- Email: [email protected]
Cardiovascular autonomic regulation in mice overexpressing the vesicular acetylcholine transporter (VAChT) gene
Abstracts / Autonomic Neuroscience: Basic and Clinical 192 (2015) 56–141
However, there is still no direct evidence to show that in utero exposure to smoking alters the dynamics of cardiac autonomic control in sleeping preterm neonates. Methods and Results: We studied healthy, preterm neonates (postmenstrual age: 36.2 ± 0.9 weeks) born to mothers who had smoked throughout pregnancy but not since birth (n = 16). In uteroexposed neonates were matched with control preterm neonates born to nonsmoking mothers (n = 18). Cardiac autonomic control was monitored as a function of the sleep state by assessing heart rate variability with both linear and non-linear methods. Preterm neonates with in utero exposure to smoking displayed alterations (relative to control neonates) in short-term cardiac autonomic control in all sleep states. These alterations included low vagal activity, elevated sympathetic activity, and low complexity and adaptability in heart rate control dynamics. Conclusion: Our results constitute direct evidence that cardiac autonomic activity and control are altered in preterm infants exposed to smoking in utero. These alterations may place the affected infants at a higher risk of neurological and cardiovascular complications, which could conceivably persist throughout childhood and adulthood. doi:10.1016/j.autneu.2015.07.075
P5.24 Inhibition of Protein Kinase C Signalling On Cardiac Noradrenaline Uptake in the Spontaneously Hypertensive Rat Julia Shanks, Jamie Mahwhinny, David J. Paterson Burdon Sanderson Cardiac Centre Department of Physiology, Anatomy and Genetics, Sherrington Building, Parks Road, Oxford, UK Background: Hypertension is associated with an increase in cardiac sympathetic transmission, although the exact mechanism underlying this is unknown. A decrease in cardiac norepinephrine reuptake transport (NET-1), and therefore the termination of the sympathetic signal has been reported in pre-hypertensive and hypertensive spontaneously hypertensive rats (SHR). NET is known to be a dynamic highly regulated transporter where protein kinase C (PKC) is thought to facilitate its phosphorylation, but also prevent its translocation to the pre-synaptic membrane. Aim: We studied the role of PKC on NET regulation, and tested if its inhibition could rescue the impaired NET activity in the SHR. Method: A novel fluorescent assay of the NET transporter was used on isolated cardiac stellate postganglionic neurons. Results: The PKC inhibitor calphostin C caused a significant dose dependent increase in NET activity (40nM n = 8, 60nM n = 8, 80nM n = 6, and 105nM n = 3) in WKY neurons (105nM n = 5, P b 0.05). Similarly NET activity in SHR neurons was also increased in the presence of calphostin C compared its control (100nM n = 15, P b 0.05). Moreover, there was no difference in NET rate between SHR and WKY neurons after calphostin C. Conclusion: Reduced NET activity in the SHR may be due to increased PKC expression and increased phosphorylation of NET transporters in the cytosol that prevents insertion of the transporter into the presynaptic membrane. Strategies that up regulate NET activity may help rescue the sympathetic hyperactivity observed in this model system. doi:10.1016/j.autneu.2015.07.076
P5.25 Emma Bardsley University of Oxford, UK Background: Spontaneously hypertensive rats (SHRs) and young pre-hypertensive SHRs have enhanced cardiac sympathetic activity; a feature underpinned by impaired cyclic nucleotide signalling linked
77
to abnormal calcium-dependent exocytosis. The crosstalk between cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in peripheral stellate neurons is poorly understood. We used Förster Resonance Energy Transfer (FRET) to test whether cAMP and protein kinase A (PKA) activity is greater in sympathetic neurons from SHR and pre-SHR compared with normotensive controls. Method: Cardiac stellate neurons were isolated from male wistar rats and SHR at 4-weeks (pre-hypertensive) or 16-weeks. On the day of culture stellates were infected with either cAMP or PKA reporter adenovirus particles for 24 hours, and FRET experiments were carried out 3-4 days post-isolation. Data were obtained from neurons expressing FRET biosensors using dualemission imaging, where YFP and CFP emission intensities were measured. During imaging, cells were perfused continuously with Tyrode’s, or stimulated with forskolin (0.1-25 μM) and saturating concentrations of 3-isobutyl-1-methylxanthine (IBMX; 100 μM). Results: There was a significant and concentration-dependent increase in cAMP and PKA activity following forskolin administration in the absence and presence of IBMX, which was significantly higher −7 in 16-week SHR vs. normotensive controls (PKA EC50: 1.2x10 M −7 and 5.1x10 M; SHR, wistar respectively). Furthermore, cAMP and PKA hyperactivity was demonstrated in pre-hypertensive SHRs −7 compared with young wistar rats (PKA EC50: 2.8x10 M and −7 5.6x10 M; SHR, wistar respectively). Summary: These results show that cAMP and PKA hyperactivity occurs early in the development of the cardiac sympathetic phenotype in this genetic based model of hypertension.
