Role of bronchopulmonary C-fiber afferents in the apneic response to cigarette smoke

The role of vagal bronchopulmonary C-fiber afferents in eliciting the immediate changes in breathing pattern after acute inhalation of cigarette smoke was assessed with a selective blockade of myelinated vagal afferents (innervating both stretch and irritant receptors) utilizing the method of differential cooling. In 15 of 17 chloralose-anesthetized dogs tested, spontaneous inhalation of cigarette smoke (19.7% avg conc, 500-700 ml vol) reproducibly caused the following immediate responses: apnea, bradycardia, and hypotension. These responses occurred within 1 to 2 breaths of smoke inhalation and were followed by a delayed hyperpnea. The apneic duration reached 326 +/- 33% (SE) (n = 15) of the mean base-line expiratory duration. Differential cold block of both vagi (coolant temperature 8.4 +/- 0.3 degrees C) abolished the reflex apnea induced by a positive-pressure (7-10 cmH2O) lung inflation but did not affect the apneic response to smoke inhalation (345 +/- 35%). The smoke-induced apnea was completely abolished by lowering the coolant temperature to -1.3 +/- 0.2 degrees C (n = 10) or by bilateral vagotomy (n = 5) and returned to the control level after both vagi were rewarmed. Based on these results, we suggest that the immediate apneic response to inhaled cigarette smoke is elicited by a stimulation of vagal C-fiber afferents in the lungs and airways.     

Acute effects of cigarette smoke on breathing in rats: vagal and nonvagal mechanisms

The acute ventilatory response to inhalation of cigarette smoke was studied in anesthetized Sprague-Dawley rats. Cigarette smoke (6 ml, 50%) generated by a machine was inhaled spontaneously via a tracheal cannula. Within the first two breaths of smoke inhalation, a slowing of respiration resulting from a prolonged expiratory duration (173 +/- 6% of the base line; n = 32) was elicited in 88% of the rats studied. This initial inhibitory effect on breathing was not affected either by an increase (410%) in the nicotine content of the cigarette smoke or by pretreatment with hexamethonium (33 mg/kg iv). However, bilateral vagotomy completely eliminated the initial ventilatory inhibition. Cooling both vagi to 5.1 degrees C blocked the reflex apneic response to lung inflation, but it did not abolish the inhibitory effect of smoke. After the initial response, a rapid shallow breathing pattern developed and reached its peak 5-12 breaths after inhalation of high-nicotine cigarette smoke; this delayed response could not be prevented by vagotomy and was undetectable after inhalation of low-nicotine smoke. We conclude that the initial inhibitory effect of smoke on breathing is mediated by vagal bronchopulmonary C-fiber afferents, which are stimulated by smoke constituents other than nicotine, whereas the delayed tachypneic response to smoke is caused by the absorbed nicotine.     

Different roles of two subgroups of lung vagal C-fiber afferents in the tachypneic response to pulmonary air embolism in dogs

It is known that lung vagal C-fiber afferents play an important role in eliciting the tachypneic response to pulmonary air embolism (PAE), and can be subgrouped as those with low resistance (LRC) and those with high resistance (HRC) to perivagal capsaicin. In this study, we investigated the relative contributions of vagal LRC and HRC C-fiber afferents to the PAE-induced tachypneic response. Phrenic activity was recorded from 10 anesthetized, paralyzed, and artificially ventilated dogs. PAE was induced by infusion of air into the vein (2 ml/min, 1 ml/kg). During control conditions, induction of PAE produced a shortening in expiratory duration with no significant change in inspiratory duration, resulting in tachypnea. The PAE-induced tachypneic response was totally abolished by perivagal capsaicin treatment with a method (capsaicin concentration, 6 mg/ml; treatment duration, 25-30 min) that blocks the conduction of LRC C-fiber afferents, but not that of HRC C-fiber afferents. This tachypneic response was not affected by cooling of both vagi to a temperature (4.5 degrees C) that blocks the conduction of HRC C-fiber afferents, but not that of LRC C-fiber afferents. A bilateral cervical vagotomy virtually eliminated this tachypneic response. These results suggest that LRC C-fiber afferents are responsible for eliciting the reflex tachypneic response to PAE, whereas HRC C-fiber afferents play no vital role.     

