The isolated perfused lung--a critical evaluation

Pulmonary in vitro instruments for the replacement of animal experiments

Advanced in vitro systems often combine a mechanical-physical instrument with a biological component e.g. cell culture models. For testing of aerosols, it is of advantage to consider aerosol behavior, particle deposition and lung region specific cell lines. Although there are many good reviews on the selection of cell cultures, articles on instruments are rare. This article focuses on the development of in vitro instruments targeting the exposure of aerosols on cell cultures. In this context, guidelines for toxicity investigation are taken into account as the aim of new methods must be the prediction of human relevant data and the replacement of existing animal experiments. We provide an overview on development history of research-based instruments from a pharmaceutical point of view. The standardized commercial devices resulting from the research-based instruments are presented and the future perspectives on pulmonary in vitro devices are discussed.

Correlation and clinical relevance of animal models for inhaled pharmaceuticals and biopharmaceuticals

Nonclinical studies are fundamental for the development of inhaled drugs, as for any drug product, and for successful translation to clinical practice. They include in silico, in vitro, ex vivo and in vivo studies and are intended to provide a comprehensive understanding of the inhaled drug beneficial and detrimental effects. To date, animal models cannot be circumvented during drug development programs, acting as surrogates of humans to predict inhaled drug response, fate and toxicity. Herein, we review the animal models used during the different development stages of inhaled pharmaceuticals and biopharmaceuticals, highlighting their strengths and limitations.

In VitroModels to Study Mechanisms of Lung Toxicity

Several functioning in vitro systems of varying complexity are currently in use for the study of mechanisms of lung toxicity. The isolated perfused lung is the model closest to the in vivo situation. It is a suitable model for combining metabolic and functional studies. It is, for instance, possible to relate changes in lung mechanics and lung perfusion flow to the release of various mediators during exposure of the lung to various agents. A simpler model may be constructed from lung slices which are less viable but suitable for uptake as well as metabolism studies.

Specific lung cells such as Clara cells and type II pneumocytes have been isolated and cultured and are valuable tools for studies of the molecular mechanisms of lung toxicity, particularly in cases of cell-specific toxicity. There is, however, a great need to develop techniques for the isolation and culture of other types of lung cells and also to improve the culturing techniques for those already isolated.

Drug Absorption Parameters Obtained Using the Isolated Perfused Rat Lung Model Are Predictive of Rat In Vivo Lung Absorption

The ex vivo isolated perfused rat lung (IPL) model has been demonstrated to be a useful tool during drug development for studying pulmonary drug absorption. This study aims to investigate the potential use of IPL data to predict rat in vivo lung absorption. Absorption parameters determined from IPL data (ex vivo input parameters) in combination with intravenously determined pharmacokinetic data were used in a biopharmaceutics model to predict experimental rat in vivo plasma concentration-time profiles and lung amount after inhalation of five different inhalation compounds. The performance of simulations using ex vivo input parameters was compared with simulations using in vitro input parameters, to determine whether and to what extent predictability could be improved by using input parameters determined from the more complex ex vivo model. Simulations using ex vivo input parameters were within twofold average difference (AAFE < 2) from experimental in vivo data for all compounds except one. Furthermore, simulations using ex vivo input parameters performed significantly better than simulations using in vitro input parameters in predicting in vivo lung absorption. It could therefore be advantageous to base predictions of drug performance on IPL data rather than on in vitro data during drug development to increase mechanistic understanding of pulmonary drug absorption and to better understand how different substance properties and formulations might affect in vivo behavior of inhalation compounds.

Development of a Novel Quantitative Structure-Activity Relationship Model to Accurately Predict Pulmonary Absorption and Replace Routine Use of the Isolated Perfused Respiring Rat Lung Model

Purpose

We developed and tested a novel Quantitative Structure-Activity Relationship (QSAR) model to better understand the physicochemical drivers of pulmonary absorption, and to facilitate compound design through improved prediction of absorption. The model was tested using a large array of both existing and newly designed compounds.

Methods

Pulmonary absorption data was generated using the isolated perfused respiring rat lung (IPRLu) model for 82 drug discovery compounds and 17 marketed drugs. This dataset was used to build a novel QSAR model based on calculated physicochemical properties. A further 9 compounds were used to test the model’s predictive capability.

Results

The QSAR model performed well on the 9 compounds in the “Test set” with a predicted versus observed correlation of R² = 0.85, and >65% of compounds correctly categorised. Calculated descriptors associated with permeability and hydrophobicity positively correlated with pulmonary absorption, whereas those associated with charge, ionisation and size negatively correlated.

Conclusions

The novel QSAR model described here can replace routine generation of IPRLu model data for ranking and classifying compounds prior to synthesis. It will also provide scientists working in the field of inhaled drug discovery with a deeper understanding of the physicochemical drivers of pulmonary absorption based on a relevant respiratory compound dataset.

Successful prolonged ex vivo lung perfusion for graft preservation in rats

OBJECTIVES

Ex vivo lung perfusion (EVLP) strategies represent a new frontier in lung transplantation technology, and there have been many clinical studies of EVLP in lung transplantation. The establishment of a reliable EVLP model in small animals is crucial to facilitating translational research using an EVLP strategy. The main objective of this study was to develop a reproducible rat EVLP (R-EVLP) model that enables prolonged evaluation of the explanted lung during EVLP and successful transplantation after EVLP.

METHODS

The donor heart-lung blocks were procured with cold low-potassium dextran solution and immersed in the solution for 1 h at 4 °C. And then, the heart-lung blocks were flushed retrogradely and warmed up to 37 °C in a circuit perfused antegradely with acellular perfusate. The perfusate was deoxygenated with a gas mixture (6% O2, 8% CO2, 86% N2). The perfusion flow was maintained at 20% of the entire cardiac output. At 37 °C, the lungs were mechanically ventilated and perfusion continued for 4 h. Every hour, the perfused lung was evaluated for gas exchange, dynamic lung compliance (Cdyn) and pulmonary vascular resistance (PVR).

RESULTS

R-EVLP was performed for 4 h. Pulmonary oxygenation ability (pO2/pCO2) was stable for 4 h during EVLP. It was noted that Cdyn and PVR were also stable. After 4 h of EVLP, pO2 was 303 ± 19 mmHg, pCO2 was 39.6 ± 1.2 mmHg, PVR was 1.75 ± 0.10 mmHg/ml/min and Cdyn was 0.37 ± 0.03 ml/cmH2O. Lungs that were transplanted after 2 h of R-EVLP resulted in significantly better post-transplant oxygenation and compliance when compared with those after standard cold static preservation.

