Variability of hypoxic pulmonary vasoconstriction in sheep. Role of prostaglandins

Practical Considerations in Dose Extrapolation from Animals to Humans

Animal studies are an important component of drug product development and the regulatory review process since modern practices have been in place, for almost a century. A variety of experimental systems are available to generate aerosols for delivery to animals in both liquid and solid forms. The extrapolation of deposited dose in the lungs from laboratory animals to humans is challenging because of genetic, anatomical, physiological, pharmacological, and other biological differences between species. Inhaled drug delivery extrapolation requires scrutiny as the aerodynamic behavior, and its role in lung deposition is influenced not only by the properties of the drug aerosol but also by the anatomy and pulmonary function of the species in which it is being evaluated. Sources of variability between species include the formulation, delivery system, and species-specific biological factors. It is important to acknowledge the underlying variables that contribute to estimates of dose scaling between species.

Cardiopulmonary effects of vatinoxan in sevoflurane-anaesthetised sheep receiving dexmedetomidine

The effects of pre-treatment with vatinoxan (MK-467) on dexmedetomidine-induced cardiopulmonary alterations were investigated in sheep. In a crossover study design with a 20-day washout, seven sheep were anaesthetised with sevoflurane in oxygen and air. The sheep were ventilated with the pressure-limited volume-controlled mode and a positive end-expiratory pressure of 5cmH₂O. Peak inspiratory pressure (PIP) was set at 25cmH₂O. The sheep received either 150μg/kg vatinoxan HCl (VAT+DEX) or saline intravenously (IV) 10min before IV dexmedetomidine HCl (3μg/kg, DEX). Cardiopulmonary variables were measured before treatments (baseline), 3min after vatinoxan or saline, and 5, 15 and 25min after dexmedetomidine. Computed tomography (CT) of lung parenchyma was performed at baseline, 2min before dexmedetomidine, and 10, 20 and 30min after DEX. Bronchoalveolar lavage (BAL) was performed after the last CT scan and shortly before sheep recovered from anaesthesia. After VAT, cardiac output significantly increased from baseline. DEX alone significantly decreased partial arterial oxygen tension, total dynamic compliance and tidal volume, whereas PIP was significantly increased. With VAT+DEX, these changes were minimal. No significant changes were detected in haemodynamics from baseline after DEX. With VAT+DEX, mean arterial pressure and systemic vascular resistance were significantly decreased from baseline, although hypotension was not detected. On CT, lung density was significantly increased with DEX as compared to baseline. No visual abnormalities were detected in bronchoscopy and no differences were detected in the BAL fluid after either treatment. The pre-administration of vatinoxan alleviates dexmedetomidine-induced bronchoconstriction, oedema and hypoxaemia in sevoflurane-anaesthetised sheep.

The Differential Absorption of a Series of P-Glycoprotein Substrates in Isolated Perfused Lungs from Mdr1a/1b Genetic Knockout Mice can be Attributed to Distinct Physico-Chemical Properties: an Insight into Predicting Transporter-Mediated, Pulmonary Specific Disposition

PURPOSE

To examine if pulmonary P-glycoprotein (P-gp) is functional in an intact lung; impeding the pulmonary absorption and increasing lung retention of P-gp substrates administered into the airways. Using calculated physico-chemical properties alone build a predictive Quantitative Structure-Activity Relationship (QSAR) model distinguishing whether a substrate's pulmonary absorption would be limited by P-gp or not.

METHODS

A panel of 18 P-gp substrates were administered into the airways of an isolated perfused mouse lung (IPML) model derived from Mdr1a/Mdr1b knockout mice. Parallel intestinal absorption studies were performed. Substrate physico-chemical profiling was undertaken. Using multivariate analysis a QSAR model was established.

RESULTS

A subset of P-gp substrates (10/18) displayed pulmonary kinetics influenced by lung P-gp. These substrates possessed distinct physico-chemical properties to those P-gp substrates unaffected by P-gp (8/18). Differential outcomes were not related to different intrinsic P-gp transporter kinetics. In the lung, in contrast to intestine, a higher degree of non-polar character is required of a P-gp substrate before the net effects of efflux become evident. The QSAR predictive model was applied to 129 substrates including eight marketed inhaled drugs, all these inhaled drugs were predicted to display P-gp dependent pulmonary disposition.

CONCLUSIONS

Lung P-gp can affect the pulmonary kinetics of a subset of P-gp substrates. Physico-chemical relationships determining the significance of P-gp to absorption in the lung are different to those operative in the intestine. Our QSAR framework may assist profiling of inhaled drug discovery candidates that are also P-gp substrates. The potential for P-gp mediated pulmonary disposition exists in the clinic.

The principal pathways involved in the in vivo modulation of hypoxic pulmonary vasoconstriction, pulmonary arterial remodelling and pulmonary hypertension

Hypoxic pulmonary vasoconstriction (HPV) serves to optimize ventilation-perfusion matching in focal hypoxia and thereby enhances pulmonary gas exchange. During global hypoxia, however, HPV induces general pulmonary vasoconstriction, which may lead to pulmonary hypertension (PH), impaired exercise capacity, right-heart failure and pulmonary oedema at high altitude. In chronic hypoxia, generalized HPV together with hypoxic pulmonary arterial remodelling, contribute to the development of PH. The present article reviews the principal pathways in the in vivo modulation of HPV, hypoxic pulmonary arterial remodelling and PH with primary focus on the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways. In summary, endothelin-1 and thromboxane A₂ may enhance, whereas nitric oxide and prostacyclin may moderate, HPV as well as hypoxic pulmonary arterial remodelling and PH. The production of prostacyclin seems to be coupled primarily to cyclooxygenase-1 in acute hypoxia, but to cyclooxygenase-2 in chronic hypoxia. The potential role of adenine nucleotides in modulating HPV is unclear, but warrants further study. Additional modulators of the pulmonary vascular responses to hypoxia may include angiotensin II, histamine, serotonin/5-hydroxytryptamine, leukotrienes and epoxyeicosatrienoic acids. Drugs targeting these pathways may reduce acute and/or chronic hypoxic PH. Endothelin receptor antagonists and phosphodiesterase-5 inhibitors may additionally improve exercise capacity in hypoxia. Importantly, the modulation of the pulmonary vascular responses to hypoxia varies between species and individuals, with hypoxic duration and age. The review also define how drugs targeting the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways may improve pulmonary haemodynamics, but also impair pulmonary gas exchange by interference with HPV in chronic lung diseases.

