bluuebunny/crossref_metadata_2025 huggingface dataset:
Acid‐induced duodenal mucosal nitric oxide output parallels bicarbonate secretion in the anaesthetized pig
Authors: HOLM  , JOHANSSON  , PETTERSSON  , FÄNDRIKS
Published: March 2003

We recently showed the involvement of the L‐arginine/nitric oxide (NO) pathway in acid‐induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg−1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and Pco2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO.

Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 ± 45% and 106 ± 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG‐monomethyl‐
L‐arginine (L‐NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L‐NMMA could be reversed by administration of L‐arginine (3 mM).

The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L‐arginine/NO pathway is involved in the acid‐induced duodenal mucosal bicarbonate secretory response.
Responses of total and free insulin‐like growth factor‐I and insulin‐like growth factor binding protein‐3 after resistance exercise and training in elderly subjects
Authors: BERMON  , FERRARI  , BERNARD  , ALTARE  , DOLISI
Published: March 2003

To investigate the effects of an acute bout of exercise on total and free insulin‐like growth factor‐I and insulin‐like growth factor binding protein‐3 plasma concentrations, 32 healthy elderly subjects (67–80 years, 16 men) performed a strength test, which consisted of two sets of 12 repetitions at 12‐repetition maximum and four sets of 5 repetitions at 5‐repetition maximum for horizontal leg press, seated chest press, and bilateral leg extension movements. Ten out of the 32 subjects served as time controls. Blood samples were drawn prior (08.30 h), immediately (10.30 h), and 6 h (16.30 hours) after the strength test in exercising and resting subjects. The 32 subjects were then randomly assigned to habitual physical activity or to an 8‐week strength training program. After 8 weeks, both sedentary and trained groups underwent blood samplings under the above‐mentioned conditions. The exercising group showed increased total and free insulin‐like growth factor‐I concentrations immediately (+17.7 and +93.8%, respectively), and 6 h (+7.5 and +31.2%, respectively) after the test, whereas no significant changes in insulin‐like growth factor binding protein‐3 concentrations were observed in either exercising or resting control groups. Strength training induced no significant changes in baseline insulin‐like growth factor‐I and insulin‐like growth factor binding protein‐3 concentrations. Trained and sedentary groups showed similar hormonal response pattern to the strength test, which consisted of increased total and free insulin‐like growth factor‐I concentrations. The data indicated that strength exercise can induce an early and sustained insulin‐like growth factor‐I release, in elderly subjects, regardless of their training status.
Carbonic anhydrase IV activity is localized on the exterior surface of human erythrocytes
Authors: WISTRAND  , CARTER  , CONROY  , MAHIEU
Published: March 2003

Carbonic anhydrase (CA) cytoplasmic isozymes CA I and CA II were found in human erythrocyte membrane ghosts, when prepared at pH 5.4 and pH 7.4, but not in ghosts prepared at pH 8.2. These findings could indicate that previously reported CA activity of ghosts was owing to contamination by CA I and CA II during the preparation of the ghosts. However, using a sensitive micro‐assay, CA activity was also found in ghosts prepared at pH 8.2. This activity constitutes 0.2% of the erythrocytes’ total CA‐activity, and originates from a membrane‐associated isoform of CA, located at the exterior membrane surface. It has immunochemical and kinetic properties like those of the membrane‐bound CA IV, previously isolated from kidney, lung and small blood vessels. Its function is possibly to interact with the red cell membrane anionic transport protein, band 3, for the bicarbonate/chloride exchange.
The Kety–Schmidt technique for repeated measurements of global cerebral blood flow and metabolism in the conscious rat
Authors: Linde  , Schmalbruch  , Paulson  , Madsen
Published: March 2003

Cerebral activation will increase cerebral blood flow (CBF) and cerebral glucose uptake (CMRglc) more than it increases cerebral uptake of oxygen (CMRO2). To study this phenomenon, we present an application of the Kety–Schmidt technique that enables repetitive simultaneous determination of CBF, CMRO2, CMRglc and CMRlac on awake, non‐stressed animals. After constant intravenous infusion with 133Xenon, tracer infusion is terminated, and systemic arterial blood and cerebral venous blood are continuously withdrawn for 9 min. In this paper, we evaluate if the assumptions applied with the Kety–Schmidt technique are fulfilled with our application of the method. When measured twice in the same animal, the intra‐individual variation for CBF, CMRO2, and CMRglc were 10% (SD: 25%), 8% (SD: 25%), and 9% (SD: 28%), respectively. In the awake rat the values obtained for CBF, CMRO2 and CMRglc were 106 mL [100 g]−1 min−1, 374 μmole [100 g]−1 min−1 and 66 μmole [100 g]−1 min−1, respectively. The glucose taken up by the brain during wakefulness was fully accounted for by oxidation and cerebral lactate efflux. Anaesthesia with pentobarbital induced a uniform reduction of cerebral blood flow and metabolism by ≈40%. During halothane anaesthesia CBF and CMRglc increased by ≈50%, while CMRO2 was unchanged.
Near‐infrared monitoring of tissue oxygenation during application of lower body pressure at rest and during dynamical exercise in humans
Authors: Nishiyasu  , Tan  , Kondo  , Nishiyasu  , Ikegami
Published: March 2003

