Phosphoramidon potentiates the endothelin-1-induced bronchopulmonary response in guinea-pigs

We investigated the effect of the endopeptidase-inhibitor, phosphoramidon, on the bronchopulmonary response induced by endothelin-1 in vivo or in isolated perfused lungs. In vivo aerosol administration of 1 or 3 μg/ml endothelin-1 for 2 min provoked no significant bronchopulmonary response. When awake animals were pretreated by an aerosol of phosphoramidon (0.1 mM, for 15 min), the bronchopulmonary response induced by 1 and 3 μg/ml endothelin-1 was markedly enhanced. In isolated guinea-pig lungs, aerosol administration of endothelin-1 (3 μg/ml, for 2 min) evoked a low increase in pulmonary inflation pressure. Treatment of awake animals with an aerosol of phosphoramidon before lung recollection led to a significant potentiation of the endothelin-1-induced increase in pulmonary inflation pressure. These results demonstrate that phosphoramidon potentiates the in vivo and in vitro bronchopulmonary response evoked by low doses of endothelin-1 and suggest that endopeptidase-like enzymes present in the airway tissue modulate the effect of the peptide.     

Effect of neutral endopeptidase inhibition of f-Met-Leu-Phe-induced bronchoconstriction in the rabbit

Inhalation of f-Met-Leu-Phe (FMLP) produces dose-dependent increases in pulmonary resistance (RL) in rabbits. We hypothesized that inhibition of neutral endopeptidase (NEP), which has high affinity for FMLP, would augment the response to FMLP inhalation. We found the increase in RL above baseline in response to FMLP to be reduced from 56 +/- 18 to 8 +/- 10% (P less than 0.01) by phosphoramidon (1 mg/kg) and to 15 +/- 6% (P less than 0.02) by thiorphan (3 mg/kg). The geometric mean dose of FMLP producing a 20% rise in RL (PC20RL FMLP) was increased by phosphoramidon from 1.1 to 4.5 mg/ml (P less than 0.05). Enkephalins, which are also NEP substrates, modulate cholinergic neurotransmission in the airway. Inhibition of the FMLP response by phosphoramidon was reversed by coadministration of naloxone (0.1 mg/kg); after atropine (2 mg/kg) the change in RL in response to FMLP was reduced to 7 +/- 4% (P less than 0.01), whereas morphine (0.15 mg/kg) increased PC20RL FMLP to 5.1 mg/ml (P less than 0.05). FMLP-induced bronchoconstriction in the rabbit is vagally mediated, and reduced responses after NEP inhibition may reflect modulation of cholinergic bronchoconstriction by enkephalins. Changes in airway NEP activity may influence the activity of a wide range of its substrates, of which some are bronchoconstrictors and others bronchodilators.     

Inhibition of neutral endopeptidase potentiates neurogenic inflammation in the rat trachea

The present study was performed to determine whether neurogenic inflammation in the rat trachea can be exaggerated by inhibiting neutral endopeptidase, an enzyme that degrades tachykinins that are believed to mediate neurogenic inflammation. Neurogenic inflammation was produced by antidromic electrical stimulation of one vagus nerve (2.5 Hz, 1 ms, 5 V for 5 min) in the presence of atropine or by an intravenous injection of capsaicin (100 micrograms/kg). Neutrophils that adhered to the endothelium of venules were visualized and counted in tracheal whole mounts that were stained by a histochemical reaction for myeloperoxidase. Neural inflammation increased the number of adherent neutrophils. Pretreatment with the neutral endopeptidase inhibitor phosphoramidon (1.0 or 2.5 mg/kg iv) increased neutrophil adhesion induced by neural inflammation. As assessed by the amount of extravasation of Monastral blue pigment, neural inflammation also increased vascular permeability, and this change was potentiated by phosphoramidon. These results are consistent with the concept that neuropeptides released from sensory nerves in the tracheal mucosa cause neutrophils to adhere to venules and increase vascular permeability and that these effects are modulated by neutral endopeptidase.     

