Gestational diabetes mellitus (GDM) is associated with vascular dysfunction. Sympathetic nervous system activity (SNA) is an important regulator of vascular function, and is influenced by glucose and insulin. The association between GDM and SNA (re)activity is unknown. We hypothesize that women with GDM would have increased SNA during baseline and during stress.

Adipose tissue (AT) expands via both hypertrophy and hyperplasia during the development of obesity. While AT hypertrophy involves the increase in size of existing adipocytes, hyperplasia is the process of creating new adipocytes from the pool of adipocyte precursor cells (APCs), which includes adipocyte progenitor cells and preadipocytes. Prior studies have implicated a role of the sympathetic nervous system (SNS) in regulation of hyperplasia in white adipose tissue (WAT). Here, we aimed to determine the mechanisms underlying SNS regulation of APC proliferation in mouse WAT. Using flow cytometry with antibodies against various cell surface markers, along with an intracellular marker of proliferation (Ki67), we quantitated the percentages and proliferative status of adipocyte progenitor cells and preadipocytes in the stromal vascular fraction (SVF) of WAT. In vivo SNS activation through cold exposure, as well as in vitro adrenergic stimulation via exposure to the canonical SNS neurotransmitter norepinephrine (NE), inhibited preadipocyte proliferation. Pretreatment with propranolol, a β1- and β2-adrenergic receptor (AR) antagonist, trended toward rescuing the inhibitory effects of NE in primary cell culture. The selective β1-AR agonist dobutamine diminished preadipocyte proliferation both in vivo and in vitro, whereas the selective β2-AR agonist, salbutamol, promoted proliferation in vitro, suggesting that the β1-AR may mediate the inhibitory effect of NE on preadipocyte proliferation. Taken together, we conclude that SNS activation suppresses preadipocyte proliferation via activation of the β1 AR in WAT.

In the intensive care and perioperative setting, circulation is often supported by intravenous fluid preceded by prediction of fluid responsiveness during a passive leg raising (PLR) maneuver. An increase in stroke volume (SV) or cardiac output (CO) of 10%-15% indicates that the subject may increase the flow upon volume expansion. However, the semi-recumbent position as an initial position in PLR likely reduces SV by gravitational displacement of central blood volume (CBV) to lower extremities, thereby accentuating volume responsiveness during leg raising in healthy people. Coincident with gravitational perturbations in hemodynamics, remedial changes occur in the autonomic nervous system (ANS), as expressed in spectral power in heart rate variability (HRV). This study aims to clarify these concomitant changes during PLR. A convenience number of healthy volunteers (N = 11) were recruited by advertisement in university departments. The subjects were exposed to the established PLR sequence and the heart rate (HR), mean arterial pressure (MAP), SV, and CO were sampled at 1 Hz, while electrocardiogram was recorded at 1000 Hz. Relative powers reflecting autonomic nervous system activity were assessed from spectral analysis of HRV. In response to PLR, SV increased (12.4% ± 8.7%, p < 0.0026), while HR (-7.6% ± 4.7%, p < 0.0009) and MAP (-7.6% ± 6.9%, p < 0.01) decreased, with no change in CO (4.1% ± 12.8%, ns). The HRV low-frequency component was reduced (-34%; p < 0.0095), while the high-frequency activity increased (78.5%; p < 0.0013), with a 63% decrease in the low/high frequency ratio (p < 0.0078). Thus, HRV indicated a reduced sympathetic index (semi-recumbent 0.808 vs. PLR -0.177 a.u., p < 0.001) and an increased parasympathetic index (-0.141 to 0.996 a.u., p < 0.0001). Gravitational depletion and expansion of CBV during PLR were associated with a counterregulatory autonomic response. Healthy volunteers appeared volume responsive in terms of SV, but not CO. Responses to PLR are influenced by the ANS, and HRV analysis should be included in the assessment of the PLR test.

