bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF BKCa CHANNELS ON THE REDUCTION OF CYTOSOLIC Ca2+ IN cGMP‐INDUCED RELAXATION OF GUINEAPIG TRACHEA
Authors: Mikawa Kenichiro , Kume Hiroaki , Takagi Kenzo
Published: June 2007

1. In order to examine the mechanisms of cGMP‐induced relaxation in airway smooth muscle, the effects of atrial natriuretic peptide (ANP) and 8‐brom cGMP on muscle tone were studied by measuring isometric tension, while the effects on cytosolic Ca2+ concentrations were studied by measuring the spectra of fura‐2 loaded in guinea‐pig tracheal strips.

2. Atrial natriuretic peptide and 8‐brom cGMP caused a concentration‐dependent inhibition of spontaneous tone in the guinea‐pig trachea. The relaxant effects of these agents on spontaneous tone were markedly suppressed in the presence of iberiotoxin (IbTX), a selective inhibitor of large‐conductance Ca2+‐activated K+ (BKca) channels. Iberiotoxin (30 nmol/L) markedly affected the maximal effect induced by ANP and 8‐brom cGMP and augmented EC70 values for ANP and EC50values for 8‐brom cGMP approximately 27‐ and 17‐fold, respectively. The inhibitory effects of IbTX on relaxation induced by these agents were diminished in the presence of 1 μmol/L nifedipine, an antagonist of voltage‐operated Ca2+channels (VOCC).

3. The inhibitory action of ANP and 8‐brom cGMP on spontaneous tone was not affected by the presence of 10 μmol/L glibenclamide, an inhibitor of ATP‐sensitive K+ channels, and 100 nmol/L apamin, an inhibitor of small‐conductance Ca2+‐activated K+ channels. When these agents were applied to tissues precontracted by high (40mmol/L) K+, the relaxant effects of these agents markedly diminished.

4. The extracellular Ca2+‐dependent contraction was inhibited in the presence of 0.3 μmoI/L ANP or 0.1 mmol/L 8‐brom cGMP. Concentration—response curves to extracellular Ca2+ (0.03—2.4 mmol/L) were markedly diminished by exposure to these agents. The maximal effect induced by extracellular Ca2+ was affected by these agents.

5. Atrial natriuretic peptide caused an inhibition of spontaneous tone accompanied by a reduction in the intracellular Ca2+ concentration. In the presence of IbTX, the elimination of both muscle tone and cytosolic Ca2+ by ANP was suppressed.

6. We conclude that ANP and 8‐brom cGMP activate BKca channels and that the inhibition of Ca2+ influx through VOCC, mediated by BKca channel activation, may be involved in cGMP‐dependent bronchodilation.
SPECIAL ARTICLE COMPARING METHODS OF MEASUREMENT
Authors: Ludbrook John
Published: June 2007

1. The purpose of comparing two methods of measurement of a continuous biological variable is to uncover systematic differences not to point to similarities.

2. There are two potential sources of systematic disagreement between methods of measurement: fixed and proportional bias.

3. Fixed bias means that one method gives values that are higher (or lower) than those from the other by a constant amount. Proportional bias means that one method gives values that are higher (or lower) than those from the other by an amount that is proportional to the level of the measured variable.

4. It must be assumed that measurements made by either method are attended by random error: in making measurements and from biological variation.

5. Investigators often use the Pearson product—moment correlation coefficient (r) to compare methods of measurement. This cannot detect systematic biases, only random error.

6. Investigators sometimes use least squares (Model I) regression analysis to calibrate one method of measurement against another. In this technique, the sum of the squares of the vertical deviations of y values from the line is minimized. This approach is invalid, because both y and x values are attended by random error.

7. Model II regression analysis caters for cases in which random error is attached to both dependent and independent variables. Comparing methods of measurement is just such a case.

8. Least products regression is the reviewer's preferred technique for analysing the Model II case. In this, the sum of the products of the vertical and horizontal deviations of the x,y values from the line is minimized.

9. Least products regression analysis is suitable for calibrating one method against another. It is also a sensitive technique for detecting and distinguishing fixed and proportional bias between methods.

10. An alternative approach is to examine the differences between methods in order to detect bias. This has been recommended to clinical scientists and has been adopted by many.

11. It is the reviewer's opinion that the least products regression technique is to be preferred to that of examining differences, because the former distinguishes between fixed and proportional bias, whereas the latter does not.
SHORT COMMUNICATION EFFECTS OF α2‐ADRENOCEPTOR ANTAGONISTS AND IMIDAZOLINE2‐RECEPTOR LIGANDS ON NEURONAL DAMAGE IN GLOBAL ISCHAEMIA IN THE RAT
Authors: Craven John A. , Conway Elizabeth L.
Published: June 2007

1. In the present study the neuroprotective effects of 3 mg/kg idazoxan, an α2‐adrenoceptor antagonist and imidazolinea‐receptor (I2‐receptor) ligand, 3 mg/kg methoxyidazoxan, a specific α2‐adrenoceptor antagonist, and 0.6 and 3 mg/kg BU224, a selective I2‐receptor ligand, were evaluated following 10 min of global ischaemia in rats.

2. Neuronal cell counts in the CA1 region of the hippocampus 8 days postischaemia indicated 46–96% cell loss compared with control (P<0.001) and a 320% increase in [3H]‐PK11195 binding (P<0.001) used as a marker of gliosis. No significant neuroprotective effect could be detected on these markers of neuronal damage in the active treatment groups. In a subset of idazoxan‐treated rats, neuronal loss and gliosis was minimal.

3. Mean body temperature over 3 h postischaemia was lower in idazoxan‐treated rats than in the other treatment groups (P< 0.001) and there was a correlation between mean body temperature and cell counts (P<0.01) and mean body temperature and gliosis in this group (P—0.057).