doi:110.1016/j.autneu.2015.07.077
P6 Cardiac-Heart Rate Variability P6.1 Cardiovascular autonomic regulation in mice overexpressing the vesicular acetylcholine transporter (VAChT) gene G.C.S.V. Tezinia, L.E.V. Silvaa, M. Oliveiraa, S. Guatimosimb, R. Fazan Jr.a, V.F. Pradoc, M.A.M. Pradoc, H.C. Salgadoa a School of Medicine of Ribeirão Preto, University of São Paulo, Brazil b Federal University of Minas Gerais, Brazil c Robarts Research Institute, The University of Western Ontario, Canada Recently, a transgenic animal with overexpression of the vesicular acetylcholine transporter (VAChT) gene, named ChAT–ChR2–EYFP, was developed. This mutant has several extra copies of VAChT exhibiting a three-fold increase in the release of acetylcholine. The consequences of overexpression of VAChT protein for the cardiovascular system were not characterized yet. Mice were assigned as Wild-type (WT, n = 7) and ChAT–ChR2–EYFP (n = 9) and were implanted with probes for arterial pressure (AP) and heart rate (HR) recording by telemetry. Ten days after probe implantation it was assessed the hemodynamics (AP and HR) and autonomic function [Cardiac sympathovagal balance evaluated by HR responses to methylatropine and propranolol; Pulse interval variability (HRV) by linear - time and frequency domain - and nonlinear methods]. As compared to WT, ChAT–ChR2–EYFP mice showed lower HR, similar AP, higher vagal tone and lower intrinsic HR (IHR). Time domain indexes of HRV were similar between groups, while spectral analysis showed lower LF (0.1-1 Hz) and higher HF (1-5 Hz) of HR spectra in ChAT–ChR2–EYFP. Symbolic analysis found lower 0 V and higher 2UV, and multiscale entropy revealed higher entropy at scales 1 to 4 in ChAT–ChR2–EYFP. The overall results suggest that cardiovascular autonomic regulation of ChAT–ChR2–EYFP mice is characterized by
78
Abstracts / Autonomic Neuroscience: Basic and Clinical 192 (2015) 56–141
higher vagal tone and parasympathetic modulation (linear and nonlinear methods), combined with lower HR and IHR. Moreover, ChAT–ChR2–EYFP mice presented higher entropy for fast temporal mechanisms, pointing to increased complexity.
doi:10.1016/j.autneu.2015.07.078
P6.2 Multiscale entropy analysis of heart rate variability in sinoaortic denervated rats L.E.V. Silva, J.A. Castania, H.C. Salgado, R. Fazan Jr. Department of Physiology, School of Medicine of Ribeirao Preto, University of São Paulo, Brazil The temporal course of heart rate fluctuations, namely heart rate variability (HRV), is the output of a complex system, involving several regulatory mechanisms at different time scales. It is well known that the autonomic nervous system and its baroreflex control play a key role on HRV regulation. Most HRV classical analysis approaches are based on linear models (such as spectral analysis), which are not able to extract complex features from HRV time series. We used multiscale entropy (MSE), a method designed for extracting multiple scale nonlinear information from time series, to address the complexity of HRV in rats submitted to sinoartic denervation (SAD) and compared to its intact control counterparts in order to evaluate how the baroreceptors contribute to the complexity of HRV in rats. Rats were anesthetized and submitted to SAD (n = 7) or SHAM surgery (n = 7) and instrumented with a catheter into femoral artery. At the following day the arterial pressure of conscious freely-moving rats was recorded during 4 h. Entropy values of pulse interval series in rats with SAD were markedly lower as compared to controls for all scales, except the first. Total entropy over scale is significantly lower in SAD group (20.7 ± 1.1 vs 12.6 ± 2.1, p = 0.007). Mean MSE curve profiles of both groups tend to fast decrease for the first four scales followed by a slow recovery onwards. However, MSE curve of SAD rats showed both faster decay and is shifted down as compared to control. Our findings suggest that both short- and long-term mechanisms are altered in SAD rats, pointing to the importance of baroreceptors to maintain the complexity of HRV. doi:10.1016/j.autneu.2015.07.079
P6.3 Use of infrared thermography, heart rate and heart rate variability in studying effect of sweeps in rhesus monkey L.C. Grandia, E.L. Heinzlb University of Parma, Department of Neuroscience, Physiology Unit, 43125, Parma, Italy b University of Milan, Department of Veterinary Science and Public Health, 20133 Milan, Italy
a
