bluuebunny/crossref_metadata_2025 huggingface dataset:
Partitioning of genetic values associated with identified genotype and residual genotype
Authors: LIN Ching Y.
Published: March 2003

A simplified partition procedure was developed to partition the genetic value associated with the identified genotype (a combined genotype of all quantitative trait loci (QTL) identified) and residual genotype. The simplified partition procedure does not require the construction of mixed model equations for both identified and residual genotypes, and therefore drastically reduces the computing requirements as compared with the direct partition procedure. Both the simplified and the direct partition procedures were shown to be equivalent theoretically and experimentally. The simplified partition procedure also applies to the partitioning of other random effects such as the partition of sire effect into two components (constant and interaction sire effects) without actually solving the mixed model equations of the partitioned sire model. The relative contribution of the identified loci and the residual genotypes to the genetic value of a trait depends on their correlation (ρqr) and the ratio of their genetic variances (σ2q/σ2r). Identifying more QTL or increasing QTL variance would add to the contribution of identified QTL to the total genetic value of a quantitative trait. However, the additional contribution of identifying each extra QTL increases at a decreasing rate when the correlation between identified and residual genotypes is positive, but at an increasing rate when the correlation is negative. An effective QTL‐assisted selection program should consider both direct and associated effects of the identified loci.
Age‐related changes in contractions of chicken aorta and ischiadic artery
Authors: ABE Asaki , OHTSUKI Kazumasa , SUZUKI Yoshiki , TAKAHASHI Takiko , KONDO Yasuhiro
Published: March 2003

The characteristics of the contraction of vascular smooth muscle were examined in thoracic aorta and ischiadic artery of chickens aged 3, 6, 10 and 18 weeks. High K+ solution induced a sustained contraction in smooth muscle preparations of aorta and ischiadic artery in vitro. The contraction of the ischiadic artery became greater with age, whereas the contraction of the aortic preparation did not. In the ischiadic artery, the magnitude of the contraction divided by the weight of the muscle preparation was constant at all ages studied. However, those in the aortic preparation decreased with age. These results suggest that the changes in the contractile responses of vascular smooth muscle owing to the age of chickens vary widely according to the preparations of blood vessels, and that the functional smooth muscle cells in the thoracic aorta of chicken do not increase with age.
Increase in expression of growth hormone secretagogues receptor on differentiation of ovine preadipocytes
Authors: ROH Sang‐gun , CHOI Ki‐choon , SHRESTHA Yogendra B. , YOON Chang , Woo Jung‐Hee , SASAKI Shin‐ichi
Published: March 2003

The mechanism by which ghrelin (endogenous growth hormone secretagogues; GHS) is involved with the differentiation of preadipocytes to adipocytes has remained largely unknown. To investigate this issue, we monitored the level of GHS receptor (GHS‐R) mRNA during the differentiation of primary cultured ovine preadipocytes. The preadipocytes, which were obtained from ovine subcutaneous adipose tissues, were proliferated to confluence and then differentiated to adipocytes in differentiation medium for 10 days. The confluent preadipocytes and differentiated adipocytes at Days 3, 7 and 10 were harvested for total RNA extraction and semiquantitative reverse transcription–polymerase chain reaction analysis of GHS‐R mRNA. The level of GHS‐R mRNA was significantly increased during the differentiation process, whereas it was undetectable in the confluent preadipocytes. Our results demonstrate that GHS‐R exists in adipocytes and ghrelin may be a new regulatory factor in the process of differentiation of ovine preadipocytes.
Effects of dietary energy levels on plasma leptin in sheep
Authors: TOKUDA Tomomi , DELAVAUD Carole , CHILLIARD Yves
Published: March 2003

This experiment investigates the changes in the plasma leptin levels of sheep fed a diet of three energy levels (low, moderate and high). Four mature wethers were used for this experiment. For the first 4 weeks, the sheep were fed diets to provide 1.2 times the maintenance metabolizable energy requirements, low energy levels (LE). During the second 4 weeks, the sheep were fed diets to provide 1.5 times the maintenance metabolizable energy requirements, moderate energy levels (ME). During third 4‐week period, the sheep were fed a diet to provide 1.8 times the maintenance metabolizable energy requirements, high energy levels (HE). Body weight was determined every week. Blood samples were collected prior to the morning meal at 3 days intervals throughout the experiment, and plasma leptin, insulin and nonesterified fatty acid (NEFA) concentrations were assayed. Body weight decreased in week 1 after the start of the experiment, it continued to decrease during the LE feeding, but it gradually increased until the end of HE period. Similarly, plasma leptin concentration decreased during LE feeding, but increased during the HE feeding. Additionally, positive correlation was obtained between leptin and insulin or glucose concentrations, whereas no clear relationship with circulating NEFA was observed. In conclusion, it was suggested that plasma leptin concentrations were affected by the metabolizable energy in feed.
Immunohistochemical study of matrix metalloproteinase‐3 (MMP‐3) at the articular cartilage in osteochondrotic pigs
Authors: OHATA Hiroyoshi , ZUSHIDA Kenji , SUGIYAMA Toshie , KUSUHARA Seiji
Published: March 2003

