The role of hypothalamic paraventricular nucleus (PVN) in cardiovascular regulation is well established. In this study, it was hypothesized that the PVN may be one of the sites of cardiovascular actions of a new angiotensin, angiotensin-(1-12). Experiments were carried out in urethane-anaesthetized, artificially ventilated, adult male Wistar rats. PVN was identified by microinjections of N-methyl-D-aspartic acid (NMDA, 10 mM). Microinjections (50 nl) of angiotensin-(1-12) (1 mM) into the PVN elicited increases in mean arterial pressure (MAP), heart rate (HR) and renal nerve activity (RSNA). The tachycardic responses to angiotensin-(1-12) were attenuated by bilateral vagotomy. The cardiovascular responses elicited by angiotensin-(1-12) were attenuated by microinjections of an angiotensin II type 1 receptor (AT1R) antagonist (losartan), but not AT2R antagonist (PD123319), into the PVN. Combined inhibition of angiotensin converting enzyme (ACE) and chymase in the PVN abolished angiotensin-(1-12)-induced responses. Angiotensin-(1-12)-immunoreactive cells and fibres were more numerous in the middle and caudal regions of the PVN. Angiotensin-(1-12) was present in many, but not all, vasopressinergic PVN cells. This peptide was also present in some non-vasopressinergic PVN cells but not in oxytocin containing PVN cells. These results indicated that: 1) microinjections of angiotensin-(1-12) into the PVN elicited increases in MAP, HR, and RSNA, 2) HR responses were mediated via both sympathetic and vagus nerves, 3) both ACE and chymase were needed to convert angiotensin-(1-12) to angiotensin II in the PVN, and 4) AT1Rs, but not AT2Rs, in the PVN mediated angiotensin-(1-12)-induced responses. It was concluded that the cardiovascular actions of angiotensin-(1-12) in the PVN are mediated via its conversion to angiotensin II.
blood pressure; captopril; chymostatin; heart rate; losartan; sympathetic nerve activity
Myocardial infarction (MI) results in cell death, development of interstitial fibrosis, ventricular wall thinning and ultimately, heart failure. Angiotensin-(1–7) [Ang-(1–7)] has been shown to provide cardioprotective effects. We hypothesize that lentivirus-mediated overexpression of Ang-(1–7) would protect the myocardium from ischaemic injury. A single bolus of 3.5 ×108 transducing units of lenti-Ang-(1–7) was injected into the left ventricle of 5-day-old male Sprague–Dawley rats. At 6 weeks of age, MI was induced by ligation of the left anterior descending coronary artery. Four weeks after the MI, echocardiography and haemodynamic parameters were measured to assess cardiac function. Postmyocardial infarction, rats showed significant decreases in fractional shortening and dP/dt (rate of rise of left ventricular pressure), increases in left ventricular end-diastolic pressure, and ventricular hypertrophy. Also, considerable upregulation of cardiac angiotensin-converting enzyme (ACE) mRNA was observed in these rats. Lentivirus-mediated cardiac overexpression of Ang-(1–7) not only prevented all these MI-induced impairments but also resulted in decreased myocardial wall thinning and an increased cardiac gene expression of ACE2 and bradykinin B2 receptor (BKR2). Furthermore, in vitro experiments using rat neonatal cardiac myocytes demonstrated protective effects of Ang-(1–7) against hypoxia-induced cell death. This beneficial effect was associated with decreased expression of inflammatory cytokines (tumour necrosis factor-α and interleukin-6) and increased gene expression of ACE2, BKR2 and interleukin-10. Our findings indicate that overexpression of Ang-(1–7) improves cardiac function and attenuates left ventricular remodelling post-MI. The protective effects of Ang-(1–7) appear to be mediated, at least in part, through modulation of the cardiac renin–angiotensin system and cytokine production.
Heat is the most abundant byproduct of cellular metabolism. As such, dynamic exercise in which a significant percentage of muscle mass is engaged generates thermoregulatory demands that are met in part by increases in skin blood flow. Increased skin blood flow during exercise adds to the demands on cardiac output and confers additional circulatory strain beyond that associated with perfusion of active muscle alone. Endurance exercise training results in a number of physiological adaptations which ultimately reduce circulatory strain and shift thermoregulatory control of skin blood flow to higher levels of blood flow for a given core temperature. In addition, exercise training induces peripheral vascular adaptations within the cutaneous microvasculature indicative of enhanced endothelium-dependent vasomotor function. However, it is not currently clear how (or if) these local vascular adaptations contribute to the beneficial changes in thermoregulatory control of skin blood flow following exercise training. The purpose of this Hot Topic review is to synthesize the literature pertaining to exercise training-mediated changes in cutaneous microvascular reactivity and thermoregulatory control of skin blood flow. In addition, we address mechanisms driving changes in cutaneous microvascular reactivity and thermoregulatory control of skin blood flow, and pose the question: what (if any) is the functional role of increased cutaneous microvascular reactivity following exercise training?
