bluuebunny/crossref_metadata_2025 huggingface dataset:
Alteration of immune function following dietary mycotoxin exposure
Authors: Pestka James J. , Bondy Genevieve S.
Published: April 2011

Mycotoxins are a group of structurally diverse fungal secondary metabolites that elicit a wide spectrum of toxicologic effects. Of particular interest is the capacity of some mycotoxins to alter normal immune function when present in foods at levels below observable overt toxicity. Aflatoxin, patulin, citrinin, and zearalenone experimentally alter immunity, and recent evidence suggests that the immunologic effects of ochratoxin A and trichothecenes may have particular significance to human and animal health. For example, the capacity of ochratoxin A to inhibit natural killer cell activity and increase growth of transplantable tumour cells has been associated with renal and hepatic carcinomas in mice and might similarly contribute to human cancer. Impaired resistance to pathogenic microorganisms occurs after exposure to the trichothecenes T-2 toxin and vomitoxin. This may predispose food animals to infectious disease and could result in decreased productivity as well as increased animal-to-human transmission of pathogens such as Salmonella and Listeria. Vomitoxin also alters normal mucosal immune function, specifically at the level of regulation of development, differentiation, and homing of IgA-producing plasma cells. Interestingly, vomitoxin-induced enhancement of IgA production in the systemic compartment contributes to manifestations in the mouse that are highly analogous to human IgA nephropathy, the most common form of human glomerulonephritis worldwide. Over the long term, the extrapolation of mycotoxin-induced immunologic effects observed in inbred mice to actual disease in livestock and humans will require investigations that both simulate natural exposure conditions as well as improve understanding of the cellular and molecular bases for these effects among different species.Key words: mycotoxins, immunotoxicity, trichothecene, ochratoxin, aflatoxin.
Uncertainties in the risk assessment of three mycotoxins: aflatoxin, ochratoxin, and zearalenone
Authors: Kuiper-Goodman T.
Published: April 2011

The risk assessment of mycotoxins is made up of two major components: an exposure assessment and a hazard assessment. There are many uncertainties in both of these components. This paper will briefly discuss the various aspects of the risk assessment process as it applies to mycotoxins and will then focus mainly on some of the uncertainties in the hazard assessment component of several carcinogenic mycotoxins. To arrive at an estimated "safe dose" (end point of the hazard assessment), we have previously used two major approaches: the no observed effect level (NOEL) divided by a safety factor approach and a mathematical (robust linear) extrapolation to a "virtual safe dose." Both of these approaches use only points from the no observed effect region of the dose–response curve and ignore valuable data from the response region. It is proposed to use the dose at which 50% of the animals would have developed tumors (the TD50) divided by a large safety factor of 50 000 as an additional estimate of "safe dose". For many studies, the TD50 lies within the observed response region of the dose–response curve and may have more validity. It is also suggested in certain cases that some of the uncertainties regarding the NOEL can be reduced if one uses a statistically derived no effect level (NEL).Key words: risk assessment, carcinogens, aflatoxins, ochratoxin, zearalenone, mycotoxins.
Interactions between the presynaptically active neurotoxins α-latrotoxin and ω-conotoxin GVIA: studies on calcium fluxes and binding parameters in rat and chicken synaptosomes
Authors: Scheer H. W.
Published: April 2011

Possible interactions between α-latrotoxin, an activator of synaptosomal calcium uptake, and ω-conotoxin GVIA, an inhibitor of voltage-sensitive calcium channels of the N-type, were investigated in rat and chicken synaptosomal preparations. While ω-conotoxin GVIA potently and effectively inhibited calcium uptake induced by elevated potassium in chick synaptosomes, little or no effect of ω-conotoxin GVIA was observed either in potassium-treated rat synaptosomes or in α-latrotoxin-exposed synaptosomes of either species. In contrast to the lack of effect of ω-conotoxin on stimulated calcium uptake in rat synaptosomes, cadmium effectively inhibited calcium uptake induced by either potassium or α-latrotoxin. Synaptosomal calcium transport induced by α-latrotoxin can be bidirectional, since α-latrotoxin also induced efflux of preaccumulated calcium. Competition experiments revealed that binding of 125I-labelled ω-conotoxin and 125I-labelled α-latrotoxin was similar in either chicken or rat synaptosomes. Neither α-latrotoxin nor ω-conotoxin competed with the binding of the other ligand in either species. The results reported here show that (1) elevated potassium evokes calcium uptake principally through N-channels in avian but not in rat synaptosomes; (2) α-latrotoxin-activated calcium fluxes are ω-conotoxin insensitive but cadmium sensitive; (3) the molecular acceptors for the two ligands are likely to be unrelated synaptic membrane constituents.Key words: synaptosomαes, calcium, α-latrotoxin, ω-conotoxin.
Potentiation of chloroform-induced hepatotoxicity by methyl isobutyl ketone and two metabolites
Authors: Vézina Manon , Kobusch Adriane B. , Souich Patrick du , Greselin Erminio , Plaa Gabriel L.
Published: April 2011