4. These results indicate that at the doses used neither BU224 nor methoxyidazoxan are neuroprotective in this ischaemia model and they raise the possibility that any neuroprotective effect of idazoxan may be related to hypothermic effects of the drug.
MEDIATORS ON HUMAN AIRWAY SMOOTH MUSCLE
Authors: Armour Carol , Johnson Peter , Anticevich Sinthia , Ammit Alaina , McKay Karen , Hughes Margaret , Black Judith
Published: June 2007

1. Bronchial hyperresponsiveness in asthma may be due to several abnormalities, but must include alterations in the airway smooth muscle responsiveness and/or volume.

2. Increased responsiveness of airway smooth muscle in vitro can be induced by certain inflammatory cell products and by induction of sensitization (atopy).

3. Increased airway smooth muscle growth can also be induced by inflammatory cell products and atopic serum.

4. Mast cell numbers are increased in the airways of asthmatics and, in our studies, in airway smooth muscle that is sensitized and hyperresponsive.

5. We propose that there is a relationship between mast cells and airway smooth muscle cells which, once an allergic process has been initiated, results in the development of critical features in the lungs in asthma.
INHIBITION OF ENDOTHELIAL CELL ADHESION MOLECULE EXPRESSION BY HIGH DENSITY LIPOPROTEINS
Authors: Barter PJ
Published: June 2007

1. A low level of high density lipoprotein (HDL) cholesterol is highly predictive of premature coronary heart disease (CHD). It is unclear from human studies whether this relationship reflects an ability of HDL to protect against coronary disease or whether a low HDL in coronary patients is simply an epi‐phenomenon.

2. Recent studies of transgenic mice provide strong evidence that HDL are directly anti‐atherogenic, although the mechanism of the protection is unknown. It is uncertain whether it relates to the involvement of HDL in plasma cholesterol transport or to a range of non‐lipid transport functions of HDL.

3. We have recently reported HDL have the ability to inhibit the cytokine‐induced expression of adhesion molecules by endothelial cells, a process well recognized as an early event in the development of atherosclerosis.
ROLE OF NITRIC OXIDE IN THE CONTROL OF GLOMERULAR MICROCIRCULATINO
Authors: Ito Sadayoshi , Carretero Oscar A. , Abe Keishi
Published: June 2007

1. Nitric oxide (NO) plays an important role in the control of glomerular haemodynamics and is synthesized from the amino acid L‐arginine by a family of enzymes, NO synthase (NOS).

2. Nitric oxide synthase is present in the endothelium and also in the macula densa, a plaque of specialized tubular epithelial cells. Endothelial NOS is known to be stimulated by shear stress and hormones, while the factor that regulates the activity of macula densa NOS remains undefined.

3. Studies with the in vitro microperfusion of glomerular arterioles have shown that the constriction of afferent arterioles (Af‐Art) induced by myogenic responses and angiotensin II (AngII) is stronger in the absence rather than in the presence of luminal flow. Furthermore, endothelial disruption or NOS inhibition abolishes such differences, suggesting that flow through the lumen stimulates the endothelium to synthesize and release NO, which in turn attenuates both the myogenic response and the action of AngII in the Af‐Art.

4. In contrast, NOS inhibitors have no effect on efferent arteriolar (Ef‐Art) constriction induced by AngII.

5. In preparations in which Af‐Art and the macula densa are simultaneously microperfused, selective inhibition of macula densa NOS has been shown to augment Af‐Art constriction when the NaCl concentration at the macula densa is high, suggesting that the macula densa produces NO, which in turn modulates tubuloglomerular feedback.

6. Thus, the differential actions of NO in the Af‐Art, Ef‐Art and the macula densa may be important in the control of glomerular haemodynamics under various physiological and pathological conditions.
INTRARENAL LOCALIZATION OF NITRIC OXIDE SYNTHASE ISOFORMS AND SOLUBLE GUANYLYL CYCLASE
Authors: Star Robert A.
Published: June 2007

1. Nitric oxide (NO) plays an important role in the regulation of renal function. To date, five isoforms of NO synthase (NOS) and four subunits of soluble guanylyl cyclase have been cloned. The kidney contains four isoforms of NOS and all sub‐units of soluble guanylyl cyclase.

2. This review focuses on the intrarenal location of the isoforms of NOS and the subunits of soluble guanylyl cyclase.
COMPETITION BY SECOND MESSENGER SYSTEMS FOR RECEPTOR INTERACTION AND ACTIVATION: IMPLICATIONS FOR TISSUE‐SPECIFIC RESPONSES AND DISEASE THERAPY
Authors: Crouch Michael F. , Frew Ian J. , Simson Ljubov , Davy Deborah A.
Published: June 2007

1. At any one instant, most receptors are now recognized to be able to stimulate multiple signal transduction pathways in a cell when activated by an appropriate hormone. These different signalling pathways appear to allow for distinct cellular responses, such as cell proliferation, differentiation, and shape change.

2. In addition, many different types of cell will possess the same type of receptor. Therefore, for a hormone to be able to transmit differential signals to the various cell types able to respond to it, cells must discriminate the stimulus at some point. Such discrimination would seem to be an absolute requirement to allow a tissue‐specific response to an identical initial stimulus. In theory, this specificity could occur at many points in the receptor signal transduction cascade, including cytosolic receptor coupling systems and tissue/cell‐specific responsive genes.

3. The present paper summarizes our work and that of others which has determined some of the coupling systems of G‐protein‐coupled receptors and tyrosine kinase receptors and how these systems may be interacting.

