Ventilated Rats Research Articles

Electrical impedance tomography is able to track changes in respiratory function in endotoxin‐challenged rodents

In order to assess and optimize the effect of new therapies for acute lung injury (ALI) in rodent models, a monitoring technique that continuously assesses the functional state of the lung is mandatory. Electrical impedance tomography (EIT) has been suggested as a technique for quantifying lung inflammation in ALI. However, EIT has not been evaluated in a rodent model of ALI. EIT measurements were compared in ventilated Sprague-Dawley rats (n = 14), randomly subjected to intratracheal administration of endotoxin (LPS) or saline (control). Lung mechanics, lung weight wet/dry ratio and inflammatory markers in bronchoalveolar lavage fluid were also evaluated. LPS caused a significant decrease in lung compliance and TLC as compared with control (-42.0%, P = 0.04, and -27.9%, P = 0.02, respectively). These changes were paralleled by differences in mean impedance changes as detected by EIT (Spearman's rank correlation coefficient: rho = 0.66 and 0.73, respectively, P < 0.01). LPS increased the lung weight wet/dry ratio (6.35 +/- 0.42 vs 5.15 +/- 0.07, P = 0.003), and the bronchoalveolar lavage total WCC (8.96 +/- 1.87 vs 1.16 +/- 0.10 x 10(9)/L, P = 0.002) as compared with control. The lung weight wet/dry ratio was inversely related to the mean impedance change (rho = -0.76, P < 0.01). This study has demonstrated for the first time that eight-electrode EIT readily tracks the inflammatory response of lung tissue in a rodent model of ALI. EIT may thus provide a promising, non-invasive technique for monitoring the time-course of ALI in rodent models, and for testing novel pharmacological strategies to counter it.

MR imaging of apparent 3He gas transport in narrow pipes and rodent airways

High sensitivity makes hyperpolarized 3He an attractive signal source for visualizing gas flow with magnetic resonance (MR) imaging. Its rapid Brownian motion, however, can blur observed flow lamina and alter measured diffusion rates when excited nuclei traverse shear-induced velocity gradients during data acquisition. Here, both effects are described analytically, and predicted values for measured transport during laminar flow through a straight, 3.2-mm diameter pipe are validated using two-dimensional (2D) constant-time images of different binary gas mixtures. Results show explicitly how measured transport in narrow conduits is characterized by apparent values that depend on underlying gas dynamics and imaging time. In ventilated rats, this is found to obscure acquired airflow images. Nevertheless, flow splitting at airway branches is still evident and use of 3D vector flow mapping is shown to reveal surprising detail that highlights the correlation between gas dynamics and lung structure.

Release of neuroendocrine products in the pulmonary circulation during intermittent hypoxia in isolated rat lung

The aim of this study was to evaluate the release of neuroendocrine (NE) products into the pulmonary circulation during intermittent hypoxia (IH) in isolated buffer-perfused and ventilated rat lungs. Isolated single-pass perfused rat lungs were repeatedly ventilated with hypoxic (2% O(2)) and normoxic (21% O(2)) gases for 5-min intervals. Perfusate collected during the study was analysed for bombesin-like-peptides (BLPs) and serotonin. In addition, immunohistochemical evaluation of the neuropeptides calcitonin gene-related peptide (CGRP) and chromogranin A (CgA) in the lung was performed. During IH, perfusate levels of BLPs decreased compared to lungs ventilated with normoxic gas only. After 15 min of IH, perfusate levels of BLPs were significantly lower than at corresponding time in normoxic lungs (2.6+/-0.7 pg ml(-1) versus 9.2+/-1.9 pg ml(-1), p=0.036). No significant difference between the study groups was observed in perfusate levels of serotonin. Immunohistochemical evaluation of the lungs revealed significantly increased number of pulmonary NE cells immunoreactive for CGRP in IH ventilated lungs compared to controls (10.1+/-1.5 neuroepithelial bodies (NEBs) (cm(2))(-1) versus 5.0+/-1.5 NEBs (cm(2))(-1), p=0.032). No change in the immunoreactivity for CgA was observed. The present study suggests that intermittent periods of hypoxia are associated with a rapid physiological modulation of the release of NE products into the pulmonary circulation in an isolated rat lung model.