The hepatonecrogenic properties of chloroform (CHCl3) can be modified by the administration of various chemicals. The ability of methyl isobutyl ketone (MIBK) and its two major metabolites, 4-methyl-2-pentanol (4MPOL) and 4-hydroxymethyl isobutyl ketone (4-OHMIBK) to potentiate the liver injury induced by CHCl3 was assessed in rats. The parent compound and both metabolites significantly increased the liver damage induced by CHCl3, as demonstrated by the elevation of the plasma activity of two transferases alanine aminotransferase and ornithine carbamoyl transferase and by the severity of the morphological changes. Moreover, the minimally effective dosage needed to potentiate CHCl3-induced hepatotoxicity was approximately 5 mmol/kg for the three compounds. We also studied the inducing properties of MIBK (cytochrome P-450 liver content and the activity of aniline hydroxylase, 7-ethoxycoumarin O-deethylase, and aminopyrine N-demethylase). Cytochrome P-450 content and the oxidation of aniline and 7-ethoxycoumarin were significantly increased with either a single (7.5 mmol/kg or greater) or a multiple (5.0 and 7.5 mmol∙kg−1∙day−1 for 5 days) administration of MIBK. An increase in the activity of the aminopyrine demethylase was also elicited by the repetitive administration of MIBK. With gel electrophoresis, we found that MIBK significantly increased the 52.1- and 54.1-kDa proteins, corresponding most probably to P-450 isozymes.Key words: methyl isobutyl ketone, methyl isobutyl ketone metabolites, CHCl3 hepatotoxicity, potentiation, enzyme induction.
Characterization of immunoreactive motilin from the rat small intestine
Authors: Vogel L. B. , Brown J. C.
Published: April 2011

Immunocytochemistry, radioimmunoassay, chromatography, and biological assay using a rabbit isolated duodenal muscle strip preparation were used in attempting to characterize motilin from the rat small intestine. Several different antisera and monoclonal antibodies directed against natural porcine motilin were used. A variety of fixation techniques using Bouin's, paraformaldehyde, and benzoquinone with different staining methods including, fluorescein-conjugated second antibody, peroxidase–antiperoxidase or peroxidase-conjugated second antibody techniques were used. All methods failed to detect immunoreactive motilin cells in the rat small intestine. The same antisera were used in radioimmunoassays for motilin to evaluate extracts of rat intestinal tissue. Two of these detected immunoreactive motilin in gut extracts, and these antisera showed a different distribution for the peptide. Samples containing immunoreactive motilin obtained from cation exchange chromatography on SP-Sephadex-G25 were concentrated and assayed for biological activity in a rabbit duodenal muscle strip preparation. Desensitization of duodenal tissue to porcine motilin could be demonstrated by pretreatment with this peptide. The biological activity of partially purified rat intestinal immunoreactive motilin was not prevented by pretreatment of the tissue with motilin. Further purification of this preparation on Bio-Gel P-10 yielded an immunoreactive motilin peak that co-eluted with natural porcine motilin. Rat intestinal immunoreactive motilin did not co-elute with natural porcine motilin following high pressure liquid chromatography on a Waters μBondapak C18 reversed-phase column using a linear gradient of water–acetonitrile (10–45%) over 30 min. Although of similar molecular size, rat motilin is probably structurally dissimilar to other mammalian motilins.Key words: motilin, radioimmunoassay, immunocytochemistry.
Diacylglycerol and protein kinase mediated noradrenergic responses in perfused rat kidneys
Authors: Baines A. D. , Ho P.
Published: April 2011

The role of protein kinases in renal noradrenergic stimulation was examined using sphingosine, 1-(5-isoquinolinylsulfonyl)-2-methyl-piperizine (H7), or staurosporine to inhibit the responses to norepinephrine (NE, 60 nM) in isolated perfused rat kidneys. Sphingosine (20 μmol/L) increased the noradrenergic vasoconstrictor response. H7 (10 μmol/L) partially blocked the immediate vasoconstrictor response and completely inhibited it after 2 min without altering the antinatriuretic and antilithuretic responses. H7 also blocked the increase in free water produced by NE, which is consistent with the inhibition of protein kinase A linked to β-adrenergic stimulation. Staurosporine (10 nmol/L) partially inhibited noradrenergic vasoconstriction and antinatriuresis, and it completely blocked the depression of glomerular filtration rate (GFR) and the antilithuresis with no effect on free water production. Staurosporine did not inhibit the gluconeogenic responses to NE in pyruvate-perfused kidneys. To examine the role of diacylglycerol and protein kinase C in the renal responses to NE, we used oleoyl-acetyl-glycerol (OAG, 50–100 μM) or phorbol-12-myristyl-13-acetate (TPA, 5–50 nM). TPA slowly vasoconstricted the kidney and reduced GFR and fractional Na+, Li+, and free water excretion. Amiloride (1 mM) prevented the TPA responses. OAG mimicked the effects of TPA except that vasoconstriction occurred more rapidly and was brief. Both TPA and OAG acted like α1-adrenergic agonists. These results indicate that diaclyglycerol and protein kinase are involved in the prolonged effects of NE on vasoconstriction, GFR, and proximal tubular reabsorption.Key words: phorbol esters, diacylglycerol, protein kinase C, kidney, α-adrenergic receptors, staurosporine, H7, sphingosine.
The α1- and α2-adrenoceptor and muscarinic responses of normal and axotomized bullfrog sympathetic ganglia
Authors: Smith P. A. , Gordon T. , Kehoe M. P. , Marshall K. C.
Published: April 2011

When neurones in bullfrog paravertebral sympathetic ganglia are studied by means of the sucrose-gap technique, muscarinic agonists produce a biphasic response (an initial hyperpolarization of ganglionic C cells followed by a depolarization of ganglionic B cells). Activation of ganglionic α2-adrenoceptors promotes hyperpolarization. The present experiments with selective α1- and α2-adrenoceptor agonists and antagonists provided evidence for the existence of hitherto undescribed α1-adrenoceptors, which are responsible for the production of depolarizing responses in these ganglia. Fifteen to twenty-five days after cutting postganglionic axons (axotomy), there was a nonselective depression of both α1- and α2-adrenoceptor mechanisms but little change in muscarinic responses. These results argue against the hypothesis that C cells assume all the properties of B cells after axotomy. Since the α-selective agonist phenylephrine failed to depolarize axotomized ganglia, it is unlikely that an α1-adrenoceptor mechanism is prominent in axotomized neurones as it is in some immature adrenergic neurones. The data are consistent with the idea that axotomy selectively affects the properties of certain types of cation channels and raise questions as to the mechanisms involved in regulating the expression and maintenance of specific neurotransmitter responses on ganglionic neurones.Key words: axotomy, α-adrenoceptor mechanisms, muscarinic receptors, sympathetic ganglion, frog.
Systemic CI-966, a new γ-aminobutyric acid uptake blocker, enhances γ-aminobutyric acid action in CA1 pyramidal layer in situ
Authors: Ebert U. , Krnjević K.
Published: April 2011