2-aminoethoxydiphenyl borate stimulates pulmonary C neurons via the activation of TRPV channels

This study was carried out to determine the effect of 2-aminoethoxydiphenyl borate (2-APB), a common activator of transient receptor potential vanilloid (TRPV) type 1, 2, and 3 channels, on cardiorespiratory reflexes, pulmonary C fiber afferents, and isolated pulmonary capsaicin-sensitive neurons. In anesthetized, spontaneously breathing rats, intravenous bolus injection of 2-APB elicited the pulmonary chemoreflex responses, characterized by apnea, bradycardia, and hypotension. After perineural treatment of both cervical vagi with capsaicin to block the conduction of C fibers, 2-APB no longer evoked any of these reflex responses. In open-chest and artificially ventilated rats, 2-APB evoked an abrupt and intense discharge in vagal pulmonary C fibers in a dose-dependent manner. The stimulation of C fibers by 2-APB was attenuated but not abolished by capsazepine, a selective antagonist of the TRPV1, which completely blocked the response to capsaicin in these C fiber afferents. In isolated pulmonary capsaicin-sensitive neurons, 2-APB concentration dependently evoked an inward current that was partially inhibited by capsazepine but almost completely abolished by ruthenium red, an effective blocker of all TRPV channels. In conclusion, 2-APB evokes a consistent and distinct stimulatory effect on pulmonary C fibers in vivo and on isolated pulmonary capsaicin-sensitive neurons in vitro. These results establish the functional evidence demonstrating that TRPV1, V2, and V3 channels are expressed on these sensory neurons and their terminals.     

Menthol attenuates respiratory irritation responses to multiple cigarette smoke irritants

Menthol, the cooling agent in peppermint, is added to almost all commercially available cigarettes. Menthol stimulates olfactory sensations, and interacts with transient receptor potential melastatin 8 (TRPM8) ion channels in cold-sensitive sensory neurons, and transient receptor potential ankyrin 1 (TRPA1), an irritant-sensing channel. It is highly controversial whether menthol in cigarette smoke exerts pharmacological actions affecting smoking behavior. Using plethysmography, we investigated the effects of menthol on the respiratory sensory irritation response in mice elicited by smoke irritants (acrolein, acetic acid, and cyclohexanone). Menthol, at a concentration (16 ppm) lower than in smoke of mentholated cigarettes, immediately abolished the irritation response to acrolein, an agonist of TRPA1, as did eucalyptol (460 ppm), another TRPM8 agonist. Menthol's effects were reversed by a TRPM8 antagonist, AMTB. Menthol's effects were not specific to acrolein, as menthol also attenuated irritation responses to acetic acid, and cyclohexanone, an agonist of the capsaicin receptor, TRPV1. Menthol was efficiently absorbed in the respiratory tract, reaching local concentrations sufficient for activation of sensory TRP channels. These experiments demonstrate that menthol and eucalyptol, through activation of TRPM8, act as potent counterirritants against a broad spectrum of smoke constituents. Through suppression of respiratory irritation, menthol may facilitate smoke inhalation and promote nicotine addiction and smoking-related morbidities.     

Response of respiratory-related hypoglossal nerve activity to capsaicin-induced pulmonary C-fiber activation in rats

This study was designed to examine respiratory-related hypoglossal nerve activity in response to activation of pulmonary C-fibers by capsaicin. Rats were anesthetized with urethane (1.2 g/kg, i.p.). Tracheostomy was performed. Catheters were introduced into the femoral vein and artery. Another catheter was placed near the entrance of the right atrium via the right jugular vein. Rats were paralyzed with gallamine triethiodide (5 mg/kg, i.v.), and ventilated artificially. Activities of the phrenic nerve (PNA) and the hypoglossal nerve (HNA) were recorded simultaneously. Varied doses of capsaicin (0.625, 1.25, and 5 µg/kg) were delivered into the right atrium to activate pulmonary C-fibers. Before bilateral vagotomy, apnea, decreases in PNA and HNA were observed in response to pulmonary C-fiber activation by the low and moderate doses of capsaicin. The high dose of capsaicin evoked an increase in PNA, an immediate tonic discharge of the hypoglossal nerve, and a decrease in phasic HNA. The onset time of HNA preceding PNA was abolished and replaced by a time lagged pattern as pulmonary C-fibers were activated. Raising CO₂ concentration did not attenuate the inhibitory effect of pulmonary C-fiber activation upon PNA and HNA. After bilateral sectioning of the vagi, administration of the moderate dose of capsaicin to activate non-vagal C-fibers produced increases in PNA and HNA. These results suggest that pulmonary vagal C-fiber activation may narrow the diameter at the oropharyngeal level by a decrease in phasic HNA, which may be disadvantageous for the maintenance of a patent upper airway.     

