Biomedical subjects

Norbert Weissmann

Publications and source records attributed to Norbert Weissmann.

51 records · Page 3Linked to original sources

PubMed2003

Effects of mitochondrial inhibitors and uncouplers on hypoxic vasoconstriction in rabbit lungs.

Hypoxic pulmonary vasoconstriction (HPV) matches lung perfusion to ventilation for optimizing pulmonary gas exchange; however, the underlying mechanism has not yet been fully elucidated. Lung nitric oxide (NO) generation appears to be involved in this process. Recently, mitochondria have been proposed as oxygen sensors, with HPV signaling via a hypoxia-induced increase in the generation of reactive oxygen species derived from mitochondrial complex III and escaping through an anion channel into the cytoplasm. In addition, complex II has been suggested to be specifically involved in hypoxia-dependent generation of reactive oxygen species in the lung. We investigated the effects of several mitochondrial inhibitors and uncouplers on the strength of HPV, and asked for their capacity to mimic HPV during normoxia in isolated buffer-perfused rabbit lungs. Specificity of the agents for HPV was tested by comparison of their effects on non-hypoxia-induced vasoconstriction, elicited by the thromboxane mimetic U46619. Interference with NO metabolism was determined by performing parallel studies with blocked lung NO generation and by measurement of exhaled NO. Rotenone, 3-nitroproprionic acid, and myxothiazol dose-dependently inhibited HPV without being mimics of HPV during normoxia. The inhibitory effect of these agents was only partly specific for HPV by comparison with U46619-induced vasoconstriction. During pre-blocked lung NO synthesis, the selectivity for HPV inhibition was increased for rotenone, but largely lost for myxothiazol. 2-tenoyltrifluoroacetone resulted in an unspecific inhibition of HPV as compared with U46619-induced vasoconstriction. 1-methyl-4-phenylpyridinium iodide and 2-heptyl-4-hydroxyquinoline-N-oxide specifically suppressed HPV and increased normoxic vascular tone. Antimycin A suppressed HPV, an effect being specific in lungs with intact NO synthesis and only partly specific while blocking NO. However, this agent did not mimic HPV during normoxia, as may be expected for interference with the mitochondrial electron transport downstream in complex III. The uncouplers 2,4-dinitrophenol (DNP, 10-200 microM) and carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP, 1-3 microM) induced sustained vasoconstriction during normoxia, with enhancement of HPV by DNP at low and suppression of HPV for both agents at high concentrations. The anion channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid inhibited HPV and U46619-induced vasoconstriction with identical dose-response curves. These findings suggest that mitochondria are in some manner involved in the regulation of HPV in intact rabbit lungs. The hypothesis that enhanced superoxide leak at complex III of mitochondria represents the underlying mechanism of acute HPV is supported by the rotenone and 2-heptyl-4-hydroxyquinoline-N-oxide data, but partly contradicted by the findings with 1-methyl-4-phenylpyridinium iodide, antimycin A, DNP, and FCCP. Further studies are mandatory to clarify the link between mitochondrial respiratory chain and hypoxic pulmonary vasoconstriction.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed2003

Interactions of peroxynitrite, tetrahydrobiopterin, ascorbic acid, and thiols: implications for uncoupling endothelial nitric-oxide synthase.