A new potent, blood–brain barrier permeable γ-aminobutyric acid (GABA) uptake blocker, 1-[2-[bis[4-(trifluoromethyl)-phenyl]methoxy]ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid (CI-966) was administered systemically by i.p. injection (5 mg/kg) in Sprague–Dawley rats under urethane anaesthesia. Twenty to thirty minutes after injection there was a highly variable, but overall significant, enhancement of the inhibition of hippocampal population spikes by GABA applied by microiontophoresis in the CA1 region. Like the effect of nipecotic acid (applied locally by iontophoresis), the potentiation by CI-966 was clearest when GABA was applied in or near the stratum pyramidale where its action normally is weakest and shows the most pronounced fading. This change in GABA potency is most simply explained by a reduction in GABA uptake.Key words: GABA, muscimol, nipecotic acid, GABA-uptake blocker, epilepsy.
Phencyclidine and related compounds evoke [3H]dopamine release from rat mesencephalic cell cultures by a mechanism independent of the phencyclidine receptor, sigma binding site, or dopamine uptake site
Authors: Mount Howard , Boksa Patricia , Chaudieu Isabelle , Quirion Rémi
Published: April 2011

At concentrations ≥100 μM, phencyclidine (PCP), N-(1-(2-thienyl)-cyclohexyl)piperidine (TCP), and MK-801 induced [3H]dopamine release from dissociated cell cultures of rat mesencephalon. This release was Ca2+ independent and tetrodotoxin insensitive. Tetrodotoxin (2 μM) itself had no effect on spontaneous release of [3H]dopamine. [3H]Dopamine release was induced by 1,3-di(2-tolyl)guanidine, a sigma ligand, and by 4-aminopyridine (1–3 mM), a K+ channel blocker. No stereoselectivity was observed for [3H]dopamine release evoked by the dioxadrol enantiomers, dexoxadrol, and levoxadrol, or by enantiomers of N-allylnormetazocine (SKF 10,047). The selective dopamine uptake inhibitor 1-(2-[bis(4-fluorophenyl)methoxy]ethyl)-4-(3-phenylpropyl)piperazine dihydrochloride (GBR 12909) did not affect spontaneous or TCP-evoked [3H]dopamine release. Together, these data suggest that the dopamine-releasing effects of PCP-like compounds on the mesencephalic cells were not mediated by actions at the PCP receptor or sigma binding site, Ca2+, or Na+ channels, or at the high affinity dopamine uptake site. It remains conceivable that blocking actions of PCP-like compounds at voltage-regulated K+ channels may at least partly explain the response. These results are discussed in comparison with findings in intact brain.Key words: dopamine, phencyclidine, cell culture, mesencephalon.
Infusion of iso-rANP(1–45) or (17–45) increases plasma immunoreactive ANP and lowers plasma renin activity and aldosterone
Authors: Jennings D. B. , McKirdy J. C. , Ohtake P. J. , Sarda I. R. , Flynn T. G. , Hira G. K.
Published: April 2011

We have reported that a second rat atrial natriuretic peptide, iso-rANP(1–45), as well as the putative ANP homologue, iso-rANP(17–45), elicited circulatory and renal responses in the rat similar to those found after administration of ANP. Iso-rANP also interacted with ANP to potentiate the observed biological activity in the rat. In the present studies in awake dogs, intravenous infusion of low doses (6.3–50 pmol∙kg−1∙min−1) of iso-rANP(1–45) and iso-rANP(17–45) increased plasma immunoreactive ANP and suppressed plasma renin activity (PRA) and aldosterone. Iso-rANP, like ring-deleted analogues of ANP, may have displaced ANP from ANP clearance receptors to increase plasma ANP concentration, since factors influencing myocardial ANP release were not changed. The effect of iso-rANP(1–45) and (17–45) in lowering PRA and plasma aldosterone may therefore have been indirect, via ANP stimulation of active guanylate cyclase-linked ANP receptors. However, an additional direct effect of iso-rANP on an active receptor cannot be excluded.Key words: clearance and active ANP receptors, arginine vasopressin, water and electrolyte balance, circulatory hemodynamics.
5-Hydroxytryptophan modulates postprandial motor patterns of canine proximal small intestine
Authors: Siegle M. L. , Bühner S. , Ehrlein H. J.
Published: April 2011

The aim of the study was to clarify whether 5-hydroxytryptophan (5-HTP) stimulates the postprandial motor pattern of the duodenum in a similar way as that of the adjacent jejunal segment in dogs. Computerized analysis of motor patterns recorded by closely spaced strain gauges focused on the temporal and spatial distribution of the contractions. Results indicate that 5-HTP increased the incidence and the length of the spread of contraction waves after both an acaloric and a nutrient meal in the duodenum as well as in the adjacent jejunal segment. Effects were more pronounced after the nutrient than after the acaloric meal. After the nutrient meal, but not after the acaloric meal, 5-HTP additionally enhanced the number of both duodenal and jejunal contractions per minute and increased the force of duodenal contractions. The acaloric meal induced significant differences in the motor patterns between the duodenum and the adjacent jejunum. 5-HTP abolished these differences owing to a relatively stronger stimulation of duodenal motility. 5-HTP did not affect gastric emptying of both meals. We conclude (i) that 5-HTP is a potent stimulator of propagated contractions both in the duodenum and the adjacent jejunal segment and (ii) that intestinal motor patterns can be regulated independently of gastric emptying.Key words: 5-hydroxytryptophan, duodenum, jejunum, gastrointestinal motility, length of contraction spread, computerized analysis.
Influence of sex and inducer treatment on the high- and low-affinity forms of hepatic microsomal erythromycin N-demethylase in rats
Authors: Chang Tom , Levine Marc , Bellward Gail D.
Published: April 2011

