bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization and metabolism of canine proximal tubules, thick ascending limbs, and collecting ducts in suspension
Authors: Tejedor A. , Noel J. , Vinay P. , Boulanger Y. , Gougoux A.
Published: April 2011

Preparations of distinct nephron segments were obtained from dog kidneys by collagenase treatment. Four morphologically different tissues were isolated: glomeruli, proximal tubules, thick ascending limbs, and papillary collecting ducts. Each segment possessed a characteristic assay of membrane-bound and cytoplasmic enzymes. Specific metabolic characteristics also were found: gluconeogenesis and ammoniagenesis in proximal tubules, glycolytic aerobic metabolism in thick ascending limbs, and glycolytic anaerobic metabolism in papillary collecting ducts. The assay of Na+–K+ ATPase, H+-ATPase, and Ca2+-ATPase activities in these nephron segments demonstrated a specific enrichment of Na+–K+ ATPase in thick ascending limbs, and of H+-ATPase in proximal tubules and papillary collecting ducts. Tubular respiration in the absence or presence of ouabain, 1,3-dicyclohexylcarbodiimide, or furosemide demonstrated that the respiration of each segment could be correlated to the activity of specific ion motive ATPases. Furthermore, a tight coupling between ion transport, ATP turnover, and substrate oxidation was demonstrated. These isolated tubular structures are thus viable and capable of transepithelial transport. Our preparation provides large amounts of defined population of tubules and are thus useful for the study of biochemical and functional heterogeneity along the nephron.
Buffer systems variably affect the interaction of norepinephrine with brain Na+–K+ ATPase
Authors: Mihic S. J. , Wu P. H. , Kalant H.
Published: April 2011

The reported effects of norepinephrine (NE) on brain Na+–K+ ATPase are quite variable. Different investigators have reported activation, inhibition, or no effect. An investigation of the importance of reaction conditions on brain Na+–K+ ATPase activity was undertaken to resolve some of these discrepancies. Using porcine cerebral cortical Na+–K+ ATPase and rat brain synaptosomal membrane preparations, it was observed that NE strongly inhibited brain Na+–K+ ATPase in Tris–HCl buffer. This inhibition of the enzyme was reversed by the addition of EDTA. In contrast, NE did not significantly inhibit Na+–K+ ATPase in imidazole–glycylglycine and Krebs–Ringer–phosphate buffers. This buffer dependence of NE inhibition of the enzyme was consistently demonstrated with three different established methods for phosphate measurement. Kinetic analysis indicated that NE, in Tris–HCl buffer, inhibited the enzyme noncompetitively at high affinity, and competitively at low affinity, ATP substrate sites.
α-Adrenergic supersensitivity and decreased number of α-adrenoceptors in heart from acute diabetic rats
Authors: Wald Miriam , Borda Enri S. , Sterin-Borda Leonor
Published: April 2011

The inotropic effect of methoxamine, as well as the α-adrenoceptor population, were measured in cardiac tissue from normal and short-term (3 days) diabetic rats. Methoxamine increased the tension of both normal and diabetic ventricles, but in diabetic ones, the dose–response curve to methoxamine was shifted to the left and the efficacy of the α-agonist was enhanced. This phenomenon was accompanied by an increase in receptor affinity, while the number of α-adrenoceptor sites decreased. Inhibitors of α1-adrenoceptors blocked, in a competitive manner, the positive inotropic effect of methoxamine in both types of ventricles. Inhibition of phospholipase C blocked the ventricular response to the methoxamine in nondiabetic as well as in diabetic hearts. Synthetic diacylglyceride (DAG) potentiated the inotropic action of the α-agonist in normal ventricles and increased the affinity with a decreased number of α-adrenoceptor sites in normal ventricles, producing values of Kd and Bmax similar to those of the acute diabetic heart. Inhibitors of protein kinase C partially reduced the supersensitivity to α-agonists in diabetic ventricles and prevented the stimulatory action of DAG upon the positive inotropic effect of methoxamine in normal ventricles. These results suggest that α-adrenergic inotropic stimulation is secondary to receptor-mediated hydrolysis of phosphoinositides, generating some oxidative metabolites (DAG) which, in turn, may be responsible for the inotropic effect. In the acute diabetic state, the supersensitivity to α-agonist could be due to high activity of phospholipase C (with an increase in DAG production) which induces alteration in the membrane α-adrenergic receptors.
Progressive hypoxia until brain electrical silence: a useful model for studying protective interventions
Authors: Cartheuser Carl F.
Published: April 2011

Anesthetized spontaneously breathing rats, fitted with epicortical electrodes and catheters for sampling arterial, venous, and cerebral venous blood, were exposed to standardized progressive hypoxia. Three minutes of hypoxia sequentially caused hyperpnea, hypopnea, apnea, and cessation of electrocorticogram "spiking," of synchronization, and of background in electroencephalogram (EEG). Blood data and cerebral blood flow and metabolism were measured throughout and at "insults," i.e., at apnea and cessation events, to clarify their interdependence. Arterial and brain venous Po2 fell linearly with inspired oxygen (final value of 2% at 280 s). Hyperpnea induced arterial alkalosis; subsequent hypopnea led to near-normal Pco2 and pH when EEG ceased. Hypercapnia was more pronounced in cerebral than in systemic venous blood; time courses of pH changes were similar. Sagittal sinus blood pressure and outflow were linearly related and resembled the time course of local cerebral blood flow. Blood flow increased by 25% at apnea and only 60% at EEG silence. Cerebral metabolic rate of O2 rose during the hyperpnea phase and fell exponentially thereafter. Cerebral glucose uptake and lactate release increased within the first 3 min but fell abruptly when cortico-electric spiking ceased. Time courses of cerebral O2 consumption and spike rate were linearly related; both showed inverse linear relations to cerebral perfusion. The hypoxic insults were well defined by blood data; critical Po2 values were lower than previously assumed. This model is proving to be a useful, controlled method by which mechanisms of cerebral hypoxia tolerance may be studied in vivo.
The role of thermogenesis in the regulation of energy balance
Authors: Richard Denis
Published: April 2011