Susceptibility to systolic dysfunction in the myocardium from chronically infarcted spontaneously hypertensive rats

We explored whether the hypertensive heart is susceptible to myocardial dysfunction in viable noninfarcted tissue post-myocardial infarction (MI), the potential mechanisms thereof, and the impact of these changes on pump function. Six to seven months after the ligation of the left anterior descending coronary artery, left ventricular (LV) myocardial systolic function, as assessed from the percent shortening of the noninfarcted lateral wall segmental length determined over a range of filling pressures (ultrasonic transducers placed in the lateral wall in anaesthetized, open-chest, ventilated rats) and the percent thickening of the posterior wall (echocardiography), was reduced in infarcted spontaneous hypertensive rats (SHR-MI) (P < 0.05) but not in normotensive Wistar-Kyoto (WKY-MI) animals compared with corresponding controls [SHR-sham operations (Sham) and WKY-Sham]. This change in the regional myocardial function in SHR-MI, but not in WKY-MI, occurred despite a similar degree of LV dilatation (increased LV end-diastolic dimensions and volume intercept of the LV end-diastolic pressure-volume relation) in SHR-MI and WKY-MI rats and a lack of difference in LV relative wall thinning, LV wall stress, apoptosis [terminal deoxynucleotidyl transferase biotin-dUTP nick-end labeling (TUNEL)], or necrosis (pathological score) between SHR-MI and WKY-MI rats. Although the change in regional myocardial function in the SHR-MI group was not associated with a greater reduction in baseline global LV chamber systolic function [end-systolic elastance (LV E(es)) and endocardial fractional shortening determined in the absence of an adrenergic stimulus], in the presence of an isoproterenol challenge, noninfarct-zone LV systolic myocardial dysfunction manifested in a significant reduction in LV E(es) in SHR-MI compared with WKY-MI and SHR and WKY-Sham rats (P < 0.04). In conclusion, these data suggest that with chronic MI, the hypertensive heart is susceptible to the development of myocardial dysfunction, a change that cannot be attributed to excessive chamber dilatation, apoptosis, or necrosis, but which in turn contributes toward a reduced cardiac adrenergic inotropic reserve.

Preconditioning by inhaled nitric oxide prevents hyperoxic and ischemia/reperfusion injury in rat lungs

Since the generation of nitric oxide (NO) is an essential step in the trigger phase of ischemic preconditioning, short-term inhalation of NO before ischemia should ameliorate ischemia/reperfusion (I/R) injury of the lung. We tested this hypothesis in high oxygen (>99%) ventilated rats in order to additionally evaluate compatibility of NO and exposure to hyperoxia. Male adult Sprague–Dawley rats inhaled NO (15 ppm, 10 min) before the left lung hilum was clamped for 1 h, and the reperfusion phase was observed for 4 h (NO group). Animals in the I/R group underwent the same treatment, but without NO inhalation. A third group without I/R served as time-matched controls. Animals in the I/R group showed severe I/R injury in terms of arterial pO 2 (apO 2), which was reduced to 22% of surgical controls (SCs) at time point 30 min reperfusion, and increased endothelial permeability (Evans blue procedure). The pretreatment with NO attenuated these effects. The pO 2 after 4 h reperfusion was still 3.0-fold higher in the NO group compared to I/R. In contrast, the I/R- and hyperoxia-induced invasion of leukocytes, as determined by measuring myeloperoxidase (MPO) activity, was not affected by NO. These data were correlated with the activity of major cellular signaling pathways by measuring the phosphorylation at activating and inhibitory sites of extracellular-signal regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, protein kinase B (AKT), and glycogen synthase kinase 3 β (GSK-3 β), and by determination of cGMP in plasma and lung tissue. Inhalation of NO partly prevented the loss of activation by I/R and hyperoxic ventilation of ERK, JNK, and AKT, and it reduced the I/R-induced activation of GSK-3 β. The level of cGMP in plasma and lung tissue was increased in the NO group after 4 h reperfusion. In conclusion, application of inhaled NO in the preconditioning mode prevented I/R injury in the rat lung without interfering effects of hyperoxic ventilation. The effects of NO on cellular signaling pathways resemble mechanisms of ischemic preconditioning, but further studies have to evaluate the physiological relevance of these results.

