Transcriptomic basis of sex loss in the pea aphid.

BACKGROUND: Transitions from sexual to asexual reproduction are common in eukaryotes, but the underlying mechanisms remain poorly known. The pea aphid-Acyrthosiphon pisum-exhibits reproductive polymorphism, with cyclical parthenogenetic and obligate parthenogenetic lineages, offering an opportunity to decipher the genetic basis of sex loss. Previous work on this species identified a single 840 kb region controlling reproductive polymorphism and carrying 32 genes. With the aim of identifying the gene(s) responsible for sex loss and the resulting consequences on the genetic programs controlling sexual or asexual embryogenesis, we compared the transcriptomic response to photoperiod shortening-the main sex-inducing cue-of a sexual and an obligate asexual lineage of the pea aphid, focusing on heads (where the photoperiodic cue is detected) and embryos (the final target of the cue). RESULTS: Our analyses revealed that four genes (one expressed in the head, and three in the embryos) of the region responded differently to photoperiod in the two lineages. We also found that the downstream genetic programs expressed during embryonic development of a future sexual female encompass ∼1600 genes, among which miRNAs, piRNAs and histone modification pathways are overrepresented. These genes mainly co-localize in two genomic regions enriched in transposable elements (TEs). CONCLUSIONS: Our results suggest that the causal polymorphism(s) in the 840 kb region somehow impair downstream epigenetic and post-transcriptional regulations in obligate asexual lineages, thereby sustaining asexual reproduction.

Cadaver models for cardiac arrest: A systematic review and perspectives.

AIM: To provide an overview of cadaver models for cardiac arrest and to identify the most appropriate cadaver model to improve cardiopulmonary resuscitation through a systematic review. METHODS: The search strategy included PubMed, Embase, Current contents, Pascal, OpenSIGLE and reference tracking. The search concepts included "heart arrest", "cardiopulmonary resuscitation" and "cadavers". All studies, published until February 2019, in English or French, on research or simulation in the field of cardiac arrest and using cadaver models were eligible for inclusion. RESULTS: Overall, 29 articles out of the 244 articles located were selected. The characteristics of the studies and the cadaver models were heterogenous. Indeed, 31% of the studies lacked a proper description of the model used and its specificities. Fresh cadavers were used in 55% of the studies and chest compressions were performed in 90%. This model was appreciated for its realism in terms of mechanical properties and tissue conservation. Thiel-embalmed cadavers also showed promising results concerning lung and chest compliance. The lack of circulation stood out as the strongest limitation of all types of human cadaver models. CONCLUSION: Four types of cadaver models are used in cardiac arrest research. The great heterogeneity of these models coupled with unequal quality in reporting makes comparisons between studies difficult. There is a need for uniform reporting and standardisation of human cadaver models in cardiac arrest research.

An integrated protocol for targeted mutagenesis with CRISPR-Cas9 system in the pea aphid.

CRISPR-Cas9 technology is a very efficient functional analysis tool and has been developed in several insects to edit their genome through injection of eggs with guide RNAs targeting coding sequences of genes of interest. However, its implementation in aphids is more challenging. Aphids are major pests of crops worldwide that alternate during their life cycle between clonality and sexual reproduction. The production of eggs after mating of sexual individuals is a single yearly event and is necessarily triggered by a photoperiod decrease. Fertilized eggs then experience an obligate 3-month diapause period before hatching as new clonal colonies. Taking into consideration these particularities, we developed in the pea aphid Acyrthosiphon pisum a step-by-step protocol of targeted mutagenesis based on the microinjection within fertilized eggs of CRISPR-Cas9 components designed for the editing of a cuticular protein gene (stylin-01). This protocol includes the following steps: i) the photoperiod-triggered induction of sexual morphs (2 months), ii) the mating and egg collection step (2 weeks), iii) egg microinjection and melanization, iv) the 3-month obligate diapause, v) the hatching of new lineages from injected eggs (2 weeks) and vi) the maintenance of stable lineages (2 weeks). Overall, this 7-month long procedure was applied to three different crosses in order to estimate the impact of the choice of the genetic combination on egg production dynamics by females as well as hatching rates after diapause. Mutation rates within eggs before diapause were estimated at 70-80%. The hatching rate of injected eggs following diapause ranged from 1 to 11% depending on the cross and finally a total of 17 stable lineages were obtained and maintained clonally. Out of these, 6 lineages were mutated at the defined sgRNAs target sites within stylin-01 coding sequence, either at the two alleles (2 lineages) or at one allele (4 lineages). The final germline transmission rate of the mutations was thus around 35%. Our protocol of an efficient targeted mutagenesis opens the avenue for functional studies through genome editing in aphids.