Effects of human eosinophil granule-derived cationic proteins on C-fiber afferents in the rat lung.

Experiments were performed to test the hypothesis that human eosinophil granule-derived cationic proteins stimulate vagal C-fiber afferents in the lungs and elicit pulmonary chemoreflex responses in anesthetized Sprague-Dawley rats. Intratracheal instillation of eosinophil cationic protein (ECP; 1-2 mg/ml, 0.1 ml) consistently induced an irregular breathing pattern, characterized by tachypnea (change in breathing frequency of 44.7%) and small unstable tidal volume (VT). The tachypnea, accompanied by decreased heart rate and arterial blood pressure, started within 30 s after the delivery of ECP and lasted for >30 min. These ECP-induced cardiorespiratory responses were completely prevented by perineural capsaicin treatment of both cervical vagi, which selectively blocked C-fiber conduction, suggesting the involvement of these afferents. Indeed, direct recording of single-unit activities of pulmonary C-fibers further demonstrated that the same dose of ECP evoked a pronounced and sustained (>30-min) stimulatory effect on pulmonary C-fibers. Furthermore, the sensitivity of these afferents to lung inflation was also markedly elevated after the ECP instillation, whereas the vehicle of ECP administered in the same manner had no effect. Other types of eosinophil granule cationic proteins, such as major basic protein and eosinophil peroxidase, induced very similar respiratory and cardiovascular reflex responses. In conclusion, these results show that eosinophil granule-derived cationic proteins induce a distinct stimulatory effect on vagal pulmonary C-fiber endings, which may play an important role in the airway hyperresponsiveness associated with eosinophil infiltration in the airways.     

Pulmonary chemoreflexes elicited by intravenous injection of lactic acid in anesthetized rats

Lee, Lu-Yuan, Robert F. Morton, and Jan M. Lundberg.Pulmonary chemoreflexes elicited by intravenous injection oflactic acid in anesthetized rats. J. Appl.Physiol. 81(6): 2349-2357, 1996.Experiments werecarried out to characterize the cardiorespiratory reflex responses tointravenous injection of lactic acid and to determine the involvementof vagal bronchopulmonary C-fiber afferents in eliciting theseresponses in anesthetized rats. Bolus injection of lactic acid (0.2 mmol/kg iv) immediately elicited apnea, bradycardia, and hypotension,which were then followed by a sustained hyperpnea. The immediate apneicand bradycardiac responses to lactic acid were completely abolished bybilateral vagotomy and were absent when the same dose of lactic acidwas injected into the left ventricle. The subsequent hyperpneicresponse was substantially attenuated by denervation of carotid bodychemoreceptors. After a perineural capsaicin treatment of both vagusnerves to block the conduction of C fibers, lactic acid no longerevoked the immediate apnea and bradycardia, whereas the hyperpneicresponse became more pronounced and sustained, presumably because ofthe removal of the inhibitory effect on breathing mediated by pulmonaryC-fiber activation. Single-unit electrophysiological recording showedthat intravenous injection of lactic acid consistently evoked an abruptand intense burst of discharge from the vagal C-fiber afferent endingsin the lungs. In conclusion, the cardiorespiratory depressor responses induced by lactic acid are predominantly elicited by activation ofvagal pulmonary C fibers.