Ca ++ influx is essential for the hypotensive response to arginine vasopressin-induced neuron activation of the area postrema in the rat

We attempted to relate the signal pathway to the hypotension induced by arginine vasopressin (AVP) injection into the area postrema (AP) in urethane-anesthetized and ventilated rats with vagotomy. A femoral artery and vein were catheterized to measure the blood pressure (BP) and administer drugs, respectively. The rat was placed on a stereotaxic apparatus to expose the calamus sriptorius (CS) by craniostomy and maintained at normocapnia in hyperoxia. In protocol 1, hypotension evoked by AVP (3.0 × 10 − 5 IU) microinjected into the AP 0.2 mm rostral to the CS of the midline was abolished by V 1A antagonist, U73122 (phospholipase C blocker), and BAPTA-AM (Ca ++ chelator), suggesting that an increasing intracellular Ca ++ is essential for AVP-induced hypotension. In protocol 2, AVP-induced hypotension was abolished by EGTA (extracellular Ca ++ chelator) and Ca ++ blockers such as nifedipine, nimodipine (L-types), and omega-conotoxin MVIIC (P/Q-type), but not by omega-conotoxin GVIA (N-type). In protocol 3, AVP-induced hypotension was blocked by calphostin C (protein kinase C inhibitor) and mimicked by an increase in intracellular K + ions that was reversed by EGTA. Vehicle injections produced no changes in BP. In protocol 4, glutamate-induced hypotension was reversed by BAPTA-AM but not by EGTA or V 1A antagonist. Our data suggest that AVP-induced hypotension depends on Ca ++ influx through a signal pathway from phospholipase C to protein kinase C which inactivates K + channels that may depolarize AP neurons to activate L- and P/Q-type Ca ++ channels. This may provide new insights into establishing a relationship between the signal pathway and physiological functions.

Sevoflurane Affects Neurogenesis After Forebrain Ischemia in Rats

The effect of sevoflurane on the neuroregenerative potential after neuronal injury is unclear. We investigated the effect of low and high concentrations of sevoflurane on endogenous neurogenesis after cerebral ischemia. Anesthetized and ventilated rats were randomized to four different treatment groups. Groups 1 and 2: 1.4% sevoflurane; Groups 3 and 4: 2.8% sevoflurane. In Groups 1 and 3, no cerebral ischemia was induced (sham-operated). In Groups 2 and 4, 10 min of forebrain ischemia was induced by bilateral carotid artery occlusion plus hemorrhagic hypotension. Physiological variables were maintained constant. Bromodeoxyuridine was given as a marker of neurogenesis. After 28 days brains were perfused. Histopathological damage of the hippocampus was evaluated in hematoxylin and eosin (HE) stained sections using the HE-index (0 = no damage; 1 = 1%-10% damage; 2 = 11%-50% damage; 3 = 51%-100% damage). Immunohistochemistry was used to detect bromodeoxyuridine-positive neurons. Eight untreated rats were investigated as naive controls (Group 5). In neither sham-operated group was histopathological damage or change in neurogenesis observed compared to naive controls. In rats anesthetized with 1.4% sevoflurane, cerebral ischemia caused mild neuronal damage (HE-index of 0.64 +/- 0.84) and increased neurogenesis by 60% when compared with respective sham-operated animals; with 2.8% sevoflurane, the HE-index was 1.22 +/- 1.14, and the number of newly generated neurons increased by 230% when compared with respective sham-operated animals. The present data suggest that high concentrations of sevoflurane stimulate neurogenesis in the dentate gyrus after cerebral ischemia.