Our knowledge of mammalian energetics has improved considerably during the last decade. Some twelve years ago energetics, which was a low priority research area (except perhaps for the agricultural nutritionists), started to revive with the publication of major contributions emphasizing the role of thermogenesis in the regulation of energy balance. Trayhum et al. (1979) observed that obesity in genetically obese mice was associated with a reduced energy expenditure for thermoregulatory thermogenesis. Meanwhile, Rothwell and Stock (1979) published results suggesting that the ability of young leanrats to resist obesity when made hyperphagic by palatable food was due to an increase in a facultative form of thermogenesis. Brown adipose tissue, which was recognized in the meantime as the main site of nonshivering thermogenesis in cold-adapted, cold-exposed rats (Foster and Frydman 1979), was also proposed as the major thermogenic effector in diet-induced thermogenesis. These studies attracted several researchers interested in understanding the etiology of obesity, an energy balance disorder that tends to be too often seen as merely the result of overfeeding. As a consequence, a tremendous amount of literature has emerged from a wide spectrum of disciplines. Although this literature supports the role of thermogenesis in energy balance of experimental animals, it does not provide all the mechanistic bases underlying this action. Besides, the role of thermogenesis in energy balance in man remains to be more firmly established. The present issue of the Canadian Journal of Physiology and Pharmacology contains a series of articles on the role of thermogenesis in energy balance. The following topics are reviewed: the role of thermogenesis in the regulation of energy balance in relation to obesity; the regulation of energy metabolism in diabetes; the role of brown adipose tissue in diet-induced thermogenesis; the role of exercise training in energy balance; and the role of thermogenesis in the energetics of pregnancy and lactation. These articles summarize the current views of some Canadian researchers who have actively contributed to the development of our knowledge on nutritional energetics during recent years.
Effect of albuterol on oxygen uptake and Na+–K+ ATPase activity of jejunal epithelia and liver in chickens
Authors: Rompala R. E. , Darre M. J.
Published: April 2011

Changes in metabolic characteristics of the liver and jejunal epithelia as a result of feeding the β-agonist albuterol to chickens for 3 and 6 weeks were studied. Feeding albuterol resulted in a change in weights of the liver and small intestines. Chickens fed albuterol for 6 weeks had greater levels of plasma nonesterified fatty acids than those fed the control diet. Oxygen uptake by liver and jejunal epithelial tissues were 25 and 26% greater for chickens fed the diet with albuterol than for those fed the control diet, respectively. No changes in Na+–K+ ATPase activity of both liver and jejunal epithelia were detected as a result of feeding albuterol. These findings indicate that certain β-agonists may elevate thermogenesis in chickens as a result of increasing metabolic rates of splanchnic tissues. However, the changes resulting in altering oxygen uptake in liver and jejunal epithelia due to feeding albuterol were not associated with Na+–K+ ATPase activity.Key words: albuterol, oxygen uptake, Na+–K+ ATPase, chickens.
Central noradrenergic activity in intact and sinoaortic denervated Dahl rats
Authors: Patel K. P. , Peuler J. D. , Morgan D. A. , Pardini B. J. , Lund D. D. , Schmid P. G.
Published: April 2011

Lesions in forebrain areas richly innervated by noradrenergic terminals and involved in cardiovascular function reduce or prevent hypertension in the Dahl salt-sensitive (S) rats fed a high (H) salt diet. This led us to examine two questions. (1) Is the noradrenergic activity altered in discrete forebrain and brainstem areas of SH rats? (2) Are these changes in noradrenergic activity eliminated by sinoaortic denervation (SAD)? Studies were done in 10-week-old female SH and Dahl salt-resistant (RH) rats. Half of the rats in each group had SAD surgery 1 week prior to study. An index of norepinephrine (NE) turnover was determined by measuring the decline in tissue NE concentration 8 h after administering α-methyl-p-tyrosine, a NE synthesis blocker, to animals from each of four groups: sham-RH, SAD-RH, sham-SH, and SAD-SH (n = 18–20 per group). Various discrete brain areas were obtained using the "punch technique." In SH rats the index of NE turnover was increased in the median preoptic nucleus and decreased in the paraventricular nucleus compared with RH rats regardless of SAD. In contrast, in SH rats the index of NE turnover was increased in the supraoptic nucleus and locus ceruleus compared with RH rats; however, SAD-RH had greater turnover of NE at these sites than SAD-SH. In summary, changes in noradrenergic activity in the median preoptic nucleus and the paraventricular nucleus may be related to genetic predisposition to hypertension in SH rats. In contrast, changes in the locus ceruleus and the supraoptic nucleus of SH rats may be related to impaired baroreflexes and thereby contribute to hypertension.Key words: hypertension, brain nuclei, norepinephrine, turnover.
Effects of hypoxia or hyperoxia on the lung of the chick embryo
Authors: Xu Lijing , Mortola Jacopo P.
Published: April 2011

