Studies of the mechanisms involved in the fate of prostacyclin (PGI2) and 06-keto-PGF1α in the pulmonary circulation

We have investigated the metabolism of [3]H-prostaglandin (PG)I₂ and its non-enzymatic breakdown product [3]H-6-keto-PGF_1α by rat pulmonary tissue and their possible uptake and metabolism upon passage through the isolated perfused rat lung. When incubated with rat lung homogenate in the presence of β-NAD, [3]H-PGI₂ was extensively degraded into at least one metabolite, while [3]H-6-keto-PGF_1α was only minimally metabolized. However, on passage through isolated perfused rat lungs, neither [3]H-PGI₂ nor [3]H-6-keto-PGF_1α were removed from the circulation into the lung or degraded. This demonstration that PGI₂ is not a substrate for the transport system for the removal of PGs from the circulation into the lung further illustrates that this system is a critical determinant for the pulmonary inactivation of circulating prostaglandins. The experimental findings are discussed in reference to the structure-activity requirements necessary for pulmonary transport and subsequent metabolism.     

Distribution of cyclooxygenase products with cyclooxygenase inhibition in isolated dog lung

Arachidonic acid metabolism can lead to synthesis of cyclooxygenase products in the lung as indicated by measurement of such products in the perfusate of isolated lungs perfused with a salt solution. However, a reduction in levels of cyclooxygenase products in the perfusate may not accurately reflect the inhibition of levels of such products as measured in lung parenchyma. We infused sodium arachidonate into the pulmonary circulation of isolated dog lungs perfused with a salt solution and measured parenchymal, as well as perfusate, levels of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), and thromboxane B2 (TxB2). These studies were repeated with indomethacin (a cyclooxygenase enzyme inhibitor) in the perfusate. We found that indomethacin leads to a marked reduction in perfusate levels of PGF2 alpha, PGE2, 6-keto-PGF1 alpha, and TxB2, as well as a marked reduction in parenchymal levels of 6-keto-PGF1 alpha and TxB2 when parenchymal levels of PGF2 alpha and PGE2 are not reduced. We conclude that, with some cyclooxygenase products, a reduction in levels of these products in the perfusate of isolated lungs may not indicate inhibition of levels of these products in the lung parenchyma and that a reduction in one parenchymal product may not predict the reduction of other parenchymal products. It can be speculated that some of the physiological actions of indomethacin in isolated lungs may result from incomplete or selective inhibition of synthesis of pulmonary cyclooxygenase products.     

Dipyridamole interferes with the incorporation of arachidonic acid and stimulates prostacyclin production in rat lungs

Following the injection of 4 nmol of 14C-arachidonic acid into the pulmonary circulation of rat isolated lungs more than 90% of the radioactivity was retained by the lung tissue. When dipyridamole (20 microM) was infused into the pulmonary circulation during 14C-arachidonate injection the amount of radiolabel was increased in diacylglycerols as well as in phosphatidylinositol and phosphatidylserine of the perfused lungs whereas the amount of radioactivity was decreased in phosphatidylethanolamine. When dipyridamole was infused into the lungs prelabelled with 14C-arachidonic acid the distribution of radiolabel in different lung lipid fractions was not changed significantly. However, dipyridamole seemed to stimulate the formation of prostacyclin in rat lungs as the amount of 6-keto-PGF1 alpha was increased in the perfusion effluent. The present study indicates that dipyridamole interferes with the incorporation of arachidonic acid into different lipids in rat lungs. In addition, the release of prostacyclin seems to be stimulated by dipyridamole.     

Effects of arachidonic acid and prostaglandin F2 alpha in isolated rat lungs

Isolated rat lungs were ventilated and perfused by saline-Ficoll perfusate at a constant flow. The baseline perfusion pressure (PAP) correlated with the concentration of 6-keto-PGF1 alpha the stable metabolite of PGI2 (r = 0.83) and with the 6-keto-PGF1 alpha/TXB2 ratio (r = 0.82). A bolus of 10 micrograms exogenous arachidonic acid (AA) injected into the arterial cannula of the isolated lungs caused significant decrease in pulmonary vascular resistance (PVR) which was followed by a progressive increase of PVR and edema formation. Changes in perfusion pressure induced by AA injection also correlated with concentrations of the stable metabolites (6-keto-PGF1 alpha: r = -0.77, TxB2: -0.76), and their ratio: (6-keto-PGF1 alpha/TXB2: r = -0.73). Injection of 10 and 100 micrograms of PGF2 alpha into the pulmonary artery stimulated the dose-dependent production of TXB2 and 6-keto-PGF1 alpha. No significant correlations were found between the perfusion pressure (PAP) which was increased by the PGF2 alpha and the concentrations of the former stable metabolites. The results show that AA has a biphasic effect on the isolated lung vasculature even in low dose. The most potent vasoactive metabolites of cyclooxygenase, prostacyclin and thromboxane A2 influence substantially not only the basal but also the increased tone of the pulmonary vessels.     