Dose- and time-dependent effects of lipopolysaccharide on technetium-99-m-labeled diethylene-triamine pentaacetatic acid clearance, respiratory system mechanics and pulmonary inflammation

Intratracheal administration of lipopolysaccharide (LPS) in animals is a commonly used model of acute lung injury, characterized by increased alveolar-capillary membrane permeability causing protein-rich edema, inflammation, deterioration of lung mechanical function and impaired gas exchange. Technetium-99-m-labeled diethylene-triamine pentaacetatic acid ((99m)Tc-DTPA) scintigraphy is a non-invasive technique to assess lung epithelial permeability. We hypothesize that the longer the exposure and the higher the dose of LPS the greater the derangement of the various indices of lung injury. After 3, 6 and 24 h of 5 or 40 μg LPS intratracheally administration, (99m)Tc-DTPA was instilled in the lung. Images were acquired for 90 min with a γ-camera and the radiotracer clearance was estimated. In another subgroup, the mechanical properties of the respiratory system were estimated with the forced oscillation technique and static pressure-volume curves, 4.5, 7.5 and 25.5 h post-LPS (iso-times with the end of (99m)Tc-DTPA scintigraphy). Bronchoalveolar lavage (BAL) was performed and a lung injury score was estimated by histology. Lung myeloperoxidase (MPO) activity was measured. (99m)Tc-DTPA clearance increased in all LPS challenged groups compared with control. DTPA clearance presented a U-shape time course at the lower dose, while LPS had a declining effect over time at the larger dose. At 7.5 and 25.5 h post-LPS, tissue elasticity was increased and static compliance decreased at both doses. Total protein in the BAL fluid increased at both doses only at 4.5 h Total lung injury score and MPO activity were elevated in all LPS-treated groups. There is differential time- and dose-dependency of the various indices of lung injury after intratracheally LPS instillation in rats.

Cyclooxygenase-2 inhibition and thromboxane A(2) receptor antagonism attenuate hypoxic pulmonary vasoconstriction in a porcine model

AIM

Hypoxic pulmonary vasoconstriction (HPV) causes pulmonary hypertension that may lead to right heart failure. We hypothesized that the COX-2 inhibitor nimesulide and the thromboxane A(2) receptor antagonist daltroban would attenuate HPV.

METHODS

Haemodynamic measurements and blood sampling were performed in 18 anaesthetized, mechanically ventilated pigs, with mean ± SEM weights of 31.3 ± 0.6 kg, in normoxia (F(i)O(2)~0.21) and hypoxia (F(i)O(2)~0.10), before and 5, 15 and 45 min after initiation of right atrial infusion of nimesulide (n = 6) or daltroban (n = 6), respectively, and in six control pigs.

RESULTS

Compared with normoxia, hypoxia (n = 18) increased mean pulmonary artery pressure by 15.8 ± 0.8 mmHg (P < 0.001), pulmonary vascular resistance (PVR) by 2.7 ± 0.3 WU (P < 0.05) and mean right atrial pressure by 2.3 ± 0.3 mmHg (P < 0.001). In the control pigs, mean pulmonary artery pressure, PVR and mean right atrial pressure remained stable (P = ns) throughout 45 min hypoxia, compared with hypoxia baseline. Nimesulide decreased mean pulmonary artery pressure by 3.7 ± 1.3 mmHg after 45 min (P < 0.013), as well as PVR by 0.8 ± 0.2 WU (P < 0.05), levelling off after 15 min. Daltroban transiently increased (P < 0.001) mean pulmonary artery pressure and mean right atrial pressure by 7.2 ± 1.2 and 2.7 ± 0.4 mmHg, respectively, but they returned to hypoxia baseline (P = ns) within 5 min. Daltroban then decreased mean pulmonary artery pressure to after 45 min be 4.2 ± 1.6 mmHg lower (P < 0.005) than at hypoxia baseline.

CONCLUSION

COX-2 inhibition and thromboxane A(2) receptor antagonism attenuate HPV by decreasing mean pulmonary artery pressure by approximately 10-11%, as measured 45 min after initiation of nimesulide or daltroban infusion respectively.

Efficacy of 99mTc-DTPA lung clearance test in the diagnosis of PCP in HIV-positive patients

The study aims to evaluate the efficacy of technetium-99m diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) lung clearance test in the diagnosis of pneumocystis carinii pneumonia (PCP) in HIV-positive paediatric patients. Twenty HIV-negative patients with no chest symptoms constituted Group A, 25 HIV antibody positive asymptomatic children formed Group B, while 45 HIV antibody positive children with respiratory infections comprised Group C. Group C was subdivided into C(1) (n = 20, documented PCP on microbiology), C(2) (n = 10, tuberculosis) and C(3) (n = 15, bacterial pneumonias). The mean age group of patients in Group A, Group B and Group C was 4.7 +/- 1.9, 4.2 +/- 1.5 and 4.8 +/- 1.7 years, respectively. All patients were subjected to complete blood count, blood culture, chest radiographs, microscopic staining of sputum (PCP stains, Ziehl-Nielsen staining, Gram staining), ABG and Mantoux test. All these patients underwent dynamic lung scans using (99m)Tc-DTPA aerosols and lung clearance was calculated in terms of half-time transfer value (T(1/2)) value. T(1/2) was compared between different groups and lung scan findings were correlated with radiological and microbiological results. Patients with PCP had T(1/2) in the range of 9.02 +/- 1.35, TB 28.2 +/- 3.03 min and other bacterial pneumonias in the range of 20.5 +/- 3.1 min (range for normal individuals was 49.8 +/- 6.13 min). T(1/2) in patients with PCP was found to be significantly lower when compared with T(1/2) in other groups. Patients with PCP had characteristic biphasic curves while the rest had monophasic curves. Some patients with PCP had low T(1/2) values even when chest radiographs and arterial blood gases were normal. (99m)Tc-DTPA lung clearance test is a sensitive, safe and non-invasive diagnostic tool for the early detection of PCP in HIV-positive paediatric patients.

Influence of hilar deposition in the evaluation of the alveolar epithelial permeability on 99mTc-DTPA aerosol inhaled scintigraphy

PURPOSE

We investigated whether hilar radioaerosol deposition affects the clearance rate of technetium-99m-labeled diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) from peripheral alveolar regions.

MATERIALS AND METHODS

A total of 38 patients underwent (99m)Tc-DTPA inhalation lung scintigraphy. Six region of interest (ROI) patterns were adopted: ROI 1 was outlined around the entire hemithorax, and ROIs 2-6 were outlined around the hemithorax but excluded square ROIs of different size in the hilar region. Half-times (T(1/2) were calculated with time-activity curves using one-compartment and two-compartment analyses. The T(1/2) of ROIs 1-5 were plotted against the T(1/2) of ROI 6, and regression lines were obtained with the least-squares method. The absolute values of the differences between surveyed values and regression line were calculated. The Wilcoxon test for trend and a single linear regression model were used to determine statistical significance.

RESULTS

There were significant reductions in the absolute values of the differences between surveyed values and regression line from ROIs 1-5 by one-component analysis and the fast component of two-compartment analysis (P < 0.001).

CONCLUSION

Our results suggest that the deposition of radioaerosol in the hilar region affects the clearance rate of (99m)Tc-DTPA from the alveoli in damaged lungs. The hilar region should be excluded from ROIs when alveolar epithelial permeability is evaluated.

Inhaling medicines: delivering drugs to the body through the lungs

Remarkably, with the exception of anaesthetic gases, the ancient human practice of inhaling substances into the lungs for systemic effect has only just begun to be adopted by modern medicine. Treatment of asthma by inhaled drugs began in earnest in the 1950s, and now such 'topical' or targeted treatment with inhaled drugs is considered for treating many other lung diseases. More recently, major advances have led to increasing interest in systemic delivery of drugs by inhalation. Small molecules can be delivered with very rapid action, low metabolism and high bioavailability; and macromolecules can be delivered without injections, as highlighted by the recent approval of the first inhaled insulin product. Here, we review these advances, and discuss aspects of lung physiology and formulation composition that influence the systemic delivery of inhaled therapeutics.