Tetrahydrobiopterin (BH4) serves as a critical co-factor for the endothelial nitric-oxide synthase (eNOS). A deficiency of BH4 results in eNOS uncoupling, which is associated with increased superoxide and decreased NO* production. BH4 has been suggested to be a target for oxidation by peroxynitrite (ONOO-), and ascorbate has been shown to preserve BH4 levels and enhance endothelial NO* production; however, the mechanisms underlying these processes remain poorly defined. To gain further insight into these interactions, the reaction of ONOO- with BH4 was studied using electron spin resonance and the spin probe 1-hydroxy-3-carboxy-2,2,5-tetramethyl-pyrrolidine. ONOO- reacted with BH4 6-10 times faster than with ascorbate or thiols. The immediate product of the reaction between ONOO- and BH4 was the trihydrobiopterin radical (BH3.), which was reduced back to BH4 by ascorbate, whereas thiols were not efficient in recycling of BH4. Uncoupling of eNOS caused by peroxynitrite was investigated in cultured bovine aortic endothelial cells (BAECs) by measuring superoxide and NO* using spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine and the NO*-spin trap iron-diethyldithiocarbamate. Bolus ONOO-, the ONOO- donor 3-morpholinosydnonimine, and an inhibitor of BH4 synthesis (2,4-diamino-6-hydroxypyrimidine) uncoupled eNOS, increasing superoxide and decreasing NO* production. Exogenous BH4 supplementation restored endothelial NO* production. Treatment of BAECs with both BH4 and ascorbate prior to ONOO- prevented uncoupling of eNOS by ONOO-. This study demonstrates that endothelial BH4 is a crucial target for oxidation by ONOO- and that the BH4 reaction rate constant exceeds those of thiols or ascorbate. We confirmed that ONOO- uncouples eNOS by oxidation of tetrahydrobiopterin and that ascorbate does not fully protect BH4 from oxidation but recycles BH3. radical back to BH4.

Animals↗

PubMed2003

Sildenafil for long-term treatment of nonoperable chronic thromboembolic pulmonary hypertension.

Only a small percentage of patients with chronic thromboembolic pulmonary hypertension are eligible for pulmonary thrombendarterectomy. We investigated the effects of oral sildenafil on hemodynamics and exercise capacity in 12 nonoperable chronic thromboembolic pulmonary hypertension patients. All patients were in disease progression despite sufficient long-term anticoagulation and the best supportive care and suffered from severe pulmonary hypertension (pulmonary vascular resistance index 1,935 +/- 228 dyn. s. cm-5. m2, cardiac index 2.0 l. min-1. m-2, 6-minute walking distance 312 +/- 30 m). After approximately 6 months of sildenafil treatment, pulmonary hemodynamics and exercise capacity improved significantly (pulmonary vascular resistance index 1,361 +/- 177 L. min-1. m2, p = 0.004, cardiac index 2.4 +/- 0.2 L. min-1. m-2, p = 0.009, 6-minute walking distance 366 +/- 28 m, p = 0.02). Therefore, oral sildenafil may offer a new option for medical treatment of this devastating disease.

Female↗

PubMed2003

Essential role of complex II of the respiratory chain in hypoxia-induced ROS generation in the pulmonary vasculature.

In the pulmonary vasculature, the mechanisms responsible for oxygen sensing and the initiation of hypoxia-induced vasoconstriction and vascular remodeling are still unclear. Nitric oxide (NO) and reactive oxygen species (ROS) are discussed as early mediators of the hypoxic response. Here, we describe a quantitative analysis of NO- and ROS-producing cells within the vascular walls of murine lung sections cultured at normoxia or hypoxia. Whereas the number of NO-producing cells was not changed by hypoxia, the number of ROS-generating cells was significantly increased. Addition of specific inhibitors revealed that mitochondria were the source of ROS. The participation of the individual mitochondrial complexes differed in normoxic and hypoxic ROS generation. Whereas normoxic ROS production required complexes I and III, hypoxic ROS generation additionally demanded complex II. Histochemically demonstrable succinate dehydrogenase activity of complex II in the arterial wall decreased during hypoxia. Inhibition of the reversed enzymatic reaction, i.e., fumarate reductase, by application of succinate, specifically abolished hypoxic, but not normoxic, ROS generation. Thus complex II plays an essential role in hypoxic ROS production. Presumably, its catalytic activity switches from succinate dehydrogenase to fumarate reductase at reduced oxygen tension, thereby modulating the directionality of the electron flow.

Animals↗

PubMed2003

Increased neutrophil mediator release in patients with pulmonary hypertension--suppression by inhaled iloprost.