To study the regulation of the multiple forms of erythromycin N-demethylase, we determined the influence of sex and inducer treatment on this mixed-function oxidase activity in adult Wistar rats injected intraperitoneally once daily for 4 days with dexamethasone, pregnenolone-16α-carbonitrile, phenobarbital, or 2% Tween 80 (control). Based on the results from a computer curve-fitting procedure (ENZFITTER) as well as Eadie–Hofstee and Lineweaver–Burk plots, at least two forms of erythromycin N-demethylase were present in control, dexamethasone, pregnenolone-16α-carbonitrile, and phenobarbital-treated male rats and in control and dexamethasone-treated female rats. Only a high-affinity form was apparent in pregneno-lone-16α-carbonitrile and phenobarbital-treated female rats. Therefore, more than one form of erythromycin N-demethylase exists in hepatic microsomes from adult rats, depending on sex and inducer treatment. As well, at a substrate concentration commonly used in the erythromycin N-demethylase assay, the relative contribution of the high- and low-affinity forms to the enzyme activity varies with sex and inducer treatment.Key words: erythromycin N-demethylase, dexamethasone, pregnenolone-16α-carbonitrile, phenobarbital, mixed-function oxidase.
Hormonal and biophysical responses to acute hypoxemia in fetal sheep at 0.7–0.8 gestation
Authors: Akagi Kozo , Challis John R. G.
Published: April 2011

We examined whether there was a minimal change in fetal arterial [Formula: see text] necessary to elicit alterations in plasma adrenocorticotropic hormone, arginine vasopressin, or cortisol or to affect the incidence of breathing movements or eye movements in fetal sheep at 106–117 days of gestation. Fetal sheep were exposed to two levels of hypoxemia, mild (4.1 mmHg [Formula: see text] drop) (1 mmHg = 133.32 Pa) and moderate (8.4 mmHg [Formula: see text] drop), for 1 h without acidemia. Hypoxemia was induced by altering the inspired percent oxygen of the mother. No significant hormonal and biophysical changes were observed in mild hypoxemia. In moderate hypoxemia, there were significant increases of fetal adrenocorticotropic hormone and arginine vasopressin and decreased incidence of fetal breathing movements. However, there were no significant changes in cortisol or eye movements. We conclude that a fetal arterial [Formula: see text] drop of between 4.1 and 8.4 mmHg is necessary to elicit responses to hypoxemia in fetal sheep at 106–117 days of gestation in adrenocorticotropic hormone, arginine vasopressin, and fetal breathing movements, but this degree of hypoxemia does not cause changes in cortisol or fetal eye movements.Key words: fetal sheep, hypoxemia, adrenocorticotropic hormone, arginine vasopressin, cortisol, fetal breathing movements, fetal eye movements.
Beneficial effect of perindopril, an angiotensin-converting enzyme inhibitor, on left ventricular performance and noradrenaline myocardial content during cardiac failure development in the rat
Authors: Ribuot Christophe , Mossiat Claude , Devissaguet Michelle , Rochette Luc
Published: April 2011

The left coronary artery in rats was ligated for a period of 15 days to induce hypertrophy of the non-infarcted myocardium. Left ventricular performances were evaluated in the working heart model. In addition, cardiac hypertrophic indices and noradrenaline content were measured. Variables were determined in the absence or presence of the angiotensin-converting enzyme inhibitor, perindopril. A 35 and 60% decrease in the coronary and cardiac output, respectively, and a 57% decrease in the noradrenaline content of the non-infarcted left ventricular free wall were seen. Furthermore, a 15% increase in the heart/body weight ratio was observed in the infarcted group. After chronic treatment of the animals with perindopril (2 mg∙kg−1 body weight, per os), coronary and cardiac output were impaired to a lesser extent: 8 and 35% respectively, with only a 15% decrease in the noradrenaline content of the non-infarcted left ventricular free wall. Furthermore, the increase in heart/body weight ratio was significantly less than in the nontreated infarct group (7%). We conclude that the beneficial effects of converting enzyme inhibition, during the development of myocardial infarction, on left ventricular performances are associated with a decrease in the hypertrophic indices and a normalization of sympathetic activity.Key words: converting enzyme inhibitor, cardiac hypertrophy, noradrenaline, isolated working heart, rat.
Renal catabolism of human glucagon-like peptides 1 and 2
Authors: Ruiz-Grande Carmen , Pintado José , Alarcón Cristina , Castilla Carlos , Valverde Isabel , López-Novoa José M.
Published: April 2011

