Nitric oxide enhances hydrogen peroxide-mediated endothelial permeability in vitro

The objective ofthis study was to evaluate the effects of nitric oxide (NO) onH₂O₂-mediatedendothelial permeability.H₂O₂ (0.1 mM) increased permeability at 90 min to 298% of baseline. Spermine NONOate (SNO), an NO donor, at 0.1 or 1 mM did not alter permeability. However, 0.1 mMH₂O₂ + 1 mM SNO increased permeability to 764%, twice that of 0.1 mMH₂O₂alone. These treatments were not directly toxic to endothelial cells.This NO effect was concentration dependent, inasmuch as 0.1 mM SNO didnot significantly change H₂O₂-mediatedpermeability. The NO-enhanced,H₂O₂-dependentpermeability required the simultaneous presence of NO andH₂O₂,inasmuch as preincubation with SNO for 30 min followed by 0.1 mMH₂O₂did not alter permeability. Staining of endothelial junctions showed widening of the intercellular space only in junctions of cells exposedtoH₂O₂(0.1 mM) + SNO (1 mM). Furthermore, NO did not affectH₂O₂metabolism by endothelial cells but significantly depletedintracellular glutathione. This reduction of cell glutathione producedby NO exposure recovered 15-30 min after removal of the NO donor.NO-enhanced permeability was completely blocked by methionine (1 mM), ascavenger of reactive oxygen species, and by the iron chelatordesferrioxamine (0.1 mM). These results suggest that NO may exacerbatethe effects ofH₂O₂-dependentincrease in endothelial monolayer permeability via the iron-catalyzedformation of reactive oxygen metabolites.

     

Oxygen sensitivity of mitochondrial metabolic state in isolated skeletal and cardiac myocytes

In striatedmuscle the coupling of blood flow to changes in tissue metabolism ishypothesized to be dependent in part on release of vasodilatingmetabolic by-products generated when mitochondrial metabolism becomesO₂ limited. Cytochrome oxidase,the terminal step in oxidative phosphorylation, is half-maximallysaturated at <1 mmHg PO₂ inisolated mitochondria. However, blood flow is regulated at tissuePO₂ of ~20 mmHg. If the affinity ofmitochondrial respiration for O₂were higher in vivo than in vitro,O₂ limitation of mitochondrialmetabolism near mean tissue levels could occur. In the present studythe PO₂ at which mitochondrialmetabolism becomes inhibited (criticalPO₂) was measured for cardiacmyocytes in suspension (1.1 ± 0.15 mmHg) and single cells (1.0 ± 0.22 and 1.25 ± 0.22 mmHg in cardiac myocytes and ratspinotrapezius cells, respectively). These measurements are consistentwith those from isolated mitochondria, indicating that vasodilatorsproduced when oxidative phosphorylation becomes inhibited may beimportant for regulating blood flow only in highly glycolytic musclesor under conditions of severe O₂limitation.

     

Effects of prior exercise on exercise-induced arterial hypoxemia in young women

Twenty-eighthealthy women (ages 27.2 ± 6.4 yr) with widely varying fitnesslevels [maximal O₂consumption (O_{2 max}),31-70 ml · kg¹ · min¹]first completed a progressive incremental treadmill test to O_{2 max} (totalduration, 13.3 ± 1.4 min; 97 ± 37 s at maximal workload), rested for 20 min, and then completed a constant-load treadmill test at maximal workload (total duration, 143 ± 31 s). Atthe termination of the progressive test, 6 subjects had maintained arterial PO₂(Pa_O2) near resting levels, whereas 22 subjects showed a >10 Torr decrease inPa_O2 [78.0 ± 7.2 Torr, arterial O₂ saturation(Sa_O2), 91.6 ± 2.4%], andalveolar-arterial O₂ difference (A-aD_O2,39.2 ± 7.4 Torr). During the subsequent constant-load test, allsubjects, regardless of their degree of exercise-induced arterialhypoxemia (EIAH) during the progressive test, showed a nearly identicaleffect of a narrowed A-aD_O2(4.8 ± 3.8 Torr) and an increase inPa_O2 (+5.9 ± 4.3 Torr) andSa_O2 (+1.6 ± 1.7%) compared with atthe end point of the progressive test. Therefore, EIAH during maximalexercise was lessened, not enhanced, by prior exercise, consistent withthe hypothesis that EIAH is not caused by a mechanismwhich persists after the initial exercise period and is aggravated bysubsequent exercise, as might be expected of exercise-inducedstructural alterations at the alveolar-capillary interface. Rather,these findings in habitually active young women point to a functionallybased mechanism for EIAH that is present only during the exerciseperiod.

