rat duodenum is controlled not only by an axon reflex but also by an intramural secretory reflex similar to that controlling fluid transport in the rat jejunum.
Increased endothelin ETB contractile activity in cultured segments of human temporal artery
Authors: WHITE  , LESETH  , JUUL  , ADNER  , CAPPELEN  , AASLY  , EDVINSSON
Published: March 2003

Contractions induced by endothelin‐1, endothelin‐3 and the selective ETB agonist, sarafotoxin S6c, were studied in segments of human temporal artery. The results in fresh arteries were compared with those obtained after 1 or 4 days in organ culture, and with the specific ETA antagonist FR 139317, the specific, mixed antagonist bosentan, or the specific ETB antagonist, BQ 788. Sarafotoxin S6c induced no contractile activity in fresh artery segments, but elicited marked contractions after culture. This contraction was only slightly inhibited by FR 139317, but was abolished by BQ 788. Contractions induced by endothelin‐1 were antagonized by FR 139317 and bosentan, but not by BQ 788. Organ culture did not change the overall pattern, but all concentration–response curves were shifted leftwards. Contractions induced by endothelin‐3 were abolished by all antagonists in fresh arteries, but some activity was restored after organ culture. Sensitivity to endothelin‐3 was markedly increased. The results suggest a change in endothelin receptors during organ culture, resulting in a marked increase in contractile ETB activity, and possibly some increase in ETA activity. Such changes illustrate the complexity of endothelin responses in this vascular bed.
Cardiac accumulation of citrate during brief myocardial ischaemia and reperfusion in the pig in vivo
Authors: HASSEL  , ILEBEKK  , TØNNESSEN
Published: March 2003

Citrate is a key intermediate in energy metabolism and an inhibitor of phosphofructokinase of the glycolytic pathway. During myocardial ischaemia glycolysis is the main source of cardiac ATP. The aim of the present study was to determine if myocardial ischaemia and reperfusion alter cardiac tissue levels of citrate. Open‐chest, anaesthetized pigs were subjected to 10 min of regional myocardial ischaemia by occlusion of the left anterior descending coronary artery, with and without reperfusion, and to 10 min of global ischaemia by circulatory arrest. Citrate, amino acids, glucose and NH3 were measured in biopsies. Ischaemia, whether regional or global, caused a 60–70% increase in tissue levels of citrate. During 1 min of reperfusion following regional ischaemia the level of citrate increased 460%, to ≈600 nmol g−1 wet weight. The level of glutamate decreased by 20–33% (corresponding to 1300–2200 nmol g−1 wet weight), indicating net consumption of this amino acid during ischaemia. The level of aspartate decreased 50% indicating conversion of aspartate to oxaloacetate for the synthesis of citrate. Theoretically, the accumulation of myocardial citrate during brief ischaemia and early reperfusion is large enough to significantly inhibit phosphofructokinase activity and could therefore affect the ability of the myocardium to increase the glycolytic rate in response to ischaemia. This could, however, be partly compensated by the metabolism of myocardial glutamate.
Effects of exhaustive exercise on biochemical characteristics of sarcoplasmic reticulum from rat soleus muscle
Authors: YASUDA  , INASHIMA  , SASAKI  , KIKUCHI  , NIIHATA  , WADA  , KATSUTA
Published: March 2003

This study examined the effects of acute high‐intensity and moderate‐intensity exercise on Ca2+‐stimulated adenosine triphosphatase (ATPase) activity and the Ca2+ and ATP dependence of Ca2+‐ATPase of the sarcoplasmic reticulum (SR) in the soleus muscle. The rats were run on 10% grade at 50 m min−1 or 25 m min−1 until fatigued (avg. time to exhaustion 2.8 and 87.7 min, respectively). The catalytic activities of SR Ca2+‐ATPase were significantly depressed immediately after both types of exercise. Kinetic analyses demonstrated that the Ca2+ affinity of Ca2+‐ATPase was elevated by both types of exercise adopted in the present investigation whereas the increase in the ATP affinity was brought about by only high‐intensity exercise. These results suggest that exhaustive exercise may induce in slow‐twitch muscle fibre the environmental changes, which adversely affect SR Ca2+‐ATPase activity and can overcome the positive influence arising from the increase in the Ca2+ and/or ATP affinities of SR Ca2+‐ATPase.
Specific blood flow reducing effects of hyperoxaemia on high flow capillaries in the pig brain
Authors: SJÖBERG  , GUSTAFSSON  , EINTREI
Published: March 2003