The renal catabolism of [125I]glucagon-like peptide 1 (GLP-1) and [125I]glucagon-like peptide 2 (GLP-2) has been studied both in vivo, by the disappearance of these peptides from the plasma of bilaterally nephrectomized (BNX), ureteral-ligated (BUL) or normal rats, and in vitro, analyzing their catabolism by the isolated, perfused rat kidney. Results from in vivo studies demonstrated that half-disappearance time for both peptides was lower in controls than in BUL rats, and this value in BUL rats was not significantly different from that in BNX rats. In addition, metabolic clearance rate of GLP-1 was higher in control rats than in the other two groups of animals. Urinary clearance rate of both peptides was negligible. In isolated kidney experiments, values for organ clearance of both [125I]GLP-1 and [125I]GLP-2 were similar to those of inulin clearance, which represents the glomerular filtration rate. Urinary clearance of trichloroacetic acid precipitable radioactivity represented less than 1% of total clearance. In conclusion, these results demonstrate a significant role for the kidney in the plasma removal of [125I]GLP-1 and [125I]GLP-2 by a mechanism that involves glomerular filtration and tubular catabolism.Key words: protein catabolism, gastrointestinal peptides, isolated kidney, renal failure.
Effects of 5-hydroxytryptamine on cat spinal motoneurons
Authors: Zhang Liang
Published: April 2011

The effects of 5-hydroxytryptamine (5-HT) on spinal motoneurons were examined in pentobarbital-anaesthetized cats and in nonanaesthetized decerebrate cats by intracellular recording and extracellular iontophoresis of 5-HT. 5-HT first induced a depolarization and then a long-lasting hyperpolarization (up to 60 min) with unchanged input resistance. The slow hyper-polarization was prevented by the 5-HT antagonists ketanserin (5-HT2), methysergide, and spiperone (5-HT1,2) and mimicked by the agonist (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (5-HT2). The post-spike afterhyperpolarization was enhanced after application of 5-HT. A depolarization was induced by the 5-HT agonists (±)-8-hydroxy-(2)-(di-n-propylamino)tetralin (5-HT1A) and 1-(2-methoxyphenyl)piperazine (5-HT1). Possible mechanisms for the 5-HT-induced hyperpolarization and its intracellular mediation are discussed. The present data suggest multiple effects of 5-HT on cat spinal motoneurons.Key words: afterhyperpolarization, depolarization, 5-hydroxytryptamine, hyperpolarization, iontophoresis, spinal motoneuron.
Role of exercise-induced potassium fluxes underlying muscle fatigue: a brief review
Authors: Sjøgaard Gisela
Published: April 2011

The site of exercise-induced muscle fatigue is suggested to be the muscle membrane, which includes the sarcolemma and T-tubule membrane; the excitability of the membrane is dependent on the membrane potential. Significant potassium flux from the intracellular space of contracting muscle may decrease the membrane potential to half its resting value. This is true for isolated muscle preparations as well as for the whole body exercise in humans. Specific K+ channels have been identified, that may account for the intracellular K+ loss. Calcium-sensitive K+ channels open when intracellular Ca2+ concentrations increase, as during excitation. ATP-sensitive K+ channels may be involved but may open only at ATP concentrations well below those attained at exhaustion. However, ATP may be compartmentalized and only the membrane-bound ATP concentration may be of significance. Ca2+ accumulation and ATP depletion cause cell destruction; these changes induce an increased K+ conductance, which may inactivate the membrane and consequently prevent tension development. It is hypothesized that such a safety mechanism is identical to the fatigue mechanism.Key words: muscle fatigue, electrolyte fluxes, Na+–K+ pump.
How important is endogenous muscle glycogen to fatigue in prolonged exercise?
Authors: Green H. J.
Published: April 2011

Endogenous muscle glycogen represents a primary fuel source during large muscle group activity in the human. The depletion of this fuel source during submaximal exercise at intensities ranging between 60 and 85% of maximal aerobic power [Formula: see text] is widely believed to be the cause of an inability to sustain exercise. Alterations of preexercise muscle glycogen reserves by dietary and exercise manipulations and changing the degree of dependency on endogenous glycogen during exercise by modifying the availability of other fuel sources have in general served to establish a close relationship between muscle glycogen and fatigue resistance. However, in spite of the evidence implicating glycogen depletion to fatigue, the mechanism remains elusive. The most popular theory is that glycogen is an essential substrate, the depletion of which results in a reduction in the rate of ATP regeneration and an inability to maintain energy supply to one or more of the processes involved in excitation and contraction in the muscle. As a consequence, the muscle is unable to translate the motor drive into an expected force and fatigue develops. However, there is little experimental evidence to support this theory. Most studies report no or only minimal changes in ATP concentration at fatigue with low glycogen and no further change in the by-products of ATP hydrolysis. These findings suggest that fatigue might be caused by other nonmetabolic factors. This review examines these other nonmetabolic factors and analyzes their potential role in fatigue during prolonged exercise with depletion of muscle glycogen reserves.Key words: muscle glycogen, prolonged exercise, fatigue, mechanisms.
Phosphofructokinase activity and acidosis during short-term tetanic contractions
Authors: Spriet Lawrence L.
Published: April 2011

Anaerobic energy production is essential for the production of muscular tension when the demand for energy is greater than can be provided aerobically and when oxygen is in short supply. The largest source of anaerobic energy is from the glycolytic pathway. With sustained tetanic contractions, muscle glycolytic activity is high and hydrogen ions (H+) accumulate while tension production decreases. The increasing [H+] and decreasing tension led to the suggestion that H+ inhibits the activity of the regulatory glycolytic enzyme phosphofructokinase (PFK). Early in vitro work confirmed the H+ sensitivity of PFK in the test tube, indicating that little PFK activity should persist at a pH of 6.9–7.0. However, in situ and in vivo experiments suggested that significant PFK activity was maintained during intense contractions when muscle pH decreased to 6.4–6.6. There are several concerns associated with the application of in vitro findings to in vivo exercise situations: (i) there is little in vitro work in mammalian skeletal muscle with substrate and modulator concentrations representative of exercise, (ii) most in vitro analyses of PFK activity are performed following the dilution of the enzyme in mediums with low protein concentration, and (iii) do the modulators identified in vitro exist in high enough in vivo concentrations at rest and during exercise to contribute to the regulation of PFK? More recent in vitro and in situ PFK experiments have overcome some of these concerns. They confirm that during intense, short-term tetanic contractions, PFK activity is well matched to the ATP demand despite decreases in pH to ~6.4–6.5. A combination of decreased inhibitor (ATP) and increased substrate (fructose 6-phosphate) contents coupled with increases in the contents of several positive modulators may be responsible for the maintained PFK activity. This combination reduces the pH-dependent ATP inhibition of PFK and extends the physiological pH range of the enzyme to the range normally measured during this type of muscular activity.Key words: glycolysis, phosphofructokinase, anaerobic metabolism, acidosis.
Adipose tissue lipolytic activity and urinary catecholamine excretion in cold-acclimated piglets
Authors: Herpin Patrick , Bertin Roseline , Marco Françoise de , Portet René , Dividich Jean Le
Published: April 2011