Adenosine transport by the lung

Adenosine, a nucleoside and potent vasodilator, has been found to be taken up by the lung and converted by deamination into inosine and hypoxanthine. In a single circulation through an isolated rat lung, 69.3 +/- 3.3% of infused [14C]adenosine (10 microM) was removed from the circulation. Uptake of [14C]adenosine remained unchanged when deamination of adenosine was inhibited by 8-azaguanine or coformycin. In a single passage of adenosine through the pulmonary artery, very little of the deaminated products appeared in the pulmonary circulation, but when adenosine was recirculated through the pulmonary circulation inosine and hypoxanthine appeared in the venous effluent. These adenosine metabolites were also taken up by the lung. A major portion of the circulating adenosine was transported into the lung, where it was used to synthesize adenine nucleotides. Inhibition of adenosine kinase by iodotubercidin resulted in reduced formation of ATP and ADP. Uptake of adenosine by the lung was saturable on a concentration gradient and was a passive process because it was not affected by the absence of glucose or the presence of ouabain. Km and Vmax for adenosine transport were 0.227 mM and 4.6 mumol.min-1.g lung-1, respectively. Adenosine transport was inhibited by adenosine analogues, and the inhibitions were found to be competitive in nature. These results suggest that a specific and rate-limiting transport system exists in the lung for adenosine.     

Leukotriene E4 causes pulmonary vasoconstriction, not inhibited by meclofenamate

Leukotriene E4 (LTE4) appears to be a rather stable product of the lipoxygenase pathway. Its action in the pulmonary circulation is unknown. Therefore we investigated its effect on the circulation of isolated rat lungs perfused with a cell- and plasma-free solution. Synthetic LTE4 in doses from .15 micrograms to 5 micrograms/.25 ml .9% NaCl injected as a bolus in the pulmonary artery during normoxia caused a fast, transient perfusion pressure increase within seconds. This was followed by a slow rise in baseline perfusion pressure (normoxia) over 25 min. In addition, 5 micrograms LTE4 caused edematogenic lung damage. Injection of 1.5 micrograms LTE4 during hypoxic vasoconstriction caused fast, transient pressure rises, similar to normoxic conditions. 6-keto-PGF1 alpha and TXB2 were measured in the lung effluent before and after LTE4 injection. Neither 6-keto-PGF1 alpha nor TXB2 production changed after LTE4 injection. Meclofenamate (.5 micrograms/ml) increased the fast, transient and the slow, sustained pressure rise. We conclude that LTE4 caused direct pulmonary vasoconstriction unrelated to cyclooxygenase products.     

Prostaglandin removal and metabolism by isolated perfused rat lung

We have investigated the mechanism(s) involved in the removal of prostaglandins (PG) from the pulmonary circulation by the lung. Unidirectional fluxes of PG from the circulation into the lung are measured in an isolated perfused rat lung preparation. Evidence is presented which suggests that a transport system for PG exists in lung tissue. This transport system is responsible for the removal of some PG from the circulation by the lung. PGE₁ and PGF_2α are substrates for this system, whereas PGB₁, PGA₁, and 15-keto-PGF_2α are not. Since PGA₁ is a substrate for the intracellular PG dehydrogenase, the selectivity of the lung's metabolism system for circulating PG is probably due to the selectivity of the transport system for PG. It is shown that the percentage of the pulmonary arterial concentration (C_A) of PGE₁ or PGF_2α that is metabolized on passage through the pulmonary circulation decreases rapidly as C_A increases. When the lungs were perfused with PGE₁ (PGF_2α), the metabolites detected in the venous effluent were 15-keto-PGE₁ (PGF_2α) and 15-keto-13,14-dihydro-PGE₁ (PGF_2α). The time course pattern of the appearance of metabolites in the venous effluent after the initiation of a constant C_A, and the relative concentrations of the metabolites in the venous effluent, were examined as a function of C_A.     