Inductive plethysmography in rats: towards a new standard for longitudinal non-invasive cardiac output monitoring in preclinical studies.

OBJECTIVE: Cardiovascular function assessment is most often a mandatory requirement in preclinical studies in all industrialized countries. The invasiveness and impact of the monitoring devices used on animals have to be reduced as far as possible for scientific as well as ethical reasons. In humans, inductive plethysmography (IP) is a commonly used wearable non-invasive technology based on volume recordings. The innovative target of the present work is to transfer the IP technology to cardiac output (CO) measurement in rodents. APPROACH: A new IP device specifically designed for rodents was developed and compared with the gold standard equipment for CO assessment in rodents. CO was monitored in anesthetized rats equipped with both the IP device and an ultrasonic flow probe during a hemodynamic challenge (volume overload). MAIN RESULTS: Cardiac blood flow measurements with the new IP device are significantly correlated with those obtained with the ultrasonic probe throughout the volume overload procedure (r = 0.97, p < 0.001). SIGNIFICANCE: Our results clearly show that the IP device has adequate technological characteristics to allow accurate CO measurement and can therefore be used for longitudinal non-invasive monitoring in rats.

High-resolution respiratory inductive plethysmography in rats: validation in anesthetized conditions.

Respiratory monitoring is often required in experimental physiological and pharmacological studies in rodents. Currently, the mostly used techniques are direct measurement of airflow on intubated animals and whole body plethysmography. OBJECTIVE: Although the reliability of these methods has been broadly demonstrated, they also have several drawbacks such as invasiveness, high cost of use or confinement of the animals. Respiratory inductive plethysmography (RIP) is a non-invasive technique already used in medium-sized mammals that has not yet been evaluated in small rodents. The implementation of inductive plethysmography in rats represents an instrumental challenge because of the small inductances that are expected. APPROACH: A rodent-specific RIP apparatus has been developed and compared to direct airflow measurement provided by a pneumotachograph (PNT) considered as the invasive gold standard for respiratory monitoring. The experiments were carried out on anesthetized rats artificially ventilated at different levels of tidal volumes (V T) covering the whole physiological range. MAIN RESULTS: Based on the Euclidian distance between signals, this study shows that after calibration, signals from RIP fit at 93% with PNT values. The Bland and Altman plot evidences differences between RIP and PNT lower than 20% and the values obtained are highly correlated (R = 0.98, p < 0.001). SIGNIFICANCE: This study demonstrates that it is possible to design RIP systems suitable for measurement of tidal volumes and airflow in anesthetized rats. Further studies will now be focused on the validation in extended physiological conditions.

Exercise-induced cardioprotection: a role for eNOS uncoupling and NO metabolites.