The infrared thermography (IRT) system, measuring the energy radiating from the subject and translate it in temperature rate, IRT can be a useful non-invasive technique to study both positive and negative emotions in humans (Ioannou et al., 2014). In non-human primates it was demonstrated that the negative emotions, but not positive ones, both induced by showing video clips with different face expressions, determined a decrement of the nasal temperature (Kuraoka and Nakamura, 2011). An important affiliative social behavior in non-human primate is grooming, that determined positive physiological effects, as the decrement of heart rate (Boccia et al., 1989) and the increment of
heart rate variability (Grandi and Ishida, 2014). Recently it was proposed that the sweeping movements of grooming determined the positive physiological effects (Dunbar, 2010). The aim of the present study was to evaluate the effect of the sweeping of a male rhesus monkey by means of IRT, heart rate and heart rate variability. The sweeping were given by human on the back of monkey, since the preferred site of grooming, and at velocity of 1-10 cm/sec. This velocity is the optimal to induce positive physiological reaction in humans (Loken et al., 2009). The preliminary results underlined that the sweeps determined the decrement of the heart rate and the increment of the heart rate variability and the nasal temperature of the monkey. Importantly we highlighted for the first time the relation among heart rate, heart rate variability and IRT. 1. Boccia ML, Reite M, Laudenslager M. (1989). On the physiology of grooming in a pigtail macaque. Physiol. Behav. 45:667–670. 2. Dunbar RI. (2010). The social role of touch in humans and primates: behavioural function and neurobiological mechanisms. Neuroscience and Behavioral Reviews. 34: 260–268. 3. Grandi LC, Ishida H. (2014). Effect of grooming on the heart rate variability of rhesus monkey. FENS Abstract, FENS-1975, 2014. 4. Ioannou S, Gallese V, Merla A. (2014). Thermal infrared imaging in psychophysiology: potentialities and limits. Psychophysiology. 51(10):951-63. 5. Kuraoka K, Nakamura K. (2011). The use of nasal skin temperature measurements in studying emotion in macaque monkeys. Physiol Behav. 102(3-4):347-55. 6. Loken LS, Wessberg J, Morrison I, McGlone F, Olausson H (2009) Coding of pleasant touch by unmyelinated afferents in humans. Nat Neurosci 12:547–548 doi:10.1016/j.autneu.2015.07.080
P6.4 Low Frequency Oscillations of Heart Rate Variability and Central Volume M. Ferrarioa, U. Moisslb, F. Garzottoc, D.N. Cruzc, C. Tettab, M.G. Signorinia, C. Roncoc, A. Grassmannb, S. Ceruttia, S. Guzzettid a Politecnico di Milano, DEIB, Milano, Italy b Fresenius Medical Care R&D, Bad Homburg Germany c San Bortolo Hospital, Vicenza, Italy d L. Sacco Hospital, Università degli Studi, Milano, Italy Background. The hypothesis that central volume plays a key role in the source of low frequency (LF) oscillations of heart rate variability (HRV) was tested in a population of end stage renal disease patients undergoing conventional hemodialysis (HD) treatment, and thus subject to large fluid shifts and sympathetic activation. Materials and Methods. Fluid overload (FO) in 58 chronic HD patients was assessed by whole body bioimpedance measurements before the midweek HD session. Heart Rate Variability (HRV) was measured using 24-hour Holter electrocardiogram recordings starting before the same HD treatment. Time domain and frequency domain analyses were performed on HRV signals. Patients were retrospectively classified in three groups according to tertiles of FO normalized to the extracellular water (FO/ECW%). These groups were also compared after stratification by diabetes mellitus. Results. Patients with the low to medium hydration status before the treatment showed a significant increase in LF power during last 30 min of HD compared to dialysis begin, while no significant change in LF power was seen in the third group [Δ = BL-last30'HD values of LF(ms2) 1st tertile: 20.4 (2.3,184.1), 2nd tertile: 85.4(0.8, 237.8) 3rd tertile: 4.5 (-11.7, 101.9)]. Conclusion. Several mechanisms can generate LF oscillations in the cardiovascular system, including
