Serotonin uptake and metabolism in isolated,perfused fetal,newborn and adult rabbit lungs

Twenty-second infusions of³H-5HT were made into the pulmonary arteries of lungs isolated at three different stages of rabbit development: 1) nonventilated lungs from previable 26- to 27-d fetuses; 2) ventilated, newborn lungs from rabbits within 12 hours of birth; and 3) ventilated, young adult lungs. The concentration of 5HT infused (0.65 to 1.12×10^?8 M) was much less than the apparent Km for the 5HT uptake process. At these low concentrations 5HT infusion produced no observable vasoactivity. In order to assure a constant ratio of flow to capillary surface area (independant of lung size), perfusate flow was adjusted to produce an approximately 7-second dye retention time. Under these conditions fetal and adult lungs allow 45–50% of³H-5HT to pass through unmetabolized, but newborn lungs allow only about 15% of the unmetabolized³H-5HT through. As previously demonstrated by other workers, essentially no³H-5HT metabolites appeared in the effluent of adult lungs. In contrast about 20 percent of the radioactivity recovered from the immature lungs was eluted with the dye peak as metabolites of³H-5HT. 10^?4 M imipramine added to the perfusate blocked 5HT uptake and metabolism similarly at all three stages of development. Therefore, uptake does not seem to be by passive diffusion in immature lungs. The presence of avid 5HT inactivation in previable, fetal lungs with peak inactivation observed in newborn lungs may correlate with the prominence and functional importance of 5HT within pulmonary neuroendocrine cells during perinatal life.     

Lung MK 351A uptake after hypoxia adaptation and subsequent hyperoxia exposure

This study investigated the effects of hypoxia adaptation (10% O₂ for 4 days) on rat lung angiotensin-converting enzyme (ACE) content before and after hyperoxia exposure (>95% O₂ for 2 days). The rationale for this investigation was that hyperoxia exposure decreases lung ACE, while hypoxia adaptation produces tolerance (improved survival) to oxygen toxicity in rats. Rats were exposed to air, hypoxia, hyperoxia alone, or hypoxia followed immediately by hyperoxia. The lungs were then excised and perfused in vitro at 12 ml/min with buffer. Lung ACE content was quantitated by measuring the single-pass binding of an iodinated ACE inhibitor,¹²⁵I-MK 351A, a derivative of lisinopril. We showed previously that¹²⁵I-MK 351A binding correlates quantitatively with ACE activity in lung homogenates and isolated, perfused lungs. Lung internal surface area was estimated by measuring the mean alveolar diameter of 5μm hematoxylin and eosin sections from lungs fixed in inflation (25 cmH₂O transpulmonary pressure). Hypoxia adaptation per se had no effect on¹²⁵I-MK 351A binding or estimated alveolar surface area, while hyperoxia exposure caused a significant decrease in both¹²⁵I-MK 351A binding and alveolar surface area. These hyperoxia-induced decreases were prevented partially by hypoxia adaptation, indicating a protective effect on both ACE content and surface area.¹²⁵I-MK 351A binding in isolated perfused lungs changed in parallel with histologically estimated surface area. These results indicate that hypoxia preadaptation minimizes the oxygen-induced decrease in lung microvascular ACE content.     

Neurohumoral control of pulmonary surfactant secretion

The effect of the muscarinic drug, carbamylcholine, on surfactant secretion by hamster lung was examined. Intracellular phosphatidylcholine was prelabeled with tritium by intraperitoneal injection of [³H]choline into adult hamsters. Carbamylcholine (18 µg/100 g body wt.) was administered IP to one group of animals 30 min before sacrifice and isotonic saline was given to another group. Following sacrifice, the lungs were perfused, sliced, and incubated in the presence or absence of 15 µg/ml carbamylcholine for 1 h. Secretion of radiolabeled phosphatidylcholine by the lung tissue slices into the medium was evaluated. Treatment of animals with carbamylcholine was associated with a significant enhancement in the secretion of [³H]phosphatidylcholine into the medium. Administration of the muscarinic antagonist, atropine, in an equimolar dose completely inhibied the stimulatory effect of carbamylcholine on surfactant secretion. Treatment of hamster fetuses with carbamylcholine had no effect on [³H]phosphatidylcholine secretion from fetal lung tissue slices. The results support the concept that surfactant secretion by adult hamster lung is regulated by neurohumoral mechanisms.     