Newborn mammals in chronic hypoxia or hyperoxia experience, respectively, an increase or decrease in lung weight:body weight ratios, possibly because of the mechanical effect on the lung accompanying the ventilatory response. Because the avian lung does not expand or contract with the breathing cycle, we asked whether or not qualitatively similar changes could be observed in the lung of chick embryos incubated in hypoxic or hyperoxic conditions. Hypoxic embryos (10% O2, days 14–18) were smaller than controls incubated in normoxia, with higher hematocrit values and larger lung weight:body weight ratios (both wet and dry). Both the total pulmonary DNA (reflecting the cellular component) and the DNA concentration were decreased in hypoxia. Hyperoxic embryos (50% O2, days 7–18 or days 14–18) had lower hematocrit values and smaller dry lung weight:body weight ratios than controls, with similar DNA concentrations. In general, the differences from controls were more apparent in those embryos hyperoxic from day 14 to 18 of incubation than from day 7 to 18. We conclude that changes in lung weights qualitatively similar to those occurring in the chronically hypoxic or hyperoxic newborn mammal can also be observed in the hypoxic or hyperoxic chick embryo, suggesting that they are not necessarily caused by changes in mechanical stretch on the lung.Key words: lung development, lung DNA, avian growth.
A comparison of the estimates of whole-body protein turnover in parenterally fed neonates obtained using three different end products
Authors: Pencharz P. , Beesley J. , Sauer P. , Aerde J. Van , Canagarayar U. , Renner J. , McVey M. , Wesson D. , Swyer P.
Published: April 2011

Protein turnover rates in neonates have been calculated largely by measuring urinary [15N]urea enrichment following administration of [15N]glycine. Although ammonia has been increasingly recognized as an end product of nitrogen metabolism, in neonates it yields a different estimate of protein turnover than does urea. Comparisons of ammonia and urea end products in parenterally fed neonates have not previously been reported. A third and independent way of estimating protein turnover, developed for adults, is to use breath 13CO2 as an end product following administration of [1-3C]leucine. We therefore carried out simultaneous measurements of protein turnover in 10 parenterally fed neonates, using the three end products. The infants were clinically stable, weighed 2.6 ± 0.2 kg, and received 3.1 ± 0.2 g∙kg−1∙d−1 of amino acid, 2.2 ± 0.1 g∙kg−1∙d−1 of lipids, and an energy intake of 90 ± 4 kcal∙kg−1∙d−1 (1 kcal = 4.186 kJ). The turnover estimates derived from the 13CO2 and [15N]urea end products were very similar. The [15N]ammonia end product produced values approximately 66% (p < 0.01) of the other two. We conclude that the ammonia and urea end products probably originate in different precursor pools. The similarity of the urea and breath carbon dioxide results helps validate the use of the urea end product in studying the nitrogen metabolism of parenterally fed neonates. Ideally in future studies two or more end products should be used, since they provide information about different aspects of the nenonates' protein metabolism.Key words: neonates, protein metabolism, nitrogen-15, [1-13C]leucine.
The effects of fluorocitrate on renal glutamine, lactate, alanine, and oxygen metabolism in the dog
Authors: Fine A.
Published: April 2011

Acid–base status is considered the major factor controlling renal [Formula: see text] production from glutamine, with maximal values found in chronic acidosis. However, metabolic inhibitors have been shown to increase [Formula: see text] production without acid–base change; the mechanism for this increase is unclear. Fluorocitrate was administered to dogs with chronic metabolic alkalosis. Following fluorocitrate total renal [Formula: see text] production rose from 32 ± 5 to 104 ± 15 μmol/(min∙100 mL glomerular filtration rate (GFR)) (p < 0.01) and glutamine extraction rose from 26 ± 8 to 65 ± 8 μmol/(min∙100 mL GFR) (p < 0.01). These values approximate maximal values found in chronic acidosis. Lactate utilization fell from 165 ± 19 to 99 ± 7 μmol/(min∙100 mL GFR) following fluorocitrate (p < 0.01). Citrate extraction fell to zero and alanine production rose from 27 ± 4 to 46 ± 7 μmol/(min∙100 mL GFR) (p < 0.01). Oxygen consumption remained unchanged following fluorocitrate, 584 ± 29 vs. 549 ± 29 μmol/(min∙100 mL GFR). These results demonstrate that in the presence of metabolic inhibition in the kidney, ATP production remains constant. This is achieved by increased utilization of one substrate, glutamine, when the ATP production from other substrates is reduced. Thus the necessity to maintain constant ATP production appears to modulate renal [Formula: see text] production.Key words: ammonium production, metabolic inhibitors, oxygen uptake.
A commentary on the interpretation of in vitro biochemical measures of brown adipose tissue thermogenesis
Authors: Trayhurn Paul , Milner Rachel E.
Published: April 2011

In this article we comment on the various in vitro biochemical measurements employed to assess the thermogenic activity and capacity of brown adipose tissue. The meaning and significance of changes in tissue weight, protein content, cell number, and mitochondrial mass are each summarized. In addition, various indices of the proton conductance pathway – mitochondrial swelling, proton conductance, uncoupling protein concentration, and GDP binding studies – are discussed. The issue of unmasking and masking of GDP binding sites is reviewed; recent reports have clearly demonstrated unmasking and masking, and it is concluded that GDP binding studies are an index of the activity of uncoupling protein, rather than a measure of its concentration. It is suggested that tissue mass, mitochondrial content, mitochondrial GDP binding, and uncoupling protein concentration represent core measurements for the biochemical assessment of the thermogenic activity and capacity of brown adipose tissue. Auxiliary measurements include Scatchard analysis of GDP binding data to distinguish changes in the number of binding sites from potential changes in Kd, and mitochondrial swelling studies, as an additional index of proton permeability. The distinction between thermogenic activity (GDP binding, proton permeability) and capacity (uncoupling protein content), both on a per unit of mitochondrial protein and per tissue basis, is emphasized.Key words: brown adipose tissue, thermogenesis, uncoupling protein, mitochondria.
Immediate hypersensitivity reactions in the guinea-pig conjunctiva: studies with a second-generation leukotriene D4 receptor antagonist, MK-571
Authors: Chan Chi-Chung , Dagenais Francois , Firby Patricia , Foster Aidan , Ford-Hutchinson Anthony W.
Published: April 2011