Polymorphonuclear neutrophils (PMN) have been implicated in various vascular inflammatory processes. We isolated PMN from venous blood samples of 10 patients with severe primary pulmonary arterial hypertension (PPH), 7 patients with pulmonary hypertension secondary to chronic thromboembolism (CTEPH), and 12 healthy controls. When stimulated with the calcium-ionophore A23187, platelet activating factor (PAF) or the microbial agent n-formyl-Methionyl-Leucyl-Phenylalanine (fMLP), significantly increased release of elastase and superoxide anion was noted in both groups with pulmonary hypertension. Moreover, the neutrophils of CTEPH patients responded with an enhanced liberation of leukotriene (LT) B(4) and 5-hydroxyeicosatetraenoic acid (5-HETE). Inhalation of aerosolized iloprost (5 microg) caused a rapid decline in pulmonary vascular resistance, in both PPH and CTEPH. This hemodynamic response was paralleled by a significant suppression of ionophore- and ligand-induced elastase and superoxide release, as well as LTB(4) and 5-HETE formation. The neutrophil inhibitory effect of the inhalation maneuver was fully reproduced by in vitro incubation of neutrophils with 1-10 pg/ml iloprost for 2 hours. This is the first study to demonstrate that circulating neutrophils from patients with PPH and CTEPH possess an enhanced readiness to respond with inflammatory mediator generation to different stimulatory agents ex-vivo, and that PMN respiratory burst, elastase secretion and leukotriene generation are promptly reduced by an iloprost inhalation maneuver. Neutrophils might participate in the inflammatory processes in pulmonary arterial hypertension.

Administration, Inhalation↗

PubMed2003

Estimate of oxygen consumption and intracellular zinc concentration of human spermatozoa in relation to motility.

AIM: To investigate the human sperm oxygen/energy consumption and zinc content in relation to motility. METHODS: In washed spermatozoa from 67 ejaculates, the oxygen consumption was determined. Following calculation of the total oxygen consumed by the Ideal Gas Law, the energy consumption of spermatozoa was calculated. In addition, the zinc content of the sperm was determined using an atomic absorption spectrometer. The resulting data were correlated to the vitality and motility. RESULTS: The oxygen consumption averaged 0.24 micromol/10(6) sperm x 24h, 0.28 micromol/10(6) live sperm x 24h and 0.85 micromol/10(6) live motile sperm x 24h. Further calculations revealed that sperm motility was the most energy consuming process (164.31 mJ/10(6) motile spermatozoa x 24h), while the oxygen consumption of the total spermatozoa was 46.06 mJ/10(6) spermatozoa x 24h. The correlation of the oxygen/energy consumption and zinc content with motility showed significant negative correlations (r= -0.759; P<0.0001 and r=-0.441; P<0.0001, respectively). However, when correlating sperm energy consumption with the zinc content, a significant positive relation (r=0.323; P=0.01) was observed. CONCLUSION: Poorly motile sperm are actually wasting the available energy. Moreover, our data clearly support the "Geometric Clutch Model" of the axoneme function and demonstrate the importance of the outer dense fibers for the generation of sperm motility, especially progressive motility.

Adult↗

PubMed2002

Downregulation of hypoxic vasoconstriction by chronic hypoxia in rabbits: effects of nitric oxide.

Hypoxic pulmonary vasoconstriction (HPV) matches lung perfusion to ventilation for optimizing pulmonary gas exchange. Chronic alveolar hypoxia results in vascular remodeling and pulmonary hypertension. Previous studies have reported conflicting results of the effect of chronic alveolar hypoxia on pulmonary vasoreactivity and the contribution of nitric oxide (NO), which may be related to species and strain differences as well as to the duration of chronic hypoxia. Therefore, we investigated the impact of chronic hypoxia on HPV in rabbits, with a focus on lung NO synthesis. After exposure of the animals to normobaric hypoxia (10% O(2)) for 1 day to 10 wk, vascular reactivity was investigated in ex vivo perfused normoxic ventilated lungs. Chronic hypoxia induced right heart hypertrophy and increased normoxic vascular tone within weeks. The vasoconstrictor response to an acute hypoxic challenge was strongly downregulated within 5 days, whereas the vasoconstrictor response to the thromboxane mimetic U-46619 was maintained. The rapid downregulation of HPV was apparently not linked to changes in the lung vascular NO system, detectable in the exhaled gas and by pharmacological blockage of NO synthesis. Treatment of the animals with long-term inhaled NO reduced right heart hypertrophy and partially maintained the reactivity to acute hypoxia, without any impact on the endogenous NO system being noted. We conclude that chronic hypoxia causes rapid downregulation of acute HPV as a specific event, preceding the development of major pulmonary hypertension and being independent of the lung vascular NO system. Long-term NO inhalation partially maintains the strength of the hypoxic vasoconstrictor response.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed2002