The sympathetic (SNS) and parasympathetic (PNS) branches of the autonomic nervous system have been implicated in the modulation of the renewal of many tissues, including the intestinal epithelium. However, it is not known whether these mechanisms are direct, requiring an interaction between autonomic neurotransmitters and receptors on proliferating epithelial cells. To evaluate the existence of a molecular framework for a direct effect of the SNS or PNS on intestinal epithelial renewal, we measured gene expression for the main autonomic neurotransmitter receptors in this tissue. We separately evaluated intestinal epithelial regions comprised of the stem, progenitor, and mature cells, which allowed us to investigate the distinct contributions of each cell population to this proposed autonomic effect. Notably, we found that the stem cells expressed the receptors for the SNS-associated alpha2A adrenoreceptor and the PNS-associated muscarinic acetylcholine receptors (M1 and M3). In a separate experiment, we found that the application of norepinephrine or acetylcholine decreases the expression of cyclin D1, a gene necessary for cell cycle progression, in intestinal epithelial organoids compared with controls (P < 0.05). Together, these results provide evidence of a direct mechanism for the autonomic nervous system influence on intestinal epithelial stem cell proliferation.

It is increasingly recognized that activation of beige adipocyte thermogenesis by pharmacological or genetic approaches increases energy expenditure and alleviates obesity. Sympathetic nervous system (SNS) directly innervating brown adipose tissue (BAT) and white adipose tissue (WAT) plays a key role in promoting nonshivering thermogenesis. However, direct evidence that supports the importance of SNS innervation for beige adipocyte formation is still lacking, and the significance of beige adipocyte thermogenesis in protection of body temperature during cold challenge is not clear. Here we tested the necessity of SNS innervation into WAT for beige adipocyte formation in mice with defective brown fat thermogenesis via interscapular BAT (iBAT) SNS denervation. SNS denervation was achieved by microinjection of 6-hydroxydopamine (6-OHDA), a selective neurotoxin to SNS nerves, into iBAT, inguinal WAT (iWAT), or both. The partial chemical denervation of iBAT SNS down-regulated UCP-1 protein expression in iBAT demonstrated by immunoblotting and immunohistochemical measurements. This was associated with an up-regulation of UCP1 protein expression and enhanced formation of beige cells in iWAT of mice with iBAT SNS denervation. In contrast, the chemical denervation of iWAT SNS completely abolished the upregulated UCP-1 protein and beige cell formation in iWAT of mice with iBAT SNS denervation. Our data demonstrate that SNS innervation in WAT is required for beige cell formation during cold-induced thermogenesis. We conclude that there exists a coordinated thermoregulation for BAT and WAT thermogenesis via a functional cross talk between BAT and WAT SNS.

Elevated nocturnal blood pressure (BP) and nocturnal non-dipping are frequently observed in patients with chronic kidney disease (CKD) and are stronger predictors of cardiovascular complications and CKD progression than standard office BP. The sympathetic nervous system (SNS) is thought to modulate diurnal hemodynamic changes and the vascular endothelium plays a fundamental role in BP regulation. We hypothesized that SNS overactivity and endothelial dysfunction in CKD are linked to elevated nocturnal BP and non-dipping. In 32 CKD patients with hypertension (56 ± 7 years), office BP, 24-hr ambulatory BP, muscle sympathetic nerve activity (MSNA) and endothelial function via flow-mediated dilation (FMD) were measured. Participants were subsequently divided into dippers (nighttime average BP > 10% lower than the daytime average BP, n = 8) and non-dippers (n = 24). Non-dippers had higher nighttime BP (p < .05), but not office and daytime BP, compared to dippers. MSNA burst incidence (81 ± 13 versus 67 ± 13 bursts/100 HR, p = .019) was higher and brachial artery FMD (1.7 ± 1.5 versus 4.7 ± 1.9%, p < .001) was lower in non-dippers compared to dippers. MSNA and FMD each predicted nighttime systolic (β = 0.48,-0.46, p = .02, 0.07, respectively) and diastolic BP (β = 0.38,-0.47, p = .04, 0.03, respectively) in multivariate-adjusted analyses. Our novel findings demonstrate that unfavorable nocturnal BP profiles are associated with elevated SNS activity and endothelial dysfunction in CKD. Specifically, CKD patients with higher nighttime BP and the non-dipping pattern have higher MSNA and lower FMD. These support our hypothesis that SNS overactivation and endothelial dysfunction are linked to the dysregulation of nighttime BP as well as the magnitude of BP lowering at nighttime in CKD.