Exercise is an efficient strategy for myocardial protection against ischemia-reperfusion (IR) injury. Although endothelial nitric oxide synthase (eNOS) is phosphorylated and activated during exercise, its role in exercise-induced cardioprotection remains unknown. This study investigated whether modulation of eNOS activation during IR could participate in the exercise-induced cardioprotection against IR injury. Hearts isolated from sedentary or exercised rats (5 weeks training) were perfused with a Langendorff apparatus and IR performed in the presence or absence of NOS inhibitors [N-nitro-L-arginine methyl ester, L-NAME or N5-(1-iminoethyl)-L-ornithine, L-NIO] or tetrahydrobiopterin (BH4). Exercise training protected hearts against IR injury and this effect was abolished by L-NAME or by L-NIO treatment, indicating that exercise-induced cardioprotection is eNOS dependent. However, a strong reduction of eNOS phosphorylation at Ser1177 (eNOS-PSer1177) and of eNOS coupling during early reperfusion was observed in hearts from exercised rats (which showed higher eNOS-PSer1177 and eNOS dimerization at baseline) in comparison to sedentary rats. Despite eNOS uncoupling, exercised hearts had more S-nitrosylated proteins after early reperfusion and also less nitro-oxidative stress, indexed by lower malondialdehyde content and protein nitrotyrosination compared to sedentary hearts. Moreover, in exercised hearts, stabilization of eNOS dimers by BH4 treatment increased nitro-oxidative stress and then abolished the exercise-induced cardioprotection, indicating that eNOS uncoupling during IR is required for exercise-induced myocardial cardioprotection. Based on these results, we hypothesize that in the hearts of exercised animals, eNOS uncoupling associated with the improved myocardial antioxidant capacity prevents excessive NO synthesis and limits the reaction between NO and O2·- to form peroxynitrite (ONOO⁻), which is cytotoxic.

Detecting variations of blood volume shift due to heart beat from respiratory inductive plethysmography measurements in man.

The simultaneous study of the cardiac and respiratory activities and their interactions is of great physiological and clinical interest. For this purpose, we want to investigate if respiratory inductive plethysmography (RIP) can be used for cardiac functional exploration. We propose a system, based on RIP technology and time-scale approaches of signal processing, for the extraction of cardiac information. This study focuses on the monitoring of blood volume shift due to heart beat, noted ▵Vtr_c and investigates RIP for the detection of ▵Vtr_c variations by comparison to stroke volume (SV) variations estimated by impedance cardiography (IMP). We proposed a specific respiratory protocol assumed to induce significant variations of the SV. Fifteen healthy volunteers in the seated and supine positions were asked to alternate rest respiration and maneuvers, consisting in blowing into a manometer. A multi-step treatment including a variant of empirical mode decomposition was applied on RIP signals to extract cardiac volume signals and estimate beat-to-beat ▵Vtr_c. These were averaged in quasi-stationary states at rest and during the respiratory maneuvers, and analysed in view of SV estimations from IMP signals simultaneously acquired. Correlation and statistical tests over the data show that RIP can be used to detect variations of the cardiac blood shift in healthy young subjects.

Sequentiality of daily life physiology: an automatized segmentation approach.

Based on the hypotheses that (1) a physiological organization exists inside each activity of daily life and (2) the pattern of evolution of physiological variables is characteristic of each activity, pattern changes should be detected on daily life physiological recordings. The present study aims at investigating whether a simple segmentation method can be set up to detect pattern changes on physiological recordings carried out during daily life. Heart and breathing rates and skin temperature have been non-invasively recorded in volunteers following scenarios made of "daily life" steps (13 records). An observer, undergoing the scenario, wrote down annotations during the recording time. Two segmentation procedures have been compared to the annotations, a visual inspection of the signals and an automatic program based on a trends detection algorithm applied to one physiological signal (skin temperature). The annotations resulted in a total number of 213 segments defined on the 13 records, the best visual inspection detected less segments (120) than the automatic program (194). If evaluated in terms of the number of correspondences between the times marks given by annotations and those resulting from both physiologically based segmentations, the automatic program was better than the visual inspection. The mean time lags between annotation and program time marks remain <60 s (the precision of annotation times marks). We conclude that physiological variables time series recorded in common life conditions exhibit different successive patterns that can be detected by a simple trends detection algorithm. Theses sequences are coherent with the corresponding annotated activity.