exercise training; physical activity; vascular adaptations; skin
Mice deficient in the transcription factor methyl-CpG-binding protein 2 (Mecp2), a mouse model of Rett syndrome, display reduced CO2 chemosensitivity, which may contribute to their breathing abnormalities. In addition, patients with Rett syndrome and male mice that are null for Mecp2 show reduced levels of brain serotonin (5-HT). Serotonin is known to play a role in central chemosensitivity, and we hypothesized that increasing the availability of 5-HT in this mouse model would improve their respiratory response to CO2. Here we determined the apnoeic threshold in heterozygous Mecp2-deficient female mice and examined the effects of blocking 5-HT reuptake on the CO2 response in Mecp2-null male mice. Studies were performed in B6.129P2(C)-Mecp2τm1.1Bird null males and heterozygous females. In an in situ preparation, seven of eight Mecp2-deficient heterozygous females showed arrest of phrenic nerve activity when arterial CO2 was lowered to 3%, whereas the wild-types maintained phrenic nerve amplitude at 53 ± 3% of maximal. In vivo plethysmography studies were used to determine CO2 chemosensitivity in null males. These mice were exposed sequentially to 1, 3 and 5% CO2. The percentage increase in minute ventilation in response to increased inspired CO2 was less in Mecp2−/y than in Mecp2+/y mice. Pretreatment with citalopram, a selective 5-HT reuptake inhibitor (2.5 mg kg−1 I.P.), 40 min prior to CO2 exposure, in Mecp2−/y mice resulted in an improvement in CO2 chemosensitivity to wild-type levels. These results suggest that decreased 5-HT in Mecp2-deficient mice reduces CO2 chemosensitivity, and restoring 5-HT levels can reverse this effect.
In this study we evaluated whether the activation of endogenous angiotensin-converting enzyme (ACE) 2 would improve the cardiovascular autonomic dysfunction of diabetic rats. Ten days after type 1 diabetes induction (Streptozotocin, STZ, 50mg/kg i.v.), the rats were orally treated with 1-[(2-dimethylamino)ethylamino]-4-(hydroxymethyl)-7-[(4-methylphenyl) sulfonyl oxy]-9H-xanthene-9-one (XNT), a newly discovered ACE2 activator (1mg/kg/day), or saline (equivalent volume) during 30 days. Autonomic cardiovascular parameters were evaluated in unanesthetized animals and an isolated heart preparation was used to analyze the cardiac function. Diabetes induced a significant decrease in the baroreflex bradycardia sensibility, as well as in the chemoreflex chronotropic response and parasympathetic tone. The XNT treatment improved these parameters by ~76% (0.82±0.09 vs. 1.44±0.17ΔPI/ΔmmHg), ~85% (−57±9 vs. −105±10 Δbpm) and ~205% (22±2 vs. 66±12 Δbpm), respectively. Also, XNT administration enhanced the bradycardia induced by the chemoreflex activation by ~74% in non-diabetic animals (−98±16 vs. −170±9 Δbpm). No significant changes were observed in the mean arterial pressure, baroreflex tachycardia sensibility, chemoreflex pressor response and sympathetic tone among any of the groups. Furthermore, chronic XNT treatment ameliorated the cardiac function of diabetic animals. However, the coronary vasoconstriction observed in diabetic rats was unchanged by ACE2 activation. These findings indicate that XNT protects against the autonomic and cardiac dysfunction induced by diabetes. Thus, our results evidenced the viability and effectiveness of oral administration of an ACE2 activator for the treatment of the cardiovascular autonomic dysfunction caused by diabetes.
Baroreflex; Chemoreflex; ACE2 activation
We tested the hypothesis that, among conditions of matched contractile work, shorter contraction durations and greater muscle fibre recruitment result in augmented skeletal muscle blood flow and oxygen consumption (V̇O2) during steady-state exercise in humans. To do so, we measured forearm blood flow (FBF; Doppler ultrasound) during 4 minutes of rhythmic handgrip exercise in 24 healthy young adults and calculated forearm V̇O2 via blood samples obtained from a catheter placed in retrograde fashion into a deep vein draining the forearm muscle. In Protocol 1 (n = 11), subjects performed rhythmic isometric handgrip exercise at mild and moderate intensities under conditions in which tension time index (TTI; isometric analog of work) was held constant but contraction duration was manipulated. In this protocol, shorter contraction durations led to greater FBF (184 ± 25 vs. 164 ± 25 ml·min-1) and V̇O2 (23 ± 3 vs. 17 ± 2 ml·min-1; both P <0.05) among mild workloads, whereas this was not the case for moderate intensity exercise. In Protocol 2 (n = 13), subjects performed rhythmic dynamic handgrip exercise at mild and moderate intensities under conditions of matched total work, but muscle fibre recruitment was manipulated. In this protocol, greater muscle fibre recruitment led to significantly greater FBF (152 ± 15 vs. 127 ±13 ml·min-1) and V̇O2 (20 ± 2 vs. 17 ± 2 ml·min-1; both P<0.05) at mild workloads and there was a trend for similar responses at the moderate intensity but this was not statistically significant. In both protocols, the ratio of the change in FBF to change in V̇O2 was similar across all exercise intensities and manipulations, and the strongest correlation among all variables was between V̇O2 and blood flow. Our collective data indicate that, among matched workloads, shorter contraction duration and greater muscle fibre recruitment augment FBF and V̇O2 during mild intensity forearm exercise, and that muscle blood flow is more closely related to metabolic cost (V̇O2) rather than contractile work per se during steady-state exercise in humans.