In order to understand the mechanism of osteochondrosis in the pig, articular cartilage was taken from the distal femoral condyles of Duroc pigs exhibiting leg weakness and then examined immunohistochemically for the localization of matrix metalloproteinases‐3 (MMP‐3), one of the enzymes involved in the resolution of cartilage matrix. The articular cartilage had the typical characteristics of osteochondrotic lesions, such as abnormal calcification, clefts of cartilage, disappearance of proteoglycan, and necrotic chondrocytes. The immunoreaction of MMP‐3 was observed in chondrocytes at the boundary between normal cartilage and proteoglycan‐deficient area. Moreover, chondrocytes expressing MMP‐3 showed normal morphology, but the surrounding cartilage matrix did not stain with toluidine blue, which indicated a lack of glycosaminoglycans. These results suggest that MMP‐3 is highly involved in the appearance and expansion of osteochondrotic lesions.
Development and age‐related change of cerebrovascular noradrenergic (NA) innervation in the Japanese quail
Authors: HAYASHI Kiyonori , FURUSE Mitsuhiro , SOH Tomoki , KUSABA Haruo , IWAMOTO Hisao , ANDŌ Kōichi
Published: March 2003

Development of cerebrovascular noradrenergic (NA) innervation was investigated in the Japanese quail, using histofluorescence technique and quantitative analysis. Cerebral perivascular NA nerves arose from the cerebral carotid (CCA), internal ethmoidal (IEA) and vertebral (VA) arteries before hatching, with the first appearance on the CCA and IEA at embryonic day (E) 8 and of the VA at E14. Nerves arising from the IEA were greater in number and spread more rapidly than those from the CCA and VA. On E16, fluorescent fiber bundles lying on the anterior circulation subdivided rapidly into thin fibers. Consequently, the number of NA nerves over the arterial system increased greatly at hatching, particularly along the distal portion of the anterior ramus. At the same developmental stage, all the major arteries of the anterior and posterior circulation were almost entirely covered by NA nerves. The abrupt reorganization of cerebrovascular NA innervation in newborn quails may be related to some specific trophic and vasomotor roles for structural and functional improvement of the cerebral circulation that is required for its brain differentiation at this critical period of development. The supply of NA nerves to the anterior and posterior circulations sequentially increased during development from posthatching day (P) 1–15. Plexuses of NA nerves in each of the major cerebral arteries at P22 and P42–50 were similar in meshwork construction to each other, and to those seen at P15. Likewise, there was no clear statistical difference in the nerve density of the corresponding arteries among the three posthatching ages, except for the caudal basilar artery.
Pathogen safety of manufacturing processes for biological products: special emphasis on KOGENATE® Bayer
Authors: Lee D. C. , Miller J. L. A. , Petteway JR S. R.
Published: March 2003

Summary.  Manufacturers of human therapeutic proteins derived from biological sources continuously strive to improve the pathogen safety profiles of these products. Efforts to improve pathogen safety margins for these biological products are directed towards several areas within the manufacturing processes including: (a) sourcing and screening of raw materials (b) determining the potential for manufacturing processes to reduce pathogen titres, and (c) incorporating methods designed specifically to remove or inactivate contaminating pathogens. Methods that could potentially reduce pathogen titres are a major focus for many manufacturers. In general, these methods are grouped into two categories, pathogen clearance and pathogen inactivation. Assessments are performed on small‐scale, laboratory simulations of the manufacturing process of interest that are spiked with a known amount of a selected pathogen. These studies provide estimates of the potential for a process step to remove or inactivate a particular pathogen. There are several pathogen clearance/inactivation methods that are inherent in manufacturing processes, however, some methods are intentionally incorporated into manufacturing for the sole purpose of reducing putative pathogen titres. Not only are well‐known pathogens such as viruses targeted, but also suspected pathogens such as those associated with the transmissible spongiform encephalopathies (TSEs). The production processes for the isolation of several biological products, including recombinant KOGENATE® Bayer (Kogenate®FS), have been evaluated for the ability to reduce pathogen titres and/or have been designed to incorporate methods for reducing potential pathogen safety risks. Several processing steps with the potential to reduce pathogen titres have been identified.
Aspects of haemophilia prophylaxis in Sweden
Authors: Ljung R. C. R.
Published: March 2003

Summary.  Prophylactic treatment of haemophilia has been gaining acceptance as the optimal therapeutic option in an increasing number of haemophilia centres in the developed world in recent years. This paper focus on three aspects of prophylactic therapy: when to start treatment, venous access and the dose/dose interval. Evidence is in favour of prophylactic treatment to be started at an early age using either a peripheral vein with 1–2 injections per week and a successive increase in the frequency depending on the child and the veins, or, using a Port‐A‐Cath which allows a better prophylactic coverage by infusions preferably every second day in haemophilia A and every third day in haemophilia B.
Comparative pharmacokinetic studies in haemophilia
Authors: Morfini M.
Published: March 2003

Summary.  The general rules of pharmacokinetics have been applied to the study of the behaviour of clotting factor concentrates in patients with haemophilia. Since 1980, the continuous development of innovative plasma‐ and rDNA‐derived concentrates and the implementation of new virucidal methods in manufacturing processes has prompted us to define a standard approach to this issue. Model‐based methods, based upon one or two open compartment models, were available when this work was initiated. Unfortunately, these methods are supported by very little biological data and are profoundly affected by the goodness‐of‐fit of the data. In contrast, the model‐independent method, which is not affected by errors in fitting, provides reproducible and reliable estimates of the behaviour of clotting factor concentrates in patients with haemophilia. Further, the calculations required for the model‐independent method are quite simple and can be computed using a pocket minicomputer. The need for an accurate standardization has been recognized by the Factor VIII/IX Sub‐Committee which, in 1991, issued the first recommendations on the pharmacokinetic evaluation of Factor VIII/IX concentrates. A recent revision of the recommendations has been made available on the web site of the International Society on Thrombosis and Haemostasis. The most crucial changes – sample size, study design, dosages in single‐dose studies, potency assessment, need for well‐defined standards, optimal number of points, and most important outcomes – are discussed in this report. In addition, the model‐independent and compartmental methods are described.
Inheritance of static and dynamic arm strength and some of its determinants
Authors: Thomis M.A.I. , Beunen G.P. , Leemputte M. Van , Maes H.H. , Blimkie C.J. , Claessens A.L. , Marchal G. , Willems E. , Vlietinck R.F.
Published: March 2003