However, there is still no direct evidence to show that in utero exposure to smoking alters the dynamics of cardiac autonomic control in sleeping preterm neonates. Methods and Results: We studied healthy, preterm neonates (postmenstrual age: 36.2 ± 0.9 weeks) born to mothers who had smoked throughout pregnancy but not since birth (n = 16). In uteroexposed neonates were matched with control preterm neonates born to nonsmoking mothers (n = 18). Cardiac autonomic control was monitored as a function of the sleep state by assessing heart rate variability with both linear and non-linear methods. Preterm neonates with in utero exposure to smoking displayed alterations (relative to control neonates) in short-term cardiac autonomic control in all sleep states. These alterations included low vagal activity, elevated sympathetic activity, and low complexity and adaptability in heart rate control dynamics. Conclusion: Our results constitute direct evidence that cardiac autonomic activity and control are altered in preterm infants exposed to smoking in utero. These alterations may place the affected infants at a higher risk of neurological and cardiovascular complications, which could conceivably persist throughout childhood and adulthood. doi:10.1016/j.autneu.2015.07.075
P5.24 Inhibition of Protein Kinase C Signalling On Cardiac Noradrenaline Uptake in the Spontaneously Hypertensive Rat Julia Shanks, Jamie Mahwhinny, David J. Paterson Burdon Sanderson Cardiac Centre Department of Physiology, Anatomy and Genetics, Sherrington Building, Parks Road, Oxford, UK Background: Hypertension is associated with an increase in cardiac sympathetic transmission, although the exact mechanism underlying this is unknown. A decrease in cardiac norepinephrine reuptake transport (NET-1), and therefore the termination of the sympathetic signal has been reported in pre-hypertensive and hypertensive spontaneously hypertensive rats (SHR). NET is known to be a dynamic highly regulated transporter where protein kinase C (PKC) is thought to facilitate its phosphorylation, but also prevent its translocation to the pre-synaptic membrane. Aim: We studied the role of PKC on NET regulation, and tested if its inhibition could rescue the impaired NET activity in the SHR. Method: A novel fluorescent assay of the NET transporter was used on isolated cardiac stellate postganglionic neurons. Results: The PKC inhibitor calphostin C caused a significant dose dependent increase in NET activity (40nM n = 8, 60nM n = 8, 80nM n = 6, and 105nM n = 3) in WKY neurons (105nM n = 5, P b 0.05). Similarly NET activity in SHR neurons was also increased in the presence of calphostin C compared its control (100nM n = 15, P b 0.05). Moreover, there was no difference in NET rate between SHR and WKY neurons after calphostin C. Conclusion: Reduced NET activity in the SHR may be due to increased PKC expression and increased phosphorylation of NET transporters in the cytosol that prevents insertion of the transporter into the presynaptic membrane. Strategies that up regulate NET activity may help rescue the sympathetic hyperactivity observed in this model system. doi:10.1016/j.autneu.2015.07.076
P5.25 Emma Bardsley University of Oxford, UK Background: Spontaneously hypertensive rats (SHRs) and young pre-hypertensive SHRs have enhanced cardiac sympathetic activity; a feature underpinned by impaired cyclic nucleotide signalling linked
77
to abnormal calcium-dependent exocytosis. The crosstalk between cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in peripheral stellate neurons is poorly understood. We used Förster Resonance Energy Transfer (FRET) to test whether cAMP and protein kinase A (PKA) activity is greater in sympathetic neurons from SHR and pre-SHR compared with normotensive controls. Method: Cardiac stellate neurons were isolated from male wistar rats and SHR at 4-weeks (pre-hypertensive) or 16-weeks. On the day of culture stellates were infected with either cAMP or PKA reporter adenovirus particles for 24 hours, and FRET experiments were carried out 3-4 days post-isolation. Data were obtained from neurons expressing FRET biosensors using dualemission imaging, where YFP and CFP emission intensities were measured. During imaging, cells were perfused continuously with Tyrode’s, or stimulated with forskolin (0.1-25 μM) and saturating concentrations of 3-isobutyl-1-methylxanthine (IBMX; 100 μM). Results: There was a significant and concentration-dependent increase in cAMP and PKA activity following forskolin administration in the absence and presence of IBMX, which was significantly higher −7 in 16-week SHR vs. normotensive controls (PKA EC50: 1.2x10 M −7 and 5.1x10 M; SHR, wistar respectively). Furthermore, cAMP and PKA hyperactivity was demonstrated in pre-hypertensive SHRs −7 compared with young wistar rats (PKA EC50: 2.8x10 M and −7 5.6x10 M; SHR, wistar respectively). Summary: These results show that cAMP and PKA hyperactivity occurs early in the development of the cardiac sympathetic phenotype in this genetic based model of hypertension.