The mechanisms behind oxygen mediated changes in tissue blood flow remain unsettled. Today these are thought to (from experiments on separate vessels and other tissues than the brain) operate through the vessels themselves, probably by involvement of the endothelium in the distal parts of the vascular tree. The aim of this study was to investigate how hyperoxaemia affects the cerebrocortical capillary blood flow distribution in order to gain further knowledge of oxygen mediated blood flow regulating mechanisms. The experiments were performed on seven ventilated anaesthetized pigs. A multiwire Clark‐type microelectrode, placed on the brain surface (motor cortex), was used for capillary blood flow (hydrogen clearance) and oxygen pressure measurements, both of which were made at normoxaemia (arterial PO2 14.4 kPa) and hyperoxaemia (arterial PO2 50.4 kPa)(the animals serving as their own control). Blood pressure, arterial PCO2 and pH remained unchanged throughout the experiments. During hyperoxaemia a 11% reduction in the cerebrocortical capillary blood flow was found (P < 0.001). This flow reduction was seen mainly in two capillary blood flow classes (6/7 animals). In parallel a heterogeneous increase in the cerebrocortical oxygen pressures from 4.5 to 10.1 kPa (mean) (P < 0.001) was found. These results show that hyperoxaemia causes a selective reduction in capillary blood flow affecting capillaries at specific flow levels. A finding that suggests, for the brain, that both the oxygen sensor and effect mechanism is situated distally, in the vascular tree.
Oxidative stress and haematological changes in immobilized rats
Authors: OISHI  , YOKOI  , MAEKAWA  , SODEYAMA  , SHIRAISHI  , KONDO  , KURIYAMA  , MACHIDA
Published: March 2003

Immobilization stress induces formation of reactive oxygen species (ROS) and leads to the oxidative injury in various tissues. In this study, the effects of immobilization stress on peripheral blood cells distribution, plasma level of thiobarbituric acid reactive substances (TBARS), and activities of antioxidant enzymes in erythrocytes were investigated in male Fischer rats. A significant increase in plasma TBARS was observed during and after the stress. Dramatic increases of neutrophils and monocytes imply that ROS formation resulted from their activation. Furthermore, the antioxidant activities of catalase and superoxide dismutase (SOD) in erythrocytes were dramatically increased during and after the stress, while a large fall in erythrocyte number was observed. These findings suggest that the activation of immune cells can be a source of the immobilization‐induced ROS production, and that antioxidant enzymes in erythrocytes play an important role in preventing the ROS‐induced injuries.
Vagal stimulation augments maximal (penta) gastrin‐stimulated acid secretion in humans
Authors: QVIGSTAD  , BJØRGAAS  , EIDE  , SANDVIK  , WALDUM
Published: March 2003