     

Superoxide, hydroxyl radical, and hydrogen peroxide effects on single-diaphragm fiber contractile apparatus

Reactive oxygenspecies contribute to diaphragm dysfunction in certainpathophysiological conditions (i.e., sepsis and fatigue). However, the precise alterations induced by reactive oxygen species orthe specific species that are responsible for the derangements inskeletal muscle function are incompletely understood. In this study, weevaluated the effect of the superoxide anion radical (O₂·), hydroxyl radical (·OH), and hydrogenperoxide (H₂O₂) on maximum calcium-activatedforce (F_max) and calcium sensitivity of the contractileapparatus in chemically skinned (Triton X-100) single rat diaphragmfibers. O₂· was generated using thexanthine/xanthine oxidase system; ·OH was generated using 1 mMFeCl₂, 1 mM ascorbate, and 1 mMH₂O₂; and H₂O₂ wasadded directly to the bathing medium. Exposure to O₂· or ·OH significantly decreasedF_max by 14.5% (P < 0.05) and 43.9%(P < 0.005), respectively. ·OH had no effect onCa²⁺ sensitivity. Neither 10 nor 1,000 µMH₂O₂ significantly altered F_max orCa²⁺ sensitivity. We conclude that the diaphragm issusceptible to alterations induced by a direct effect of ·OH andO₂·, but not H₂O₂, on thecontractile proteins, which could, in part, be responsible forprolonged depression in contractility associated with respiratorymuscle dysfunction in certain pathophysiological conditions.

     

Alae nasi activation decreases nasal resistance during hyperoxic hypercapnia

It has beenproposed that decreases in nasal resistance (Rn) during hypercapnia areentirely due to vasoconstriction in the nasal cavity. We hypothesizedthat alae nasi (AN) muscle activity dilates the nasal vestibule andcontributes to the decrease in Rn during hypercapnia. Nine normalsubjects were studied during hyperoxic hypercapnia (HH). Rn andvestibular resistance (Rvest) for one nasal passage were measuredsimultaneously with the AN electromyogram before and after nasaldecongestion. HH decreased Rvest from 1.6 ± 0.6 to 0.8 ± 0.9 cmH₂O · l¹ · s(predecongestant) and from 1.3 ± 0.8 to 0.6 ± 0.7 cmH₂O · l¹ · s(postdecongestant; both P < 0.01).Nasal decongestant decreased Rn but not Rvest. Significant inverselinear relationships between Rvest and AN electromyogram weredemonstrated for all subjects. We conclude that in normal subjectsduring HH 1) decreases in Rvest arepredominantly due to increases in AN activity; and2) decreases in Rn are due to acombination of mucosal vasoconstriction and ANactivation.

     

Atrial natriuretic peptide levels and plasma volume contraction in acute alveolar hypoxia

Albert, T. S. E., V. L. Tucker, and E. M. Renkin.Atrial natriuretic peptide levels and plasma volume contraction in acute alveolar hypoxia. J. Appl.Physiol. 82(1): 102-110, 1997.Arterial oxygentensions (Pa_O2), atrial natriureticpeptide (ANP) concentrations, and circulating plasma volumes (PV) weremeasured in anesthetized rats ventilated with room air or 15, 10, or8% O₂(n = 5-7). After 10 min ofventilation, Pa_O2 values were 80 ± 3, 46 ± 1, 32 ± 1, and 35 ± 1 Torrand plasma immunoreactive ANP (irANP) levels were 211 ± 29, 229 ± 28, 911 ± 205, and 4,374 ± 961 pg/ml, respectively. AtPa_O2 40 Torr, irANP responses weremore closely related to inspiredO₂(P = 0.014) than toPa_O2 (P = 0.168). PV was 36.3 ± 0.5 µl/g in controls but 8.5 and9.9% lower (P  0.05) for10 and 8% O₂, respectively.Proportional increases in hematocrit were observed in animals withreduced PV; however, plasma protein concentrations were not differentfrom control. Between 10 and 50 min of hypoxia, small increases (+40%)in irANP occurred in 15% O₂;however, there was no further change in PV, hematocrit, plasma protein,or irANP levels in the lower O₂groups. Urine output tended to fall during hypoxia but was notsignificantly different among groups. These findings are compatiblewith a role for ANP in mediating PV contraction during acute alveolarhypoxia.