Local formation and degradation of endothelin-1 in guinea pig airway tissues

Endothelin(ET)-1 and big ET-1 caused potent and sustained constriction of isolated guinea pig bronchus. The response to ET-1 was enhanced by phosphoramidon in a simple dose-related manner (0.01-1000 microM), while the response to big ET-1 was enhanced at lower doses (0.01-0.1 microM) but was suppressed at higher doses (100-1000 microM) of phosphoramidon. Big ET-1, when given intravenously (i.v.) to anesthetized guinea pigs, increased both bronchopulmonary inflation pressure and mean arterial blood pressure (2.5, 5, 10 nmol/kg i.v.). The pressor response to big ET-1 was attenuated by phosphoramidon dose-relatedly, while the pulmonary response was modified in a complex fashion composed of delayed onset and prolonged duration of action. These results suggest that ET converting as well as degrading enzymes coexist in the airway tissue and both enzymes are sensitive to phosphoramidon, so that phosphoramidon acts bifunctionally to reduce and stimulate the airway responses to big ET-1.     

Vasoactive intestinal peptide stimulates ciliary motility in rabbit tracheal epithelium: modulation by neutral endopeptidase.

We studied the effect of vasoactive intestinal peptide (VIP) on ciliary activity in rabbit cultured tracheal epithelium by a photoelectric method in vitro. Administration of VIP (10(-7) M) elicited an increase in ciliary beat frequency (CBF) from the baseline values of 970 +/- 52 to 1139 +/- 75 beats/min (mean +/- S.E., P less than 0.01). This ciliostimulatory effect was dose-dependent, with the maximal increase and EC50 value being 17.4 +/- 1.0% (P less than 0.05) and 6.10(-11) M, respectively. The VIP-induced increase in CBF was abolished by pretreatment of cells with [4-Cl-D-Phe6, Leu17]-VIP, a VIP receptor antagonist. The neutral endopeptidase inhibitor phosphoramidon (10(-5) M) potentiated the effect of VIP, so that the CBF dose-response curve for VIP was shifted to lower concentrations by 0.5 log U. The administration of VIP increased cyclic AMP levels in epithelial cells, an effect that was also potentiated by phosphoramidon. These results suggest that VIP may interact with its specific receptors and stimulate airway ciliary activity probably through the activation of adenylate cyclase, and that neutral endopeptidase may play a role in modulating this effect of VIP.     

Viral infection increases contractile but not secretory responses to substance P in ferret trachea.

Viral infection increases the airway smooth muscle response to substance P. This effect is due to decreased activity of neutral endopeptidase (EC 3.4.24.11), an enzyme that degrades substance P. Inhibition of neutral endopeptidase activity also potentiates substance P-induced 35SO4-labeled macromolecule secretion. Therefore we examined the in vitro effects of substance P on 35SO4-macromolecule secretion from the tracheae of influenza-infected ferrets. Despite a virus-induced loss of neutral endopeptidase activity (demonstrated in muscle bath experiments), there was no difference between control and infected tracheae in either baseline secretion [697 +/- 125 vs. 579 +/- 67 (SE) cpm/15 min; n = 15 tissues) or in the response to 10(-6) M substance P (increased by 218 +/- 63 and 195 +/- 51, respectively) or 10(-5) M substance P (increased by 416 +/- 95 and 354 +/- 54, respectively). Although phosphoramidon (10(-6) M) potentiated the secretory response to substance P, there was again no difference between control and infected tracheae. These data show that although viral infection decreases airway neutral endopeptidase activity, virus-induced hypersecretion is not due to a resulting increase in the secretory response to substance P.     