Sildenafil for treatment of lung fibrosis and pulmonary hypertension: a randomised controlled trial.

BACKGROUND: Lung fibrosis can be complicated by pulmonary hypertension, limiting exercise tolerance and life expectancy. Furthermore, vasodilators might cause deterioration in gas exchange. Our aim was to compare acute effects of sildenafil, nitric oxide, and epoprostenol in individuals with pulmonary hypertension secondary to lung fibrosis. METHODS: We did a randomised controlled, open-label trial, in 16 individuals admitted to our hospital with pulmonary hypertension secondary to lung fibrosis. After inhalation of nitric oxide (10-20 ppm), we assigned patients to either maximum tolerated dose of intravenous epoprostenol (mean 8.0 ng/kg per min; n=8) or oral sildenafil (50 mg; n=8). Our primary objective was to assess pulmonary vasodilative potency (decrease in pulmonary vascular resistance index) of sildenafil by comparison with inhaled nitric oxide and infused epoprostenol. Analyses were by intention to treat. FINDINGS: Pulmonary vascular resistance index was reduced by nitric oxide (-21.9%, 95% CI -14.1 to -36.2), epoprostenol (-36.9%, -24.4 to -59.6), and sildenafil (-32.5%, -10.2 to -54.1). However, ratio of pulmonary to systemic vascular resistance decreased only in individuals who received nitric oxide and sildenafil. Baseline measurement of multiple-inert-gas elimination showed right-to-left shunt flow (4.8%, 0.0-28.2) and little perfusion of low ventilation(V)/perfusion(Q) areas (0.1%, 0.0-13.0). Prostacyclin increased V/Q mismatch (shunt 16.8%, 10.8-35.9; low V/Q 3.8%, 0.0-13.0) and decreased arterial oxygenation. By contrast, nitric oxide (4.5%, 0.0-18.0; 0.0%, 0.0-17.3) and sildenafil (3.3%, 0.0-11.3; 0.0%, 0.0-12.4) maintained V/Q matching, with raised arterial partial pressure of oxygen (14.3 mm Hg, -1.7 to 31.3) noted for sildenafil. We recorded no adverse events. INTERPRETATION: Sildenafil causes preferential pulmonary vasodilation and improves gas exchange in patients with severe lung fibrosis and secondary pulmonary hypertension.

Adult↗

PubMed2002

Hypoxic pulmonary artery fibroblasts trigger proliferation of vascular smooth muscle cells: role of hypoxia-inducible transcription factors.

Chronic lung hypoxia causes vascular remodeling with pulmonary artery smooth muscle cell (SMCPA) hyperplasia, resulting in pulmonary hypertension and cor pulmonale. We investigated SMCPA and pulmonary artery adventitial fibroblasts (FBPA) for their proliferative response to hypoxia. Strong SMCPA growth occurred under hypoxic conditions in SMCPA/FBPA co-cultures, but not in SMCPA monocultures. SMCPA growth was fully reproduced by transferring serum-free supernatant from hypoxic cultured FBPA to normoxic SMCPA. Hypoxia-inducible-transcription-factor subtypes (HIF-1alpha, HIF-2alpha, HIF-3alpha) and its dependent target genes, carrying the hypoxia-responsive-element as regulatory component, were strongly activated in both hypoxic FBPA and SMCPA. HIF-transcription-factor decoy technique, employed to FBPA during hypoxic culturing, blocked the mitogenic activity of FBPA conditioned medium on SMCPA. The data suggest that hypoxia-driven gene regulation in pulmonary artery fibroblasts results in a mitogenic stimulus on adjacent pulmonary artery smooth muscle cells, and HIF-transcription-decoy may offer a new therapeutic approach to suppress these events.