Maximal static, eccentric and concentric torques and arm components estimated by anthropometry and measured by computed tomography were evaluated in 25 male monozygotic twins and 16 dizygotic twins (22.4 ± 3.7 years). The importance of genetic and environmental factors in the observed variation in these measurements was estimated by genetic model‐fitting techniques. In this sample of young adult male twins, genetic factors were significant in most of the strength measurements, arm muscle components and muscle activation variables. The contribution of genetic factors in strength measures depended on the angle, contraction type and to some extent on contraction velocity. For isometric strength, angle‐specificity in genetic and environmental variation could be attributed to the degree of variability in muscle activation and performance discomfort at each specific angle, with the highest unique environmental impact at extreme angles. The high genetic contribution at 170°, but not at 50°, possibly expressed different contributions of genetic factors in the muscle‐length factor and moment arm in torques at both angles. The importance of genetic factors in eccentric arm flexor strength (62–82%) was larger than for concentric flexion (29–65%), as the pattern of genetic determination followed the torque‐velocity curve. Genetic variations in contractile and elastic components, contributing differently to eccentric and concentric torques, together with velocity‐dependent actin‐myosin binding factors, could account for the observed differences. The broad heritability was very high for all anthropometric and arm cross‐sectional area measurements (>85%) and common environmental factors were only significant for anthropometrically estimated mid‐arm muscle tissue area (48%). Heritability estimates of different arm muscularity measurements were comparable.
Blockade of nitrergic neuroeffector transmission in guinea‐pig colon by a selective inhibitor of soluble guanylyl cyclase
Authors: OLGART  , HALLÉN  , WIKLUND  , IVERSEN  , GUSTAFSSON
Published: March 2003

The role of soluble guanylyl cyclase in nitrergic inhibitory neuroeffector transmission was investigated in the longitudinal muscle from guinea‐pig colon, by using an inhibitor of soluble guanylyl cyclase, 1H‐[1,2,4]oxadiazolo[4,3,‐a]quinoxalin‐1‐one (ODQ). In preparations precontracted with histamine, electrical field stimulation (EFS) or exogenous nitric oxide (NO) induced relaxations. The relaxation induced by NO‐application was abolished by ODQ. Both ODQ and the NO‐synthase inhibitor N ω‐nitro‐
L‐arginine (
L‐NOARG) partially inhibited the EFS‐evoked relaxation to a similar extent. These effects were dose‐dependent. The inhibition was more pronounced in the late phase of the EFS‐induced relaxation. The inhibitory effect of ODQ on EFS‐induced relaxation was not affected by additional application of
L‐NOARG. When NO‐formation was blocked by
L‐NOARG, a subsequent addition of ODQ gave no further inhibition of the relaxation. These findings suggest that inhibitory non‐adrenergic, non‐cholinergic neurotransmission in guinea‐pig colon is dependent on endogenous formation of NO, and that the NO‐effect is exclusively mediated via the soluble guanylyl cyclase pathway. The existence of an NO‐independent inhibitory transmission, which is not mediated through the cyclic GMP pathway, is also indicated. Furthermore, it is demonstrated that the NO/soluble guanylyl cyclase‐independent transmission has an earlier onset as compared with the NO/soluble guanylyl cyclase‐dependent pathway.
Effects of nitric oxide inhalation on pulmonary gas exchange during exercise in highly trained athletes
Authors: DURAND  , MUCCI  , SAFONT  , PREFAUT
Published: March 2003

The pathophysiology of exercise‐induced hypoxaemia in elite athletes is still unclear but several studies indicate that a diffusion limitation, which could be explained by an interstitial pulmonary oedema, is a major contributing factor. Stress failure would induce a haemodynamical interstitial oedema with inflammatory reaction and release of mediators like histamine. Histamine release was found to be correlated with the hypoxaemia in elite athletes. If stress failure is involved, inhalation of pulmonary vasodilatators such as nitric oxide during exercise in athletes should induce an inhibition of the histamine release and a reversal of the hypoxaemia. Nine male endurance‐trained young athletes performed two randomized exercise tests: one without and the other with 15 p.p.m. of inhaled NO. Measurements of histamine release and arterial blood gas analysis were performed at rest and at 50, 75 and 100% V˙O2max. At rest, inhaled NO induced a decrease inPaO2and an increase in (Ai‐a)DO2suggesting increased perfusion of units with low V˙A /V˙Q˙. During exercise, NO inhalation suppressed the histamine release observed without NO and induced a moderation in the decrease inPaO2and the increase in (Ai‐a)DO2observed between 75 and 100% of V˙O2max(P < 0.005). In conclusion, this study showed that NO inhalation inhibited exercise‐induced histamine release in highly trained athletes, but we were unable to confirm the suppression of exercise‐induced hypoxaemia (EIH). An unexpected result was that inhaled NO seemed to have a marked effect on arterial oxygenation in highly trained‐athletes, by disturbing gas exchanges.
Thermogenic response to adrenaline during restricted blood flow in the forearm
Authors: Simonsen  , Stefl  , Christensen  , Bülow
Published: March 2003