Tachykinins mediate bronchoconstriction elicited by isocapnic hyperpnea in guinea pigs

We tested the hypothesis that tachykinins mediate hyperpnea-induced bronchoconstriction (HIB) in 28 guinea pigs. Stimulus-response curves to increasing minute ventilation with dry gas were generated in animals depleted of tachykinins by capsaicin pretreatment and in animals pretreated with phosphoramidon, a neutral metalloendopeptidase inhibitor. Sixteen anesthetized guinea pigs received capsaicin (50 mg/kg sc) after aminophylline (10 mg/kg ip) and terbutaline (0.1 mg/kg sc). An additional 12 animals received saline (1 ml sc) instead of capsaicin. One week later, all animals were anesthetized, given propranolol (1 mg/kg iv), and mechanically ventilated (6 ml/kg, 60 breaths/min, 50% O2 in air fully water saturated). Phosphoramidon (0.5 mg iv) was administered to five of the noncapsaicin-treated guinea pigs. Eucapnic dry gas (95% O2-5% CO2) hyperpnea "challenges" were performed by increasing the tidal volume (2-6 ml) and frequency (150 breaths/min) for 5 min. Capsaicin-pretreated animals showed marked attenuation in HIB, with a rightward shift of the stimulus-response curve compared with controls; the estimated tidal volume required to elicit a twofold increase in respiratory system resistance (ES200) was 5.0 ml for capsaicin-pretreated animals vs. 3.7 ml for controls (P less than 0.03). Phosphoramidon-treated animals were more reactive to dry gas hyperpnea compared with control (ES200 = 2.6 ml; P less than 0.0001). Methacholine dose-response curves (10(-11) to 10(-7) mol iv) obtained at the conclusion of the experiments were similar among capsaicin, phosphoramidon, and control groups. These findings implicate tachykinin release as an important mechanism of HIB in guinea pigs.     

Phosphoramidon inhibits the vasoconstrictor effects evoked by big endothelin-1 but not the elevation of plasma endothelin-1 in vivo

Intravenous injections of big endothelin (ET)-1 (700 pmol/kg) in the pig increased arterial plasma levels of ET-1-like immunoreactivity (ET-1-LI) from 11.1 +/- 0.7 pM to 46.3 +/- 6.7 pM in the control situation and from 11.5 +/- 0.4 pM to 58.2 +/- 17 pM in the presence of the neutral endopeptidase inhibitor phosphoramidon (3 mg/kg). Big ET-1 increased splenic vascular resistance by 29% in the control situation. The vasoconstriction evoked by big ET-1 in the spleen was reduced after phosphoramidon treatment whereas the elevation of arterial ET-1-LI was not influenced. Furthermore the splenic vasoconstriction evoked by ET-1 was reduced after phosphoramidon without influencing plasma ET-1-LI. Also in rats the pressor effect of big ET-1 (1 nmol/kg) was inhibited by phosphoramidon (5 mg/kg) whereas the elevation of plasma ET-1 was not influenced. It is concluded that the vasoconstrictor effects of both big ET-1 and ET-1 are inhibited, but the increase in plasma ET-1 is unaffected by phosphoramidon.     

Tibenelast, 5,6-diethoxybenzo(B)thiophene-2-carboxylic acid, sodium salt (LY186655), is an orally active anti-asthma compound in the guinea pig

Anaphylactic shock was induced in actively sensitized guinea pigs by free inhalation of a high dose of ovalbumin (10 mg/ml) aerosol. Tibenelast (LY186655), 5,6-diethoxybenzo(b)-thiophene-2-carboxylic acid, sodium salt, proved to be a potent orally active compound against anaphylactic shock induced by high dose antigen aerosol. When a lower aerosol challenge (0.05 mg/ml) was employed, bronchoconstriction was observed with a concomitant increase in lung resistance (RL) and a fall in dynamic compliance (Cdyn). Tibenelast at 25 mg/kg p.o. prevented these changes. Tibenelast was 10 times more potent than aminophylline by i.v. administration; normalization of pulmonary function was achieved at 1 mg/kg i.v. Tibenelast was synergistic with epinephrine. Combination of no-effect doses of epinephrine (0.025 mg/kg s.c.) and tibenelast (0.1 mg/kg i.v.) normalized pulmonary function. The oral dose response curve of tibenelast was enhanced with the co-administration of epinephrine. These data suggest that tibenelast may act at a site different from that of epinephrine, although the mechanism of action of tibenelast is unclear at present. Tibenelast may be of significant value in the treatment of asthma and other respiratory diseases.     