Basic Helix-Loop-Helix Proteins↗

PubMed2002

Apical, but not basolateral, endotoxin preincubation protects alveolar epithelial cells against hydrogen peroxide-induced loss of barrier function: the role of nitric oxide synthesis.

The influence of LPS preincubation on hydrogen peroxide (H(2)O(2))-induced loss of epithelial barrier function was investigated in rat alveolar epithelial type II cells (ATII). Both apical and basolateral H(2)O(2) administration caused a manyfold increase in transepithelial [(3)H]mannitol passage. Apical but not basolateral preincubation of ATII with LPS did not influence control barrier properties but fully abrogated the H(2)O(2)-induced leakage response. The effect of apical LPS was CD14 dependent and was accompanied by a strong up-regulation of NO synthase II mRNA and protein and NO release. Inhibition of NO by N(G)-monomethyl-L-arginine suppressed the LPS effect, whereas it was reproduced by exogenous application of gaseous NO or NO donor agents. Manipulation of the glutathione homeostasis (buthionine-(S,R)-sulfoximine) and the cGMP pathway (1H-(1,2,4)oxadiazolo[4,3-alpha]quinoxaline-1-one; zaprinast) did not interfere with the protective effect of LPS. Superoxide (O*(-)(2)) generation by ATII cells was reduced by exogenous NO and LPS preincubation. O*(-)(2) scavenging with exogenous superoxide dismutase, the intracellular superoxide dismutase analog Mn(III)tetrakis(4-benzoic acid) porphyrin, and the superoxide scavenger nitroblue tetrazolium and, in particular, hydroxyl radical scavenging with hydroxyl radical scavenger 1,3-dimethyl-thiourea inhibited the H(2)O(2)-induced epithelial leakage response. In conclusion, apical but not basolateral LPS preincubation of ATII cells provides strong protection against H(2)O(2)-induced transepithelial leakage, attributable to an up-regulation of epithelial NO synthesis. It is suggested that the LPS-induced NO formation is effective via interaction with reactive oxygen species, including superoxide and hydroxyl radicals. The polarized epithelial response to LPS may be part of the lung innate immune system, activated by inhaled endotoxin or under conditions of pneumonia.

Animals↗

PubMed2002

Combination therapy with oral sildenafil and inhaled iloprost for severe pulmonary hypertension.

BACKGROUND: Inhalation of the stable prostacyclin analogue iloprost is being studied for treatment of pulmonary hypertension. The selective phosphodiesterase-5 inhibitor sildenafil has been reported to cause pulmonary vasodilatation. OBJECTIVE: To evaluate the safety and effectiveness of oral sildenafil, alone and in combination with inhaled iloprost, for treatment of pulmonary hypertension. DESIGN: Randomized, controlled, open-label trial. SETTING: Intensive care unit. PATIENTS: 30 patients with severe pulmonary arterial hypertension (n = 16), chronic thromboembolic pulmonary hypertension (n = 13), or pulmonary hypertension due to aplasia of the left pulmonary artery (n = 1), all classified as New York Heart Association class III or IV. INTERVENTION: All patients received inhaled nitric oxide and aerosolized iloprost (inhaled dose, 2.8 microg). They were then randomly assigned to receive 12.5 mg of oral sildenafil, 50 mg of sildenafil, 12.5 mg of sildenafil plus inhaled iloprost, or 50 mg of sildenafil plus inhaled iloprost. MEASUREMENTS: Systemic and pulmonary arterial pressure, pulmonary arterial occlusion pressure, cardiac output, central venous pressure, peripheral arterial oxygen saturation, and arterial and mixed venous blood gases were measured during right-heart catheterization by using a Swan-Ganz catheter. RESULTS: In rank order of pulmonary vasodilatory potency (maximum reduction of pulmonary vascular resistance and increase in cardiac index), 50 mg of sildenafil plus iloprost was most effective, followed by 12.5 mg of sildenafil plus iloprost. Iloprost alone and 50 mg of sildenafil were almost equally effective but were less potent than the combination regimens, and the least potent treatments were 12.5 mg of sildenafil and nitric oxide. In patients who received 50 mg of sildenafil plus iloprost, the maximum change in pulmonary vasodilatory potency was -44.2% (95% CI, -49.5% to -38.8%), compared with -14.1% (CI, -19.1% to -9.2%) in response to nitric oxide. With administration of 50 mg of sildenafil plus iloprost, the area under the curve for reduction in pulmonary vasodilatory resistance surpassed that of administration of 50 mg of sildenafil alone and iloprost alone combined, the vasodilatory effect lasted longer than 3 hours, and systemic arterial pressure and arterial oxygenation were maintained. No serious adverse events occurred. CONCLUSION: Although limited by the small sample and lack of long-term observations, the study shows that oral sildenafil is a potent pulmonary vasodilator that acts synergistically with inhaled iloprost to cause strong pulmonary vasodilatation in both severe pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed2002