During the application of a wide range of graded lower body pressures (LBP) (–50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used near‐infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during –25 and –50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was the reverse of that in the thigh. Measurements from the forehead showed changes only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower parts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above –25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O2 content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non‐invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.
Post‐ischaemic dysfunction does not correlate with release of cardiac troponin T in isolated rat hearts
Authors: Kawakami  , Löwbeer  , Valen  , Vaage
Published: March 2003

Cardiac troponin T (cTnT) is a highly sensitive and specific serum marker of irreversible cardiomyocyte injury. It is not clear whether cTnT also is a suitable marker of subtle, reversible injury. In the present investigation the relationship between cTnT release and function during the first 30 min of reperfusion after 30 min of global ischaemia, was investigated in isolated, retrogradely perfused rat hearts. Left ventricular systolic (LVSP), end‐diastolic (LVEDP) and developed (LVDP) pressures, heart rate (HR), and coronary flow (CF) were measured. In one series of experiments (n=7) the kinetics of cTnT release during 30 min of reperfusion was investigated. An early, short‐lasting peak of cTnT release appeared after 30 s of reperfusion. Then cTnT release gradually increased with a maximum after 20 min (from 0.08 ± 0.03 before ischaemia to 2.16 ± 0.40 ng min–1) (mean ± SEM). In a second series of experiments (n=52) the relationship between cTnT release and cardiac function was investigated after 20 min of reperfusion. At this time point LVEDP increased (0 to 62 ± 3 mmHg) and LVDP decreased (84 ± 2 to 33 ± 3 mmHg), but without any correlation with cTnT release. cTnT release was positively correlated to LVSP (P < 0.04, r=0.29), and negatively correlated to HR (P < 0.03, r=–0.31). cTnT concentration in the coronary effluent increased in parallel to increasing CF (P < 0.03, r=0.31). In conclusion, during the early reperfusion period there was no consistent correlation between cTnT release and dysfunction after global ischaemia in the isolated rat heart. Release of cTnT and post‐ischaemic function appear to provide supplementary information in this particular model.
Ca2+‐, Sr2+‐force relationships and kinetic properties of fast‐twitch rat leg muscle fibre subtypes
Authors: Galler
Published: March 2003

Force generation of fast‐twitch and slow‐twitch fibres exhibits large differences in its sensitivity to Ca2+ and Sr2+ (e.g.
Fink et al. 1986
). Little is known about fast‐twitch fibre subtypes. Thus, a variety of mechanical measurements on segments of rehydrated freeze‐dried fast‐twitch rat leg muscle fibres were executed in this study. Among these, the Ca2+‐ and Sr2+‐force relationship and the unloaded shortening velocity were determined. The fibres were classified into subtypes according to their kinetics of stretch activation (
Galler et al. 1994
). In all fibres, the maximal force under Sr2+ activation was about 0.9 of that under Ca2+ activation. The Ca2+‐ and Sr2+‐force relationship exhibited a biphasic shape with a steeper part (Hill coefficient, n1) below 50% and a flatter part (Hill coefficient, n2) above 50% of maximal force. The difference between the Ca2+ ‐ and Sr2+ ‐sensitivity was independent of the fibre subtypes. The Hill coefficients were only partially correlated with kinetic properties. The correlation was more pronounced for the unloaded shortening velocity than for the kinetics of stretch activation. The data are consistent with the idea that the Ca2+ and Sr2+ sensitivities of fast‐twitch fibres are mainly determined by a single isoform of troponin C. Among several protein isoforms, the isoforms of the myosin light chains seem to be involved for determining the slope of the Ca2+‐ and Sr2+‐force relationship of fast‐twitch muscle fibres.
Control of muscle fibre size: a crucial factor in ageing
Authors: Hughes  , Schiaffino
Published: March 2003

Force generation by skeletal muscle declines during ageing. This change contributes substantially to increased physical dependency in the aged. The decline in muscle mass is not entirely accounted for by a fall in muscle fibre number: fibres appear to lose volume. Here we review data that address the fundamental question of how muscle fibres regulate their size. In muscles, the problem has two elements because muscle fibres are syncitia formed by the fusion of mononucleate precursor cells. Thus, fibre size appears to be regulated both by the number of nuclei incorporated into each fibre and by a second variable, the volume of cytoplasm that each nucleus supports. We conclude that understanding of the regulation of muscle cell size is in its infancy and highlight directions that might productively be pursued.
Catecholamine biosynthesis and physiological regulation in neuroendocrine cells
Authors: Flatmark
Published: March 2003

The catecholamines are widely distributed in mammals and their levels and physiological functions are regulated at many sites. These include their release from neuroendocrine cells, the type and sensitivity of the multiple receptors in target cells, the efficacy of the reuptake system in the secretory cells, and the rates of catecholamine biosynthesis and degradation. In the present review the main focus will be on the more recent studies on the biosynthesis in neuroendocrine cells which involves a specific set of enzymes, with special reference to physiologically important regulatory mechanisms. Eight enzymes of the biosynthetic pathway have now been identified, cloned, expressed as recombinant proteins, characterized with respect to catalytic and regulatory properties, and some of them also crystallized. The identification of the tyrosine hydroxylase catalysed reaction as the rate‐limiting step in the normal catecholamine biosynthesis has attracted most attention, both in terms of transcriptional and post‐translational regulation. In certain human genetic disorders of catecholamine biosynthesis other enzymes in the pathway may become rate‐limiting, notably those involved in the biosynthesis/regeneration of the natural co‐factor tetrahydrobiopterin in the tyrosine hydroxylase reaction. The enzymes involved seem to be regulated by a variety of physiological factors, both on a long‐term scale and a short‐term basis, and include the relative rates of synthesis, degradation and state of activation of the biosynthetic enzymes, notably of tyrosine hydroxylase. Multiple surface receptors and signalling pathways are activated in response to extracellular stimuli and play an essential role in the regulation of catecholamine biosynthesis.
The collecting duct, dopamine and vasopressin‐dependent hypertension
Authors: Schafer  , Li  , Sun
Published: March 2003