CONCLUSIONS

Our R-EVLP model maintained stable lung oxygenation, compliance and vascular resistance for up to 4 h of perfusion duration. This reliable model should facilitate further advancement of experimental work using EVLP.

In vitro, in vivo and ex vivo models for studying particle deposition and drug absorption of inhaled pharmaceuticals

Delivery of therapeutic agents via the pulmonary route has gained significant attention over the past few decades because this route of administration offers multiple advantages over traditional routes that include localized action, non-invasive nature and favorable lung-to-plasma ratio. However, assessment of post administration behavior of inhaled pharmaceuticals-such as deposition of particles over the respiratory airways, interaction with the respiratory fluid and movement across the air-blood barrier-is challenging because the lung is a very complex organs that is composed of airways with thousands of bifurcations with variable diameters. Thus, much effort has been put forward to develop models that mimic human lungs and allow evaluation of various pharmaceutical and physiological factors that influence the deposition and absorption profiles of inhaled formulations. In this review, we sought to discuss in vitro, in vivo and ex vivo models that have been extensively used to study the behaviors of airborne particles in the lungs and determine the absorption of drugs after pulmonary administration. We have provided a summary of lung cast models, cascade impactors, noninvasive imaging, intact animals, cell culture and isolated perfused lung models as tools to evaluate the distribution and absorption of inhaled particles. We have also outlined the limitations of currently used models and proposed future studies to enhance the reproducibility of these models.

Comparative study of the disposition of levofloxacin, netilmicin and cefepime in the isolated rat lung

An experimental model of artificially perfused and mechanically ventilated lung has been applied to compare the kinetic behaviour of levofloxacin, cefepime and netilmicin in this body tissue. The study has been performed to explore the usefulness of the isolated lung technique in the pharmacokinetic field, particularly to study the disposition of antibiotics in pulmonary tissue. The lung was perfused with Krebs-Henseleit medium containing 3% bovine albumin at a flow rate of 5 mL min−1. It was ventilated at 60 respirations/min with a 2-mL tidal volume of air previously humidified and warmed to 37°C. The concentrations of the above antibiotics were determined by HPLC techniques and the outflow curves were analysed by stochastic, as well as by model-dependent, methods. The results show pharmacokinetic differences among these antibiotics, which are in accordance with previously reported data, levofloxacin being the drug with the highest distribution coefficient in this tissue (1.25 ± 0.14 vs 0.39 ± 0.07 and 0.41 ± 0.06 mL g−1 for netilmicin and cefepime, respectively). Accordingly, the isolated lung of the rat, under the experimental conditions used here, constitutes an alternative model to be incorporated to pharmacokinetic studies with a great potential use for those drugs that show a pharmacological or toxicological action depending on the kinetic profile in the lung tissue.

A Novel Method to Aerosolize Powder for Short Inhalation Exposures at High Concentrations: Isolated Rat Lungs Exposed to Respirable Diesel Soot

More efficient methods are needed to aerosolize dry powders for short-duration inhalation exposures at high concentrations. There is an increasing need to reach the peripheral lung with dry powder medications as well as with collected ambient aerosol particulates in environmental research projects. In a novel aerosol generator, a fixed volume of compressed air was used to create a short burst of a highly concentrated aerosol in a 300-ml holding chamber. Collected diesel soot was deagglomerated to a fine aerosol with a mass median aerodynamic diameter (MMAD) of 0.55 microm, not much larger than the 0.25 microm MMAD of diesel exhaust particles measured in air. A fine powder such as 3-microm silica particles was completely deagglomerated to an aerosol with a MMAD of 3.5 microm. Immediately after generation, the aerosol was available for exposure at a chosen flow rate by the use of an automated valve system. Tritium-labeled diesel soot was thus used to expose the isolated perfused rat lung at an air concentration of approximately 3 mg/L and a flow rate of 370 ml/min in a 1-min-long exposure. The lungs were ventilated at 75 breaths/min and a tidal volume of 1.13 +/- 0.11 ml (SD, n = 3). Results showed that 19.8 +/- 1.1 microg (SD, n = 3) soot was deposited in the lungs. This amount constitutes 9.5% of the amount inhaled and is close to literature data on deposition of similar sized particles in the rat lung. More than 97% of the deposited soot was located distal to the extrapulmonary bronchi, indicating that the system delivers a highly respirable aerosol. The aerosol system is particularly useful for peripheral lung delivery of collected ambient aerosols or dry powder pharmaceuticals following a minimal effort in formulation of the powder.

In vivo, in vitro and ex vivo models to assess pulmonary absorption and disposition of inhaled therapeutics for systemic delivery

Despite the interest in systemic delivery of therapeutic molecules including macromolecular proteins and peptides via the lung, the accurate assessment of their pulmonary biopharmaceutics is a challenging experimental task. This article reviews in vivo, in vitro and ex vivo models currently available for studying lung absorption and disposition for inhaled therapeutic molecules. The general methodologies are discussed with recent advances, current challenges and perspectives, especially in the context of their use in systemic pulmonary delivery research. In vivo approaches in small rodents continue to be the mainstay of assessment by virtue of the acquisition of direct pharmacokinetic data, more meaningful when attention is given to reproducible dosing and control of lung-regional distribution through use of more sophisticated lung-dosing methods, such as forced instillation, microspray, nebulization and aerosol puff. A variety of in vitro lung epithelial cell lines models and primary cultured alveolar epithelial (AE) cells when grown to monolayer status offer new opportunity to clarify the more detailed kinetics and mechanisms of transepithelial drug transport. While continuous cell lines, Calu-3 and 16HBE14o-, show potential, primary cultured AE cell models from rat and human origins may be of greater use, by virtue of their universally tight intercellular junctions that discriminate the transport kinetics of different therapeutic entities. Nevertheless, the relevance of using these reconstructed barriers to represent complex disposition of intact lung may still be debatable. Meanwhile, the intermediate ex vivo model of the isolated perfused lung (IPL) appears to resolve deficiencies of these in vivo and in vitro models. While controlling lung-regional distributions, the preparation alongside a novel kinetic modeling analysis enables separate determinations of kinetic descriptors for lung absorption and non-absorptive clearances, i.e., mucociliary clearance, phagocytosis and/or metabolism. This ex vivo model has been shown to be kinetically predictive of in vivo, with respect to macromolecular disposition, despite limitations concerning short viable periods of 2-3 h and likely absence of tracheobronchial circulation. Given the advantages and disadvantages of each model, scientists must make appropriate selection and timely exploitation of the best model at each stage of the research and development program, affording efficient progress toward clinical trials for future inhaled therapeutic entities for systemic delivery.