Neurohumoral control of pulmonary surfactant secretion

The effect of the muscarinic drug, carbamylcholine, on surfactant secretion by hamster lung was examined. Intracellular phosphatidylcholine was prelabeled with tritium by intraperitoneal injection of [³H]choline into adult hamsters. Carbamylcholine (18 µg/100 g body wt.) was administered IP to one group of animals 30 min before sacrifice and isotonic saline was given to another group. Following sacrifice, the lungs were perfused, sliced, and incubated in the presence or absence of 15 µg/ml carbamylcholine for 1 h. Secretion of radiolabeled phosphatidylcholine by the lung tissue slices into the medium was evaluated. Treatment of animals with carbamylcholine was associated with a significant enhancement in the secretion of [³H]phosphatidylcholine into the medium. Administration of the muscarinic antagonist, atropine, in an equimolar dose completely inhibied the stimulatory effect of carbamylcholine on surfactant secretion. Treatment of hamster fetuses with carbamylcholine had no effect on [³H]phosphatidylcholine secretion from fetal lung tissue slices. The results support the concept that surfactant secretion by adult hamster lung is regulated by neurohumoral mechanisms.     

Dibutyryl cyclic adenosine monophosphate inhibits pulmonary vasoconstriction

The effects of the cell-permeable dibutyryl derivative of cyclic AMP on the vascular reactivity of isolated perfused rat lungs were examined. In lungs perfused with homologous blood, pulmonary arterial infusion of db-cAMP (30μg/min) inhibited hypoxia-induced vasoconstriction (IC₅₀=6.3×10⁻⁵ M) and vasoconstriction due to bolus injection of angiotensin II (IC₅₀=8.2×10⁻⁵ M). Cyclic AMP phosphodiesterase inhibition by aminophylline acted synergistically with db-cAMP in the reduction of hypoxia-induced vasoconstriction. Somatostatin, an inhibitor of adenylate cyclase, prevented the decay of hypoxic vasoconstriction typically observed in isolated lungs, suggesting that a rise in intracellular cAMP may occur during hypoxic vasoconstriction as a consequence of activation of the adenylate cyclase. In lungs perfused with cell and protein-free salt solution, db-cAMP inhibited both initial and prolonged vasoconstriction following bolus injection of 2μg leukotriene C₄. Thus, db-cAMP inhibited pulmonary vascular reactivity nonspecifically.     

Capillary filtration and permeability coefficients calculated from measurements of interendothelial cell junctions in rabbit lung and skeletal muscle

The depth and width of interendothelial junctions were measured in pulmonary capillaries of the adult and fetal rabbit and in capillaries of the gastrocnemius muscle of the adult rabbit. These dimensions were used to determine the resistance to filtration and diffusion of junctions in each tissue. The resistances, together with the stereologically determined values for the total length of junction per unit weight of tissue, were used to calculate maximal capillary filtration coefficients (CFC) and diffusion coefficients (CDC) for sodium and inulin under conditions in which all vessels (except those in the fetal lung) were assumed to be perfused. The calculated filtration coefficients, expressed per 100 g tissue, were 2.7, 0.8, and 0.05 ml min^?1 mm Hg^?1 100 g^?1 for capillaries in adult lung, fetal lung, and skeletal muscle, respectively. The corresponding values for capillary surface area in each tissue were 3490, 844, and 62 cm² g^?1, respectively. When the data were expressed per square centimeter of capillary surface area the resultant filtration and permeability coefficients were similar for all three tissues. Permeability coefficients for sodium ranged from 33 × 10^?5 to 42 × 10^?5 cm sec^?1 and for inulin from 1.2 × 10^?5 to 1.9 × 10^?5 cm sec^?1. The filtration and diffusion coefficients per 100 g tissue were approximately 50 times greater in adult lung than muscle and 16 to 20 times greater in fetal lung than muscle. These differences were due to the greater length of junction (open along the capillary axis) per unit depth of junction in lung compared to muscle. The effective width of the junctions in all three tissues was similar.     