Exercise can improve morbidity and mortality in heart failure patients; however, the underlying mechanisms remain to be fully investigated. Thus, we investigated the effects of exercise on cardiac function and ventricular arrhythmias in myocardial infarction (MI) induced heart failure mice. Wild-type male mice underwent sham-operation or permanent left coronary artery ligation to induce MI. MI mice were divided into a sedentary (MI-Sed) and two intervention groups: MI-Ex (underwent 6-week treadmill exercise training) and MI-βb (oral bisoprolol treatment (1 mg/kg/d) without exercise). Cardiac function and structure were assessed by echocardiography and histology. Exercise capacity and cardiopulmonary function was accepted as oxygen consumption at peak exercise (peak VO2 ). Autonomic nervous system function and the incidence of spontaneous ventricular arrhythmia were evaluated via telemetry recording. mRNA and protein expressions in the left ventricle (LV) were investigated by real-time PCR and Western blotting. There were no differences in survival rate, MI size, cardiac function and structure, while exercise training improved peak VO2 . Compared with MI-Sed, MI-Ex, and MI-βb showed decreased sympathetic tone and lower incidence of spontaneous ventricular arrhythmia. By Western blot, the hyperphosphorylation of CaMKII and RyR2 were restored by exercise and β-blocker treatment. Furthermore, elevated expression of miR-1 and decreased expression of its target protein PP2A were recovered by exercise and β-blocker treatment. Continuous intensive exercise training can suppress ventricular arrhythmias in subacute to chronic phase of MI through restoring autonomic imbalance and impaired calcium handling, similarly to that for β-blockers.

Our previous immunoprecipitation analysis of nicotinic acetylcholine receptors (nAChRs) in the mouse superior cervical ganglion (SCG) revealed that approximately 55%, 24%, and 21% of receptors are comprised of α3β4, α3β4α5, and α3β4β2 subunits, respectively. Moreover, mice lacking β4 subunits do not express α5-containing receptors but still express a small number of α3β2 receptors. Here, we investigated how synaptic transmission is affected in the SCG of α5β4-KO and α5β2-KO mice. Using an ex vivo SCG preparation, we stimulated the preganglionic cervical sympathetic trunk and measured compound action potentials (CAPs) in the postganglionic internal carotid nerve. We found that CAP amplitude was unaffected in α5β4-KO and α5β2-KO ganglia, whereas the stimulation threshold for eliciting CAPs was significantly higher in α5β4-KO ganglia. Moreover, intracellular recordings in SCG neurons revealed no difference in EPSP amplitude. We also found that the ganglionic blocking agent hexamethonium was the most potent in α5β4-KO ganglia (IC50 : 22.1 μmol/L), followed by α5β2-KO (IC50 : 126.7 μmol/L) and WT ganglia (IC50 : 389.2 μmol/L). Based on these data, we estimated an IC50 of 568.6 μmol/L for a receptor population consisting solely of α3β4α5 receptors; and we estimated that α3β4α5 receptors comprise 72% of nAChRs expressed in the mouse SCG. Similarly, by measuring the effects of hexamethonium on ACh-induced currents in cultured SCG neurons, we found that α3β4α5 receptors comprise 63% of nAChRs. Thus, in contrast to our results obtained using immunoprecipitation, these data indicate that the majority of receptors at the cell surface of SCG neurons consist of α3β4α5.