The pharmacokinetics of pulmonary insulin in the in vitro isolated perfused rat lung: Implications of metabolism and regional deposition

The pharmacokinetics of several lung disposition pathways for pulmonary insulin were studied and modeled in the isolated perfused rat lung (IPRL). Insulin solution was administered by forced instillation into the airways of the IPRL as 0.1 or 0.02 ml doses of coarse spray, with or without bacitracin (BAC), N-ethylmaleimide (NEM) and atrial natriuretic peptide (ANP). Each insulin absorption profile was fitted to a kinetic model that incorporated the distribution fraction of the dose reaching the lobar region (DF) and the rate constants for absorption into perfusate (k(a)) and non-absorptive loss (k(nal)); k(nal) was shown to be due to the sum of mucociliary clearance and metabolism. Insulin absorption occurred largely by passive diffusion with values for k(a) = 0.39-0.50 h(-1). With DF = 0.91 following 0.1 ml doses, 11.9 +/- 3.4% of bioavailabilities were observed in 1h. In contrast, derived values for k(nal) = 2.34-3.45 h(-1) were significantly larger than the rate constant for mucociliary clearance determined previously in this IPRL (0.96-1.74 h(-1)) due to lung metabolism. Indeed, BAC, but neither NEM nor ANP, was found to decrease the value of k(nal), which suggested that BAC-inhibitable lung ectopeptidases, and not insulin degrading enzyme (IDE), were responsible for this pulmonary metabolism. Shallower lung distribution with DF = 0.73 following 0.02 ml doses resulted in reduced values for k(a) = 0.27 h(-1) and k(nal) = 2.79 h(-1), indicating that these kinetic processes may be lung-region dependent, even within this model and emphasizing the likely importance of reliable lung deposition in vivo.

Decreasing the oxidant stress from paraquat in isolated perfused rat lung using captopril and niacin

The abilities of captopril and niacin to protect against the lung toxicity of paraquat (PQ) were studied. The anti-oxidative action of captopril, an angiotensin-converting enzyme inhibitor, appears to be attributable to the sulphahydryl group (SH) in the compound, which gives captopril the ability to scavenge reactive oxygen species. Niacin replenishes the NAD and ATP depletion caused by reactive oxygen species. PQ causes lung damage in man and in several species of laboratory animals. The damage is initially manifested by hemorrhage and edema, and later by consolidation of the lung and fibrosis development. In this study, the lungs of male Wistar rats (250-300 g in weight) were perfused by Krebs-Ringer buffer alone (control), niacin (150 microM), captopril (10 microM) and PQ (600 microM) in perfusion fluid, and the biochemical changes that occurred in isolated rat lung were examined within 1 h and compared to PQ alone. The results show that captopril significantly decreases the lung weight/body weight ratio when used as a pretreatment and a post-treatment to captopril (p<0.0001). The results also show that captopril (10 microM) and niacin (150 microM) significantly decreases PQ-induced lung toxicity. Lactate dehydrogenase (LDH) activity significantly decreased in treatment groups as compared to the PQ group (p<0.0001). This study suggests that paraquat causes increased lipid peroxidation and LDH activity and decreased glutathione (GSH) and total protein in isolated perfused rat lung. These effects are reduced under these experimental conditions by captopril and niacin.

Drug absorption from the isolated perfused rat lung--correlations with drug physicochemical properties and epithelial permeability

The pulmonary absorption of nine low-molecular-weight (225-430 Da) drugs (atenolol, budesonide, enalaprilat, enalapril, formoterol, losartan, metoprolol, propranolol and terbutaline) and one high-molecular-weight membrane permeability marker compound (FITC-dextran 10000 Da) was investigated using the isolated, perfused and ventilated rat lung (IPL). The relationships between pulmonary transport characteristics, epithelial permeability of Caco-2 cell monolayers and drug physicochemical properties were evaluated using multivariate data analysis. Finally, an in vitro-in vivo correlation was made using in vivo rat lung absorption data. The absorption half-life of the investigated drugs ranged from 2 to 59 min, and the extent of absorption from 21 to 94% in 2 h in the isolated perfused rat lung model. The apparent first-order absorption rate constant in IPL (ka(lung)) was found to correlate to the apparent permeability (P(app)) of Caco-2 cell monolayers (r = 0.87), cLog D(7.4) (r = 0.70), cLog P, and to the molecular polar surface area (%PSA) (r = -0.79) of the drugs. A Partial Least Squares (PLS)-model for prediction of the absorption rate (log ka(lung)) from the descriptors log P(app), %PSA and cLogD(7.4) was found (Q2 = 0.74, R2 = 0.78). Furthermore, a strong in vitro-in vivo correlation (r = 0.98) was found for the in vitro (IPL) drug absorption half-life and the pulmonary absorption half-life obtained in rats in vivo, based on a sub-set of five compounds.

Solute disposition in the rat lung in vivo and in vitro: determining regional absorption kinetics in the presence of mucociliary escalator

Solute absorption from the airways was compared and modeled in vivo and in vitro isolated perfused rat lung (IPRL), and its regional kinetic descriptors in the presence of competing mucociliary escalator were estimated. 7.4 kDa fluorophore-labeled polyhydroxyethylaspartamide (F-PHEA), FITC-labeled dextran 40 (FD-4) and sodium fluorescein (F-Na) were used as model solutes. They were reproducibly administered into the airways in a range of doses in vivo and in vitro IPRL, and their initial deposition and subsequent absorption profiles compared. Each of the absorption data was fitted across doses to a kinetic model in which rate constants for Michaelis-Menten-type active (V(max,P) and K(m,P)) and/or first-order passive (k(a,P)) absorption and mucociliary escalator (k(E)) were estimated simultaneously. Statistically indistinguishable initial solute distribution was ensured in vivo and in vitro. The absorption profiles for F-PHEA were kinetically identical in vivo and in vitro, and their modeling analysis revealed the presence of competing, solute-independent pulmonary-to-bronchial mucociliary escalator with a half-life of 28.9 min. F-PHEA's active absorption was found to be 77 times faster than its passive absorption, yet this was present only in the pulmonary region. Passive solute absorption was inversely related to solute molecular weight [F-PHEA < FD-4 < F-Na]. Bronchial absorption was shown for F-Na in vivo and its rate indistinguishable from that from the pulmonary region. Thus, a single kinetic model was developed, enabling regional absorption kinetic analysis both in vivo and in vitro, in the presence of competing, solute-independent mucociliary escalator.

A novel paracorporeal method for isolated rodent lung reperfusion

BACKGROUND

The isolated perfused lung model is commonly used in small animals to study lung function after preservation and cold storage. Measurements of oxygenation, compliance, and capillary filtration coefficient (Kf) permit analysis of preservation solutions or modifications of these solutions. However, inter-investigator variability using different perfusates makes comparisons difficult. Whole blood perfusion more closely mimics the in vivo situation, but extracorporeal circulation may alter the physiologic integrity of the model. Paracorporeal support has been used, but this technique required mechanical ventilation of the support rodent and did not incorporate a method for determining Kf. We evaluated a less-invasive technique, of providing cross-circulatory syngeneic support, maintaining the ability to compute Kf.

