bluuebunny/crossref_metadata_2025 huggingface dataset:
Hyperthyroidism stimulates mitochondrial proton leak and ATP turnover in rat hepatocytes but does not change the overall kinetics of substrate oxidation reactions
Authors: Harper Mary-Ellen , Brand Martin D.
Published: April 2011

Thyroid hormones have well-known effects on oxidative phosphorylation, but there is little quantitative information on their important sites of action. We have used top-down elasticity analysis, an extension of metabolic control analysis, to identify the sites of action of thyroid hormones on oxidative phosphorylation in rat hepatocytes. We divided the oxidative phosphorylation system into three blocks of reactions: the substrate oxidation subsystem, the phosphorylating subsystem, and the mitochondrial proton leak subsystem and have identified those blocks of reactions whose kinetics are significantly changed by hyperthyroidism. Our results show significant effects on the kinetics of the proton leak and the phosphorylating subsystems. Quantitative analyses revealed that 43% of the increase in resting respiration rate in hyperthyroid hepatocytes compared with euthyroid hepatocytes was due to differences in the proton leak and 59% was due to differences in the activity of the phosphorylating subsystem. There were no significant effects on the substrate oxidation subsystem. Changes in nonmitochondrial oxygen consumption accounted for −2% of the change in respiration rate. Top-down control analysis revealed that the distribution of control over the rates of mitochondrial oxygen consumption, ATP synthesis and consumption, and proton leak and over mitochondrial membrane potential (Δψm) was similar in hepatocytes from hyperthyroid and littermate-paired euthyroid controls. The results of this study include the first complete top-down elasticity and control analyses of oxidative phosphorylation in hepatocytes from hyperthyroid rats.Key words: thyroid hormones, oxidative phosphorylation, mitochondria, proton leak, thermogenesis.
Alterations in hepatic adrenergic receptor status in Rana sylvatica in response to freezing and thawing: implications to the freeze-induced glycemic response
Authors: Hemmings Susan J. , Storey Kenneth B.
Published: April 2011

In Rana sylvatica, freeze-induced liberation of glucose from hepatic glycogen stores plays a critical role in conferring freeze tolerance. To determine whether an alteration in hepatic adrenergic receptor status, which dictates catecholamine-directed hepatic glycogenolytic responses, is involved in the glycemic response to freezing, hepatic α1 α2, and β2 adrenergic receptors and calcium transport were characterized by radioligand and radioisotopic techniques, respectively, in plasma membranes isolated from the livers of control, −2.5 °C-exposed, and frozen–thawed frogs. The three adrenergic receptors display marked and different patterns of changes in response to freezing, with two distinct receptor shifts clearly evident. In the control state, the β2 adrenergic receptor dominates over the α1 receptor. At 12 h, β2 adrenergic receptor dominance intensifies by a receptor shift involving a decrease in the α1 and α2 adrenergic receptors. Coincident with the initiation of the glycemic response, this early shift may be causally related to it. At 24 h, the α1 adrenergic receptor dominates, achieved by a receptor shift involving a decrease in the β2 adrenergic receptor and an increase in the α1 and α2 adrenergic receptors. This shift may be related to the maintenance of the glycemic response. Receptor shifts are associated with changes in calcium transport, which accentuate them. The thawed state is characterized by recovery of α, but not β2, receptor expression correlatable with, and perhaps allowing, a switch to hepatic glycogenesis. The role of thyroid hormone, whose levels are lower in the frozen state, in inducing receptor shifts is discussed.Key words: hepatic adrenergic receptors, Rana sylvatica, freeze tolerance, glycemic response, thyroid hormones.
Effect of bradykinin B2 receptor antagonist and indomethacin on natriuretic and hypotensive responses to atrial natriuretic factor
Authors: Veress A. T. , Chong C. K. , Honrath U. , Sonnenberg H.
Published: April 2011

The effects of inhibition of bradykinin and prostaglandin on the renal and blood pressure responses to atrial natriuretic factor (ANF) were studied in anesthetized rats. Intraarterial infusion of the receptor antagonist D-Arg[Hyp3,Thi5,8,D-Phe7]bradykinin (BKA) at 14 μg/min, a rate sufficient to block the hypotensive response to 250 μg of bradykinin, did not affect the natriuresis due to injection of ANF (UNaV: control, before ANF, 393 ± 101, after ANF, 2322 ± 400 nmol/min; BKA, before ANF, 261 ± 72, after ANF, 2259 ± 390 nmol/min). In contrast, infusion of indomethacin (Indo) reduced the level of sodium excretion both before and especially after ANF administration (UNaV: Indo, before ANF, 75 ± 15, after ANF, 320 nmol/min). The effect of combining BKA with Indo was not different from the effect of Indo alone (UNaV: BKA + Indo, before ANF, 119 ± 26, after ANF, 469 ± 167 nmol/min). The bradykinin antagonist, with or without Indo, was associated with significant hypotension relative to control. Indo, both in the absence and presence of the antagonist, was associated with a progressive decrease in blood pressure compared with control. However, in each case the hypotensive responses to ANF were not different from those in the control group. We conclude that under the present experimental conditions bradykinin does not modify ANF-induced natriuresis. However, inhibition of prostaglandin synthesis by Indo is associated with renal salt retention, reducing natriuresis both before and after ANF administration.Key words: prostaglandin inhibition, D-Arg[Hyp3,Thi5,8,D-Phe7]bradykinin, atrial natriuretic factor.
Potential defect in the vascular control of nonshivering thermogenesis in the obese Zucker rat hind limb
Authors: Eldershaw Tristram P. D. , Rattigan Stephen , Dora Kim A. , Colquhoun Eric Q. , Clark Michael G. , Cawthorne Michael A. , Buckingham Robin E.
Published: April 2011