Carbon monoxide pollution impairs myocardial perfusion reserve: implication of coronary endothelial dysfunction.

Chronic exposure to simulated urban CO pollution is reported to be associated with cardiac dysfunction. Despite the potential implication of myocardial perfusion alteration in the pathophysiology of CO pollution, the underlying mechanisms remain today still unknown. Therefore, the aim of this work was to evaluate the effects of prolonged exposure to simulated urban CO pollution on the regulation of myocardial perfusion. Cardiac hemodynamics and myocardial perfusion were assessed under basal conditions and during the infusion of a ß-Adrenergic agonist. The effects of CO exposure on capillary density, coronary endothelium-dependent vasodilatation, eNOS expression and eNOS uncoupling were also evaluated. Our main results were that prolonged CO exposure was associated with a blunted myocardial perfusion response to a physiological stress responsible for an altered contractile reserve. The impairment of myocardial perfusion reserve was not accounted for a reduced capillary density but rather by an alteration in coronary endothelium-dependent vasorelaxation (-45% of maximal relaxation to ACh). In addition, though chronic CO exposure did not change eNOS expression, it significantly increased eNOS uncoupling. Therefore, the present work underlines the fact that chronic CO exposure, at levels found in urban air pollution, is associated with reduced myocardial perfusion reserve. This phenomenon is explained at the coronary-vessel level by deleterious effects of CO exposure on the endothelium NO-dependent vasorelaxation via eNOS uncoupling.

Inhibition of cardiac leptin expression after infarction reduces subsequent dysfunction.

Leptin is known to exert cardiodepressive effects and to induce left ventricular (LV) remodelling. Nevertheless, the autocrine and/or paracrine activities of this adipokine in the context of post-infarct dysfunction and remodelling have not yet been elucidated. Therefore, we have investigated the evolution of myocardial leptin expression following myocardial infarction (MI) and evaluated the consequences of specific cardiac leptin inhibition on subsequent LV dysfunction. Anaesthetized rats were subjected to temporary coronary occlusion. An antisense oligodesoxynucleotide (AS ODN) directed against leptin mRNA was injected intramyocardially along the border of the infarct 5 days after surgery. Cardiac morphometry and function were monitored by echocardiography over 11 weeks following MI. Production of myocardial leptin and pro-inflammatory cytokines interleukin (IL)-1ß and IL-6 were assessed by ELISA. Our results show that (1) cardiac leptin level peaks 7 days after reperfused MI; (2) intramyocardial injection of leptin-AS ODN reduces early IL-1ß and IL-6 overexpression and markedly protects contractile function. In conclusion, our findings demonstrate that cardiac leptin expression after MI could contribute to the evolution towards heart failure through autocrine and/or paracrine actions. The detrimental effect of leptin could be mediated by pro-inflammatory cytokines such as IL-1ß and IL-6. Our data could constitute the basis of new therapeutic approaches aimed to improve post-MI outcome.

Moderate exercise prevents impaired Ca2+ handling in heart of CO-exposed rat: implication for sensitivity to ischemia-reperfusion.

Sustained urban carbon monoxide (CO) exposure exacerbates heart vulnerability to ischemia-reperfusion via deleterious effects on the antioxidant status and Ca(2+) homeostasis of cardiomyocytes. The aim of this work was to evaluate whether moderate exercise training prevents these effects. Wistar rats were randomly assigned to a control group and to CO groups, living during 4 wk in simulated urban CO pollution (30-100 parts/million, 12 h/day) with (CO-Ex) or sedentary without exercise (CO-Sed). The exercise procedure began 4 wk before CO exposure and was maintained twice a week in standard filtered air during CO exposure. On one set of rats, myocardial ischemia (30 min) and reperfusion (120 min) were performed on isolated perfused rat hearts. On another set of rats, myocardial antioxidant status and Ca(2+) handling were evaluated following environmental exposure. As a result, exercise training prevented CO-induced myocardial phenotypical changes. Indeed, exercise induced myocardial antioxidant status recovery in CO-exposed rats, which is accompanied by a normalization of sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a expression and then of Ca(2+) handling. Importantly, in CO-exposed rats, the normalization of cardiomyocyte phenotype with moderate exercise was associated with a restored sensitivity of the myocardium to ischemia-reperfusion. Indeed, CO-Ex rats presented a lower infarct size and a significant decrease of reperfusion arrhythmias compared with their sedentary counterparts. To conclude, moderate exercise, by preventing CO-induced Ca(2+) handling and myocardial antioxidant status alterations, reduces heart vulnerability to ischemia-reperfusion.

