Strain dependence of the airway response to dry-gas hyperpnea challenge in the rat

The aim of thestudy was to investigate strain dependence and mechanisms of airwayresponses to dry-gas hyperpnea challenge in the rat. We studiedresponses in a strain that is hyperresponsive to methacholine, Fischer344 (F-344); in two normoresponsive strains, Lewis and ACI; and in anatopic but normoresponsive strain, Brown Norway (BN). We examined theeffects of a neurokinin (NK) 1-receptor (CP-99994), anNK₂-receptor (SR-48968), and aleukotriene D₄(LTD₄)-receptor antagonist(pranlukast) on responses to hyperpnea challenge in BN rats. Theanimals were ventilated with a tidal volume of 8 ml/kg and a frequencyof 150 breaths/min with either a dry or humidified mixture of 5%CO₂-95%O₂ for 5 min for hyperpneachallenge, whereas responses to challenge were measured duringspontaneous breathing. Pulmonary resistance increased after dry-gaschallenge in BN and ACI but not in F-344 and Lewis rats. CP-99994,SR-48968, and pranlukast significantly attenuated the increase inpulmonary resistance after dry-gas challenge. There were no significant differences in responsiveness to airway challenge withLTD₄ among the BN, F-344 and ACIrats. We conclude that responses to dry-gas hyperpnea challenge arestrain dependent in rats and are mediated by NKs andLTD₄.

     

Time course of bronchoconstriction induced by dry gas hyperpnea in guinea pigs

We examined the effects of hyperpnea duration and abrupt changes in inspired gas heat and water content on the magnitude and time course of hyperpnea-induced bronchoconstriction (HIB) in anesthetized mechanically ventilated male Hartley guinea pigs. In 12 animals subjected to 5, 10, and 15 min (random order) of dry gas isocapnic hyperpnea [tidal volume (VT) 4-6 ml, 150 breaths/min) followed by quiet breathing of humidified air (VT 2-3 ml, 60 breaths/min), severe bronchoconstriction developed only after the cessation of hyperpnea; the magnitude of respiratory system resistance (Rrs) increased with the duration of dry gas hyperpnea [peak Rrs 1.0 +/- 0.2, 1.8 +/- 0.3, and 2.3 +/- 0.3 (SE) cmH2O.ml-1.s, respectively]. Seven other guinea pigs received, in random order, 10 min of warm humidified gas hyperpnea, 10 min of room temperature dry gas hyperpnea, and 5 min of dry gas hyperpnea immediately followed by 5 min of warm humidified gas hyperpnea. After each hyperpnea period, the animal was returned to quiet breathing of humidified gas. Rrs rose appreciably after the 10 min of dry and 5 min of dry-5 min of humidified hyperpnea challenges (peak Rrs 1.3 +/- 0.2 and 0.7 +/- 0.2 cmH2O.ml-1.s, respectively) but not after 10 min of humidified hyperpnea (0.2 +/- 0.04 cmH2O.ml-1.s). An additional five animals received 10 min of room temperature dry gas hyperpnea followed by quiet breathing of warm humidified air and 10 min of room temperature dry gas hyperpnea followed by 30 min of warm humidified gas hyperpnea in random order.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of furosemide on hyperpnea-induced airway obstruction, injury, and microvascular leakage

Freed, Arthur N., Varsha Taskar, Brian Schofield, andChiharu Omori. Effect of furosemide on hyperpnea-induced airway obstruction, injury, and microvascular leakage. J. Appl. Physiol. 81(6): 2461-2467, 1996.Furosemideattenuates hyperpnea-induced airway obstruction (HIAO) in asthmaticsubjects via unknown mechanism(s). We studied the effect of furosemideon dry air-induced bronchoconstriction, mucosal injury, andbronchovascular hyperpermeability in a canine model of exercise-inducedasthma. Peripheral airway resistance (Rp) was recorded before and aftera 2-min dry-air challenge (DAC) at 2,000 ml/min. After pretreatmentwith aerosolized saline containing 0.75% dimethyl sulfoxide, DACincreased Rp 72 ± 11% (SE, n = 7) above baseline; aerosolized furosemide(10³ M) reduced thisresponse by ~50 ± 6% (P < 0.01). To assess bronchovascular permeability, colloidal carbon wasinjected (1 ml/kg iv) 1 min before DAC, and after 1 h, the vehicle- andfurosemide-treated airways were prepared for morphometric analysis.Light microscopy confirmed previous studies showing that DAC damagedthe airway epithelium and enhanced bronchovascular permeability.Furosemide did not inhibit dry air-induced mucosal injury orbronchovascular hyperpermeability and in fact tended to increase airwaydamage and vascular leakage. This positive trend toward enhancedbronchovascular permeability in DAC canine peripheral airways isconsistent with the hypothesis that furosemide inhibits HIAO in part byenhancing microvascular leakage and thus counterbalancing theevaporative water loss that occurs during hyperpnea.