Dexmedetomidine-induced pulmonary alterations in sheep

Alpha(2) agonist-induced pulmonary oedema in sheep might be related to alterations in pulmonary haemodynamics and/or activation of inflammatory processes. In seven sevoflurane-anaesthetized sheep pulmonary haemodynamics, arterial oxygen tensions, nitric oxide and prostaglandin E(2) concentrations were determined before and after intravenous dexmedetomidine (2microg kg(-1)). In a second trial, lung tissue was sampled for histopathology and quantitative real-time PCR for IL-1beta and iNOS mRNA in a control sheep and 2, 10 and 30min after dexmedetomidine. Computer tomography of the lung under sevoflurane anaesthesia before and after dexmedetomidine was performed. Two minutes after dexmedetomidine mean pulmonary artery pressure, pulmonary arterial occlusion pressure and estimated capillary pressurewere significantly increased to 34.5mmHg, 22.2mmHg and 27.1mmHg, respectively. On computer tomography, lung density increased immediately after dexmedetomidine, with maximal density occurring between 9 and 12min. Histopathology was consistent with vascular congestion followed by protein and erythrocyte extravasation into alveoli. Increased iNOS mRNA levels were detected in sevoflurane anaesthetized animals only. An IL-1beta signal occurred after morphological changes had occurred in lung tissue. These findings support hydrostatic stress as the underlying cause of alpha(2) agonist-induced pulmonary oedema in sheep.

Clearance of technetium-99m-labeled DTPA in hyperthyroidism without clinical evidence of lung disease, and relation to pulmonary function

OBJECTIVE

The mechanisms of dyspnea and exercise intolerance have not been fully elucidated. We aimed to investigate the clearance rate of technetium-99m diethyltriaminepentaaceticacid (Tc-99m DTPA) from lungs in hyperthyroid patients without clinical evidence of lung disease and to explore the interactions between their Tc-99m DTPA radioaerosol lung scintigraphy, spirometric measurements, and the levels of thyroid hormones.

METHODS

We studied 19 hyperthyroid patients and 16 sex- and age-matched controls. Thyroid hormone levels were assessed. Spirometric lung function tests, diffusing capacity of the lung for carbon monoxide (DLCO) and the clearance rate of Tc-99m DTPA were performed in all participants. Ratio of DLCO value to the alveolar ventilation (DLCO/VA) and the means of half-time (T1/2) of Tc-99m DTPA clearance rate, which were used to evaluate alveolar-capillary membrane permeability, were calculated.

RESULTS

There were no statistical differences between spirometric parameters (VC, FVC, FEV1/FVC, FEF 25-75) of the two groups (p > 0.05). Although the mean FEV1 level was significantly lower in the hyperthyroid patients than the control subjects (p < 0.01), in five patients FEV1 was only less than 80 percent of the predicted value. No significant difference in the means of DLCO, DLCO/VA or T1/2 values of Tc-99m DTPA clearance was observed between the two groups (p > 0.05). In hyperthyroid patients, there was a positive relation between DLCO/VA, DLCO/VA % and T1/2 values of Tc-99m DTPA clearance (p < 0.01, r = 0.732, p < 0.01, r = 0.742, respectively). The lung volumes and the levels of thyroid hormones did not show a significant relationship to T1/2 values of Tc-99m DTPA clearance in hyperthyroid group (p > 0.05).

CONCLUSIONS

We conclude that increased thyroid hormones have no effect on permeability of alveolar-capillary membrane in hyperthyroid patients.

Use of iodine-123 metaiodobenzylguanidine scintigraphy for the detection of amiodarone induced pulmonary toxicity in a rabbit model: A comparative study with technetium-99m diethyltriaminepenta acetic acid radioaerosol scintigraphy

The purpose of the study was; (i) to determine whether 123I-MIBG scintigraphy is sensitive for detection of amiodarone induced pulmonary toxicity (AIPT) and (ii) to compare it with 99mTc-DTPA radioaerosol. Twelve white New Zealand rabbit with initial mean body weight 4.24 +/- 0.47 g were divided into two groups. AIPT group (n = 7) was administered amiodarone (20 mg/kg BW). The control group (n = 5) received the same amount of 0.9% saline. All animals underwent 123I-MIBG and 99mTc-DTPA radioaerosol scintigraphy at the end of the treatment period. 123I-MIBG static thorax images were obtained during 10 minutes at 15 minutes and 3-hours after intravenous injection of the radiopharmaceutical. Lung to heart ratios (LHR) and lung to mediastinum ratios (LMR), and retention index (LRI) of 123I-MIBG were determined. Two days after 123I-MIBG scintigraphy, 99mTc-DTPA radioaerosol scintigraphy was performed, and clearance from the lungs was measured for 10 min (1 min/frame) following termination of inhalation. 123I-MIBG lung retention index (LRI) was significantly higher in the AIPT group than the control (61 +/- 4.6 vs. 40 +/- 4.5, p = 0.01). Early LHR and LMR were significantly lower in the AIPT group than in the control group (p = 0.04, p = 0.01, respectively), whereas those of late LHR and LMR were not significantly different. T1/2 values of DTPA clearance were significantly increased in AIPT group according to the control group (55 +/- 7.2 vs. 86.6 +/- 18.5, p = 0.02). 123I-MIBG scintigraphy is a valuable tool for detecting AIPT in a rabbit model. Additionally, 99mTc-DTPA radioaerosol scintigraphy is an excellent comprehensive investigational tool for detecting AIPT with the added advantage of lower cost.

Protein transport across the lung epithelial barrier

Alveolar lining fluid normally contains proteins of important physiological, antioxidant, and mucosal defense functions [such as albumin, immunoglobulin G (IgG), secretory IgA, transferrin, and ceruloplasmin]. Because concentrations of plasma proteins in alveolar fluid can increase in injured lungs (such as with permeability edema and inflammation), understanding how alveolar epithelium handles protein transport is needed to develop therapeutic measures to restore alveolar homeostasis. This review provides an update on recent findings on protein transport across the alveolar epithelial barrier. The use of primary cultured rat alveolar epithelial cell monolayers (that exhibit phenotypic and morphological traits of in vivo alveolar epithelial type I cells) has shown that albumin and IgG are absorbed via saturable processes at rates greater than those predicted by passive diffusional mechanisms. In contrast, secretory component, the extracellular portion of the polymeric immunoglobulin receptor, is secreted into alveolar fluid. Transcytosis involving caveolae and clathrin-coated pits is likely the main route of alveolar epithelial protein transport, although relative contributions of these internalization steps to overall protein handling of alveolar epithelium remain to be determined. The specific pathways and regulatory mechanisms responsible for translocation of proteins across lung alveolar epithelium and regulation of the cognate receptors (e.g., 60-kDa albumin binding protein and IgG binding FcRn) expressed in alveolar epithelium need to be elucidated.