vasodilatation; metabolic cost; oxygen delivery
We hypothesize that moderate cardiac-selective overexpression of the angiotensin type 2 receptor (AT2R) would protect the myocardium from ischemic injury after a myocardial infarction (MI) induced by coronary artery ligation.
METHODS AND RESULTS
For the in vitro studies, Ad-G-AT2R-EGFP was used to overexpress AT2R in rat neonatal cardiac myocytes (RNCM). Expression of AT2R, measured by real-time PCR and immunostaining demonstrated efficient transduction of AT2R in a dose-dependent pattern. AT2R constitutively induced apoptosis in RNCM in dose-dependent patterns. For the in vivo studies, 4×1010 vector genome (vg) of rAAV9-CBA-AT2R was injected into the left ventricle chamber of the heart in 5-day-old Sprague-Dawley rats. At six weeks of age, hearts were harvested and expression of AT2R determined by real time PCR and western blotting. Expression was increased one fold over controls and no apoptosis was detected. Two subsequent in vivo studies were performed. In a prevention study 4×1010 vg of rAAV9-CBA-AT2R was injected into the left ventricle chamber of the heart in 5-day-old Sprague-Dawley rats and MI was induced at six week of age. For a post treatment study 4×1010 vg of rAAV9-CBA-AT2R was administrated to the peri-infarcted myocardium area immediately after MI in six week old animals. For both in vivo studies, cardiac functions were assessed using echocardiography and hemodynamic measurements four weeks after coronary artery ligation. In the in vivo studies the MI rats showed significant decreases in fractional shortening and dP/dt with an increased left ventricular end diastolic pressure and a ventricular hypertrophy. For the prevention study, the moderate cardiac-selective overexpression of AT2R attenuated the above MI-induced impairments and also caused a decrease in ventricular wall thinning. In the post treatment study, the overexpression of AT2R partially reversed the MIinduced cardiac dysfunction. MI also induced the up-regulation of AT1R, ACE, and Collagen I mRNA expression, all of which were attenuated by the overexpression of AT2R.
Moderate cardiac-selective overexpression of AT2R protects heart function from ischemic injury, which may be mediated, at least in part, through modulation of components of the cardiac RAS and collagen levels in the myocardium.
Myocardial infarction; Angiotension type 2 receptor; Apoptosis; Gene Therapy
House dust mite (HDM) is a major source of allergen in house dust and has been suggested to be involved in the pathogenesis of asthma. In this study, we aimed to investigate whether HDM can modulate the sensitivity of pulmonary sensory neurons, and if so, to elucidate the underlying mechanism. Fura-2 based ratiometric Ca2+ imaging was carried out to determine the effect of HDM extract on the capsaicin-evoked Ca2+ transient in mouse vagal pulmonary sensory neurons. Pretreatment with HDM (50 μg/ml, 5 min) significantly enhanced the Ca2+ transient evoked by capsaicin in these neurons isolated from wildtype mice. This potentiating effect of HDM was not antagonized by E-64, a selective cysteine protease inhibitor, but was completely prevented by AEBSF, a specific serine protease inhibitor. In addition, the potentiating effect of HDM on capsaicin-evoked Ca2+ transient was absent in the pulmonary sensory neurons isolated from protease-activated receptor-2 (PAR2) knockout mice. Further, the sensitizing effect of HDM was completely abolished by U73122, a PLC inhibitor, or chelerythrine, a PKC inhibitor. In summary, our results demonstrate that HDM, mainly through its serine protease activity, potentiates capsaicin-evoked Ca2+ transient in mouse pulmonary sensory neurons via the activation of PAR2 and PLC-PKC intracellular transduction cascade.