Elevated Resting Blood Pressure (ERBP) in the prehypertensive range is associated with increased risk of hypertension and cardiovascular disease, the mechanisms of which remain unclear. Prior studies have suggested that ERBP may be associated with overactivation and dysregulation of the sympathetic nervous system (SNS). We hypothesized that compared to normotensives (≤120/80 mmHg), ERBP (120/80-139/89 mmHg) has higher SNS activity, impaired arterial baroreflex sensitivity (BRS), and increased vascular inflammation. Twenty-nine participants were studied: 16 otherwise healthy individuals with ERBP (blood pressure (BP) 130 ± 2/85 ± 2 mmHg) and 13 matched normotensive controls (mean BP 114 ± 2/73 ± 2 mmHg). We measured muscle sympathetic nerve activity (MSNA), beat-to-beat BP, and continuous electrocardiogram at rest and during arterial BRS testing via the modified Oxford technique. Blood was analyzed for the following biomarkers of vascular inflammation: lipoprotein-associated phospholipase A2 (Lp-PLA2), E-selectin, and intercellular adhesion molecule 1 (ICAM-1). Resting MSNA burst frequency (22 ± 2 vs. 16 ± 2 bursts/min, P = 0.036) and burst incidence (36 ± 3 vs. 25 ± 3 bursts/100 heart beats, P = 0.025) were higher in ERBP compared to controls. Cardiovagal BRS was blunted in ERBP compared to controls (13 ± 2 vs. 20 ± 3 msec/mmHg, P = 0.032), while there was no difference in sympathetic BRS between groups. Lp-PLA2 (169 ± 8 vs. 142 ± 9 nmol/min/mL, P = 0.020) and E-selectin (6.89 ± 0.6 vs. 4.45 ± 0.51 ng/mL, P = 0.004) were higher in ERBP versus controls. E-selectin (r = 0.501, P = 0.011) and ICAM-1 (r = 0.481, P = 0.015) were positively correlated with MSNA, while E-selectin was negatively correlated with cardiovagal BRS (r = -0.427, P = 0.030). These findings demonstrate that individuals with ERBP have SNS overactivity and impaired arterial BRS that are linked to biomarkers of vascular inflammation.

The heart is controlled by the sympathetic and parasympathetic limbs of the autonomic nervous system with inhibitory signaling mechanisms recruited in both limbs. The aim of this study was to determine the role of inhibitory heterotrimeric G proteins in the central nervous mechanisms underlying autonomic control of the heart and its potential role in arrhythmogenesis. Mice with conditional deletion of the inhibitory heterotrimeric G protein GαO in the presympathetic area of the rostral ventral lateral medulla (RVLM) were generated to determine the role of GαO-mediated signalling in autonomic control and electrophysiological properties of the heart. GαO deletion within the RVLM was not associated with changes in heart rate (HR) or the arterial blood pressure at rest (home cage, normal behavior). However, exposure to stressful conditions (novel environment, hypoxia, or hypercapnia) in these mice was associated with abnormal HR responses and an increased baroreflex gain when assessed under urethane anesthesia. This was associated with shortening of the ventricular effective refractory period. This phenotype was reversed by systemic beta-adrenoceptor blockade, suggesting that GαO depletion in the RVLM increases central sympathetic drive. The data obtained support the hypothesis that GαO-mediated signaling within the presympathetic circuits of the RVLM contributes to the autonomic control of the heart. GαO deficiency in the RVLM has a significant impact on cardiovascular responses to stress, cardiovascular reflexes and electrical properties of the heart.

Abstract Growth hormone secretagogue receptor (GHS-R) signaling has been associated with growth hormone release, increases in food intake and pleiotropic cardiovascular effects. Recent data demonstrated that acute GHS-R antagonism leads to increases in mean arterial pressure mediated by the sympathetic nervous system in rats; a highly undesirable effect if GHS-R antagonism was to be used as a therapeutic approach to reducing food intake in an already obese, hypertensive patient population. However, our data in conscious, freely moving GHS-R deficient mice demonstrate that chronic absence of GHS-R signaling is protective against obesity-induced hypertension. GHS-R deficiency leads to reduced systolic blood pressure variability (SBPV); in response to acute high-fat diet (HFD)-feeding, increases in the sympathetic control of SBPV are suppressed in GHS-R KO mice. Our data further suggest that GHS-R signaling dampens the immediate HFD-mediated increase in spontaneous baroreflex sensitivity. In diet-induced obesity, absence of GHS-R signaling leads to reductions in obesity-mediated hypertension and tachycardia. Collectively, our findings thus suggest that chronic blockade of GHS-R signaling may not result in adverse cardiovascular effects in obesity.