     

Cerebral vasomotor reactivity at high altitude in humans

The purpose of this study was twofold:1) to determine whether at highaltitude cerebral blood flow (CBF) as assessed during CO₂ inhalation and duringhyperventilation in subjects with acute mountain sickness (AMS) wasdifferent from that in subjects without AMS and2) to compare the CBF as assessedunder similar conditions in Sherpas at high altitude and in subjects atsea level. Resting control values of blood flow velocity in themiddle cerebral artery (V_MCA), pulseoxygen saturation (Sa_O2), andtranscutaneous PCO₂ were measured at4,243 m in 43 subjects without AMS, 17 subjects with AMS, 20 Sherpas,and 13 subjects at sea level. Responses ofCO₂ inhalation andhyperventilation onV_MCA,Sa_O2, and transcutaneous PCO₂ were measured, and the cerebralvasomotor reactivity (VMR = V_MCA/PCO₂)was calculated as the fractional change ofV_MCA per Torrchange of PCO₂, yielding ahypercapnic VMR and a hypocapnic VMR. AMS subjects showeda significantly higher resting controlV_MCA than didno-AMS subjects (74 ± 22 and 56 ± 14 cm/s, respectively;P < 0.001), andSa_O2 was significantly lower (80 ± 8 and 88 ± 3%, respectively; P < 0.001). Resting control V_MCA values inthe sea-level group (60 ± 15 cm/s), in the no-AMS group, and inSherpas (59 ± 13 cm/s) were not different. Hypercapnic VMR valuesin AMS subjects were 4.0 ± 4.4, in no-AMS subjects were 5.5 ± 4.3, in Sherpas were 5.6 ± 4.1, and in sea-level subjects were 5.6 ± 2.5 (not significant). Hypocapnic VMR values were significantly higher in AMS subjects (5.9 ± 1.5) compared with no-AMS subjects (4.8 ± 1.4; P < 0.005) but werenot significantly different between Sherpas (3.8 ± 1.1) and thesea-level group (2.8 ± 0.7). We conclude that AMS subjects havegreater cerebral hemodynamic responses to hyperventilation, higherV_MCAresting control values, and lower Sa_O2 compared with no-AMSsubjects. Sherpas showed a cerebral hemodynamic patternsimilar to that of normal subjects at sea level.     

Lactate and epinephrine during exercise in altitude natives

Kayser, Bengt, Roland Favier, Guido Ferretti, DominiqueDesplanches, Hilde Spielvogel, Harry Koubi, Brigitte Sempore, and HansHoppeler. Lactate and epinephrine during exercise in altitudenatives. J. Appl. Physiol. 81(6):2488-2494, 1996.We tested the hypothesis that the reported lowblood lactate accumulation ([La]) during exercise inaltitude-native humans is refractory to hypoxia-normoxia transitions byinvestigating whether acute changes in inspiredO₂ fraction(FI_O2) affect the[La] vs. power output ()relationship or, alternatively, as reported for lowlanders, whetherchanges in [La] vs. on changes inFI_O2 are related tochanges in blood epinephrine concentration ([Epi]). Altitude natives [n = 8, age 24 ± 1 (SE) yr, body mass 62 ± 3 kg, height 167 ± 2 cm]in La Paz, Bolivia (3,600 m) performed incremental exercise with twolegs and one leg in chronic hypoxia and acute normoxia (AN). Submaximalone- and two-leg O₂ uptake (O₂) vs. relationships were not altered byFI_O2. AN increased two-legpeak O₂ by 10% and peak by 7%. AN paradoxically decreasedone-leg peak O₂ by 7%,whereas peak remained the same. The[La] vs. relationships were similar tothose reported in unacclimatized lowlanders. There was a shift to theright on AN, and maximum [La] was reduced by 7 and 8% forone- and two-leg exercises, respectively. [Epi] and[La] were tightly related (mean r = 0.81) independently ofFI_O2. Thus normoxiaattenuated the increment in both [La] and [Epi]as a function of , whereas the correlation between[La] and [Epi] was unaffected. These data suggest loose linkage of glycolysis to oxidative phosphorylation under influence from [Epi]. In conclusion, high-altitudenatives appear to be not fundamentally different from lowlanders with regard to the effect of acute changes inFI_O2 on [La] during exercise.