Secondary release of thromboxane A2 in aerosol leukotriene C4-induced bronchoconstriction in guinea pigs

Effect of a thromboxane synthetase inhibitor (OKY-046) on bronchoconstriction induced by aerosol leukotriene C4 and histamine was studied in anesthetized, artificially ventilated guinea pigs in order to examine whether secondary release of thromboxane A2 is produced by aerosol leukotriene C4 or not. 0.01-1.0 micrograms/ml of leukotriene C4 and 12.5-400 micrograms/ml of histamine inhaled from ultrasonic nebulizer developed for small animals caused dose-dependent increase of pressure at airway opening (Pao) which is considered to be an index representing bronchial response. Pretreatment of the animals with intravenous OKY-046 (100mg/kg) significantly reduced the airway responses produced by inhalation of 0.1, 0.33 and 1.0 micrograms/ml of leukotriene C4, while the pretreatment did not affect the histamine dose-response curve. Based on these findings and previous reports (6,7), it is suggested that aerosol leukotriene C4 activates arachidonate cyclooxygenase pathway including thromboxane A2 synthesis and the released cyclooxygenase products have bronchodilating effect as a whole.     

Virus induces airway hyperresponsiveness to tachykinins: role of neutral endopeptidase

We examined the effects of viral respiratory infection by Sendai virus on airway responsiveness to tachykinins in guinea pigs. We measured the change in total pulmonary resistance induced by substance P or capsaicin in the presence or absence of the neutral endopeptidase inhibitor, phosphoramidon, in infected and in noninfected animals. In the absence of phosphoramidon, the bronchoconstrictor responses to substance P and to capsaicin were greater in infected than in noninfected animals. Phosphoramidon did not further potentiate the responses to substance P and to capsaicin in the infected animals, whereas it did so in noninfected animals. Studies performed in vitro showed that nonadrenergic noncholinergic bronchial smooth muscle responses to electrical field stimulation were also increased in tissues from infected animals and that phosphoramidon increased the response of tissues from noninfected animals greatly but increased the responses of tissues from infected animals only slightly. Responses to acetylcholine were unaffected by viral infection. Neutral endopeptidase activity was decreased by 40% in the tracheal epithelial layer of the infected animals. We suggest that respiratory infection by Sendai virus causes enhanced airway responsiveness to tachykinins by decreasing neutral endopeptidase-like activity in the airway epithelium.     

Secondary release of thromboxane A2 in aerosol leukotriene C4-induced bronchoconstriction in guinea pigs

Effect of a thromboxane synthetase inhibitor (OKY-046) on bronchoconstriction induced by aerosol leukotriene C4 and histamine was studied in anesthetized, artificially ventilated guinea pigs in order to examine whether secondary release of thromboxane A2 is produced by aerosol leukotriene C4 or not. 0.01–1.0μg/ml of leukotriene C4 and 12.5–400μg/ml of histamine inhaled from ultrasonic nebulizer developed for small animals caused dose-dependent increase of pressure at airway opening (Pao) which is considered to be an index representing bronchial response. Pretreatment of the animals with intravenous OKY-046 (100mg/kg) significantly reduced the airway responses produced by inhalation of 0.1, 0.33 and 1.0μg/ml of leukotriene C4, while the pretreatment did not affect the histamine dose-response curve. Based on these findings and previous reports (6, 7), it is suggested that aerosol leukotriene C4 activates arachidonate cyclooxygenase pathway including thromboxane A2 synthesis and the released cyclooxygenase products have bronchodilating effect as a whole     

Mechanisms of metabisulfite-induced bronchoconstriction: evidence for bradykinin B2-receptor stimulation.