Autoradiographic Assessment of Blood Flow Heterogeneity in the Hamster Heart

Objective: Provide regional flow measurement in the hearts of small mammals using a new, higher-resolution technique based on the deposition of a molecular marker. Methods: We determined the instantaneous extraction and retention of the “molecular microsphere” radiolabeled desmethylimipramine in retrogradely perfused hamster hearts. In a separate series of experiments, autoradiography was used to measure regional myocardial deposition densities in hamster hearts of about 0.5 g with spatial area resolution of 16 × 16 μm. Results: Radiolabeled desmethylimipramine is almost 100% extracted during a single transcapillary passage and is retained in the tissue for many minutes. Autoradiographic images demonstrated a spatial flow heterogeneity with standard deviations of 31 ± 4% of the mean flow (N = 5) in 16 × 16 × 20-μm³ voxels. This is equivalent to the projections made using fractal relationships from cruder observations obtained with microspheres in the hearts of baboons, sheep, and rabbits. Conclusion: Autoradiography using a molecular deposition marker provides quantitative information on myocardial flow heterogeneities with resolution at the size of cardiac myocytes. Because the regions resolved are smaller than the volume of regions supplied by single arterioles, the results must slightly exaggerate the true heterogeneity of regional flows.     

Glucose utilization by edematous rat lungs

Edema was produced in the isolated perfused rat lung by raising left atrial pressure. Eleven control lungs consumed 18±3.9 µmoles glucose/lung · hr⁻¹ and released 17.1±4.2 µmoles lactate/lung · hr⁻¹. During pulmonary edema in 13 isolated perfused lungs, glucose consumption was 35.5±8.8 µmoles/lung · hr⁻¹ (P<.05) and lactate production was 37±5.9 µmoles/lung · hr⁻¹ (P<.05). Separation of radiolabeled glucose and lactate indicated that all lactate was derived from glucose in control and edematous lungs. We found no important difference in¹⁴CO₂ production from 1-¹⁴C, 6-¹⁴C, or¹⁴C(U)-glucose. Tissue slices of lungs made edematous in vivo had differences in glucose consumption and lactate production which were similar to those observed in the isolated lungs. Oxygen consumption by 1 mm thick lung slices was 224±9.7 µl O₂/mg DNA · hr⁻¹ in control and 218±18 µl O₂/mg DNA · hr⁻¹ in edematous lungs. When dinitrophenol was added to the medium, the QO₂ was greater in the control than in the edematous lung slices (391±22 µl O₂/mg DNA · hr⁻¹ control vs. 334±33 µl O₂/mg DNA · hr⁻¹ edema,P<.05). We concluded that pulmonary edema in the isolated rat lung is accompanied by: 1) greater glucose consumption; 2) greater lactate production; 3) no important difference in¹⁴CO₂ production from pentose pathway or tricarboxylic cycle activity; and 4) lower response of edematous tissue slices to dinitrophenol stimulation.     