     

Synthetic smoke with acrolein but not HCl produces pulmonary edema

The chemical toxins in smoke and not the heat are responsible for the pulmonary edema of smoke inhalation. We developed a synthetic smoke composed of carbon particles (mean diameter of 4.3 microns) to which toxins known to be in smoke, such as HCl or acrolein, could be added one at a time. We delivered synthetic smoke to dogs for 10 min and monitored extravascular lung water (EVLW) accumulation thereafter with a double-indicator thermodilution technique. Final EVLW correlated highly with gravimetric values (r = 0.93, P less than 0.01). HCl in concentrations of 0.1-6 N when added to heated carbon (120 degrees C) and cooled to 39 degrees C produced airway damage but no pulmonary edema. Acrolein, in contrast, produced airway damage but also pulmonary edema, whereas capillary wedge pressures remained stable. Low-dose acrolein smoke (less than 200 ppm) produced edema in two of five animals with a 2- to 4-h delay. Intermediate-dose acrolein smoke (200-300 ppm) always produced edema at an average of 147 +/- 57 min after smoke, whereas high-dose acrolein (greater than 300 ppm) produced edema at 65 +/- 16 min after smoke. Thus acrolein but not HCl, when presented as a synthetic smoke, produced a delayed-onset, noncardiogenic, and peribronchiolar edema in a roughly dose-dependent fashion.     

Sensitization of pulmonary chemosensitive neurons by bombesin-like peptides in rats

Small cell lung cancer (SCLC) patients suffer from pulmonary stresses such as dyspnea and chest pain, and the pathogenic mechanisms are not known. SCLC cells secrete a variety of bioactive neuropeptides, including bombesin-like peptides. We hypothesize that these peptides may enhance the sensitivity of the pulmonary chemosensitive nerve endings, contributing to the development of these pulmonary stresses in SCLC patients. This study was therefore carried out to determine the effects of bombesin and gastrin-releasing peptide (GRP), a major bombesin-like peptide, on the sensitivities of pulmonary chemoreflex and isolated pulmonary vagal chemosensitive neurons. In anesthetized, spontaneously breathing rats, intravenous infusion of bombesin or GRP significantly amplified the pulmonary chemoreflex responses to chemical stimulants such as capsaicin and ATP. The enhanced responses were completely abolished by perineural capsaicin treatment of both cervical vagi, suggesting the involvement of pulmonary C-fiber afferents. In isolated pulmonary vagal chemosensitive neurons, pretreatment with bombesin or GRP potentiated the capsaicin-induced Ca(2+) transient. This sensitizing effect was further demonstrated in patch-clamp recording studies; the sensitivities of these neurons to both chemical (capsaicin and ATP) and electrical stimuli were significantly enhanced by the presence of either bombesin or GRP. In summary, our results have demonstrated that bombesin and GRP upregulate the pulmonary chemoreflex sensitivity in vivo and the excitability of isolated pulmonary chemosensitive neurons in vitro.     

Possible sensory receptor of nonadrenergic inhibitory nervous system

To determine the sensory receptor of the nonadrenergic inhibitory nervous system (NAIS), 22 cats were anesthetized and serotonin was continuously administered (50-250 micrograms.kg-1.min-1 iv) to increase pulmonary resistance (RL) to 377 +/- 57% (SE) of the control value. We then 1) mechanically irritated the trachea, 2) intravenously administered capsaicin (5 micrograms/kg), or 3) induced hypoxia (arterial PO2 30-40 Torr) to stimulate irritant and bronchial C-fiber receptors, pulmonary C-fiber receptors, or the carotid body (chemoreceptors), respectively. After treatment with atropine (3 mg/kg iv) and propranolol (2 mg/kg iv), the serotonin-induced change in RL was reduced by 58.6 +/- 14.3% by mechanical irritation and 63.3 +/- 12.1% by intravenous capsaicin. However, hypoxia produced no dilatation of the airways. In further experiments, we employed capsaicin inhalation to stimulate bronchial C-fiber receptors. Inhaled capsaicin (0.1%, for 5 breaths) also reduced RL by 79.2 +/- 9.2% of the elevated value, after atropine and propranolol. Treatment with a ganglionic blocking agent, hexamethonium (2 mg/kg iv), abolished bronchodilator responses, implying that a reflex pathway through vagal nerves is involved in this phenomenon. These results suggest that pulmonary and bronchial C-fiber receptors may be involved as sensory receptors in NAIS reflex bronchodilatation.     