Vascular control of nonshivering thermogenesis in the perfused hind limb of obese and lean Zucker rats was compared using two vasoconstrictors, norepinephrine and serotonin. For hind limbs of both phenotypes, norepinephrine infusions resulted in a dose-dependent uninterrupted increase in perfusion pressure and a biphasic change in oxygen uptake [Formula: see text], characterized by a stimulation at low concentrations, and an increasing inhibition at higher concentrations that gradually overcame the stimulation in a dose-dependent manner. At concentrations of norepinephrine greater than 1 μM, the inhibitory effect predominated and gave rise to values for [Formula: see text] less than basal. The obese hind limb had a lower basal [Formula: see text] and a lower maximal [Formula: see text] mediated by norepinephrine than the lean rat, but these differences appeared to relate largely to the lower muscle mass and higher content of fat of the obese hind limb. Serotonin infusions resulted in a dose-dependent increase in perfusion pressure and an accompanying decrease in [Formula: see text]. Pressure changes were identical for the obese and lean hind limbs, but the decrease in [Formula: see text] due to serotonin was greater in the hind limbs from the lean rats, and this difference remained when the data were expressed in terms of muscle mass perfused. It is concluded that the relatively lower content of muscle of the obese hind limb accounts for its lower basal and lower maximal norepinephrine-mediated thermogenesis. In addition, an intrinsic defect in obese hind limb muscle response to serotonin is present, which may be indicative of a decrease in the potential for vasoconstrictor-regulated thermogenesis that could have implications for whole-body energy balance by the obese phenotype.Key words: muscle thermogenesis, muscle oxygen uptake, genetically obese rat, norepinephrine, serotonin.
Physical exercise as a human model of limited inflammatory response
Authors: Shek Pang N , Shephard Roy J
Published: April 2011

An inflammatory response represents a fundamental series of humoral and cellular reaction cascades in response to infection, tissue injury, and related insults. An excessive response is commonly seen under the pathological conditions of trauma, sepsis, and burns. It is becoming increasingly evident that most, if not all, of the distinguishing features of a classical inflammatory response are detectable in an exercising individual, namely mobilization and activation of granulocytes, lymphocytes, and monocytes; release of inflammatory factors and soluble mediators; involvement of active phase reactants; and activation of the complement and other reactive humoral cascade systems. While the manifestation of many exercise-induced immune and related changes has been reported and confirmed repeatedly, the underlying mechanisms triggering and modulating the elicited immune responses are, at best, poorly understood. Unlike the exaggerated and sometimes uncontrollable inflammatory response in septic and trauma patients resulting in morbidity and mortality, strenuous and severe exercise normally elicits an inflammatory response of a subclinical nature to facilitate the repairing process for site-specific tissue damage. Regardless of the inciting event, for example trauma, infection, or exercise, and given an appropriate triggering signal, a remarkably similar sequence of inflammatory reactions can be reproduced in the affected host. Therefore, physical exercise and training represent an acceptable and good model for the study of limited inflammatory responses in humans.Key words: trauma, infection, exercise, inflammatory response, cytokines.
Sleep and stress in man: an approach through exercise and exposure to extreme environments
Authors: Buguet Alain , Cespuglio Raymond , Radomski Manny W
Published: April 2011

In this paper, the effects of exercise on human sleep (in temperate, cold, and hot climates) are compared with those of exposure to extreme environments (tropical, polar climates). Exercise has two effects: (i) when the exercise load is too heavy or if the subject is not trained to the exercise conditions, the hypothalamo-pituitary-adrenocortical axis (HPA) is strongly activated (somatic stress reaction), and a diachronic (delayed) decrease in total sleep time and slow-wave sleep (SWS) occurs with a synchronic (concomitant) sleep disruption (such as a decrease in REM sleep); (ii) a diachronic enhancement of SWS and (or) REM sleep occurs during moderate training and in athletes, with a moderate HPA activation (neurogenic stress reaction). Heat acclimatization (neurogenic stress response) results in a diachronic increase in SWS, contrary to acute heat exposure (somatic stress) which leads to a diachronic decrease in SWS. Nocturnal cold exposure (somatic and (or) neurogenic stress) provokes a synchronic decrease in REM sleep with an activation of stress hormones, which are reduced by previous acclimation (neurogenic pathway); SWS remains undisturbed in the cold, as it occurs at the beginning of the night before body cooling. In conclusion, when the brain can deal with the stressor (neurogenic stress), diachronic increases in SWS and (or) REM sleep occur. When these "central" mechanisms are overloaded, the classical "somatic" stress reaction occurs with diachronic and synchronic disruptions of the sleep structure.Key words: sleep, exercise, extreme environments, stress.
Exercise-induced hyperthermia and hormonal responses to exercise
Authors: Radomski M W , Cross M , Buguet A
Published: April 2011