Bronchial circulation and cyclooxygenase products in acute lung injury

The role of cyclooxygenase products in the response of the bronchial circulation to acute lung injury was examined in 30 dogs. By use of an open-chest preparation the left lower lobe (LLL) pulmonary circulation was isolated, continuously weighed, and perfused in situ. The anastomotic bronchial blood flow [Qbr(s-p)] was measured as the rate of increase in the volume of the LLL-perfusion circuit. Four groups of dogs were studied. In group A, six dogs received cyclooxygenase inhibition (COI) with either indomethacin (2 mg/kg) or ibuprofen (10 mg/kg). In group B (n = 10) lung injury caused by airway instillation of glucose (15 mg) with glucose oxidase (500 micrograms/kg) (G/GO) or LLL pulmonary arterial infusion of alpha-napthyl thiourea (ANTU, 2 mg/kg). Group C (n = 10) received COI, and 30 min later injury was induced as above with either ANTU or G/GO. Group D (n = 4) received COI immediately after anesthesia; then, 30 min after completion of the surgical preparation, injury was induced with ANTU or G/GO. After COI, Qbr(s-p) decreased to 35 +/- 9% of the basal values (P less than 0.05). After administration of ANTU or G/GO, Qbr(s-p) increased irrespective of whether COI was present. 6-Ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TxB2) were measured by radioimmunoassay in the LLL pulmonary artery and systemic venous blood, demonstrating an increase in 6-keto-PGF1 alpha due to surgical preparation and confirming complete COI in those animals receiving COI immediately after anesthesia. These findings demonstrate that 1) the bronchial circulation is capable of a sevenfold increase in flow in response to acute lung injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential uptake of endothelin-1 by the coronary and pulmonary circulations.

Substantial removal of the vasoconstrictor peptide endothelin-1 (ET-1) by the pulmonary circulation has been reported to occur in perfused guinea pig and rat lungs. We examined the uptake of ET-1 by coronary and pulmonary circulations of the rabbit by measuring single-pass extraction of ET-1 in the isolated heart and lung. In separate experiments, each organ was perfused at 30 ml/min with Krebs-albumin (3%) solution. A bolus of 125I-ET-1 and [14C]dextran in 0.3 ml Krebs-albumin solution was injected, and extraction of endothelin (EET), relative to that of an intravascular reference indicator, [14C]dextran, was determined by multiple indicator-dilution technique. EET was 5 +/- 2% (SE) in the heart and 49 +/- 4% in the lung. Increasing flow rate in the lung preparation to approximate the mean transit time in the heart preparation did not significantly alter EET. Despite insignificant uptake of ET-1, the coronary circulation extracted an angiotensin-converting enzyme inhibitor (351A) and metabolized a synthetic angiotensin-converting enzyme substrate (benzoyl-phenyl-alanyl-proline), both properties of the normal pulmonary circulation. We therefore conclude that there is no significant ET-1 uptake in the coronary vascular bed.     

Prostaglandin profiles in nervous tissue and blood vessels of the brain of various animals

The endogenous formation of prostaglandin (PG) D2, E2, F2 alpha, and 6-keto-PGF1 alpha was determined in homogenates of mouse, rat, and rabbit brain, and of rat cerebral blood vessels, using gas chromatography mass spectrometry. In all species tested, 6-keto-PGF1 alpha could be identified in the brain homogenates, but was a minor component in relation to other PGs. In contrast 6-keto-PGF1 alpha was the most abundant PG in the blood vessels, being present in about 40-fold higher levels than in the brain tissue. PGD2 was the most abundant PG in rat and mouse brains, but was below detection limits in the analyzed blood vessels. These studies indicating differential metabolism of PG endoperoxides in nervous and vascular tissue, provide a biochemical basis for further studies on the role of the PGs in brain circulation and neuronal activity.     