Endothelin in the equine hypoxic pulmonary vasoconstrictive response to acute hypoxia

Elevated concentrations of endothelin (ET), a potent endothelium-derived vasoactive peptide, have been reported in a number of pathophysiological conditions associated with pulmonary hypertension, both in the horse and other species. We have previously shown, both in vitro and in vivo, that the pulmonary and systemic vascular response to exogenous ET is mediated predominantly via ET(A) receptors. Our hypothesis in the present study was that ET is involved in the equine hypoxic pulmonary vasoconstrictive response to acute hypoxia. In this study, we investigated the effects of a selective ET(A) receptor antagonist on hypoxic pulmonary hypertension in the mature horse. Horses were exposed to a 10 min period of hypoxia (F(I)O2 approximately 0.11) on 2 occasions, with and without pretreatment with the selective ET(A) receptor antagonist TBC11251 (10 mg/kg bwt i.v.). Hypoxia increased mean pulmonary artery pressure (PAP) from 18.3+/-0.9 (mean +/- s.e. normoxia) to 28.0+/-0.8 mmHg (hypoxia) in the session without ET(A) receptor antagonism. Carotid arterial pressure (CAP) also increased progressively throughout the period of hypoxic challenge and at the end was 153+/-5 mmHg (hypoxia) compared to during normoxia (140+/-5 mmHg). There was no significant overall effect of ET(A) receptor antagonism on the haemodynamic or ventilatory responses to acute hypoxia. However, between 5 and 10 min of hypoxia there was a trend for the mean PAP to diverge in the 2 treatments, which just failed to reach significance at 10 min of hypoxia (P = 0.053). In conclusion, this study describes the haemodynamic and ventilatory changes in response to a period of acute hypoxia in the adult horse. The results do not support a role for ET as a mediator of acute HPV in the horse, but suggest that it may be involved as a modulator or in the slower (>10 min) phase of HPV.

Clearance of Tc-99m DTPA aerosol in mismatched and matched pulmonary perfusion defects

PURPOSE

To evaluate clearance changes of Tc-99m DTPA aerosol in mismatched and matched pulmonary perfusion defects.

MATERIALS AND METHODS

Twenty-one patients (14 women, 7 men; mean age, 51 +/- 14 years) with possible pulmonary embolism were included in the study. On the day after perfusion (Q) scintigraphy with 5 mCi Tc-99m MAA, radioaerosol inhalation scintigraphy was performed using 45 mCi Tc-99m DTPA. Immediately and 45 minutes after the inhalation, early and delayed inhalation images (EI and DI, respectively) were obtained. Group 1 included 11 patients with mismatched defects who had a high probability of pulmonary embolism according to the Q/EI scan results. Group 2 included 10 patients with matched defects who had a low probability of PE. Contralateral normal lungs of 7 patients in group 2 served as controls (group 3). In groups 1 and 2, regions of interest were drawn over the mismatched and matched perfusion defects where they were best visualized, and this region of interest was mirrored to the same region on EI and DI images. For the control group, this was done in the contralateral normal lung. Mean counts in each region of interest were used for quantitative analysis, and the percentage clearance ratio was calculated using the following formula: early counts - late counts/early counts x 100.

RESULTS

The average percentage clearances for the three groups were as follows: group 1, 37% +/- 10%; group 2, 21% +/- 4%; group 3, 24% +/- 7%. Differences between groups 1 and 3 were significant, as were those between groups 1 and 2 (P < 0.05). Patients with mismatched perfusion defects had increased DTPA clearance compared with the control group and those with matched defects.

CONCLUSIONS

Vascular occlusion may lead to impairment of the alveolar-capillary barrier and consequently an increase in the clearance of Tc-99m DTPA aerosol in embolized regions. Immediately after inhalation, Tc-99m DTPA imaging should be started in the projection where perfusion defects are best seen to avoid potential misinterpretation of pulmonary embolism.

Safety of inhaled proteins for therapeutic use

The use of the inhalation route for delivery of inhaled proteins has received increasing attention recently. The purpose of this article is to review the available information related to the safety aspects of inhaled proteins. The review focuses primarily on possible toxicity to the respiratory tract, because usually one is either considering an agent to treat the lung or an agent for which the systemic toxicity has been investigated following subcutaneous (s.c.) administration in its clinical use as a therapeutic agent. Some background is provided on mechanisms of absorption and reasons why inhalation delivery is considered for many proteins. Available data are summarized from clinical trials of proteins and protein-like biomolecules, generally showing minimal, if any, adverse respiratory effects. The results of the animal toxicology studies that have been published are presented. In general, the observed lung toxicity has been relatively low, and it has been difficult to interpret in cases where the animal protein differs considerably from the human protein. Discussion is presented on the possibility of adverse immune reactions, suggesting that this is not likely to be any greater issue than it is for subcutaneously injected materials. Although the safety information is relatively sparse at present, the available data suggest that the inhalation route can be an attractive route to consider for many therapeutic proteins.

Daytime pulmonary hemodynamics in patients with obstructive sleep apnea without lung disease

It is controversial whether obstructive sleep apnea (OSA) causes pulmonary hypertension (PH) in the absence of hypoxemic lung disease. To investigate this further we measured awake pulmonary hemodynamics, pulmonary gas exchange, and small airways function in 32 patients with OSA (apnea- hypopnea index, mean +/- SE, 46.2 +/- 3. 9/h) who had normal screening lung function. Pulmonary artery pressure (Ppa) and cardiac output were measured by Doppler echocardiography at three levels of inspired oxygen (FIO2 0.50, 0.21, and 0.11) and during incremental increases in pulmonary blood flow (10, 20, and 30 microgram/kg/min dobutamine infusions) while breathing 50% oxygen. Eleven patients had PH (mean Ppa >/= 20 mm Hg, Group I). They did not differ from patients without PH (Group II) in lung function, severity of sleep-disordered breathing, age, or body mass. Compared with Group II, Group I patients had increased small airways closure during tidal breathing (FRC-closing capacity: Group I, -0.16 +/- 0.11; Group II, 0.27 +/- 0.09 L; p < 0.05), more ventilation-perfusion inequality (AaPO2: 23.8 +/- 2.8; 19.8 +/- 1.4 mm Hg; p = 0.08), a greater pulmonary artery pressor response to hypoxia (DeltaPpa FIO2, 0.50 to 0.11: 16.4 +/- 1.93; 6.4 +/- 0.77 mm Hg; p < 0.05) and a marked rise in Ppa during increased pulmonary blood flow. We conclude that PH may develop in some patients with OSA without lung disease and that it is associated with small airways closure during tidal breathing and heightened pulmonary pressor responses to hypoxia and during increased pulmonary blood flow. Such changes are consistent with remodeling of the pulmonary vascular bed in affected patients with OSA, seemingly unrelated to severity of sleep-disordered breathing.

Development of a new method for simultaneously evaluating mucociliary clearance and pulmonary epithelial permeability in rabbit experiments by means of 18FDG, three-dimensional positron emission tomography and rectilinear scan

We tried to simultaneously obtain the elimination constant of mucociliary clearance and the pulmonary epithelial permeability constant after inhalation of 2-[18F]fluoro-2-deoxy-D-glucose (18FDG) solution by carrying out whole lung positron emission tomography and a rectilinear scan in rabbit experiments. The elimination constant of pulmonary epithelial permeability was obtained from the decrease in the amount of the radioactivity with time in the region of interest (ROI) confined to the lungs, trachea and tracheal cannula in the rectilinear scan. The total elimination constant of the radioactivity in the lungs was obtained from the ROI confined to the lungs in the tomography. The mucociliary clearance rate constant in the lungs was then obtained after subtracting the elimination constant of the pulmonary epithelial permeability from the total elimination constant of the 18FDG in the lungs. The mucociliary clearance constant in the trachea was calculated from the residual radioactivity in the trachea and the mucociliary clearance constant in the lungs. The mean pulmonary epithelial permeability constant was 0.0020% min(-1) obtained from the rectilinear scan. The mean mucociliary clearance constants of the lungs and the trachea were 0.0006 and 0.025% min(-1), respectively. These results indicated that the pulmonary epithelial permeability and mucociliary clearance could be evaluated simultaneously with 18FDG by using three-dimensional positron emission tomography and a rectilinear scan.