To elucidate the underlying mechanism behind the thermogenic effect of adrenaline in human skeletal muscle, nine healthy subjects were studied during intravenous infusion of adrenaline. Restriction of blood flow to one forearm was obtained by external compression of the brachial artery, to separate a direct metabolic effect of adrenaline from an effect dependent on increased blood flow. The other arm served as the control arm. In the control arm, the forearm blood flow increased 4.7‐fold (from 2.0 ± 0.3 to 9.3 ± 1.5 mL 100 g–1 min–1, P < 0.001) during the adrenaline infusion. Adrenaline significantly increased forearm oxygen consumption (from 4.7 ± 2.1 to 7.0 ± 3.6 μmol 100 g–1 min–1, P < 0.025). In the arm with restricted blood flow, the forearm blood flow increased 2.9‐fold (from 1.6 ± 0.3 to 4.6 ± 0.8 mL 100 g–1 min–1, P < 0.002) but the forearm oxygen consumption did not increase (baseline period: 5.6 ± 2.3 μmol 100 g–1 min–1, adrenaline period: 6.1 ± 2.1 μmol 100 g–1 min–1, P = 0.54). The experimental design and the difficulties in interpretation of the result are discussed. The results give evidence for the hypothesis that the vascular system plays a key role in the thermogenic effect of adrenaline in skeletal muscle in vivo.
Calcium‐dependent modulation of the plateau phase of action potential in isolated ventricular cells of rabbit heart
Authors: Papp  , Peineau  , Szigeti  , Argibay  , Kovács
Published: March 2003

[Ca2+]i‐dependent modulation of the action potential has been studied in Fura‐2 dialysed ventricular myocytes of the rabbit using the whole‐cell current‐clamp method. Fifteen consecutive action potentials (AP1–AP15) and [Ca2+]i transients were elicited at a frequency of 0.2 Hz. A single, brief application of caffeine (during AP9) first enhanced and thereafter attenuated the [Ca2+]i transients accompanying AP9 and AP10–AP12, respectively. This approach provided direct comparison between time courses of action potentials: during the initial steady state (e.g. AP8) and when Ca2+ release from the sarcoplasmic reticulum was increased by caffeine (AP9) or decreased by depletion (AP10). The increase in [Ca2+]i facilitated repolarization and decreased action potential duration. However, action potentials at reduced Ca2+ release (AP10) had longer duration than during steady state. The caffeine‐induced changes in
L‐type Ca2+ current (ICa,L), during voltage‐clamp conditions partially explained the effects of caffeine on action potentials. When ICa,L was blocked by 500 μmol L–1 Cd2+, enhanced [Ca2+]i transients revealed an extra current component which was outward at +10 mV and inward at the resting membrane potential (most probably the transient inward current). In the presence of Cd2+, however, AP8 and AP10 had identical time courses, suggesting that ICa,L alone was responsible for the lengthening of AP10. Alterations in the transmembrane Na+ gradient resulted in changes of the steady state action potential durations (AP8) consistently with the expected modulation of the Na+–Ca2+ exchange current. However, the contribution of this current to the [Ca2+]i‐dependent behaviour of action potential plateau could not be demonstrated.
Nitric oxide–angiotensin II interactions in angiotensin II‐dependent hypertension
Authors: Navar  , Ichihara  , Chin  , Imig
Published: March 2003

Many studies indicate that renal haemodynamic function in angiotensin II‐ (ANG II) dependent hypertension is not reduced as much as would be predicted from the elevated ANG II levels suggesting that counteracting renoprotective mechanisms are activated. One important renoprotective effect is mediated by increased levels of nitric oxide. Recent studies using the ANG II‐infused hypertensive rat model have shown that inhibition of nitric oxide synthesis (NOS) causes greater decreases in renal blood flow and glomerular filtration rate in ANG II‐infused hypertensive rats than in control rats. This augmented nitric oxide‐dependent influence is localized primarily in the cortex and to the preglomerular vasculature. The differential effects on the renal cortex and medulla are also reflected by the differences in NOS activities and protein expression. Ca2+‐dependent NOS activity was significantly greater in the cortex but not the medulla of the ANG II‐infused hypertensive rats compared with control rats. This was associated with marked activation of endothelial NOS protein levels and smaller increases in neuronal NOS protein levels in the cortex but not in the medulla. In contrast, the Ca2+‐independent NOS activity and the inducible NOS protein levels in the cortex were significantly lower in the ANG II‐infused hypertensive rats. These data support the hypothesis that cortical Ca2+‐dependent NOS, primarily endothelial NOS, is stimulated during the early phases of ANG II‐induced hypertension and exerts a renoprotective effect on cortical haemodynamics.
Angiotensin II type 1 receptors stimulate protein synthesis in human cardiac fibroblasts via a Ca2+‐sensitive PKC‐dependent tyrosine kinase pathway
Authors: Hou  , Pantev  , Möller  , Erlinge  , Edvinsson
Published: March 2003