House dust mite; protease-activated receptor; pulmonary chemosensitivity
Ataxia telangiectasia mutated kinase (ATM) is involved in cell cycle checkpoints, DNA repair and apoptosis. β-adrenergic receptor (β-AR) stimulation induces cardiac myocyte apoptosis. Here we analyzed basal myocardial structure and function in ATM knockout (KO) mice, and tested the hypothesis that ATM modulates β-AR-stimulated myocyte apoptosis. Left ventricular (LV) structure and function, myocyte apoptosis, fibrosis and expression of fibrosis-, hypertrophy- and apoptosis-related proteins were examined in wild-type (WT) and KO mice with or without L-isoproterenol treatment for 24h. Body and heart weights were lower in KO mice. M-mode echocardiography showed reduced septal wall thicknesses and LV diameters in KO mice. Doppler echocardiography showed increased ratio of early peak velocity (E wave) to that of the late (A wave) LV filling in KO mice. Basal fibrosis and myocyte cross-sectional area was greater in KO hearts. Expression of fibrosis-related genes (CTGF, PAI-1 and MMP-2) and hypertrophy-related gene (ANP) was higher in KO hearts. β-AR stimulation increased myocyte apoptosis to a similar extent in both groups. Activation of JNKs, and expression and phosphorylation of p53 in response to β-AR stimulation was only observed in WT group. Akt phosphorylation was lower in KO-sham and remained lower following β-AR stimulation in KO group. β-AR stimulation activated GSK-3β to a similar extent in both groups. Thus, lack of ATM induces structural and functional changes in the heart with enhanced myocardial fibrosis and myocyte hypertrophy. β-AR-stimulated apoptosis in WT hearts is associated with p53- and JNKs-dependent mechanism, while decreased Akt activity may play a role in increased myocyte apoptosis in the absence of ATM.
ATM; apoptosis; heart; AKT; p53
Cough and swallow are airway protective behaviors. The pharyngeal phase of swallow prevents aspiration of oral material (saliva, food and liquid), by epiglottal movement, laryngeal adduction, and clearing of the mouth and pharynx. Cough is an aspiration-response behavior which removes material from the airway. Coordination of these behaviors is vital to protect the airway from further aspiration-promoting events, such as a swallow occurring during the inspiratory phase of cough. The operational characteristics, primary strategies, and peripheral inputs which coordinate cough and swallow are unknown. This lack of knowledge impedes understanding and treatment of deficits in airway protection, such as the co-occurrence of dystussia and dysphagia common in Parkinson's and Alzheimer's diseases, as well as stroke.
Cyclo-oxygenase (COX) enzymes are responsible for the formation from arachidonic acid of prostaglandins, among other metabolites. Prior studies have suggested that inhibition of the COX pathway attenuates the responses of sympathetic nerve activity and blood pressure during static muscle contraction. Static muscle contraction activates the exercise pressor reflex, which in turn increases sympathetic nerve activity and blood pressure. Also, COX products contribute to exaggeration of the exercise pressor reflex in heart failure (HF). This dysfunction of the exercise pressor reflex has previously been shown to be mediated primarily by muscle mechanoreflex overactivity. It is well known that COX-1 and COX-2 are two isoforms of the enzyme that lead to formation of these important biological mediators involved in the muscle reflex. Thus, in the present study, we determined whether the COX-1 and/or COX-2 pathway contribute(s) to the augmented mechanoreflex activity in HF. First, Western blot analysis was employed to examine protein expression of COX-1 and COX-2 in skeletal muscle tissue of control rats and rats with HF induced by myocardial infarction. Our data show that there is no significant difference in COX-1 expression in both experimental groups. However, COX-2 displays significant overexpression in rats with HF compared with control rats (optical density 1.06 ± 0.05 in control and 1.6 ± 0.05 in HF, P < 0.05 versus control). Second, the mechanoreflex was evoked by passive tendon stretch, and the reflex sympathetic and pressor responses to muscle stretch were examined after COX-1 and COX-2 inhibitors (FR-122047 and SC-236) were individually injected into the arterial blood supply of the hindlimb muscles. The results demonstrate that the stretch-evoked reflex responses in rats with HF were significantly attenuated by administration of SC-236, but not by FR-122047, i.e. renal sympathetic nerve activity and mean arterial pressure responses evoked by 0.5 kg of muscle tension were 52.3 ± 8.9% and 19 ± 1.4 mmHg, respectively, in control conditions and 26.4 ± 5.6% and 5.7 ± 1.6 mmHg (P < 0.05 versus control group) after 0.25 mg kg−1 of SC-236. Muscle stretch-evoked renal sympathetic nerve activity and mean arterial pressure responses were 51.8 ± 8.2% and 18.7 ± 1.2 mmHg, respectively, in control conditions and 48.3 ± 5.3% and 17.5 ± 1.9 mmHg (P > 0.05 versus control group) after 1.0 mg kg−1 of FR-122047. Accordingly, the results obtained from this study support our hypothesis that heightened COX-2 expression within the hindlimb muscles contributes to the exaggerated muscle mechanoreflex in congestive HF.
The demographics of ageing are changing dramatically such that there will be many more older adults in the near future. This setting likely will produce a new “boomer-driven” epidemic of physiological dysfunction, disability and risk of chronic degenerative disorders, including cardiovascular diseases (CVD). Standing out against this dreary biomedical forecast are Masters athletes, a group of middle-aged and older adults who engage in regular vigorous physical training and competitive sport. Compared with their sedentary/less active (untrained) peers, Masters athletes who perform endurance training-based activities demonstrate a more favorable arterial function-structure phenotype, including lower large elastic artery stiffness, enhanced vascular endothelial function and less arterial wall hypertrophy. As such, they may represent an exemplary model of healthy or “successful” vascular ageing. In contrast, Masters athletes engaged primarily/exclusively in intensive resistance training exhibit less favorable arterial function-structure than their endurance-trained peers and, in some instances, untrained adults. These different arterial properties likely are explained in large part by the different intravascular mechanical forces generated during endurance vs. resistance exercise-related training activities. The more favorable arterial function-structure profile of Masters endurance athletes may contribute to their low risk of clinical CVD.
arterial stiffness; endothelium
This study investigated the effect of changes in inspiratory intrathoracic pressure (ITP) on stroke volume (SV) at rest and during moderate exercise in patients with heart failure and reduced ejection fraction (HFREF) as well as healthy individuals.