     

Increased VO2 max with right-shifted Hb-O2 dissociation curve at a constant O2 delivery in dog muscle in situ

If the diffusive component ofO₂ transport in muscle isimportant in determining exercise capacity, an increasedcapillary-to-tissue PO₂ differenceshould enhance gas exchange from blood to skeletal muscle duringexercise. Thus a rightward shift in theO₂ dissociation curve shouldtheoretically increase O₂extraction and improve maximal O₂uptake (O_{2 max}). Totest this hypothesis, we used the canine gastrocnemius muscle to studymaximal exercise in eight dogs at a normalP₅₀ (33.1 ± 0.4 Torr) and withthe O₂ dissociation curve shifted to the right by anallosteric modifier of hemoglobin (Hb) (methylpropionic acid, RSR-13;P₅₀ = 53.2 ± 5.0 Torr). Fourcontrol dogs were also studied before and after infusion of vehicle.O₂ (100%) was inspired duringexercise to maintain arterial saturation in both conditions. The musclewas surgically isolated and electrically stimulated (tetanic train: 0.2-ms stimuli for 200-ms duration at 50 Hz, once per s). Tomaintain O₂ delivery (pre-RSR-13 = 19.1 ± 2.9; RSR-13 = 19.6 ± 2.5 ml · 100 g¹ · min¹),the muscle was pump perfused. At a constantO₂ delivery, RSR-13 significantlyincreased percent O₂ extraction(pre-RSR-13 = 61 ± 4.0; RSR-13 = 75.5 ± 4.7) andmuscle O_{2 max}(pre-RSR-13 = 11.8 ± 2.1; RSR-13 = 14.2 ± 1.5 ml · 100 g¹ · min¹).This improvement inO_{2 max} with increasedP₅₀ demonstrates itsO₂ supply dependence whenP₅₀ is normal and the importance of O₂ diffusive transport tomuscle at maximal exercise.

     

Effect of crystalloid administration on oxygen extraction in endotoxemic pigs

We asked whethercrystalloid administration improves tissue oxygen extraction inendotoxicosis. Four groups of anesthetized pigs(n = 8/group) received either normalsaline infusion or no saline and either endotoxin or no endotoxin. Wemeasured whole body (WB) and gut oxygen delivery and consumption duringhemorrhage to determine the critical oxygen extraction ratio(ER_O2 crit). Just after onset of ischemia (critical oxygen delivery rate), gut was removed for determination of area fraction of interstitial edema and capillary hematocrit. Radiolabeled microspheres were used todetermine erythrocyte transit time for the gut. Endotoxin decreased WBER_O2 crit(0.82 ± 0.06 to 0.55 ± 0.08, P < 0.05) and gutER_O2 crit(0.77 ± 0.07 to 0.52 ± 0.06, P < 0.05). Unexpectedly, saline administration also decreased WBER_O2 crit (0.82 ± 0.06 to 0.62 ± 0.08, P < 0.05) and gutER_O2 crit (0.77 ± 0.07 to 0.67 ± 0.06, P < 0.05) in nonendotoxin pigs. Saline administration increased thearea fraction of interstitial space (P < 0.05) and resulted in arterial hemodilution(P < 0.05) but not capillaryhemodilution (P > 0.05). Salineincreased the relative dispersion of erythrocyte transit times from0.33 ± 0.08 to 0.72 ± 0.53 (P < 0.05). Thus saline administration impairs tissue oxygen extractionpossibly by increasing interstitial edema or increasing heterogeneityof microvascular erythrocyte transit times.

     

Differential MAP kinase activation and Na(+)/H(+) exchanger phosphorylation by H(2)O(2) in rat cardiac myocytes

Bursts in reactive oxygen species productionare important mediators of contractile dysfunction duringischemia-reperfusion injury. Cellular mechanisms that mediatereactive oxygen species-induced changes in cardiac myocyte functionhave not been fully characterized. In the present study,H₂O₂ (50 µM) decreased contractility of adultrat ventricular myocytes. H₂O₂ caused aconcentration- and time-dependent activation of extracellularsignal-regulated kinases 1 and 2 (ERK1/2), p38, and c-JunNH₂-terminal kinase (JNK) mitogen-activated protein (MAP)kinases in adult rat ventricular myocytes. H₂O₂ (50 µM) caused transient activation of ERK1/2 and p38 MAP kinase thatwas detected as early as 5 min, was maximal at 20 min (9.6 ± 1.2- and 9.0 ± 1.6-fold, respectively, vs. control), and returned tobaseline at 60 min. JNK activation occurred more slowly (1.6 ± 0.2-fold vs. control at 60 min) but was sustained at 3.5 h. Theprotein kinase C inhibitor chelerythrine completely blocked JNKactivation and reduced ERK1/2 and p38 activation. The tyrosine kinaseinhibitors genistein and PP-2 blocked JNK, but not ERK1/2 and p38,activation. H₂O₂-inducedNa⁺/H⁺ exchanger phosphorylation was blocked bythe MAP kinase kinase inhibitor U-0126 (5 µM). These resultsdemonstrate that H₂O₂-induced activation of MAPkinases may contribute to cardiac myocyte dysfunction duringischemia-reperfusion.