Biochemical and metabolic properties of bovine type II pneumocytes in primary culture

Bovine type II pneumocytes were isolated from lungs of adult cattle by enzymatic tissue dissociation and subsequent purification by density gradient centrifugation on a 1.040 g/ml Percoll gradient. By quantitative and qualitative high-performance liquid chromatographic (HPLC) analysis of freshly isolated, highly purified bovine type II pneumocytes, six phospholipid components (phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin) were detected regularly and their composition was compared to that of whole lung homogenates. Total phospholipid content of 10⁶ bovine type II cells was 34.7 μg (quantitative HPLC). Suspended and adherent bovine type II cells incorporated [¹⁴C]choline into their phospholipids. The rate of synthesis of suspended cells (289 pmol/h×10⁶ cells) was constant for at least 4 h, while adherent type II cells incorporated [¹⁴C]choline with a constant rate of 160 pmol/h×10⁶ cells for at least 20 h. These data further establish the use of cultured bovine type II pneumocytes as a high-purity model for the in vitro investigation of the surfactant system.     

Mechanism of airway narrowing caused by inhaled platelet-activating factor. Role of airway microvascular leakage

In order to study the mechanism of airway narrowing after inhaled platelet-activating factor (PAF) we measured concomitant changes in lung resistance (RL) and in airway microvascular leakage in anesthetized guinea pigs. RL and its recovery after hyperinflation at 5 min were measured until 6 min after PAF aerosol (0.1, 0.3, 1, and 3 mM), and in the case of 3 mM PAF also until 10 min. Microvascular leakage in trachea, main bronchi, and proximal and distal intrapulmonary airways was determined by measurement of extravasated Evans blue dye content. For comparison, the responses to inhaled histamine (3 mM) and 5-hydroxytryptamine (5HT) (3 mM), which act directly on airway smooth muscle, were also examined. Inhaled PAF increased RL dose-dependently, with a maximal response (peak RL) at 4 min after the inhalation, whereas the response to histamine or 5HT was maximal within a few seconds after the inhalation. Peak RL (cm H2O/ml/s) was significantly less after PAF (1.03 +/- 0.09) than after histamine (8.39 +/- 1.07) or 5HT (18.3 +/- 6.48), although there was no significant difference in RL after hyperinflation (recovery RL). No additional increase in RL was seen between 5 and 10 min after exposure. PAF caused a dose-dependent increase in Evans blue dye extravasation; 3 mM PAF induced significantly higher leakage than did histamine or 5HT at all airway levels at 6 min. PAF did not cause any additional extravasation of Evans blue dye at 10 min compared with that at 6 min after exposure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of thromboxane A2 analogue on vascular resistance distribution and permeability in isolated blood-perfused dog lungs

This study was designed to determine the effects of thromboxane A₂ (TxA₂) on the distribution of vascular resistance, lung weight, and microvascular permeability in isolated dog lungs perfused at a constant pressure with autologous blood. The stable TxA₂ analogue (STA₂; 30 g, n = 5) caused an increase in pulmonary capillary pressure (Pc) assessed as double-occlusion pressure to 14.0 ± 0.4 mmHg from the baseline of 7.9 ± 0.3 mmHg with progressive lung weight gain. Pulmonary vascular resistance increased threefold exclusively due to pulmonary venoconstriction. Pulmonary venoconstriction was confirmed in lungs perfused in a reverse direction from the pulmonary vein to the artery (n = 5), as evidenced by marked precapillary vasoconstriction and a sustained lung weight loss. Furthermore, in lungs perfused at a constant blood flow (n = 5), STA₂ also caused selective pulmonary venoconstriction. Vascular permeability measured by the capillary filtration coefficient and the isogravimetric Pc at 30 and 60 min after STA₂ infusion did not change significantly from baseline in any lungs studied. Moreover, elevation of Pc by raising the venous reservoir of the intact lobes (n = 5) to the same level as the STA₂ lungs caused a greater or similar weight gain compared with the STA₂ lungs. Thus, we conclude that TxA₂ constricts selectively the pulmonary vein resulting in an increase in Pc and lung weight gain without significant changes in vascular permeability in isolated blood-perfused dog lungs. Offprint requests to: T. Shibamoto     

Effect of volatile anesthetics on endogenous tryptophan, 5-hydroxytryptophan and 5-hydroxytryptamine in rat lung