Acetylcholine but not adenosine triggers preconditioning through PI3-kinase and a tyrosine kinase

Acrolein is a highly reactive aldehyde pollutant and an endogenous product of lipid peroxidation. Increased generation of, or exposures to, acrolein incites pulmonary and vascular injury. The effects of acrolein on the vasomotor responses of rat aortic rings were studied to understand its mechanism of action. Incubation with acrolein (10-100 microM) alone did not affect the resting tone of aortic vessels; however, a dose-dependent relaxation of phenylephrine-precontracted aortic rings was observed. Acrolein-induced relaxation was slow and time dependent and the extent of relaxation after 100 min of application was 44.7 +/- 4.1% (10 microM), 56.0 +/- 5.6% (20 microM), 61.0 +/- 7.9% (40 microM), and 96.1 +/- 2.1 (80 microM), respectively, versus 14.2 +/- 3.3% relaxation in the absence of acrolein. Acrolein-induced vasorelaxation was prevented by endothelial denudation and was abolished on pretreatment with the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester, the guanylyl cyclase inhibitor 1H-[1,2,4]oxidazolo[4,3-a]quinoxaline-1-one, or the cyclooxygenase inhibitor indomethacin. Inhibition of K+ channels (by tetrabutylammonium) or Na+-K+-ATPase (by ouabain) did not significantly prevent acrolein-mediated vasorelaxation. Exposure to acrolein in the presence or absence of other compounds elicited slow wave vasomotor effect in 77% of aortic vessels versus 1.4% in control. Vasomotor responses were also studied on aortic rings prepared from rats fed 2 mg. kg-1. day-1 acrolein for 3 alternate days by oral gavage. These vessels developed a significantly lower contractile response to phenylephrine compared with controls. Together, these results indicate that acute acrolein exposure evokes delayed vasorelaxation due to a nitric oxide- and prostacyclin-dependent mechanism, whereas in vivo acrolein exposure compromises vessel contractility.     

Breathing response to lung congestion with and without left heart distension

This study compared the effect of lung congestion with and without left heart (LH) distension on breathing frequency (fr) and discriminated among responses mediated by myelinated and nonmyelinated vagal afferents. Cardiopulmonary bypass perfusion of anesthetized dogs was used to isolate reflexes. The following three groups were prepared: 1) lung vessels pressurized by pumping into the main pulmonary artery (MPA); 2) lungs and fibrillating LH pressurized by pumping into MPA while draining from LH; 3) lungs congested by occluding several pulmonary veins while holding cardiac output constant. Congestion of lungs alone in groups 1 and 3 depressed fr. Congestion of lungs and distension of LH (group 2) caused transient depression of fr but a steady-state excitation. Cooling cervical vagi to 8 degrees C prevented depression of fr by congestion in all groups. In groups 1 and 2, in which MPA pressure was higher than in group 3, congestion during vagal cooling stimulated breathing. I conclude that lung congestion may stimulate fr via C-fiber afferents, but this may be overcome by a depressor effect via myelinated afferents. Simultaneous LH distension may reflexly stimulate breathing and overcome the lung depressor reflex.     

Sensory nerve-mediated immediate nasal responses to inspired acrolein.

To investigate the role of sensory C-fiber stimulation and tachykinin release in the immediate nasal responses to the sensory irritant acrolein, the upper respiratory tract of the urethan-anesthetized male Fischer 344 rat was isolated via insertion of an endotracheal tube, and acrolein-laden air [2, 5, 10, or 20 parts/million (ppm)] was drawn continuously through that site at a flow rate of 100 ml/min for 50 min. Uptake of the inert vapor acetone was measured throughout the exposure to assess nasal vascular function. Plasma protein extravasation into nasal tissue and nasal lavage fluid was also assessed via injection of Evans blue dye. At 20 ppm, acrolein induced 1) a twofold increase in acetone uptake, indicative of vasodilation, followed by a progressive decline toward basal levels and 2) increased plasma protein extravasation, as indicated by dye leakage into nasal tissue and nasal lavage. These responses were inhibited by capsaicin pretreatment and the neurokinin type 1 antagonist N-acetyltrifluoromethyl tryptophan benzyl ester and were potentiated by the peptidase inhibitors phosphoramidon and captopril, suggesting that these responses were mediated by tachykinin. At lower exposure concentrations, acrolein was without effect on dye leakage but produced vasodilation, as indicated by increased acetone uptake. The responses at the lower concentrations were inhibited by capsaicin pretreatment, implicating nasal sensory C-fiber involvement, but were not influenced by N-acetyltrifluoromethyl tryptophan benzyl ester, phosphoramidon, or captopril, suggesting the involvement of a mediator other than the tachykinins substance P and neurokinin A.     