     

Effect of ventilation on vascular permeability and cyclic nucleotide concentrations in ischemic sheep lungs

Ventilation during ischemia attenuatesischemia-reperfusion lung injury, but the mechanism is unknown.Increasing tissue cyclic nucleotide levels has been shown to attenuatelung ischemia-reperfusion injury. We hypothesized thatventilation prevented increased pulmonary vascular permeability duringischemia by increasing lung cyclic nucleotide concentrations.To test this hypothesis, we measured vascular permeability and cGMP andcAMP concentrations in ischemic (75 min) sheep lungs that wereventilated (12 ml/kg tidal volume) or statically inflated with the samepositive end-expiratory pressure (5 Torr). The reflection coefficientfor albumin (_alb) was 0.54 ± 0.07 and 0.74 ± 0.02 (SE) in nonventilated and ventilatedlungs, respectively (n = 5, P < 0.05). Filtration coefficientsand capillary blood gas tensions were not different. The effect ofventilation was not mediated by cyclic compression of alveolarcapillaries, because negative-pressure ventilation(n = 4) also was protective (_alb = 0.78 ± 0.09). Thefinal cGMP concentration was less in nonventilated than in ventilatedlungs (0.02 ± 0.02 and 0.49 ± 0.18 nmol/g blood-free dry wt,respectively, n = 5, P < 0.05). cAMP concentrations werenot different between groups or over time. Sodium nitroprussideincreased cGMP (1.97 ± 0.35 nmol/g blood-free dry wt) and_alb (0.81 ± 0.09) innonventilated lungs (n = 5, P < 0.05). Isoproterenol increasedcAMP in nonventilated lungs (n = 4, P < 0.05) but had no effect on_alb. The nitric oxide synthaseinhibitor N^G-nitro-L-arginine methylester had no effect on lung cGMP (n = 9) or _alb(n = 16) in ventilated lungs but didincrease pulmonary vascular resistance threefold(P < 0.05) in perfused sheep lungs (n = 3). These results suggest thatventilation during ischemia prevented an increase in pulmonaryvascular protein permeability, possibly through maintenance of lungcGMP by a nitric oxide-independent mechanism.

     

Molecular-weight-dependent effects of nonanticoagulant heparins on allergic airway responses

We have hypothesized that antiallergic activity of inhaledheparin is molecular weight dependent and mediated by"nonanticoagulant fractions" (NAF-heparin). Therefore, we studiedcomparative effects of high-, medium-, and ultralow-molecular-weight(HMW, MMW, and ULMW, respectively) NAF-heparins on acutebronchoconstrictor response (ABR) and airway hyperresponsiveness (AHR)in allergic sheep. Specific lung resistance was measured in 23 allergicsheep, before and immediately after challenge withAscaris suum antigen, without andafter pretreatment with inhaled NAF-heparins. Airwayresponsiveness was estimated before and 2 h postantigen as thecumulative provocating dose of carbachol in breath units, whichincreased specific lung resistance by 400%. NAF-heparins attenuatedABR and AHR in a molecular-weight-dependent fashion. HMW NAF-heparin(n = 8) was the least effective agent: it attenuated ABR [inhibitory dose causing 50% protection(ID₅₀) = 4 mg/kg] but hadno effect on AHR. MMW NAF-heparin (n = 8) showed intermediate efficacy (ABRID₅₀ = 0.8 mg/kg, AHRID₅₀ = 1.4 mg/kg), whereas ULMWNAF-heparin (n = 7) was the mosteffective agent (ABR ID₅₀ = 0.4 mg/kg, AHR ID₅₀ = 0.2 mg/kg). ULMWNAF-heparin was 3.5 times more potent in attenuating antigen-inducedAHR when administered "after" antigen challenge and failed toinhibit the bronchoconstrictor response to carbachol and histamine. In15 additional sheep, segmental antigen challenge caused a marked increase in histamine in bronchoalveolar lavage fluid that was notprevented by any of the inhaled NAF-heparins. These data indicate thatantiallergic activity of inhaled heparin is independent of itsanticoagulant action and resides in the <2,500 ULMW chains. Theantiallergic activity of NAF-heparins is mediated by an unknown biological action and may have therapeutic potential.     