Simulated urban carbon monoxide air pollution exacerbates rat heart ischemia-reperfusion injury.

Myocardial damages due to ischemia-reperfusion (I/R) are recognized to be the result of a complex interplay between genetic and environmental factors. Epidemiological studies suggested that, among environmental factors, carbon monoxide (CO) urban pollution can be linked to cardiac diseases and mortality. The aim of this work was to evaluate the impact of exposure to CO pollution on cardiac sensitivity to I/R. Regional myocardial I/R was performed on isolated perfused hearts from rats exposed for 4 wk to air enriched with CO (30-100 ppm). Functional variables, reperfusion ventricular arrhythmias (VA) and cellular damages (infarct size, lactate dehydrogenase release) were assessed. Sarcomere length shortening and Ca(2+) handling were evaluated in intact isolated cardiomyocytes during a cellular anoxia-reoxygenation protocol. The major results show that prolonged CO exposure worsens myocardial I/R injuries, resulting in increased severity of postischemic VA, impaired recovery of myocardial function, and increased infarct size (60 +/- 5 vs. 33 +/- 2% of ischemic zone). The aggravating effects of CO exposure on I/R could be explained by a reduced myocardial enzymatic antioxidant status (superoxide dismutase -45%; glutathione peroxidase -49%) associated with impaired intracellular Ca(2+) handling. In conclusion, our results are consistent with the idea that chronic CO pollution dramatically increases the severity of myocardial I/R injuries.

Transcriptomic and proteomic analyses of seasonal photoperiodism in the pea aphid.

BACKGROUND: Aphid adaptation to harsh winter conditions is illustrated by an alternation of their reproductive mode. Aphids detect photoperiod shortening by sensing the length of the night and switch from viviparous parthenogenesis in spring and summer, to oviparous sexual reproduction in autumn. The photoperiodic signal is transduced from the head to the reproductive tract to change the fate of the future oocytes from mitotic diploid embryogenesis to haploid formation of gametes. This process takes place in three consecutive generations due to viviparous parthenogenesis. To understand the molecular basis of the switch in the reproductive mode, transcriptomic and proteomic approaches were used to detect significantly regulated transcripts and polypeptides in the heads of the pea aphid Acyrthosiphon pisum. RESULTS: The transcriptomic profiles of the heads of the first generation were slightly affected by photoperiod shortening. This suggests that trans-generation signalling between the grand-mothers and the viviparous embryos they contain is not essential. By analogy, many of the genes and some of the proteins regulated in the heads of the second generation are implicated in visual functions, photoreception and cuticle structure. The modification of the cuticle could be accompanied by a down-regulation of the N-beta-alanyldopamine pathway and desclerotization. In Drosophila, modification of the insulin pathway could cause a decrease of juvenile hormones in short-day reared aphids. CONCLUSION: This work led to the construction of hypotheses for photoperiodic regulation of the switch of the reproductive mode in aphids.

Alteration of endothelium-mediated vasodilator response in the rat hindlimb vasculature consecutive to chronic hypoxic stress: NO and EDHF involvement.