METHODS

Angiocatheters were inserted into both femoral arteries and one femoral vein of the support rat. The venous cannula was connected to the pulmonary artery of the ex vivo lung block to provide inflow. Pulmonary effluent blood from the lung block was collected via a left atrial cannula and returned to the support rat via the femoral artery. A separate, height-adjustable column was included in the circuit for measurement of Kf.

RESULTS

Each support rat was used to sequentially perfuse three double-lung blocks. The inflow sample to each lung block was analyzed for pH, pO2, pCO2, and hematocrit to follow alterations in support rat physiology. There were no statistical differences in the pH, PO2, or hematocrit. No significant differences were noted in the pO2 of the pulmonary effluent blood or the Kf; analyzed to determine whether the sequence of reperfusion affected the pulmonary function assessment.

CONCLUSIONS

The syngeneic support rat delivers constant pressure systemic venous blood at stable physiologic parameters to the ex vivo lung block. Recirculation of the perfusate through the support rat diminishes the need to pool blood from donors, detoxifies and deoxygenates pulmonary effluent blood, and permits examination of sequential lung blocks. This technique represents a hybrid model between isolated perfused and orthotopic transplant models, maintaining Kf determination, a sensitive indicator of reperfusion injury. This technique could be applicable to reperfusion injury models of other organs (using arterial inflow instead) and may permit increased standardization among investigators.

Kinetic aspects of drug disposition in the lungs

1. The pharmacokinetic role of the lungs has been extensively studied using in vitro preparations, but this information has not been well integrated into many systemic pharmacokinetic models. 2. The lung is characterized by short diffusion distances, extremely high relative perfusion and heterogeneous cell types. Anionic and neutral lipophilic drugs have relatively small distribution volumes in the lungs due to their low lipid content. Cationic lipophilic drugs can accumulate in the lungs, probably due to trapping in mitochondria and lysosomes, forming very slowly eluting pools. 3. Drug metabolism in the lungs is possible, but not universal. The lung, generally, has a low activity for many of the metabolic enzymes found in the liver, although this activity is relatively more inducible. The resultant drug extraction would be 'enzyme limited', variable and flow dependent. 4. Double indicator studies of first-pass lung kinetics can characterize short-term distribution in the lungs, but not longer-term distribution or metabolism; the converse applies for studies of drug concentration gradients across the lungs. No single study or model has adequately defined the short- and long-term kinetics of drugs in the lungs. 5. Drug clearance in the lungs can contribute to an apparent total body clearance in excess of hepatic blood flow and cardiac output. The lung is a first pass filter for any drug administered on the venous side of the circulation and can act as a 'capacitor' that damps the first-pass concentration peak in the blood after intravenous bolus injection.

Catecholamine release from isolated guinea pig lungs during sympathetic stimulation with varied ventilation and perfusion

This study was performed to elucidate catecholamine release in the pulmonary circulation of isolated lungs due to the sympathetic nerve stimulation and to assess the experimental conditions which can modify the release, i.e., stimulus intensity, ventilation state of the lung and flow rate of perfusion. In artificially ventilated lungs, electrical stimulation of stellate ganglions evoked large noradrenaline efflux from the lung, but adrenaline efflux was below the detection limit, and dopamine was not detected in any case. In the unventilated preparations, the lung parenchyma were not bleached and the arterial pressure was significantly higher than in ventilated preparations. Noradrenaline efflux from the unventilated group was significantly lower than that from the ventilated preparations. The effect of the perfusion flow rate was investigated under pressure-operated ventilation. The pulmonary arterial pressure (Pa) was not varied at 5-10 ml min-1, but it was increased significantly at 20 ml min-1. Noradrenaline efflux was also increased significantly at 20 ml min-1. These results indicate that noradrenaline was the catecholamine exclusively released from pulmonary vasculature due to the sympathetic nerve stimulation, and that both ventilation and the perfusion flow rate could affect the release. The concomitant increase in arterial pressure indicates that noradrenaline efflux would be affected by the alteration in resistive small arteries. Circulatory change in these arteries is supposed to be one of the factors that modify noradrenaline release from the lungs. The analysis of noradrenaline should be a useful method to evaluate the sympathetic effect on the pulmonary vasculature.

Lung uptake of lidocaine during hyperoxia and hypoxia in the dog

BACKGROUND

Lidocaine has been shown to accumulate in the lung following its administration. This study was undertaken to determine effects of dose of lidocaine on lung uptake during hyperoxic and hypoxic ventilation.

METHODS

Using cross-circulation of ventilation and constant-flow perfusion of the left lower lobe independently from all other lobes of the dog lung under nitrous oxide and halothane anesthesia, lidocaine was infused into the inflow system, so that plasma lidocaine concentrations in the inflow blood were maintained at 5, 10, 20, 40 and 70 micrograms/ml respectively during ventilation with 50% O2 or 3% O2. During 20 micrograms/ml lidocaine infusion, indocyanine green (ICG), an intravascular marker, was mixed with the lidocaine solution, in such a fashion that plasma ICG concentration in the inflow blood was maintained at 20 micrograms/ml. Actual plasma lidocaine and ICG concentrations in blood drawn from the inflow ([Lid]pa,[ICG]pa) and the outflow ([Lid]pv,[ICG]pv)systems were measured, 1, 3, 5, 7 and 10 minutes after the beginning of lidocaine infusion. Percent lung uptake of perfused lidocaine was calculated as ¿1-([Lid]pv/[Lid]pa)/([ICG]pv/[ICG]pa)¿ x 100.

RESULTS

During ventilation hyperoxia, mean percent lung uptakes of lidocaine were 41-52% 1 minute after the beginning of lidocaine infusion, and decreased in time-dependent fashion to 7-12% 10 minutes later. Curves of percent lung uptake of lidocaine over time were similar for the 5 predetermined lidocaine concentration groups (5-70 micrograms/ml). There were no significant differences in percent lung uptakes of lidocaine between the ventilation hyperoxia and hypoxia conditions.

CONCLUSIONS

These findings suggest that percent lung uptake of lidocaine is unaffected by hypoxic ventilation and by varying the concentration of lidocaine in the perfusion through the recipient dog lung lobe.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.