Baro‐activated neurons in the caudal ventrolateral medulla (CVLM) are differentially affected by stimulation of the ventrolateral periaqueductal gray (vlPAG)

The vlPAG evokes autonomic responses related to pain and motivated behaviors. Activation of the vlPAG decreases sympathetic nerve activity (SNA) and arterial pressure (AP) in anesthetized rats, but the central pathways are not completely understood. The vlPAG projects to the CVLM, but the nature and function of this projection are unknown. Stimulation of the CVLM decreases SNA and AP by excitation of baro-activated GABAergic CVLM neurons. We examined the hypotheses that the projection from the vlPAG to the CVLM is excitatory and that stimulation of the vlPAG excites baro-activated CVLM neurons. Injection of the retrograde tracer, Fluoro-gold, into the CVLM (6 rats) yielded a robust ipsilateral projection from the vlPAG. The retrogradely labeled neurons spanned −6.5 to −8.0 mm caudal to bregma and most neurons expressed vesicular glutamate transporter 2 mRNA (75 %, 51–100%), suggesting they were glutamatergic. In chloralose-anesthetized, ventilated rats stimulation of the vlPAG (20 nmol DLH/100 nl) decreased SNA 25+/−2% and AP 15+/−1 mmHg and produced heterogeneous responses in ipsilateral baro-activated CVLM neurons (n=27). A subset were clearly activated (82+/−13%, n=7), and others were unaffected (n=7), or inhibited (−74+/−12%, n=13; perhaps by the decreased AP). These results suggest that the vlPAG may be an excitatory input to a subset of baro-activated CVLM neurons and that these CVLM neurons may contribute to the observed vlPAG-mediated decreases in SNA and AP. Funding NIH HL075174 to AMS.

Altered regulation of sympathetic nerve activity and arterial pressure by the rostral ventrolateral medulla in obese Zucker rats

Adult obese Zucker rats (OZR) have elevated sympathetic nerve activity (SNA) and arterial pressure (AP) with blunted baroreflexes compared to lean Zucker rats (LZR). In addition, sympatho-excitatory reflexes mediated by glutamatergic activation of the rostral ventrolateral medulla (RVLM) are exaggerated in OZR. In contrast, in juvenile OZR, although sympatho-excitatory responses appear to be exaggerated, baseline AP and baroreflexes are comparable to those observed in LZR. We examined the hypothesis that glutamatergic activation of the RVLM would yield exaggerated increases in sympathetic nerve activity (SNA) in juvenile and adult OZR. Furthermore, we determined whether the increased SNA and AP observed in adult OZR could be explained by an enhanced drive from the RVLM. In urethane-anesthetized, ventilated rats microinjection of glutamate (1nmol) increased SNA and AP more in both juvenile (7 wks) and adult (14 wks) OZR compared to age-matched LZR (n=8/group, P <0.05). In adult OZR bilateral inhibition of the RVLM with muscimol (100 pmol) virtually eliminated SNA (>85%) and produced a larger decrease in AP compared to adult LZR (P <0.05). In contrast, in juvenile rats inhibition of the RVLM produced comparable decreases in AP in OZR and LZR. These data suggest that exaggerated sympatho-excitatory reflexes may be due to enhanced excitability of the RVLM in juvenile and adult OZR. In addition the increased baseline AP in adult OZR is associated with an enhanced drive from the RVLM that is not present in juvenile OZR. Support NIH HL075174 to AMS.

Inhibitory input from slowly adapting lung stretch receptors to retrotrapezoid nucleus chemoreceptors

The retrotrapezoid nucleus (RTN) contains CO(2)-activated interneurons with properties consistent with central respiratory chemoreceptors. These neurons are glutamatergic and express the transcription factor Phox2b. Here we tested whether RTN neurons receive an input from slowly adapting pulmonary stretch receptors (SARs) in halothane-anaesthetized ventilated rats. In vagotomized rats, RTN neurons were inhibited to a variable extent by stimulating myelinated vagal afferents using the lowest intensity needed to inhibit the phrenic nerve discharge (PND). In rats with intact vagus nerves, RTN neurons were inhibited, also to a variable extent, by increasing positive end-expiratory pressure (PEEP; 2-6 cmH(2)O). The cells most sensitive to PEEP were inhibited during each lung inflation at rest and were instantly activated by stopping ventilation. Muscimol (GABA-A agonist) injection in or next to the solitary tract at area postrema level desynchronized PND from ventilation, eliminated the lung inflation-synchronous inhibition of RTN neurons and their steady inhibition by PEEP but did not change their CO(2) sensitivity. Muscimol injection into the rostral ventral respiratory group eliminated PND but did not change RTN neuron response to either lung inflation, PEEP increases, vagal stimulation or CO(2). Generalized glutamate receptor blockade with intracerebroventricular (i.c.v.) kynurenate eliminated PND and the response of RTN neurons to lung inflation but did not change their CO(2) sensitivity. PEEP-sensitive RTN neurons expressed Phox2b. In conclusion, RTN chemoreceptors receive an inhibitory input from myelinated lung stretch receptors, presumably SARs. The lung input to RTN may be di-synaptic with inhibitory pump cells as sole interneurons.