This study was designed to investigate the effect of chronic cold exposure (12 °C for 3 weeks) on catecholamine production and noradrenaline-induced lipolytic rate to further describe thermoregulatory mechanisms in 5- to 8-week-old pigs. Lipolytic activity in white adipose tissue was assessed in vitro while catecholamine production was estimated by measuring noradrenaline, adrenaline, and dopamine levels in 24-h urine samples. Animals were fed ad libitum and food intake was 20% greater in the cold. In control piglets maintained in a 23 °C environment, the addition of increasing amounts of noradrenaline (10−6, 10−5, 10−4 M) stimulates lipolysis (p < 0.05) and enhances the basal lipolytic rate (5.4 μequiv. fatty acids∙120 min−1∙g−1 tissue) by 2.5-, 2.7-, and 3.9-fold, respectively. Three weeks of cold acclimation had no effect on basal lipolytic rate but increased significantly noradrenaline responsiveness: incubation of subcutaneous white fat in the presence of 10−4 M noradrenaline does increase the basal lipolytic rate by sixfold. Noradrenaline effects were maximally activated by theophylline. Daily dopamine and noradrenaline excretions (3 – 10 μg/24 h) were increased significantly (up to eightfold) after 10 days of cold acclimation. By contrast, adrenaline excretion was quite low (0.6 – 1.6 μg/24 h) and showed no significant variation with time. It is likely that these hormonal and biochemical modifications play a prominent part in the mechanism of cold acclimation in the piglet. Their significance in the development of shivering and nonshivering thermogenesis is discussed in relation to the supply of energy substrates to the fatty acid utilizing tissues and to the possible uncoupling effect of free fatty acids.Key words: pigs, thermogenesis, cold, catecholamines, lipolysis.
Effect of serotonin on intracellular free calcium of rat cerebrovascular smooth muscle cells in culture
Authors: Wang Y. , Baimbridge K. G. , Mathers D. A.
Published: April 2011

Smooth muscle cells were dissociated from conducting cerebral arteries of adult rats and maintained in culture for 2–4 days. The calcium-sensitive fluorescent probe, fura-2, was used to study the effect of the vasoconstrictor serotonin (5-HT) on the level of free intracellular Ca2+ in these cells. The baseline level of free intracellular calcium was 39 ± 3.6 nM. In 74 out of 110 cells, 5-HT application transiently increased the free Ca2+ content. This effect was dose-dependent and was suppressed by nanomolar concentrations of the 5-HT2 receptor antagonist, ketanserin. The 5-HT induced rise in free intracellular calcium was not prevented by the presence of Co2+, La3+, or nifedipine, blockers of voltage-sensitive calcium channels. These results indicate that 5-HT mobilizes intracellular Ca2+ in cultured smooth muscle cells derived from the rat cerebrovasculature. The mobilization of intracellular Ca2+ appears to be triggered by a 5-HT2 type receptor, although further pharmacological experiments are required to verify this hypothesis.Key words: serotonin, smooth muscle, cerebral artery, intracellular calcium, fura-2.
Evidence for bumetanide-sensitive, Na+-dependent, partial Na–K–Cl co-transport in red blood cells of a primitive fish
Authors: Ellory J. Clive , Wolowyk Michael W.
Published: April 2011

Tracer uptake studies identified the major routes for K+ transport in hagfish red cells, resolving them into ouabain-sensitive, loop diuretic-sensitive, and residual components. The K½ values for ouabain, bumetanide, and furosemide were 10−5, 6 × 10−7, and 5 × 10−6 M, respectively. The properties of the Na–K–Cl co-transporter were investigated further by varying K+, Na+, and Cl− concentrations. The measured K½ values were similar to those for human red cells. Finally, the stoichiometry of Na:K:Cl uptake was determined, giving 1:1 for K+:Cl−; in contrast, no significant Na+ flux could be measured, although Na+ content must be present for measurable bumetanide-dependent K+ or Cl− flux to occur. The Na–K–Cl transport therefore shows Na+-dependent KCl co-transport or partial flux of the system.Key words: Na–K–Cl co-transport, hagfish red blood cells, Eptatretus stouti.
Feeding diets containing 2% cheno- or urso-deoxycholic acid or cholestyramine to rats for two weeks alters intestinal morphology and bile acid absorption
Authors: Keelan M. , Thomson A. B. R.
Published: April 2011