4. In addition to these theoretical considerations, a potential therapeutic strategy underlies the ability of receptors to couple to more than one signal transduction system. If a response to a hormone were, for example, either cell proliferation or cell morphological change or differentiation and separate receptor‐coupled signalling systems were responsible for these effects, pharmacological intervention may allow the transfer from one signalling system to another. If such a change allowed a permanent change to the differentiated phenotype, this could potentially form the basis of a signal‐based cancer therapy.
ROLE OF THE BRAIN RENIN‐ANGIOTENSIN SYSTEM IN THE MAINTENANCE OF BLOOD PRESSURE IN CONSCIOUS SPONTANEOUSLY HYPERTENSIVE AND SINOAORTIC BARORECEPTOR‐DENERVATED RATS
Authors: Paul Jeremy RA , Bunting Michael W. , Widdop Robert E.
Published: June 2007

1. Evidence suggesting an involvement of the brain renin‐angiotensin system (RAS) in the development/maintenance of hypertension in spontaneously hypertensive rats (SHR) relies, in part, on early experimental data reporting centrally mediated antihypertensive effects of saralasin. However, recent data using non‐peptide ATi receptor antagonists does not always support this theory because these compounds usually do not lower blood pressure when given centrally.

2. In the present study we have re‐assessed the central effects of saralasin in conscious SHR as well as in sinoaortic baroreceptor‐denervated (SAD) rats. Both of these models exhibit heightened sensitivity to the central pressor effects of angiotensin II (AngII) and, thus, any potential antihypertensive activity would provide functional evidence of activated brain RAS mechanisms in these models.

3. In SHR, saralasin failed to lower mean arterial pressure (MAP) when given intracerebroventricularly (i.e.v.) as bolus or infusion doses that blocked the centrally mediated pressor effect of AngII.

4. In SAD rats, there was a marked impairment of the baroreceptor‐heart rate reflex function and enhanced centrally mediated pressor responses to AngII. However, i.e.v. saralasin infusions again did not alter MAP.

5. Collectively, these results suggest that the central RAS is not involved in the maintenance of MAP in SHR and SAD rats, both of which are models exhibiting a functional hyper‐responsiveness to AngII.
ASTROCYTE‐CONDITIONED MEDIUM INDUCES BLOOD‐BRAIN BARRIER PROPERTIES IN ENDOTHELIAL CELLS
Authors: Yamagata Kazuo , Tagami Motoki , Nara Yasuo , Mitani Mitsuaki , Kubota Akiyoshi , Fujino Hideaki , Numano Fujio , Kato§ Taiji , Yamori# Yukio
Published: June 2007

1. We evaluated the induction of endothelial barrier functions by the type 1 astrocyte‐derived supernatant in culture using horseradish peroxidase (HRP) as a parameter.

2. A gel filtration fraction (molecular weight 16‐20 kDa) of type 1 astrocyte‐derived supernatant reduced plasmalemmal vesicles and induced tight junctions in endothelial cells.

3. In addition, this fraction promoted the uptake of [3H]‐glucosamine by endothelial cells. This cell activity disappeared after heating at 95°C for 10 min and was sensitive to trypsin.

4. These results suggest that a type 1 astrocyte‐derived protein factor(s) promotes proteoglycan synthesis with a resultant increase in charge selectivity in endothelial cells and plays an important role in the induction of blood‐brain barrier functions.
SUPRAMEDULLARY MODULATION OF SYMPATHETIC VASOMOTOR FUNCTION
Authors: Verberne Anthony JM , Lam William , Owens Neil C. , Sartor Daniela
Published: June 2007

1. Supramedullary structures including the ventral medial prefrontal cortex (MPFC) and the midbrain cuneiform nucleus (CnF) project directly and indirectly to premotor sympatho‐excitatory neurons of the rostral ventrolateral medulla (RVLM) that are critically involved in the generation of sympathetic vasomotor tone.

2. Electrophysiological studies have demonstrated that activation of depressor sites within the MPFC is associated with splanchnic sympathetic vasomotor inhibition and inhibition of the activity of RVLM sympathoexcitatory neurons.

3. Antidromic mapping and anatomical studies support the notion that a relay in the nucleus tractus solitarius is involved in the cardiovascular response to MPFC stimulation.

4. The midbrain CnF, which lies adjacent to the midbrain periaqueductal grey, is a sympathoexcitatory region of the midbrain reticular formation. Sympathoexcitatory responses evoked from the CnF are associated with short‐latency excitation of RVLM neurons.

5. Cuneiform nucleus stimulation induces the expression of mRNA for the immediate early genes c‐fos and NGFI‐A in midbrain, pontine and hypothalamic structures.

6. The MPFC and CnF are supramedullary structures with opposing modulatory influences on sympathetic vasomotor drive, whose roles in cardiovascular control mechanisms warrant further investigation.
DETECTION OF WEAKLY EXPRESSED GENES IN THE ROSTRAL VENTROLATERAL MEDULLA OF THE RAT USING MICROPUNCH AND REVERSE TRANSCRIPTION‐POLYMERASE CHAIN REACTION TECHNIQUES
Authors: Comer AM , Yip S. , Lipski J.
Published: June 2007

1. The present study describes the use of reverse transcription‐polymerase chain reaction (RT‐PCR) to detect weakly expressed neurotransmitter receptor mRNA in tissue micropunched from the rostral ventrolateral medulla (RVLM) and other discrete areas of the medulla oblongata of the rat.

2. Micropunches were made from 240 fJim transverse medullary sections. Punched regions included the RVLM, hypoglossal nucleus (XIIn), ventrolateral subnucleus of the nucleus tractus solitarius (NTS) and spinal trigeminal nucleus (STN). RNA was extracted and reverse transcribed into cDNA, which was probed for the presence of seven genes: glyceralde‐hyde phosphate dehydrogenase (GAPDH), neuron‐specific enolase (NSE), tyrosine hydroxylase (TH), phenylethanolamine N‐methyltransferase (PNMT), glucocorticoid receptor (GCR), mineralocorticoid receptor (MCR) and the adenosine 5‐triphosphate (ATP) receptor subunit P2X2‐1. Each transcript was detected using a semi‐nested PCR protocol, which used three primers.

3. Tyrosine hydroxylase was detected in the RVLM and NTS and PNMT was also detected in the RVLM, which agrees with the distribution of catecholamine neurons in the medulla. Expression of GCR mRNA was detected in the RVLM and the XIIn but not in the NTS (it was not probed for in the STN punches). The P2X2‐1 receptor message was detected in all areas. Expression of MCR mRNA was detected in the RVLM only.