The role of leukotriene D4 (LTD4) as a mediator of immediate hypersensitivity reactions in the guinea-pig conjunctiva was examined using a potent, second-generation LTD4 receptor antagonist, MK-571 (also known as L-660,711). The microvascular permeability changes in the guinea-pig conjunctiva following challenge with either LTD4 or antigen were measured through accumulation of intravenously administered 99mtechnetium-labeled albumin. Topical application of MK-571 (up to 2 h pretreatment) significantly inhibited the conjunctival responses to LTD4 (ED50 of 18–60 ng/eye) but not to histamine. The responses to a single topical antigen challenge in ovalbumin-sensitized guinea pigs were significantly inhibited (44%) by topical treatment with MK-571, in contrast to the lack of effect previously observed with prototypic antagonists. The inhibitory effects of MK-571 did not involve an action on conversion of [3H]LTC4 to LTD4 and LTE4. Following a second antigen challenge (24 h after the first), MK-571 inhibited the resultant permeability changes by 78%. Specific histamine H1 and H2 antagonists similarly inhibited the responses to the first and second challenges (63 and 74%, respectively). The present study suggests that LTD4 is involved in conjunctival hypersensitivity reactions and that potent LTD4 receptor antagonists may be of therapeutic value in the treatment of allergic conjunctivitis.Key words: allergic conjunctivitis, leukotriene D4, leukotriene D4 antagonists, MK-571, vascular permeability changes.
Effects of age on the anisotropy of the descending human thoracic aorta determined by uniaxial tensile testing and digestion by NaOH under load
Authors: Sherebrin Marvin H. , Hegney Jane E. , Roach Margot R.
Published: April 2011

Strips of human thoracic aortic wall taken at autopsy from 23 individuals aged 15–81 years have been tested in two ways: in uniaxial loading and by digestion in 0.1 M NaOH at 75 °C under a load of 50 g. The circumferentially oriented strips were more extensible in loading and took a longer time to fail while being digested under load than the longitudinal strips from the same location. The stress versus strain curve was fitted to an exponential equation of the form, stress = A[exp(B strain)]. For circumferentially oriented strips from 19 subjects, parameter A was independent of age. Parameter B increased by a factor of 2.75 from 19 to 81 years. For longitudinally oriented strips for 14 subjects, A was also independent of age and B increased by 2.4 times from 25 to 81. With digestion under load for 11 matched pairs of strips aged from 32 to 75 the circumferential strips failed in 117 ± 23 min (standard error), while the longitudinal ones failed in 20.3 ± 3.2 min (standard error) (p < 0.003). The results have important implications for vessel attachments to the aorta in heart transplantation and in vascular surgery.Key words: aorta, aging, anisotropy, modulus of elasticity, connective tissue mechanics, elastin–collagen, stress–strain.
Comparison of the effects of several endotoxin preparations on body temperature and metabolic rate in the rat
Authors: Horan M. A. , Little R. A. , Rothwell N. J. , Strijbos P. J. L. M.
Published: April 2011

The effects of several bacterial endotoxins on body temperature and resting oxygen consumption [Formula: see text] were compared in normal rats. Low doses (0.05 mg/kg, i.m.) of 0127:B8 phenol-extracted endotoxin caused significant increases in both parameters. Maximal febrile responses (+1.6 °C) occurred at a dose of 0.05 mg/kg, but higher doses produced smaller effects. The maximal increase in [Formula: see text] (17%) occurred at doses of 0.5–1.0 mg/kg. A TCA extract of the same strain of endotoxin elicited a similar pattern of responses but was less potent than the phenol extract, whereas another endotoxin 026:B6 (TCA extract) was much less potent. The data illustrate the importance of constructing dose–response curves when comparing different endotoxins and indicate that in the rat, oxygen consumption provides a useful index of the response to pyrogens.Key words: fever, endotoxin, temperature, oxygen consumption, rat.
Hepatic zonation of drug metabolizing enzymes. Studies on hepatocytes isolated from the periportal or perivenous region of the liver acinus
Authors: Gascon-Barré Marielle , Benbrahim Nawel , Tremblay Chantale
Published: April 2011

Models of hepatic intraacinar zonation have been proposed previously; in most models, direct visualization of the acinar destruction is not possible while intact hepatocyte recovery–viability often presents a problem for subsequent metabolic studies. In the present studies, the liver is isolated in situ and perfused with Krebs–Henseleit buffer, pH 7.4. A 1.5-mL intrahepatic volume of a 7 mM digitonin solution is then injected at a flow rate of 6 mL/min for 15 s via the portal vein or via the vena cava for selective destruction of the periportal (PP) or perivenous (PV) region of the acinus. To avoid diffusion of the detergent throughout the acinus, the liver is then immediately perfused with oxygenated Hanks buffer in the direction opposite to that of digitonin injection. The preparation can then be used for histological evaluation, for studies on isolated-perfused liver, or for isolation of hepatocytes. Direct visualization of the acinar destruction can be achieved by coloring the permeabilized cells with 0.2 mM trypan blue; the liver is then fixed in situ by a 10-min perfusion with paraformaldehyde and histological evaluation is achieved by eosine staining of liver slices. Following isolation of hepatocytes by collagenase perfusion, a highly significant PV localization was found for the synthesis of glutamine, the N-demethylation of aminopyrine, and the glucuronidation of p-nitrophenol, whereas a highly significant PP zonation was found for alanine aminotransferase. By contrast, no specific acinar zonation was found for the enzymes 7-ethoxycoumarin O-deethylase and aniline p-hydroxylase. Total cytochrome P-450 was 0.42 ± 0.006 and 0.4 ± 0.03 nmol/106 hepatocytes in PV and PP, respectively (nonsignificant). Our data show, using histological evaluation, that selective and reproducible destruction of the liver acinus is achieved by the method used. Moreover, our findings indicate that, under unstimulated conditions, intraacinar regionalization of several enzymes involved in the biotransformation of xenobiotics is present in normal rat hepatocytes.Key words: hepatic acinar zonation, cytochrome P-450, mixed function oxidases, glucuronyl transferase, hepatocytes, digitonin.
The effects of 4-aminopyridine and tetraethylammonium on the kinetics of transmitter release at the mammalian neuromuscular synapse
Authors: Saint David A.
Published: April 2011