The aim of the present study was to investigate the proliferative effects of Ang II in human cardiac fibroblasts. The effects of Ang II in human cardiac fibroblasts on the 3H‐thymidine incorporation, the cell number, the 3H‐leucine incorporation and the total protein content were measured. The expression of receptor mRNA was performed by reverse transcription‐polymerase chain reaction (RT‐PCR). Ang II increased 3H‐leucine incorporation in a concentration‐dependent manner but not 3H‐thymidine incorporation in primary cultures of human cardiac fibroblasts. The maximum effect (24 ± 3% over control) was obtained at a concentration of 10 n
M. There were no significant alterations of cell number or total protein content, suggesting that Ang II stimulated protein synthesis but did not induce hypertrophy. The accumulation of 3H‐leucine was blocked by the AT1 receptor antagonist candesartan but not by the AT2 receptor antagonist PD123319. By using RT‐PCR, both AT1 and AT2 receptors mRNA were found to be expressed in human cardiac fibroblasts. The selective MAPKK inhibitor PD098059, the protein kinase C inhibitor K252a or the phospholipase C inhibitor U73122 did not significantly inhibit Ang II augmented 3H‐leucine incorporation. However, this was significantly blocked by the Ca2+‐dependent protein kinase C inhibitor GÖ6976, the non‐selective protein kinase inhibitor staurosporine and the tyrosine kinase inhibitor tyrphostin 25. The effects of Ang II were unaffected by the Gi‐protein blocker pertussis toxin, indicating a Gi‐protein‐independent pathway. Ang II was synergistic with insulin but showed no significant increase on 3H‐leucine incorporation when combined with PDGF or EGF. In summary, Ang II stimulates protein synthesis through AT1 receptors in human cardiac fibroblasts, but has no hypertrophic or hyperplastic effect. The response is mediated by a MAPKK‐independent and Ca2+‐sensitive PKC‐dependent pathway.
Gastrin has a specific proliferative effect on the rat enterochromaffin‐like cell, but not on the parietal cell: A study by elutriation centrifugation
Authors: Bakke  , Qvigstad  , Brenna  , Sandvik  , Waldum
Published: March 2003

Gastrin has a general growth‐promoting effect on gastric oxyntic mucosa, and a more pronounced one on the enterochromaffin‐like (ECL) cell. Whether gastrin has a proliferative effect on the parietal cell lineage beyond the general effect is uncertain. Hypergastrinaemia was evoked in rats using pantoprazole (group II: 100 μmol kg–1, group III: 400 μmol kg–1) for 45 days. Plasma gastrin was 43 ± 8 pmol L–1 (control), 283 ± 54 pmol L–1 (group II) and 577 ± 63 pmol L–1 (group III). Gastric mucosal cells were isolated and fractionated by elutriation centrifugation. Total cell number, percentage and number of ECL and parietal cells, and histamine were determined in each fraction. The number of mucosal cells increased 1.5‐fold in both hypergastrinaemic groups. Enterochromaffin‐like cell content was 2.6 ± 0.5% (control), 6.0 ± 0.6% (group II) and 9.0 ± 0.8% (group III). Histamine concentration in oxyntic mucosal cells rose similarly. The size of the ECL cells was 8.5 ± 0.1 μm (control), 10.8 ± 0.2 μm (group II) and 12.1 ± 0.2 μm (group III), and the increased size was confirmed by shifted distribution in elutriation fractions. Histamine per ECL cell increased with cell size. The number of parietal cells increased parallel to the total number of mucosal cells (1.5‐fold). Parietal cell size and percentage, assessed by image analysis and distribution in elutriation fractions, were unchanged after pantoprazole dosing. Gastrin has a pronounced, concentration‐dependent specific trophic effect on ECL cells and a general proliferative effect on gastric mucosa, including parietal cells.
Metabolic modulation of sympathetic vasoconstriction in exercising skeletal muscle
Authors: Hansen J. , Sander M. , Thomas G.D.
Published: March 2003

The tight coupling of oxygen supply and utilization in exercising skeletal muscle is the result of complex interactions between local mechanisms that control muscle blood flow and substrate utilization and systemic mechanisms that control cardiac output and arterial pressure. The role of the sympathetic nervous system in the integration of these responses, specifically the interaction between sympathetic activation and local vasodilator mechanisms in exercising muscle, has been an active area of research for many years yet remains incompletely understood. The functional consequence of sympathetic activation in exercising skeletal muscle has been the subject of considerable debate. Previous studies in animals and humans have suggested that sympathetic vasoconstricton in active muscle is (a) well maintained and serves to limit active hyperaemia, thereby preventing muscle blood flow from outstripping cardiac output in order to preserve blood pressure and vital organ perfusion or (b) greatly attenuated in order to optimize muscle perfusion, a concept that has been termed ‘functional sympatholysis’. Studies performed over the past 70 years have provided conflicting evidence regarding the relative importance of sympathetic vasoconstriction vs. functional sympatholysis in exercising skeletal muscle. The focus of this review is mainly on recent studies in anaesthetized animal preparations and in conscious humans that have provided evidence for the metabolic modulation of sympathetic vasoconstriction in contracting skeletal muscle and have identified a number of key underlying mechanisms that extend the initial concept of sympatholysis.
Distribution of adenosine A1, A2A and A2B receptors in human skeletal muscle
Authors: Lynge  , Hellsten
Published: March 2003