Since the late sixties, the pentagastrin test has been the standard method to examine maximal gastric acid secretion in humans. However, studies on rats and dogs have shown that maximal pentagastrin‐stimulated acid secretion can be augmented by concomitant cholinergic stimulation. The aim of this study was to examine whether the combined stimulation of the vagal nerves and pentagastrin infusion could increase maximal gastric acid secretion compared with pentagastrin alone. Eight healthy medical students (seven males) were included in the study. Gastric acid secretion was determined thrice in each subject. On day one, pentagastrin (6 μg kg−1 h−1) was infused. On day two, insulin‐induced hypoglycaemia (plasma glucose ≈2.3 m
M during 30 min) was obtained by applying the glucose clamp technique. On day three, pentagastrin infusion and insulin induced‐hypoglycaemia were combined. The combination of insulin‐induced hypoglycaemia and pentagastrin infusion increased peak acid output about 20% (P = 0.018) compared with pentagastrin alone. The hypoglycaemia did not cause significant release of gastrin. It is concluded that vagal stimulation of gastric acid secretion may be safely obtained by insulin‐induced hypoglycaemia when applying the glucose clamp technique. In addition, maximal pentagastrin‐stimulated acid secretion does not represent the maximal acid secretory capacity in humans.
Post‐partum prolongation of the atrial repolarization in rabbit
Authors: Pacher  , Ungvári  , Nánási  , Mucha  , Kecskeméti  , Losonczy
Published: March 2003

Female sexual steroids are known to modify the expression of various K+ channels and thus they can alter cardiac repolarization. In the present work, using conventional microelectrode techniques, action potential characteristics were studied in atrial myocardium isolated from virgin, late pregnant, early (1–3 days) post‐partum and late (2–3 weeks) post‐partum rabbits. No changes in action potential configuration were observed during pregnancy. However, the duration, overshoot and amplitude of action potentials were significantly increased in the early (1–3 days) post‐partum period. Resting potential and maximum rate of depolarization remained unchanged. The observed changes were transient, normal action potential characteristics were obtained at weeks 2–3 post‐partum. 4‐aminopyridine (1 mmol L–1). caused a marked lengthening of action potential duration in all preparations obtained from non‐pregnant and pregnant rabbits, whereas this 4‐aminopyridine‐induced prolongation was moderate in those preparations excised from the hearts of early post‐partum animals. Action potential configuration was not affected by pinacidil (10 μmol L–1) or glibenclamide (5 μmol L–1) in non‐pregnant or pregnant animals. In preparations obtained from early post‐partum rabbits, pinacidil significantly shortened action potential duration, which was reverted by glibenclamide. The lengthening of action potential duration together with the decreased sensitivity to 4‐aminopyridine observed in early post‐partum animals may probably be caused by reduction of the transient outward K+ current at this stage. The results also suggest that electrophysiological alterations in the early post‐partum period may probably be more pronounced than those associated with pregnancy itself.
The effect of age on in vitro motility speed of slow myosin extracted from single rat soleus fibres
Authors: Höök  , Li  , Sleep  , Hughes  , Larsson
Published: March 2003

The effect of age on the motor protein myosin was examined in a novel in vitro motility assay. Myosin was extracted from soleus fibres of young (3–6 month) and old (20–24 month) rats. All fibres expressed the type I myosin heavy chain (MyHC) and the slow isoforms of the myosin light chains (MyLCs). In vitro motility speed was significantly (P < 0.001) faster in the young adult (1.43 ± 0.23 μm s–1) than in the aged group (1.27 ± 0.23 μm s–1). The result indicates that the age‐related decrease in contractile speed observed in slow fibres may be the effect of a change in the properties of myosin with age.
Vasoconstrictor responses in thromboxane receptor knockout mice: tubuloglomerular feedback and ureteral obstruction
Authors: Schnermann  , Traynor  , Pohl  , Thomas  , Coffman  , Briggs
Published: March 2003