     

Peripheral circulatory factors limit rate of increase in muscle O2 uptake at onset of heavy exercise

We used anexercise paradigm with repeated bouts of heavy forearm exercise to testthe hypothesis that alterations in local acid-base environment thatremain after the first exercise result in greater blood flow andO₂ delivery at the onset of the second bout of exercise.Two bouts of handgrip exercise at 75% peak workload were performed for5 min, separated by 5 min of recovery. We continuously measured bloodflow using Doppler ultrasound and sampled venous blood forO₂ content, PCO₂, pH, and lactateand potassium concentrations, and we calculated muscle O₂uptake (O₂). Forearm blood flow waselevated before the second exercise compared with the first andremained higher during the first 30 s of exercise (234 ± 18 vs. 187 ± 4 ml/min, P < 0.05). Flow was notdifferent at 5 min. Arteriovenous O₂ content difference waslower before the second bout (4.6 ± 0.9 vs. 7.2 ± 0.7 mlO₂/dl) and higher by 30 s of exercise(11.2 ± 0.7 vs. 10.8 ± 0.7 ml O₂/dl,P < 0.05). Muscle O₂was unchanged before the start of exercise but was elevated during thefirst 30 s of the transition to the second exercise bout(26.0 ± 2.1 vs. 20.0 ± 0.9 ml/min, P < 0.05). Changes in venous blood PCO₂, pH, andlactate concentration were consistent with reduced reliance onanaerobic glycolysis at the onset of the second exercise bout. Thesedata show that limitations of muscle blood flow can restrict theadaptation of oxidative metabolism at the onset of heavy muscular exertion.

     

Phosphocreatine hydrolysis during submaximal exercise: the effect of FIO2

There isevidence that the concentration of the high-energy phosphatemetabolites may be altered during steady-state submaximal exerciseby the breathing of different fractions of inspiredO₂ (FI_O2). Whereasit has been suggested that these changes may be the result ofdifferences in time taken to achieve steady-state O₂ uptake(O₂) at differentFI_O2 values, we postulated that they are due to a direct effect ofO₂ tension. We used³¹P-magnetic resonancespectroscopy during constant-load, steady-state submaximal exercise todetermine 1) whether changes inhigh-energy phosphates do occur at the sameO₂ with variedFI_O2 and2) that these changes are not due todifferences in O₂onset kinetics. Six male subjects performed steady-state submaximal plantar flexion exercise [7.2 ± 0.6 (SE) W] for 10 minwhile lying supine in a 1.5-T clinical scanner. Magnetic resonancespectroscopy data were collected continuously for 2 min beforeexercise, 10 min during exercise, and 6 min during recovery. Subjectsperformed three different exercise bouts at constant load with theFI_O2 switched after 5 min ofthe 10-min exercise bout. The three exercise treatments were1)FI_O2 of 0.1 switched to0.21, 2)FI_O2 of 0.1 switched to1.00, and 3)FI_O2 of 1.00 switched to0.1. For all three treatments, theFI_O2 switch significantly (P  0.05) altered phosphocreatine:1) 55.5 ± 4.8 to 67.8 ± 4.9% (%rest); 2) 59.0 ± 4.3 to72.3 ± 5.1%; and 3) 72.6 ± 3.1 to 64.2 ± 3.4%, respectively. There were no significantdifferences in intracellular pH for the three treatments. The resultsdemonstrate that the differences in phosphocreatine concentration withvaried FI_O2 are not theresult of different O₂onset kinetics, as this was eliminated by the experimental design.These data also demonstrate that changes in intracellular oxygenation,at the same work intensity, result in significant changes in cell homeostasis and thereby suggest a role for metabolic control by O₂ even during submaximalexercise.