Many important physiological functions of skeletal muscle, such as glucose uptake, contraction and blood flow, have been proposed to be regulated via the action of adenosine on adenosine receptors. The cellular location of adenosine receptors in skeletal muscle is however, not known. The present study examined the distribution of A1, A2A and A2B adenosine receptors in human skeletal muscle using immunohistochemistry. All three receptor types were localized to vascular smooth muscle and endothelial cells, only the adenosine A2A and A2B receptors were observed in the plasma membrane and cytosol of the skeletal muscle. The finding was supported by results from western‐blotting analysis. The cytosolic staining of the adenosine A2A receptor was slightly more intense in the type I muscle fibres, whereas the A2B receptor was almost absent in type I fibres. The present findings demonstrate for the first time, direct evidence for the existence of A2A and A2B adenosine receptors but absence of the A1 receptor in the sarcolemma and cytosol of skeletal muscle cells. The data also show existence of all three of the A1, A2A and A2B adenosine receptors in vascular cells of skeletal muscle tissue.
Diurnal variation in circulating leptin is dependent on gender, food intake and circulating insulin in mice
Authors: Ahrén
Published: March 2003

Leptin is an adipocyte hormone involved in the regulation of energy homeostasis. Its circulating levels show a diurnal rhythm with a nocturnal peak. We examined the influences of gender, feeding state, and plasma insulin and glucose on the diurnal rhythm in normal mice. Plasma was sampled at 4‐h interval for 24 h in female (n=80) and male (n=80) mice, which were freely fed or fasted. In both genders, plasma leptin displayed a diurnal rhythm with a nadir at 8 or 10 AM and a nocturnal peak at 10 PM to 2 AM. The nocturnal increase in leptin was higher in females (+160 ± 18%) than in males (61 ± 16%; P < 0.001), completely abolished by fasting, and correlated significantly to the diurnal variation in plasma insulin both in females (r=0.44, P=0.003) and males (r=0.46, P < 0.001). Baseline plasma leptin in non‐fasted animals were not different between the genders, whereas during fasting, the reduction in leptin was more pronounced in males than in females, resulting in a higher plasma leptin after fasting in females. Plasma insulin was higher in males under non‐fasted conditions (P=0.003), but not significantly different between genders in fasted animals. In conclusion, plasma leptin displays a nocturnal increase in mice, which is more pronounced in female mice than in male mice, is completely abolished by fasting and correlates to the diurnal variation in circulating insulin. It is suggested that the nocturnal rise in leptin shows gender dependency and is caused by the increase in plasma insulin caused by food intake.
Eccentric muscle damage: mechanisms of early reduction of force
Authors: Allen D. G.
Published: March 2003

Pain and weakness are prominent symptoms which occur after a delay in muscles which have been stretched during contraction (eccentric contraction). These symptoms are particularly severe when the exercise is unaccustomed and when the stretch occurs in muscles on the descending limb of the force–length relation, i.e. at long muscle lengths. It is known that sarcomeres are potentially unstable on the descending limb and it has been proposed by Morgan that uncontrolled elongation of some sarcomeres occurs during eccentric contractions on the descending limb. In this article, the evidence that this mechanism leads to the reduced force is considered. If overextended sarcomeres persist after the eccentric exercise it will cause a shift in the peak of the force–length curve. There is also evidence that in some types of muscle, excitation–contraction coupling is impaired and contributes to the muscle weakness. Cytoskeletal proteins stabilize the sarcomeric structure and may be injured either by the overextended sarcomeres or by activation of proteases. The potential of these mechanisms to contribute to the effects of muscle training and to the symptoms of muscle disease, such as muscular dystrophy, is considered.
Power and peak blood lactate at 5050 m with 10 and 30 s ‘all out’ cycling
Authors: Grassi B. , Mognoni P. , Marzorati M. , Mattiotti S. , Marconi C. , Cerretelli P.
Published: March 2003

Anecdotal observations suggest that the reduction in peak lactate accumulation in blood ([La]b peak) after exhausting exercise, in chronic hypoxia vs. normoxia, may be related to the duration of the exercise protocol, being less pronounced after short supramaximal exercise than after incremental exercise (IE) lasting several minutes. To test this hypothesis, six healthy male Caucasians (age 36.8 ± 7.3, x¯ ± SD) underwent three exercise protocols on a cycle ergometer, at sea level (SL) and after 21 ± 10 days at 5050 m altitude (ALT): (1) 10 s, (2) 30 s ‘all out’ exercise and (3) IE leading to exhaustion in ∼20–25 min. ‘Average’ power output (p¯) was calculated for 10 or 30 s ‘all out’; maximal power output (Pmax) was determined for IE. Lactate concentration in arterialized capillary blood ([La]b) was measured at rest and at different times during recovery; the highest [La]b during recovery was taken as [La]b peak. No significant differences in p¯ were observed between SL and ALT, for either 10 or 30 s ‘all out’ exercise; Pmax during IE was significantly lower at ALT than at SL. [La]b peak after 10 s ‘all out’ was unaffected by chronic hypoxia (7.0 ± 0.9 at ALT vs. 6.3 ± 1.8 mmol L–1 at SL). After 30 s ‘all out’ the [La]b peak decrease, at ALT (10.6 ± 0.6 mmol L–1) vs. SL (12.9 ± 1.4 mmol L–1), was only ∼50% of that observed for IE (6.7 ± 1.6 mmol L–1 vs. 11.3 ± 2.8 mmol L–1). Muscle power output and blood lactate accumulation during short supramaximal exercise are substantially unaffected by chronic hypoxia.
Effect of training intensity on muscle lactate transporters and lactate threshold of cross‐country skiers
Authors: Evertsen F. , Medbø J. I. , Bonen A.
Published: March 2003