Retention of soluble 99mTc-DTPA in the human lung: 24-h postdeposition

Clearance of low-molecular-weight solutes, e.g., radiolabeled chelate diethylenetriaminepentaacetate (DTPA), across epithelial surfaces of distal airways and the lung parenchyma is a broadly used technique to assess epithelial integrity. It has been generally assumed that clearance of solute follows a simple first-order process and that DTPA clearance through the respiratory epithelium and into blood and lymphatic channels is complete within a few hours. Using gamma-camera imaging and a radiolabeled aerosol of 99mTc-labeled DTPA, we observed in eight healthy subjects lung retention of radioisotope approximately 24 h postdeposition of the 99mTc-DTPA. Residual lung retention at the 24-h end point averaged 6.0 +/- 1.8 (SD)% of the amount of radioisotope initially deposited in the lung. This suggests that for normal healthy subjects a small amount of the 99mTc radioisotope, either in a dissociated or chelated form, is nonpermeable or slowly cleared from respiratory tisssues.

Airway and alveolar permeability and surface liquid thickness: theory

The thickness of airway surface liquid (ASL) can be calculated as the ratio of the permeability coefficient of an absorbed inert tracer to the percentage rate in which it decreases in content in the airway lumen. The percentage clearance of radiolabeled diethylenetriaminepentaacetic acid (DTPA) from human airways or lungs has been measured many times, with a mean value of 1.04 +/- 0.25 (SD) %/min. Rates of clearance from animal lungs of most species give values of the same order, although they are lower in the sheep and higher in the dog. Permeability coefficients have not been measured simultaneously with percentage clearances and not at all for human tissues. Values for mannitol and sucrose, of which the former gives a permeability coefficient approximately 25% greater than that for sucrose and DTPA in airway tubes and isolated mucosal sheets from experimental animals, give a mean approximately 7.1 x 10(-7) cm/s. This corresponds to thickness of ASl of approximately 20-150 microns for various species. The assumptions underlying this estimate are discussed. It is concluded that ASL thickness in vivo may be considerably greater than in vitro measurements involving rapid freezing of the airway wall. Estimates of alveolar permeability suggest that either it is very considerably lower than that of the airway epithelium, that methods to measure alveolar permeability mainly reflect airway permeability, or both.

An exploration of intrapulmonary insulin administration in anaesthetized and mechanically ventilated pigs

We investigated the efficacy of intrapulmonary administration of short-acting porcine insulin in anaesthetized pigs (n = 14) in a randomized intervention study. Insulin was administered by a new jet nebulizer (Maxin) in a random order at different doses, 0 (saline), 10 or 40 U. The hypoglycaemic effect was compared to control (0.9% saline). Blood glucose and serum insulin concentrations were followed at specified time intervals for 90 min. Plasma catecholamine concentrations were measured in order to estimate the concurrent stress. Nebulized insulin caused a significant decrease in blood glucose concentrations (p < 0.0001) (n = 28) at all doses used. The decrease in mean blood glucose concentration from the start of nebulization was 39 +/- 3% (mean +/- SEM), falling from 4.6 +/- 0.1 to 2.8 +/- 0.2 mmol 1(-1), with a nadir at 40 min after the 40 U insulin dose (n = 10). Serum insulin concentration rose from (mean +/- SEM) 5.2 +/- 0.1 to 25 +/- 9 mU 1(-1) after the insulin dose of 40 U (n = 10), the peak value occurred at 30 min. The plasma catecholamine concentrations increased significantly (p < 0.0001) (n = 28) from 0 to 60 min, this increase was similar for control and for different insulin doses. We conclude that intrapulmonary administration of insulin can cause a significant decrease in blood glucose concentrations in anaesthetized and mechanically ventilated pigs and results in clinically relevant serum insulin levels. Similar effects in humans would make inhaled insulin possible for clinical use.

Effect of detergent combined with large tidal volume ventilation on alveolocapillary permeability

The combined effect of large tidal volume ventilation (LTVV) and detergent-induced surfactant dysfunction on the clearance kinetics of technetium-99m-labelled diethylene triamine pentaacetate was investigated. Four groups of rabbits (n = 6 in each) were studied: (1) controls, (2) detergent, (3) LTVV, and (4) detergent + LTVV. Clearance was measured for 3 h and the kinetics was analysed by fitting mono- and biexponential equations to the clearance curve and was expressed as a half-life (T 1/2). Pulmonary clearance of 99mTc-DTPA was monoexponential in control animals (T 1/2 = 194 min) and in animals ventilated with LTVV (T 1/2 = 43 min, P < 0.01 compared with controls). In contrast, clearance was biexponential after detergent administration with or without LTVV. T 1/2 values of the fast and slow compartments were 5.4 and 80 min, respectively, with the fast fraction comprising 81% of the radioactivity after detergent alone. When detergent was combined with LTVV, clearance was bicompartmental as with detergent alone, with the same size of the fast fraction. However, clearance from each of the slow (P < 0.01) and fast compartments (P < 0.05) increased significantly. Clearance from the slow compartment was thus similar to T 1/2 during LTVV alone. Large tidal volume ventilation induced a faster than normal clearance of a single compartment, whereas detergent induced kinetics that was distinctly bicompartmental. The mechanisms increasing permeability of the alveolocapillary barrier after detergent and during LTVV seem different and may be additive.

Additive effects of exposure to silica dust and smoking on pulmonary epithelial permeability: a radioaerosol study with technetium-99m labelled DTPA

BACKGROUND

Increased pulmonary epithelial permeability evaluated by the rate of clearance from lung to blood of the radioaerosol solute technetium-99m labelled diethylenetriamine pentaacetate (99mTc-DTPA) has been reported in smokers and in workers exposed to silica dust. A study was carried out to determine whether there are additive effects of cigarette smoke and exposure to silica dust on clearance rates of 99mTc-DTPA in ceramic workers.

METHODS

Thirty one subjects with silicosis were studied, of whom 18 smoked cigarettes and 13 were non-smokers. They had similar histories of exposure to silica dust, and radiological alterations consistent with silicosis. The results from these patients were compared with those from normal subjects and smokers previously studied by the authors.

RESULTS

Pulmonary function values were normal in most patients and not significantly different among groups. The median (range) rate of clearance of 99mTc-DTPA in smokers with silicosis was 4.1 (1.9-12.7) %/minute, which was higher than the rates in non-smoking patients with silicosis of 2.2 (1.1-6.6) %/minute and in smokers without exposure to silica dust of 2.9 (1.6-4.5) %/minute. These differences were more evident and significant when the clearance rates of the lower lobes of the three groups were compared. Clearance rates higher than 3%/minute were much more frequent in smokers with silicosis (85%) than in non-smoking patients with silicosis (15%) and in smokers (40%).

CONCLUSION

In ceramic workers with radiographic changes resulting from exposure to silica dust, there is an additive effect of inhalation of silica dust and cigarette smoking on clearance rates of 99mTc-DTPA.