Methods and Results
SV was obtained by echocardiography during 2 minutes of spontaneous breathing (S), 2 progressive levels of inspiratory unloading (UL1 and UL2) using a ventilator, and 2 progressive levels of inspiratory loading using resistors in 11 patients with HFREF (61±9 years, EF: 32±4 %, NYHA class I-II) and 11 age-matched healthy individuals at rest and during exercise at 60% of maximal aerobic capacity on a semi-recumbent cycle ergometer. At rest, inspiratory unloading progressively decreased stroke volume index (SVI) (S: 35.2 ± 5.4, UL1: 33.3 ± 5.1, UL2: 32.2 ± 4.4 ml/m2) in healthy individuals while it increased SVI (S: 31.4 ± 4.6, UL1: 32.0 ± 5.9, UL2: 34.0 ± 7.2 ml/m2) in patients with HFREF (p=0.04). During moderate exercise, inspiratory unloading similarly decreased SVI (S: 43.9 ± 7.1, UL1: 40.7 ± 4.7, UL2: 39.9 ± 3.7 ml/m2) in healthy individuals while it increased SVI (S: 40.8 ± 6.5, UL1: 42.8 ± 6.9, UL2: 44.1 ± 4.8 ml/m2) in patients with HFREF (p=0.02). Inspiratory loading did not significantly change SVI at rest or during moderate exercise in both groups.
Inspiratory unloading improved SVI at rest and during moderate exercise in patients with HFREF, possibly due to a reduction in LV afterload.
afterload; left ventricular dysfunction; cardiorespiratory
Interstitial cells of Cajal (ICC) generate electrical pacemaker activity in gastrointestinal (GI) smooth muscles. We investigated whether Tmem16a, which encodes Anoctamin 1 (ANO1), a Ca2+-activated Cl− channel might be involved in pacemaker activity in ICC. Tmem16a transcripts and ANO1 were expressed robustly in GI muscles, specifically in ICC in murine, non-human primate (Macaca fascicularis) and human GI tracts. Splice variants of Tmem16a are expressed in GI muscles, as well as other paralogues of the Tmem16 family. Ca2+-activated Cl− (CaCC) channel blocking drugs, niflumic acid and 4,4′-diisothiocyano-2,2′-stillbene-disulfonic acid (DIDS), blocked slow waves in intact muscles of mouse, primate, and human small intestine and stomach. Slow waves failed to develop in Tmem16a knock-out mice (Tmem16atm1Bdh/tm1Bdh). The pacemaker mechanism was investigated in isolated ICC from transgenic mice with constitutive expression of copGFP. Depolarization of ICC activated inward currents due to a Cl− selective conductance. Removal of extracellular Ca2+, replacement of Ca2+ with Ba2+, or extracellular Ni2+ (30 μm) blocked the inward current. Single Ca2+-activated Cl− channels with a unitary conductance of 7.8 pS were resolved in excised patches from ICC. The inward current was blocked in a concentration-dependent manner by niflumic acid (IC50 = 4.8 μm). The role of ANO1 in cholinergic responses in ICC was also investigated. CCh activated Ca2+-activated Cl− currents in ICC, and responses to cholinergic nerve stimulation were blocked by niflumic acid in intact muscles. ANO1 is a prominent conductance in ICC and these channels appear to be involved in pacemaker activity and in responses to enteric excitatory neurotransmitters.
Interstitial cells of Cajal; electrical rhythmicity; smooth muscle; gastrointestinal motility; enteric nervous system; Tmem16a
To assess the effects of exercise on liver and brain bioenergetic infrastructures, we exposed C57BL/6 mice to 6 weeks of moderate-intensity treadmill exercise. During the training period, fasting blood glucose was lower in exercised mice than in sedentary mice, but serum insulin levels were not reduced. At week 6, trained mice showed a paradoxical decrease in plasma lactate during exercise, which was accompanied by an increase in the liver monocarboxylate transporter 2 protein level (~30%, P < 0.05). Exercise increased liver peroxisomal proliferator-activated receptor-γ coactivator 1α expression (approximately twofold, P < 0.001), NAD-dependent deacetylase sirtuin-1 protein (~30%, P < 0.05), p38 protein (~15%, P < 0.05), cytochrome c oxidase subunit 4 isoform 1 protein (~50%, P < 0.05) and AMP-activated protein kinase phosphorylation (~40%, P < 0.05). Despite this, liver mitochondrial DNA copy number (~30%, P = 0.05), mitochondrial transcription factor A expression (~15%, P < 0.05), cytochrome c oxidase subunit 2 expression (~10%, P < 0.05), cAMP-response element binding protein phosphorylation (~60%, P < 0.05) and brain-derived neurotrophic factor expression (~40%, P < 0.05) were all reduced, while cytochrome oxidase and citrate synthase activities were unchanged. The only altered brain parameter observed was a reduction in tumour necrosis factor α expression (~35%, P < 0.05); tumour necrosis factor α expression was unchanged in liver. Our data suggest that lactate produced by exercising muscle modifies the liver bioenergetic infrastructure, and enhanced liver uptake may in turn limit the ability of exercise-generated lactate to modify brain bioenergetics. Also, it appears that, at least in the liver, a dissociated mitochondrial biogenesis, in which some components are strategically enhanced while others are minimized, can occur.