The training intensity may affect the monocarboxylate transporters MCT1 and MCT4 in skeletal muscle. Therefore, 20 elite cross‐country skiers (11 men and nine women) trained hard for 5 months at either moderate (MIG, 60–70% of VO2max) or high intensity (HIG, 80–90%). The lactate threshold, several performance parameters, and the blood lactate concentration (cLa) after exhausting treadmill running were also determined. Muscle biopsies taken from the vastus lateralis muscle before and after the training period were analysed for the two MCTs and for muscle fibre types and six enzymes. The concentration of MCT1 did not change for HIG (P=0.3) but fell for MIG (−12 ± 3%, P=0.01); the training response differed between the two groups (P=0.05). The concentration of MCT4 did not change during the training period (P > 0.10). The concentration of the two MCTs did not differ between the two sexes (P=0.9). The running speed at the lactate threshold rose for HIG (+3.2 ± 0.9%, P=0.003), while no change was seen for MIG (P=0.54); the training response differed between the two groups (P=0.04). The cLa after long‐lasting exhausting treadmill running correlated with the concentration of MCT1 (rs=0.69, P=0.002), but not with that of MCT4 (rs=0.2, P=0.2). There were no other significant correlations between the concentrations of the two MCTs and the performance parameters, muscle fibre types, or enzymes (r ≤ 0.36, P > 0.10). Thus, the training response differed between MIG and HIG both in terms of performance and of the effect on MCT1. Training at high intensity may be more effective for cross‐country skiers. Finally, MCT1 may be important for releasing lactate to the blood during long‐lasting exercise.
Adhesion molecules and atherogenesis
Authors: Huo Y. , Ley K.
Published: March 2003

Atherosclerosis is an inflammatory disease of the vessel wall characterized by monocyte infiltration in response to pro‐atherogenic factors such as oxidized lipids. Recently, the role of specific adhesion molecules in this process has been explored. The endothelium overlying atherosclerotic lesions expresses P‐selectin and the shoulder regions express vascular cell adhesion molecule‐1 (VCAM‐1) and intercellular adhesion molecule‐1 (ICAM‐1), which is also expressed on endothelium in regions not prone to plaque development. Serum levels of soluble P‐selectin, ICAM‐1 and VCAM‐1 are elevated in patients with angina pectoris or peripheral atherosclerotic disease. Reconstituted in vitro systems using monocytes on cytokine‐activated endothelial cells under shear flow suggested the involvement of P‐selectin, L‐selectin, VCAM‐1, its ligand, VLA‐4 integrin and CD18 integrins. Studies of monocyte adhesion in isolated perfused carotid arteries harvested from atherosclerotic (apoE−/−) mice show a predominant involvement of P‐selectin and its ligand P‐selectin glycoprotein‐1 (PSGL‐1) in rolling and of VLA‐4 and VCAM‐1 in firm adhesion. Consistent with these findings, apoE−/− mice that are also deficient for P‐selectin show significantly reduced atherosclerotic lesion sizes and are almost completely protected from neointimal growth after vascular injury. Milder effects are also seen in the low‐density lipoprotein (LDL) receptor deficient (LDLR−/−) mouse. In a high cholesterol/cholate model, a role of ICAM‐1 and CD18 integrins was also shown, but this awaits confirmation in more physiologic models. Transient blockade of the VLA‐4/VCAM‐1 adhesion pathway by antibodies or peptides in apoE−/− or LDLR−/− mice reduced monocyte and lipid accumulation in lesions. These data suggest that P‐selectin, PSGL‐1, VLA‐4 and VCAM‐1 are the most important adhesion molecules involved in monocyte recruitment to atherosclerotic lesions.
Biphasic effects of substance P on respiratory activity and respiration‐related neurones in ventrolateral medulla in the neonatal rat brainstem in vitro
Authors: Shvarev Y. N. , Lagercrantz H. , Yamamoto Y.
Published: March 2003

The effects of substance P (SP) on respiratory activity in the brainstem–spinal cord preparation from neonatal rats (0–4 days old) were investigated. The respiratory activity was recorded from C4 ventral roots and intracellularly from three types of respiration‐related neurones, i.e. pre‐inspiratory (or biphasic E), three subtypes of inspiratory; expiratory and tonic neurones in the ventrolateral medulla (VLM). After the onset of SP bath application (10 nM–1 μM) a dose‐dependent decline of burst rate (by 48%) occurred, followed by a weaker dose‐dependent increase (by 17.5%) in burst rate. The biphasic effect of SP on inspiratory burst rate was associated with sustained membrane depolarization (in a range of 0.5–13 mV) of respiration‐related and tonic neurones. There were no significant changes in membrane resistance in any type of neurones when SP was applied alone or when synaptic transmission was blocked with tetrodotoxin (TTX). The initial depolarization was associated with an increase in inspiratory drive potential (by 25%) as well as in bursting time (by 65%) and membrane excitability in inspiratory and pre‐inspiratory neurones, which corresponded to the decrease in burst rate (C4 activity). The spiking frequency of expiratory and tonic neurones was also increased (by 36 and 48%). This activation was followed by restoration of the synaptic drive potential and bursting time in inspiratory and to a less extent in pre‐inspiratory neurones, which corresponded to the increase in burst rate. The discharge frequency of expiratory and tonic neurones also decreased to control values. This phase followed the peak membrane depolarization. At the peak depolarization, SP reduced the amplitude of the action potential by 4–8% in all types of neurones. Our results suggest that SP exerts a general excitatory effect on respiration‐related neurones and synaptic coupling within the respiratory network in the VLM. The transient changes in neuronal activity in the VLM may underlie the biphasic effect of SP in the brainstem respiration activity recorded in C4 roots. However, the biphasic effect of SP on inspiratory burst rate seems to be also defined by the balance in activity of other SP‐sensitive systems and neurones in the respiratory network in the brainstem and spinal cord, which can modify the activity of medullary respiratory rhythm generator.
Responses of human elbow flexor muscles to electrically stimulated forced lengthening exercise
Authors: NOSAKA K. , NEWTON M. , SACCO P.
Published: March 2003