Obstructive sleep apnea is associated with hypertension and cardiovascular disease. Chronic intermittent hypoxia is used to model the arterial hypoxemia seen in sleep apnea patients and is associated with increased sympathetic nerve activity and a sustained diurnal increase in blood pressure. The renin angiotensin system has been associated with hypertension seen in chronic intermittent hypoxia. Angiotensin converting enzyme 1, which cleaves angiotensin I to the active counterpart angiotensin II, is present within the central nervous system and has been shown to be regulated by AP-1 transcription factors, such as ΔFosB. Our previous study suggested that this transcriptional regulation in the median preoptic nucleus contributes to the sustained blood pressure seen following chronic intermittent hypoxia. Viral mediated delivery of a short hairpin RNA against angiotensin converting enzyme 1 in the median preoptic nucleus was used along with radio-telemetry measurements of blood pressure to test this hypothesis. FosB immunohistochemistry was utilized in order to assess the effects of angiotensin converting enzyme 1 knockdown on the activity of nuclei downstream from median preoptic nucleus. Angiotensin converting enzyme 1 knockdown within median preoptic nucleus significantly attenuated the sustained hypertension seen in chronic intermittent hypoxia. Angiotensin converting enzyme 1 seems to be partly responsible for regulating downstream regions involved in sympathetic and blood pressure control, such as the paraventricular nucleus and the rostral ventrolateral medulla. The data suggest that angiotensin converting enzyme 1 within median preoptic nucleus plays a critical role in the sustained hypertension seen in chronic intermittent hypoxia.

Glucose is the most important energy substrate for the maintenance of tissues function. The liver plays an essential role in the control of glucose production, since it is able to synthesize, store, and release glucose into the circulation under different situations. Hormones like insulin and catecholamines influence hepatic glucose production (HGP), but little is known about the role of the central actions of physiological doses of insulin in modulating HGP via the autonomic nervous system in nonanesthetized rats especially in SHR where we see a high degree of insulin resistance and metabolic dysfunction. Wistar and SHR received ICV injection of insulin (100 nU/μL) and hepatic venous glucose concentration (HVGC) was monitored for 30 min, as an indirect measure of HGP. At 10 min after insulin injection, HVGC decreased by 27% in Wistar rats, with a negligible change (3%) in SHR. Pretreatment with atropine totally blocked the reduction in HVGC, while pretreatment with propranolol and phentolamine induced a decrease of 8% in HVGC after ICV insulin injection in Wistar. Intracarotid infusion of insulin caused a significant increase in subdiaphragmatic vagus nerve (SVN) activity in Wistar (12 ± 2%), with negligible effects on the lumbar splanchnic sympathetic nerve (LSSN) activity (-6 ± 3%). No change was observed in SVN (-2 ± 2%) and LSSN activities (2 ± 3%) in SHR after ICA insulin infusion. Taken together, these results show, in nonanesthetized animals, the importance of the parasympathetic nervous system in controlling HVGC, and subdiaphragmatic nerve activity following central administration of insulin; a mechanism that is impaired in the SHR.

Sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) influences on cardiac rhythm at the onset of exercise, a time of rapid autonomic adjustments, are clinically important areas of investigation. Continuous wavelet transform (CWT) involves time-frequency-based heart rate variability (HRV) analysis allowing investigation of autonomic influences on cardiac rhythm during short durations of exercise. Therefore, the purpose of this study was to characterize SNS and PNS influences on cardiac rhythm at the onset of isometric exercise in healthy young adults. CWT analysis was retrospectively applied to R-R interval data (electrocardiogram) previously collected from 14 healthy young adults (26 ± 2 years) who performed 30-s, one-legged, isometric, calf exercise at 70% maximal voluntary contraction (MVC; 70% MVC trial) or rested (0% MVC trial). Absolute and normalized low-frequency (aLF, nLF; 0.04-0.15 Hz) and high-frequency (aHF, nHF; 0.15-0.4 Hz) bands and LF/HF were used to analyze one 30-s baseline period and six 5-s time windows during the 30-s exercise (70% MVC) or rest (0% MVC). Statistical analysis involved two-way analysis of variance with post-hoc analysis. aHF, aLF, LF/HF, nHF, and nLF displayed a trial-time interaction (all p ≤ 0.027). In the 70% compared to the 0% MVC trial, aHF and nHF were lower after 5-30 s (all p ≤ 0.040), aLF was lower after 20-30 s (all p ≤ 0.011) and LF/HF and nLF were higher after 5-20 s (all p ≤ 0.045). These results indicate the reduction of the PNS influence on cardiac rhythm begins sooner than the augmentation of the SNS influence at the onset of isometric exercise in healthy young adults.