Changes in plasma hormonal concentrations during exercise have been ascribed to the type, duration, and intensity of exercise, physical fitness of subjects, oxygen availability and debt, and acid-base balance. However, relatively few studies have examined the possible role of exercise-induced hyperthermia. This paper reviews previous studies on this subject and describes a series of experiments carried out in our laboratories to define the role of changes in body temperature in the release of hormones during exercise. In a first series of experiments, we studied the relationship between thermoregulatory and growth hormone responses to severe exercise at 23°C for 2 h in fit euhydrated subjects, controlling the core temperature increase to a maximum of 40°C by varying wind speed. Exponential relationships were found between increases in core temperature and plasma growth hormone, prolactin, and catecholamines during exercise, suggesting the existence of a thermal threshold for stimulation of hormonal release during exercise. The effect of endurance exercise with and without a thermal clamp (immersion in cold and warm water) on hormonal and leukocyte responses was examined. Again, a significant exponential relationship was found between increases in core temperature and hormonal responses. Thermal clamping significantly diminished the hormonal and the leukocytic responses to exercise, suggesting that an exercise-induced thermal threshold of ~38°C exists where hormonal responses are observed. Therefore, core temperature increases may be integrated in the controlling system of hormonal and leukocytic responses to exercise.Key words: exercise, hyperthermia, body temperature, growth hormone, catecholamines, hormones.
Lymphocyte recirculation, exercise, and immune responses
Authors: Hay John B , Andrade William N
Published: April 2011

Alterations in leukocyte concentrations in the blood are associated with exercise, stress, and other pathophysiological perturbations. The continuous migration and redistribution of cells of the recirculating lymphocyte pool between the blood and lymphatic systems can be influenced by a variety of physiological, immunological, and pathological processes. The phenotypic distribution of lymphocyte subsets is not the same in blood, afferent lymph, and efferent lymph, and cell-tracking experiments have shown that lymphocytes vary in their migratory properties. The most comprehensive physiological studies tracking these cells in vivo have been done in sheep. It has been shown that lymph-derived cells have different migratory capacities than blood-derived lymphocytes, that antigenic challenge of a single lymph node can first reduce the output of lymphocytes from the node and then markedly increase the recruitment from the blood and subsequently the output into efferent lymph. In most mammals, the blood pool of lymphocytes represents only about 1% of the total lymphocytes and only a small fraction of the recirculating lymphocyte pool. Therefore, testing the effects of exercise on lymphocyte recirculation by examining blood samples only requires considerable deduction and inference to interpret multicompartmental effects.Key words: lymphocyte migration, blood, lymph, lymph nodes.
Effects of lactate on force production by mouse EDL muscle: implications for the development of fatigue
Authors: Spangenburg Espen E , Ward Christopher W , Williams Jay H
Published: April 2011

Numerous studies suggest that the accumulation of lactate during exercise contributes to the fatigue process. This notion is based on close negative correlations between force and intracellular muscle lactate concentrations during fatigue and recovery. In this investigation, we attempted to determine if lactate directly affects muscle force output. This was accomplished by incubating mouse extensor digitorum longus muscles in extracellular concentrations of 10, 20, 30 and 50 mM L-(+)-lactate at 21 and 37°C and monitoring force output. At 21°C, 30 and 50 mM, extracellular lactate significantly reduced tetanic force (Po, 250 ms, 100 Hz) to 95 and 93% of initial, respectively. In addition, the rate of force development (+dP/dt) was reduced to 93 and 89% of initial. At 37°C, the effects of extracellular lactate were augmented as Po was reduced to 73 and 62% of initial and +dP/dt was reduced to 55 and 44% of initial at 30 and 50 mM, respectively. We next sought to determine if the reduction in Po was due to altered sarcoplasmic reticulum (SR) function using a muscle homogenate fraction. The rate of AgNO3-induced SR Ca2+ release was depressed by 31% in the presence of 25 mM lactate. These results suggest that elevated lactate depresses force production by whole muscle and may play some role in the fatigue process. In addition, it appears that lactate depresses force production, in part, by inhibiting Ca2+ release from the SR.Key words: fatigue, skeletal muscle, sarcoplasmic reticulum, calcium.
Role of NO and angiotensin II in the early development of endothelial functions impairment and cardiac hypertrophy in deoxycorticosterone acetate - salt hypertension
Authors: -Laflamme Annik K , Oster Laurence , Cardinal René , de Champlain Jacques
Published: April 2011

This study was designed to investigate the effects of chronic inhibition of NO synthesis as well as chronic angiotensin receptor blockade with losartan in the development of hypertension, on mesenteric arterial bed reactivity as well as on the development of cardiac and kidney hypertrophy in deoxycorticosterone - salt (DOCA) hypertension. Uninephrectomized rats were divided in four experimental groups all receiving saline water to drink and treated or not with losartan over a period of 9 days. Two of these groups were administered DOCA, one of which received also NG-nitro-L-arginine-methyl ester (L-NAME) to drink. A third group received only L-NAME, while another group received only saline. Systolic blood pressure was similarly increased in L-NAME, DOCA, DOCA-L-NAME groups. Cardiac and kidney weights were increased in DOCA but significantly reduced in DOCA-L-NAME. Losartan prevented the development of hypertension in all groups and also prevented cardiac and kidney hypertrophy in DOCA. The hyperreactivity of mesenteric arteries to phenylephrine, measured in the presence of indomethacin, was endothelium-dependent in both L-NAME groups but not in DOCA rats. Pretreatment with BQ 123 did not modify these endothelium-dependent responses in L-NAME rats. Chronic losartan prevented endothelium-dependent phenylephrine hyperreactivity only in DOCA, whereas only the removal of the endothelium attenuated the responsiveness in both L-NAME-treated groups. Vasorelaxations to acetylcholine and isoproterenol were attenuated in the three hypertensive groups and were normalized only in DOCA and L-NAME treated with losartan. In summary, in all hypertensive groups, blood pressure was normalized by losartan independently of its effects on endothelial functions. In DOCA, losartan normalized the phenylephrine hyperreactivity through an endothelial-dependent mechanism. However, in L-NAME-treated groups an endothelial-derived contracting factor, other than angiotensin II, endothelin, or vasoconstrictor prostanoids, appears to be activated. Both NO and angiotensin II seem to play a role in the early development of hypertension and organ hypertrophy in DOCA hypertension. Key words: experimental hypertension, NG-nitro-L-arginine-methyl ester, deoxycorticosterone acetate, vascular reactivity, hypertrophy, losartan.
Effect of cyclic AMP on the calcium-dependent potassium conductances of rat Leydig cells
Authors: Desaphy Jean-François , Joffre Michel
Published: April 2011