Volatile anesthetics inhibit the pulmonary inactivation of 5-hydroxytryptamine (5-HT) possibly via an effect on endogenous lung 5-HT. The consequent higher systemic arterial 5-HT concentrations may predispose the heart to dysrhythmias. The direct effect of the anesthetics on endogenous 5-HT, its metabolites, and precursors in the isolated ventilated perfused rat lung was determined by high-pressure liquid chromatography. Halothane (0.45, 1.4, and 2.3 minimum alveolar concentration (MAC)) and 35% nitrous oxide (N₂O) increased lung 5-HT (11, 70, 94, and 54% respectively). The effect of 0.45 MAC halothane and 35% N₂O on 5-HT was synergistic. Isoflurane (2.9 MAC) had no effect on lung 5-HT. The lung concentration of tryptophan (TRP) was increased 51% by 2.9 MAC isoflurane, but the rate of efflux of TRP from the lung was unchanged. There was no effect of the anesthetics on 5-hydroxytryptophan (5-HTP). The ratio of 5-HT: 5-HTP was significantly increased by 2.3 MAC halothane and 0.5 MAC halothane + 35% N₂O. The 5-HTP: TRP ratio was unchanged. The metabolite of 5-HT, 5-hydroxyindole acetic acid (5-HIAA), was not always detected. The results suggest that the increase in lung 5-HT by halothane reflects an increase in 5-HTP decarboxylase activity and that halothane and isoflurane exert selective effects on lung 5-HT synthesis. The results do not support the hypothesis that lung 5-HT controls the inactivation of 5-HT in the pulmonary circulation.     

Effects of streptozotocin-induced diabetes on calmodulin and cyclic AMP phosphodiesterase activity in rat lungs

Streptozotocin-induced diabetes caused a depression of rat lung tissue cyclic AMP-phosphodiesterase activity. This reduced activity was evident in both the 105,000×g particulate and supernatant fractions prepared from the tissue homogenates. Total calmodulin activity in the lungs from the diabetic rats was also reduced. Calmodulin and phosphodiesterase appeared to be translocated from the particulate to the supernatant fractions during the experimental diabetes. The presence of a heat-stable inhibitor of calmodulin-activated Ca²⁺-sensitive cyclic AMP-phosphodiesterase was evident in the rat lung and its activity was increased during diabetes. The data suggest that supression of the rat lung cyclic AMP-phosphodiesterase activity during experimental diabetes may result from changes in the subcellular distribution and concentration of the modulators of cyclic AMP-phosphodiesterase in rat lung.     

Canine lung uptake of plasma and platelet serotonin

Platelet-endothelial interaction and serotonin release were studied in 20 in vitro pump perfused lung lobes. Indicator dilution studies were performed in sequence using an injectate composed of indocyanine green and platelets labelled with either ¹⁴C-serotonin (¹⁴C-5-HT) or ⁵¹Cr. In control experiments all tracer transit times were equivalent (¹⁴C-5-HT, ⁵¹Cr and indocyanine green) without entrapment of the tracer or platelets by the system. In six lungs with normal pulmonary function platelet transit times were not prolonged and no platelet entrapment was observed. These lungs took up to 72% of the total ¹⁴C-5-HT contained in the injected platelets and plasma. The remaining 14 lobes showed variable degrees of pulmonary insufficiency such as elevated intrapulmonary shunt, low compliance and high vascular resistance; platelet entrapment was related to these phenomena (p 0.01). Six lobes were studied with ¹⁴C-5-HT, and despite entrapment of 22% of the injected platelets and transit time prolongations no 5-HT uptake was observed. The platelet-plasma ¹⁴C-5-HT ratio was higher in the effluent blood than in the injectate. The data suggest that in the pump perfused lung lobe with normal pulmonary function: (1) Serotonin released from platelets is rapidly taken up by the pulmonary circulation during a single transit through the lung lobe; (2) the serotonin uptake occurs without any observable prolongation of platelet time. In the pump perfused lung lobe with abnormal pulmonary function: (1) Serotonin released from the platelets is not taken up by the pulmonary circulation despite significant platelet entrapment; (2) the released serotonin is removed by the circulating platelets.     