Pharmacokinetics of detirelix following intratracheal instillation and aerosol inhalation in the unanesthetized awake sheep

The unanesthetized awake sheep was employed as large animal model for the determination of bioavailability and pharmacokinetics following the pulmonary instillation of the decapeptide detirelix. After intratracheal administration of a 80 micrograms/kg dose, the average t1/2 of elimination was 9.8 +/- 1.3 hours (n = 5) which was similar to the elimination kinetics of a 30 micrograms/kg i.v. dose (7.2 +/- 2.9 hours). Mean residence time (MRT) was prolonged to 10.3 +/- 2.0 hours vs. 2.7 +/- 0.8 hours i.v., and mean absorption time (MAT) was calculated to be 7.5 +/- 1.8 hours. Maximum plasma levels (cmax) of 9.2 ng/ml were reached after 2 hours. The average bioavailability was 9.8 +/- 3.9% of the dose. The pharmacokinetic profile was found to be similar after aerosol administration. It was concluded that detirelix was absorbed systemically when administered by pulmonary instillation or aerosolization and that the unanesthetized awake sheep is a suitable model to study resulting drug profiles.

The isolated heart-lung preparation in the cat. An in situ model to study the role of the lungs in the disposition of drugs

In the search for drugs with an extreme short time course of action, compounds should be developed that are rapidly distributed to and temporarily stored in well-perfused organs. Since the lungs receive the complete cardiac output and have the ability to temporarily store drugs, we have developed an in situ, isolated lung preparation in the cat to study the contribution of the lungs to the disposition of drugs. The cat's own heart perfuses the lung in situ with autologous blood. The circulation between the left ventricle and the right atrium is short-circuited via an aorta-caval shunt. The right forelimb is added to study pharmacodynamics simultaneously (only for muscle relaxants). Validation of the model for 180 min of perfusion showed complete isolation of the organs without major biochemical changes or edema and a stable muscle response. In pilot experiments with two structurally related muscle relaxants, initial muscle relaxation was followed by spontaneous recovery of neuromuscular function and a gradually decreasing plasma concentration, indicating partial disposition by the lungs. This was confirmed by direct concentration measurements in the lung. The present model may provide a powerful experimental tool to elucidate the role of the lungs in the disposition of drugs.

Amiodarone- and desethylamiodarone-induced pulmonary phospholipidosis, inhibition of phospholipases in vivo, and alteration of [14C]amiodarone uptake by perfused lung

Amiodarone (AM) pulmonary phospholipidosis in patients receiving this drug is well recognized. We investigated the in vivo phospholipidosis-inducing potency of AM and its major nonpolar metabolite, desethylamiodarone (DEA), in rats, their ability to inhibit phospholipases, and also the effects on pulmonary uptake of [14C] AM. Fisher-344 male rats (200 to 250 g) were given AM or DEA (100 mg/kg/d orally) for 2, 7, or 21 d. Food consumption and body weight gain were significantly reduced by both AM and DEA treatment. The control rats, therefore, were pair-fed. Both drugs increased the number of cells in lavage during the treatment. Lung/body weight ratio increased after 21 d of treatment in AM rats. Mortality increased to 100% by day 10 in DEA-treated rats, unlike in AM-treated rats, where 20 to 30% of the animals died during this period and thereafter. No further mortality occurred during 21 d of treatment. Levels of phospholipids increased in lavaged lung, alveolar lavage cells, and surfactant material in AM- as well as DEA-treated rats. However, there was no significant difference between the two treatment groups. Phospholipases A and C were measured in lysosomal soluble fractions of lavaged lung and sonicated lung lavage cells. Both drugs exerted inhibitory action on phospholipases in the lavage cells but, to some extent, spared phospholipases in lysosomal plus mitochondrial soluble fraction isolated from lavaged lung with reversibility in enzyme inhibition despite continuous treatment. [14C] AM uptake by perfused lung, lavage cells as well as surfactant supernatant was increased in AM- and DEA-treated rats. Again, increase in pulmonary uptake of [14C]AM was similar in AM- and DEA-treated rats. These results thus suggest: (1) DEA is more toxic to rats than is AM, at the dose level used. The ability to sequester AM and the parameters related to phospholipidosis revealed no significant differences between these two analogs. (2) Both drugs are inhibitors of lavage cell phospholipases and also are inhibitory to lung lysosomal phospholipases to a lesser extent. Recovery of lung phospholipases occurred despite continuous treatment. (3) AM- and DEA-induced phospholipidosis increased the uptake of [14C]AM by perfused lung. (4) The mechanism of AM-induced pulmonary phospholipidosis includes selective in vivo inhibition of phospholipases.

Influence of ethanol on glutathione-S-transferase activity and glutathione content in the isolated perfused rabbit lung

The induction of pulmonary glutathione-S-transferase (GST) by ethanol was investigated using the isolated perfused rabbit lung (IPRL) preparation with particular attention paid to the duration and route of ethanol administration. For perfusion with buffer containing 0.2% ethanol or acute ethanol treatment (4 g/kg by gastric intubation) 4 h before the IPRL preparation, there were no differences in the rate of glutathione (GSH) conjugation with 1-chloro-2,4-dinitrobenzene (CDNB) at low substrate concentrations (100-400 microM) but a decrease was observed in the rate at high substrate concentrations (500-1000 microM). Lungs from rabbits treated acutely showed the lowest maximal rate of GSH conjugation in the IPRL. Prolonged treatment with ethanol (10% in drinking water for 3 weeks) increased GSH conjugation (CDNB concentration of 300-750 microM). None of these ethanol treatments altered GSH conjugation with 1,2-epoxy(p-nitrophenoxy)propane (ENP). Upon termination of perfusion, there were no differences in pulmonary GSH concentration between control and ethanol-treated groups. Therefore, the effect of altered GSH level as a co-substrate on GST activity in lung might be excluded as an explanation for the effects of ethanol. These data suggest that ethanol has differential effects on GST activity depending upon the substrate and duration of ethanol administration.

Ethanol induces acute pulmonary vasoconstriction in salt-perfused rat lungs

Ethanol is a pulmonary vasoconstrictor in rat lungs perfused in situ with Krebs-Henseleit salt solution. Pentobarbital-anesthetized rats were tracheotomized, and an in situ recirculating isolated lung perfusion was instituted using a Krebs-Henseleit buffer with 3% bovine albumin at 37 degrees C. Changes in pulmonary arterial pressure and tracheal inspiratory pressure during intravenous ethanol infusion at four different cumulative doses were measured in normoxic (n = 6) and hyperoxic (n = 6) lungs, compared to normoxic perfusate (no ethanol infusion) controls (n = 6). Perfusate alcohol levels progressively increased in experimental groups. Perfusate gas and pH values were normal and not altered by ethanol. PAP increased by the end of ethanol infusion from 9.7 +/- 2 to 26 +/- 13 mm Hg in the normoxic group and from 10.6 to 22 +/- 9 mm Hg in the hyperoxic lungs (p less than .02); no change occurred in control lungs. Severe pulmonary edema occurred in 83% of the ethanol exposed lungs (vs. 0% of perfusate controls). Postethanol wet/dry weight ratios were twice normal (p less than .02). Pulmonary arterial pressure rose in two stages. First there was a 25-100% increase before airway pressure increased, representing pulmonary vasoconstriction. This was followed by a precipitous 100-500% transmitted pressure rise as severe pulmonary edema developed. Thus, we conclude that the vasoconstrictor effect of ethanol on the pulmonary circulation occurs in rats as well as in lambs, dogs, and humans. In isolated perfused rat lungs, the response is locally mediated.