Acetylcholine induces vasodilation and prostacyclin synthesis in rat lungs

Acetylcholine causes pulmonary vasodilation, but its mechanism of action is unclear. We hypothesized that acetylcholine-induced pulmonary vasodilation might be associated with prostacyclin formation. Therefore, we used isolated rat lungs perfused with a recirculating cell- and plasma-free physiological salt solution to study the effect of acetylcholine infusion on pulmonary perfusion pressure, vascular responsiveness and lung prostacyclin production. Acetylcholine (20 micrograms infused over 1 minute) caused immediate vasodilation during ongoing hypoxic vasoconstriction and prolonged depression of subsequent hypoxic and angiotensin II-induced vasoconstrictions. Both effects of acetylcholine were abolished by atropine pretreatment. The prolonged acetylcholine effect, but not the immediate response, was blocked by meclofenamate, an inhibitor of cyclooxygenase. The prolonged effect, but not the immediate response, of acetylcholine was associated with an increase in perfusate 6-keto-PGF1 alpha concentration. The acetylcholine stimulated increase in 6-keto-PGF1 alpha production was inhibited by meclofenamate and by atropine. Thus, blockade of prostacyclin production corresponded with blockade of the prolonged acetylcholine effect. In conclusion, acetylcholine caused in isolated rat lungs an immediate vasodilation and a prolonged, time-dependent depression of vascular responsiveness. Whereas both acetylcholine effects were under muscarinic receptor control, only the prolonged effect depended on the cyclooxygenase pathway and, presumably, prostacyclin synthesis.     

The effect of hypoxia on rat splanchnic prostanoid output

The effect of hypoxia on isolated perfused rat mesenteric basal venous prostanoid output was studied. Male rat splanchnic vasculature was removed without (SV) or with its end organ (SV + SI) and perfused with Krebs' buffer with a pO2 of 460 or 60 mm torr. Basal splanchnic venous effluent was assayed for 6-keto-PGF1 alpha, TxB2 and PGE by radioimmunoassay at 30, 60, 120 and 180 min of perfusion. Basal output of SV 6-keto-PGF1 alpha was five and ten fold higher than for PGE and TxB2 respectively and comprised 36% or greater of SV + SI 6-keto-PGF1 alpha output. SV PGE and TxB2 output comprised less than 19 and 12% respectively of SV + SI output. Hypoxia decreased SV + SI PG output, 6-keto-PGF1 alpha being most affected. Hypoxia did not alter SV 6-keto-PGF1 alpha output indicating the SI as the anatomic location most influenced by hypoxia. The relative amounts of distribution of PGE or TxB2 output were not altered by hypoxia. These data suggest that there are two distinct areas of splanchnic prostanoid output, the SV and the SI. Decreased 6-keto-PGF1 alpha output might alter splanchnic blood flow at two levels, the splanchnic vasculature, and/or within the bowel wall.     

Sites of uptake of3H-5-hydroxytryptamine in rat isolated lung

Summary The localisation of radioactivity in rat lungs after perfusion of³H-5-hydroxytryptamine (5-HT) was studied by autoradiography. Rat isolated lungs, perfused with Krebs bicarbonate solution, via the pulmonary circulation, were rapidly frozen after the infusion of³H-5-HT. All subsequent handling was carried out at −30 to −40°C. Developed sections were examined by the light microscope and showed that radioactivity was concentrated around the alveoli with little or no label in other parts of the lung. Lungs perfused with³H-5-HT in the presence of mebanazine, a monoamine oxidase inhibitor, showed label in the endothelial cells of arteries and arterioles as well as the alveolar label. Lungs treated with amitriptyline were essentially devoid of label. These results indicate that the site of the avid uptake and metabolism of 5-HT in the lung is the endothelial cells of the vasculature.     

ADPase activity of isolated perfused rat lung.

More than 90% of 3H-ADP was metabolized following bolus injection into rat isolated perfused lungs. The major metabolite was inosine, with lesser amounts of adenosine and AMP. The mean pulmonary transit time for the radioactivity associated with ADP and its metabolites was the same as that for the vascular marker 14C-dextran, indicating that ADP is metabolized by enzymes in the pulmonary vessel walls. The metabolism of 3H-ADP was apparently unaffected by the simultaneous injection of prostacyclin or by continuous infusion of indomethacin or aspirin. 3H-ADP was similarly metabolized by the lung following continuous infusion, although relatively higher amounts of adenosine were observed. The metabolism of ADP by the lung represents biological inactivation since over 95% of the platelet-aggregatory activity of ADP was lost on passage through the lung.     