     

Nitric oxide regulates oxygen uptake and hydrogen peroxide release by the isolated beating rat heart

Isolated rat heart perfused with 1.5-7.5µM NO solutions or bradykinin, which activates endothelial NOsynthase, showed a dose-dependent decrease in myocardial O₂uptake from 3.2 ± 0.3 to 1.6 ± 0.1 (7.5 µM NO, n = 18,P < 0.05) and to 1.2 ± 0.1 µM O₂ · min¹ · gtissue¹ (10 µM bradykinin, n = 10,P < 0.05). Perfused NO concentrations correlated with aninduced release of hydrogen peroxide (H₂O₂) inthe effluent (r = 0.99, P < 0.01). NO markedlydecreased the O₂ uptake of isolated rat heart mitochondria(50% inhibition at 0.4 µM NO, r = 0.99,P < 0.001). Cytochrome spectra in NO-treated submitochondrial particles showed a double inhibition of electron transfer at cytochrome oxidase and between cytochrome b andcytochrome c, which accounts for the effects in O₂uptake and H₂O₂ release. Most NO was bound tomyoglobin; this fact is consistent with NO steady-state concentrationsof 0.1-0.3 µM, which affect mitochondria. In the intact heart,finely adjusted NO concentrations regulate mitochondrial O₂uptake and superoxide anion production (reflected byH₂O₂), which in turn contributes to thephysiological clearance of NO through peroxynitrite formation.

     

Raising P50 increases tissue PO2 in canine skeletal muscle but does not affect critical O2 extraction ratio

Curtis, Scott E., Thomas A. Walker, W. E. Bradley, andStephen M. Cain. Raising P₅₀increases tissue PO₂ in canineskeletal muscle but does not affect criticalO₂ extraction ratio.J. Appl. Physiol. 83(5):1681-1689, 1997.Affinity of hemoglobin (Hb) forO₂ determines in part the rate ofO₂ diffusion from capillaries tomyocytes by altering capillary PO₂.We hypothesized that a decrease in HbO₂ affinity (increasedP₅₀) would increase capillary and tissue PO₂(Pti_O2) andimprove O₂ consumption duringischemia. To test this hypothesis, blood flow to the pump-perfused lefthindlimb of 18 anesthetized and paralyzed dogs was progressively decreased over 90 min while hindlimb O₂ consumption andO₂ delivery (O₂)and Pti_O2 weremeasured at the muscle surface. Arterial PO₂ was maintained at 150 ± 10 Torr in all dogs. We increased P₅₀by 12.3 ± 0.9 (SE) Torr in nine dogs with RSR-13, an allosteric modifier of Hb. This decreased arterialO₂ saturation to 90-92% butincreased meanPti_O2 from 35.5 ± 11.6 to 44.1 ± 15.2 (SD) Torr(P < 0.05) with no change incontrols (n = 9).O₂ extraction ratio at criticalO₂was 74 ± 2% in controls and 79 ± 1% in RSR-13-treated dogs(P = not significant).Pti_O2 was30-40% higher in the RSR-13-treated group at anyO₂above critical but did not differ between groups below criticalO₂.Perfusion heterogeneity and convergence of the dissociation curvesnear criticalO₂ may have mitigated any effect of increasedP₅₀ onO₂ diffusion. Still, increasingP₅₀ by 12 Torr with RSR-13significantly increased Pti_O2 atO₂values above critical.

     

Cardiopulmonary effects of inhaled nitric oxide in normal dogs and during E.coli pneumonia and sepsis