4. This method offers a simple way to detect the presence of low‐abundance receptor mRNA in discrete brain regions.
PRESSOR RESPONSES TO BRAIN DOPAMINERGIC STIMULATION
Authors: van den Buuse Maarten
Published: June 2007

1. Systemic administration of a dopamine D2 receptor agonist, such as quinpirole, causes a centrally mediated rise in blood pressure (BP) with a maximum at 1‐2 min after injection. At 30 min after injection, when BP has returned to baseline, further treatment with these drugs has little effect on BP. Moreover, the antihypertensive effects of sympathoinhibitory drugs, such as clonidine and rilmenidine, is markedly inhibited. Increased circulating levels of vasopressin contribute to the initial rise in BP, but return to baseline thereafter. Differential changes in sympathetic vasomotor tone may be involved in the apparent de‐sensitization induced by quinpirole.

2. Stimulation of the region of origin of the mesolimbic dopamine (DA) system in the brain, the ventral tegmental area, causes a long‐lasting increase in BP. In this model, circulating levels of vasopressin are moderately increased through a non‐dopaminergic mechanism. Dopaminergic stimulation causes a functional potentiation of the effect of vasopressin, resulting in an increase in BP.

3. Spontaneously hypertensive rats (SHR) display several changes in central dopaminergic responses. Dopamine levels in the brain are normal, while resting DA activity appears reduced. Partial depletion of forebrain DA levels, particularly in the nigrostriatal system, causes an inhibition of the development of hypertension and normalizes deficient functional responses to dopaminergic drugs in the SHR.

4. These results show that brain DA is involved in several aspects of cardiovascular regulation and may be involved in the development of hypertension. The widespread involvement of brain DA systems in behavioural, hormonal and cardiovascular mechanisms suggests that these systems play an important role in the integration of stress and environmental stimuli with homeostatic mechanisms in the body.
INHIBITION OF K+ TRANSPORT IN HUMAN SICKLE CELL ERYTHROCYTES BY OKADAIC ACID AND SODIUM FLUORIDE
Authors: Gharaibeh Nayef Saleh Al‐Rohil , Al‐Sheyyab† Mahmoud
Published: June 2007

1. The effect of okadaic acid and sodium fluoride on swelling‐and N‐ethylmaleimide (NEM)‐stimulated KC1 cotransport was examined in blood cells from homozygote sickle cell anaemia patients.

2. Blood was drawn into heparin or EDTA by vein puncture from sickle cell patients previously diagnosed in the haematology clinics of Princess Badee'a Teaching Hospital. A standard method for measuring flux by using radioactive rubidium was used.

3. Okadaic acid strongly inhibited swelling‐stimulated KC1 cotransport if added before swelling. Okadaic acid and sodium fluoride added before NEM inhibited the activation of transport by NEM. Okadaic acid added after NEM did not inhibit transport.

4. The inhibition of the effects of NEM by okadaic acid and sodium fluoride indicates that activation of the flux by NEM requires the action o. phosphatase.
RELATIONSHIP BETWEEN GASTRIC MUCUS SYNTHESIS, SECRETION AND SURFACE GEL EROSION MEASURED IN AMPHIBIAN STOMACH IN VITRO
Authors: Keogh JP , Allen A , Garner A
Published: June 2007

1. The layer of adherent mucus that protects the surface of the stomach reflects a dynamic balance between biosynthesis of glycoprotein, secretion of preformed mucus and erosion of the adherent gel layer. The present study is the first in which all these processes have been measured concomitantly and was undertaken to define interrelationships between the three parameters.

2. A chambered sac preparation of amphibian gastric mucosa is described. Biosynthesis was determined by specific incorporation of radiolabeled sugars into purified glycoprotein. Mucus secretion was determined by measuring the thickness of the adherent gel and erosion of the surface layer was assessed from the appearance of soluble mucin in the luminal solution.

3. 16,16‐Dimethyl‐prostaglandin (PG. E2 stimulated glucosamine incorporation by 10‐fold, but did not alter the rate of incorporation of galactose. There was a rapid two‐fold increase in the thickness of the adherent mucus layer but no change in the rate of erosion. Dibutyryl‐cAMP also stimulated mucus release but, unlike PG, increased glycoprotein labelling by galactose.

4. Both distention or the application of a cholinergic agonist increased adherent mucus thickness. Stimulation of mucus release in response to carbachol was accompanied by a decrease in glycoprotein labelling by galactose. In contrast, the adrenergic agent noradrenaline decreased secretion but did not influence labelling.

5. These results indicate that biosynthesis and secretion of gastric mucus are subject to differential regulation. Moreover, the profile of incorporation of sugars in response to secreta‐gogues also differs, indicating the need for caution when interpreting effects on glycoprotein biosynthesis.
EFFECTS OF DRUGS ON UTEROPLACENTAL BLOOD FLOW AND THE HEALTH OF THE FOETUS
Authors: Lumbers Eugenie R.
Published: June 2007

1. The placental vascular bed is normally fully dilated. Therefore, changes in vascular resistance elsewhere in the body can affect uteroplacental blood flow (UBF). For example, antihypertensive drugs, such as diazoxide, hydralazine and the angiotensin‐converting enzyme inhibitor captopril, cause falls in arterial pressure and, hence, in UBF.

2. Angiotensin II (AngII), prostacyclin and nitric oxide (NO) all influence uteroplacental vascular tone. Angiotensin II in a pharmacological dose (62.5 μg/h) had a biphasic effect on UBF in the sheep. Initially, there was a rise in UBF as pressure rose; however, by 16–24 h, UBF had fallen. The AngII‐induced fall in UBF caused severe foetal hypoxia and hypercapnia.

3. Prostacyclin may protect the uteroplacental circulation from vasoconstrictors such as AngII, as the vasoconstrictor effect of AngII in the uteroplacental circulation is enhanced followin. indomethacin.

