Estrogen-dependent KCa1.1 modulation is essential for retaining neuroexcitation of female-specific subpopulation of myelinated Ah-type baroreceptor neurons in rats.

Female-specific subpopulation of myelinated Ah-type baroreceptor neurons (BRNs) in nodose ganglia is the neuroanatomical base of sexual-dimorphic autonomic control of blood pressure regulation, and KCa1.1 is a key player in modulating the neuroexcitation in nodose ganglia. In this study we investigated the exact mechanisms underlying KCa1.1-mediated neuroexcitation of myelinated Ah-type BRNs in the presence or absence of estrogen. BRNs were isolated from adult ovary intact (OVI) or ovariectomized (OVX) female rats, and identified electrophysiologically and fluorescently. Action potential (AP) and potassium currents were recorded using whole-cell recording. Consistently, myelinated Ah-type BRNs displayed a characteristic discharge pattern and significantly reduced excitability after OVX with narrowed AP duration and faster repolarization largely due to an upregulated iberiotoxin (IbTX)-sensitive component; the changes in AP waveform and repetitive discharge of Ah-types from OVX female rats were reversed by G1 (a selective agonist for estrogen membrane receptor GPR30, 100 nM) and/or IbTX (100 nM). In addition, the effect of G1 on repetitive discharge could be completely blocked by G15 (a selective antagonist for estrogen membrane receptor GPR30, 3 µM). These data suggest that estrogen deficiency by removing ovaries upregulates KCa1.1 channel protein in Ah-type BRNs, and subsequently increases AP repolarization and blunts neuroexcitation through estrogen membrane receptor signaling. Intriguingly, this upregulated KCa1.1 predicted electrophysiologically was confirmed by increased mean fluorescent intensity that was abolished by estrogen treatment. These electrophysiological findings combined with immunostaining and pharmacological manipulations reveal the crucial role of KCa1.1 in modulation of neuroexcitation especially in female-specific subpopulation of myelinated Ah-type BRNs and extend our current understanding of sexual dimorphism of neurocontrol of BP regulation.

Transient Receptor Potential Vanilloid 4 Regulation of Adenosine Triphosphate Release by the Adenosine Triphosphate Transporter Vesicular Nucleotide Transporter, a Novel Therapeutic Target for Gastrointestinal Baroreception and Chronic Inflammation.

BACKGROUND: Transient receptor potential vanilloid 4 (TRPV4) is activated by stretch (mechanical), warm temperature, some epoxyeicosatrienoic acids, and lipopolysaccharide. TRPV4 is expressed throughout the gastrointestinal epithelia and its activation induces adenosine triphosphate (ATP) exocytosis that is involved in visceral hypersensitivity. As an ATP transporter, vesicular nucleotide transporter (VNUT) mediates ATP storage in secretory vesicles and ATP release via exocytosis upon stimulation. SUMMARY: TRPV4 is sensitized under inflammatory conditions by a variety of factors, including proteases and serotonin, whereas methylation-dependent silencing of TRPV4 expression is associated with various pathophysiological conditions. Gastrointestinal epithelia also release ATP in response to hypo-osmolality or acid through molecular mechanisms that remain unclear. These synergistically released ATP could be involved in visceral hypersensitivity. Low concentrations of the first generation bisphosphate, clodronate, were recently reported to inhibit VNUT activity and thus clodronate may be a safe and potent therapeutic option to treat visceral pain. Key Messages: This review focuses on: (1) ATP and TRPV4 activities in gastrointestinal epithelia; (2) factors that could modulate TRPV4 activity in gastrointestinal epithelia; and (3) the inhibition of VNUT as a potential novel therapeutic strategy for functional gastrointestinal disorders.

Selective denervation of the aortic and carotid baroreceptors in rats.