Quezado, Zenaide M. N., Charles Natanson, WaheedullahKarzai, Robert L. Danner, Cezar A. Koev, Yvonne Fitz, Donald P. Dolan, Steven Richmond, Steven M. Banks, Laura Wilson, and Peter Q. Eichacker. Cardiopulmonary effects of inhaled nitric oxide in normal dogs andduring E. coli pneumonia and sepsis.J. Appl. Physiol. 84(1): 107-115, 1998.We investigated the effect of inhaled nitric oxide (NO) atincreasing fractional inspired O₂concentrations (FI_O2) onhemodynamic and pulmonary function during Escherichia coli pneumonia. Thirty-eight conscious,spontaneously breathing, tracheotomized 2-yr-old beagles hadintrabronchial inoculation with either 0.75 or 1.5 × 10¹⁰ colony-forming units/kg ofE. coli 0111:B4(infected) or 0.9% saline (noninfected) in one or four pulmonarylobes. We found that neither the severity nor distribution (lobar vs.diffuse) of bacterial pneumonia altered the effects of NO. However, in infected animals, with increasingFI_O2 (0.08, 0.21, 0.50, and0.85), NO (80 parts/million) progressively increased arterial PO₂ [0.3 ± 0.6, 3 ± 1, 13 ± 4, 10 ± 9 (mean ± SE) Torr, respectively] and decreased the mean arterial-alveolarO₂ gradient (0.5 ± 0.3, 4 ± 2, 8 ± 7, 10 ± 9 Torr, respectively). Incontrast, in noninfected animals, the effect of NO was significantlydifferent and opposite; NO progressively decreased meanPO₂ with increasingFI_O2 (2 ± 1, 5 ± 3, 2 ± 3, and 12 ± 5 Torr, respectively;P < 0.05 compared with infectedanimals) and increased mean arterial-alveolarO₂ gradient (0.3 ± 0.04, 2 ± 2, 1 ± 3, 11 ± 5 Torr; P < 0.05 compared with infected animals). In normal and infectedanimals alike, only at FI_O20.21 did NO significantly lower mean pulmonary artery pressure,pulmonary artery occlusion pressure, and pulmonary vascular resistanceindex (all P < 0.01).However, inhaled NO had no significant effect on increases in meanpulmonay artery pressure associated with bacterial pneumonia. Thus,during bacterial pneumonia, inhaled NO had only modest effects onoxygenation dependent on highFI_O2 and did not affectsepsis-induced pulmonary hypertension. These data do not support a rolefor inhaled NO in bacterial pneumonia. Further studies are necessary todetermine whether, in combination with ventilatory support, NO may havemore pronounced effects.

     

Pulmonary diffusing capacities for oxygen-labeled CO2 and nitric oxide in rabbits

Heller, Hartmut, Gabi Fuchs, and Klaus-DieterSchuster. Pulmonary diffusing capacities foroxygen-labeled CO₂ and nitric oxide in rabbits.J. Appl. Physiol. 84(2): 606-611, 1998.We determined the pulmonary diffusing capacity(DL) for¹⁸O-labeledCO₂(C¹⁸O₂)and nitric oxide (NO) to estimate the membrane component of therespective gas conductances. Six anesthetized paralyzed rabbits wereventilated by a computerized ventilatory servo system. Single-breath maneuvers were automatically performed by inflating the lungs with gasmixtures containing 0.9%C¹⁸O₂or 0.05% NO in nitrogen, with breath-holding periods ranging from 0 to1 s forC¹⁸O₂and from 2 to 8 s for NO. The alveolar partial pressures of C¹⁸O₂and NO were determined by using respiratory mass spectrometry. DL was calculated from gasexchange during inflation, breath hold, and deflation. We obtainedvalues of 14.0 ± 1.1 and 2.2 ± 0.1 (mean value ± SD)ml · mmHg¹ · min¹forDL_C¹⁸O2and DL_NO,respectively. The measured DL_C¹⁸O2/DL_NOratio was one-half that of the theoretically predicted value accordingto Graham's law (6.3 ± 0.5 vs. 12, respectively).Analyses of the several mechanisms influencing the determination ofDL_C¹⁸O2and DL_NOand their ratio are discussed. An underestimation of the membranediffusing component for CO₂ isconsidered the likely reason for the lowDL_C¹⁸O2/DL_NOratio obtained.

     

Potentiation of hypoxic ventilatory response by hyperoxia in the conscious rat: putative role of nitric oxide

In humans, the hypoxic ventilatory response(HVR) is augmented when preceded by a short hyperoxic exposure (Y. Honda, H. Tani, A. Masuda, T. Kobayashi, T. Nishino, H. Kimura, S. Masuyama, and T. Kuriyama. J. Appl.Physiol. 81: 1627-1632, 1996). To examine whetherneuronal nitric oxide synthase (nNOS) is involved in such hyperoxia-induced HVR potentiation, 17 male Sprague-Dawley adult ratsunderwent hypoxic challenges (10%O₂-5%CO₂-balanceN₂) preceded either by 10 min ofroom air (O₂) or of 100%O₂(+O₂). At least 48 h later,similar challenges were performed after the animals received theselective nNOS inhibitor 7-nitroindazole (25 mg/kg ip). InO₂ runs, minute ventilation(E)increased from 121.3 ± 20.5 (SD) ml/min in room air to 191.7 ± 23.8 ml/min in hypoxia (P < 0.01). After +O₂,E increasedfrom 114.1 ± 19.8 ml/min in room air to 218.4 ± 47.0 ml/min inhypoxia (+O₂ vs.O₂:P < 0.005, ANOVA). After7-nitroindazole administration, HVR was not affected in theO₂ treatment group withE increasingfrom 113.7 ± 17.8 ml/min in room air to 185.8 ± 35.0 ml/min inhypoxia (P < 0.01).However, HVR potentiation in+O₂-exposed animals was abolished(111.8 ± 18.0 ml/min in room air to 184.1 ± 35.6 ml/min inhypoxia; +O₂ vs.O₂:P not significant). We conclude that in the conscious rat nNOS activation mediates essential components ofthe HVR potentiation elicited by a previous short hyperoxic exposure.