The role of thromboxane (TP) in the vasoconstriction induced by tubuloglomerular feedback or 18‐h ureteral obstruction was studied in wild type mice (TP +/+), and in heterozygous (TP +/–) and homozygous TP receptor knockout mice (TPR –/–). TGF function was assessed from the response of stop flow pressure (PSF) to a maximum increase in loop of Henle flow rate (0–30 nL min–1). PSF fell by 6.4 ± 0.4 mmHg in wild‐type mice, by 6.1 ± 0.6 mmHg in TP +/–, and by 7.9 ± 0.7 mmHg in TP –/– mice. In the presence of the TP receptor agonist U46,619 (10–5 M) the PSF reduction increased to 10.4 ± 0.8 mmHg in TP +/+, and to 10.6 ± 2.8 mmHg in TP +/–, but was unchanged at 7.7 ± 0.7 mmHg in TP –/–. Mean arterial blood pressures were comparable between groups (103 ± 3 mmHg in TP +/+, 113 ± 4.6 in TP +/– and 113 ± 2.4 mmHg in TP –/– mice). Intratubular pressure following unilateral ureteral obstruction was significantly higher in TP –/– than in TP +/+ mice both in the early phase (0–3 h) and late phase (18 h) of obstruction. These results indicate that chronic TP receptor deficiency does not significantly alter maximum TGF responses in mice, and that it is accompanied by exaggerated vasodilatation during short‐term unilateral ureteral obstruction and attenuated vasoconstriction during longer lasting obstruction. We conclude that thromboxane is primarily a regulator of renal vascular tone under pathophysiological conditions.
Intrarenal dopamine coordinates the effect of antinatriuretic and natriuretic factors
Authors: Holtbäck  , Kruse  , Brismar  , Aperia
Published: March 2003

The precision by which sodium balance is regulated suggests an intricate interaction between modulatory factors released from intra‐ and extrarenal sources. Intrarenally produced dopamine has a central role in this interactive network. Dopamine, produced in renal tubular cells acts as an autocrine and paracrine factor to inhibit the activity of Na+,K+‐ATPase as well as of a number of sodium influx pathways. The natriuretic effect of dopamine is most prominent under high salt diet. The antinatriuretic effects of noradrenaline, acting on α‐adrenoceptors and angiotensin II are opposed by dopamine as well as by atrial natriuretic peptide (ANP). Several lines of evidence have suggested that ANP acts via the renal dopamine system and recent studies from our laboratory have shown that this effect is attributed to recruitment of silent D1 receptors from the interior of the cell towards the plasma membrane. Taken together, the observations suggest that dopamine coordinates the effects of antinatriuretic and natriuretic factors and indicate that an intact renal dopamine system is of major importance for the maintenance of sodium homeostasis and normal blood pressure.
Impact of oestradiol and progesterone on the glycosaminoglycans and their depolymerizing enzymes of the rat mammary gland
Authors: Sunil  , Srinivasan  , Aruldhas  , Govindarajulu
Published: March 2003

The influence of oestradiol and progesterone either singly or in combination with each other on the levels of hyaluronic acid, heparan sulphate, chondroitin sulphate, and on the activity of hyaluronidase and chondroitinase were investigated in the mammary gland of ovary‐intact and in ovariectomized rats, administered oestradiol and/or progesterone. Administration of oestradiol to ovary‐intact rats elevated the levels of hyaluronic acid and decreased the levels of heparan sulphate while progesterone, when administered alone, could elevate only chondroitin sulphate when compared with controls. The steroids when administered in combination, however, increased the levels of all glycosaminoglycans studied. Ovariectomized animals showed a decrease in heparan sulphate alone as compared with controls while administration of oestradiol to these rats elevated the levels of both heparan sulphate and chondroitin sulphate as compared with ovariectomized rats. Also the administration of progesterone either singly or in combination increased the levels of heparan sulphate and also decreased the levels of hyaluronic acid with no impact on the levels of chondoritin sulphate. In ovary‐intact animals administration of oestradiol alone had no effect on hyaluronidase activity. Progesterone either singly or in combination with oestradiol reduced the activity of hyaluronidase, whereas it had no influence on the activity of chondroitinase. The activities of both the enzymes were decreased in ovariectomized animals and administration of oestradiol and/or progesterone to the above groups resulted in an increase. This study demonstrates that oestradiol anzd progesterone play an important role in modulating glycosaminoglycans and their depolymerizing enzymes, thereby influencing the activities of the mammary epithelium.
Lactate as a fuel for mitochondrial respiration
Authors: Van Hall G.
Published: March 2003