The effect of 4-aminopyridine and tetraethylammonium on the time course of neurotransmitter release was examined at the neuromuscular junction using a computer-aided method which directly measured the time of occurrence of individual quanta. It is apparent that the action of 4-aminopyridine, at concentrations of 0.1 to 1 mM, when examined in isolation from other experimental manipulations, is to cause a greatly enhanced probability of release at times subsequent to the time over which release normally occurs. In contrast to previous reports of an increased latency of release, however, the probability of release in the initial phase is essentially unchanged, i.e., there is no evidence of an increased latency of release caused by 4-aminopyridine. Similar results were obtained with tetraethylammonium, although the prolongation of release was much less, even at a concentration of 1 mM. The results are consistent with the view that the predominant action of 4-aminopyridine is to block the potassium conductance responsible for repolarization of the action potential and hence cause a prolonged Ca2+ current. The action of tetraethylammonium is consistent with the block of a different K+ conductance, with consequent enhancement of action potential effectiveness, but with little prolongation of release. The observation of multiple peaks, or oscillations in the release probability function at high (ca. 1 mM) concentrations of 4-aminopyridine, may be related, as is suggested, to oscillations of presynaptic membrane potential, or perhaps to changes in the electrochemical gradient for Ca2+ influx.Key words: transmitter release, 4-aminopyridine, tetraethylammonium, synapse, excitation-secretion coupling, nerve terminal.
The effect of adrenal denervation on the metabolic effects of hyperammonemia in sheep
Authors: Wiechetek Maria , Podgurniak Pawel , Zabielski Romuald , Podgurniak Malgorzata
Published: April 2011

The metabolic effect of intravenous infusion of ammonium chloride (60 μmol/(kg body weight∙min)) was compared in five sheep before and after adrenal denervation. Adrenal denervation completely abolished the hyperglycemic effect of ammonium chloride, diminished the rise of pyruvate and lactate concentration, and failed to influence the lipolytic effect of NH4Cl It is suggested that the metabolic effects of ammonia are in a different degree related to the action of ammonia on the central nervous system and (i) the hyperammonemic effect of ammonia completely depends on the neurogenic increase of adrenal medullary hormones; (ii) the rise of blood lactate and pyruvate level observed during hyperammonemia is only partially mediated by adrenaline; and (iii) the lipolytic effect of ammonia ion does not depend on the nerve-controlled secretion of adrenal medullary hormones.Key words: adrenal denervation, hyperammonemia, metabolism, sheep.
Endocrine and neurochemical actions of cocaine
Authors: Paolo Thérèse Di , Rouillard Claude , Morissette Marc , Lévesque Daniel , Bédard Paul J.
Published: April 2011

The endocrine and neurochemical actions of cocaine in human and animal studies are reviewed. In humans, cocaine has been shown to influence plasma prolactin and growth hormone, as well as the dexamethasone suppression of cortisol and the thyroid-stimulating hormone response to thyroid-releasing hormone. In rats, cocaine affects plasma prolactin, luteinizing hormone, and testosterone, and can lead to adrenocortical hypertrophy. Behavioral sensitization to cocaine in rats has been shown to be related to the gender of the animals and appears to be modulated by vasopressin. A review of the neurochemical actions of cocaine indicates the important role of dopamine systems in the euphoric effects of the drug, as well as its withdrawal symptoms. Cocaine is a potent dopamine uptake inhibitor, as shown by its competition with [3H]GBR-12935 (a specific ligand for the dopamine uptake sites) for striatum binding sites. However, it does not acutely affect the high-affinity agonist sites of the D-2 dopamine receptors, which are suggested to be the active form of the presynaptic receptor. Using microdialysis techniques, cocaine is shown to rapidly cause a large increase of rat striatal dopamine levels, while its metabolites dihydroxyphenylacetic acid and homovanillic acid are slightly decreased and increased, respectively.Key words: cocaine, dopamine, hormones, neurochemistry, microdialysis.
Pharmacological characterization of the binding of [3H]bremazocine in guinea-pig brain: evidence for multiplicity of the κ-opioid receptors
Authors: Tiberi Mario , Magnan Jacques
Published: April 2011