Hypertension caused by chronic infusion of angiotensin II (AngII) in experimental animals is dependent, in part, on increased activity of the sympathetic nervous system. This chronic sympathoexcitatory response is amplified by a high salt diet suggesting an interaction of circulating AngII and dietary salt on sympathetic regulatory pathways in the brain. The present study tested the hypothesis that the subfornical organ (SFO), a forebrain circumventricular organ known to be activated by circulating AngII, is crucial to the pathogenesis of hypertension induced by chronic AngII administration in rats on a high salt diet (AngII-salt model). Rats were randomly selected to undergo either subfornical organ lesion (SFOx) or sham surgery (SHAM) and then placed on a high salt (2% NaCl) diet. One week later rats were instrumented for radiotelemetric measurement of mean arterial pressure (MAP) and heart rate (HR) and placed in metabolic cages to measure sodium and water balance. Baseline MAP was slightly (but not statistically) lower in SFOx compared to SHAM rats during the 5 day control period. During the subsequent 10 days of AngII administration, MAPwas statistically lower in SFOx rats. However, when MAP responses to AngII were analyzed by comparing the change from the 5 day baseline period, only on the 5th day of AngII was MAP significantly different between groups. There were no differences between groups for water or sodium balance throughout the protocol. We conclude that, although the SFO is required for the complete expression of AngII-salt hypertension in the rat, other brains sites are also involved.
sympathetic; telemetry; blood pressure; angiotensin; brain; subfornical organ
The Cystic Fibrosis Transmembrane Conductance Regulator, CFTR, is both an anion channel and a regulator of other transport proteins. CFTR gene mutations underlie the human disease, Cystic Fibrosis (CF). The most common CFTR mutation, ΔF508, produces a misfolded protein which traffics improperly. The availability of transgenic CFTRΔF508/ΔF508 pigs allows measurement of the impact of ΔF508 in native tissue. Thyroid epithelia respond to cAMP-elevating agents by increasing anion transport, a process hinging on functional CFTR. To assess whether endogenous levels of ΔF508 CFTR mediate thyroid transport, primary thyroid epithelial cultures (pThECs) were grown from newborn CFTR+/+ (WT) and CFTRΔF508/ΔF508 (ΔF) pig thyroids and the stimulated, secretory components of short-circuit current (Isc) compared. Surface biotinylation studies assessed the surface presentation of ΔF508 CFTR. Baseline Isc levels of both wt and ΔF pThECs consisted of an amiloride-sensitive component. In ΔF pThECs, this mirrored previous measurements in CFTR−/− (KO) pThECs. Surprisingly, elevation of cAMP transiently increased Isc to peak levels ~ 65% those achieved by wt. In contrast, KO pThECs were indifferent to cAMP activation. In ΔF pThECs, total ΔF508 CFTR expression was ~ 9% that of WT, consistent with misfolding and enhanced degradation. Surface biotinylation studies indicated that ~ 4% of the total ΔF508 resided at the surface and did not increase with cAMP elevation. The present findings show that low endogenous levels of pig ΔF508 CFTR can mediate substantial anion transport by thyroid epithelia. These data suggest that both wt and ΔF508-CFTR regulate additional, thyroid transporters, and together coordinate the overall Isc response.
CFTR; mutation; chloride secretion; membrane surface
The Murphy Roths Large (MRL) mouse, a strain capable of regenerating right ventricular myocardium, has a high post-myocardial infarction (MI) survival rate compared with C57BL/6J (C57) mice. The biological processes responsible for this survival advantage are unknown. To assess the effect of genetic background, the LG/J strain, which harbors 75% of the MRL composite genome, was included in the study. The MRL survival advantage versus C57 mice (92% vs. 68%, P < 0.05) occurred primarily in the first 5 days; LG/J survival was intermediate (P = NS). Microarray data analysis revealed an attenuation of apoptotic (P < 0.05) and stress response transcripts in MRL hearts compared with C57 hearts after MI. Supporting the microarray results, there were fewer TUNEL-positive cells 1 day post-MI in MRL infarcts compared with C57 infarcts (P = 0.001) and fewer CD45-positive cells in the MRL infarct border zone 2 days post-MI (P < 0.01). LG/J results were intermediate (P = NS). MRL hearts had smaller infarct scars and attenuated ventricular dilation 30 days post-MI compared with C57 hearts (P < 0.05). We conclude that the early post-MI survival advantage of MRL mice over the C57 strain is mediated at least in part by reductions in apoptosis and inflammatory infiltration, and that these reductions may influence chronic remodeling. The intermediate survival, apoptosis and inflammation profile of LG/J mice suggests this high tolerance for MI in the MRL could be derived from its shared genetic background with the LG/J.