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.     

Large and small airway responses to bronchoconstrictors in the guinea pig and ferret

In the isolated, perfused lung lobe of the ferret we evaluated the bronchoconstrictor response of its airways to methacholine and histamine, pharmacologic agents associated with the asthmatic state. The bronchus of excised lobes was cannulated and needle scarifications were made on the pleural surface to allow perfusate to exit. Lung airways were perfused at constant flow with equilibrated 95% O₂/5% CO₂, warmed Krebs-Ringers solution. Perfusion pressure was measured as a gauge of airway resistance. A concentration-dependent smooth muscle contraction of the ferret lung lobes was observed to methacholine and histamine. The ED₅₀’s of methacholine and histamine were 6.41 × 10^?6 M ± 1.38 × 10^?6 (SEM) and 2.39 × 10^?6 M ± 0.53 × 10^?6 (SEM), respectively. The maximum level of bronchoconstriction developed in the ferret (2.42 mmHg/ml/min ± 0.28 SEM (resistance units)) in response to methacholine, was six times greater than that found for histamine (0.42 mmHg/ml/min ± 0.05 SEM). Responses to both agonists were less pronounced in the ferret lung preparation than those in a similar lung preparation of guinea pig [17]. Compliance changes in both animals were also evaluated. The ferret did not demonstrate a compliance change in response to histamine as was seen for methacholine, suggesting that resistance changes precede compliance changes, or that the ferret airways are particularly resistant to histamine. Despite a lesser contractile response, the ferret has the advantage of a relatively large lung and long trachea that allow study in several preparations obtained from a single animal. It should prove a useful animal model for study of pulmonary pharmacology.     

Intrinsic 5-lipoxygenase activity is required for neutrophil responsivity.

We found that intrinsic neutrophil 5-lipoxygenase activity was necessary for human neutrophil adherence and chemotaxis in vitro and human neutrophil-mediated acute edematous injury in isolated perfused rat lungs given interleukin 8 intratracheally. Treatment with either Zileuton (a specific reversible competitive inhibitor of 5-lipoxygenase) or MK886 (a specific irreversible inhibitor of the 5-lipoxygenase activator protein) prevented stimulated neutrophil adherence and chemotaxis (but not superoxide anion production) in vitro. Zileuton- or MK886-inhibited neutrophil chemotaxis was not restored by adding leukotriene B4 in vitro. Perfusion with neutrophils and either Zileuton or MK886, or with MK886-pretreated neutrophils (without adding MK886 to the perfusate), also prevented lung injury (reflected by lung weight gain and lung Ficoll retention) and perfusate leukotriene B4 increases in isolated rat lungs given interleukin 8 intratracheally. Again, adding leukotriene B4 to the perfusate did not damage interleukin 8-treated isolated lungs perfused with Zileuton-inhibited neutrophils. We conclude that intrinsic 5-lipoxygenase activity is required for neutrophil adherence and chemotaxis and neutrophil-mediated lung injury.     

The effect of maternal diabetes on the synthesis and secretion of phosphatidylcholine in fetal and maternal rat lungs in vitro