AVP not only increases osmotic water permeability (Pf) in the rat cortical collecting duct (CCD), but also acts synergistically with aldosterone to augment sodium reabsorption (JNa). These effects are inhibited by catecholamines via α2 adrenergic receptors, and by dopamine. We review here studies designed to determine the mechanism and receptor involved in dopamine action. The inhibitory effect of dopamine on Na+ and water transport was found to be reversible, and was not produced by agonists specific to D1A and D1B receptors. D2‐type (D2, D3 or D4) receptors and activation of the GTP‐binding protein Gi were implicated by the observation that dopamine had no inhibitory effect when JNa and Pf were stimulated by a cyclic AMP analogue plus isobutylmethylxanthine. The only dopaminergic antagonist that reversed the inhibitory effect of dopamine was clozapine, which is relatively D4‐specific. We also found that dopamine or D1‐specific agonists by themselves had no effect on cAMP production. However, dopamine inhibited the high rate of AVP‐dependent cAMP production, and this effect of dopamine was reversed by clozapine but not other antagonists or by inhibitors of protein kinase C. The D4 receptor was observed in western blots of renal cortical proteins, and it was localized to the collecting duct by RT‐PCR and immuno‐histochemistry using a D4‐specific antibody. These results show that at least a portion of the natriuretic effect of dopamine can be attributed to inhibition of AVP‐dependent Na+ reabsorption by the CCD, and they introduce another signalling system as a candidate in the aetiology of low‐renin, salt‐dependent hypertension.
Dopamine D3 receptors in the rat kidney: role in physiology and pathophysiology
Authors: Mühlbauer  , Küster  , Luippold
Published: March 2003

It is well accepted that dopamine receptors play an important role in the regulation of cardiovascular and kidney function. Most of the knowledge on the renal actions of dopamine has been accumulated focussing on the prototypes of the two known dopamine receptor subfamilies, i.e. D1 and D2. The dopamine D3 receptor is a member of the D2‐like subfamily and has been intensively studied in the neurosciences. Recently, the peripheral actions of this receptor subtype have also raised considerable interest as well because its effects on kidney function appear to be different from that of the other dopamine receptors. This short overview will summarize the data reported and add new results on the role of D3 receptors in the regulation of renal function as well as their potential pathophysiological implications.
Renal NO production and the development of hypertension
Authors: Persson  , Gutierrez  , Pittner  , Ring  , Ollerstam  , Brown  , Liu  , Thorup
Published: March 2003

The juxtaglomerular apparatus (JGA) has the very important functions of detecting the fluid flow rate to the distal tubule and thus controlling the glomerular filtration rate (GFR) (tubuloglomerular feedback mechanism [TGF]) and renin release from the afferent arteriole. In studies of the TGF it has been evident that the sensitivity of this mechanism can be reset. Volume expansion will reset it to a low sensitivity leading to a high GFR and urine excretion rate, while dehydration will sensitize the TGF mechanism, giving rise to a low GFR and low urine excretion rate. Furthermore, we have found that in animals that spontaneously develop hypertension there is initially a sensitization of the TGF, leading to a reduced GFR and urine excretion rate, with fluid volume retention in the body and a consequent rise in blood pressure. When the pressure is raised, the TGF characteristics are normalized. In the macula densa (MD) cells in the JGA, there is a large production of NO from neuronal NOS. This production continuously reduces TGF sensitivity and is apparently impaired in animals that spontaneously develop hypertension. When we added an nNOS inhibitor to the drinking water for several weeks while measuring blood pressure, we found an increase in blood pressure after 3–4 weeks of treatment. This effect was abolished by a high salt diet. From these investigations, it also appeared as if nNOS‐derived NO inhibited renin release. Experiments have also indicated that NO may resensitize inhibited G‐protein coupled purinergic receptors.
Renal dopamine and noradrenaline excretion during CNS‐induced natriuresis in spontaneously hypertensive rats: influence of dietary sodium
Authors: Hansell  , Isaksson  , Sjöquist
Published: March 2003