4. Oestrogen‐induced uterine artery vasodilation is nitrergic dependent. As well, nitrergic nerves alter the responsiveness of pregnant uterine arteries to noradrenaline.

5. Thus, both systemic and local factors are important in the control of UBF and in promoting foetal health an. growth.
CURRENT ISSUES IN EXERCISE METABOLISM: THE CROSSOVER CONCEPT
Authors: Tipton Charles M.
Published: June 2007

1. Since ancient times, athletes have consumed proteins because of the belief they were the necessary substrate for optimal performance. Even though this concept was proven to be incorrect before the beginning of the 19th century, the practice continued until several decades ago.

2. By 1939, careful metabolic investigations on the changes in the respiratory exchange ratio had demonstrated that the metabolic transformations of lipids and carbohydrates were the primary sources of energy for muscula. exercise.

3. Metabolic investigations on the profile of energy transformations during exercise have indicated that aspects related to exercise intensity, state of training, the availability of circulating free fatty acids, the activity of the sympathetic nervous system, resting levels of muscle and liver glycogen and muscle triglyceride concentrations have to be considered to explain a specifi. response.

4. In 1994, Brooks and Mercier introduced the concept of ‘crossover’ in their review manuscript to explain the shift in substrate utilization from lipids to carbohydrates by trained subjects when the power output was increased. In addition, the concept was advanced to reconcile divergent results by different investigators.

5. In 1995, Coggan and associates investigated the glucose kinetics of non‐trained and trained subjects performing power outputs equal to 80. Vo2max and concluded that the crossover concept was unable to explain their metabolic results from trained subjects.

6. Because of the importance of the topic to exercise physiologists and the uncertainties the controversy has created for teachers and researchers, the American Physiological Society Section on Environmental and Exercise Physiology scheduled a Point‐Counterpoint forum at the 1997 Experimental Biology Meeting. The subsequent manuscripts of Brooks and Coggan are a result of that forum.
IMPORTANCE OF THE ‘CROSSOVER’ CONCEPT IN EXERCISE METABOLISM
Authors: Brooks George A.
Published: June 2007

1. The ‘crossover’ concept is a model of substrate supply during exercise which makes the following predictions.

2. Lipid is the major fuel (approximatel. 60%) for non‐contracting skeletal muscle and the body at rest.

3. Energy flux, as determined by exercise intensity, is the major factor in determining the balance of substrate utilization during exercise. Thus, moderate and greater exercise intensities increase contraction‐induced muscle glycogenosis and glycolysis, increase recruitment of fast‐twitch muscle fibres, increase sympathetic nervous system activity and down‐regulate mitochondrial fatty acid uptake.

4. Glycogen and glucose utilization scales exponentially to relative exercise power output with a greater gain in glycogen than in glucose use at high power. The relationship between free fatty acid flux and power output is an inverted hyperbola. Consequently, at high power outputs, the role of lipid oxidation is diminished.

5. Factors such as endurance training, energy supply, as influenced by dietary manipulation, and prior exercise play secondary roles in determining the balance of substrate utilization durin. exercise.

6. Comparisons of the metabolic responses in subjects engaged in activities requiring vastly different metabolic rates or comparisons of subjects of different gender, age or training status require normalization of dat. to total energy flux.
THE GLUCOSE CROSSOVER CONCEPT IS NOT AN IMPORTANT NEW CONCEPT IN EXERCISE METABOLISM
Authors: Coggan Andrew R.
Published: June 2007

1. The basic premise of the ‘crossover’ concept (i.e. that the balance of carbohydrate (CHO) and fat utilization during exercise depends on the interaction between exercise intensity and the individual's endurance training status) has been accepted since at least the 1930s.

2. The crossover concept differs from earlier perspectives mostly in its greater emphasis on the absolute exercise intensity as an important determinant of substrate selection during exercise. Because of this emphasis, it is argued that while trained subjects may utilize less CHO than their untrained counterparts during low‐ or moderate‐intensity exercise, this is not true during high‐intensity exercise, because during such exercise even trained persons must ‘crossover’ to CHO dependency. In fact, the crossover concept predicts that utilization of at least one CHO source (i.e. plasma‐borne glucose) should be greater in trained subjects during intense exercise. This increase in glucose utilization is hypothesized to be supported by an enhanced rate of gluconeogenesis.

3. In direct contradiction of the crossover concept, the literature consistently shows that, compared with untrained individuals, trained subjects rely less on CHO for fuel, even during high‐intensity exercise. In particular, it has been shown that the rate of glucose utilization is lower in trained subjects under these conditions. Recent data from Dr Brooks’ own laboratory support this conclusion and also show that this reduction in glucose use is associated with a decrease in the rate of gluconeogenesis. These recent observations confirm prior studies of moderate‐intensity exercise.

4. Based on the above, it is clear that the crossover concept cannot be considered an important new concept in exercise metabolism. Instead, the crossover concept actually serves to hinder understanding in this area.
MITOCHONDRIAL FUNCTION IN RAT RENAL CORTEX IN RESPONSE TO PROTEINURIA AND IRON
Authors: Harris David CH , Tay Yuet‐Ching
Published: June 2007

1. Proximal tubular cell dysfunction in chronic glomerular disease (CGD) has been ascribed, in part, to reabsorption of transferrin‐iron from tubular fluid and subsequent cytosolic peroxidative injury. To investigate a possible role for altered mitochondrial function in tubular cell injury in CGD, renal cortical mitochondrial respiratory function was examined in rats with adriamycin nephrosis.

2. State 4 (resting) respiration was increased in adriamycin nephrosis in comparison with control (51±2 vs 43±2ng atoms oxygen (0)/min per mg protein, respectively; P < 0.02).

3. Mitochondrial iron concentration was increased in nephrotic rats compared with contro. (9.52±0.70 vs 5.97±0.26 nmol Fe/mg protein, respectively; P < 0.001) and rates of state 3, state 4 and uncoupled respiration and the severity of proteinuria correlated with mitochondrial iron concentration.