Clearance of 99mTc-labeled albumin from lungs in anesthetized guinea pigs

Gamma imaging was used to measure the rate of clearance of aerosolized 99mTc-human serum albumin (HSA) from the lungs of control guinea pigs and guinea pigs that received increased lung inflation or lung injury. Anesthetized guinea pigs were ventilated for 6 min with an aerosol of HSA and the radioactivity in the chest was monitored for 2 h with a gamma camera to determine whether the clearance rate would be a reliable assessment of lung epithelial permeability. Increased lung volumes were effected by application of 5 or 7 cm H2O positive end-expired pressure (5-PEEP and 7-PEEP, respectively). Lung injury was induced either by intravenous oleic acid (OA, 27-73 microliters/kg) or inhalation of nitrogen dioxide (NO2, 80-100 ppm) for 2 h. Postmortem extravascular lung water volume (EVLW) provided an assessment of the degree of lung injury. Tracer clearance rates in animals receiving 5 or 7 cm H2O PEEP were not significantly different from controls (K = 0.15 +/- 0.05 and 0.24 +/- 0.10 vs 0.12 +/- 0.03%/min, respectively, p > .05). Animals exposed to NO2 had faster tracer clearance rates (K = 0.33 +/- 0.21%/min, p < .05) and higher EVLW (5.8 +/- 3.0 vs 3.7 +/- 0.2 mL/g dry lung, p < .05) than controls. Clearance rates of HSA from the lungs of NO2-exposed guinea pigs correlated well with injury as assessed by EVLW (r = .93, p < .01). Clearance rates of HSA and EVLW in animals receiving oleic acid were significantly higher than controls and the group receiving 5 cm H2O PEEP (K = 0.58 +/- 0.41%/min, EVLW = 8.1 +/- 0.8 mL/g dry lung tissue, p < .05), but there was no correlation between these parameters in this injury model. It is concluded that imaging of the disappearance of radiolabeled HSA in the guinea pig can be a useful index of lung epithelial permeability, but this technique is limited to certain models of lung injury.

Absorption of intra-bronchial diprophylline-methodology and preliminary results

With the objective of measuring alveolo-capillary permeability, a diprophylline solution (molecular weight 254 D) was instilled as a bolus. Instillation was performed through distallized impacted fiber bronchoscope and 3 normal volunteers and 3 patients with pulmonary fibrosis were evaluated. Blood samples were collected at regular intervals with subsequent pharmacokinetic study, mainly aimed at determining absorption kinetics. This technique enabled us to distinguish the two groups of individuals which had different absorption rates. In controls, kinetics apparently followed a simple, one compartment model for absorption, which was slower and occurred to a lesser extent. Patients with a pulmonary fibrosis had a faster and higher degree of absorption, with a larger plasma Cmax. In the latter group two-compartment kinetics for absorption was found. We conclude that absorption kinetic parameters can disclose data on structural integrity of epithelia and possible lesions of the lung interstitium.

Effect of pattern of aerosol inhalation on clearance of technetium-99m-labeled diethylenetriamine pentaacetic acid from the lungs of normal humans

The clearance rate of inhaled aerosols of technetium-99m-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) from the lungs provides a rapid, clinically useful, noninvasive index of pulmonary epithelial permeability. In order to identify a method that minimizes intrasubject and intersubject variability and thereby provides a reliable means to identify patients with abnormal values, we administered a submicronic aerosol of 99mTc-DTPA to 10 healthy, nonsmoking male subjects with either tidal breathing (Vtidal) or multiple vital capacity maneuvers (VVC). Subjects then spontaneously breathed room air while counting continued for 30 min. Monoexponential clearance rates over 7, 15, and 30 min were compared with a two-compartment, biexponential analysis over 30 min. Intrasubject reproducibility was evaluated by repeating clearance 2 to 156 days later. Monoexponential clearance following VVC at 30 min equaled 1.36 +/- 0.55%/min compared with 0.83 +/- 0.25%/min for Vtidal (p less than 0.025). VVC inhalations resulted in a larger fast compartment of 16 +/- 12% compared with 3 +/- 2% with tidal breathing (p less than 0.01). The least intrasubject variability with coefficient of variation (CV) of +/- 18% was obtained with monoexponential analyses after Vtidal during 15 min of scanning and with either breathing maneuver over 30 min. Monoexponential clearance for 30 min with Vtidal gave the least scatter between subjects, with CV of +/- 30%. These data show that simple tidal inhalations of 99mTc-DTPA followed by a monoexponential analysis of the 30-min time-activity curve from both lungs minimize the degree of variability between and among subjects and provide a predicted normal value of clearance of 0.83 +/- 0.25%/min. The development of a more rapid curvilinear clearance followed by delivery VVC suggests that several deep breaths transiently increase epithelial permeability or reduce the volume of liquid in the alveolar subphase in some regions. Resting for 20 min prior to inhaling the aerosol of 99mTc-DTPA is recommended to avoid alterations in clearance rates from deep breathing.

The pulmonary circulation in acute lung injury: a review of some recent advances

1. According to the Starling resistor model of the pulmonary circulation, the pulmonary hypertension of oleic acid lung injury, an experimental model close to the early stage of clinical ARDS, primarily results from an increased vascular closing pressure which exceeds Pla and becomes the effective outflow pressure of the pulmonary circulation. Therefore, calculated pulmonary vascular resistance should be interpreted cautiously during haemodynamic investigations in patients with ARDS. 2. Part of this increased vascular closing pressure is functional. During acute lung injury pulmonary vasomotor tone can be reduced by vasodilators, or increased by cyclooxygenase inhibitors and almitrine. 3. Pulmonary vasodilation due to infused vasodilators usually impairs gas exchange in ARDS. 4. There is evidence that HPV is altered during ARDS. Drugs capable of enhancing the efficacy of HPV could improve gas exchange. If proven safe in the future, cyclooxygenase inhibitors and almitrine are interesting compounds to be tested in ARDS.

Pindolol inhibits the development of hypoxic pulmonary vasoconstriction

We examined the effects of beta-adrenoceptor antagonists, propranolol and pindolol, on hypoxic pulmonary vasoconstriction using isolated, blood-perfused dog lung lobes. Pindolol markedly inhibited the development of hypoxic pulmonary vasoconstriction, whereas propranolol had no effect. The different role of the drugs on hypoxic pulmonary vasoconstriction is discussed.

Restored hypoxic pulmonary vasoconstriction by peripheral chemoreceptor agonists in dogs

Hypoxic stimulation of the peripheral chemoreceptors inhibits hypoxic pulmonary vasoconstriction (HPV). On the other hand, almitrine, a peripheral chemoreceptor agonist, has been reported in some studies to enhance HPV. To further explore this apparent contradiction, we investigated the effects of two different low intravenous doses of almitrine on pulmonary arterial pressure (Ppa) versus cardiac index (Q) plots in 32 pentobarbital-anesthetized dogs ventilated alternatively in hyperoxia (FIO2, 0.4) and in hypoxia (FIO2 0.1). HPV, defined as a hypoxia-induced increase in Ppa over the entire range of Q studied, from 2 to 5 L/min/m2, was elicited in 16 dogs. In the first eight of these "responders," almitrine 2 micrograms/kg/min had no vascular effect, and in the other eight, almitrine 4 micrograms/kg/min inhibited HPV. In 16 other dogs, hypoxia did not affect Ppa over the entire range of Q. In these "nonresponders," almitrine 2 micrograms/kg/min (n = 8) as well as 4 micrograms/kg/min (n = 8) restored HPV. To answer the question whether the ability to restore HPV would be specific to almitrine, we administered intravenously the structurally unrelated chemoreceptor agonist doxapram at the dose of 20 micrograms/kg/min to an additional group of eight "nonresponders," and this treatment also restored HPV. Intravenous infusion of the malic acid solution solvent of almitrine had no effect on Ppa/Q plots in a final group of eight "nonresponders". We conclude that low dose almitrine and doxapram restore HPV in dogs with a naturally absent hypoxic pulmonary pressor response, probably by a direct effect at the pulmonary vessels.