Abnormalities in dopamine (DA) and noradrenaline (NA) activities and sodium handling may be involved in the pathogenesis of hypertension. The present study was designed to investigate whether any differences exist between normotensive Wistar–Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) in urinary excretion of DA, NA and sodium after 15 weeks on a low, medium or high sodium diet and during a subsequent elevation of the cerebroventricular fluid sodium concentration (CNS‐induced natriuresis). Seven features were noted: (1) Basal sodium and DA excretion after the diet regimen was correlated to the dietary sodium content in both strains, except that sodium and DA excretion in SHR showed no further increase after the high sodium diet over and above that after medium sodium diet. (2) For any given sodium diet, SHR excreted more DA and NA as compared with WKY. (3) Blood pressure in SHR, as opposed to that in WKY, was higher after medium and high sodium diet than after low sodium diet. (4) During CNS‐induced natriuresis NA excretion decreased or remained unchanged in WKY, but increased in SHR. (5) The DA/NA excretion ratio during CNS‐induced natriuresis increased in WKY while decreased in SHR, which would not favour a natriuretic/vasodilatory response in the latter. (6) The ability of SHR to respond with CNS‐induced natriuresis was attenuated after high sodium diet. (7) The magnitude of CNS‐induced natriuresis was in both strains correlated to the sodium diet; the higher the dietary sodium content, the greater the natriuretic response. In conclusion, the study shows some clear differences in the catecholamine and sodium handling between WKY and SHR which may be involved in the pathogenesis of hypertension in SHR. Furthermore, increased sodium in the diet sensitizes the brain and kidney to increase the ability to respond with natriuresis for a given sodium stimulus.
Corticotropic and serotonergic responses to acute stress with/without prior exercise training in different rat strains
Authors: Martin  , Duclos  , Aguerre  , Mormede  , Manier  , Chaouloff
Published: March 2003

The ability to cope with exercise training depends both on environmental and genetic background; however, whether the genetic status may affect (i) the hormonal status of trained subjects and, (ii) its responses to a heterotypic stressor is unknown. Herein, we have used Spontaneously Hypertensive Rats (SHR) and Lewis rats, that differ with regard to their psychoneuroendocrine profiles, to study the influences of an 8‐week training programme and/or a 1‐h immobilization stress on plasma adrenocorticotropin (ACTH) and corticosterone levels. In addition, brain serotonin metabolism was also measured as an index of neurochemical reactivity to stress. The amplitude of immobilization‐elicited increases in ACTH levels which differed with the rat strain (Lewis > SHR), was amplified by prior training; besides, training decreased the strain difference in basal corticosterone (SHR > Lewis) and affected corticosterone response to immobilization in a strain‐dependent manner. Thus, immobilization, which increased corticosterone levels in sedentary Lewis but not in SHRs, did not reveal interstrain differences in trained rats. Taken with the observation of a stimulatory effect of training on adrenal weights in SHRs, but not in Lewis, it is concluded that the effects of training on the corticotropic axis depend on the genetic profile of the individual. Lastly, training amplified the response of midbrain (but not striatum or hippocampus) serotonin metabolism to immobilization in a strain‐independent manner although the levels of serotonin precursor, namely tryptophan, varied with training and immobilization in a strain‐dependent manner. This study shows that some neuroendocrine and neurochemical effects of training undergo interindividual variability.
Effects of peritoneal hyaluronidase treatment on transperitoneal solute and fluid transport in the rat
Authors: Carlsson  , Rosengren  , Rippe
Published: March 2003

The importance of the interstitium and its major ground substance component, hyaluronan (HA), for solute and fluid transport across the peritoneal membrane has been debated during the last few years. We therefore partly removed HA from the peritoneal membrane using enzymatic digestion with hyaluronidase for 2 h, after which the transport properties of the peritoneal membrane were studied in peritoneal dialysis dwells. A dialysis fluid containing 3.86% glucose was used. As a marker of macromolecular transport, the total peritoneal clearance of radiolabelled albumin out of the peritoneal cavity and its clearance to plasma were measured, as well as the albumin clearance from plasma to dialysate. Transport of small solutes between plasma and dialysate was measured by assessing the mass transfer area coefficient of 51Cr‐EDTA and glucose. Hyaluronidase preincubation yielded a 78% reduction of HA in the superficial layer of the peritoneal membrane, without alterations in the transport of either small or large solutes compared with the situation in preincubated controls. The only changes observed were between rats incubated with either hyaluronidase or vehicle alone compared to non‐incubated controls. In conclusion, despite a large reduction of the HA content of the tissues surrounding the peritoneal cavity, hyaluronidase incubation did not produce any significant changes in solute and fluid transport across the peritoneal membrane. Our data indicate that peritoneal membrane HA in physiological concentrations plays a rather subordinate role in the overall transport of small solutes and water across the capillary–interstitial peritoneal barrier.
Changes in reactivity of rat arteries subjected to dynamic stretch
Authors: Dvoretsky  , Yartsev  , Karachentseva  , Granstrem
Published: March 2003

The effect of dynamic stretch on the reactivity of the rat tail and mesenteric artery segments was studied. Segments mounted on a myograph were stretched by a computer‐controlled motorized micromanipulator. Dynamic stretch (1, 5 or 7 Hz) inhibited the artery constriction induced by noradrenaline (10 μM), 5‐hydroxytryptamine (0.7 μM), or electrical field stimulation of intramural nerves. In contrast, dynamic stretch enhanced the tetrodotoxin‐insensitive dilation induced by electrical field stimulation of noradrenaline‐contracted arteries. Maximal increase of dilation evoked by electrical field stimulation (24.5 ± 5.0% in mesenteric and 50.3 ± 15.6% in the tail artery) was observed at a dynamic stretch‐frequency of 5 Hz. An inhibitor of nitric oxide synthesis, NG‐nitro‐
L‐arginine (100 μM), abolished the difference in reactivity between static and dynamic conditions. The results indicate that dynamic stretch of the arteries activates nitric oxide synthesis/secretion, thus reducing constrictor and increasing dilator responses to the stimuli used.
Role of the creatine/phosphocreatine system in the regulation of mitochondrial respiration
Authors: Saks V.A. , Kongas O. , Vendelin M. , Kay L.
Published: March 2003