Glutathione metabolism and utilization of external thiols by cigarette smoke-challenged, isolated rat and rabbit lungs

The purpose of the present investigation was to understand the acute effects of cigarette smoke on glutathione (GSH) metabolism and on utilization of external thiols by cigarette smoke-exposed, perfused rat and rabbit lungs. Most of the experiments were carried out using freshly drawn cigarette smoke. However, cigarette smoke condensate was used in some perfusions for the comparison of the effects between the types of exposures on utilization of external thiols. Cigarette smoke decreased GSH levels significantly (50%) without any increase in glutathione disulfide (GSSG) in both rabbit and rat lungs. In smoke-exposed rabbit lungs, protein thiol groups (protein-SH) decreased significantly (17%) without a significant change in protein-GSH mixed disulfides. However, in the rat lungs, cigarette smoke did not decrease protein-SH and protein-GSH mixed disulfides, indicating species variation in the effect of cigarette smoke. Cigarette smoke inhibited selenium-dependent and -independent GSH peroxidase activities in the rat lung (33%), but not in the rabbit lung. GSH S-transferase and GSSG reductase activities were not altered in cigarette smoke-challenged rabbit and rat lungs. gamma-Glutamylcysteine synthetase and glucose-6-phosphate dehydrogenase activities were significantly lower in smoke-exposed rat lungs as against control lungs, indicating that rat lung enzymes were more susceptible to the effects of cigarette smoke when compared to those of rabbits. N-Acetylcysteine, but not GSH, added to the perfusate significantly protected rabbit lung from smoke-induced GSH depletion. Smoke condensate added to the perfusate also caused GSH depletion in rabbit lung, and GSH or N-acetylcysteine added to the perfusion medium protected the lung indicating that GSH in the media directly interacts with condensate in the media before coming in contact with cellular GSH. These results indicate that acute smoke inhalation decreases pulmonary GSH and that the decreased GSH was not related to disulfide formation. Inhibited GSH synthesis in rat lung could account for the loss of GSH in part after exposure to cigarette smoke. The alternative pathway of GSH utilization could be conjugation with electrophilic smoke components. Thiols, like N-acetylcysteine, were protective against cigarette smoke-induced damage to the rabbit lung. The mechanism could be either by the increased GSH synthesis or by the direct delivery of sulfhydryls from N-acetylcysteine.

A novel dosing method for drug administration to the airways of the isolated perfused rat lung

A novel method is described for the reproducible administration of known liquid quantities to the peripheral airways of the isolated perfused rat lung. The basis of the technique was to use a 25-microL metered dose of fluorocarbon propellant to expel liquid (as a coarse spray) from an intratracheal dosing cartridge into the airways, while simultaneously inflating the lungs with a fixed volume of gas. The methodology is illustrated by administration of 100-microL volumes of aqueous disodium fluorescein solutions to a series of lung preparations. The reproducibility and regional distribution of dosing were determined by dissection, homogenization, and fluorimetric assay. Even though the dye was distributed nonuniformly between the lung lobes, in a series of preparations, 65.9 +/- 4.8% of the recovered dose was still deposited in the lung periphery, the site from which absorption is believed to occur. The method will enable the study of airway-to-perfusate transfer kinetics for compounds administered in a variety of different liquid formulations.

Passive sequestration of putrescine, spermidine and spermine by rat lungs

The pulmonary uptake and accumulation of the three polyamines putrescine, spermidine and spermine by isolated ventilated and perfused rat lungs was investigated using 0.1, 1 or 5 mM concentrations of these compounds. The lung uptake of putrescine for all concentrations was greater than that of spermidine and spermine, but all three showed concentration-dependent linear uptake. A significant uptake of all three polyamines was also observed when incubated separately with rat lung slices for 60 min. Harmaline (0.4 mM), ouabain (0.2 mM) and perfusate with decreased Na+ (50 mEq/l) did not affect the uptake of any of the three polyamines by isolated perfused rat lungs or rat lung slice incubations. HPLC analysis of the whole lung or slices and media after perfusion or incubation studies, respectively, with polyamines did not reveal the presence of any metabolites. Likewise, the analysis of the lung homogenate incubated at 37 degrees C for 60 min with polyamines did not show any metabolites, confirming the absence of detectable pulmonary metabolism. These findings indicate a significant accumulation of polyamines in the rat lungs, accumulation predominantly occurring via simple diffusion, at variance with the reported active polyamine uptake process in the lung.

Lung mechanics of the guinea-pig isolated perfused lung

In the isolated perfused guinea-pig lung, lung resistance (RL) and dynamic compliance (CDYN) as well as flow, pH, PO2 and PCO2 of the perfusate were recorded. The baseline values were stable up to 2.5 h. Mean values (+/- SEM) for RL and CDYN were 0.36 cm H2O ml-1 s-1 +/- 0.04 and 0.27 ml cm-1 H2O +/- 0.02, respectively, which agree with in vivo values reported for unanaesthetized guinea-pigs. The pH was always slightly raised and the PCO2 always lowered in the effluent compared to the inflowing medium (P less than 0.001), indicating that the lung had an operative ventilation. Intravascularly administered acetylcholine, histamine and adenosine caused reproducible dose-dependent bronchoconstrictions recorded as increased RL and decreased CDYN. It is noteworthy that adenosine in this model and in vivo consistently produced bronchoconstriction which is in contrast to findings in other in vitro airway preparations. We conclude that this isolated perfused guinea-pig lung preparation has stable in vivo-like characteristics offering interesting possibilities for combining studies of respiratory effects with, for example, metabolism, pharmacokinetic and vascular reactivity studies.