Two potassium conductances have been isolated in rat Leydig cells by their sensitivity to cytosolic calcium and to K+ channel blockers. We used the whole-cell configuration of the patch-clamp technique to investigate their sensitivity to cyclic AMP, the main messenger of luteinizing hormone, which stimulates Leydig cell steroidogenesis. The voltage-dependent potassium conductance is not modified by exposing the cell to 1 mM chlorophenylthio-cyclic AMP (CPT-cAMP), a membrane-permeant analogue of cAMP. By contrast, the large, calcium-activated potassium conductance is upregulated by CPT-cAMP. Furthermore, the latter is potentiated by the chloride channel blocker 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid, sodium salt (SITS).Key words: Leydig cell, calcium-dependent potassium conductances, cyclic AMP, 4-acetamido- 4'-isothiocyanato-stilbene-2,2'-disulfonic acid, sodium salt (SITS).
Alterations of KCl- and ATP-induced increase in [Ca2+]i in cardiomyocytes from vitamin B6 deficient rats
Authors: Dakshinamurti Krishnamurti , Wang Xi , Musat Sorin , Dandekar Masumi , Dhalla Naranjan S
Published: April 2011

Although vitamin B6 deficiency is related to coronary heart disease, no information regarding changes in myocardium due to vitamin B6 deficiency is available in the literature. In view of the critical role played by Ca2+ in cellular function, we investigated alterations in [Ca2+]i induced by KCl or ATP in vitamin B6 deficient and age-matched control rats. [Ca2+]i was measured in isolated cardiomyocytes by using the Fura-2 fluorescence technique. The KCl-induced increase in [Ca2+]i was augmented in vitamin B6 deficient cardiomyocytes, whereas the ATP-induced increase in [Ca2+]i was attenuated. The specific ATP binding to sarcolemma from hearts of vitamin B6 deficient rats was decreased. A single injection of vitamin B6 (10 mg/kg) to vitamin B6 deficient animals completely reversed the KCl- or ATP-induced changes in [Ca2+]i in cardiomyocytes as well as ATP binding with sarcolemma. These results regarding altered regulation of [Ca2+]i in cardiomyocytes and sarcolemmal ATP receptors indicate myocardial abnormalities due to vitamin B6 deficiency.Key words: Ca2+-handling in heart, myocardial purinergic receptors, rat cardiomyocytes, vitamin B6 deficiency.
Individual effects of dietary EPA and DHA on the functioning of the isolated working rat heart
Authors: Sergiel J -P , Martine L , Raederstorff D , Grynberg A , Demaison L
Published: April 2011

The aim of this study was to evaluate the effects of dietary pure eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the physiology of the heart in normoxic conditions and during postischemic reperfusion. These effects were compared with those of dietary n-6 polyunsaturated fatty acids (PUFA). Rats were fed a diet containing either sunflower seed oil (75 g·kg-1, SSO group), or a mixture of EPA (20:5 n-3) ethyl ester and SSO (10:90, EPA group), or a mixture of DHA (22:6 n-3) ethyl ester and SSO (10:90, DHA group), or a mixture of EPA + DHA ethyl esters and SSO (4.2:5.8:90, e+D group) for 6 weeks. The hearts were then perfused according to the working mode. The perfusion was maintained either in normoxic conditions or stopped for 17 min (global zero-flow ischemia) and restored for 33 min (reperfusion). The aortic and coronary flows, aortic developed pressure, and electrocardiogram were continuously monitored. When rats were fed a diet containing either EPA and (or) DHA, the n-6/n-3 PUFA ratio of cardiac phospholipids decreased. The proportion of arachidonic acid was reduced more with DHA than dietary EPA. In the EPA group, the percentage of DHA was lower than in the DHA group, but the percentage of EPA and docosapentaenoic acid (22:5 n-3) was higher. These changes in membrane fatty acid composition altered the cardiac function. In normoxic conditions, the coronary flow was higher in the SSO group than in the DHA and EPA groups. The heart rate was lower in the DHA and e+D groups than in the EPA and SSO groups. The aortic flow, cardiac output, and aortic developed pressure were not affected. During postischemic reperfusion, the recovery of aortic flow, coronary flow, and aortic developed pressure was similar in the four groups. A slightly improved recovery of cardiac function was noticed in the EPA group, but the difference was not significant. Feeding rats 5% fish oil + 5% SSO instead of 10% SSO for 8 weeks increased the incorporation of EPA in cardiac phospholipids and favored the recovery (+120%) of aortic flow during postischemic reperfusion. In conclusion, the beneficial effect of dietary fish oil on the recovery of cardiac pump activity during reperfusion was not observed with DHA or EPA alone. It appears to be positively related to the accumulation of EPA in membrane phospholipids. The dietary conditions favouring EPA accumulation remain to be determined.Key words: dietary polyunsaturated fatty acids, myocardial ischemia, reperfusion.
The 1996 Veylien Henderson Award of the Society of Toxicology of Canada. Current concepts: neutrophils and the activation of carcinogens in the breast and other organs
Authors: Josephy P David , Coomber Brenda L
Published: April 2011