The mechanism of metabolic regulation of mitochondrial respiration in cardiac muscle cells was studied experimentally in the permeabilized heart fibres of mice and by computer modelling in silico. The experiments showed that the rate of mitochondrial respiration could be controlled by local production of ADP by mitochondrial creatine kinase in the intermembrane space of mitochondria. The spatially inhomogenous reaction–diffusion model of compartmentalized energy transfer was used to analyse which metabolite level in cytoplasm may be important for regulation of respiration. At low and moderate workloads, up to VO2 equal to 70 μmol min−1 g−1 dry weight, the only factor to which respiration responded was inorganic phosphate. At the values of VO2 higher than 70 μmol min−1 g−1 dry weight, the respiration rate responded mostly to changes in creatine, phosphocreatine and then time‐averaged (over the contractile cycle) ADP concentrations in the cytoplasm. These results are taken to show that under conditions of moderate workloads, creatine kinase activity at given physiological creatine and phosphocreatine concentrations (apparent maximal activity achievable under these conditions) is in excess to oxidative phosphorylation rate, which is controlled by Pi concentration changes starting from very low values of the latter. At higher workloads mi‐CK should be upregulated by increasing creatine and decreasing phosphocreatine concentrations, and only at very high workloads the ADP diffusion flux should be increased to upregulate oxidative phosphorylation. Thus, on the basis of the study in silico of compartmentalized energy transfer by phophocreatine/creatine system, the authors conclude that there exist multiple parallel regulatory factors controlling the rate of oxygen consumption in dependence of the workload. If creatine kinase is inhibited (and there is no myokinase activity), respiration requires high diffusive flux of ADP back into mitochondria, which is the sole regulator of respiration. This needs, however, increased ADP concentrations in the cytoplasm, which in turn result in inhibition of contraction.
Response of jejunal Na+, K+‐ATPase to 5‐hydroxytryptamine in young and adult rats: Effect of fasting and refeeding
Authors: Lucas‐Teixeira  , SerrÃo  , Soares‐Da‐Silva
Published: March 2003

The present study is aimed to evaluate the effects of 5‐hydroxytryptamine (5‐HT) upon jejunal Na+,K+‐ATPase in young (20‐day‐old) and adult (60‐day‐old) rats, and determine the effect of food intake on the response of the sodium pump to the amine. Basal Na+,K+‐ATPase activity in jejunal epithelial cells from young rats was twice that in adult animals and responded to 5‐HT with stimulation. In adult rats, fasting reduced by 25% basal jejunal Na+,K+‐ATPase activity, whereas in young rats, no such change was observed. The sensitivity of jejunal Na+,K+‐ATPase to 5‐HT in young fasted rats was similar to that observed in fed animals. The effect of refeeding in young rats was a 2‐fold increase in jejunal Na+,K+‐ATPase activity, this being accompanied by insensitivity to 5‐HT. In adult rats, refeeding was accompanied by an increase in jejunal Na+,K+‐ATPase activity. It is concluded that the stimulatory effect of 5‐HT upon jejunal Na+,K+‐ATPase activity is a phenomenon dependent on both age and type of diet. In young rats, it is the food intake that plays an important role in development of insensitivity of Na+,K+‐ATPase to stimulation by 5‐HT, while in adult animals fasting or fasting followed by refeeding does not play a major role in regulating its sensitivity to the amine.
Calorie restriction increases insulin‐stimulated tyrosine phosphorylation of insulin receptor and insulin receptor substrate‐1 in rat skeletal muscle
Authors: Dean  , Cartee
Published: March 2003

A moderate reduction in calorie intake (calorie restriction, CR) improves insulin‐stimulated glucose transport in skeletal muscle. Therefore, we studied muscle insulin signalling in ad libitum (AL) and CR (~60% AL intake for 20 days) fed rats, which received a control injection (sterile water) or an insulin injection (30 U kg–1 body weight). In control (not insulin‐treated) rats, there was no detectable tyrosine phosphorylation of insulin receptor (IR), regardless of diet; no diet effect on tyrosine phosphorylation of insulin receptor substrate‐1 (IRS1) or IRS1‐associated phosphatidylinositol 3‐kinase (PI3K) protein and 21% higher IRS1‐associated PI3K activity in AL vs. CR. In insulin‐treated rats, tyrosine‐phosphorylated IR was 79% higher for CR vs. AL; tyrosine‐phosphorylated IRS1 was 109% higher for CR vs. AL; IRS1‐associated PI3K protein and IRS1‐associated PI3K activity were unaffected by diet. Calorie restriction amplifies early insulin signalling steps without changing IRS1‐associated PI3K, suggesting enhanced glucose transport is mediated by altering: IRS1‐PI3K localization, PI3K associated with proteins other than IRS1 or post‐PI3K events.
Effect of creatine supplementation on creatine and glycogen content in rat skeletal muscle
Authors: Op ‘t Eijnde B. , Richter E. A. , Henquin J.‐C. , Kiens B. , Hespel P.
Published: March 2003