In guinea-pig brain, [3H]bremazocine has a binding capacity of 27.2 pmol/g wet tissue, which is statistically different from that of [3H]ethylketazocine (14.7 pmol/g wet tissue) or the sum of the individual binding capacities of μ-, δ-, and κ-selective ligands (15.0 pmol/g wet tissue). Saturation studies of [3H]bremazocine performed in the presence of unlabelled μ-, δ-, and κ-blockers still reveal a homogeneous population of binding sites. [3H]Bremazocine under suppressed conditions displays at these sites a Kd of 2.51 nM with a binding capacity of 9.15 pmol/g wet tissue. We have performed the pharmacological characterization of these additional opioid binding sites. Displacement curves measured with a number of opioid substances were all best fitted to a one-site model. The stereoselectivity of these additional sites was demonstrated by using two groups of stereoisomers. Oripavine and benzomorphan opioids were among the most potent drugs at the [3H]bremazocine sites (μ + δ + κ suppressed). Diprenorphine, bremazocine, cyclazocine, and ethylketazocine displayed apparent affinities constants (1/Ka) of 8.66, 7.57, 21.4, and 38.0 nM, respectively at those sites. The κ-selective drugs U50488, U69593, PD117302, and tifluadom were inhibitors of the binding of [3H]bremazocine at these sites with apparent affinities of 113, 268, 76.9, and 47.9 nM. All μ- or δ-selective drugs tested in this study have caused weak or no inhibition of the binding. Correlation analyses were done between the different affinities measured at the [3H]bremazocine sites (μ + δ + κ suppressed) and those observed at the known μ-, δ-, and κ-sites of the guinea-pig brain. The results were highly and significantly correlated with the κ-binding profile, while no correlation could be established with the μ,- or δ-binding profiles. Moreover, the results reported here do not correspond to a pharmacological profile that belongs to the σ- or ε-receptors. Thus, it is likely that in the guinea-pig brain the [3H]bremazocine sites (μ + δ + κ suppressed) are a subtype of κ-site family, namely κ2-sites. Finally, apparent affinities displayed at those sites are correlated with the biological activity of opioids in the guinea-pig ileum and rat vas deferens, suggesting that those sites could be considered as receptors.Key words: opioid receptors, kappa subtype, guinea-pig brain.
Selective utilization of L-isomer of lactate in the smooth muscle of the guinea pig taenia caeci
Authors: Endo Isamu , Suzuki Tadahiko , Takahashi Hiroaki , Karaki Hideaki
Published: April 2011

Utilization of D- and L-lactate in the isolated intestinal smooth muscle of the guinea pig taenia caeci was examined by measuring contractile tension, oxygen consumption, and adenosine triphosphate (ATP) and creatine phosphate (PCr) concentrations. In the absence of glucose in the medium, muscle contraction induced by a high concentration of K+ was inhibited and the rate of oxygen consumption and the concentrations of ATP and PCr were decreased. Addition of glucose, L-lactate, and D,L-lactate, but not D-lactate, led to recovery of muscle contraction, rate of oxygen consumption, and ATP and PCr concentrations when the tissue had been incubated in the high K+, glucose-free solution. These results suggest that the isolated guinea pig taenia caeci selectively utilizes the L-isomer of lactate as a substrate for energy metabolism.Key words: lactate isomers, smooth muscle, oxygen consumption, adenosine triphosphate, creatine phosphate.
Selective inhibition of [3H]nitrendipine binding to brain and cardiac membranes by bacitracin
Authors: Smith Janet D. , Bolger Gordon T.
Published: April 2011

The effects of bacitracin were investigated on [3H]nitrendipine binding to rat brain and cardiac membranes in a low ionic strength (5 mM Tris–HCl) buffer. Bacitracin inhibited [3H]nitrendipine binding to rat brain and cardiac membranes with IC50 values of 400 ± 100 and 4600 ± 400 μg/mL, respectively. Scatchard analysis in brain membranes revealed that bacitracin inhibited [3H]nitrendipine binding primarily by reducing the Bmax but also by producing a small increase in the Kd. In brain membranes, Na+ (100 mM) and Ca2+ (2 mM) reduced the potency of bacitracin to inhibit [3H]nitrendipine binding by approximately sixfold with IC50 values of 2600 ± 300 and 2100 ± 400 μg/mL observed for bacitracin in the presence of 100 mM Na+ and 2 mM Ca2+, respectively. The EC50 values for the effects of Na+ and Ca2+ were 800 ± 200 μM and 25 ± 5 mM. K+, Mg2+, choline, and increasing the assay buffer of Tris–HCl to 50 mM also decreased the inhibition of [3H]nitrendipine binding by bacitracin. These results suggest that bacitracin specifically modulates [3H]nitrendipine binding in a cation-dependent manner and that brain and cardiac dihydropyridine binding sites are either biochemically different or exist in a different membrane environment.Key words: bacitracin, [3H]nitrendipine, brain, heart.
Dopamine D1 and D2 receptors in spontaneously hypertensive rat brain striatum
Authors: Watanabe Masayuki , Tsuruta Satoshi , Inoue Yasuhiro , Kinuya Masayuki , Ogawa Kazuko , Mamiya Gunji , Tatsunuma Toshihiko
Published: April 2011

Since it has been reported that dopamine D2 receptors are elevated in the brain striatum of spontaneously hypertensive (SH) rats, and since both D1 and D2 receptors may interact with one another, we measured the densities of both these receptors in SH rat striatum, as well as those in the normotensive Wistar–Kyoto rat striatum. The D1 receptor density in both strains was virtually the same, 72.9 ± 2.2 and 71.3 ± 3.2 pmol/g, respectively (mean ± SD). The D2 receptor densities were also almost identical, 16.3 ± 0.6 and 16.8 ± 1.0 pmol/g, respectively (mean ± SD). Thus, these data do not support the concept of a dopamine receptor related role in spontaneous hypertension.Key words: spontaneously hypertensive rat, D1 dopamine receptor, D2 dopamine receptor.
Neural mechanisms of emesis
Authors: Carpenter David O.
Published: April 2011