The previously documented impairment of hindlimb blood flow consecutive to chronic hypoxia might be related to endothelial vasomotor dysfunction. The aim of this study was to assess in-vivo the effect of chronic hypoxic stress on endothelium-mediated vasodilator response of hindlimb vascular bed, especially as regards to endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide (NO) pathway contribution. Dark Agouti rats were randomly assigned to live at barometric pressure approximately 760 mmHg (N rats) or approximately 550 mmHg (CH rats). Under anesthesia, catheters were placed in the carotid artery for arterial pressure measurement, and in the saphenous vein and iliac artery for drug delivery. Hindlimb blood flow (HBF) was measured by transit-time ultrasound flowmetry, at baseline and during endothelium-dependent vasodilator response induced by intra-arterial injection of acetylcholine (0.75 ng and 7.5 ng) with and without specific blockers of NOS (L-NAME) and EDHF (Charybdotoxin+Apamin). HBF and hindlimb vascular conductance changes in response to ACh infusion were significantly lower in CH than in N rats. The mechanisms responsible for this blunted response involved impairment in both NO pathway and EDHF. The chronic hypoxia-induced alteration of NO pathway was mainly related to the bioavailability of its substrate l-Arginine, since the infusion of l-Arginine restored the endothelial response to ACh in CH rats to the level of N rats. These results demonstrate that the impairment in endothelium-mediated vasodilator response of the hindlimb vascular tree induced by chronic hypoxic stress involves both NO and EDHF.

Does selenium exert cardioprotective effects against oxidative stress in myocardial ischemia?

In the mid-1960s, a small number of scientists postulated the role of oxidative stress and oxygen-derived free radicals in the pathophysiological mechanisms underlying ischemic heart disease. However, because of the technical difficulty of measuring free radicals and quantitating oxidative damage, it was very difficult to prove that free radicals could contribute to cell pathology. The role of oxidative stress in biological systems was not definitely recognized until the early 1980s when measurement of short-lived oxygen-derived reactive species was made possible by the advent of sophisticated techniques such as EPR spectroscopy or fluorescent probes. These enabled both the study of free radical biochemistry and the acquisition of useful information about the nature and consequences of free radical-induced protein and lipid oxidation. The hypothesis that reactive oxygen species mediate cellular damage produced upon reperfusion of ischemic myocardium has gained considerable support during the past 10-15 years. Several experimental studies indicated that the administration of antioxidant enzymes or non-enzymatic antioxidants offers a significant degree of protection against ischemic damage, improving functional recovery and reducing morphological alterations to cardiomyocytes. In this context, selenium, as an essential component of glutathione peroxidase, plays a critical role in protecting aerobic tissues from oxygen radical-initiated cell injury.

Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity.

This study aimed to determine the changes in soleus myofibrillar ATPase (m-ATPase) activity and myosin heavy chain (MHC) isoform expression after endurance training and/or chronic hypoxic exposure. Dark Agouti rats were randomly divided into four groups: control, normoxic sedentary (N; n = 14), normoxic endurance trained (NT; n = 14), hypoxic sedentary (H; n = 10), and hypoxic endurance trained (HT; n = 14). Rats lived and trained in normoxia at 760 mmHg (N and NT) or hypobaric hypoxia at 550 mmHg (approximately 2,800 m) (H and HT). m-ATPase activity was measured by rapid flow quench technique; myosin subunits were analyzed with mono- and two-dimensional gel electrophoresis. Endurance training significantly increased m-ATPase (P < 0.01), although an increase in MHC-I content occurred (P < 0.01). In spite of slow-to-fast transitions in MHC isoform distribution in chronic hypoxia (P < 0.05) no increase in m-ATPase was observed. The rate constants of m-ATPase were 0.0350 +/- 0.0023 s(-1) and 0.047 +/- 0.0050 s(-1) for N and NT and 0.033 +/- 0.0021 s(-1) and 0.038 +/- 0.0032 s(-1) for H and HT. Thus, dissociation between variations in m-ATPase and changes in MHC isoform expression was observed. Changes in fraction of active myosin heads, in myosin light chain isoform (MLC) distribution or in MLC phosphorylation, could not explain the variations in m-ATPase. Myosin posttranslational modifications or changes in other myofibrillar proteins may therefore be responsible for the observed variations in m-ATPase activity.