NEW FINDINGS: What is the central question of this study? The traditional surgical approach for sino-aortic denervation in rats leads to simultaneous carotid baroreceptor and chemoreceptor deactivation, which does not permit their individual study in different situations. What is the main finding and its importance? We have described a new surgical approach capable of selective denervation of the arterial (aortic and carotid) baroreceptors, keeping the carotid bodies (chemoreceptors) intact. It is understood that this technique might be a useful tool for investigating the relative role of the baro- and chemoreceptors in several physiological and pathophysiological conditions. ABSTRACT: Studies have demonstrated that the traditional surgical approach for sino-aortic denervation in rats leads to simultaneous carotid baroreceptor and chemoreceptor deactivation. The present study reports a new surgical approach to denervate the aortic and the carotid baroreceptors selectively, keeping the carotid bodies (peripheral chemoreceptors) intact. Wistar rats were subjected to specific aortic and carotid baroreceptor denervation (BAROS-X) or sham surgery (SHAM). Baroreflex activation was achieved by i.v. administration of phenylephrine, whereas peripheral chemoreflex activation was produced by i.v. administration of potassium cyanide. The SHAM and BAROS-X rats displayed significant hypertensive responses to phenylephrine administration. However, the reflex bradycardia following the hypertensive response caused by phenylephrine was remarkable in SHAM, but not significant in the BAROS-X animals, confirming the efficacy of the surgical procedure to abolish the baroreflex. In addition, the baroreflex activation elicited by phenylephrine increased carotid sinus nerve activity only in SHAM, but not in the BAROS-X animals, providing support to the notion that the baroreceptor afferents were absent. Instead, the classical peripheral chemoreflex hypertensive and bradycardic responses to potassium cyanide were similar in both groups, suggesting that the carotid body chemoreceptors were preserved after BAROS-X. In summary, we describe a new surgical approach in which only the baroreceptors are eliminated, while the carotid chemoreceptors are preserved. Therefore, it is understood that this procedure is potentially a useful tool for examining the relative roles of the arterial baroreceptors versus the chemoreceptors in several pathophysiological conditions, for instance, arterial hypertension and heart failure.

Enhanced Firing in NTS Induced by Short-Term Sustained Hypoxia Is Modulated by Glia-Neuron Interaction.

Humans ascending to high altitudes are submitted to sustained hypoxia (SH), activating peripheral chemoreflex with several autonomic and respiratory responses. Here we analyzed the effect of short-term SH (24 h, FIO210%) on the processing of cardiovascular and respiratory reflexes using an in situ preparation of rats. SH increased both the sympatho-inhibitory and bradycardiac components of baroreflex and the sympathetic and respiratory responses of peripheral chemoreflex. Electrophysiological properties and synaptic transmission in the nucleus tractus solitarius (NTS) neurons, the first synaptic station of afferents of baroreflexes and chemoreflexes, were evaluated using brainstem slices and whole-cell patch-clamp. The second-order NTS neurons were identified by previous application of fluorescent tracer onto carotid body for chemoreceptor afferents or onto aortic depressor nerve for baroreceptor afferents. SH increased the intrinsic excitability of NTS neurons. Delayed excitation, caused by A-type potassium current (IKA), was observed in most of NTS neurons from control rats. The IKA amplitude was higher in identified second-order NTS neurons from control than in SH rats. SH also blunted the astrocytic inhibition of IKA in NTS neurons and increased the synaptic transmission in response to afferent fibers stimulation. The frequency of spontaneous excitatory currents was also increased in neurons from SH rats, indicating that SH increased the neurotransmission by presynaptic mechanisms. Therefore, short-term SH changed the glia-neuron interaction, increasing the excitability and excitatory transmission of NTS neurons, which may contribute to the observed increase in the reflex sensitivity of baroreflex and chemoreflex in in situ preparation.

The baroreflex as a long-term controller of arterial pressure.

Because of resetting, a role for baroreflexes in long-term control of arterial pressure has been commonly dismissed in the past. However, in recent years, this perspective has changed. Novel approaches for determining chronic neurohormonal and cardiovascular responses to natural variations in baroreceptor activity and to electrical stimulation of the carotid baroreflex indicate incomplete resetting and sustained responses that lead to long-term alterations in sympathetic activity and arterial pressure.

Hormone phase influences sympathetic responses to high levels of lower body negative pressure in young healthy women.

We tested the hypothesis that sympathetic responses to baroreceptor unloading may be affected by circulating sex hormones. During lower body negative pressure at -30, -60, and -80 mmHg, muscle sympathetic nerve activity (MSNA), heart rate, and blood pressure were recorded in women who were taking (n = 8) or not taking (n = 9) hormonal contraceptives. All women were tested twice, once during the low-hormone phase (i.e., the early follicular phase of the menstrual cycle and the placebo phase of hormonal contraceptive use), and again during the high-hormone phase (i.e., the midluteal phase of the menstrual cycle and active phase of contraceptive use). During baroreceptor unloading, the reductions in stroke volume and resultant increases in MSNA and total peripheral resistance were greater in high-hormone than low-hormone phases in both groups. When normalized to the fall in stroke volume, increases in MSNA were no longer different between hormone phases. While stroke volume and sympathetic responses were similar between women taking and not taking hormonal contraceptives, mean arterial pressure was maintained during baroreceptor unloading in women not taking hormonal contraceptives but not in women using hormonal contraceptives. These data suggest that differences in sympathetic activation between hormone phases, as elicited by lower body negative pressure, are the result of hormonally mediated changes in the hemodynamic consequences of negative pressure, rather than centrally driven alterations to sympathetic regulation.