Immediate sensory nerve-mediated respiratory responses to irritants in healthy and allergic airway-diseased mice.

The immediate responses of the upper respiratory tract (URT) to the irritants acrolein and acetic acid were examined in healthy and allergic airway-diseased C57Bl/6J mice. Acrolein (1.1 ppm) and acetic acid (330 ppm) vapors induced an immediate increase in flow resistance, as measured in the surgically isolated URT of urethane-anesthetized healthy animals. Acrolein, but not acetic acid, induced a small URT vasodilatory response. In awake spontaneously breathing mice, both vapors induced a prolonged pause at the start of expiration (a response mediated via stimulation of nasal trigeminal nerves) and an increase in total respiratory specific airway flow resistance, the magnitude of which was similar to that observed in the isolated URT. Both responses were significantly reduced in animals pretreated with large doses of capsaicin to defunctionalize sensory nerves, strongly suggesting a role for sensory nerves in development of these responses. The breathing pattern and/or obstructive responses were enhanced in mice with ovalbumin-induced allergic airway disease. These results suggest that the primary responses to acrolein and acetic acid vapors are altered breathing patterns and airway obstruction, that sensory nerves play an important role in these responses, and that these responses are enhanced in animals with allergic airway disease.     

The contribution of VR1 and CB1 receptors and the role of the afferent vagal pathway in modelling of cardio-respiratory effects of anandamide in rats

Anaesthetized and spontaneously breathing rats were used to study the cardio-respiratory effects of intravenous anandamide administration. To investigate the role of particular levels of the afferent pathway in this response rats were challenged with bolus injection of anandamide (1 mg kg(-1)) into the femoral vein while intact, following bilateral superior laryngeal nerves (SLNs) section and after midcervical vagotomy. To test the hypothesis that the activation of the vanilloid receptors (VR1) as well as cannabinoid receptors (CB1) contributes to the anandamide-induced response administrations of anandamide were preceded by nonselective VR1 antagonist ruthenium red or selective CB1 antagonist AM281. Anandamide evoked apnoea of mean duration of 4.84+/-0.75 s in all animals while intact which was shortened by subsequent neurotomies, after SLNs section to 3.3+/-0.57 s (P<0.05) and after midcervical vagi section to 1.99+/-0.24 s (P<0.01). In post-apnoeic breathing tidal volume (V(T)) was reduced in all neural states. Anandamide evoked hypotension in the intact and SLNs neurotomized rats. Midcervical vagotomy reduced this fall in blood pressure. Both antagonists ruthenium red and AM281 eliminated post-anandamide apnoea and hypotension but had no effect on post-apnoeic depression of V(T). Subsequent SLNs and cervical vagi sections did not eliminate but only reduced post-anandamide depression of breathing. Midcervical vagotomy lessened anandamide-induced hypotension. Apnoeic and hypotensive response to anandamide was mediated by both VR1 and CB1 receptors. Post-anandamide decline of V(T) might depend on different type of receptors.     

隐神经C类纤维传入诱发小脑皮层电反应

当弱刺激只引起隐神经A类纤维传入时,小脑皮层出现A-CEP,由潜伏期为11.8±3.5ms的早成分和312.1±17.5ms的晚成分组成;当强刺激同时引起A类和C类纤维传入时,出现AC-CEP类似A-CEP;用极化电流选择性阻断A类纤维传导后,只让C类纤维传入时,出现潜伏期为134.2±18.4ms的C-CEP。在Ⅵ小叶蚓部原裂附近C-CEP以正波为主,幅值最大,并在深层位相倒转。C-CEP的潜伏期较长,频率响应较低,幅值较小,随C类纤维传入量而变化,且对镇痛剂较敏感。结果表明C-CEP是由单纯C类纤维传入引起的,在小脑皮层内产生,是小脑皮层对慢痛信息传入的反应。提示C类纤维传入可以到达小脑皮层,引起诱发电位。当A和C类纤维同时传入时,C-CEP不出现,可能是被A类纤维传入所抑制。     

Natural antimicrobial agent (reuterin) produced by lactobacillus reuteri for sanitization of biological tissues inoculated with pseudomonas aeruginosa