This study was undertaken to examine the effect of supplementing chow for 2 weeks with 2% cheno- (CDC) or ursodeoxycholic (UDC) acid or cholestyramine (CHOL) on the intestinal morphology and in vitro uptake of bile acids in adult rats. Food intake was higher in UDC and CHOL as compared with animals fed chow or CDC, or in animals pair-fed a chow-restricted diet (CRD). Body weight gain was lower in CDC and CRD but was unchanged by feeding UDC or CHOL. Jejunal mucosal surface area was similar in the five groups, although the ileal mucosal surface area was lower in UDC than in the other animals. Feeding UDC reduced the ileal uptake of cholic acid (C), taurocholic acid (TC), and glycocholic acid (GC). Feeding CDC had no effect on bile acid uptake except when compared with animals fed a chow-restricted diet. Feeding CHOL reduced the active ileal uptake of C, had no effect on the uptake of TC or GC or CDC, and was associated with increased uptake of stearic, linoleic, and linolenic acids. These effects were likely related to a direct effect of changes in the luminal bile acids rather than due to an indirect effect of the reduced food intake, since the ileal uptake of CDC and GC was greater in animals fed CDC than in those fed a chow-restricted diet with comparable weight gain. Thus, 2 weeks of feeding bile acids or bile acid binding agents may alter the form and function of the rat intestine, and as well may lead to changes in food intake and body weight gain.Key words: active transport, adaptation, bile acids.
The contribution of the nervous system to inflammation and inflammatory disease
Authors: Basbaum Allan I. , Levine Jon D.
Published: April 2011

Recent studies have identified a major contribution of the nervous system to inflammation and to inflammatory disease. In particular, substances released from the peripheral terminals of small diameter primary afferent fibers and from sympathetic postganglionic nerve (SPGN) terminals have been implicated in several of the major components of acute inflammation (e.g., vasodilatation and plasma extravasation) as well as in the regulation of tissue injury in an inflammatory disease model, experimental arthritis in the rat. Although the release of peptides from primary afferent terminals has received the most attention, our studies have established an important contribution of mast cells and the SPGN terminals to acute inflammation. We describe studies which indicate that plasma extravasation provoked by activation of small diameter primary afferents in the knee joint of the rat involves a cascade of events in which the mast cell and then the sympathetic terminal are sequentially activated. Our studies indicate that release of prostaglandins, but neither norepinephrine nor neuropeptide Y, from the SPGN terminal contributes to increased plasma extravasation. Although activation of the SPGN terminal (via the mast cell) or more directly, via injection of bradykinin, increased plasma extravasation, surgical or pharmacological sympathectomy decreased the severity of experimental arthritis. In related studies we demonstrated that adrenal medullary-derived epinephrine can exacerbate arthritis through a β-receptor-mediated regulation of the release of an as yet unidentified substance(s) from the SPGN terminal. Our results raise important questions as to whether acute inflammation contributes to tissue repair or to further injury in the setting of disease.Key words: arthritis, inflammation, peptides, primary afferents, sympathetic nervous system.
Effects of postnatal growth and denervation on characteristics of the saphenous artery in SHR and WKY rats between 3 and 6 weeks of age: an in vitro study
Authors: Todd Mary E. , Bevan Rosemary D.
Published: April 2011

Thigh vessels of spontaneously hypertensive (SHR) and Wistar–Kyoto (WKY) rats were unilaterally surgically denervated at 10 days of age by femoral nerve section. Denervated and contralateral control segments of saphenous arteries from 3- and 6-week-old rats were mounted in a small vessel myograph for study. Both strains showed growth changes in blood pressure, but there was no significant difference between WKY and SHR. Both strains also had significant growth changes in vessel dimensions and the in vitro measurements suggested that SHR vessels had a thicker wall. Denervation did not affect vessel size. Transmural nerve stimulation indicated loss of innervation due to the surgical procedure. In the denervated vessels, both norepinephrine (NE) and 5-hydroxytryptamine (5-HT) dose response curves were shifted to the left, indicating a postjunctional increase in sensitivity. Maximum tension developed was in the order K+ > 5-HT > NE. In comparing the two strains, vessels from 6-week-old SHR were less sensitive to 5-HT. Relaxation to acetylcholine was significantly decreased in denervated arteries from WKY, whereas in SHR the significant decrease occurred only at 3 weeks. Denervated vessels from both rat strains at 3 weeks showed greater relaxation to β-receptor activation, but not at 6 weeks of age. Therefore, the absence of functional innervation resulted in altered function of the saphenous artery wall.Key words: blood vessel, artery, denervation, smooth muscle, development.
Evidence that the hypothermic response of mice to Δ9-tetrahydrocannabinol is not mediated by changes in thermogenesis in brown adipose tissue
Authors: Pertwee Roger G. , Nash Kevin , Trayhurn Paul
Published: April 2011

Δ9-Tetrahydrocannabinol (20 mg/kg i.p.) and propranolol (20 and 50 mg/kg i.p.) produced marked falls in the rectal temperatures of mice kept at an ambient temperature of 22 °C. Propranolol (50 mg/kg i.p.) also decreased the thermogenic activity of brown fat, as measured by a decrease in the level of [3H]GDP binding to mitochondria obtained from mouse interscapular brown adipose tissue. In contrast, Δ9-tetrahydrocannabinol (20 mg/kg i.p.) did not affect mitochondrial GDP binding even though the dose used was one shown previously to depress heat production. GDP binding was also unaffected by this cannabinoid in brown adipose tissue taken from mice that had been kept at 13 °C instead of 22 °C. In mice kept at 34 °C, isoprenaline (0.25 and 1.0 mg/kg s.c.) induced a marked rise in rectal temperature and increased the level of GDP binding to brown fat mitochondria. Propranolol (50 mg/kg i.p.) prevented the hyperthermic response to isoprenaline, the mice becoming hypothermic instead. Δ9-Tetrahydrocannabinol (20 mg/kg i.p.) had no effect on isoprenaline-induced hyperthermia. We conclude from these data that there is no significant involvement of brown adipose tissue in the hypothermic response of mice to Δ9-tetrahydrocannabinol.Key words: Δ9-tetrahydrocannabinol, body temperature, brown adipose tissue, GDP binding, thermogenesis.
Selective depletion of dopamine in the goldfish pituitary caused by domperidone
Authors: Sloley B. D. , Trudeau V. L. , Dulka J. G. , Peter R. E.
Published: April 2011