Effects of JTV-519 on stretch-induced manifestations of mechanoelectric feedback.

JTV-519 is a 1,4-benzothiazepine derivative with multichannel effects that inhibits Ca2+ release from the sarcoplasmic reticulum and stabilizes the closed state of the ryanodine receptor, preventing myocardial damage and the induction of arrhythmias during Ca2+ overload. Mechanical stretch increases cellular Na+ inflow, activates the reverse mode of the Na+ /Ca2+ exchanger, and modifies Ca2+ handling and myocardial electrophysiology, favoring arrhythmogenesis. This study aims to determine whether JTV-519 modifies the stretch-induced manifestations of mechanoelectric feedback. The ventricular fibrillation (VF) modifications induced by acute stretch were studied in Langendorff-perfused rabbit hearts using epicardial multiple electrodes under control conditions (n=9) or during JTV-519 perfusion: 0.1 µmol/L (n=9) and 1 µmol/L (n=9). Spectral and mapping techniques were used to establish the baseline, stretch and post-stretch VF characteristics. JTV-519 slowed baseline VF and decreased activation complexity. These effects were dose-dependent (baseline VF dominant frequency: control=13.9±2.2 Hz; JTV 0.1 µmol/L=11.1±1.1 Hz, P<.01; JTV 1 µmol/L=6.6±1.1 Hz, P<.0001). The stretch-induced acceleration of VF (control=38.8%) was significantly reduced by JTV-519 0.1 µmol/L (19.8%) and abolished by JTV 1 µmol/L (-1.5%). During stretch, the VF activation complexity index was reduced in both JTV-519 series (control=1.60±0.15; JTV 0.1 µmol/L=1.13±0.3, P<.0001; JTV 1 µmol/L=0.57±0.21, P<.0001), and was independently related to VF dominant frequency (R=.82; P<.0001). The fifth percentile of the VF activation intervals, conduction velocity and wavelength entered the multiple linear regression model using dominant frequency as the dependent variable (R=-.84; P<.0001). In conclusion, JTV-519 slowed and simplified the baseline VF activation patterns and abolished the stretch-induced manifestations of mechanoelectric feedback.

Reduced carotid baroreceptor distensibility-induced baroreflex resetting contributes to impairment of sodium regulation in rats fed a high-fat diet.

Decreased carotid arterial compliance has been reported in obese subjects and animals. Carotid baroreceptors are located at the bifurcation of the common carotid artery, and respond to distension of the arterial wall, suggesting that higher pressure is required to obtain the same distension in obese subjects and animals. A hyperosmotic NaCl solution induces circulatory volume expansion and arterial pressure (AP) increase, which reflexively augment renal excretion. Thus, we hypothesized that sodium regulation via the baroreflex might be impaired in response to chronic hyperosmotic NaCl infusion in rats fed a high-fat diet. To examine this hypothesis, we used rats fed a high-fat (Fat) or normal (NFD) diet, and measured mean AP, water and sodium balance, and renal function in response to chronic infusion of hyperosmotic NaCl solution via a venous catheter. Furthermore, we examined arterial baroreflex characteristics with static open-loop analysis and distensibility of the common carotid artery. Significant positive water and sodium balance was observed on the 1st day of 9% NaCl infusion; however, this disappeared by the 2nd day in Fat rats. Mean AP was significantly higher during 9% NaCl infusion in Fat rats compared with NFD rats. In the open-loop analysis of carotid sinus baroreflex, a rightward shift of the neural arc was observed in Fat rats compared with NFD rats. Furthermore, distensibility of the common carotid artery was significantly reduced in Fat rats. These results indicate that a reduced baroreceptor distensibility-induced rightward shift of the neural arc might contribute to impairment of sodium regulation in Fat rats.

Systemic vascular effects of acute electrical baroreflex stimulation.