The effects of high dose creatine feeding (5 g kg–1 BW day–1, 5 days) on creatine content, glucose transport, and glycogen accumulation in white gastrocnemius, red gastrocnemius and soleus muscles of the rat was investigated. Isolated rat hindquarters of creatine fed and control rats were perfused with a standard medium containing either insulin alone (0, 100 or 20 000 μU mL–1) or in combination with creatine (2 or 10 mmol L–1). Furthermore, plasma insulin concentration was measured in normal rats during creatine feeding, as well as in anaesthetized rats during intravenous creatine infusion. Five days of creatine feeding increased (P < 0.05) total creatine content in soleus (+20%) but not in red gastrocnemius (+15%, n.s.) and white gastrocnemius (+10%, n.s.). In parallel, glycogen content was markedly elevated (P < 0.05) in soleus (+40%), less (P < 0.05) in red gastrocnemius (+15%), and not in white gastrocnemius (+10%, n.s.). Glucose transport rate, muscle GLUT‐4 content, glycogen synthase activity in perfused muscles and glycogen synthesis rate were not significantly altered by creatine feeding in either muscle type. Furthermore, high dose creatine feeding raised (P < 0.05) plasma creatine concentration fivefold but did not alter circulating insulin level. It is concluded that short‐term high dose creatine feeding enhances creatine disposal and glycogen storage in rat skeletal muscle. However, the creatine and glycogen response to creatine supplementation is markedly greater in oxidative than in glycolytic muscles.
Reducing plasma free fatty acids by acipimox improves glucose tolerance in high‐fat fed mice
Authors: Ahrén Bo
Published: March 2003

To study whether free fatty acids (FFAs) contribute to glucose intolerance in high‐fat fed mice, the derivative of nicotinic acid, acipimox, which inhibits lipolysis, was administered intraperitoneally (50 mg kg−1) to C57BL/6J mice which had been on a high‐fat diet for 3 months. Four hours after administration of acipimox, plasma FFA levels were reduced to 0.46 ± 0.06 mmol L−1 compared with 0.88 ± 0.10 mmol L−1 in controls (P < 0.001). At this point, the glucose elimination rate after an intravenous glucose load (1 g kg−1) was markedly improved. Thus, the elimination constant (KG) for the glucose disposal between 1 and 50 min after the glucose challenge was increased from 0.54 ± 0.01% min−1 in controls to 0.66 ± 0.01% min−1 by acipimox (P < 0.001). In contrast, the acute insulin response to glucose (1–5 min) was not significantly different between the groups, although the area under the insulin for the entire 50‐min period after glucose administration was significantly reduced by acipimox from 32.1 ± 2.9 to 23.9 ± 1.2 nmol L−1 × 50 min (P=0.036). This, however, was mainly because of lower insulin levels at 20 and 50 min because of the lowered glucose levels. In contrast, administration of acipimox to mice fed a normal diet did not affect plasma levels of FFA or the glucose elimination or insulin levels after the glucose load. It is concluded that reducing FFA levels by acipimox in glucose intolerant high‐fat fed mice improves glucose tolerance mainly by improving insulin sensitivity making the ambient islet function adequate, suggesting that increased FFA levels are of pathophysiological importance in this model of glucose intolerance.
Role of adenosine in exercise‐induced human skeletal muscle vasodilatation
Authors: Rådegran G. , Calbet J. A. L.
Published: March 2003

The role of adenosine in exercise‐induced human skeletal muscle vasodilatation remains unknown. We therefore evaluated the effect of theophylline‐induced adenosine receptor blockade in six subjects and the vasodilator potency of adenosine infused in the femoral artery of seven subjects. During one‐legged, knee‐extensor exercise at ∼48% of peak power output, intravenous (i.v.) theophylline decreased (P < 0.003) femoral artery blood flow (FaBF) by ∼20%, i.e. from 3.6 ± 0.5 to 2.9 ± 0.5 L min−1, and leg vascular conductance (VC) from 33.4 ± 9.1 to 27.7 ± 8.5 mL min−1  mmHg−1, whereas heart rate (HR), mean arterial pressure (MAP), leg oxygen uptake and lactate release remained unaltered (P = n.s.). Bolus injections of adenosine (2.5 mg) at rest rapidly increased (P < 0.05) FaBF from 0.3 ± 0.03 L min−1 to a 15‐fold peak elevation (P < 0.05) at 4.1 ± 0.5 L min−1. Continuous infusion of adenosine at rest and during one‐legged exercise at ∼62% of peak power output increased (P < 0.05) FaBF dose‐dependently to level off (P = ns) at 8.3 ± 1.0 and 8.2 ± 1.4 L min−1, respectively. One‐legged exercise alone increased (P < 0.05) FaBF to 4.7 ± 1.7 L min−1. Leg oxygen uptake was unaltered (P = n.s.) with adenosine infusion during both rest and exercise. The present findings demonstrate that endogenous adenosine controls at least ∼20% of the hyperaemic response to submaximal exercise in skeletal muscle of humans. The results also clearly show that arterial infusion of exogenous adenosine has the potential to evoke a vasodilator response that mimics the increase in blood flow observed in response to exercise.
Effects of right and left vagal stimulation on left ventricular acetylcholine levels in the cat
Authors: Akiyama T. , Yamazaki T.
Published: March 2003