Many chemical carcinogens target epithelial tissues, but the biological and biochemical bases of carcinogen specificity remain largely unknown. Focusing on the mammary gland, we discuss the concept that neutrophils metabolize carcinogens to reactive species that damage adjacent epithelial cells. This mechanism may help to explain why epithelial cells are sensitive targets for chemical carcinogenesis, despite their limited bioactivation capacity.Key words: carcinogenesis, neutrophil, bioactivation, peroxidase, epithelial tissue, inflammation.
Characterization of cytochrome P450 2E1 activity by the [14C]nitrosodimethylamine breath test
Authors: Bastien Marie-Claude , Villeneuve Jean-Pierre
Published: April 2011

The objective of this study was to measure the rate of demethylation of nitrosodimethylamine in vivo in the rat and determine its value to assess CYP2E1 activity in intact animals. Nitrosodimethylamine labeled with 14C on both methyl groups was administered to rats and exhaled 14CO2 was collected during 2-3 h. The nitrosodimethylamine breath test was increased by inducers of CYP2E1, such as ethanol (+139%) and 4-methylpyrazole (+115%), and decreased by the inhibitor diallyl sulfide (-53%). In addition, the nitrosodimethylamine breath test was not changed significantly by inducers specific for other cytochrome P450 such as beta-naphthoflavone, dexamethasone, and phenobarbital. The specificity of the induction by 4-methylpyrazole and of the inhibition by diallyl sulfide for CYP2E1 was determined using the [14C]caffeine (CYP1A2), [14C]aminopyrine (CYP2C11), and [14C]erythromycin (CYP3A2) breath tests. 4-Methylpyrazole treatment caused a small increase of the caffeine (+33%) and aminopyrine (+9%) breath tests and no change of the erythromycin breath test. Diallyl sulfide treatment led to a small decrease of the caffeine breath test (-33%) and of the aminopyrine breath test (-13%) but a 23% increase of the erythromycin breath test. It is concluded that the [14C]nitrosodimethylamine breath test is useful to assess CYP2E1 activity in vivo in the rat.Key words: breath test, CYP2E1, nitrosodimethylamine.
GABAB receptor antagonism by 7-MBFG, a benzo[b]furan analogue of baclofen, in central and peripheral tissues
Authors: Ong Jennifer , Kerr David I , Ansar M'Hammed , Vaccher Claude , Berthelot Pascal
Published: April 2011

(R,S)-4-Amino-3-(7-methylbenzo[b]furan-2-yl)-butanoic acid (7-MBFG), a new benzofuran analogue of the GABAB receptor agonist baclofen, has been evaluated for pharmacological activity on GABAB receptors in the guinea-pig isolated ileum and rat neocortical slices. 7-MBFG (300 and 500 µM) reversibly antagonized the (R,S)-baclofen induced depression of cholinergic twitch contractions in the guinea-pig ileum and shifted the concentration-response curve for baclofen to the right, in a parallel manner, giving an apparent pA2 value of 3.7 ± 0.3. Likewise, 7-MBFG (300 and 500 µM) reversibly blocked the baclofen-induced suppression of spontaneous discharges, in rat neocortical slices maintained in Mg2+-free Krebs medium, and caused a rightward, parallel shift of the baclofen concentration-response curve, giving an apparent pA2 value of 4.1 ± 0.1. The compound 7-MBFG belongs to a novel, new class of antagonist at central and peripheral GABAB receptors, in which the antagonist properties reside in the pseudo-aromatic character of their 3-benzo[b]furan-2-yl substituents, and might provide useful leads for further development of GABAB receptor ligands.Key words: (R,S)-baclofen, 4-amino-3-(7-methylbenzo[b]furan-2-yl)-butanoic acid, GABAB receptor antagonist, rat neocortex, guinea-pig ileum.
Effects of a nonpeptide bradykinin B2 receptor antagonist, FR167344, on guinea-pig tracheal smooth muscle bradykinin receptors
Authors: Asano Masayuki , Sawai Hiroe , Hatori Chie , Inamura Noriaki , Fujiwara Tatsujiro , Nakahara Kunio
Published: April 2011

It is speculated that bradykinin may play an important role in asthma. Thus, bradykinin receptor antagonists may have therapeutic potential against asthma. Orally active bradykinin antagonists would be more desirable for the treatment of the disease. In the present study, we examined the effects of a novel, potent, selective, and orally active nonpeptide bradykinin B2 receptor antagonist, FR167344 (N-[N-[3-[(3-bromo-2-methylimidazo[1,2-a]pyridin-8-yl)oxymethyl]- 2,4-dichlorophenyl]-N-methylaminocarbonylmethyl]-4-(dimethylaminocarbonyl)cinnamylamide hydrochloride), on guinea-pig tracheal smooth muscle bradykinin receptors. FR167344 inhibited [3H]bradykinin binding to bradykinin receptors in epithelium-denuded guinea-pig tracheal membrane with an IC50 of 2.1 nM and a Ki of 0.44 nM. This compound also inhibited bradykinin-induced contraction of epithelium-denuded guinea-pig trachea with a pKB of 10.8, but had no effect on carbachol-induced contraction of the trachea even at 10-6 M. These results indicate that FR167344 has the specific antagonistic activity against guinea-pig tracheal smooth muscle bradykinin receptors.Key words: bradykinin, receptor, antagonist, FR167344, trachea.
The effect of estradiol on output of adrenocorticotropin and prolactin by fetal sheep anterior pituitary cells
Authors: Wang S , Matthews S G , Yang K , Challis JRG
Published: April 2011