4. To further define the relationship between mitochondrial iron accumulation and altered respiratory function, rats were loaded wit. iron.

5. In comparison with control, acute iron loading of normal rats impaired creatinine clearanc. (1.48±0.02 vs 0.40±0.29 mL/min), increased kidney weight (1.33±0.07 vs 1.74±0.14g) and impaired mitochondrial enzyme activity (e.g. cytochrome oxidase 185.0±46.6 vs 362.0±32.8Alog [cytochrome C]/min per mg protein; P < 0.05), but had no significant effect on rates of mitochondrial respiration or on mitochondrial fragility.

6. Mitochondrial iron concentration was not increased by iron loading, despite a similar increment in cytoplasmic iron to that seen in rats with adriamyci. nephrosis.

7. In summary, resting mitochondrial respiration is increased in nephrotic rats in proportion to mitochondrial iron accumulation. Changes in mitochondrial oxygen consumption do not appear to be a primary event in the tubular cell injury of iron loading.
POTENTIATION OF DIPSOGENIC ACTIONS BY CENTRALLY ADMINISTERED TYPE‐C NATRIURETIC PEPTIDE IN SPONTANEOUSLY HYPERTENSIVE BUT NOT WISTAR‐KYOTO RATS
Authors: Goto Eiichi , Shibata Kazuhiko , Furukawa Tatsuo
Published: June 2007

1. The effects of type‐C natriuretic polypeptides (CNP) on the central dipsogenic and pressor responses to angiotensin II (AngII) were studied by the administration of agents into the lateral cerebral ventricle under conscious and unrestrained conditions in normotensive Wistar‐Kyoto (WKY) and spontaneously hypertensive rats (SHR).

2. The fluid intake induced by AngII (25 ng) and water deprivation were potentiated after pretreatment with CNP in SHR but not in WKY rats. However, carbachol‐induced water intake was not altered by pretreatment with CNP (2.5 μg) in either WKY rats or SHR.

3. In contrast, CNP did not influence the pressor responses to AngII in either WKY rats o. SHR.
VOLUME‐ACTIVATED TAURINE TRANSPORT IS DIFFERENTIALLY ACTIVATED IN HUMAN CERVICAL CANCER HT‐3 CELLS BUT NOT IN HUMAN PAPILLOMAVIRUS‐IMMORTALIZED Z183A AND NORMAL CERVICAL EPITHELIAL CELLS
Authors: Chou Cheng‐Yang , Shen Meng‐Ru , Chen Tzer‐Ming , Huang Ko‐En
Published: June 2007

1. Previous studies demonstrate that volume‐sensitive chloride currents are distinctly activated in cervical cancer cells, but not in human papillomavirus (HPV)‐immortalized and normal cervical cells. In the present study, the Na+‐independent volume‐activated transport of taurine in three cervical cell types was investigated.

2. Osmotic swelling of cervical cancer HT‐3 cells suspended i. Na+‐free hypotonic medium led to increased membrane uptake of taurine. This taurine uptake was effectively blocked by various C1‐ channel blockers with a similar potency in blocking volume‐sensitive C1‐ channels: l,9‐dideoxyforskolin > 5‐nitro‐2‐(3‐phenyl‐propylamino)‐benzoic acid (NPPB) > 4‐acetamido‐4′‐isothiocyanastilbene‐2,2′‐disulphonic acid (SITS) > 4,4′‐diisothio‐cyanatostilbene‐2,2‐disulphonic acid (DIDS)>furosemide. The taurine influx was also abolished by pertussis toxin. In contrast, Na+‐independent volume‐activated taurine transport was not significantly activated in HPV‐immortalized Z183A cells and in normal cervical cells.

3. Exposure of HT‐3 cells to hypotonic medium also resulted in a marked increase in taurine efflux. The volume‐activated taurine efflux was osmolality dependent and the pattern of pharmacological inhibition by C1‐ channel blockers was indistinguishable from that for taurine uptake.

4. These results suggest that volume‐sensitiv. C1‐ channels in HT‐3 cells can mediate the transport of amino acids. In addition, the pertussis toxin‐sensitive G‐protein is linked with the activation of this transport mechanism.
AUTONOMIC CONTROL OF BRONCHIAL CIRCULATION IN AWAKE SHEEP DURING REST AND BEHAVIOUR
Authors: Mcllveen Stephen , White Saxon , Parsons Gibbe
Published: June 2007

1. We tested the hypothesis that the pattern and the intensity of autonomic mechanisms causing vasoconstriction in the resting bronchial circulation of awake dogs also exists in awake sheep. It was also postulated that sighing behaviour and the associated bron‐chovascular dilatation induced by non‐adrenergic, non‐cholinergic (NANC) mechanisms observed in the dog exist in sheep.

2. Bronchial arterial blood flow to lower airways of both lungs of awake sheep was measured continuously using pulsed Doppler flow probes mounted on the bronchial artery at prio. thoracotomy.

3. Cumulative and factorial analysis of responses to randomized combinations of autonomi. α1‐, α2‐, β1‐ and β2‐adrenoceptors and cholinoceptor autonomic blockade suggests that resting vasoconstrictor activity is less in sheep than in dogs. At normal aortic pressure, the autonomic activity of these receptor groups in the sheep lowers bronchial blood flow and conductance by 30%, whereas in the awake dog, the corresponding autonomic effect is 50%.

4. Tonic autonomic control of bronchial conductance can be partitioned in sheep to show significant and separat. α‐ and β‐adrenoceptor vasoconstrictor activity at a ratio of 1.8:1, an effect normally offset by a weaker vasodilator α‐/β‐adrenoceptor interaction. In contrast to the situation in awake dogs, cholinoceptors do not play a role in awake sheep.