To test the effectiveness of, and the interactions between, right and left vagal stimulation on left ventricular acetylcholine (ACh) levels, we applied the dialysis technique to the heart of anaesthetized cats. Dialysis probes were implanted in the left ventricular myocardium and perfused with Krebs–Henseleit buffer containing eserine. Dialysate ACh content was measured as an index of ACh release from post‐ganglionic vagal nerve terminals in the left ventricular myocardium. We electrically stimulated the right and left cervical vagal nerves separately or together and investigated the dialysate ACh response. In two different regions of the left ventricle, substantial dialysate ACh responses were observed by the stimulation (20 Hz) of both right and left cervical vagal nerves. At stimulation frequencies of both 10 and 20 Hz, the dialysate ACh response to the bilateral vagal stimulation was almost algebraically the calculated sum of the individual dialysate ACh responses to unilateral vagal stimulation. In conclusion, ACh levels in the left ventricle are affected by both right and left vagal nerves and show little evidence of interactions between right and left vagal nerves at the level of the cardiac ganglia.
2,3‐Butanedione monoxime increases speed of relaxation in single muscle fibres of frog
Authors: Sun Y.‐B. , Lou F. , Edman K. A. P.
Published: March 2003

The effects of 2,3‐butanedione monoxime (BDM) on intracellular Ca2+ transient and cross‐bridge function were studied in frog single fibres from the anterior tibialis muscle of Rana temporaria (sarcomere length, 2.2 μm; temperature, 2–4 °C). The fluorescent dye fluo‐3 was used to monitor the intracellular free calcium concentration ([Ca2+]i) during isometric contractions. BDM (1–5 mM) reduced the amplitude of the Ca2+ transient during twitches, but this effect was too small to explain the marked inhibition of BDM on twitch force. [Ca2+]i reached at the end of 1‐s tetanic stimulation was not significantly affected by BDM (1.0 and 1.8 mM) while the maximum tetanic tension was substantially reduced. The rate of relaxation during isometric tetanus was increased by BDM whereas the rate of decay of the Ca2+ transient was reduced in the presence of BDM. The results strongly suggest that BDM, under the experimental conditions used, mainly affects the contractile machinery resulting in altered performance of the cross‐bridges. These effects of BDM were evaluated in terms of the cross‐bridge model of Huxley (1957) which was fitted to the experimental force–velocity data in the presence and absence of BDM.
Glutathione deficiency intensifies ischaemia‐reperfusion induced cardiac dysfunction and oxidative stress
Authors: Leichtweis S. , Ji L. L.
Published: March 2003

The efficacy of glutathione (GSH) in protecting ischaemia‐reperfusion (I‐R) induced cardiac dysfunction and myocardial oxidative stress was studied in open‐chest, stunned rat heart model. Female Sprague–Dawley rats were randomly divided into three experimental groups: (1) GSH‐depletion, by injection of buthionine sulphoxamine (BSO, 4 mmol kg–1, i.p.) 24 h prior to I‐R, (2) BSO injection (4 mmol kg–1, i.p.) in conjunction with acivicin (AT125, 0.05 mmol kg–1, i.v.) infusion 1 h prior to I‐R, and (3) control (C), receiving saline treatment. Each group was further divided into I‐R, with surgical occlusion of the main left coronary artery (LCA) for 30 min followed by 20 min reperfusion, and sham. Myocardial GSH content and GSH : glutathione disulphide (GSSG) ratio were decreased by ˜50% (P < 0.01) in both BSO and BSO + AT125 vs. C. Ischaemia‐reperfusion suppressed GSH in both left and right ventricles of C (P < 0.01) and left ventricles of BSO and BSO + AT125 (P < 0.05). Contractility (+dP/dt and –dP/dt) in C heart decreased 55% (P < 0.01) after I and recovered 90% after I‐R, whereas ±dP/dt in BSO decreased 57% (P < 0.01) with ischaemia and recovered 76 and 84% (P < 0.05), respectively, after I‐R. For BSO + AT125, ±dP/dt were 64 and 76% (P < 0.01) lower after ischaemia, and recovered only 67 and 61% (P < 0.01) after I‐R. Left ventricular systolic pressure in C, BSO and BSO + AT125 reached 95 (P > 0.05) 87 and 82% (P < 0.05) of their respective sham values after I‐R. Rate‐pressure double product was 11% (P > 0.05) and 25% (P < 0.05) lower in BSO and BSO + AT125, compared with Saline, respectively. BSO and BSO + AT125 rats demonstrated significantly lower liver GSH and heart Mn superoxide dismutase activity than C rats after I‐R. These data indicate that GSH depletion by inhibition of its synthesis and transport can exacerbate cardiac dysfunction inflicted by in vivo I‐R. Part of the aetiology may involve impaired myocardial antioxidant defenses and whole‐body GSH homeostasis.
Exercise‐induced changes in brain glucose and serotonin revealed by microdialysis in rat hippocampus: effect of glucose supplementation
Authors: Béquet F. , Gomez‐Merino D. , Berthelot M. , Guezennec C. Y.
Published: March 2003