Aortic vasoconstriction related to smooth muscle cells ET-A and ET-B receptors is not involved in hypoxia-induced sustained systemic arterial hypertension in rats.

OBJECTIVES: We report in the present study the role of endothelin (ET-1) and ET-1 receptors in the sustained hypoxia-induced systemic hypertension. METHODS: Wistar rats were randomly assigned to live continuously in hypobaric hypoxia (CH rats) or normoxia (N rats). At the end of hypoxic stress exposure (5 weeks at 450 mm Hg), measurements of mean systemic arterial pressure were done. The effects of ET-1 in the presence or not of the endothelium and/or of specific ET-A inhibitors (BQ-123) or ET-B inhibitors (BQ-788), have been investigated in an isolated model of rat thoracic aorta. Finally, plasmatic ET-1 concentrations have been determined by assay procedure. RESULTS: Following five weeks of chronic hypoxic stress, CH rats presented a significant increase of mean systemic arterial pressure (N: 129.1+/-6.8 mm Hg vs CH: 152.5+/-3.4 mm Hg; P<0.05). Despite of this hypoxia-induced hypertension, ET-1 plasmatic concentration was not different between N and CH rats. Finally, CH rats presented a reduce response to ET-1 when compared to N rats. This phenomenon seems to be associated to the ET-A vascular smooth muscle cell receptors, since difference between N and CH rats was still present in endothelium denuded aortic rings in the presence or not of the specific ET-B inhibitors (BQ-788). In addition, in the presence of the specific ET-A inhibitor (BQ-123) response to ET-1 was abolished in N and CH rats to the same extent (N:-98%; CH:-99%). CONCLUSION: This work clearly suggests that, following long term exposure to hypoxia, ET-1 and ET-1 receptors are not involved in the persistence of systemic hypertension in a rat model, and that chronic exposure to severe hypoxic stress was associated with a downregulation of the ET-A receptors response to ET-1.

Alterations of beta3-adrenoceptors expression and their myocardial functional effects in physiological model of chronic exercise-induced cardiac hypertrophy.

Physical training induces cardiovascular autonomic nervous system regulation adaptations, which could result from beta adrenergic receptor (AR) modifications. Among them, beta(3 )AR alterations have been recently reported but their functional effect remained to discuss. To explain the beta(3) AR gene expression in relation to function, we simultaneously studied the left ventricle (LV) beta(3) AR mRNA and protein levels and the myocardial functional effects of a beta(3) AR agonist following physical training. Forty rats were assigned to either a control (C; N = 20) or a trained (T; N = 20) group. The treadmill running protocol was performed for 8 weeks. Histological measurements on LV slices were quantified. The beta(3) AR mRNA abundance was studied with RT-PCR and beta(3) AR protein density with Western-Blot analysis. Myocardial functional effects of a beta(3) AR agonist, BRL37344 (10(-8) M), were studied in Langendorff-perfused hearts. Histological data confirmed the adapted patterns of the physiological cardiac hypertrophy observed in T (P < 0.01), with a significant increase in arteries density (P < 0.01) and an unchanged collagen concentration. The beta(3) AR protein density was increased in T (154 +/- 38% in T vs. 100 +/- 24% in C; P < 0.05), but no change was noted concerning the beta(3) AR mRNA level. After BRL37344 perfusion LVDP, +dP/dT and -dP/dT, in C (P < 0.01), and only +dP/dT in T (P < 0.05) were decreased. Moreover, all LV hemodynamic parameters were more altered after BRL37344 in C than in T (P < 0.01).Thus, in this physiological model of cardiac hypertrophy, an increase of beta(3) AR density without beta(3) AR mRNA alteration was observed. Classical negative myocardial lusitropic and inotropic effects induced by a specific agonist of beta(3) AR were diminished in trained rats.