Emesis is a reflex, developed to different degrees in different species, that allows an animal to rid itself of ingested toxins or poisons. The reflex can be elicited either by direct neuronal connections from visceral afferent fibers, especially those from the gastrointestinal tract, or from humoral factors. Emesis from humoral factors depends on the integrity of the area postrema; neurons in the area postrema have excitatory receptors for emetic agents. Emesis from gastrointestinal afferents does not depend on the area postrema, but probably the reflex is triggered by projections to some part of the nucleus tractus solitarius. As with a variety of other complex motor functions regulated by the brain stem, it is likely that the sequence of muscle excitation and inhibition is controlled by a central pattern generator located in the nucleus tractus solitarius, and that information from humoral factors via the area postrema and visceral afferents via the vagus nerve converge at this point. This central pattern generator, like those for motor functions such as swallowing, presumably projects to the various motor nuclei, perhaps through interneuronal pathways, to elicit the sequential excitation and inhibition that controls the reflex.Key words: area postrema, emesis, neurotransmitters, cyclic AMP, neuropeptides.
The neuropharmacology of emesis: the role of receptors in neuromodulation of nausea and vomiting
Authors: Leslie R. A. , Shah Y. , Thejomayen M. , Murphy K. M. , Robertson H. A.
Published: April 2011

The basic pharmacological mechanisms involved in mediating nausea and vomiting are still poorly understood. Several classes of drags have been identified that alleviate the symptoms of nausea and vomiting, either prophylactically or acutely. None of these is completely effective in all cases. They include antihistamines, dopamine antagonists, steroids, cannabinoids, benzodiazepines, serotonin antagonists, and anticholinergics. This paper examines the evidence that links each of these classes of drugs with the distribution of specific neurotransmitter receptor sites on which they may be acting. Studies on the central nervous system distribution of binding sites for one of these classes of drugs, the anticholinergics, are described. Binding sites for the muscarinic cholinergic radioligand [3H]quinuclidinyibenzilate occur in different concentrations throughout the dorsal vagal complex of the rabbit medulla oblongata. The distribution of such sites in this nonvomiting experimental animal is markedly different from that in the cat, an animal that has been used for many physiological and pharmacological studies of emesis. A previous study has suggested that muscarinic binding sites may occur presynaptically on vagal afferent terminals that synapse in the dorsal vagal complex of the cat; this appears not to be the case in the rabbit. Possible implications of these findings for the identification of the site of action of anticholinergic, antiemetic drags are discussed.Key words: neuromodulation, nausea, vomiting, receptors.
Propranolol metabolism by isolated hepatocytes from normal and cirrhotic rat livers: the effect of albumin
Authors: Gariepy Louise , Fenyves Daphna , Petit Jean-Luc , Raymond Ginette , Villeneuve Jean-Pierre
Published: April 2011

Several recent reports have shown that the hepatic uptake and subsequent elimination of some substrates is faster in the presence of albumin than in its absence, as if some of the substrate bound to albumin was also available for uptake. In the present study, we examined the effect of albumin on the clearance of propranolol by isolated rat hepatocyte suspensions. The clearance of total drug decreased progressively as albumin concentration increased. There was also a progressive decrease in the free fraction of propranolol and the net result was an increase in the clearance of unbound drug (+50% at 40 g/L albumin). This increase was not due to an oncotic pressure effect of albumin, nor to the presence of fatty acids bound to albumin. The clearance of propranolol by isolated hepatocytes from cirrhotic rats was decreased compared with controls (−50%), and albumin also increased propranolol free clearance, albeit to a lesser extent than in control animals. Our results indicate that albumin facilitates the elimination of propranolol by hepatocytes, possibly because of surface-mediated catalysis of the albumin–propranolol complexes.Key words: propranolol clearance, albumin, isolated rat hepatocytes, cirrhosis.
Neutrophil-mediated increased permeability of microcarrier-cultured endothelial monolayers: a model for the in vitro study of neutrophil-dependent mediators of vasopermeability
Authors: Killackey John J. F. , Killackey Barbara A.
Published: April 2011

Changes in the permeability of human endothelial monolayers in response to activated human neutrophils were examined in a novel, in vitro model of vasopermeability changes. Microcarrier-cultured human umbilical vein endothelial monolayers were used in a system that responds to histamine. Human neutrophils did not increase Evans Blue staining of the endothelium-covered microcarriers if added alone or if added with the neutrophil-dependent mediator of vasopermeability, formyl-methionyl-leucyl-phenylalanine (FMLP, 0.1 μM). In contrast, neutrophils added to the endothelial cells in a ratio as low as 2.5:1 caused time-dependent increases in microcarrier staining if pretreated with cytochalasin B (5 μg/mL) before addition with FMLP. Neutrophil cell-free releasate and purified human sputum elastase also caused concentration-related increases in Evans Blue staining of the endothelial-covered microcarriers and these effects were inhibited by the elastase inhibitor methoxysuccinyl-alanyl-alanyl-prolyl-valyl chloromethyl ketone. This compound also inhibited neutrophil-mediated endothelial permeability increases. The microcarrier-cultured human endothelial monolayer system rapidly detects permeability alterations of endothelial monolayers in response to activated human neutrophils. This model is a potentially useful screening assay for the development of therapeutic agents, directed at neutrophil degranulation or degranulation products, for the control of inflammatory vasopermeability abnormalities.Key words: neutrophil, endothelium, permeability, elastase, microcarrier.
Release of essential fatty acids from the rat mesenteric vascular bed perfused in vitro: modulation by zinc
Authors: Cunnane Stephen C. , Nassar Bassam A.
Published: April 2011