The study was done to evaluate the efficacy of using reuterin produced by Lactobacillus reuteri to sanitize biological tissues. The microorganism tested in the study was Pseudomonas aeruginosa, a common cause of nosocomial biomaterial-related infections. The inhibitory effect of reuterin on P. aeruginosa for an inoculated tissue was investigated at different conditions of concentration, temperature, and pH. Additionally, the cellular compatibility of the reuterin-sanitized tissue was evaluated. Glutaraldehyde was employed as a control. It was noted that the minimum inhibitory concentration (MIC, 33.0 +/- 2.9 ppm) and minimum bactericidal concentration (MBC, 50.0 +/- 0.0 ppm) values of reuterin for P. aeruginosa were significantly lower than their glutaraldehyde counterparts (MIC, 130.0 +/- 8.2 ppm and MBC, 180.0 +/- 18.3 ppm). This indicated that reuterin was more efficient than glutaraldehyde as an antimicrobial agent. The addition of reuterin on the inoculated tissue led to a reduced viability of P. aeruginosa. The reduction in the P. aeruginosa culture was more pronounced with increasing the concentration of reuterin (0-100 ppm). At increasing temperature (25-45 degrees C), there was an increasing effect of reuterin on its sanitization activity. However, it should be pointed out that the growth of P. aeruginosa in the nutrient broth was also significantly affected by temperature. The sanitization activity of reuterin was more evident with increasing the pH level (pH 6.5-8.5). The cytotoxicity of reuterin was significantly lower than that of glutaraldehyde. Additionally, the cellular compatibility of the reuterin-sanitized tissue was superior to its glutaraldehyde-sanitized counterpart.     

Nitrogen dioxide enhances allergic airway inflammation and hyperresponsiveness in the mouse

In addition to being an air pollutant, NO2 is a potent inflammatory oxidant generated endogenously by myeloperoxidase and eosinophil peroxidase. In these studies, we sought to determine the effects of NO2 exposure on mice with ongoing allergic airway disease pathology. Mice were sensitized and challenged with the antigen ovalbumin (OVA) to generate airway inflammation and subsequently exposed to 5 or 25 ppm NO2 for 3 days or 5 days followed by a 20-day recovery period. Whereas 5 ppm NO2 elicited no pathological changes, inhalation of 25 ppm NO2 alone induced acute lung injury, which peaked after 3 days and was characterized by increases in protein, LDH, and neutrophils recovered by BAL, as well as lesions within terminal bronchioles. Importantly, 25 ppm NO2 was also sufficient to cause AHR in mice, a cardinal feature of asthma. The inflammatory changes were ameliorated after 5 days of inhalation and completely resolved after 20 days of recovery after the 5-day inhalation. In contrast, in mice immunized and challenged with OVA, inhalation of 25 ppm NO2 caused a marked augmentation of eosinophilic inflammation and terminal bronchiolar lesions, which extended significantly into the alveoli. Moreover, 20 days postcessation of the 5-day 25 ppm NO2 inhalation regimen, eosinophilic and neutrophilic inflammation, pulmonary lesions, and AHR were still present in mice immunized and challenged with OVA. Collectively, these observations suggest an important role for NO2 in airway pathologies associated with asthma, both in modulation of degree and duration of inflammatory response, as well as in induction of AHR.     

Phrenic afferents and ventilatory control at increased end-expiratory lung volumes in cats

The role of phrenic afferents in controlling inspiratory duration (TI) at elevated end-expiratory lung volume (EEV) has been studied in pentobarbital-anesthetized, spontaneously breathing cats with intact vagi. Responses to increases in EEV, induced by imposition of an expiratory threshold load (ETL) of 10 cmH2O, were monitored before and after section of cervical dorsal roots C3-C7. The immediate (first-breath) effect of application of ETL was a prolongation of both TI and expiratory duration (TE). After 10 min of breathing against the ETL, average TI returned to control values but TE remained prolonged. Abolishing feedback from the diaphragm did not affect these responses. When steady-state responses to ETL were compared with those elicited by inhalation of 5-6% CO2 in O2, changes in EEV had, on average, no independent effect on respiratory drive (rate of rise of integrated phrenic activity), although phrenic activity increased greatly in some cats despite little or no change in arterial partial pressure of CO2. These data indicate that diaphragmatic receptors do not contribute to either the immediate (first-breath) or steady-state responses of phrenic motoneurons to increases in EEV in intact cats.