doi:110.1016/j.autneu.2015.07.077
P6 Cardiac-Heart Rate Variability P6.1 Cardiovascular autonomic regulation in mice overexpressing the vesicular acetylcholine transporter (VAChT) gene G.C.S.V. Tezinia, L.E.V. Silvaa, M. Oliveiraa, S. Guatimosimb, R. Fazan Jr.a, V.F. Pradoc, M.A.M. Pradoc, H.C. Salgadoa a School of Medicine of Ribeirão Preto, University of São Paulo, Brazil b Federal University of Minas Gerais, Brazil c Robarts Research Institute, The University of Western Ontario, Canada Recently, a transgenic animal with overexpression of the vesicular acetylcholine transporter (VAChT) gene, named ChAT–ChR2–EYFP, was developed. This mutant has several extra copies of VAChT exhibiting a three-fold increase in the release of acetylcholine. The consequences of overexpression of VAChT protein for the cardiovascular system were not characterized yet. Mice were assigned as Wild-type (WT, n = 7) and ChAT–ChR2–EYFP (n = 9) and were implanted with probes for arterial pressure (AP) and heart rate (HR) recording by telemetry. Ten days after probe implantation it was assessed the hemodynamics (AP and HR) and autonomic function [Cardiac sympathovagal balance evaluated by HR responses to methylatropine and propranolol; Pulse interval variability (HRV) by linear - time and frequency domain - and nonlinear methods]. As compared to WT, ChAT–ChR2–EYFP mice showed lower HR, similar AP, higher vagal tone and lower intrinsic HR (IHR). Time domain indexes of HRV were similar between groups, while spectral analysis showed lower LF (0.1-1 Hz) and higher HF (1-5 Hz) of HR spectra in ChAT–ChR2–EYFP. Symbolic analysis found lower 0 V and higher 2UV, and multiscale entropy revealed higher entropy at scales 1 to 4 in ChAT–ChR2–EYFP. The overall results suggest that cardiovascular autonomic regulation of ChAT–ChR2–EYFP mice is characterized by
78
Abstracts / Autonomic Neuroscience: Basic and Clinical 192 (2015) 56–141
higher vagal tone and parasympathetic modulation (linear and nonlinear methods), combined with lower HR and IHR. Moreover, ChAT–ChR2–EYFP mice presented higher entropy for fast temporal mechanisms, pointing to increased complexity.
doi:10.1016/j.autneu.2015.07.078
P6.2 Multiscale entropy analysis of heart rate variability in sinoaortic denervated rats L.E.V. Silva, J.A. Castania, H.C. Salgado, R. Fazan Jr. Department of Physiology, School of Medicine of Ribeirao Preto, University of São Paulo, Brazil The temporal course of heart rate fluctuations, namely heart rate variability (HRV), is the output of a complex system, involving several regulatory mechanisms at different time scales. It is well known that the autonomic nervous system and its baroreflex control play a key role on HRV regulation. Most HRV classical analysis approaches are based on linear models (such as spectral analysis), which are not able to extract complex features from HRV time series. We used multiscale entropy (MSE), a method designed for extracting multiple scale nonlinear information from time series, to address the complexity of HRV in rats submitted to sinoartic denervation (SAD) and compared to its intact control counterparts in order to evaluate how the baroreceptors contribute to the complexity of HRV in rats. Rats were anesthetized and submitted to SAD (n = 7) or SHAM surgery (n = 7) and instrumented with a catheter into femoral artery. At the following day the arterial pressure of conscious freely-moving rats was recorded during 4 h. Entropy values of pulse interval series in rats with SAD were markedly lower as compared to controls for all scales, except the first. Total entropy over scale is significantly lower in SAD group (20.7 ± 1.1 vs 12.6 ± 2.1, p = 0.007). Mean MSE curve profiles of both groups tend to fast decrease for the first four scales followed by a slow recovery onwards. However, MSE curve of SAD rats showed both faster decay and is shifted down as compared to control. Our findings suggest that both short- and long-term mechanisms are altered in SAD rats, pointing to the importance of baroreceptors to maintain the complexity of HRV. doi:10.1016/j.autneu.2015.07.079
P6.3 Use of infrared thermography, heart rate and heart rate variability in studying effect of sweeps in rhesus monkey L.C. Grandia, E.L. Heinzlb University of Parma, Department of Neuroscience, Physiology Unit, 43125, Parma, Italy b University of Milan, Department of Veterinary Science and Public Health, 20133 Milan, Italy