cDNA array hybridization after laser-assisted microdissection from nonneoplastic tissue.

Differential gene expression can be investigated effectively by cDNA arrays. Because tissue homogenates result inevitably in an average expression of a bulk of different cells, we aimed to combine mRNA profiling with cell-type-specific microdissection. Using a polymerase chain reaction (PCR)-based preamplification technique, the expression profile was shown to be preserved. We modified the existing protocol enabling to apply the total amount of extracted RNA from microdissected cells. A mean amplification factor of nearly 1000 allowed to reduce the demand of initial RNA to approximately 10 ng. This technique was used to investigate intrapulmonary arteries from mouse lungs ( approximately 500 cell equivalents). Using filters with 1176 spots, three independent experiments showed a high consistency of expression for the preamplified cDNAs. These profiles differed primarily from those of total lung homogenates. Additionally, in experimental hypoxia-induced pulmonary hypertension, amplified cDNA from intrapulmonary vessels of these lungs was compared to cDNA from vessels dissected from normoxic lungs. Validation by an alternative method was obtained by linking microdissection with real-time polymerase chain reaction (PCR). As suggested by the array data, nine selected genes with different factors of up-regulation were fully confirmed by the PCR technique. Thus, a rapid protocol is presented combining microdissection and array profiling that demands low quantities of initial RNA to assess reliably cell-type-specific gene regulation even within nonneoplastic complex tissues.

Animals↗

PubMed2002

Amplification of the pulmonary vasodilatory response to inhaled iloprost by subthreshold phosphodiesterase types 3 and 4 inhibition in severe pulmonary hypertension.

OBJECTIVE: Aerosolized iloprost causes specific pulmonary vasodilation for about 60 mins in patients with severe primary and secondary pulmonary hypertension. Repeated daily inhalations are currently in use for chronic treatment. The aim of the current study was to evaluate if phosphodiesterase type 3 and 4 inhibition might amplify the prostanoid effect on pulmonary vasodilatation by stabilization of intracellular second messenger cyclic adenosine monophosphate. DESIGN: Uncontrolled clinical trial. SETTING: Medical intensive care unit, Department of Internal Medicine, University Hospital, Giessen, Germany. PATIENTS: A total of 11 patients with precapillary pulmonary hypertension (eight with primary pulmonary hypertension; one with pulmonary hypertension associated with calcinosis, Raynaud phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia [CREST syndrome]; one with pulmonary hypertension associated with systemic lupus erythematodes, and one with chronic pulmonary embolism) were included. All were classified as New York Heart Association class III or class IV. INTERVENTIONS: During right heart catheterization, a single inhalation with iloprost (1.4 microg per inhalation) was performed, and hemodynamics and gas exchange variables were recorded for the next 2.5 hrs. After the iloprost effects had completely leveled off, the dual-selective phosphodiesterase types 3 and 4 inhibitor tolafentrine was infused in seven patients and aerosolized in five patients at doses that were per se ineffective (80 mg per 2.5 hrs intravenously; approximately 0.8 mg deposited by aerosol), followed by a second iloprost inhalation procedure. MEASUREMENTS: Decrease in pulmonary vascular resistance, duration of drug effect, safety, and tolerability of combined pharmacologic intervention. RESULTS: The decrease in pulmonary vascular resistance to sole iloprost nebulization lasted for approximately 60 mins. This response was enhanced and prolonged to approximately 120 mins in the presence of both infused and aerosolized tolafentrine, without loss of pulmonary selectivity. No adverse events were observed. CONCLUSIONS: These data support the principle that subthreshold selective phosphodiesterase types 3 and 4 inhibition amplifies the lung vasodilatory response to inhaled iloprost, with minute doses being sufficient via the inhalative route.