The aim of this study was to assess extracellular glucose changes in hippocampus in response to physical exercise and to determine the influence of glucose supplementation. In the same time, we have observed the changes in serotonin, in order to study the relationship between glucose and serotonin during exercise. Both glucose and serotonin were assessed using microdialysis. Exercise induced an increase in extracellular glucose levels over baseline during exercise to 121.1 ± 3.0% (P < 0.001), then a decrease to baseline during recovery. The serotonin followed glucose changes during the first 90 min of exercise, but followed a different pattern during recovery, increasing to a maximum of 129.9 ± 7.0% after 30 min of recovery (P < 0.001). When a 15% glucose solution was infused (10 μL min–1) during exercise and recovery, blood glucose concentration was increased, but extracellular brain glucose decreased to reach a minimum of 73.3 ± 4.6% after 90 min of recovery (P < 0.001). Serotonin was always the mirror‐reflect of cerebral glucose, with a maximum increase of 142.0 ± 6.9% after 90 min of recovery (P < 0.001). These results show that exercise induces changes in brain glucose and 5‐hydroxytryptamine (5‐HT) levels, which were dramatically modified by glucose infusion. Taking into account the implication of brain 5‐HT in central fatigue, they suggest that if glucose supplementation, before and during exercise, undoubtedly increase performance because of its peripheral positive action, it would have a negative impact on the quality of recovery after the end of the exercise.
The α1 isoform of Na+,K+‐ATPase in rat soleus and extensor digitorum longus
Authors: Hansen Otto
Published: March 2003

A novel immunochemical method was used for determination of the concentration of Na,K‐adenosine triphosphatase (ATPase) containing the ouabain‐insensitive α1 peptide in rat m. soleus and extensor digitorum longus (EDL). Homogenates of soleus and EDL from 4‐week or 10–11‐week rats were run on sodium dodecyl sulphate (SDS) gels and in parallel lanes was run a well‐characterized preparation of Na,K‐ATPase isolated from rat kidney that is known to contain only the α1 isoform. After electroblotting to PVDF membranes blots were incubated with the α1 specific monoclonal antibody 3B, then with an 125I‐coupled secondary antibody, and finally the specific labelling of adjacent α spots was analysed by means of an electronic autoradiography system (Packard InstantImager). As the α1 content of reference Na,K‐ATPase was known from the specific Na+‐dependent 32P‐phosphorylation capacity, the α1 content of adjacent α spots in homogenates from soleus and EDL could be calculated. In soleus and EDL from 4‐week rats an α1 concentration of 135–220 pmol (g tissue)–1 was found, dependent on the conditions of the experiments but without significant differences between the two types of muscle. In 10–11‐week rats a significantly lower concentration of 70–80 and 40–60 pmol (g tissue)–1 in soleus and EDL, respectively, was found. Ouabain‐insensitive Na,K‐ATPase containing the α1 peptide may thus represent 15–25% of the total number of pumps in skeletal muscle if another 20–30% has to be added to the pool known from (3H)ouabain binding.
Cyclopiazonic acid and thapsigargin reduce Ca2+ influx in frog skeletal muscle fibres as a result of Ca2+ store depletion
Authors: MÊME W. , LÉOTY C.
Published: March 2003

We have investigated the influence of the sarcoplasmic reticulum (SR) Ca2+ content on the retrograde control of skeletal muscle L‐type Ca2+ channels activity by ryanodine receptors (RyR). The effects of cyclopiazonic acid (CPA) and thapsigargin (TG), two structurally unrelated inhibitors of SR Ca2+‐adenosine triphosphatase (ATPase), were examined on the SR Ca2+ content, the calcium current and contraction in single frog semitendinosus fibres using the double mannitol‐gap technique. At moderate concentrations that only partially inhibited Ca2+ sequestration by the SR, CPA (2–4 μM) induces a concentration dependent depression of contraction and Ca2+ current amplitudes. When Ba2+ is the charge carrier, the inward current is not changed by CPA suggesting that this Ca2+‐pump inhibitor does not directly affect dihydropyridine Ca2+ channels. Similar effects were obtained with TG (1–5 μM). Changes in Ca2+ currents and contraction were accompanied by a reduced Ca2+ loading of the SR. We attribute the modulation of the Ca2+ current to the selective inhibition of the SR Ca2+ ATPase, resulting in a decreased Ca2+ release and thereby a reduced activation of calcium inward currents. This is therefore taken to represent a calcium release‐dependent modulation of skeletal muscle L‐type Ca2+ channels.
Immunomodulatory action of chronic exercise on macrophage and lymphocyte cytokine production in mice
Authors: SUGIURA H. , NISHIDA H. , SUGIURA H. , MIRBOD S. M.
Published: March 2003

This study was designed to evaluate the effects of 8‐week voluntary running exercise on cytokine production of macrophages and lymphocytes. Seven‐week‐old‐male BALB/c inbred mice were divided into two groups: a group given voluntary exercise (exercise group, n=32), and the other, a non‐exercise group (control group, n=32). Exercise consisted of spontaneous running in wheels for 3 days per week over 8 weeks. The levels of nitric oxide (NO2–) and interleukin (IL)‐1β production by lipopolysaccharide (LPS)‐stimulated peritoneal macrophages from the exercise group was significantly higher than that in the control group (P < 0.05–P < 0.01). In the exercise group, stimulation indices by concanavalin A (Con A) was significantly higher than they were in the control group (P < 0.05–P < 0.001). When compared with the control group, the exercise group showed a significant (P < 0.05) increase in the splenic lymphocyte production of IL‐2 stimulated by Con A (449.5 ± 28.2 and 853.7 ± 116.0 pg 4 × 105 cells–1 48 h–1 for the control group and the exercise group, respectively). IL‐4 production of splenocytes stimulated by Con A in the exercise group (37.6 ± 5.1 pg 4 × 105 cells–1 48 h–1) was higher than that in the control group (30.9 ± 3.9 pg 4 × 105 cells–1 48 h–1); however, the difference was not statistically significant. These results suggest that 8‐week voluntary running exercise effectively enhanced macrophage and lymphocyte functions in mice.