Heart; inflammation; ischaemia
After considerable debate and key experimental evidence, the importance of the arterial baroreflex in contributing to and maintaining the appropriate neural cardiovascular adjustments to exercise is now well accepted. Indeed, the arterial baroreflex resets during exercise in an intensity-dependent manner to continue to regulate blood pressure as effectively as at rest. Studies have indicated that the exercise resetting of the arterial baroreflex is mediated by both the feed-forward mechanism of central command and the feed-back mechanism associated with skeletal muscle afferents (the exercise pressor reflex). Another perhaps less appreciated neural mechanism involved in evoking and maintaining neural cardiovascular responses to exercise is the cardiopulmonary baroreflex. The limited information available regarding the cardiopulmonary baroreflex during exercise provides evidence for a role in mediating sympathetic nerve activity and blood pressure responses. In addition, recent investigations have demonstrated an interaction between cardiopulmonary baroreceptors and the arterial baroreflex during dynamic exercise, which contributes to the magnitude of exercise-induced increases in blood pressure as well as the resetting of the arterial baroreflex. Furthermore, neural inputs from the cardiopulmonary baroreceptors appear to play an important role in establishing the operating point of the arterial baroreflex. This symposium review will highlight recent studies in these important areas indicating that the interactions of four neural mechanisms (central command, the exercise pressor reflex, the arterial baroreflex and cardiopulmonary baroreflex) are integral in mediating the neural cardiovascular adjustments to exercise.
arterial blood pressure; baroreceptors; central blood volume; baroreflex resetting; muscle sympathetic nerve activity
Power spectral analysis of heart rate variability (HRV) has been used frequently to assess cardiac autonomic function; however, the relationship of low frequency (LF) power of HRV to cardiac sympathetic tone has been unclear. With or without adjustment for high frequency (HF) power, total power, or respiration, LF power seems to provide an index not of cardiac sympathetic tone but of baroreflex function. Manipulations and drugs that change LF power or LF:HF may do so not by affecting cardiac autonomic outflows directly but by affecting modulation of those outflows by baroreflexes.
An in vitro motility assay approach was used to investigate the mechanisms of the functional differences between myosin isoforms, by studying the effect of MgATP and MgADP on actin sliding velocity (Vf) of pure slow and fast rat skeletal myosin at different temperatures. The value of Vf depended on [MgATP] according to Michaelis–Menten kinetics, with an apparent constant (Km) of 54.2, 64.4 and 200 μm for the fast isoform and 18.6, 36.5 and 45.5 μm for the slow isoform at 20, 25 and 35°C, respectively. The presence of 2 mm MgADP decreased Vf and yielded an inhibition constant (Ki) of 377, 463 and 533 μm for the fast isoform at 20, 25 and 35°C, respectively, and 120 and 355 μm for the slow isoform at 25 and 35°C, respectively. The analysis of Km and Ki suggested that slow and fast isoforms differ in the kinetics limiting Vf. Moreover, the higher sensitivity of the fast myosin isoform to a drop in [MgATP] is consistent with the higher fatigability of fast fibres than slow fibres. From the Michaelis–Menten relation in the absence of MgADP, we calculated the rate of actomyosin dissociation by MgATP (k+ATP) and the rate of MgADP release (k–ADP). We found values of k+ATP of 4.8 × 106, 6.5 × 106 and 6.6 × 106 M−1 s−1 for the fast isoform and 3.3 × 106, 2.9 × 106 and 6.7 × 106 M−1 s−1 for the slow isoform and values of k–ADP of 263, 420 and 1320 s−1 for the fast isoform and 62, 107 and 306 s−1 for the slow isoform at 20, 25 and 35°C, respectively. The results suggest that k–ADP could be the major determinant of functional differences between the fast and slow myosin isoforms at physiological temperatures.