Summary Incorporation of (methyl-¹⁴C)choline into phosphatidylcholine and the release of prelabelled phosphatidylcholine was investigated in vitro using lung slices from pregnant rats and their offspring near term. Tissue from normal, diabetic and insulin-treated diabetic pregnant rats and their offspring was utilized to assess the effects of maternal diabetes on fetal lung maturation. The results show that the synthesis of phosphatidylcholine in fetal/newborn lungs through the cytidine 5-diphosphocholine pathway was not affected by maternal diabetes. However, secretion of phosphatidylcholine from the lungs of fetuses of diabetic mothers was very much suppressed one day after parturition. Insulin treatment of the diabetic pregnant rats restored secretion of phosphatidylcholine from the fetal/newborn lungs to control values. These re sults suggest that an impaired secretion of phosphatidylcholine from the lungs of fetuses of diabetic mothers may be partly responsible for the higher incidence of respiratory distress syndrome among children of diabetic mothers. The results also revealed some correlation between the secretion of phosphatidylcholine from maternal lungs, maternal serum phospholipids and synthesis of phosphatidylcholine by fetal lungs during late gestation, suggesting a possible relationship between maternal phospholipid metabolism and fetal lung maturation.     

NS1619-Induced Vasodilation is Enhanced and Differentially Mediated in Chronically Hypoxic Lungs

Purpose

To identify the effect of the benzimidazalone derivative, NS1619, on modulating pulmonary vascular tone in lungs from rats exposed to normoxia (21 % FiO₂) or chronic hypoxia (10 % FiO₂) for three weeks.

Methods

Isolated perfused lungs were preconstricted (U46619), and dose-dependent vasodilation to NS1619 was assessed. To elucidate the mechanisms responsible, NS1619 vasodilatory responses were assessed following inhibition of large-conductance Ca²⁺-activated (BK_Ca; iberiotoxin and paxilline), L-type Ca²⁺ (nifedipine), K⁺ (tetraethylammonium), Cl^? (niflumic acid), and cation/TRP (lanthanum) channels, as well as nitric oxide synthase (L-NAME).

Results

Compared to normoxia, NS1619-induced vasodilation was significantly greater following hypoxia; however, NO-dependent vasodilation and BK_Ca-mediated vasodilation, in response to NS1619, were similar in the normoxic and hypoxic lungs. In contrast, direct activation of L-type Ca²⁺ and non-BK_Ca K⁺ channel was involved in the NS1619-induced vasodilation only in hypoxic lungs.

Conclusions

NS1619 causes pulmonary vasodilation by affecting multiple complementary pathways, including stimulation of NO production, activation of BK_Ca channels, other TEA-sensitive K⁺ channels, and L-type Ca²⁺ channels, and could be considered as a therapeutic agent in hypoxic PH.     

The perfused rat lung as a model for studies on the formation of surfactant and the effect of Ambroxol on this process

The isolated perfused rat lung was used as a model to investigate the synthesis of surfactant phospholipids from various radioactive precursors and the effect of Ambroxol, a bronchial secretolyticum, on this process. Lungs were ventilated and perfused for periods up to 5 h without detectable development of pulmonary edema. The lungs remained metabolically stable during the entire period of perfusion. Both in whole lung tissue and in the surfactant fraction the radioactive substrates incorporated predominantly into phosphatidylcholine and phosphatidylglycerol. The degree of saturation of labelled phosphatidylcholines synthesized during perfusion with [Me-¹⁴C]choline, D [U-¹⁴C]glucose, [1(3)-³H]glycerol and [1-¹⁴C]palmitate was higher in surfactant than in whole lung tissue. A delayed incorporation into surfactant phospholipids was observed for all precursors. Under the conditions employed, glucose carbon was recovered mainly in the glycerol backbone of phosphatidylcholine and phosphatidylglycerol. Compared to glucose, glycerol appeared to be a minor substrate for lung lipid formation. If the lungs were perfused after pretreatment of the rats with Ambroxol on three consecutive days, the incorporation of labelled choline and glycerol into pulmonary phospholipids was found to be enhanced. This stimulation was more pronounced in the surfactant fraction than in whole lung tissue. The stimulatory effect on the formation of surfactant lipids was smaller after pretreatment of the animals with Ambroxol for one day. The results of the present study suggest that Ambroxol may specifically stimulate the synthesis of phospholipids in the alveolar type II cells and that the drug may not only affect the formation but also the secretion of surfactant lipids by these cells.