We intended to determine if acute baroreflex activation therapy (BAT) increases venous capacitance and aortic conductance. BAT is effective in resistant hypertension, but its effect on the systemic vasculature is poorly understood. Left ventricular (LV) and aortic pressures and subdiaphragmatic aortic and caval flows (ultrasonic) were measured in six anesthetized dogs. Changes in abdominal blood volume (Vabdominal) were estimated as the integrated difference in abdominal aortic inflow and caval outflow. An electrode was implanted on the right carotid sinus. Data were measured during control and BAT. Next, sodium nitroprusside (SNP) was infused and BAT was subsequently added. Finally, angiotensin II (ANG II) was infused, and three increased BAT currents were added. We found that BAT decreased mean aortic pressure (PAo) by 22.5 ± 1.3 mmHg (P < 0.001) and increased aortic conductance by 16.2 ± 4.9% (P < 0.01) and Vabdominal at a rate of 2.2 ± 0.6 ml·kg(-1)·min(-1) (P < 0.01). SNP decreased PAo by 17.4 ± 0.7 mmHg (P < 0.001) and increased Vabdominal at a rate of 2.2 ± 0.7 ml·kg(-1)·min(-1) (P < 0.05). During the SNP infusion, BAT decreased PAo further, by 26.0 ± 2.1 mmHg (P < 0.001). ANG II increased PAo by 40.4 ± 3.5 mmHg (P = 0.001). When an increased BAT current was added, PAo decreased to baseline (P < 0.01) while aortic conductance increased from 62.3 ± 5.2% to 80.2 ± 3.3% (P < 0.05) of control. Vabdominal increased at a rate of 1.8 ± 0.9 ml·kg(-1)·min(-1) (P < 0.01), reversing the ANG II effects. In conclusion, BAT increases arterial conductance, decreases PAo, and increases venous capacitance even in the presence of powerful vasoactive drugs. Increasing venous capacitance may be an important effect of BAT in hypertension.

Stimulation of the cardiopulmonary baroreflex enhances ventricular contractility in awake dogs: a mathematical analysis study.

The cardiopulmonary baroreflex responds to an increase in central venous pressure (CVP) by decreasing total peripheral resistance and increasing heart rate (HR) in dogs. However, the direction of ventricular contractility change is not well understood. The aim was to elucidate the cardiopulmonary baroreflex control of ventricular contractility during normal physiological conditions via a mathematical analysis. Spontaneous beat-to-beat fluctuations in maximal ventricular elastance (Emax), which is perhaps the best available index of ventricular contractility, CVP, arterial blood pressure (ABP), and HR were measured from awake dogs at rest before and after ß-adrenergic receptor blockade. An autoregressive exogenous input model was employed to jointly identify the three causal transfer functions relating beat-to-beat fluctuations in CVP to Emax (CVP → Emax), which characterizes the cardiopulmonary baroreflex control of ventricular contractility, ABP to Emax, which characterizes the arterial baroreflex control of ventricular contractility, and HR to Emax, which characterizes the force-frequency relation. The CVP → Emax transfer function showed a static gain of 0.037 ± 0.010 ml(-1) (different from zero; P < 0.05) and an overall time constant of 3.2 ± 1.2 s. Hence, Emax would increase and reach steady state in ∼16 s in response to a step increase in CVP, without any change to ABP or HR, due to the cardiopulmonary baroreflex. Following ß-adrenergic receptor blockade, the CVP → Emax transfer function showed a static gain of 0.0007 ± 0.0113 ml(-1) (different from control; P < 0.10). Hence, Emax would change little in steady state in response to a step increase in CVP. Stimulation of the cardiopulmonary baroreflex increases ventricular contractility through ß-adrenergic receptor system mediation.

Effects of peripheral and spinal κ-opioid receptor stimulation on the exercise pressor reflex in decerebrate rats.