Altered responses to modulators of guanine nucleotide binding protein activity in endotoxin tolerance

The effects of cholera toxin or pertussis toxin and nonhydrolyzable GTP analogs on Salmonella enteritidis endotoxin stimulation of iTxB2 and i6-keto-PGF1 alpha synthesis in control and endotoxin tolerant rat peritoneal macrophages were determined. Pretreatment with pertussis toxin alone had no effect on basal macrophage iTxB2 or i6-keto-PGF1 alpha production, but pertussis toxin (0.1, 1.0 and 10 ng/ml) significantly inhibited endotoxin-stimulated iTxB2 and i6-keto-PGF1 alpha synthesis. Pretreatment with cholera toxin, which did not affect basal iTxB2 or i6-keto-PGF1 alpha synthesis, significantly enhanced endotoxin-induced synthesis of iTxB2 and i6-keto-PGF1 alpha. The effects of pertussis and cholera toxin with or without endotoxin were significantly (P less than 0.05) less in macrophages from endotoxin tolerant rats compared to control macrophages. GTP[gamma-S] (100 microM) significantly increased iTxB2 synthesis and significantly augmented endotoxin-stimulated iTxB2 synthesis in control macrophages (P less than 0.05). However, in macrophages from endotoxin tolerant rats the effect of GTP[gamma-S] on iTxB2 synthesis was significantly less (P less than 0.05) compared to control macrophages. Collectively, these data suggest that: (1) guanine nucleotide binding regulatory proteins mediate endotoxin-stimulated arachidonic acid metabolism in rat peritoneal macrophages; and (2) endotoxin tolerance induces alterations in guanine nucleotide binding protein activity.     

Basal prostaglandin synthesis by the isolated perfused rat kidney

In order to assess the main characteristics of the prostaglandin (PG) biosynthesis by the isolated perfused rat kidney, the urinary and venous outputs of PGE2, PGF2alpha, 6-keto-PGF1alpha and of thromboxane (Tx)B2 were followed during 120 min after an equilibration period of 30 min. Single pass kidneys were perfused with a Krebs-Henseleit solution added with Polygeline at a constant flow rate providing a perfusion pressure about 90 mm Hg. From the beginning of the study, major differences could be observed in the renal biosynthetic rate of the 4 PG studied which were mainly excreted into the venous effluent. During the perfusion, urinary and venous outputs of PGE2, PGF2alpha and of TxB2 remained stable whereas those of 6-keto-PGF1alpha sharply increased and were found inversely related to the glomerular filtration rate (r = -0.95; p n 0.001). Finally, the urinary and venous outputs of each of the four PGs studied were found positively related. It is concluded that the isolated perfused rat kidney is a valuable preparation for studying the biosynthesis of PGs and that, at least in thi model, the urinary excretion of PGs is a good index of their renal synthesis.     

Effect of insulin, prostaglandin E1 and uptake inhibitors on glucose transport in the perfused guinea-pig placenta

The effects of insulin, prostaglandin E1 (PGE1) and uptake inhibitors on unidirectional D-glucose influx at brush border (maternal) and basal (fetal) sides of the guinea-pig syncytotrophoblast were investigated in the intact, perfused guinea-pig placenta by rapid, paired-tracer dilution. Experiments were performed in either an in situ preparation artificially perfused through the umbilical vessels (intact maternal circulation) or in the fully isolated dually-perfused placenta in which both interfaces were studied simultaneously. Kinetic characterization of unidirectional D-glucose influx gave apparent Km values (mean +/- SEM) at maternal and fetal sides of 70 +/- 6 and 87 +/- 16 mM respectively; corresponding Vmax values were 53 +/- 3 and 82 +/- 6 mumol min-1g-1. At the fetal side (singly-perfused placenta) cytochalasin B (50 microM), ethylidene-D-glucose (100 mM) and PGE1 (1 microM) partially inhibited D-glucose uptake whereas cortisol (50 microM) and progesterone (100 microM) had no effect. Abolition of the sodium gradient across the fetal interface did not modulate the kinetics of influx. In the presence of 150 mu units ml-1 insulin (dually-perfused placenta), unidirectional uptake into the trophoblast and transplacental D-[3H]glucose transfer were unaltered. In contrast, prostaglandin E1 (1 microM) markedly reduced the Km and Vmax for D-glucose at both interfaces and the inhibitory effect was reflected in a reduction in specific transplacental D-glucose transfer. Further experiments showed that the isolated placenta releases prostaglandins (PGE; PGF2 alpha) into both circulations. Bilateral insulin perfusion did not affect either lactate release by the placenta or rapid metabolism of D-[14C]glucose to [3H]lactate (usually less than 10% effluent [14C]lactate in 5 min). An asymmetric degradation of exogenous insulin was observed in the dually-perfused placenta: uterine venous samples contained 24 +/- 7 microunits ml-1 immunoreactive insulin when compared to the arterial concentration (151 +/- 3 microU ml-1 perfusate) while no change was measureable in the fetal circulation within the same time period (152 +/- 5 microU ml-1). This asymmetry was confirmed in experiments employing [125I]insulin. These results demonstrate that glucose transport in the intact guinea-pig placenta occurs by a sodium-independent, cytochalasin B-inhibitable system which is insulin-insensitive. Prostaglandin E1 appeared to be a potent transport inhibitor which suggests that prostaglandins may be involved in the 'down' regulation of placental glucose transport in vivo.     