We examined the hypothesis that estradiol (E2) would affect fetal anterior pituitary corticotroph and lactotroph function in vitro, and that any effects would be influenced by gestational age. Anterior pituitary cells from fetal sheep at day 129 (n = 4) and at day 139 (n = 5) of gestation were cultured. After 96 h in culture, cells were treated for 18 h with E2 concentrations ranging from 0 to 1000 nM, in the presence or absence of 100 nM of corticotropin-releasing hormone (CRH), cortisol, arginine vasopressin (AVP), or CRH and cortisol, to examine their effects on corticotroph function. Cells were also treated with bromocriptine or increasing concentrations of E2 to study their effects on lactotroph function. Immunoreactive (ir) adrenocorticotropin (ACTH) and prolactin in the culture medium were measured by radioimmunoassay. Levels of cellular pro-opiomelanocortin (POMC) mRNA and prolactin mRNA were determined by in situ hybridization. Immunohistochemistry was used to determine the percentage of cells that were immunopositive for ACTH (corticotrophs) or prolactin (lactotrophs). ACTH output was stimulated by CRH treatment at day 139 but not at day 129 of gestation, and cortisol attenuated this response. ACTH output by cells cultured with 10 nM E2 and 100 nM CRH, at 139 days of gestation, was greater than with CRH alone (p < 0.05). E2 did not affect basal ACTH output or ACTH output with any other treatment or levels of POMC mRNA. Prolactin output was not affected by E2 treatment. Bromocriptine significantly decreased prolactin output but not levels of prolactin mRNA. We conclude that E2 may affect CRH-stimulated fetal sheep pituitary corticotroph function late in gestation, but only within a narrow, physiological range of concentration.Key words: estradiol, adrenocorticotropin, prolactin, anterior pituitary, fetal sheep.
The fate of nitrogen from 15N-labeled nitrate after single intravenous administration of Na15NO3 in sheep
Authors: Lewicki J , Wiechetek M , Souffrant W B , Karlik W , Garwacki S
Published: April 2011

The metabolic fate of nitrogen from 15N-labeled sodium nitrate has been investigated in four healthy Polish Merino ewes. 15N-labeled sodium nitrate was administered intravenously at the dosage of 400 mu mol·kg-1 body weight. Blood plasma and urine concentrations of nitrate, ammonia, and urea and 15N enrichment of ammonia and urea were estimated over a 50-h period following 15N-nitrate administration. Nitrate (NO3-) was slowly eliminated from the blood plasma, and the presence of NO3- in the blood plasma above the nitrate "background" was observed for 50 h. 15N enrichment of blood plasma urea already appeared at 15 min and reached the maximum 6 h after 15N-nitrate administration. The urinary excretion of nitrate occured during 50 h after 15N-nitrate injection; the total urine excretion of NO3- was 23.63 ± 2.39% of the administered dose. The mean urinary recoveries of nitrogen as 15N-urea and 15N-ammonia were 14.76 ± 1.32% and 0.096 ± 0.015% of the administered 15N-nitrate dose, respectively. It should be pointed out that in total only 38.49% of the administered nitrate-N was excreted in urine (as nitrate, ammonia and urea nitrogen) during 50 h. The results obtained indicate that sheep are able to store nitrate nitrogen in their body. The fate of the remaining approximately 60% of the 15NO3- administered dose is unknown. The results obtained do not allow one to conclude what fraction of the unrecovered approximately 60% of the 15NO3- dose was utilized by gastrointestinal microorganisms, and (or) metabolized, or stored in sheep tissues.Key words: nitrate, ammonia, urea, metabolism, excretion, sheep.
Modification of β-adrenoceptors and adenylyl cyclase in hearts perfused with hypochlorous acid
Authors: Persad Sujata , Dhalla Naranjan S
Published: April 2011

It is now well known that the signal transduction pathway involving beta-adrenoceptors and adenylyl cyclase is altered in ischemic heart disease. Since leukocytes accumulate in the ischemic heart and produce hypochlorous acid (HOCl), we investigated the effects of HOCl upon beta-adrenoceptors and adenylyl cyclase activities by perfusing rat hearts with 0.1 mM HOCl for 10 min and isolating cardiac membranes. Marked depressions in both the density and affinity of beta1-adrenoceptors were observed, whereas no significant change in the affinity or density of beta2-adrenoceptors was seen in hearts perfused with HOCl. After treatment of hearts with HOCl, competition curves using isoproterenol, a beta-adrenoceptor agonist, revealed a decrease in the proportion of high affinity binding sites. The adenylyl cyclase activities in the absence and presence of forskolin, NaF, Gpp(NH)p, or isoproterenol were depressed in hearts perfused with HOCl; however, the stimulatory effects of these agents on adenylyl cyclase were either unaltered or augmented. The presence of methionine in the perfusion medium prevented the HOCl-induced changes in beta1-adrenoceptors and adenylyl cyclase activity. These results suggest that HOCl may produce a defect in the beta-adrenoceptor linked signal transduction mechanism by affecting both beta1-adrenoceptors and adenylyl cyclase enzyme in the myocardium.Key words: signal transduction, adrenergic mechanisms, beta-adrenoceptors, adenylyl cyclase, heart membranes.
Pharmacological profile of the isomers of the GluR-specific agonist ATPA
Authors: Curry Kenneth , Pajouhesh Hassan
Published: April 2011

We have synthesized the (R)- and (S)-isomers of 2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoate (ATPA) by stereochemically certain routes. Our studies in the rat cortical wedge preparation indicate that (R)-ATPA has no observable excitatory effect, while (S)-ATPA has an apparent KD of 16 µM. This excitatory response is unaffected by the specific N-methyl-D-aspartate (NMDA) antagonist, D-2-amino-5-phosphonopentanoic acid (DAP5) but is partially blocked by 6-nitro-sulfamoyl[f]quinoxalinedione (NBQX) at concentrations that attenuate the effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA), the effects are however reduced by the nonspecific antagonist kynurenate (KYN), indicating an interaction with a class of kainate receptor.Key words: glutamate subreceptors, GluR5, (S)- and (R)-ATPA, cortical slices.
Caffeine and length dependence of staircase potentiation in skeletal muscle
Authors: Rassier Dilson E , Tubman L Aaron , MacIntosh Brian R
Published: April 2011