This study developed an electrical stimulation model for human elbow flexors to examine eccentric exercise‐induced muscle damage and adaptation. Male students (n=17) were randomly placed into one of two groups; isometric (ES‐ISO, n=8) and eccentric (ES‐ECC, n=9). The elbow joint was fixed at 90° (1.57 rad) and the elbow flexors stimulated percutaneously by an electronic muscle stimulator for 5 s through two electrodes placed over the muscles for ES‐ISO. In ES‐ECC, the muscles were stimulated similarly to the ES‐ISO, but the elbow joint was forcibly extended from an elbow flexed (90° 1.57 rad) to a full‐extended position (180°, 3.14 rad) in 3 s. Maximal voluntary isometric force, range of motion, upper arm circumference, muscle thickness by ultrasonography, muscle soreness, plasma creatine kinase and aspartate aminotransferase activities were assessed before and for 4 days after exercise. ES‐ECC produced significantly larger changes in all criterion measures compared with ES‐ISO (P < 0.01). These findings confirmed that eccentric muscle actions induced muscle damage, but isometric contractions resulted in little or no damage. Six subjects from the ES‐ECC group repeated the same eccentric exercise (ECC2) 2 weeks after the first bout (ECC1), and changes in the criterion measures were compared between the bouts. Changes in all criterion measures after ECC2 were significantly smaller than ECC1 (P < 0.01). These results suggest that the first eccentric exercise produced a protective effect against muscle damage in the subsequent eccentric exercise bout, which does not involve adaptations in the central nervous system.
Renal denervation abolishes the protective effects of ischaemic preconditioning on function and haemodynamics in ischaemia‐reperfused rat kidneys
Authors: OGAWA T. , MIMURA Y. , KAMINISHI M.
Published: March 2003

Studies were conducted to investigate the role of renal sympathetic nerves in the process of acquiring ischaemic tolerance in ischaemic preconditioned ischaemia‐reperfused rat kidneys. Two periods of 3‐min occlusion of bilateral renal arteries was performed prior to 30‐min bilateral ischaemia and 90‐min reperfusion in acute renal denervated or innervated kidneys. The glomerular filtration rate (GFR), fractional excretion of sodium (FENa) and lithium (FELi), and renal blood flow (RBF) were assessed in reperfused kidneys. Ischaemic preconditioning significantly improved values for all these parameters as compared with no treated ischaemia‐reperfused kidneys. Denervation caused slight increase in GFR, diuresis and natriuresis without improving RBF after reperfusion. However, protecting effects of ischaemic preconditioning on renal function were disappeared in denervated kidneys, while in innevated kidneys the effects of ischaemic preconditioning were maintained. These results clearly showed that ischaemic preconditioning pre‐treatment protects kidneys against ischaemia–reperfusion injury, and the effects are, at least in part, mediated by sympathetic nerves, as the protective effects were abolished by denervation.
Mechanisms of transjunctional transport of NaCl and water in proximal tubules of mammalian kidneys
Authors: KIIL F.
Published: March 2003

Tight junctions and the intercellular space of proximal tubules are not accessible to direct measurements of fluid composition and transport rates, but morphological and functional data permit analysis of diffusion and osmosis causing transjunctional NaCl and water transport. In the S2 segment NaCl diffuses through tight junctions along a chloride gradient, but against a sodium gradient. Calculation in terms of modified Nernst–Fick diffusion equation after eliminating electrical terms shows that transport rates (300–500 pmol min–1 mm–1 tubule length) and transepithelial voltage of +2 mV are in agreement with observations. Diffusion coefficients are Dtj=1500 μm2 s–1 in the S1 segment, and Dtj=90–100 μm2 s–1 in the S2 segment where apical intercellular NaCl concentration is 132 mM, 1 mM below complete stop (Dtj=0 and Donnan equilibrium). Tight junctions with gap distance 6 Å are impermeable to mannitol (effective molecular radius 4 Å); reflection coefficients are σ=0.92 for NaHCO3 and σ=0.28 for NaCl, because of difference in anion size. The osmotic force is provided by a difference in effective transjunctional osmolality of 10 mOsm kg–1 in the S1 segment and 30 mOsm kg–1 in the S2 segment, where differences in transjunctional concentration contribute with 21 mOsm kg–1 for NaHCO3 and –4 mOsm kg–1 for NaCl. Transjunctional difference of 30 mOsm kg–1 causes a volume flow of 2 nL min–1 mm–1 tubule length. Luminal mannitol concentration of 30 mM stops all volume flow and diffusive and convective transport of NaCl. In conclusion, transjunctional diffusion and osmosis along gradients generated by transcellular transport of other solutes account for all NaCl transport in proximal tubules.