Pulmonary synthesis of 5-hydroxytryptamine in isolated perfused rabbit and rat lung preparations

The present investigation was designed to determine the pulmonary biosynthesis of 5-hydroxytryptamine (5-HT) from L-tryptophan. Artificially ventilated, isolated rabbit and rat lungs were perfused with a constituted medium. Tryptophan and its metabolites were detected by high pressure liquid chromatography using an electrochemical detector. 14C-tryptophan uptake by the rabbit lung was 5.6% and 3.9% in the rat lung after 1 hr of perfusion. The perfusate (100 ml) concentrations of 5-hydroxytryptophan and 5-hydroxytryptamine increased significantly (1.1 to 1.8 micrograms 5-HT and 4.4 to 6.5 micrograms 5-HTP) during rabbit lung perfusion. However, no metabolites were detected in the perfusate during rat lung perfusion. 5-Hydroxytryptamine and 5-hydroxyindoleacetic acid levels were greater in both rabbit and rat lungs when they were perfused with 0.4 mM tryptophan, compared to their levels in lungs perfused without tryptophan. The increase of 5-HT content in rat lung alone was statistically significant. 5-Hydroxytryptophan was not detected in the rabbit or rat lungs. These results suggest the presence of a mechanism for tryptophan metabolism in lung, similar to that in brain and gastrointestinal tract. However, since the rate of pulmonary metabolism of tryptophan is very low, pulmonary synthesis of 5-HT from tryptophan and its contribution to the circulating 5-HT pool is unlikely to be of significance.

Effect of a homologous series of halogenated methanes on pulmonary uptake of 5-hydroxytryptamine in isolated perfused rat lung

The potency of halogenated methanes to inhibit uptake of 5-hydroxytryptamine (5-HT) from the pulmonary circulation was studied using an isolated, perfused and ventilated rat lung preparation. The agents were vaporized and mixed with the inlet air. The results indicate that the degree of chlorination is the most important factor for potency of the methanes to inhibit lung uptake of 5-HT. When hydrogen was substituted with fluorine the potency was decreased dramatically. Bromine seemed to have the opposite effect. The data also suggested that the degree of chlorination was more important rather than hydrophobic/hydrophilic balance of the solvent molecule. These effects seem to be correlated with the narcotic effects of the substances studied.

Comparison of pulmonary accumulation of pyrilamine and pyrilamine N-oxide

Our previous studies have indicated that a phenothiazine drug, chlorpromazine, and a tricyclic antidepressant, imipramine, are metabolized by the isolated perfused rat lungs via N-oxidation from whence their N-oxides are released into the circulation. This work was undertaken to compare the pulmonary accumulation of another pneumophilic tertiary amine drug, pyrilamine, with that of its N-oxide. Approximately 10-fold greater accumulation of pyrilamine than that of its N-oxide was observed in the mouse lung after a single pass perfusion with 40 microM of the drug for a 3 min period. The largest difference between accumulation of pyrilamine and its N-oxide was noted in the lung among the various tissue slices tested, suggesting the tissue specificity of affinity.

Isolated perfused rabbit lung as a model to study the absorption of organic aerosols

An improved technique for perfused lung preparations adapted for absorption studies with organic aerosols is described. The model developed by Niemeier and Bingham (1972) was modified to place greater emphasis on the respiratory functions of the lung as an index of viability. Perfusion of this preparation for 2 hr showed that tidal volume, pulmonary blood flow, and visual appearance were the most sensitive indicators of physiological change. The importance of relevant criteria for assessment of viability is discussed. In addition, a simple technique for on-line computerized measurement of tidal volume and respiratory frequency is described.

The pharmacokinetics of benzo[alpha]pyrene in the isolated perfused rabbit lung: the influence of benzo[alpha]pyrene, n-dodecane, particulate, or sulfur dioxide

The pharmacokinetics of benzo[a]pyrene (BaP) in the isolated perfused rabbit lung (IPL) following pretreatment of the whole animal or simultaneous administration to the IPL with n-dodecane, ferric oxide, crude airborne particulate (CAP), fly ash or sulfur dioxide have been investigated using a one compartment model. The rate constant for the appearance (ka) of BaP in the blood, the clearance of BaP from the blood, and the rate of appearance of BaP metabolites (RAM) were the kinetic parameters determined. BaP entered the blood rapidly with an average half-life of 11 min in experiments in which the IPLs received only BaP on perfusion. The logarithms of the clearances from these experiments were linearly correlated with the RAMs. In these experiments, pretreatment of the whole animal with BaP produced a 48-55-fold increase in BaP clearance while pretreatment with n-dodecane increased the clearance 4-fold in comparison with no pretreatment. Pretreatment with ferric oxide or ferric oxide and BaP increased the clearance by factors of 5.5 and 1.5, respectively, over those of unpretreated and BaP pretreated experiments.

Glutathione biosynthesis in the isolated perfused rat lung: utilization of extracellular glutathione

The isolated perfused rat lung catalyzed the biosynthesis of GSH when the sulfur amino acids cysteine or N-acetylcysteine, but not methionine, were supplied in the perfusion medium. The lung also had the capacity to utilize extracellular GSH for this purpose. Replenishment of intracellular GSH in perfused lungs from diethylmaleate-treated rats was pronounced even at 25 microM GSH in the perfusion medium. The utilization of extracellular GSH is probably primarily through extracellular break-down and resynthesis rather than direct uptake as indicated by the inhibitory effect of the gamma-glutamylcysteine synthetase inhibitor, buthionine sulfoximine and the gamma-glutamyl transferase inhibitor, anthglutin. The results indicate that the lung in addition to the kidney may utilize circulating plasma GSH.

The effects of a cocarcinogen, ferric oxide, on the metabolism of benzo[a]pyrene in the isolated perfused lung

An isolated perfused New Zealand rabbit lung preparation was used to investigate the effects of a cocarcinogen, ferric oxide (Fe2O3), on the metabolism of benzo[a]pyrene (BaP), a ubiquitous potent carcinogen that has been associated with the increased incidence of human bronchiogenic carcinoma in occupational and urban settings. [14C]-BaP was administered intratracheally to an isolated perfused lung (IPL) preparation with and without Fe2O3 after intraperitoneal pretreatment of the whole animal with BaP or intratracheal pretreatment of the whole animal with Fe2O3 and/or BaP. BaP and its metabolites were isolated from serial blood samples up to 180 min after administration of [14C]BaP to the IPL. BaP and its metabolites were also isolated from lung tissue, washout fluid, macrophage, and trachea bronchi at the end of the perfusion at 180 min. Patterns of BaP metabolites were determined by chromatographic techniques and liquid scintillation counting. Fe2O3 pretreatment to the whole animal or administration of Fe2O3 to the IPL altered BaP metabolism by the perfused lung. Fe2O3 pretreatment to the whole animal resulted in an increase in the total rate of appearance of metabolites of BaP in the blood (ng/g lung X h), while Fe2O3 administration to the IPL resulted in a decrease in the total rate of appearance of BaP metabolites in the blood and inhibited the effect of pretreatment. Administration of Fe2O3 with BaP to the IPL with or without Fe2O3 pretreatment to the whole animal, or BaP administration to the IPL preceded by Fe2O3 pretreatment to the whole animal, enhanced dihydrodiol formation and depressed formation of water-soluble metabolites. Since dihydrodiol formation is considered to be the active pathway of BaP metabolism, these data suggest that pulmonary exposure to a known cocarcinogen, Fe2O3, in the presence of BaP results in increased production of dihydrodiols of BaP, which may be further metabolized to the ultimate carcinogenic form(s) of BaP. Therefore, Fe2O3 can enhance the metabolic activation of BaP by the lung, as well as act as a carrier for penetration and retention of BaP in the lung.