The exercise pressor reflex is greater in rats with ligated femoral arteries than it is in rats with freely perfused femoral arteries. The exaggerated reflex in rats with ligated arteries is attenuated by stimulation of µ-opioid and δ-opioid receptors on the peripheral endings of thin-fiber muscle afferents. The effect of stimulation of κ-opioid receptors on the exercise pressor reflex is unknown. We tested the hypothesis that stimulation of κ-opioid receptors attenuates the exercise pressor reflex in rats with ligated, but not freely perfused, femoral arteries. The pressor responses to static contraction were compared before and after femoral arterial or intrathecal injection of the κ-opioid receptor agonist U62066 (1, 10, and 100 µg). Femoral arterial injection of U62066 did not attenuate the pressor responses to contraction in either group of rats. Likewise, intrathecal injection of U62066 did not attenuate the pressor response to contraction in rats with freely perfused femoral arteries. In contrast, intrathecal injection of 10 and 100 µg of U62066 attenuated the pressor response to contraction in rats with ligated femoral arteries, an effect that was blocked by prior intrathecal injection of the κ-opioid receptor antagonist nor-binaltorphimine. In rats with ligated femoral arteries, the pressor response to stimulation of peripheral chemoreceptors by sodium cyanide was not changed by intrathecal U62066 injections, indicating that these injections had no direct effect on the sympathetic outflow. We conclude that stimulation of spinal, but not peripheral, κ-opioid receptors attenuates the exaggerated exercise pressor reflex in rats with ligated femoral arteries.

The left ventricle increases contractility in response to baroreceptor unloading, which is sympathetically mediated in the anesthetized rat.

Contemporary discussion of the baroreflex includes the efferent vascular-sympathetic and cardiovagal arms. Since sympathetic postganglionic neurons also innervate the left ventricle (LV), it is often assumed that the LV produces a sympathetically mediated increase in contractility during baroreceptor unloading, but this has not been characterized using a load-independent index of contractility. We aimed to determine 1) whether LV contractility increases in response to baroreceptor unloading and 2) whether such increases are mediated via the sympathetic or parasympathetic arm of the autonomic nervous system. Ten male Wistar rats were anesthetized (urethane) and instrumented with arterial and LV pressure-volume catheters to measure mean arterial pressure (MAP) and load-independent LV contractility [maximal rate of increase in pressure adjusted to end-diastolic volume (PAdP/dtmax)], respectively. Rats were placed in a servo-controlled lower-body negative pressure (LBNP) chamber to reduce MAP by 10% for 60 s to mechanically unload baroreceptors under control conditions. LBNP was repeated in each animal following infusions of cardiac autonomic blockers using esmolol (sympathetic), atropine (parasympathetic), and esmolol + atropine. Under control conditions, PAdP/dtmax increased during baroreceptor unloading (26 ± 6 vs. 31 ± 9 mmHg·s-1·µL-1, P = 0.031). During esmolol, there was no increase in LV contractility during baroreceptor unloading (11 ± 2 vs. 12 ± 2, P = 0.125); however, during atropine, there was an increase in LV contractility during baroreceptor unloading (26 ± 6 vs. 31 ± 9, P = 0.019). During combined esmolol and atropine, there was a small increase in contractility versus control (13 ± 3 vs. 15 ± 4, P = 0.046). Our results demonstrate that, in anesthetized rats, LV contractility increases in response to baroreceptor unloading, which is largely sympathetically mediated.NEW & NOTEWORTHY This study empirically demonstrates a sympathetically mediated increase in LV contractility in response to baroreceptor unloading using a load-independent index of cardiac contractility in the anesthetized rat.

Short-term administration of progesterone and estradiol independently alter carotid-vasomotor, but not carotid-cardiac, baroreflex function in young women.

The individual effects of estrogen and progesterone on baroreflex function remain poorly understood. We sought to determine how estradiol (E2) and progesterone (P4) independently alter the carotid-cardiac and carotid-vasomotor baroreflexes in young women by using a hormone suppression and exogenous add-back design. Thirty-two young women were divided into two groups and studied under three conditions: 1) after 4 days of endogenous hormone suppression with a gonadotropin releasing hormone antagonist (control condition), 2) after continued suppression and 3 to 4 days of supplementation with either 200 mg/day oral progesterone (N = 16) or 0.1 to 0.2 mg/day transdermal 17ß-estradiol (N = 16), and 3) after continued suppression and 3 to 4 days of supplementation with both hormones. Changes in heart rate (HR), mean arterial pressure (MAP), and femoral vascular conductance (FVC) were measured in response to 5 s of +50 mmHg external neck pressure to unload the carotid baroreceptors. Significant hormone effects on the change in HR, MAP, and FVC from baseline at the onset of neck pressure were determined using mixed model covariate analyses accounting for P4 and E2 plasma concentrations. Neither P4 (P = 0.95) nor E2 (P = 0.95) affected the HR response to neck pressure. Higher P4 concentrations were associated with an attenuated fall in FVC (P = 0.01), whereas higher E2 concentrations were associated with an augmented fall in FVC (P = 0.02). Higher E2 was also associated with an augmented rise in MAP (P = 0.01). We conclude that progesterone blunts whereas estradiol enhances carotid-vasomotor baroreflex sensitivity, perhaps explaining why no differences in sympathetic baroreflex sensitivity are commonly reported between low and high combined hormone phases of the menstrual cycle.