Effects of the combination of skin cooling and hyperpnea of frigid air in asthmatic and normal subjects

McDonald, James S., Joann Nelson, K. A. Lenner, Melissa L. McLane, and E. R. McFadden, Jr. Effects of the combination of skincooling and hyperpnea of frigid air in asthmatic and normal subjects.J. Appl. Physiol. 82(2): 453-459, 1997.To investigate whether reducing integumental temperatures influences pulmonary mechanics and interacts with inhaling cold air, 10 normal and 10 asthmatic subjects participated in a three-part trial in which coolingthe skin of the head and thorax and isocapnic hyperventilation offrigid air were undertaken as isolated challenges and then administeredin combination. Integumental cooling for 30 min caused airwayobstruction to develop in both populations [change in 1-s forcedexpiratory volume (FEV₁)asthmatic subjects = 10%; normal subjects = 6%)].Hyperventilation, however, only affected the asthmatic subjects(FEV₁ asthmatic subjects = 18%; normal subjects = 3%). In contrast to expectations, the combinedchallenge did not produce a summation effect(FEV₁ asthmatic subjects = 21%; normal subjects = 7%). These data demonstrate that the skin of the trunk and head is cold sensitive and when stimulated causes similardegrees of bronchial narrowing in both normal subjects and patientswith airway disease independent of any ventilatory effect. They alsoindicate that cooling of the skin does not add to the obstructiveconsequences of hyperpnea.

     

Bronchoconstriction elicited by isocapnic hyperpnea in guinea pigs

We demonstrated spontaneous self-limited bronchoconstriction after eucapnic dry gas hyperpnea in 22 anesthetized, mechanically ventilated guinea pigs pretreated with propranolol (1 mg/kg iv). Eucapnic hyperpnea "challenges" of room temperature dry or humidified gas (5% CO2-95% O2) were performed by mechanically ventilating animals (150 breaths/min, 3-6 ml tidal volume) for 5 min. During a "recovery" period after hyperpnea, animals were returned to standard ventilation conditions (6 ml/kg, 60 breaths/min, 50% O2 in air, fully saturated at room temperature). After dry gas hyperpnea (5 ml, 150 breaths/min), respiratory system resistance (Rrs) increased in the recovery period by 7.7-fold and dynamic compliance (Cdyn) decreased by 79.7%; changes were maximal at approximately 3 min posthyperpnea and spontaneously returned to base line in 10-40 min. This response was markedly attenuated by humidification of inspired air. Four consecutive identical dry air challenges resulted in similar posthyperpnea responses in four animals. Increasing the minute ventilation during hyperpnea (by varying tidal volume from 3 to 6 ml) caused increased bronchoconstriction in a dose-dependent fashion in six animals. Neither vagotomy nor atropine altered the airway response to dry gas hyperpnea. We conclude that dry gas hyperpnea in anesthetized guinea pigs results in a bronchoconstrictor response that shares five similar features with hyperpnea-induced bronchoconstriction in human asthma: 1) time course of onset and spontaneous resolution, 2) diminution with humidification of inspired gas, 3) reproducibility on consecutive identical challenges, 4) stimulus-response relationship with minute ventilation during hyperpnea, and 5) independence of parasympathetic neurotransmission.     

Distribution of airway narrowing during hyperpnea-induced bronchoconstriction in guinea pigs

Increasing minute ventilation of dry gas shifts the principal burden of respiratory heat and water losses from more proximal airway to airways farther into the lung. If these local thermal transfers determine the local stimulus for bronchoconstriction, then increasing minute ventilation of dry gas might also extend the zone of airway narrowing farther into the lung during hyperpnea-induced bronchoconstriction (HIB). We tested this hypothesis by comparing tantalum bronchograms in tracheostomized guinea pigs before and during bronchoconstriction induced by dry gas hyperpnea, intravenous methacholine, and intravenous capsaicin. In eight animals subjected to 5 min of dry gas isocapnic hyperpnea [tidal volume (VT) = 2-5 ml, 150 breaths/min], there was little change in the diameter of the trachea or the main stem bronchi up to 0.75 cm past the main carina (zone 1). In contrast, bronchi from 0.75 to 1.50 cm past the main carina (zone 2) narrowed progressively at all minute ventilations greater than or equal to 300 ml/min (VT = 2 ml). More distal bronchi (1.50-3.10 cm past the main carina; zone 3) did not narrow significantly until minute ventilation was raised to 450 ml/min (VT = 3 ml). The estimated VT during hyperpnea needed to elicit a 50% reduction in airway diameter was significantly higher in zone 3 bronchi [4.3 +/- 0.8 (SD) ml] than in zone 2 bronchi (3.5 +/- 1.1 ml, P less than 0.012).(ABSTRACT TRUNCATED AT 250 WORDS)     