Benzo(a)pyrene metabolism in the isolated perfused mouse lung

A method is described for preparing and maintaining an isolated perfused and ventilated mouse lung. The preparation is especially suited for studying xenobiotic metabolism or toxicological interactions, in a species with a broad spectrum of studies in pulmonary toxicology. The preparation is viable with respect to drug metabolism for up to two hours, as judged from studies of aniline oxidation to p-aminophenol. With [14C]-benzo(a)pyrene as substrate for the lungs of male ICR Swiss mice, the major ethyl acetate-extractable metabolites are the 3-hydroxy, 9,10-dihydrodiol, 7,8-dihydrodiol, and 4,5-dihydrodiol derivatives. The rates of individual BaP metabolite production are increased in lungs from mice pretreated with Aroclor 1254 or beta-naphthoflavone, substances known to induce increased synthesis of cytochrome P-450. Small amounts of water-soluble BaP metabolites were hydrolyzed by beta-glucuronidase and aryl sulfatase, suggesting the presence of enzymes required for these conjugations. These results support the existence of significant cytochrome P-450-dependent and conjugative BaP metabolism in the intact mouse lung, similar to that examined in other species, and capable of contributing to the systemic metabolism of this carcinogen.

Influence of airborne particulate on the metabolism of benzo[a]pyrene in the isolated perfused lung

Benzo[a]pyrene (BaP), a ubiquitous potent carcinogen, has been associated with the increased incidence of human bronchiogenic carcinoma in occupational and urban settings. A detailed knowledge of the rate and pattern of metabolite formation and factors affecting their formation is essential for understanding the mechanism of action of BaP in the lung. An isolated perfused New Zealand rabbit lung preparation was used to investigate the effects of a crude airborne particulate mixture on the metabolism of BaP. [14C]BaP with and without crude air particulate (CAP) was administered intratracheally to an isolated perfused lung (IPL) preparation after intratracheal pretreatment of the whole animal with CAP and/or BaP, or intraperitoneal pretreatment of the whole animal with BaP. BaP and its metabolites were extracted from perfusing blood at 6 time points up to 180 min after administration of [14C]BaP to the IPL. BaP and its metabolites were also extracted from lung tissue, washout fluid, aveolar macrophages, and trachea bronchi at the end of the perfusion at 180 min. Patterns of BaP metabolites were determined by chromatographic techniques and liquid scintillation counting. Particulate pretreatment of the whole animal or administration of the particulate to the IPL altered BaP metabolism by the perfusing lung. Particulate pretreatment of the whole animal resulted in increases in the total rates of appearance of metabolites of BaP in the blood (ng/g lung . h), while particulate administration to the IPL resulted in decreases in the total rate of appearance of metabolites of BaP in the blood and negated the effects of pretreatments. Coadministration of particulate with BaP to the IPL with and without particulate pretreatment of the whole animal, or BaP administration to the IPL preceded by particulate pretreatment of the whole animal, enhanced dihydrodiol formation and depressed formation of water-soluble materials. This is important because dihydrodiol formation is considered part of the active pathway of BaP carcinogenicity. These data suggest that pulmonary particulate exposure in the presence of BaP results in the initial increased production of dihydrodiols of BaP that may be further metabolized to compounds believed to be the ultimate carcinogenic form(s) of BaP.

Urea metabolism in isolated perfused lungs of the laboratory rat and of a desert rodent, Notomys alexis

1. Using the isolated perfused lung preparation we have demonstrated a low-activity ureolytic enzyme present in rodent lung tissue. The enzyme shares four characteristic features with jack bean urease (EC 3.5.1.5). 2. Ureolytic activity was inhibited by fluoride ions and methionine hydroxamic acid; using the latter inhibitor, the I50 value and maximum inhibition were similar to those reported for jack bean urease. The apparent Km for rat lung urease was similar to the plasma urea level. 3. The low level of urease activity in the rat lung and in that of Notomys alexis, a desert rodent, suggests that the enzyme is not involved in urea excretion, rather that pulmonary ammonia production may influence fluid balance at the alveolus.

Rat nasal tissue activation of benzo(a)pyrene and 2-aminoanthracene to mutagens in Salmonella typhimurium

Cytochrome P-450-dependent monooxygenase activity has been measured in the nasal turbinates of dogs and rats. The capacity of male Fischer-344 rat nasal tissue to bioactivate benzo(a)pyrene (BaP) and 2-aminoanthracene (2-AA) to mutagens in Salmonella typhimurium was investigated. 2-AA was mutagenic in strains TA98 and TA100 when nasal tissue S-9 was utilized as the activating enzyme system and BaP was mutagenic in strain TA100. At all doses and protein concentrations tested, 2-AA displayed nearly 500-1000 times greater bacterial mutagenicity than BaP. In strain TA-100, nasal tissue S-9 was approximately twice as active toward 2-AA as lung S-9 and 75% as active as liver S-9. Aryl hydrocarbon hydroxylase activity was detected in rat nasal tissue when 14C-BaP was used as a substrate. Rat nasal tissue metabolized BaP to several oxidized metabolites which included dihydrodiols, quinones, and phenols. 3-Hydroxybenzo(a)pyrene and BaP-3, 6-quinone were the major metabolites detected (150 pmoles/mg protein/30 min). These results indicate that rat nasal tissue can metabolize promutagens to reactive species which may play an important role in xenobiotic-induced nasal tumors.

The isolation of rat lung cells for the purpose of studying drug metabolism

A method was developed for the isolation of viable cells from rat lungs. The cells were a heterogeneous population, which maintained a high percentage viability for up to 3 hr on incubation at 37 degrees. Reduced cofactor levels (NADH, NADPH) decreased on incubation, but ATP remained constant. The cells were active in the metabolism of the two xenobiotics studied. A model compound, 7-ethoxycoumarin, was O-deethylated and subsequently conjugated with glucuronic acid and sulphate, whilst a pharmaceutical agent, N-acetylcysteine, was de-acetylated.