NONISCHEMIC LUNG INJURY BY MEDIATORS FROM UNILATERAL ISCHEMIC REPERFUSED LUNG

We hypothesized that the ischemic reperfused (I/R) lung expresses and liberates tumor necrosis factor-alpha (TNF-alpha) to injure the nonischemic lung, and that a TNF-alpha-converting enzyme inhibitor (TACEI) prevents injury of the nonischemic lung by blocking TNF-alpha liberation from the I/R lung. In isolated ventilated rat lungs in which differential perfusion to the right (RL) or left (LL) lung was feasible, LLs were selectively made ischemic (60 min) while maintaining perfusion to RLs, then reperfused (30 min) in a nonrecirculating manner with buffer solution (non-R; n = 18) or in a recirculating manner with buffer containing TACEI (TACEI[+]; n = 18) or without TACEI (TACEI[-]; n = 18). Ischemia reperfusion induced TNF-alpha messenger RNA expression in the ischemic LLs; the expression was highest in TACEI(+) group (P < 0.01). The expression of TNF-alpha, which was detected as immunofluorescence signals on CD34-positive endothelial cells, was observed in ischemic LLs; the highest expression being that in the TACEI(+) group. Wet/dry ratio and protein content in bronchoalveolar lavage fluid were higher in LLs than in RLs, and among the RLs, these 2 parameters were significantly increased in the TACEI(-) group (P < 0.01) in which the RLs were exposed to the TNF-alpha-rich perfusate. On the other hand, protein content in bronchoalveolar lavage fluid of the TACEI(+) group in which RLs were exposed to recirculating perfusate containing little TNF-alpha was decreased to a level close to but still higher than that in the non-R group (P < 0.05). The unilateral I/R lung affected the permeability of the nonischemic lung by liberating mainly TNF-alpha and induced TNF-alpha, interleukin (IL)-1beta, IL-6, and IL-10 messenger RNA expression in the nonischemic lung. These findings support the idea of organ-organ interaction in which an injured organ affects a remote organ by liberating humoral mediators.

Protein permeability in lung injury: now in real time again?

the formation and the resolution of pulmonary edema is determined by several mechanisms, including lung vascular pressure, lung endothelial and epithelial permeability to protein, and the capacity of the alveolar epithelium to effectively remove alveolar edema fluid. Impaired alveolar fluid

Tempol Reduces Warm Ischemic Damage of Lung Functions In Non‐Heart‐Beating Donors if Added Pre‐arrestly but Doesn’t Have any Protective Effect on Ischemia – Reperfusion Injury

Lungs retrieved from non-heart-beating donors (NHBD) may alleviate the critical shortage of suitable organs for transplantation. We tested the role of cell permeable reactive oxygen species scavenger – Tempol – in protection of warm ischemic and reperfusion injury of lung functions in experimental model of NHBD. We measured perfusion pressure, weight gain and arterio - venous difference in O2 partial pressure in Salt solution + Ficol perfused lungs isolated from Wistar rats in following two experiments: A Experimental rats underwent the protocol of NHBD lung harvesting: 1 hour of warm ischemia after pentobarbital euthanasia followed with 90 min of cold ischemia (12°C). Under these conditions we compared room-air ventilated rats with non-ventilated during warm ischemia and we were interested in possible protective effect of Tempol (100mg/kg) added pre-arrestly. In controls, lungs were harvested immediately after euthanasia. B We used the same protocol as in A and observed the effect of Tempol added into perfusate at the beginning of reperfusion of NHBD lungs. Ventilation during warm ischemia deteriorates lung functions by the effect of reactive oxygen species. This mechanism was in part A inhibited by pre-arrest administration of Tempol, which prevented development of lung edema and improved oxygen transport ability. In part B Tempol added into the perfusate deteriorated lung functions by causing pulmonary edema. This could be caused by Tempol-mediated inhibition of hypoxic pulmonary vasoconstriction Supported by GAUK 45/2005/C