Strain difference in pulmonary vascular responsiveness to hypoxia in rats

The difference in pulmonary vascular response to hypoxia between Hilltop Sprague-Dawley (HT) rats and Wistar (W) rats was studied. Effects of inhibitor of leukotriene (LT) synthesis or prostaglandin (PG) synthesis on hypoxic pulmonary vasoconstriction (HPV) and chronic pulmonary hypertension were observed, and variations in plasma TXB2 and 6-keto-PGF1 alpha during hypoxia were determined. The results showed that in rats of both strains LTs are the major mediator of HPV, which is also mediated by vasoconstrictive PGs in HT rats, while modulated by vasodilative PGs in W rats. This might be the crucial mechanism responsible for the higher pulmonary vascular responsiveness in HT rats. Differences in the modulating effect of histamine and in the structural feature of pulmonary arteriole might be contributing factors as well.

Pulmonary absorption of instilled and inhaled DTPA in smokers

Pulmonary absorption of DTPA (diamine-triethylene-penta-acetic acid) has been widely adopted as an index of pulmonary epithelial permeability. The aim of this study was to analyse: (1) if measurements of pulmonary absorption are influenced by the amount of fluid being administered to the lungs together with the DTPA; and (2) if all DTPA administered to the lungs is equally accessible for pulmonary absorption. To this end DTPA was instilled into a lung segment of six smokers in association with a bronchoscopy. In six other subjects (five smokers and one ex-smoker) the DTPA was inhaled as an aerosol. Pulmonary absorption of DTPA was calculated from the plasma DTPA content, as determined for 4-10 h after the administration of the DTPA. We found that the mean transit time for the absorption of instilled DTPA, t(L), across the pulmonary membranes was significantly (P less than 0.05) longer (median 1498 min, range 955-2636 min) than the t(L) of the absorption of the inhaled DTPA (median 131 min, range 44-512 min). Pulmonary clearance of the inhaled aerosolized DTPA tended to be faster when determined by external detection for 4 h, than when estimated from plasma samples, suggesting that not all pulmonary DTPA may be equally accessible for absorption from the pulmonary lining fluids. We conclude that pulmonary absorption of DTPA is influenced by the volume of fluid being administered to the lungs in association with the measurements. Not all pulmonary DTPA, however, is equally accessible for absorption, rendering external detection of pulmonary clearance of DTPA sensitive to a variety of factors other than pulmonary absorption.

Lung function declines in patients with pulmonary sarcoidosis and increased respiratory epithelial permeability to 99mTc-DTPA

Respiratory epithelial clearance of 99mTc-DTPA (RC-Tc-DTPA) and pulmonary function tests (PFT) were determined at intervals of 6 or 12 months in 37 untreated, nonsmoking patients with sarcoidosis over a period of 6 to 36 months. PFT included the measurements of total lung capacity (TLC), vital capacity (VC), FEV1, and diffusing capacity for carbon monoxide. No difference was found between the respiratory clearance of 113mIn-DTPA (2.25 +/- 1.00%/min) and RC-Tc-DTPA (2.29 +/- 1.11%/min) in eight patients with pulmonary sarcoidosis. Pulmonary function decreased 15% or more in at least 2 function tests during 11 follow-up periods, but it remained stable during 47 follow-up periods. In patients whose lung function deteriorated, RC-Tc-DTPA increased to 3.51 +/- 1.55%/min; in contrast, in patients whose lung function remained stable, regardless of the initial values, RC-Tc-DTPA was normal (1.00 +/- 0.50%/min; p less than 0.001). In eight patients who were treated with corticosteroids, RC-Tc-DTPA decreased from 3.48 +/- 1.31%/min to 1.56 +/- 0.64%/min (p less than 0.001), and PFT improved. We conclude that in nonsmokers with pulmonary sarcoidosis, increased RC-Tc-DTPA is not related to dissociation of 99mTc from DTPA, RC-Tc-DTPA is increased when pulmonary function decreases, and, when increased, RC-Tc-DTPA decreases with corticosteroid therapy.

Adenosine produces pulmonary vasoconstriction in sheep. Evidence for thromboxane A2/prostaglandin endoperoxide-receptor activation

Adenosine, an intermediate product in the metabolism of ATP, is thought to produce vasodilation in all vascular beds with the exception of the kidney. Due to its theoretical potential as a pulmonary vasodilator, we studied the hemodynamic effects of adenosine in the pulmonary vasculature of chronically instrumented awake sheep. Adenosine produced significant pulmonary vasoconstriction instead of the expected vasodilatation. Bolus injections of adenosine into the superior vena cava produced a dose-dependent increase in pulmonary artery pressure that was entirely due to an increase in vascular resistance, since cardiac output decreased slightly. This effect is produced via activation of specific cell surface adenosine receptors, since it was blocked by the adenosine-receptor antagonists theophylline and dipropylsulfophenylxanthine. The cell type involved in adenosine-induced pulmonary vasoconstriction appears to be located within the lung, since vasoconstriction was blunted when adenosine was infused into the left atrium, distal to the lung. However, adenosine does not directly vasoconstrict the pulmonary vasculature, because its effect could be completely abolished by cyclooxygenase inhibition with either indomethacin or ibuprofen and by a thromboxane A2/prostaglandin endoperoxide-receptor antagonist (SQ 29,548). Adenosine-induced vasoconstriction was also greatly reduced after inhibition of thromboxane synthesis. Thus, adenosine produced pulmonary vasoconstriction through generation of a thromboxane/endoperoxide product. Whether endogenous adenosine is involved in the generation of pulmonary vasoconstriction seen in pathophysiological states remains to be determined. To our knowledge, this is the first clear evidence for adenosine-induced vasoconstriction outside the kidney and for an interaction between adenosine and eicosanoid mechanisms.