ET-1-induced bronchoconstriction is mediated via ETB receptor in mice

Nagase, Takahide, Tomoko Aoki, Teruaki Oka, YoshinosukeFukuchi, and Yasuyoshi Ouchi. ET-1-induced bronchoconstriction ismediated via ET_B receptor in mice.J. Appl. Physiol. 83(1): 46-51, 1997.Endothelin (ET)-1 is one of the most potent agonists of airwaysmooth muscle and can act via two different ET receptor subtypes, i.e.,ET_A andET_B. To determine the effects ofET-1 on in vivo pulmonary function and which ET receptors are involved in murine lungs, we investigated 1)the effects of ET and sarafotoxin S6c (S6c), a selectiveET_B agonist, on pulmonary functionand 2) the effects of BQ-123 andBQ-788, specific ET_A- andET_B-receptor antagonists, onET-1-induced bronchoconstriction. ICR mice were anesthetized and mechanically ventilated (frequency = 2.5 Hz, tidalvolume = 8 ml/kg, positive end-expiratory pressure = 3 cmH₂O). Intravenous ET-1, ET-2,and ET-3 increased lung resistance similarly and equipotently, whereasS6c elicited a greater degree of bronchoconstriction. Mice were thenpretreated with saline (Sal), BQ-123 (0.2, 1, and 5 mg/kg), or BQ-788(0.2, 1, and 5 mg/kg) before administration of ET-1(10⁷ mol/kg iv). No dose ofBQ-123 blocked ET-1-induced constriction, whereas pretreatment witheach dose of BQ-788 significantly inhibited ET-1-induced responses.There were significant differences in morphometrically assessed airwayconstriction between Sal and BQ-788 and between BQ-123 and BQ-788,whereas no significant difference was observed between Sal and BQ-123.There were no significant morphometric differences in the airway wallarea among the three groups. These observations suggest that theET_B- but notET_A-receptor subtype may mediatethe changes in murine pulmonary function in response to ET-1. Inaddition, the ET_B-receptorantagonist reduces ET-1-induced airway narrowing by affecting airwaysmooth muscle contraction in mice.

     

H2O2 increases sheep tracheal blood flow, permeability, and vascular response to luminal capsaicin

Wells, U. M., S. Duneclift, and J. G. Widdicombe.H₂O₂increases sheep tracheal blood flow, permeability, and vascular response to luminal capsaicin. J. Appl.Physiol. 82(2): 621-631, 1997.Exogenous hydrogenperoxide(H₂O₂)causes airway epithelial damage in vitro. We have studied the effectsof luminalH₂O₂in the sheep trachea in vivo on tracheal permeability tolow-molecular-weight hydrophilic (technetium-99m-labeleddiethylenetriamine pentaacetic acid;^99mTc-DTPA) and lipophilic([¹⁴C]antipyrine;[¹⁴C]AP) tracers andon the tracheal vascular response to luminal capsaicin, whichstimulates afferent nerve endings. A tracheal artery was perfused, andtracheal venous blood was collected. H₂O₂exposure (10 mM) reduced tracheal potential difference(42.0 ± 6.4 mV) to zero. It increased arterial andvenous flows (56.7 ± 6.1 and 57.3 ± 10.0%,respectively; n = 5, P < 0.01, paired t-test) but not tracheal lymph flow(unstimulated flow 5.0 ± 1.2 µl ^· min^{1 ·} cm¹,n = 4). DuringH₂O₂exposure, permeability to ^99mTc-DTPA increased from2.6 to 89.7 × 10⁷ cm/s(n = 5, P < 0.05), whereas permeability to[¹⁴C]AP (3,312.6 × 10⁷ cm/s,n = 4) was not altered significantly(2,565 × 10⁷cm/s). Luminal capsaicin (10 µM) increased tracheal blood flow (10.1 ± 4.1%, n = 5)and decreased venous ^99mTc-DTPAconcentration (19.7 ± 4.0, P < 0.01), and these effects weresignificantly greater after epithelial damage (28.1 ± 6.0 and45.7 ± 4.3%, respectively,P < 0.05, unpairedt-test). Thus H₂O₂increases the penetration of a hydrophilic tracer into tracheal bloodand lymph but has less effect on a lipophilic tracer. It also enhancesthe effects of luminal capsaicin on blood flow and tracer uptake.