In rats with salt-induced hypertension or post myocardial infarction (MI), AT1 receptor (AT1R) densities and oxidative stress increase and neuronal nitric oxide synthase (nNOS) levels decrease in the paraventricular nucleus (PVN). The present study was designed to determine whether these changes may depend on activation of the aldosterone – “ouabain” neuromodulatory pathway. After intracerebroventricular (icv) infusion of aldosterone (20ng/h) for 14 days, blood pressure (BP) and heart rate (HR) were recorded in conscious Wistar rats, and mRNA and protein for nNOS, endothelial NOS (eNOS), AT1R and NADPH oxidase subunits were assessed in brain tissue. BP and HR were significantly increased by aldosterone. Aldosterone significantly increased mRNA and protein of AT1R, P22phox, P47phox, P67phox and Nox2, and decreased nNOS but not eNOS mRNA and protein in the PVN, and increased angiotensin converting enzyme (ACE) and AT1R binding densities in the PVN and SON. The increases in BP and HR as well as changes in mRNA, proteins and ACE and AT1R binding densities were all largely prevented by concomitant icv infusion of Digibind (to bind “ouabain”) or benzamil (to block presumably epithelial sodium channels). These data indicate that aldosterone via “ouabain” increases in the PVN ACE, AT1R and oxidative stress but decreases nNOS, and suggest that endogenous aldosterone may cause this similar pattern of changes observed in salt sensitive hypertension and heart failure post MI.
brain aldosterone; NADPH oxidase; oxidative stress; NO; AT1R; “ouabain”; sodium channels
Ghrelin is a gut peptide that has been studied extensively for its role in food intake and energy balance. More recent studies show that ghrelin reduces water intake in rats and some non-mammalian species. Despite the importance of the regulation of NaCl intake in body fluid homeostasis, the effects of ghrelin on saline intake have not been investigated. Accordingly, we tested the effect of ghrelin on water and 1.8% NaCl intake in two-bottle test conditions under five stimuli that increase hypertonic saline intake: central angiotensin II administration, 24 h fluid deprivation, water deprivation followed by partial rehydration, dietary sodium deficiency, and polyethylene glycol administration combined with dietary sodium deficiency. We found that ghrelin attenuated saline intake stimulated by angiotensin II, by water deprivation followed by partial rehydration, and by dietary sodium deficiency. We did not detect an effect of ghrelin on saline intake after 24 h fluid deprivation without partial rehydration or after the combination of polyethylene glycol and dietary sodium deficiency. The finding that ghrelin reduced hypertonic saline intake under some, but not all, natriorexigenic conditions mirrors the previously published findings that in one-bottle tests of drinking, ghrelin reduces water intake under only some conditions. The results provide evidence for a new role for ghrelin in the regulation of body fluid homeostasis.
angiotensin; osmoregulation; fluid balance
We recently observed a marked increase in brachial artery (BA) diameter during prolonged leg cycling exercise. The purpose of the present study was to test the hypothesis that this increase in BA diameter during lower limb exercise is shear stress mediated. Accordingly, we determined whether recapitulation of cycling-induced BA shear rate with forearm heating, a known stimulus evoking shear-induced conduit artery dilatation, would elicit comparable profiles and magnitudes of BA vasodilatation to those observed during cycling. In 12 healthy men, BA diameter and blood velocity were measured simultaneously using Doppler ultrasonography at baseline and every 5 min during 60 min of either steady-state semi-recumbent leg cycling (120 W) or forearm heating. At the onset of cycling, the BA diameter was reduced (−3.9 ± 1.2% at 5 min; P < 0.05), but it subsequently increased throughout the remainder of the exercise bout (+15.1 ± 1.6% at 60 min; P < 0.05). The increase in BA diameter during exercise was accompanied by an approximately 2.5-fold rise in BA mean shear rate (P < 0.05). Similar increases in BA mean shear with forearm heating elicited an equivalent magnitude of BA vasodilatation to that observed during cycling (P > 0.05). Herein, we found that in the absence of exercise the extent of the BA vasodilator response was reproduced when the BA was exposed to comparable magnitudes of shear rate via forearm heating. These results are consistent with the hypothesis that shear stress plays a key role in signalling brachial artery vasodilatation during dynamic leg exercise.
New ideas about the relative importance of the autonomic nervous system (and especially its sympathetic arm) in long-term blood pressure regulation are emerging. It is well known that mean arterial blood pressure is normally regulated in a fairly narrow range at rest and that blood pressure is also able to rise and fall ‘appropriately’ to meet the demands of various forms of mental, emotional and physical stress. By contrast, blood pressure varies widely when the autonomic nervous system is absent or when key mechanisms that govern it are destroyed. However, 24 h mean arterial pressure is still surprisingly normal under these conditions. Thus, the dominant idea has been that the kidney is the main long-term regulator of blood pressure and the autonomic nervous system is important in short-term regulation. However, this ‘renocentric’ scheme can be challenged by observations in humans showing that there is a high degree of individual variability in elements of the autonomic nervous system. Along these lines, the level of sympathetic outflow, the adrenergic responsiveness of blood vessels and individual haemodynamic patterns appear to exist in a complex, but appropriate, balance in normotension. Furthermore, evidence from animals and humans has now clearly shown that the sympathetic nervous system can play an important role in longer term blood pressure regulation in both normotension and hypertension. Finally, humans with high baseline sympathetic traffic might be at increased risk for hypertension if the ‘balance’ among factors deteriorates or is lost. In this context, the goal of this review is to encourage a comprehensive rethinking of the complexities related to long-term blood pressure regulation in humans and promote finer appreciation of physiological relationships among the autonomic nervous system, vascular function, ageing, metabolism and blood pressure.