Dual pathway clearance of 99mTc-DTPA from the bronchial mucosa

Many studies have reported clearance rates of 99mTc-DTPA from the alveolar epithelial surface, but few have measured clearance of this solute from the bronchial mucosa. Those that have attempted such measurements have discounted the possibility that 99mTc-DTPA may be removed from the bronchial airways by mucocilliary transport as well as by absorption through the epithelium. This study was designed to better approximate the rate of 99mTc-DTPA absorption across the bronchial epithelium by correcting the measurements of total 99mTc-DTPA clearance for mucus transport. On two separate study days, each normal, nonsmoking subject (n = 8) breathed an aqueous aerosol (2.0 microns MMAD, sigma g = 2.0) containing 99mTc bound to DTPA or human serum ablumin (HSA) (a relatively nonpermeable solute that is cleared only by mucus transport over the period of measured clearance) while seated in front of a gamma camera. Breathing pattern was standardized to produce a similar central deposition of particles on both study days. From measurements of retention versus time over a 1-h period, exponential rate constants (Ktot and Km) were determined for the clearance of 99mTc-DTPA and 99mTc-HSA, respectively. By modeling the airways as a single compartment with two possible routes of clearance, we determined the permeability rate constant, Kp, as Ktot minus Km. Results showed that mucus clearance (Km) accounted for two thirds of the total rate of 99mTc-DTPA clearance (Ktot) (mean Ktot = 0.00985, Km = 0.00698, and Kp = 0.00287/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Permeability of the bronchial mucosa to 99mTc-DTPA in asthma

Previous investigators, using 99mTc-DTPA aerosol as a marker to assess epithelial permeability in asthma, did not find an increased permeability in this group. However, they either failed to deliver the aerosol to the optimal site (bronchial mucosa, not alveoli) or failed to account for mucociliary clearance in analyzing their results. We studied 10 asthmatics and eight age-matched control subjects using a dosimeter (Spira-Elektra 2) and a carefully controlled breathing pattern to deliver aerosol to the subjects' airways. Two aerosols were delivered on separate days in each patient; 99mTc-DTPA aerosol, and 99mTc-HSA (human serum albumin), using similar breathing patterns to ensure reproducibility of the deposition pattern with the two aerosols. From measurements of retention versus time over a 1-h period, rate constants Ktot and Km were determined for the clearance of 99mTc-DTPA and 99mTc-HSA, respectively. By modelling the airways as a single compartment with two possible routes of clearance, we determined the permeability rate constant, Kp, as Ktot minus Km. There was no significant difference between Ktot in normal subjects and asthmatics; however, because of the slower mucociliary clearance in the asthmatic group, and the relative importance of mucociliary clearance in determining the washout of 99mTc-DTPA aerosol, there was a significant difference in airway permeability between the normal subjects and the asthmatics (t1/2 = 296 min +/- 141 SD and 126 min +/- 58, p less than 0.01, in normal subjects and asthmatics, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of SO2 exposure on canine pulmonary epithelial functions

We examined the effects of a single exposure of high concentrations of sulfur dioxide (SO2) on the pulmonary epithelium in adult dogs over a period of several weeks. Mucociliary tracheal transport rates and alveolar clearance of 99mTc-labeled diethylene triamine pentacetate (99mTcO4-) were measured in vivo, before and immediately after inhalation of 100 ppm or 500 ppm SO2, and then weekly for 3-5 weeks. At the completion of the in vivo studies, tracheal epithelium was studied in Ussing chambers for bioelectric properties (short-circuited current, transepithelial potential difference), nonelectrolyte permeability for calculation of pore sizes, and changes in bioelectric properties following pharmacological manipulations. These tissues were then fixed for scanning electron microscopy studies. Additional dogs were sacrificed for microscopy studies at several time intervals to provide a histological basis for the altered mucociliary transport. We found that despite marked derangement of mucociliary transport caused by damage to the ciliated cells, recovery occurred over a period of several weeks, and alveolar permeability as assessed by the radioaerosol technique did not change. We concluded that the solubility of SO2 and perhaps a more severe damaging effect of SO2 specific on the ciliated cells might be the explanation for the observations.

Altered clearance of inhaled 99mTc-pentetate aerosols following exposure to cadmium chloride aerosols in ferrets

The rate of clearance of inhaled 99mTc-pentetate aerosols has been used as an indicator of pulmonary epithelial "permeability" in human and animal studies. In order to evaluate this technique further, groups of eight male ferrets (Mustela putorius furo) were given acute exposures to aerosols of CdCl2 or NaCl via endotracheal tube. Serial evaluations of the thoracic clearance rate of inhaled 99mTc-pentetate aerosols (MMAD = 0.6 microns, sigma g = 1.6) were made before exposure and at fixed time points after toxicant exposure (3 or 6, 24, 48 h, and 5 days after CdCl2). These serial evaluations of 99mTc-pentetate thoracic clearance were conducted at three cadmium intake levels (3, 10, and 30 min exposure to 10 mg/m3 CdCl2) in order to evaluate possible dose-related response relationships. The rate of thoracic clearance of Tc-pentetate was observed to be slowed at 3 h after exposure to CdCl2 aerosol and subsequently increased to well above control rates. The time sequence observed strongly suggests that increased Tc-pentetate clearance rates are indicative of a tissue response or repair process, rather than acute lung injury. Tracheal epithelial penetration of macromolecular tracers was not observed to increase in histological evaluations following serial sacrifice.

Cyclooxygenase inhibition and effects of hypoxia on pulmonary circulation and gas exchange in anesthetized dogs

To investigate whether endogenously produced prostanoids are involved in hypoxic pulmonary vasoconstriction, pulmonary hemodynamic and gas exchange parameters and eicosanoid metabolites were measured in 5 anesthetized, artificially ventilated dogs (mean body weight 27 kg). Hypoxia elicited pulmonary vasoconstriction, but blood plasma levels of thromboxane B2 (TXB2) and 6-keto-prostaglandin F 1 alpha (6kPGF1 alpha) (stable metabolites of TXA2 and prostaglandin I2, respectively) remained unchanged. Administration of the cyclooxygenase inhibitor indomethacin blocked the synthesis of prostanoids, so that 6kPGF1 alpha and TXB2 levels decreased to values below the detection level (10 pg.ml-1) both during normoxia or hypoxia, but did not affect pulmonary vascular resistance or the alveolar-arterial PO2 difference (PAi-Pa)O2. The pulmonary vascular bed remained, however, responsive to TXA2 as evidenced by infusion of the TXA2 mimetic, U 46619, which significantly increased the pulmonary vascular resistance and (PAi-Pa)O2. Our data suggest that prostanoids are not involved in eliciting the effects of hypoxia on pulmonary hemodynamics and gas exchange efficiency.

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.

Pulmonary artery pressure: flow relationships in hyperoxic and in hypoxic dogs. Effects of methylprednisolone

Methylprednisolone has been reported to impair hypoxic pulmonary vasoconstriction in isolated lungs, possibly by inhibiting the generation of vasoconstricting products of arachidonic acid metabolism. We investigated the effects of methylprednisolone on mean pulmonary artery pressure (PAP):cardiac index (Q) relationships in intact pentobarbital anaesthetized dogs ventilated alternatively in hyperoxia (fraction of inspired O2, FiO2 0.4) and in hypoxia (FiO2 0.1). Cardiac output was increased by opening an arterio-venous femoral fistula or reduced by stepwise inflations of a balloon in the inferior vena cava. Five point PAP:Q relationships were found to be rectilinear in all experimental conditions. Over the entire range of Q studied (2 to 5 l/min.m2), hypoxia increased PAP in seven dogs ("responders") and did not affect PAP in three other dogs ("non-responders"). A hypoxic pulmonary pressor response was restored in these three "non-responders" by administration of 1 g acetylsalicylic acid iv. Methylprednisolone 30 mg/kg iv had no effect on hyperoxic and on hypoxic pulmonary vascular tone in the "responders" and in the "non-responders" treated with acetylsalicylic acid. An additional dog pretreated with methylprednisolone 30 mg/kg iv 24 h before the experiment still had a marked hypoxia-induced increase in PAP over the entire range of Q studied. Thus a large dose of methylprednisolone does not affect hypoxic or hyperoxic pulmonary vascular tone in intact dogs. These data do not support the hypothesis that products of arachidonic acid metabolism mediate hypoxic pulmonary vasoconstriction.