     

Nociceptive mechanisms modulate ozone-induced human lung function decrements

We have previously suggested that ozone(O₃)-induced pain-relatedsymptoms and inhibition of maximal inspiration are due to stimulationof airway C fibers (M. J. Hazucha, D. V. Bates, and P. A. Bromberg.J. Appl.Physiol. 67: 1535-1541, 1989). If this were so,pain suppression or inhibition by opioid-receptor agonists shouldpartially or fully reverseO₃-induced symptomatic and lung functional responses. The objectives of this study were to determine whether O₃-induced pain limitsmaximal inspiration and whether endogenous opioids contribute tomodulation of the effects of inhaledO₃ on lung function. Theparticipants in this double-blind crossover study were healthyvolunteers (18-59 yr) known to be "weak" (WR;n = 20) and "strong"O₃ responders (SR;n = 42). They underwent either two 2-hexposures to air or two 2-h exposures to 0.42 parts/millionO₃ with moderate intermittentexercise. Immediately afterpost-O₃ spirometry, the WR wererandomly given either naloxone (0.15 mg/kg iv) or saline, whereas SRrandomly received either sufentanil (0.2 µg/kg iv) or saline.O₃ exposure significantly(P < 0.001) impaired lung function.In SR, sufentanil rapidly, although not completely, reversed both thechest pain and spirometric effects (forced expiratory volume in 1 s;P < 0.0001) compared with saline.Immediate postexposure administration of saline or naloxone had nosignificant effect on WR. Plasma -endorphin levels were not relatedto an individual's O₃responsiveness. Cutaneous pain variables showed a nonsignificantweak association with O₃responsiveness. These observations demonstrate that nociceptive mechanisms play a key role in modulatingO₃-induced inhibition ofinspiration but not in causing lack of spirometric response toO₃ exposure in WR.

     

Effect of cardiogenic and noncardiogenic pulmonary edema on histamine responsiveness in sheep

We compared the effects of cardiogenic pulmonaryedema, brief pulmonary vascular congestion without frank edema, andnoncardiogenic pulmonary edema on responsiveness to inhaled histaminein chronically instrumented awake sheep. Histamine responsiveness wasmeasured before and after 1)cardiogenic pulmonary edema induced by raising left atrial pressure to35 cmH₂O(Pla) for 3.5 h by partial obstruction of flowacross the mitral valve, 2) briefcardiogenic congestion via Pla for 0.5 h,3) noncardiogenic pulmonary edemainduced by 25 mg/kg intravenous perilla ketone (PK), and4) 3.5 h of monitoring withoutPla or PK (controls). Treatment for 3.5 h with Pla(n = 9) and PK(n = 11) each significantly lessenedthe histamine dose required to cause a fall to 65% of baseline dynamiclung compliance (ED₆₅Cdyn), i.e.,increased responsiveness. Sheep treated for 0.5 h with Pla(n = 7) and controls(n = 5) showed no significant changein ED₆₅Cdyn. Intravenous atropine(0.1 mg/kg) before the second histamine challenge altered neither thereduction of ED₆₅Cdyn inPla (n = 8) and PK(n = 9) sheep nor theED₆₅Cdyn level of controls(n = 9). These data imply that thelocal effects of edema, rather than bronchial vascular hemodynamics,cholinergic reflexes, and permeability changes, are germane to lunghyperresponsiveness during pulmonary edema in sheep.

     

Amiloride-sensitive sodium current in everted Ambystoma initial collecting tubule: short-term insulin effects