Lactate production in skeletal muscle has now been studied for nearly two centuries and still its production and functional role at rest and during muscle contraction is a subject of debate. Historically, skeletal muscle was seen mainly as the site of lactate production during contraction and lactate production associated with a lack of muscle oxygenation and fatigue. Later, it was recognized that skeletal muscle not only plays an important role in lactate production but also in lactate clearance and this in turn has led to a renewed interest in the metabolic fate of lactate in skeletal muscle and also in other tissues. Studies using lactate isotopes have shown that skeletal muscle extracts lactate from the circulation despite a substantial net lactate release, and that skeletal muscle has a large capacity for lactate oxidation; these processes being enhanced with exercise. Lactate dehydrogenase (LDH) controls the formation of lactate and may regulate the turnover of lactate in the muscle cell. Skeletal muscle contains five LDH isoforms (LDH1–5). Of the five LDH isoforms, the heart‐specific LDH1,2 is generally suggested to favour the reaction of lactate to pyruvate whereas the muscle‐specific LDH4,5 isoform favours lactate formation. However, in this paper, it is argued that compartmentalization of the muscle cell and LDH association with cell structures may play a more predominant role in whether the LDH reaction proceeds towards lactate or pyruvate formation. The model for skeletal muscle lactate metabolism presented is in essence based on a synthesis of old and more recent studies on skeletal muscle lactate transport, uptake, release, oxidation, and the role of LDH at rest and during exercise.
The influence of nitric oxide on in vivo human skeletal muscle properties
Authors: Folland  , Maas  , Jones
Published: March 2003

We have investigated the action of exogenous nitric oxide (NO) on the strength and contractile properties of human skeletal muscle working in vivo. Maximum isometric voluntary contraction force (MVC) of the quadriceps was measured and superimposed electrical stimulation was used to estimate the level of activation and ‘true maximum force’ (TMF). Force–frequency relationships were determined to assess changes in contractile properties of the muscle. Subjects in the experimental group (E, n=10) were measured before and during two separate periods of treatment with different doses of glyceryl trinitrate, a NO donor, delivering 100 (GTN100) or 200 (GTN200) μg h–1 as a trans‐dermal patch. A control group (C, n=6) was measured during two similar periods whilst taking an oral placebo. There was a significant increase in strength with GTN200 (MVC: +5.15%; TMF: +3.87%). There was no change in the strength of group C. There was a trend towards reduced forces at submaximal frequencies with GTN administration but the most notable change was a decline in twitch force (approximately 12%, P < 0.05) with GTN100 treatment and this remained depressed throughout the study. No changes were seen in the contractile properties of the control group C. The present results show that GTN treatment increased maximum voluntary strength but decreased twitch tension. The time course and dose–response characteristics indicate that these are two separate actions of NO on human muscle working in vivo.
The inhibitory effects of allopregnanolone and pregnanolone on the population spike, evoked in the rat hippocampal CA1 stratum pyramidale in vitro, can be blocked selectively by epiallopregnanolone
Authors: Wang  , Bäckström  , Landgren
Published: March 2003