The rat mesenteric vascular bed releases prostaglandins when perfused in vitro. The present study evaluated the effect of perfusion of the rat mesenteric vascular bed in vitro with a buffer containing 0, 3, 6, or 9 nM of added zinc on the release of essential fatty acids over a 150-min period. Long chain fatty acids in the mesenteric lipids and in total lipid of the perfusion effluent were assayed by gas liquid chromatography. The presence of 6 nM zinc in the perfusing buffer almost completely prevented the change in 16–22 carbon long chain fatty acids in the mesenteric phospholipids and decreased the release of free fatty acids in comparison to that occurring in the absence of additional zinc. The results sugest that physiological amounts of zinc in the perfusion medium reduce the release of essential fatty acids from rat mesenteric lipids.Key words: zinc, phospholipid, linoleic acid, arachidonic acid, prostaglandin.
Metabolic effects of trichothecene T-2 toxin
Authors: Khachatourians George G.
Published: April 2011

Cereals and other agricultural products contaminated with trichothecene mycotoxins are unfit for consumption. Until recently, the metabolic effects of T-2 toxin (T-2) were thought to reside in its ability to inhibit protein synthesis. It is now clear that trichothecenes have multiple effects, including inhibition of DNA, RNA, and protein synthesis in several cellular systems, inhibition of in vitro protein synthesis, inhibition of mitochondrial functions, effects on cell division, normal cell shape, and hemolysis of erythrocytes. It is argued that these effects are pleiotropic responses of the cell's biosynthetic network to protein synthesis inhibition. However, in studies with erythrocytes, which lack nuclei and protein synthesis, changes in cell shape and lytic response towards T-2 are observed. Susceptibility to lysis is species dependent and correlates with the presence of phosphatidylcholine. Owing to their amphipathic nature, T-2 and other trichothecenes could exert their cytotoxicity by acting on cell membranes. As for cell energetics, T-2 inhibits the mitochondrial electron transport system, with succinic dehydrogenase as one site of action. Although initial investigations of the metabolic effects of T-2 mediated cytotoxicity suggested the inhibition of protein synthesis as the principal site of action, current thought suggests that the effects of trichothecenes are much more diverse.Key words: T-2 toxin, erythrocyte deformability, membrane lipids, yeast, anaesthetics.
Excitation–contraction coupling model to estimate the recirculating fraction of activator calcium in intact cardiac muscle
Authors: Urthaler Ferdinand , Walker Alfred A. , Reeves Russell C. , Hefner Lloyd L.
Published: April 2011

Potentiated contractions were evoked with a rapid pace pause maneuver in 14 length-clamped ferret papillary muscles paced 12 times/min at 25 °C. At 1.25 mM [Ca2+]o the average steady-state force was 2.94 ± 1.08 g/mm2 and the potentiated contraction averaged 10.96 ± 1.61 g/mm2. At 5.0 mM [Ca2+]o the steady-state force increased to 6.18 ± 1.23 g/mm2 and the potentiated contraction averaged 12.08 ± 1.15 g/mm2. Under the conditions of these experiments the potentiated contraction obtained at 5.0 mM [Ca2+]o is equal to the maximum twitch tension (Fmax) these muscles can generate. We have previously shown that Fmax is an equivalent of maximal calcium activated force. Since there is a beat to beat nearly exponential decay of the evoked potentiation, the fraction (= fraction x) of the potentiation that is not dissipated with each beat is nearly constant. Using an excitation–contraction coupling model we have previously found that x reflects a measure of the recirculating fraction of activator calcium. Because the tension–calcium relationship is better characterized by a sigmoidal curve, we have now incorporated the Hill equation in the model. To account for the inverse relationship between [Ca2+]i and the magnitude of the slow inward current, a term for negative feedback (h) was also included. We have determined the quantity (x – h) because x and h could not be determined separately. The quantity (x – h) was denoted as x′. The average values of x′ at 1.25 and 5.0 mM [Ca2+]o were significantly different (p < 0.0001), approximately 20% at the lower [Ca2+]o and about 50% at the higher [Ca2+]o. An attempt to estimate both x′ and the Hill coefficient N simultaneously has shown that the determination of N must be considered inaccurate, but even larger variations of N have little influence on x′. Thus, in intact ferret ventricular muscle, the model predicts that at 1.25 mM [Ca2+]o only about 20% of the activator calcium recirculates, while some 80% comes across the sarcolemma from the extracellular compartment. The model also predicts that the recirculating fraction doubles when [Ca2+]o is elevated to 5 mM.Key words: length-clamped papillary muscle, maximum twitch tension, excitation–contraction coupling model, recirculating fraction of activator calcium, transsarcolemmal fraction of activator calcium.
Cysteine enhances in vivo natriuretic potency of ethacrynic acid in the rat
Authors: Kompanowska-Jezierska E. , Dobrowolski L. , Sadowski J.
Published: April 2011

Total renal blood flow, glomerular filtration rate, and renal excretory function were determined in anesthetized rats treated with intravenous infusion of ethacrynic acid, 0.36 mg∙min−1∙kg−1, alone or in combination with cysteine. Simultaneously, the corticomedullary electrolyte gradient was evaluated in vivo from measurement of tissue electrical admittance (reciprocal impedance). Renal hemodynamics was not altered by drag infusion. Sodium excretion increased 1.7-fold with ethacrynic acid alone and 5-fold after the addition of cysteine. Tissue electrolytes of inner medulla decreased much more in rats given ethacrynic acid plus cysteine. We conclude that the addition of cysteine to intravenous infusion of ethacrynic acid greatly enhances its in vivo natriuretic potency in the rat.Key words: tubular NaCl transport, loop diuretics, loop of Henle, tissue electrolyte gradient.