     

Peripheral O2 diffusion does not affect VO2 on-kinetics in isolated in situ canine muscle

To test thehypothesis that muscle O₂ uptake(O₂) on-kinetics islimited, at least in part, by peripheralO₂ diffusion, we determined theO₂ on-kinetics in1) normoxia (Control);2) hyperoxic gas breathing(Hyperoxia); and 3) hyperoxia andthe administration of a drug (RSR-13, Allos Therapeutics), whichright-shifts the Hb-O₂dissociation curve (Hyperoxia+RSR-13). The study was conducted inisolated canine gastrocnemius muscles(n = 5) during transitions from restto 3 min of electrically stimulated isometric tetanic contractions(200-ms trains, 50 Hz; 1 contraction/2 s; 60-70% peakO₂). In all conditions,before and during contractions, muscle was pump perfused withconstantly elevated blood flow (), at a levelmeasured at steady state during contractions in preliminary trials withspontaneous . Adenosine was infusedintra-arterially to prevent inordinate pressure increases with theelevated . was measuredcontinuously, arterial and popliteal venousO₂ concentrations were determinedat rest and at 5- to 7-s intervals during contractions, andO₂ was calculated as · arteriovenous O₂ content difference.PO₂ at 50%HbO₂saturation (P₅₀) was calculated.Mean capillary PO₂(c_O2)was estimated by numerical integration.P₅₀ was higher in Hyperoxia+RSR-13[40 ± 1 (SE) Torr] than in Control and in Hyperoxia (31 ± 1 Torr). After 15 s of contractions,c_O2was higher in Hyperoxia (97 ± 9 Torr) vs. Control (53 ± 3 Torr) and in Hyperoxia+RSR-13 (197 ± 39 Torr) vs. Hyperoxia. Thetime to reach 63% of the difference between baseline and steady-stateO₂ during contractions was 24.7 ± 2.7 s in Control, 26.3 ± 0.8 s in Hyperoxia, and 24.7 ± 1.1 s in Hyperoxia+RSR-13 (not significant). Enhancement ofperipheral O₂ diffusion (obtainedby increasedc_O2at constant O₂ delivery) duringthe rest-to-contraction (60-70% of peakO₂) transition did notaffect muscle O₂on-kinetics.

     

Improved oxygenation with prostaglandin F2alpha with and without inhaled nitric oxide in dogs

Dogs of mixedbreed (n = 7) were anesthetized, rightlung atelectasis was established, and the cyclooxygenase pathway was blocked with ibuprofen. Measurements of pulmonary gas exchange wereperformed (fractional concentration of inspiredO₂ = 0.95) after infusions ofprostaglandin F₂(PGF₂; 2 µg · kg¹ · min¹),ventilation with nitric oxide (NO; 40 ppm), or both(PGF₂ + NO) in random order.The arterial PO₂(Pa_O2) under control conditions was 117 ± 16 Torr (shunt = 33 ± 2.5%), was unchanged with NO alone(Pa_O2 = 114 ± 17 Torr; shunt = 35.7 ± 3.1%), but was significantlyimproved with PGF₂ alone(Pa_O2 = 180 ± 28 Torr; shunt = 23.2 ± 2.8%) and with the combination ofPGF₂ + NO(Pa_O2 = 202 ± 30 Torr; shunt = 20.9 ± 2.5%). The addition of NO didnot significantly enhance the effectiveness of thePGF₂ onPa_O2.Simulation of these data in a computer model, combining pulmonary gasexchange and pulmonary blood flow, reproduced the results on the basisthat vasoconstriction with PGF₂was maximal under hypoxia in the atelectatic lung and reduced byhyperoxia in the ventilated lung, consistent with the hypothesis ofO₂ dependence ofPGF₂ vasoconstriction.