The progesterone metabolites allopregnanolone (Allo, 3α‐hydroxy‐5α‐pregnan‐20‐one) and pregnanolone (Preg, 3α‐hydroxy‐5β‐pregnan‐20‐one) enhance the γ‐aminobutyric acid (GABA) action through a distinct site on the GABAA‐receptor. Their 3β‐isomers epiallopregnanolone (Epiallo, 3β‐hydroxy‐5α‐pregnan‐20‐one) and epipregnanolone (Epipreg, 3β‐hydroxy‐5β‐pregnan‐20‐one), do not have these effects on GABAA‐receptors. We have studied the interaction between Allo/Preg and their 3β‐isomers on action potentials in rat hippocampal slices in vitro. The Schaffer collaterals were stimulated electrically in CA1 striatum radiatum and the population spike (POPSP) was recorded in stratum pyramidale. A 0.5‐nL droplet of drug was applied locally onto stratum oriens–pyramidale via a pressure pipett. Muscimol (Mus) (12.5 fmol), Allo and Preg (6.25 fmol) caused a reversible inhibition of POPSP. On the other hand, 6.25 fmol Epiallo had no significant effect on POPSP compared with the vehicle control. Combined Epiallo and Allo application caused a dose‐dependent reduction of the Allo inhibition of POPSP. A full blockage was seen at a molar ratio of 1:1. Epiallo also blocked the Preg inhibition of POPSP, when the two drugs were combined in a molar ratio of 1:1. Epiallo did not block the Mus inhibition of POPSP, when the two drugs were combined at a molar ratio of 1:2. Bath perfusion of 12.5 μM Epiallo blocked the inhibition of 6.25 fmol Allo on POPSP, but not the inhibition caused by 12.5 fmol Mus. Epipreg did not block the inhibition of Allo and Preg on POPSP, when it was combined with the two latter drugs at a molar ratio of 1:1. Our data suggest that the steroid modulation of the GABAA transmitted inhibition of the CA1 pyramidal neurones is selectively and dose dependently blocked by Epiallo, the 3β‐hydroxy‐isomer of Allo, but not by Epipreg, the 3β‐hydroxy‐isomer of Preg.
Constitutive nitric oxide synthesis in the kidney – functions at the juxtaglomerular apparatus
Authors: Persson  , Bachmann
Published: March 2003

Tubulo‐vascular information transfer at the renal juxtaglomerular apparatus (JGA) serves to adjust the biosynthesis and release of renin, the key enzyme of the renin angiotensin system, and to regulate glomerular arteriolar muscle tone. The macula densa serves as a sensor of tubular NaCl. Concentration‐dependent salt uptake through the Na‐K‐2Cl cotransporter located in the apical membrane of macula densa cells triggers a signal transduction cascade that involves the synthesis of nitric oxide (NO) through a type 1 NO synthase (NOS1) which is described with respect to its complex mRNA structure and regulatory aspects. The anatomical and functional targets of the NO‐soluble guanylyl cyclase‐cGMP pathway at the JGA are reviewed.
Cytokines and oxidative signalling in skeletal muscle
Authors: Reid M. B. , Li Y.‐P.
Published: March 2003

A growing body of literature indicates that cytokines regulate skeletal muscle function, including gene expression and adaptive responses. Tumour necrosis factor‐α (TNF‐α) is the cytokine most prominently linked to muscle pathophysiology and, therefore, has been studied most extensively in muscle‐based systems. TNF‐α is associated with muscle catabolism and loss of muscle function in human diseases that range from cancer to heart failure, from arthritis to AIDS. Recent advances have established that TNF‐α causes muscle weakness via at least two mechanisms, accelerated protein loss and contractile dysfunction. Protein loss is a chronic response that occurs over days to weeks. Changes in gene expression required for TNF‐α induced catabolism are regulated by the transcription factor nuclear factor‐κB which is essential for the net loss of muscle protein caused by chronic TNF‐α exposure. Contractile dysfunction is an acute response to TNF‐α stimulation, developing over hours and resulting in decreased force production. Both actions of TNF‐α involve a rapid rise in endogenous oxidants as an essential step in post‐receptor signal transduction. These oxidants appear to include reactive oxygen species derived from mitochondrial electron transport. Such information provides insight into the cellular and molecular mechanisms of TNF‐α action in skeletal muscle and establishes a scientific basis for continued research into cytokine signalling.
Lessons from interleukin‐deficient mice: the interleukin‐1 system
Authors: Fantuzzi G.
Published: March 2003

The study of cytokine‐deficient mice has provided important information for a better understanding of inflammatory processes. In this report, the characterization of mice deficient for various components of the interleukin (IL)‐1 system is reviewed. Results obtained by studying mice deficient for IL‐1α, IL‐1β, IL‐1 receptor antagonist, IL‐1 receptor type I, IL‐1 receptor accessory protein, IL‐1 receptor‐associated kinase, and the IL‐1β‐converting enzyme caspase‐1 are summarized. Because some of the components of the IL‐1 system are shared with IL‐18, similarities between IL‐1β and IL‐18 are also discussed.
Effect of glycogen loading on skeletal muscle cross‐sectional area and T2 relaxation time
Authors: Nygren A. T. , Karlsson M. , Norman B. , Kaijser L.
Published: March 2003