Spinal cord GABA receptors modulate the exercise pressor reflex in decerebrate rats.

Neurotransmitters and neuromodulators released by contraction-activated skeletal muscle afferents into the dorsal horn of the spinal cord initiate the central component of the exercise pressor reflex (EPR). Whether γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter within the mammalian central nervous system, is involved in the modulation of the EPR at the level of dorsal horn remains to be determined. We performed local microinjection of either the GABA(A) antagonist bicuculline or the GABA(B) antagonist CGP 52432 into the ipisilateral L4/L5 dorsal horns to investigate the effect of GABA receptor blockade on the pressor response to either static contraction induced by stimulation of the peripheral end of L4/L5 ventral roots, passive stretch, or hindlimb arterial injection of capsaicin (0.1 µg/0.2 ml) in decerebrate rats. Microinjection of either bicuculline (1 mM, 100 nl) or CGP 52432 (10 mM, 100 nl) into the L4/5 dorsal horns significantly increased the pressor and cardioaccelerator responses to all stimuli. Microinjection of either bicuculline or CGP 52432 into the L5 dorsal horn significantly increased the pressor and cardioaccelerator responses to direct microinjection of l-glutatmate (10 mM, 100 nl) into this spinal segment. The disinhibitory effect of both GABA receptor antagonists on the EPR was abolished by microinjection of the broad-spectrum glutamate receptor antagonist kynurenate (10 mM/100 nl). These data suggest that 1) GABA exerts a tonic inhibition of the EPR at the level of dorsal horn; and 2) that an interaction between glutamatergic and GABAergic inputs exist at the level of dorsal horn, contributing to spinal control of the EPR.

Effects of isoflurane anesthesia on aortic compliance and systemic hemodynamics in compliant and noncompliant aortas.

OBJECTIVES: To investigate the effect of general anesthesia on aortic compliance and other cardiovascular hemodynamics in chronically instrumented pigs with compliant and noncompliant (stiff) aortas. DESIGN: Experimental study. SETTING: University animal laboratory. PARTICIPANTS: Twelve adult Yucatan miniature pigs. INTERVENTIONS: Chronic instrumentation of a compliant (control; n = 7) and noncompliant (n = 5) group to measure pressure and flow in the ascending aorta. A Teflon prosthesis was wrapped around the aorta (noncompliant group) to limit wall compliance. MEASUREMENTS AND MAIN RESULTS: Hemodynamic parameters were recorded on the 15th postoperative day, both awake and after general anesthesia. Banding the aorta caused a significant decrease in arterial compliance (-49%, p<0.001) and increases in systolic blood pressure (SBP: +38%, p = 0.001) and pulse pressure (+107%, p< 0.01). Induction of anesthesia in the control group produced a 15% increase in arterial compliance (p<0.05), resulting in a subtle decrease in SBP (-12%), diastolic blood pressure (DBP; -13%) and mean blood pressure (MBP; -12%). Induction of anesthesia in the noncompliant group also caused a significant increase in arterial compliance (17%, p<0.001), but caused significant decreases in SBP (21%, p<0.01), DBP (23%, p<0.01) and MBP (22%, p<0.01) as compared with controls. CONCLUSIONS: Induction of general anesthesia caused a similar increase in total arterial compliance and was associated with a decrease in SBP that was more pronounced in animals with noncompliant aortas. These results indicated that anesthesia caused a greater hemodynamic effect on noncompliant (stiff) aortas and may explain the extensive hemodynamic fluctuation and instability often observed in atherosclerotic, elderly patients with stiff aortas.

Enhanced activation of RVLM-projecting PVN neurons in rats with chronic heart failure.