Effects of high-altitude exercise training on contractile function of rat skinned cardiomyocyte.

OBJECTIVE: Previous studies have questioned whether there is an improved cardiac function after high-altitude training. Accordingly, the present study was designed specifically to test whether this apparent blunted response of the whole heart to training can be accounted for by altered mechanical properties at the cellular level. METHODS: Adult rats were trained for 5 weeks under normoxic (N, NT for sedentary and trained animals, respectively) or hypobaric hypoxic (H, HT) conditions. Cardiac morphology and function were evaluated by echocardiography. Calcium Ca2+ sensitivity of the contractile machinery was estimated in skinned cardiomyocytes isolated from the left ventricular (LV) sub-epicardium (Epi) and sub-endocardium (Endo) at short and long sarcomere lengths (SL). RESULTS: Cardiac remodelling was harmonious (increase in wall thickness with chamber dilatation) in NT rats and disharmonious (hypertrophy without chamber dilatation) in HT rats. Contrary to NT rats, HT rats did not exhibit enhancement in global cardiac performance evaluated by echocardiography. Stretch- dependent Ca2+ sensitization of the myofilaments (cellular index of the Frank-Starling mechanism) increased from Epi to Endo in N rats. Training in normoxic conditions further increased this stretch-dependent Ca2+ sensitization. Chronic hypoxia did not significantly affect myofibrilar Ca2+ sensitivity. In contrast, high-altitude training decreased Ca2+ sensitivity of the myofilaments at both SL, mostly in Endo cells, resulting in a loss of the transmural gradient of the stretch-dependent Ca2+ sensitization. Expression of myosin heavy chain isoforms was affected both by training and chronic hypoxia but did not correlate with mechanical data. CONCLUSIONS: Training at sea level increased the transmural gradient of stretch-dependent Ca2+ sensitization of the myofilaments, accounting for an improved Frank-Starling mechanism. High-altitude training depressed myofilament response to Ca2+, especially in the Endo layer. This led to a reduction in this transmural gradient that may contribute to the lack of improvement in LV function via the Frank-Starling mechanism.

Chronic exercise does not prevent hypoxia-induced increased aortic sensitivity to endothelin in rats.

OBJECTIVES: We report in the present study the effect of regular exercise on vascular reactivity alterations to endothelin (ET-1) following prolonged exposure to hypoxic stress. METHODS: Male Dark Agouti rats were randomly assigned to N (sedentary rats), NCE (normoxic exercised rats), CH (chronic hypoxic sedentary rats) and CHCE (chronic hypoxic exercised rats) groups. The effects of ET-1 in the presence or not of the endothelium and/or of the specific inhibitor, bosentan, have been investigated in an isolated model of rat thoracic aorta. RESULTS: Prolonged exposure to hypoxia induced a significant increase in aortic sensitivity to ET-1 (-log ED50 in CH = 8.15 +/- 0.01 vs in N = 7.98 +/- 0.02, p < 0.05). Despite exercise training reduced the sensitivity to ET-1 in normoxic rats, it has no effects in hypoxic rats (-log ED50 in CH = 8.15 +/- 0.01 vs in CHCE = 8.19 +/- 0.01, NS). Moreover, although the removal of endothelium has no effect in N rats, it leads, in NCE rats, to a significant increase in sensitivity to ET-1 (-log ED50 in endothelium intact rings = 7.89 +/- 0.04 vs in denuded rings = 8.04 +/- 0.02, p < 0.05). The implication of ET-1 receptors on both endothelial and smooth muscle cells is confirmed by the significant reduced sensitivity to ET-1 in the four groups when bosentan is present in organ bath. CONCLUSION: Our study clearly suggests that part of the beneficial effect of chronic exercise could be mediated by enhancing endothelial function associated with endothelin reactivity in peripheric vessels. However, chronic exercise training does not seem to be able to limit the increased vasoconstriction to ET-1 stimulation induced by chronic hypoxia exposure.