Whole cellpatch-clamp techniques were used to investigate amiloride-sensitivesodium conductance (G_Na) in the everted initial collecting tubule of Ambystoma. Accessibility to both theapical and basolateral membranes made this preparation ideal forstudying the regulation of sodium transport by insulin.G_Na accounted for 20% of total cell conductance(G_T) under control conditions. A restingmembrane potential of 75 ± 2 mV (n = 7)together with the fact that G_T is stable withtime suggested that the cells studied were viable. Measurements ofcapacitance and use of a known uncoupling agent, heptanol, suggestedthat cells were not electrically coupled. Thus the values ofG_T and G_Na represented individual principal cells. Exposure of the basolateral membrane toinsulin (1 mU/ml) for 10-60 min significantly (P < 0.05) increased the normalized G_Na [1.2 ± 0.3 nS (n = 6) vs. 2.0 ± 0.4 nS(n = 6)]. Cell-attached patch-clamp techniques wereused to further elucidate the mechanism by which insulin increasesamiloride-sensitive epithelial sodium channel (ENaC) activity. In thepresence of insulin there was no apparent change in either the numberof active levels/patch or the conductance of ENaC. The openprobability increased significantly (P < 0.01) from0.21 ± 0.04 (n = 6) to 0.46 ± 0.07 (n = 6). Thus application of insulin enhanced sodium reabsorption by increasing the fraction of time the channel spent inthe open state.

     

Acute response of the lung mechanics of the rabbit to hypoxia

We measured thechange in total lung resistance(RL) and that in total lungelastance (EL) induced byhypoxia (n = 7) and compared theresults with those by intravenous histamine bolus (n = 5) at three different positiveend-expiratory pressure (PEEP) levels (2, 5, and 8 hPa) in open-chestand vagotomized rabbits. The percent increase ratio ofRL(PIR_R) andEL(PIR_E) was defined as the changein RL andEL, respectively, induced byhypoxia compared with that in the normoxic condition, expressed as apercentage. PIR values for the change inRL andEL induced by bolus injection ofhistamine were also calculated. ThePIR_R andPIR_E induced by hypoxia and byhistamine were positive by a statistically significant amount at everyPEEP level, except for the PIR_Evalue at 8-hPa PEEP in the hypoxic challenge. ThePIR_E-to-PIR_Rratio values in the hypoxic challenge at 2-hPa PEEP were significantlylarger than those in the histamine challenge (hypoxia: 0.91 ± 0.23%; histamine: 0.37 ± 0.065%,P < 0.05). The increasein EL induced by histamine inthe acute phase has been reported to be mainly derived from tissuedistortion secondary to bronchial constriction. Thus our resultssuggest that a part of the increase inEL by hypoxia was originated indifferent parenchymal responses from histamine and imply that thishypoxic response of lung parenchyma is sensitive to the increase inparenchymal tethering at high PEEP levels.

     

Nucleus raphe obscurus modulates hypoglossal output of neonatal rat in vitro transverse brain stem slices

Nucleus raphéobscurus (NRo) modulates hypoglossal (XII) nerve motor output in the invitro transverse brain stem slice of neonatal rats (1-5 days old);chemical ablation of NRo and its focal CO₂ acidificationmodulated the bursting rhythm of XII nerves. We microinjected a 4.5 mMsolution of kainic acid into the NRo to disrupt cellular activity andobserved that XII nerve activity was temporarily abolished(n = 10). We also microinjected CO₂-acidified (pH = 6.00 ± 0.01) artificialcerebrospinal fluid (aCSF) into the NRo (n = 6), thepre-Bötzinger complex (PBC) (n = 6), as well as acontrol region in the lateral tegmental field equidistant to NRo, PBC,and the XII motor nuclei (n = 12). CO₂acidification of the control region had no effect on XII motor output.CO₂ acidification of the NRo significantly(P < 0.05) increased the burst discharge frequency ofXII nerves by 77%; integrated burst amplitude and burst durationincreased by 64% and 52%, respectively. CO₂ acidificationof the PBC significantly (P < 0.05) increased theburst discharge frequency of XII nerves by 65%, but neither integratedburst amplitude nor burst duration changed. These results demonstratethat chemical ablation of the NRo can abolish XII nerve bursting rhythmand that stimulation of the NRo with CO₂-acidified aCSF canexcite XII nerve bursting activity. From these observations, weconclude that, in transverse brain stem slices, the NRo containspH/CO₂-sensitive cells that modulate XII motor output.

     

Relationship between T-wave amplitude and oxygen pulse in guinea pigs in hyperbaric helium and hydrogen

Diving isknown to induce a change in the amplitude of the T wave(A_Tw) ofelectrocardiograms, but it is unknown whether this is linked to achange in cardiovascular performance. We analyzed A_Tw in guinea pigs at 10-60atm and 25-36°C, breathing 2%O₂ in either helium (heliox;n = 10) or hydrogen (hydrox;n = 9) for 1 h at each pressure. Coretemperature and electrocardiograms were detected by using implantedradiotelemeters. O₂ consumption rate was measured by using gas chromatography. In a previous study (S. R. Kayar and E. C. Parker. J. Appl.Physiol. 82: 988-997, 1997), we analyzed theO₂ pulse, i.e., theO₂ consumption rate per heartbeat, in the same animals. By multivariate regression analysis, weidentified variables that were significant toO₂ pulse: body surface area,chamber temperature, core temperature, and pressure. In this study,inclusion of A_Tw made asignificantly better model with fewer variables. After normalizing forchamber temperature and pressure, theO₂ pulse increased with increasing A_Tw in heliox(P = 0.001) but with decreasingA_Tw in hydrox(P < 0.001). ThusA_Tw is associated with thedifferences in O₂ pulse foranimals breathing heliox vs. hydrox.