Previous studies have indicated that there is increased activation of the paraventricular nucleus (PVN) in rats with chronic heart failure (CHF); however, it is not clear if the preautonomic neurons within the PVN are specifically overactive. Also, it is not known if these neurons have altered responses to baroreceptor or osmotic challenges. Experiments were conducted in rats with CHF (6-8 wk after coronary artery ligation). Spontaneously active neurons were recorded in the PVN, of which 36% were antidromically activated from the rostral ventrolateral medulla (RVLM). The baseline discharge rate in RVLM-projecting PVN (PVN-RVLM) neurons from CHF rats was significantly greater than in sham-operated (sham) rats (6.0 ± 0.6 vs. 2.6 ± 0.3 spikes/s, P < 0.05). Picoinjection of the N-methyl-D-aspartate (NMDA) receptor antagonist D,L-2-amino-5-phosphonovaleric acid significantly decreased the basal discharge of PVN-RVLM neurons by 80% in CHF rats compared with 37% in sham rats. Fifty-two percent of spontaneously active PVN-RVLM neurons responded to changes in the mean arterial pressure (MAP). The changes in discharge rate in PVN-RVLM neurons after a reduction in MAP (+52 ± 7% vs. +184 ± 61%) or an increase in MAP (-42 ± 8% vs. -71 ± 6%) were significantly attenuated in rats with CHF compared with sham rats. Most PVN-RVLM neurons (63%), including all barosensitive PVN-RVLM neurons, were excited by an internal carotid artery injection of hypertonic NaCl (2.1 osmol/l), whereas a smaller number (7%) were inhibited. The increase in discharge rate in PVN-RVLM neurons to hypertonic stimulation was significantly enhanced in rats with CHF compared with sham rats (134 ± 15% vs. 92 ± 13%). Taken together, these data suggest that PVN-RVLM neurons are more active under basal conditions and this overactivation is mediated by an enhanced glutamatergic tone in rats with CHF. Furthermore, this enhanced activation of PVN-RVLM neurons may contribute to the altered responses to baroreceptor and osmotic challenges observed during CHF.

Vardenafil in pulmonary arterial hypertension: a randomized, double-blind, placebo-controlled study.

RATIONALE: Although the phosphodiesterase type 5 inhibitors sildenafil and tadalafil have demonstrated efficacy in patients with pulmonary arterial hypertension (PAH), monotherapy with these agents has not been conclusively shown to reduce clinical worsening events. OBJECTIVES: To evaluate the safety and efficacy of the phosphodiesterase type 5 inhibitor vardenafil in Chinese patients with PAH. METHODS: In a randomized, double-blind, placebo-controlled study, 66 patients with PAH were randomized 2:1 to vardenafil (5 mg once daily for 4 wk then 5 mg twice daily; n = 44) or placebo (n = 22) for 12 weeks. Patients completing this phase were then treated with open-label vardenafil (5 mg twice daily) for a further 12 weeks. MEASUREMENTS AND MAIN RESULTS: At Week 12, the mean placebo-corrected 6-minute walking distance was increased with vardenafil (69 m; P < 0.001), and this improvement was maintained for at least 24 weeks. Vardenafil also increased the mean placebo-corrected cardiac index (0.39 L·min(-1)·m(-2); P = 0.005) and decreased mean pulmonary arterial pressure and pulmonary vascular resistance (-5.3 mm Hg, P = 0.047; -4.7 Wood U, P = 0.003; respectively) at Week 12. Four patients in the placebo group (20%) and one in the vardenafil group (2.3%) had clinical worsening events (hazard ratio 0.105; 95% confidence interval, 0.012-0.938; P = 0.044). Vardenafil was associated with only mild and transient adverse events. CONCLUSIONS: Vardenafil is effective and well tolerated in patients with PAH at a dose of 5 mg twice daily.

Detrimental effects of mechanical stretch on smooth muscle function in saphenous veins.

OBJECTIVE: This study evaluated the smooth muscle functional response and viability of human saphenous vein (HSV) grafts after harvest and explored the effect of mechanical stretch on contractile responses of porcine saphenous vein (PSV). METHODS: The contractile responses (stress, 10(5) N/m(2)) of deidentified, remnant HSV grafts to depolarizing potassium chloride and the agonist norepinephrine were measured in a muscle organ bath. Cellular viability was evaluated using a methyl thiazole tetrazolium (MTT) assay. A PSV model was used to evaluate the effect of radial, longitudinal, and angular stretch on smooth muscle contractile responses. RESULTS: Contractile responses varied greatly in HSV harvested for autologous vascular and coronary bypass procedures (0.04198 ± 0.008128 × 10(5) N/m(2) to 0.1192 ± 0.02776 × 10(5) N/m(2)). Contractility of the HSV correlated with the cellular viability of the grafts. In the PSV model, manual radial distension of ≥ 300 mm Hg had no impact on the smooth muscle responses of PSV to potassium chloride. Longitudinal and angular stretch significantly decreased the contractile function of PSV by 33.16% and 15.26%, respectively (P < .03). CONCLUSIONS: There is considerable variability in HSV harvested for use as an autologous conduit. Longitudinal and angular stretching during surgical harvest impairs contractile responsiveness of the smooth muscle in saphenous vein. Avoiding stretch-induced injuries to the conduits during harvest and preparation for implantation may reduce adverse biologic responses in the graft (eg, intimal hyperplasia) and improve patency of autologous vein graft bypasses.