Proximal tubule fructose metabolism is key to fructose-induced hypertension, but the roles of sex and stress are unclear. We hypothesized that females are resistant to the salt-sensitive hypertension caused by low amounts of dietary fructose compared to males and that the magnitude of the increase in blood pressure (BP) depends, in part, on amplification of the stress response of renal sympathetic nerves. We measured systolic BP (SBP) in rats fed high salt with either no sugar (HS), 20% glucose (GHS) or 20% fructose (FHS) in the drinking water for 7-8 days. FHS increased SBP in both males (Δ22 ± 9 mmHg; p < 0.046) and females (Δ16 ± 3 mmHg; p < 0.0007), while neither GHS nor HS alone induced changes in SBP in either sex. The FHS-induced increase in SBP as measured by telemetry in the absence of added stress (8 ± 2 mmHg) was significantly lower than that measured by plethysmography (24 ± 5 mmHg) (p < 0.014). However, when BP was measured by telemetry simulating the stress of plethysmography, the increase in SBP was significantly greater (15 ± 3 mmHg) than under low stress (8 ± 1 mmHg) (p < 0.014). Moderate-stress also increased telemetric diastolic (p < 0.006) and mean BP (p < 0.006) compared to low-stress in FHS-fed animals. Norepinephrine excretion was greater in FHS-fed rats than HS-fed animals (Male: 6.4 ± 1.7 vs.1.8 ± 0.4 nmole/kg/day; p < 0.02. Female 54 ± 18 vs. 1.2 ± 0.6; p < 0.02). We conclude that fructose-induced salt-sensitive hypertension is similar in males and females unlike other forms of hypertension, and the increase in blood pressure depends in part on an augmented response of the sympathetic nervous system to stress.

It is well known that the main forms of innervation are synapses and free nerve endings, while other forms of innervation have not been reported. Here, we explore a new way of innervating lymphoid organs. Male Sprague-Dawley rats were used for studying the innervation of sympathetic nerve fibers in lymph nodes by means of anterograde tracking, immunoelectron microscopy, three-dimension reconstruction analysis, and immunofluorescence labeling. The results showed that the Fluoro-Ruby labeled nerve endings targeted only a group of cells in the lymph nodes and entered the cells through the plasma membrane. The electron microscopy showed that the biotinylated glucan amine reaction elements were distributed in the cytoplasm, and most of the biotinylated glucan amine active elements were concentrated on the microtubule and microfilament walls. Birbeck particles with rod-shaped and/or tennis racket like structures can be seen in the labeled cells at high magnification, and Birbeck particles contain biotinylated glucan amine-reactive elements. The immunofluoresence results showed that the Fluoro-Ruby-labeled nerve innervating cells expressed CD207 and CD1a protein. This result confirmed that the labeled cells were Langerhans cells. Our findings suggested that Langerhans cells might serve as a "bridge cell" for neuroimmune cross-talking in lymph organs, which play an important role in transmitting signals of the nervous system to immune system. This study also opened up a new way for further study of immune regulation mechanism.