Adult↗

PubMed2002

Pharmacokinetics and metabolism of infused versus inhaled iloprost in isolated rabbit lungs.

Iloprost is a potent prostacyclin analog, which has been shown to exert beneficial effects in several vascular disorders. Inhalation of aerosolized iloprost was found to cause selective pulmonary vasodilatation, and this approach is under current investigation for treatment of chronic pulmonary hypertension. The present study investigated pharmacokinetics and metabolism of aerosolized iloprost in isolated buffer-perfused rabbit lungs, compared with intravascular administration of the prostanoid. After buffer admixture of iloprost, a steady decline of perfusate concentrations of the intact prostanoid was noted (half-life approximately 3.5 h), mostly attributable to progressive metabolism to dinor- and tetranoriloprost. Inhaled iloprost rapidly entered the intravascular compartment, with peak buffer concentrations being noted after 30 min (bioavailability approximately 63%). Compared with infused iloprost, significantly more rapid metabolism to dinor- and tetranoriloprost was noted for iloprost administered via the inhalative route of application. However, the percentage of the nebulized agent that enters the intravascular space as intact iloprost displays the same clearance rate as directly perfusate-admixed prostanoid. We conclude that a high percentage of inhaled iloprost rapidly enters the intravascular compartment in intact rabbit lungs. The lung is capable of metabolizing iloprost via beta-oxidation, and more rapid appearance of dinor- and tetranoriloprost is noted for the inhalative as compared with the intravascular route of iloprost administration.

Administration, Inhalation↗

PubMedDate not supplied

Measurement of exhaled hydrogen peroxide from rabbit lungs.

Exhaled H2O2 is considered an indicator of lung inflammatory and oxidative stress. Moreover, H2O2 may be involved in signal transduction processes. It is not fully elucidated to what extent (i) H2O2 escapes from the intravascular compartment, and (ii) pulmonary H2O2 generation and nasopharyngeal H2O2 generation contribute to exhaled H2O2. We investigated H2O2 concentrations in breath condensate from isolated buffer-perfused and ventilated rabbit lungs, and from both intubated and spontaneously breathing rabbits with a horseradish peroxidase/2',7'dichlorofluorescin assay. For the perfused lungs, a H2O2 concentration of 58 +/- 19 nM was found. Addition of H2O2 to the buffer fluid resulted in only minute appearance in the exhaled air (<0.001%). Levels of exhaled H2O2 in intubated rabbits and perfused lungs were virtually identical. Nearly ten-fold higher levels were detected in spontaneously breathing rabbits. Decreasing the inspired oxygen concentration from 21% to 1% resulted in a tendency toward decreased H2O2 exhalation in perfused lungs. In contrast, phorbol-12-myristate-13-acetate (PMA) prompted a approximately 4-fold increase in H2O2 exhalation. We conclude that the horseradish peroxidase/2',7'dichlorofluorescin assay is a feasible technique to measure H2O2 in exhaled breath condensate in rabbits. When collecting exhaled air via the tracheal tube, the signal represents pulmonary H2O2 generation with the contribution of the remaining body being negligible.

Animals↗