Sodium metabisulfite (MBS) is a food preservative that can trigger bronchoconstriction in asthmatic subjects. Previous studies designed to identify the mechanisms involved in this response have yielded conflicting results. We noted certain similarities between the pharmacology of MBS-induced airway responses and those elicited by bradykinin (BK), another provocating agent in asthmatic subjects. Therefore we used allergic sheep to determine whether MBS-induced bronchoconstriction 1) had a pharmacology similar to that previously seen with BK in this model, including protection by a BK B2-receptor antagonist, NPC-567, and 2) was associated with increased concentrations of immunoreactive kinins in bronchoalveolar lavage. We measured specific lung resistance before and immediately after inhaled buffer and increasing concentrations of MBS (30 breaths of 25, 50, and 100 mg/ml) and calculated the concentration producing 100% increase in specific lung resistance over baseline (PC100). In seven sheep, geometric mean control PC100 was 33.1 mg/ml. Pretreatment with either the anticholinergic agent ipratropium bromide (180 micrograms; PC100 87.1 mg/ml) or the antiasthma drug nedocromil sodium (1 mg/kg aerosol; PC100 97.7 mg/ml) blocked the MBS-induced bronchoconstriction (P less than 0.05), whereas the histamine H1-receptor antagonist chlorpheniramine (2 mg/kg iv) was ineffective. Furthermore the MBS-induced bronchoconstriction was not affected by the neutral endopeptidase inhibitor thiorphan (40 breaths of a 1 mg/ml solution) or the angiotensin-converting enzyme inhibitor enalaprilat (2.5 mg aerosol). In six sheep the MBS-induced bronchoconstriction was completely blocked by NPC-567 (20 breaths, 5 mg/ml aerosol): after treatment with NPC-567 mean PC100 was 100 mg/ml compared with 57.5 mg/ml in the control trial (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Epithelium removal alters responsiveness of guinea pig trachea to substance P

Removal of epithelium from mammalian tracheae has been shown to enhance responsiveness to a variety of contractile and relaxant agents. One of the most dramatic shifts reported has been for guinea pig tracheal tissue denuded of epithelium and treated with substance P. We investigated whether this shift in responsiveness was because of 1) removal of an epithelium-associated enzyme, neutral endopeptidase, which degrades substance P and 2) loss of an epithelium-derived noncyclooxygenase relaxant factor. Using a muscle bath preparation we performed concentration-response curves with substance P and acetylcholine on indomethacin-treated tissues with and without intact epithelium and with and without pretreatment with the neutral endopeptidase inhibitor, phosphoramidon. Epithelium removal potentiated the mean agonist concentration calculated to causes 30% of the maximal contractile response by 148-fold for substance P and by 7-fold for acetylcholine. Phosphoramidon potentiated the contractile response to substance P, but not to acetylcholine, by both the epithelium-intact and denuded tissues (P less than 0.05). However, the degree of enhancement by phosphoramidon was much greater in the intact tissues. With phosphoramidon treatment, therefore, the difference in responsiveness to substance P between the intact and denuded tissues was reduced from 148-fold to 18-fold. This effect of phosphoramidon suggests that the hyperresponsiveness to substance P of epithelium-denuded airway tissue is largely because of removal of neutral endopeptidase. Because all tissues were treated with indomethacin, the leftward shifts in substance P and in acetylcholine responsiveness induced by epithelium removal further suggest that an epithelium-derived noncyclooxygenase factor other than neutral endopeptidase also modulates the contractile response to substance P and to acetylcholine.     

The increased proliferation of cultured neuroblastoma cells treated with vasoactive intestinal peptide is enhanced by simultaneous inhibition of neutral endopeptidase

Vasoactive intestinal peptide (VIP) stimulates the neuroblastoma cell line (NMB) to proliferate. Neuropeptide activity can be inhibited by neutral endopeptidases that function intracellularly and in the extracellular milieu. NMB cells express neutral endopeptidase (NEP) activity that can be specifically inhibited by phosphoramidon (PA). Our data now show that phosphoramidon treatment increases the efficacy of VIP-stimulated neuroblastoma proliferation. These results suggest that membrane endopeptidases modulate VIP-associated cell proliferation and enhancement of endopeptidase activity may serve as a target for cancer therapy.     