Does propofol or caffeic acid phenethyl ester prevent lung injury after hindlimb ischaemia-reperfusion in ventilated rats?

To investigate the effects of propofol and caffeic acid phenethyl ester (CAPE) on prevention of lung injury as a remote organ after performing hindlimb ischaemia-reperfusion (IR) in a rat model. The animals were divided randomly into one of four groups: sham, no IR (n = 8), control, IR, (n = 8), CAPE group, IR with CAPE, (n = 8), propofol group, IR with P, (n = 8). After the rats were anaesthetised, the animals in the CAPE group received CAPE of 10 micromol, in the propofol group received propofol 50 mg/kg, in the control group received a similar volume of saline solution by means of intraperitoneal injection 1 h before reperfusion. After 4 h of ischaemia the tourniquet was removed and the animals were released for reperfusion for 4 h thereafter. At the end of the reperfusion period, a median sternotomy was performed. A blood sample was obtained for plasma malondialdehyde (MDA). The lung tissues were also removed for MDA assays, myeloperoxidase (MPO) activity, and histopathological examination. Plasma and lung MDA levels, and lung MPO activity were significantly higher in the control group compared to the other groups (p < 0.0005). In the CAPE group, these were significantly lower compared to the control group (p < 0.0005). Also, propofol caused a marked reduction in the MDA levels and MPO activity compared with control group (p < 0.0005), with no significant difference compared to that of the sham group. Histopathologically, the scores resulted in a grade zero (8/8) in the sham group, 3 (3/8) or 4 (5/8) in the control group, 1 (2/8) or 2 (6/8) in the CAPE group, and 1 (3/8) or 2 (5/8) in the propofol group. Propofol and CAPE seem to be effective in protecting against lung injury caused by increased oxidative stress and neutrophil accumulation after hindlimb IR in a rat model.

EXOGENOUS SURFACTANT RESTORES LUNG FUNCTION BUT NOT PERIPHERAL IMMUNOSUPPRESSION IN VENTILATED SURFACTANT-DEFICIENT RATS

The authors have previously shown that mechanical ventilation can result in increased pulmonary inflammation and suppressed peripheral leukocyte function. In the present study the effect of surfactant therapy on pulmonary inflammation and peripheral immune function in ventilated surfactant-deficient rats was assessed. Surfactant deficiency was induced by repeated lung lavage, treated rats with surfactant or left them untreated, and ventilated the rats during 2 hours. Nonventilated rats served as healthy control group. Expression of macrophage inflammatory protein (MIP)-2 was measured in bronchoalveolar lavage (BAL), interleukin (IL)-1β, and heat shock protein 70 (HSP70) were measured in total lung homogenates. Outside the lung phytohemagglutinin (PHA)-induced lymphocyte proliferation, interferon (IFN)-γ and IL-10 production, and natural killer activity were measured in splenocytes. After 2 hours of mechanical ventilation, expression of MIP-2, IL-1β, and HSP70 increased significantly in the lungs of surfactant-deficient rats. Outside the lung, mitogen-induced proliferation and production of IFN-γ and IL-10 reduced significantly. Only natural killer cell activity remained unaffected. Surfactant treatment significantly improved lung function, but could not prevent increased pulmonary expression of MIP-2, IL-1β, and HSP70 and decreased peripheral mitogen-induced lymphocyte proliferation and IFN-γ and IL-10 production in vitro. In conclusion, 2 hours of mechanical ventilation resulted in increased lung inflammation and partial peripheral leukocyte suppression in surfactant-deficient rats. Surfactant therapy ameliorated lung function but could not prevent or restore peripheral immunosuppression. The authors postulate that peripheral immunosuppression may occur in ventilated surfactant deficient patients, which may enhance susceptibility for infections.