     

Cigarette smoke-induced bronchoconstriction: causative agents and role of thromboxane receptors

Hong, Ju-Lun, and Lu-Yuan Lee. Cigarette smoke-inducedbronchoconstriction: causative agents and role of thromboxane receptors. J. Appl. Physiol. 81(5):2053-2059, 1996.Inhalation of cigarette smoke induces a biphasicbronchoconstriction in guinea pigs: the first phase is induced by acombination of cholinergic reflex and tachykinins, whereas the secondphase involves cyclooxygenase metabolites (J.-L. Hong, I. W. Rodger,and L.-Y. Lee. J. Appl. Physiol. 78:2260-2266, 1995). This study was carried out to further determinethe causative agents in the smoke and the types of prostanoid receptorsand endogenous prostanoids mediating the bronchoconstriction. Inhalation of 10 ml of high-nicotine cigarette smoke consistently elicited the biphasic bronchoconstriction in anesthetized and artificially ventilated guinea pigs. Pretreatment with hexamethonium (10 mg/kg iv) significantly reduced the first-phase bronchoconstriction but did not have any measurable effect on the second-phase response. Insharp contrast, gas-phase smoke did not elicit any bronchoconstrictive effect. Furthermore, when the animals were challenged with low-nicotine cigarette smoke, only a single second-phase response was evoked, accompanied by increases in thromboxane (Tx)B₂ (a stable metabolite ofTxA₂), prostaglandin (PG)D₂,PGF₂ in the bronchoalveolar lavage fluid. The bronchoconstrictive response induced by low-nicotine smoke was completely prevented by pretreatment with SQ-29548 (0.3 mg/kgiv), a TxA₂-receptor antagonist.These results indicate that 1)nicotine is the primary causative agent responsible for the first-phasebronchoconstriction and 2)nonnicotine smoke particulates evoke the release ofTxA₂,PGD₂, andPGF₂, which act onTxA₂ receptors on airway smoothmuscles and induce the second-phase response to cigarette smoke.

     

Physiological and Genomic Consequences of Intermittent Hypoxia: Selected Contribution: Variation in acute hypoxic ventilatory response is linked to mouse chromosome 9

Genetic determinants confervariation among inbred mouse strains with respect to the magnitude andpattern of breathing during acute hypoxic challenge. Specifically,inheritance patterns derived from C3H/HeJ (C3) and C57BL/6J (B6)parental strains suggest that differences in hypoxic ventilatoryresponse (HVR) are controlled by as few as two genes. The present studydemonstrates that at least one genetic determinant is located on mousechromosome 9. This genotype-phenotype association was established byphenotyping 52 B6C3F₂ (F₂) offspring for HVRcharacteristics. A genome-wide screen was performed usingmicrosatellite DNA markers (n = 176) polymorphicbetween C3 and B6 mice. By computing log-likelihood values (LODscores), linkage analysis compared marker genotypes with minuteventilation (E), tidal volume (VT), andmean inspiratory flow (VT/TI, whereTI is inspiratory time) during acute hypoxic challenge(inspired O₂ fraction = 0.10, inspired CO₂fraction = 0.03 in N₂). A putative quantitative traitlocus (QTL) positioned in the vicinity of D9Mit207 wassignificantly associated with hypoxic E (LOD = 4.5), VT (LOD = 4.0), andVT/TI (LOD = 5.1). For each of the threeHVR characteristics, the putative QTL explained more than 30% of thephenotypic variation among F₂ offspring. In conclusion,this genetic model of differential HVR characteristics demonstratesthat a locus ~33 centimorgans from the centromere on mouse chromosome9 confers a substantial proportion of the variance inE, VT, and VT/TIduring acute hypoxic challenge.