Skeletal muscle sensitivity to Ca2+ is greater at long lengths, and this results in an optimal length for twitch contractions that is longer than optimal length for tetanic contractions. Caffeine abolishes this length dependence of Ca2+ sensitivity. Muscle length (ML) also affects the degree of staircase potentiation. Since staircase potentiation is apparently caused by an increased Ca2+ sensitivity of the myofilaments, we tested the hypothesis that caffeine depresses the length dependence of staircase potentiation. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 10 s of 10-Hz stimulation were analyzed at seven different lengths to evaluate the length dependence of staircase potentiation. In the absence of caffeine, length dependence of Ca2+ sensitivity was observed, and the degree of potentiation after 10-Hz stimulation showed a linear decrease with increased length (DT = 1.47 - 0.05ML, r2 = 0.95, where DT is developed tension). Length dependence of Ca2+ sensitivity was decreased by caffeine when caffeine was administered in amounts estimated to result in 0.5 and 0.75 mM concentrations. Furthermore, the negative slope of the relationship between staircase potentiation and muscle length was diminished at the lower caffeine dose, and the slope was not different from zero after the higher dose (DT = 1.53 - 0.009ML, r2 = 0.43). Our study shows that length dependence of Ca2+ sensitivity in intact skeletal muscle is diminished by caffeine. Caffeine also suppressed the length dependence of staircase potentiation, suggesting that the mechanism of this length dependence may be closely related to the mechanism for length dependence of Ca2+ sensitivity.Key words: skeletal muscle, twitch contraction, Ca2+ sensitivity, muscle length, staircase.
Inhibitory effect of gymnemic acid on intestinal absorption of oleic acid in rats
Authors: Wang L F , Luo H , Miyoshi M , Imoto T , Hiji Y , Sasaki T
Published: April 2011

Gymnemic acid, a mixture of triterpene glycosides extracted from the leaves of Gymnema sylvestre, is known to inhibit the intestinal absorption of glucose in human and rats. This work examined the effect of gymnemic acid on oleic acid absorption by the method of intestinal perfusion in rats. The results showed the following. (i) Gymnemic acid potently inhibited the absorption of oleic acid in intestine. (ii) This inhibition was dose dependent and reversible. (iii) The extent of inhibition and the recovery progress were extremely similar to that of glucose absorption. (iv) Taurocholate did not affect the inhibitory effect of gymnemic acid on oleic acid absorption, but lowering its concentration facilitated the recovery from the inhibition. (v) The absorption of oleic acid was not affected by other glycosides such as phloridzin, stevioside, and glycyrrhizin. These new findings are important for understanding the roles of gymnemic acid in therapy of diabetes mellitus and obesity.Key words: gymnemic acid, oleic acid, glucose, intestinal absorption, rat.
New insights into body composition assessment in obese women
Authors: De Lorenzo A , Sorge R P , Candeloro N , Di Campli C , Sesti G , Lauro R
Published: April 2011

During treatment of patients with non-insulin-dependent diabetes mellitus, there may be marked body weight loss. Therefore, body composition should be monitored to check for a decrease in fat mass alone, without an excessive decrease of both fat-free mass and total body water. Accordingly, it is useful to monitor the hydration of these patients. One method that allows us to check the status of body hydration is the multifrequency bioelectric impedance analysis (MFBIA). It makes use of formulas that estimate total body water on the basis of the concept that the human body may be approximated to a cylinder of length equal to body height. In normal subjects body water estimates are sufficiently accurate, but in obese subjects the true hydration status may be overestimated. In this report, we describe the accuracy of mathematical models previously described in the literature, and correct for the overestimation of total body water in obese subjects by means of a new equation based on a new model. The coefficients for each model have been recalculated by the weighing of our sample in order to test the accuracy of estimates obtained with the equations. This new model includes both body volume and two impedances at appropriate frequencies useful for identifying two terms strictly related to extra- and intra-cellular water. The new formulas do not include body weight, but they include the body volume, a parameter more closely related to the biophysical reference model. Fifty-five overweight females, body mass index ranging from 26.8 to 50.2 kg/m2, were enrolled in the study. The proposed equations, taking advantage of two impedance values at appropriate frequencies, better predict total body water in obese women. This was particularly evident when the results obtained with the multifrequency bioelectric impedance analysis and deuterium isotopic oxide dilution method were compared. Although this last method is considered the "gold standard," it is not suitable for use in routine clinical practice. In conclusion, evaluation of total body composition by means of bioelectric impedance analysis might be included in programs for the prevention of non-insulin-dependent diabetes and for monitoring weight loss during overt pathology.Key words: body composition, bioelectrical impedance, obesity, diabetes mellitus, extracellular water, intracellular water.
Renal and vascular effects of chronic nitric oxide synthase inhibition: involvement of endothelin 1 and angiotensin II
Authors: D'Amours Martin , Lebel Marcel , Grose John H , Larivière Richard
Published: April 2011