Influence of phosphatidylglycerol on the uptake of liposomes by alveolar cells and on lung function

The effect of phosphatidylglycerol on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages as well as the effect on endogenous surfactant function was studied in vivo. Healthy ventilated rats were intratracheally instilled with fluorescent labeled liposomes with different concentrations of phosphatidylglycerol. Lung function was determined by monitoring arterial oxygenation and, at the end of the experiment, by recording static pressure-volume curves. In addition, alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that, in the presence of cofactors (Ca(2+), Mg(2+)), phosphatidylglycerol stimulates the uptake by alveolar macrophages but hardly affects the uptake by alveolar type II cells. High concentrations of phosphatidylglycerol reduce the number of alveolar macrophages in the alveolar space and deteriorate lung function. On the other hand, the presence of cofactors protects the lung against the negative effects of phosphatidylglycerol on endogenous surfactant and alveolar macrophages. This study indicates that the phosphatidylglycerol concentration may play a fundamental role in the surfactant function and metabolism depending on the presence of so-called cofactors like calcium and magnesium; further study is needed to clarify the mechanisms involved.

Nociceptin in rVLM mediates electroacupuncture inhibition of cardiovascular reflex excitatory response in rats

Electroacupuncture (EA) at Neiguan-Jianshi acupoints through an opioid mechanism inhibits the cardiovascular pressor response induced by mechanical stimulation of the stomach. Because nociceptin also may regulate cardiovascular activity through its action in the brain stem, we hypothesized that this neuromodulator serves a role in the EA-related inhibitory effect. Blood pressure in ventilated male Sprague-Dawley rats (400-600 g) anesthetized by ketamine and alpha-chloralose was measured during balloon inflation of the stomach. Gastric distension with 6-8 ml of air induced consistent pressor reflexes of 26 +/- 1 mmHg that could be repeated every 10 min for 100 min. When nociceptin (10 nM) was microinjected into the rostral ventrolateral medulla (rVLM), the pressor response induced by gastric distension was inhibited by 68 +/- 6%. Thirty minutes of EA also decreased the reflex response by 75 +/- 11%; microinjection of saline into the rVLM did not alter the inhibitory effect of EA. In contrast, microinjection of a nociceptin receptor antagonist into the rVLM promptly reversed the EA response. Pretreatment with the opioid receptor antagonist naloxone did not influence the EA-like inhibitory effect of nociceptin on the distension-induced pressor reflex (22 +/- 1 to 8 +/- 2 mmHg). Furthermore, a mu-opioid receptor agonist microinjected into the rVLM after microinjection of a nociceptin receptor antagonist during EA promptly reversed the nociceptin receptor antagonist-related inhibition of the EA effect. Thus, in addition to the classical opioid system, nociceptin, through opioid receptor-like-1 receptor stimulation in the rVLM, participates in the modulatory influence of EA on reflex-induced increases in blood pressure.

Host response to intratracheally instilled bacteria in ventilated and nonventilated rats

Pneumonia occurs in approximately 7% of hospitalized patients. Susceptibility to certain bacteria such as Pseudomonas aeruginosa increases in critically ill patients, particularly those requiring mechanical ventilation. Previous studies investigating this susceptibility have used injurious modes of ventilation. The objective of this study was to evaluate the host's response to intratracheal instillation of P. aeruginosa in the setting of noninjurious mechanical ventilation and compare this with normal, spontaneously breathing animals receiving bacteria. Randomized, controlled in vivo animal study. Research laboratory at a university-affiliated institution. Adult male Sprague-Dawley rats. Rats were randomized into four groups: spontaneously breathing given saline, spontaneously breathing given bacteria, mechanically ventilated given saline, and mechanically ventilated given bacteria. The ventilation strategy used involved low stretch (tidal volume of 8 mL/kg) with a positive end-expiratory pressure of 5 cm H2O. Lung compliance, bacterial recovery, surfactant, total cells, and cytokine concentrations in the lung lavage were analyzed after 4 hrs. Results showed that neither ventilation nor bacteria alone altered lung function, although the combination of ventilation and Pseudomonas significantly decreased arterial oxygenation and lung compliance. Increases in lavage cell counts, cytokines, and surfactant were observed in both groups administered bacteria compared with animals given saline. However, there were no significant differences in bacterial recovery, cell counts, cytokines, and surfactant measurements in the groups given bacteria. These data suggest that bacterial instillation with low-stretch ventilation had a significant effect on lung function but did not alter the inflammatory response to a bacterial challenge over this time course compared with spontaneously breathing animals.