     

Pharmacological modulation of ion transport across wild-type and DeltaF508 CFTR-expressing human bronchial epithelia

Forskolin,UTP, 1-ethyl-2-benzimidazolinone (1-EBIO), NS004, 8-methoxypsoralen(Methoxsalen; 8-MOP), and genistein were evaluated for theireffects on ion transport across primary cultures of human bronchialepithelium (HBE) expressing wild-type (wt HBE) and F508(F-HBE) cystic fibrosis transmembrane conductance regulator. In wtHBE, the baseline short-circuit current (I_sc)averaged 27.0 ± 0.6 µA/cm² (n = 350). Amiloride reduced this I_sc by 13.5 ± 0.5 µA/cm² (n = 317). In F-HBE,baseline I_sc was 33.8 ± 1.2 µA/cm² (n = 200), and amiloride reducedthis by 29.6 ± 1.5 µA/cm² (n = 116), demonstrating the characteristic hyperabsorption of Na⁺ associated with cystic fibrosis (CF). In wt HBE,subsequent to amiloride, forskolin induced a sustained,bumetanide-sensitive I_sc(I_sc = 8.4 ± 0.8 µA/cm²; n = 119). Addition ofacetazolamide, 5-(N-ethyl-N-isopropyl)-amiloride, and serosal 4,4'-dinitrostilben-2,2'-disulfonic acid further reduced I_sc, suggesting forskolin also stimulatesHCO₃ secretion. This was confirmed by ionsubstitution studies. The forskolin-induced I_scwas inhibited by 293B, Ba²⁺, clofilium, and quinine,whereas charybdotoxin was without effect. In F-HBE the forskolinI_sc response was reduced to 1.2 ± 0.3 µA/cm² (n = 30). In wt HBE, mucosal UTPinduced a transient increase in I_sc ( I_sc = 15.5 ± 1.1 µA/cm²;n = 44) followed by a sustained plateau, whereas inF-HBE the increase in I_sc was reduced to5.8 ± 0.7 µA/cm² (n = 13). In wtHBE, 1-EBIO, NS004, 8-MOP, and genistein increased I_sc by 11.6 ± 0.9 (n = 20), 10.8 ± 1.7 (n = 18), 10.0 ± 1.6 (n = 5), and 7.9 ± 0.8 µA/cm²(n = 17), respectively. In F-HBE, 1-EBIO, NS004, and8-MOP failed to stimulate Cl secretion. However, additionof NS004 subsequent to forskolin induced a sustained Clsecretory response (2.1 ± 0.3 µA/cm²,n = 21). In F-HBE, genistein alone stimulatedCl secretion (2.5 ± 0.5 µA/cm²,n = 11). After incubation of F-HBE at 26°C for24 h, the responses to 1-EBIO, NS004, and genistein were allpotentiated. 1-EBIO and genistein increased Na⁺ absorptionacross F-HBE, whereas NS004 and 8-MOP had no effect. Finally,Ca²⁺-, but not cAMP-mediated agonists, stimulatedK⁺ secretion across both wt HBE and F-HBE in aglibenclamide-dependent fashion. Our results demonstrate thatpharmacological agents directed at both basolateral K⁺ andapical Cl conductances directly modulate Clsecretion across HBE, indicating they may be useful in ameliorating theion transport defect associated with CF.

     

Role of tachykinins in hyperpnea-induced bronchovascular hyperpermeability in guinea pigs

Isocapnic dry gas hyperpnea causes bronchoconstriction in guinea pigs that is mediated by release of tachykinins from airway sensory nerves. Exogenous neuropeptides can induce microvascular leak. Therefore we tested whether dry gas hyperpnea also elicits bronchovascular hyperpermeability by measuring Evans blue-labeled albumin extravasation along the airways of mechanically ventilated guinea pigs. We found that 1) room temperature dry gas hyperpnea increased Evans blue extravasation in extrapulmonary and intrapulmonary airways as a specific consequence of local airway heat/water losses, 2) capsaicin pretreatment ablated the bronchoconstrictor response to dry gas hyperpnea and reduced bronchovascular leak only in intrapulmonary airways, 3) phosphoramidon given to capsaicin-pretreated animals partially restored dry gas hyperpnea-induced bronchoconstriction and increased the vascular hyperpermeability response to hyperpnea in intrapulmonary airways, and 4) propranolol administration had no important effects on any of these airway responses. We conclude that dry gas hyperpnea causes bronchovascular hyperpermeability in guinea pigs. Tachykinins have a dominant role in this response in the intrapulmonary airways, although another mechanism may also contribute to the microvascular leak in the extrapulmonary airways.