Responses of neurons in paraventricular nucleus to activation of cardiac afferents and acute myocardial ischaemia in rats.

Stimulation of cardiac sympathetic afferents increases sympathetic outflow and blood pressure. Chemicals released during myocardial ischaemia activate cardiac afferents. This study was to determine the responses of neurons in paraventricular nucleus (PVN) to the cardiac afferent activation caused by exogenous chemicals or myocardial ischaemia using an extracellular single-unit recording method. Rats were anaesthetized and underwent bilateral cervical vagal denervation (VD) and carotid and aortic baroreceptor denervation (BD). In 196 spontaneously active neurons in parvicellular PVN, 60 (30.6%), 36 (18.4%) and 91 (46.4%) neurons were respectively sensitive, mildly sensitive and insensitive to capsaicin, while nine (4.6%) neurons showed inhibitory responses to capsaicin. Epicardial application of capsaicin activated capsaicin-sensitive neurons in the PVN and increased mean arterial pressure. These neurons were also sensitive to exogenous bradykinin, adenosine and H(2)O(2). The neuron response is not secondary to a capsaicin-induced increase in mean arterial pressure because a similar degree of pressor response induced by aortic coarctation did not increase the neuron activity. Compared with intact rats, VD or BD or combined VD and BD increased the response of capsaicin-sensitive neurons to epicardial application of capsaicin, while stimulation of vagal afferents inhibited the response. Myocardial ischaemia caused increases in the activity of capsaicin-sensitive neurons and renal sympathetic nerve activity. The results indicate that chemical stimulation of cardiac sympathetic afferents activates capsaicin-sensitive neurons in parvicellular PVN, which is inhibited by the afferent activities of vagi and arterial baroreceptors. Acute myocardial ischaemia activates capsaicin-sensitive neurons in PVN and enhances sympathetic outflow.

α-Adrenergic effects on low-frequency oscillations in blood pressure and R-R intervals during sympathetic activation.

The present study was designed to address the contribution of α-adrenergic modulation to the genesis of low-frequency (LF; 0.04-0.15 Hz) oscillations in R-R interval (RRi), blood pressure (BP) and muscle sympathetic nerve activity (MSNA) during different sympathetic stimuli. Blood pressure and RRi were measured continuously in 12 healthy subjects during 5 min periods each of lower body negative pressure (LBNP; -40 mmHg), static handgrip exercise (HG; 20% of maximal force) and postexercise forearm circulatory occlusion (PECO) with and without α-adrenergic blockade by phentolamine. Muscle sympathetic nerve activity was recorded in five subjects during LBNP and in six subjects during HG and PECO. Low-frequency powers and median frequencies of BP, RRi and MSNA were calculated from power spectra. Low-frequency power during LBNP was lower with phentolamine versus without for both BP and RRi oscillations (1.6 ± 0.6 versus 1.2 ± 0.7 ln mmHg(2), P = 0.049; and 6.9 ± 0.8 versus 5.4 ± 0.9 ln ms(2), P = 0.001, respectively). In contrast, the LBNP with phentolamine increased the power of high-frequency oscillations (0.15-0.4 Hz) in BP and MSNA (P < 0.01 for both), which was not observed during saline infusion. Phentolamine also blunted the increases in the LBNP-induced increase in frequency of LF oscillations in BP and RRi. Phentolamine decreased the LF power of RRi during HG (P = 0.015) but induced no other changes in LF powers or frequencies during HG. Phentolamine resulted in decreased frequency of LF oscillations in RRi (P = 0.004) during PECO, and a similar tendency was observed in BP and MSNA. The power of LF oscillation in MSNA did not change during any intervention. We conclude that α-adrenergic modulation contributes to LF oscillations in BP and RRi during baroreceptor unloading (LBNP) but not during static exercise. Also, α-adrenergic modulation partly explains the shift to a higher frequency of LF oscillations during baroreceptor unloading and muscle metaboreflex activation.