Airway neutral endopeptidase-like enzyme modulates tachykinin-induced bronchoconstriction in vivo

To determine whether neutral endopeptidase (NEP), also called enkephalinase (EC 3.4.24.11), modulates the effects of exogenous and endogenous tachykinins in vivo, we studied the effects of aerosolized phosphoramidon, a specific NEP inhibitor, on the responses to aerosolized substance P (SP) and on the atropine-resistant response to vagus nerve stimulation (10 V, 5 ms for 20 s) in guinea pigs. SP alone (10(-7) to 10(-4) M; each concentration, 7 breaths) caused no change in total pulmonary resistance (RL, P greater than 0.5). Phosphoramidon (10(-4) M, 90 breaths) caused no change either in base-line RL (P greater than 0.5) or in the response to aerosolized acetylcholine (P greater than 0.5). However, in the presence of phosphoramidon, SP (7 breaths) produced a concentration-dependent increase in RL at concentrations greater than or equal to 10(-5) M (P less than 0.001). Phosphoramidon (10(-7) to 10(-4) M; each concentration, 90 breaths) induced a concentration-dependent potentiation of SP-induced bronchoconstriction (10(-4) M, 7 breaths; P less than 0.01). Vagus nerve stimulation (0.5-3 Hz), in the presence of atropine, induced a frequency-dependent increase in RL (P less than 0.001). Phosphoramidon potentiated the atropine-resistant responses to vagus nerve stimulation (P less than 0.001) at frequencies greater than 0.5 Hz. The tachykinin antagonist [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-substance P abolished the effects of phosphoramidon on the atropine-resistant response to vagus nerve stimulation (2 Hz, P less than 0.005). NEP-like activity in tracheal homogenates of guinea pig was inhibited by phosphoramidon with a concentration producing 50% inhibition of 5.3 +/- 0.8 nM.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bronchial responses to substance P after antigen challenge in the guinea-pig: in vivo and in vitro studies

The effect of antigen challenge on the airway responses to substance P and on the epithelial neutral endopeptidase (NEP) activity was investigated in aerosol sensitized guinea-pigs. In vivo, bronchial responses to aerosolized substance P were similar to the responses observed in antigen-challenged guinea-pigs and in the control groups. In contrast, when the guinea-pigs were pretreated with the NEP inhibitor, phosphoramidon, a significant increase in the airway responses to substance P was observed after antigen challenge in vivo. However, in vitro, the contractile responses of the tracheal smooth muscle to substance P were similar between groups of guinea-pigs, in respect to the presence or absence of the epithelium and/or phosphoramidon. Histological studies showed an accumulation of eosinophils in the tracheal submucosa after antigen challenge and intact epithelial cells. These results show that in vivo bronchial hyperresponsiveness to substance P after antigen challenge in the guinea-pig is not associated with increased responses of the smooth muscle to exogenous SP in vitro. In addition, the results with phosphoramidon suggest that loss of NEP activity cannot account for the in vivo bronchial hyperresponsiveness to substance P presently observed.     

IL-2 induces pulmonary edema and vasoconstriction independent of circulating lymphocytes

We investigated the effect of IL-2 in the isolated guinea pig lung perfused with phosphate-buffered Ringer's solution (containing 0.5 g/100 ml albumin and 5.5 mM dextrose) to determine the mechanism of IL-2-induced pulmonary edema. IL-2 (0 to 10,000 U/ml) was added to the perfusate following a 10 min baseline steady-state period. Pulmonary arterial pressure (Ppa), pulmonary capillary pressure (Ppc), and change in lung weight (as a measure of developing pulmonary edema) were recorded at 0, 10, 30, 40, and 60 min. The capillary filtration coefficient (Kf.c), an index of vascular permeability to water, was measured at 30 and 60 min. Infusion of IL-2 increased Ppc (from 3.9 +/- 0.1 cm H2O at baseline to 8.8 +/- 1.1 cm H2O at 60 min for IL-2 at 2000 U/ml, p less than 0.01; and from 3.8 +/- 0.1 cm H2O at baseline to 8.9 +/- 0.6 cm H2O at 60 min for IL-2 at 10,000 U/ml, p less than 0.01. The lung weight also increased (32% at IL-2 concentration of 2000 U/ml, and 26% at IL-2 concentration of 10,000 U/ml) The capillary filtration coefficient did not change with IL-2 infusion. The IL-2 response was prevented using the pulmonary vasodilator, papaverine. The infusion of IL-2 was associated with the generation of thromboxane A2(TxA2) in the effluent perfusate. Inhibition of TxA2 synthetase using Dazoxiben prevented the pulmonary vasoconstriction and edema response to IL-2. In addition, IL-2 had no effect on the transendothelial clearance of 125I-albumin. The results indicate that IL-2 causes pulmonary edema secondary to an increase in Ppc. The response is mediated by IL-2 stimulation of TxA2 generation from the lung.     