Cerebral pyruvate carboxylase flux is unaltered during bicuculline‐seizures

Glutamine synthesis in the astroglia reflects the sum of neurotransmitter cycling (glutamate and gamma-aminobutyric acid [GABA]) and de novo synthesis (anaplerosis), the latter catalyzed by pyruvate carboxylase. Previous studies have shown that the glutamate plus GABA cycling flux is correlated strongly with neuronal activity; however, the relationship between pyruvate carboxylase flux and neuronal activity is not known. In this study, pyruvate carboxylase flux was assessed during intravenous infusion of [2-(13)C]glucose using localized (1)H-[(13)C] NMR spectroscopy at 7 Tesla in vivo in halothane-anesthetized and ventilated adult Wistar rats during 85 min of bicuculline-induced seizures (1 mg/kg, intravenously) and in nontreated controls. During seizures, concentrations of lactate, alanine, glutamine, GABA, and succinate increased whereas glutamate and aspartate decreased such that the decrease in glutamate plus aspartate equaled the increase in glutamine plus GABA. Pyruvate carboxylase flux was assessed by the sum of [2-(13)C] and [3-(13)C] of glutamine and glutamate (Glx(2+3)) labeling during [2-(13)C]glucose infusion. During seizures the initial rate of Glx(2+3) synthesis (0.069 +/- 0.013 micromol/g/min) was not significantly different (P = 0.68) from that of the controls (0.059 +/- 0.010 micromol/g/min), indicating that anaplerotic flow through pyruvate carboxylase was unaltered. Intense neuronal activation of seizures did not seem to increase anaplerosis through pyruvate carboxylase, despite the substantial increase in neuronal activity and glutamate/glutamine cycling shown in a previous study (Patel et al., 2004b).

Activation of 5-HT1A receptors in raphe pallidus inhibits leptin-evoked increases in brown adipose tissue thermogenesis

To elucidate the central neural pathways contributing to the thermogenic component of the autonomic response to intravenous administration of leptin, experiments were conducted in urethane-chloralose-anesthetized, ventilated rats to address 1) the role of neurons in the rostral ventromedial medulla, including raphe pallidus (RPa), in the leptin-evoked stimulation of brown adipose tissue (BAT) sympathetic nerve activity (SNA); and 2) the potential thermolytic effect of 5-hydroxytryptamine(1A) (5-HT(1A)) receptors on RPa neurons that influence BAT thermogenesis. Leptin (1 mg/kg) administration increased BAT SNA by 1,219% of control, BAT temperature by 2.8 degrees C, expired CO(2) by 1.8%, heart rate by 90 beats/min, and mean arterial pressure by 12 mmHg. Microinjection of the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) into RPa resulted in a prompt and sustained reversal of the leptin-evoked stimulation of BAT SNA, BAT thermogenesis, and heart rate, with these variables returning to their pre-leptin control levels. Subsequent microinjection of the selective 5-HT(1A) receptor antagonist WAY-100635 into RPa reversed the BAT thermolytic effects of 8-OH-DPAT, returning BAT SNA and BAT temperature to the elevated levels after leptin. In conclusion, activation of neurons in RPa, possibly BAT sympathetic premotor neurons, is essential for the increases in BAT SNA, BAT thermogenesis, and heart rate stimulated by intravenous administration of leptin. Neurons in RPa express 5-HT(1A) receptors whose activation leads to reversal of the BAT thermogenic and the cardiovascular responses to intravenous leptin, possibly through hyperpolarization of local sympathetic premotor neurons. These results contribute to our understanding of central neural substrates for the augmented energy expenditure stimulated by leptin.