5. Nitric oxide (NO) synthase inhibition in sheep using NG‐nitro‐L‐arginine following blockade of α‐ and β‐adrenoceptors and cholinoceptors causes hypertension, but minor changes, if any, in pulmonary pressures or heart rate. Bronchial flow and conductance, however, fall from a higher resting conductance by approximately 50%, suggesting that, normally, resting bronchial flow conductance is dominated by strong tonic NO vasodilator effects that interact with weaker tonic autonomic vasoconstrictor effects.

6. Superimposed (respiratory) behaviours of sighing, sneezing and coughing, which involve negative swings in intrathoracic pressure and the movement of inspired air, evoke large active bronchovascular dilator effects. These appear to be largely NANC in origin and appear to be dependent, in part, on mechanisms associated with NO release. It is postulated that the C‐fibre axon reflex using substance P, calcitonin gene‐related peptide and neurokinin A may be involved. Vocalization and eructation do not evoke bronchovascular effects.
PROSTANOID ACTION ON THE HUMAN PULMONARY VASCULAR SYSTEM
Authors: Jones Robert L. , Qian Yue‐ming , Wong Henry NC , Chan Ho‐wai , Yim Anthony PC
Published: June 2007

1. Four types of prostanoid receptor are present on pulmonary arterial vessels of man. Thromboxane (TP) receptors mediate constriction and are blocked by antagonists such as BAY u‐3405, GR 32191 and EP169. Prostaglandin (PG) EP3 receptors also mediate constriction, the agonist potency ranking being SC 46275 > sulprostone > misoprostol≥PGE2; this action needs to be borne in mind when PGE analogues are used therapeutically.

2. Prostaglandi. E2 causes relaxation in a few pulmonary artery preparations: an EP2 receptor may be involved. Prostacyclin, acting through IP receptors, consistently produces relaxation and studies are in progress to determine the contribution made by K+‐channel opening. Agonist potencies of stable prostacyclin analogues and non‐prostanoid prostacyclin mimetics, such as BMY 45778 and the novel diphenylindole CU 23, on human pulmonary artery and platelets are well correlated. Interestingly, the non‐prostanoid mimetics show persistent relaxant effects in vitro, which may be related to their high lipophilicities.

3. Prostacyclin and iloprost are being used to treat severe pulmonary hypertension; further study of the pharmacodynamic and pharmacokinetic properties of other IP receptor agonists could produce improve. therapy.
ELECTRICAL REMODELLING OF CHRONIC ATRIAL FIBRILLATION
Authors: Lau Chu‐Pak , Tse Hung‐Fat
Published: June 2007

1. It is now recognized that atrial fibrillation (AF) is not a benign condition, as it is associated with a 40% increase in mortality and a doubling of the risk of stroke.

2. The development of AF leads to mechanical, electrophysiological and cellular changes in the atria that tend to sustain AF. This process is known as atrial remodelling.

3. The three electrophysiological elements in the atria that initiate and sustain AF are: (i) shortening of the refractory period and an increase in dispersion; (ii) slowing of conduction velocity; and (iii) the presence of triggerin. foci.

4. As AF is a heterogeneous disorder, therapeutic strategies include the use of devices (pacemakers and atrial defibrillators), radiofrequency ablation (focal ablation or the creation of linear lines) and drug therapy that may reverse a remodelle. atrium.
EFFECT OF CATIONIC DRUGS ON THE RENAL SECRETION OF RANITIDINE IN THE RAT ISOLATED PERFUSED KIDNEY
Authors: Nation Roger L. , Evans Allan M. , Cabot Juanita L. , Shanahan Kathryn M. , Hsyu Poe‐Hirr
Published: June 2007

1. The rat isolated perfused kidney (IPK) was used to determine whether the renal tubular secretion of ranitidine is influenced by clinically relevant concentrations of other organic cationic drugs (amantadine, pseudoephedrine, triamterene and trimethoprim) that also undergo tubular secretion.

2. Ranitidine and [3H]‐ranitidine were administered to the recirculating perfusion medium as a loading dose followed by a constant infusion to maintain clinically relevant perfusate ranitidine concentrations in the range 400–700 ng/mL. The renal clearance of ranitidine (CLR) was calculated, as was glomerular filtration rate (GFR), from the renal clearance of [14C]‐inulin.

3. A total of 20 perfusions were performed and, in each case, ranitidine was administered for 80 min. In four control IPK, no drug other than ranitidine was administered. In the remaining IPK, amantadine, pseudoephedrine, triamterene or trimethoprim (n= 4 in each case) were administered to achieve low, medium and high concentrations during the 20–40, 40–60 and 60–80 min periods, respectively.

4. The mean (± SD) unbound fraction of ranitidine in the perfusion medium was 0.889±0.046 and was not altered (P>0.05) by the presence of the other drugs.

5. The CLR/GFR ratio for ranitidine in all kidneys was substantially greater than unity and had a mean value of 10.65 or greater in control kidneys, indicating extensive net tubular secretion.

6. The CLR/GFR was not affected (P>0.05) by amantadine, pseudoephedrine or triamterene at any concentration or by trimethoprim at the low concentration. However, medium (2000 ng/mL) and high (5000 ng/mL) concentrations of trimethoprim caused significant reductions in CLR/GFR of 20 and 28%, respectively (P<0.05).

7. The results indicate that at clinically relevant concentrations the renal tubular secretion of ranitidine is inhibited by trimethoprim, but not by amantadine, pseudoephedrine or triamterene.
EFFECT OF cGMP INHIBITORS ON THE ACTIONS OF NITRODILATORS IN RAT AORTA
Authors: van der Zypp Andrea , Majewski Henryk
Published: June 2007

1. The involvement of cGMP in vasodilatation produced by a range of nitrodilators was investigated using two different protein kinase G inhibitors, r(p) 8‐bromoguanosine‐3′5′‐cyclic monophosphothioate (RBrcGMPS) and KT5823.