a
The infrared thermography (IRT) system, measuring the energy radiating from the subject and translate it in temperature rate, IRT can be a useful non-invasive technique to study both positive and negative emotions in humans (Ioannou et al., 2014). In non-human primates it was demonstrated that the negative emotions, but not positive ones, both induced by showing video clips with different face expressions, determined a decrement of the nasal temperature (Kuraoka and Nakamura, 2011). An important affiliative social behavior in non-human primate is grooming, that determined positive physiological effects, as the decrement of heart rate (Boccia et al., 1989) and the increment of
heart rate variability (Grandi and Ishida, 2014). Recently it was proposed that the sweeping movements of grooming determined the positive physiological effects (Dunbar, 2010). The aim of the present study was to evaluate the effect of the sweeping of a male rhesus monkey by means of IRT, heart rate and heart rate variability. The sweeping were given by human on the back of monkey, since the preferred site of grooming, and at velocity of 1-10 cm/sec. This velocity is the optimal to induce positive physiological reaction in humans (Loken et al., 2009). The preliminary results underlined that the sweeps determined the decrement of the heart rate and the increment of the heart rate variability and the nasal temperature of the monkey. Importantly we highlighted for the first time the relation among heart rate, heart rate variability and IRT. 1. Boccia ML, Reite M, Laudenslager M. (1989). On the physiology of grooming in a pigtail macaque. Physiol. Behav. 45:667–670. 2. Dunbar RI. (2010). The social role of touch in humans and primates: behavioural function and neurobiological mechanisms. Neuroscience and Behavioral Reviews. 34: 260–268. 3. Grandi LC, Ishida H. (2014). Effect of grooming on the heart rate variability of rhesus monkey. FENS Abstract, FENS-1975, 2014. 4. Ioannou S, Gallese V, Merla A. (2014). Thermal infrared imaging in psychophysiology: potentialities and limits. Psychophysiology. 51(10):951-63. 5. Kuraoka K, Nakamura K. (2011). The use of nasal skin temperature measurements in studying emotion in macaque monkeys. Physiol Behav. 102(3-4):347-55. 6. Loken LS, Wessberg J, Morrison I, McGlone F, Olausson H (2009) Coding of pleasant touch by unmyelinated afferents in humans. Nat Neurosci 12:547–548 doi:10.1016/j.autneu.2015.07.080
P6.4 Low Frequency Oscillations of Heart Rate Variability and Central Volume M. Ferrarioa, U. Moisslb, F. Garzottoc, D.N. Cruzc, C. Tettab, M.G. Signorinia, C. Roncoc, A. Grassmannb, S. Ceruttia, S. Guzzettid a Politecnico di Milano, DEIB, Milano, Italy b Fresenius Medical Care R&D, Bad Homburg Germany c San Bortolo Hospital, Vicenza, Italy d L. Sacco Hospital, Università degli Studi, Milano, Italy Background. The hypothesis that central volume plays a key role in the source of low frequency (LF) oscillations of heart rate variability (HRV) was tested in a population of end stage renal disease patients undergoing conventional hemodialysis (HD) treatment, and thus subject to large fluid shifts and sympathetic activation. Materials and Methods. Fluid overload (FO) in 58 chronic HD patients was assessed by whole body bioimpedance measurements before the midweek HD session. Heart Rate Variability (HRV) was measured using 24-hour Holter electrocardiogram recordings starting before the same HD treatment. Time domain and frequency domain analyses were performed on HRV signals. Patients were retrospectively classified in three groups according to tertiles of FO normalized to the extracellular water (FO/ECW%). These groups were also compared after stratification by diabetes mellitus. Results. Patients with the low to medium hydration status before the treatment showed a significant increase in LF power during last 30 min of HD compared to dialysis begin, while no significant change in LF power was seen in the third group [Δ = BL-last30'HD values of LF(ms2) 1st tertile: 20.4 (2.3,184.1), 2nd tertile: 85.4(0.8, 237.8) 3rd tertile: 4.5 (-11.7, 101.9)]. Conclusion. Several mechanisms can generate LF oscillations in the cardiovascular system, including