This study was performed to investigate if glycogen loading of skeletal muscles, by binding water, would effect the cross‐sectional area (CSA) and if an altered water content would alter the transverse relaxation time (T2) measured by magnetic resonance imaging (MRI). Five healthy volunteers participated in a programme with 4 days of extremely carbohydrate‐restricted meals followed by 4 days of extremely high carbohydrate intake. The CSA and T2 of thigh and calf muscles were related to the intramuscular glycogen content evaluated at days 4 and 8. An increase in glycogen content from 281 to 634 mmol kg–1 dry wt increased the CSA of the vastus muscles by 3.5% from 78 ± 11 to 80 ± 12 cm2 and the thigh circumference by 2.5% from 146 ± 20 to 150 ± 23 cm2. Calf circumference increased non‐significantly by 4% from 78 ± 15 to 82 ± 19 cm2. Mono‐exponential T2 decreased in m tibialis anterior from 27.8 ± 1.2 to 26.9 ± 1.7 ms, did not change in m. vastus lateralis 26.5 ± 1.9 ms/26.6 ± 1.3 ms or in m. gastrocnemius 29.5 ± 1.0 ms/29.8 ± 1.9 ms. Glycogen loading increased the signal intensity mainly at different echo times (TE) 15 and 30 ms. The study shows that increased glycogen filling in the muscles increases muscle CSA and that this can be detected by MRI. The signal intensity increased the most at shorter TEs suggesting a more tight intracellular binding of water in glycogen loaded muscles.
Differential effect of oestrogen on post‐exercise cardiac muscle myeloperoxidase and calpain activities in female rats
Authors: TIIDUS P. M. , ZAJCHOWSKI S. , ENNS D. , HOLDEN D. , BOMBARDIER E. , BELCASTRO A. N.
Published: March 2003

The effects of oestrogen administration on 1 h post‐exercise cardiac muscle myeloperoxidase (MPO) and calpain activities were determined in female rats. Rats were ovariectomized and implanted for 2 weeks with either oestrogen (25 mg 17‐oestradiol) or placebo pellets or left with ovaries intact. Rats were then run for 1 h at 21 m min–1, 12% grade, killed 1 h post‐exercise and cardiac muscle and blood samples were removed. Control animals from each group were killed without prior exercise. Serum oestrogen levels in the order of the highest to lowest were; ovariectomized oestrogen replaced rats > intact ovaries rats > ovariectomized placebo rats. Oestrogen induced significant (P < 0.05) elevations in cardiac MPO activity at rest and at 1 h post‐exercise in ovariectomized rats. No significant elevations in cardiac MPO activity were evident in placebo ovariectomized or normal ovary rats at rest or post‐exercise. Cardiac calpain activities were similar in all unexercised groups. Ovariectomized placebo and intact ovary rats had significantly (P < 0.05) elevated cardiac calpain activities 1 h post‐exercise while calpain activity was not significantly elevated in hearts from ovariectomized oestrogen rats. These results demonstrate that oestrogen supplementation in ovariectomized rats induces elevations in cardiac muscle MPO activities at rest and at 1 h post‐exercise. This is opposite to the effect of oestrogen in post‐exercise skeletal muscle and implies a greater neutrophil infiltration into cardiac muscle caused by oestrogen. This effect cannot be explained by changes in 1 h post‐exercise cardiac muscle calpain activity, the elevation of which was suppressed by oestrogen administration. Oestrogen influences cardiac calpain activity similarly to its effect in skeletal muscle. Thus, oestrogen administration to ovariectomized rats induces elevations in cardiac MPO activity while suppressing cardiac calpain activity.