The effects of the dopamine type-2 receptor (D-2) antagonist domperidone on pituitary and brain amine concentrations and serum gonadotropin levels in the goldfish were investigated. Domperidone caused a long-lasting, dose-dependent depletion of dopamine in the goldfish pituitary. Pituitary concentrations of 5-hydroxytryptamine (5HT) were unaffected by domperidone treatment. Concentrations of noradenaline, dopamine, and 5HT in the hypothalamus and telencephalon were also unaffected by domperidone treatment. In contrast to the goldfish, dopamine levels in both mouse pituitary and hypothalamus were unaffected by domperidone treatment. The depletion of dopamine was observed in both sexually regressed and recrudescent male and female fish, but elevation of serum gonadotropin levels in response to domperidone treatment occurred only in sexually recrudescent fish. Treatment of sexually recrudescent fish with the D-2 antagonists pimozide, (−)-sulpiride and eticlopride and the dopamine type-1 (D-1) antagonists SKF 83566 and SCH 23390 failed to elicit a depletion of pituitary dopamine or elevation of serum gonadotropin. Treatment of sexually recrudescent fish with domperidone, α-methyl-p-tyrosine or carbidopa elicited comparable depletions of pituitary dopamine and elevations of serum gonadotropin. The results suggest that in addition to D-2 receptor antagonist activity, domperidone has some other neuropharmacological action on dopaminergic neurones in the goldfish pituitary.Key words: domperidone, dopamine, noradrenaline, 5-hydroxytryptamine, pituitary, hypothalamus, telencephalon, gonadotropin, goldfish.
Muscarinic-receptor functioning in tracheas from normal and ovalbumin-sensitive guinea pigs
Authors: Yang Z-J. , Biggs D. F.
Published: April 2011

Responses to bilateral vagal nerve stimulation, to field stimulation, and to exogenous methacholine and histamine were compared in tracheas isolated from (a) saline injected (i.p.) and saline-aerosol exposed guinea pigs (control), (b) ovalbumin-sensitized and saline-aerosol exposed (sensitized) guinea pigs, and (c) ovalbumin-sensitized and 2% ovalbumin-aerosol exposed (challenged) guinea pigs. Tracheal pressor responses (cmH2O; 1 cmH2O = 98.1 Pa) to nerve and field stimulation, and maximal responses to methacholine and histamine were significantly increased in animals from group c compared with groups a and b. Dose–response lines in response to the two agonists, expressed as percent maximal contraction, did not differ among the groups. The M1 antagonist pirenzepine (0.1–10 nM) selectively reduced responses to nerve stimulation in all three groups. The M2 antagonist gallamine potentiated responses to nerve or field stimulation in all three groups. We conclude that M1, M2, and M3 muscarinic receptor functioning is similar in control and ovalbumin-sensitized guinea pigs. Changes in post-receptor transduction mechanisms may mediate the increased responsiveness noted in animals from group c.Key words: muscarinic receptors, asthma, guinea-pig trachea.
Forskolin and phosphodiesterase inhibitors release adenosine but inhibit morphine-evoked release of adenosine from spinal cord synaptosomes
Authors: Nicholson D. , White T. D. , Sawynok J.
Published: April 2011

The effects of forskolin, Ro 20-1724, rolipram, and 3-isobutyl-1-methylxanthine (IBMX) on morphine-evoked release of adenosine from dorsal spinal cord synaptosomes were evaluated to examine the potential involvement of cyclic AMP in this action of morphine. Ro 20-1724 (1–100 μM), rolipram (1–100 μM), and forskolin (1–10 μM) increased basal release of adenosine, and at 1 μM inhibited morphine-evoked release of adenosine. Release of adenosine by Ro 20-1724, rolipram, and forskolin was reduced 42–77% in the presence of α, β-methylene ADP and GMP, which inhibits ecto-5′-nucleotidase activity by 81%, indicating that this adenosine originated predominantly as nucleotide(s). Significant amounts of adenosine also were released from the ventral spinal cord by these agents. Ro 20-1724 and rolipram did not significantly alter the uptake of adenosine into synaptosomes. Although Ro 20-1724 and rolipram had only limited effects on the extrasynaptosomal conversion of added cyclic AMP to adenosine, IBMX, a phosphodiesterase inhibitor with a broader spectrum of inhibitory activity for phosphodiesterase isoenzymes, significantly inhibited the conversion of cyclic AMP to adenosine and resulted in recovery of a substantial amount of cyclic AMP. As with the non-xanthine phosphodiesterase inhibitors, IBMX increased basal release of adenosine and reduced morphine-evoked release of adenosine. Adenosine released by IBMX was reduced 70% in the presence of α, β-methylene ADP and GMP, and release from the ventral spinal cord was 61% of that from the dorsal spinal cord. Collectively, these results indicate that forskolin and phosphodiesterase inhibitors release nucleotide(s) which is (are) converted extrasynaptosomally to adenosine. For forskolin, Ro 20-1724, and rolipram, the nucleotide released could be cyclic AMP. Morphine releases adenosine per se, and forskolin and phosphodiesterase inhibitors reduce this release. The lack of increase in the action of morphine with phosphodiesterase inhibitors in particular does not support a role for stimulation of cyclic AMP production by morphine in the release of adenosine. The reduction in morphine-evoked release of adenosine by forskolin and phosphodiesterase inhibitors suggests either (a) that a reduction in cyclic levels by morphine promotes adenosine release, or (b) that cyclic AMP interferes with the release process.Key words: forskolin, Ro 20-1724, 3-isobutyl-1-methylxanthine, cyclic AMP, morphine, adenosine release, spinal cord.