The present study aims to analyze the systemic response to auditory stimulation by means of hemodynamic (cephalic and peripheral) and autonomic responses in a broad range of auditory intensities (70.9, 77.9, 84.5, 89.5, 94.5 dBA). This approach could help to understand the possible influence of the autonomic nervous system on the cephalic blood flow. Twenty-five subjects were exposed to auditory stimulation while electrodermal activity (EDA), photoplethysmography (PPG), electrocardiogram, and functional near-infrared spectroscopy signals were recorded. Seven trials with 20 individual tones, each for the five intensities, were presented. The results showed a differentiated response to the higher intensity (94.5 dBA) with a decrease in some peripheral signals such as the heart rate (HR), the pulse signal, the pulse transit time (PTT), an increase of the LFnu power in PPG, and at the head level a decrease in oxygenated and total hemoglobin concentration. After the regression of the visual channel activity from the auditory channels, a decrease in deoxyhemoglobin in the auditory cortex was obtained, indicating a likely active response at the highest intensity. Nevertheless, other measures, such as EDA (Phasic and Tonic), and heart rate variability (Frequency and time domain) showed no significant differences between intensities. Altogether, these results suggest a systemic and complex response to high-intensity auditory stimuli. The results obtained in the decrease of the PTT and the increase in LFnu power of PPG suggest a possible vasoconstriction reflex by a sympathetic control of vascular tone, which could be related to the decrease in blood oxygenation at the head level.

Duchenne muscular dystrophy (DMD) is a progressive striated muscle disease that is characterized by skeletal muscle weakness with progressive respiratory and cardiac failure. Together respiratory and cardiac disease account for the majority of mortality in the DMD patient population. However, little is known regarding the effects of respiratory dysfunction on the dystrophic heart. The studies described here examine the effects of acute hypoxia on cardiac function. These studies demonstrate, for the first time, that a mouse model of DMD displays significant mortality following acute exposure to hypoxia. This mortality is characterized by a steady decline in systolic function. Retrospective analysis reveals that significant decreases in diastolic dysfunction, especially in the right ventricle, precede the decline in systolic pressure. The initial hemodynamic response to acute hypoxia in the mouse is similar to that observed in larger species, with significant increases in right ventricular afterload and decreases in left ventricular preload being observed. Significant increases in heart rate and contractility suggest hypoxia-induced activation of the sympathetic nervous system. These studies provide evidence that while hypoxia presents significant hemodynamic challenges to the dystrophic right ventricle, global cardiac dysfunction precedes hypoxia-induced mortality in the dystrophic heart. These findings are clinically relevant as the respiratory insufficiency evident in patients with DMD results in significant bouts of hypoxia. The results of these studies indicate that hypoxia may contribute to the acceleration of the heart disease in DMD patients. Importantly, hypoxia can be avoided through the use of ventilatory support.

Hypertension induced by chronic administration of angiotensin II (AngII) is exacerbated by high-salt intake. Previous studies have demonstrated that this salt-sensitive component is due to increased activity of the sympathetic nervous system, suggesting an interaction of plasma AngII with sodium-sensitive regions of the brain. This study tested the hypothesis that the salt-sensitive component of AngII-induced hypertension would be prevented by intracerebroventricular (ICV) administration of the sodium channel/transporter blocker benzamil. Male Sprague Dawley rats were instrumented to measure mean arterial pressure (MAP) by radio telemetry and for ICV administration of benzamil or vehicle and placed in metabolic cages for measurement of sodium and water intake and excretion. In rats consuming a high-salt diet (2.0% NaCl) and treated with ICV vehicle, administration of AngII (150 ng/kg/min, sc) for 13 days increased MAP by ~30 mmHg. ICV administration of benzamil (16 nmol/day) had no effect during the first 5 days of AngII, but returned MAP to control levels by Day 13. There were minimal or no differences between ICV vehicle or benzamil groups in regards to sodium and water balance. A lower dose of ICV benzamil administered ICV at 8 nmol/day had no effect on the MAP response to AngII in rats on a high-salt diet. Finally, in contrast to rats on a high-salt diet, AngII had negligible effects on MAP in rats consuming a low-salt diet (0.1% NaCl) and there were no differences in any variable between ICV benzamil (16 nmol/day) and ICV vehicle-treated groups. We conclude that the salt-sensitive component of AngII-induced hypertension is dependent on benzamil blockable sodium channels or transporters in the brain.