Endothelin 1 (ET-1) is a potent vasoconstrictor implicated in the control of blood pressure and renal function. Its effects can be modulated by nitric oxide (NO), which inhibits ET-1 production and action. Recently, we reported that ET-1 production can also be modulated by angiotensin II (AngII) in vivo. To investigate the interactions between NO, ET-1, and AngII in hypertension and renal dysfunction, we assessed immunoreactive ET-1 (ir-ET-1) concentration in plasma and urine as well as in vascular and renal tissues of rats with chronic inhibition of NO synthesis, in the presence and the absence of the AngII type 1 receptor antagonist losartan. Normal (protocols A and B) and uninephrectomized rats (protocol C) received the L-arginine analog NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthesis, 0.05% (protocol A) or 0.1% (protocols B and C), with or without losartan (20 mg·kg-1·day-1). After 6 weeks, systolic blood pressure was significantly increased in L-NAME rats compared with the controls (p < 0.01), while serum creatinine and urea, creatinine clearance, and proteinuria were similar to control values. However, ir-ET-1 concentration in plasma and in the thoracic aorta was augmented in animals receiving 0.1% L-NAME (p < 0.01), while it was unchanged in the mesenteric arterial bed, preglomerular arteries, and glomeruli. In contrast, ir-ET-1 concentration was decreased in the renal papilla (p < 0.05) as well as in the urine of L-NAME rats (p < 0.01). Treatment with losartan significantly attenuated the rise in systolic blood pressure induced by L-NAME (p < 0.01). Losartan also normalized the increased ir-ET-1 concentration in plasma and in the thoracic aorta, but had no effect on tissues with normal or reduced ir-ET-1 levels. These results indicate that chronic inhibition of NO synthase with L-NAME induces hypertension without renal dysfunction. Increased ET-1 production in some blood vessels and elevated circulating ET-1 concentration may contribute to the maintenance of high blood pressure. The reduction of systolic blood pressure by losartan supports a role for AngII in the pathogenesis of this form of hypertension, which may be due, at least in part, to the modulation of ET-1 production.Key words: endothelin, nitric oxide, L-NAME, angiotensin II, losartan, hypertension, blood vessel, glomeruli.
Persistent functional and structural retinal anomalies in newborn rats exposed to hyperoxia
Authors: Lachapelle Pierre , Dembinska Olga , Rojas Luz Marina , Benoit Julie , Almazan Guillermina , Chemtob Sylvain
Published: April 2011

Previous studies have shown that newborn rats exposed postnatally to hyperoxia will develop a permanent impairment of the retinal function as determined with the electroretinogram (ERG). The purpose of our study was to examine whether postnatal hyperoxia equally alters the light- and dark-adapted ERGs and oscillatory potentials (OPs) as well as leads to permanent structural modification of the retina. During the first 14 days of life, cohorts of Sprague-Dawley rats were exposed to a hyperoxic environment, and ERGs were recorded at mean ages of approximately 25 and 55 days. Our results indicate that both light- and dark-adapted ERGs and OPs are already significantly altered within a few days following exposure to hyperoxia. None of the ERG and (or) OP parameters, with the exception of the a-wave, returned to normal values by 55 days of age. In fact some dark-adapted OPs were completely abolished following postnatal O2 exposure. Histological analysis revealed that the retina of rats exposed to hyperoxia failed to develop an outer plexiform layer and had a reduced count of horizontal cells, consistent with the permanent postreceptoral anomalies seen in the ERG responses. Our results suggest that postnatal hyperoxia causes a generalized retinal disorder leading to permanent structural modifications of the retinal cytoarchitecture and lasting anomalies of the rod and cone functions.Key words: rods, cones, electroretinography, oscillatory potentials, hyperoxia, retina, development.
Concentration-dependent effects of angiotensin II on sinus rate in canine isolated right atrial preparations
Authors: Yin Ya-Lin , Pagé Pierre , Cardinal René
Published: April 2011

To investigate the concentration-response relationship of angiotensin II with respect to its chronotropic effects, the sinus rate was recorded from canine isolated right atrial preparations perfused through the sinus node artery. Nicotine (5 × 10-5 M) injection induced an early, atropine-sensitive bradycardic response and a more delayed propranolol-sensitive tachycardic response, suggesting that the preparations contained both cholinergic and adrenergic neurons. The former response, but not the latter, was markedly reduced in preparations in which the right atrial ganglionated plexus was removed. Positive chronotropic responses were induced by angiotensin II over a wide range of concentrations (10-12 - 5 × 10-6 M), with a maximum increment of 29.9 ± 9.6 beats/min. Responses to low concentrations (angiotensin II, 10-11 M) were monophasic and were abolished by propranolol. In contrast, the responses to higher concentrations (angiotensin II, 10-6 M) were not abolished by propranolol and were biphasic (early response, 29.9 ± 12.1 beats/min; later response, 18.6 ± 9.0 beats/min), the early response being blocked by losartan (AT1 antagonist) but not the later one, both being blocked by saralasin (nonselective angiotensin II antagonist). In conclusion, the data suggest that angiotensin II exerts its stimulant effects on the heart through receptors located either on cardiomyocytes or neurons, depending on the agonist concentration.Key words: angiotensin II, heart rate, right atrium, intracardiac neurons.
On the barometric method for measurements of ventilation, and its use in small animals
Authors: Mortola Jacopo P , Frappell Peter B
Published: April 2011

The barometric method is a common technique for measurements of pulmonary ventilation in unrestrained animals. It basically consists of recording the changes in chamber pressure generated during breathing. In fact, as the air inspired is warmed and humidified from the ambient to the pulmonary values, the total pressure in the animal chamber increases; the opposite occurs in expiration. The present commentary is an introduction to this method, briefly reviewing its historical development, the conceptual pitfalls, and potential sources of errors during practical applications.Key words: barometric technique, plethysmography, pulmonary ventilation, respiratory techniques, tidal volume.