Increased leukotriene C4 in ethchlorvynol-induced acute lung injury in dogs

We investigated whether ethchlorvynol (ECV)-induced acute lung injury (ALI) is associated with an increase in leukotriene C4 (LTC4) production. In six pentobarbital sodium-anesthetized dogs, ECV (15 mg/kg iv) introduced into the pulmonary circulation resulted in a 164 +/- 31% increase in extravascular lung water 120 min after ECV administration. Concomitantly, the mean (+/- SE) concentration of LTC4 in arterial plasma measured by radioimmunoassay following 80% EtOH precipitation, XAD-7 extraction and high-pressure liquid chromatography purification was 5.0 +/- 1.3 pg/ml, unchanged from control (pre-ECV) values. In contrast, in pulmonary edema fluid 120 min post-ECV, the LTC4 concentration was 35.2 +/- 10.8 pg/ml, sevenfold greater than those values found in the arterial plasma (P less than 0.01). In six additional dogs, 120 min after unilateral ALI had been induced with ECV (9 mg/kg iv), LTC4 in the bronchoalveolar lavage (BAL) of the uninjured lung was 12.1 +/- 1.5 pg/ml, unchanged from pre-ECV values, whereas, LTC4 in the BAL of the injured lung increased from a control value of 10.2 +/- 1.6 to 24.2 +/- 3.5 pg/ml (P less than 0.01) 120 min after ECV administration. These results demonstrate that, in ECV-induced acute lung injury, LTC4 concentrations in pulmonary edema fluid are considerably greater than those found in arterial plasma in the case of bilateral acute lung injury and significantly greater in the BAL of the injured lung compared with the uninjured lung in the case of unilateral acute lung injury. The results are a necessary first step in support of the hypothesis that leukotrienes participate in the altered permeability of ECV-induced acute lung injury.     

Effects of lung inflation on pulmonary arterial blood volume in intact dogs.

The isolated effects of alterations of lung inflation and transmural pulmonary arterial pressure (pressure difference between intravascular and pleural pressure) on pulmonary arterial blood volume (Vpa) were investigated in anesthetized intact dogs. Using transvenous phrenic nerve stimulation, changes in transmural pulmonary arterial pressure (Ptm) at a fixed transpulmonary pressure (Ptp) were produced by the Mueller maneuver, and increases in Ptp at relatively constant Ptm by a quasi-Valsalva maneuver. Also, both Ptm and Ptp were allowed to change during open airway lung inflation. Vpa was determined during these three maneuvers by multiplying pulmonary blood flow by pulmonary arterial mean transit time obtained by an ether plethysmographic method. During open airway lung inflation, mean (plus or minus SD) Ptp increased by 7.2 (plus or minus 3.7) cmH2O and Ptm by 4.3 (plus or minus 3.4) cmH2O for a mean increase in Vpa by 26.2 (plus or minus 10.7) ml. A pulmonary arterial compliance term (Delta Vpa/Delta Ptm) calculated from the Mueller maneuver was 3.9 ml/cmH2O and an interdependence term (Delta Vpa/Delta Ptp) calculated from the quasi-Valsalva maneuver was 2.5 ml/cmH2O for a 19% increase in lung volume, and 1.2 ml/cmH2O for an increase in lung volume from 19% to 35%. These findings indicate that in normal anesthetized dogs near FRC for a given change in Ptp and Ptm the latter results in a greater increase of Vpa.