2. The nitric oxide donors sodium nitroprusside (SNP), glyceryltrinitrate (GTN) and s‐nitroso‐acetylpenicillamine (SNAP), the endothelium‐dependent vasodilator acetylcholine (ACh) as well as the cGMP analogues 8‐(4‐chlorophenylthio)‐cGMP (CPTcGMP) and β‐phenyl‐1‐N2‐etheno‐8‐bromo‐cGMP (PETcGMP) all relaxed rat aortic rings preconstricted with phenylephrine (0.1 μmol/L).

3. The protein kinase G inhibitor KT 5823 (10 μmol/L) produced a very small inhibition of the vasodilatation produced by GTN, but had no effect against vasodilatation produced by SNP, CPTcGMP or PETcGMP, which suggests that KT 5823 is not a useful tool in this system.

4. In contrast, RBrcGMPS (0.5 mmol/L) produced a rightward shift of the concentration‐response curves to SNP, CPTcGMP and PETcGMP. RBrcGMPS (0.5 mmol/L) also completely abolished vasodilatation to ACh and GTN but, surprisingly, had no effect on vasodilatation produced by SNAP.

5. The guanylate cyclase inhibitor 1H‐[1,2,4] oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ; 1 and 10 μmol/L) completely inhibited the relaxation produced by GTN, whereas SNAP still had an appreciable relaxant effect after ODQ (1 μmol/L).

6. The differential effect of RBrcGMPS and ODQ on the nitrodilators suggests that there are differences in the mechanism of dilatation between the nitrodilators.
CARDIOVASCULAR CONSEQUENCES OF OBESITY: ROLE OF LEPTIN
Authors: Haynes William G. , Morgan Donald A. , Walsh Susan A. , Sivitz William I. , Mark Allyn L.
Published: June 2007

1. Several mechanisms have been implicated in the association between obesity and hypertension, including salt‐sensitivity, insulin resistance and sympathetic activation. Obese animals and humans exhibit exaggerated blood pressure responses to increases in salt intake.

2. Although insulin resistance is common in obesity, it is clear that abnormal insulin action is not the sole or sufficient cause of hypertension in obesity. Obesity is associated with increased activity of the sympathetic nervous system. Sympathetic blockade has been reported to attenuate sodium retention and hypertension in experimental models of obesity.

3. The mediators responsible for salt sensitivity, insulin resistance and sympathetic activation in obesity remain unclear.

4. The novel protein hormone leptin is produced almost exclusively by adipose tissue and acts in the central nervous system through a specific receptor and multiple neuropeptide pathways to decrease appetite and increase energy expenditure.

5. Increasing evidence suggests that leptin may have wider actions influencing autonomic, cardiovascular, renal and endocrine function. We have shown that leptin increases sympathetic nerve activity to kidney, hindlimb and adrenal gland, in addition to brown adipose tissue.

6. Despite this sympathoexcitatory action, acute systemic administration of leptin does not acutely increase arterial pressure or heart rate in anaesthetized animals. This may reflect opposing antihypertensive actions of leptin. For example, leptin increases renal sodium and water excretion, apparently through a direct tubular action. In addition, leptin increases systemic insulin sensitivity, even in the absence of weight loss.

7. In conclusion, leptin may act as a mediator linking body adiposity with changes in insulin action, sympathetic neural outflow and renal sodium excretion. Alterations in leptin generation or action may, in part, underlie the sympathetic, endocrine and renal consequences of obesity.
ROLE OF HEPATIC FATTY ACID:COENZYME A LIGASES IN THE METABOLISM OF XENOBIOTIC CARBOXYLIC ACIDS
Authors: Knights Kathleen M.
Published: June 2007

1. Formation of acyl‐coenzymes (Co)A occurs as an obligatory step in the metabolism of a variety of endogenous substrates, including fatty acids. The reaction is catalysed by ATP‐dependent acid:CoA ligases (EC 6.2.1.1‐2.1.3; AMP forming), classified on the basis of their ability to conjugate saturated fatty acids of differing chain lengths, short (C2‐C4), medium (C4‐C12) and long (C10‐C22). The enzymes are located in various cell compartments (cytosol, smooth endoplasmic reticulum, mitochondria and peroxisomes) and exhibit wide tissue distribution, with highest activity associated with liver and adipose tissue.

2. Formation of acyl‐CoA is not unique to endogenous substrates, but also occurs as an obligatory step in the metabolism of some xenobiotic carboxylic acids. The mitochondrial medium‐chain CoA ligase is principally associated with metabolism via amino acid conjugation and activates substrates such as benzoic and salicylic acids. Although amino acid conjugation was previously considered an a priori route of metabolism for xenobiotic‐CoA, it is now recognized that these highly reactive and potentially toxic intermediates function as alternative substrates in pathways of intermediary metabolism, particularly those associated with lipid biosyntheses.

3. In addition to a role in fatty acid metabolism, the hepatic microsomal and peroxisomal long‐chain‐CoA‐ligases have been implicated in the formation of the acyl‐CoA thioesters of a variety of hypolipidaemic and peroxisome proliferating agents (e.g. cloflbric acid) and of the r(‐)‐enantiomers of the commonly used 2‐arylpropionic acid non‐steroidal anti‐inflammatory drugs (e.g. ibuprofen). In vitro kinetic studies using rat hepatic microsomes and peroxisomes have alluded to the possibility of xenobiotic‐CoA ligase multiplicity. Although cDNA encoding a long‐chain ligase have been isolated from rat and human liver, there is currently no molecular evidence of multiple isoforms. The gene has been localized to chromosome 4 and homology searches have revealed a significant similarity with enzymes of the luciferase family.

4. Increasing recognition that formation of a CoA conjugate increases chemical reactivity of xenobiotic carboxylic acids has led to an awareness that the relative activity, substrate specificity and intracellular location of the xenobiotic‐CoA ligases may explain differences in toxicity.

5. Continued characterization of the human xenobiotic‐CoA ligases in terms of substrate/inhibitor profiles and regulation, will allow a greater understanding of the role of these enzymes in the metabolism of carboxylic acids.