Inhibition of pulmonary prostaglandin metabolism by exposure of animals to oxygen or nitrogen dioxide.

The effects of exposure of animals to 100% O2 and NO2 on the rate of prostaglandin metabolism by lung and kidney were studied in vitro. Exposure of guinea pigs to 100% O2 for 48 h inhibited the metabolism of prostaglandin F2 alpha by both NAD+- and NADP+-dependent prostaglandin dehydrogenase in lung, but had no effect on the metabolism in kidney. Succinate dehydrogenase, but not glucose 6-phosphate dehydrogenase, in guinea-pig lung was inhibited by exposure to 100% O2. Exposure to 46 p.p.m. but not 16 or 29 p.p.m. NO2 for 6 h inhibited guinea-pig lung prostaglandin dehydrogenase in vitro. The inhibition of pulmonary prostaglandin dehydrogenase by exposure to 100% O2 or to 49 p.p.m. NO2 was dependent on the duration of exposure, but returned to control values within 7 days after cessation of the exposure. The pulmonary transport system responsible for removing circulating prostaglandins from the blood was not affected by exposure to 100% O2 as measured by using the isolated perfused lung. Kinetic analysis of the inhibition of pulmonary prostaglandin dehydrogenase activity in guinea pig exposed to 100% O2 showed non-competitive inhibition with respect to both prostaglandin F2 alpha and NAD+, which suggests destruction or inactivation of the enzyme. Pulmonary prostaglandin dehydrogenase appears to be inhibited by exposure to oxidant gases, which may lead to elevated prostaglandin concentrations in the lungs or in the systemic circulation.     

Regulation of increase in anastomotic blood flow following pulmonary arterial occlusion

We have previously shown that there is an acute increase in anastomotic bronchial blood flow (Qbr) after pulmonary arterial obstruction in dogs. We examined the role of arachidonic acid metabolites in mediating this increase. The left lower lobe (LLL) was isolated and perfused (zone 2) with autologous blood in open-chested anesthetized dogs (n = 19). Qbr was measured from the amount of blood that overflowed from the closed vascular circuit of the suspended LLL and changes in its weight. In the control animals, there was a prompt and significant increase in Qbr following pulmonary arterial obstruction. Pretreatment with indomethacin (n = 6) or sodium salicylate (n = 4) almost completely blocked this rise in Qbr. Following pulmonary arterial occlusion, there was a rise in both thromboxane and a prostacyclin metabolite (6-keto-PGF1 alpha) in the blood of the pulmonary circulation of the LLL, although the 6-keto-PGF1 alpha rose relatively more. Pretreatment with indomethacin caused a fall in both thromboxane and prostacyclin levels (n = 3), which no longer rose after pulmonary arterial occlusion. These findings suggested that the balance of the vasodilator (prostacyclin) and vasoconstrictor (thromboxane) prostaglandins may play an important role in mediating the rise in Qbr that follows pulmonary arterial obstruction.     

Coenzyme Q(1) as a probe for mitochondrial complex I activity in the intact perfused hyperoxia-exposed wild-type and Nqo1-null mouse lung

Previous studies showed that coenzyme Q(1) (CoQ(1)) reduction on passage through the rat pulmonary circulation was catalyzed by NAD(P)H:quinone oxidoreductase 1 (NQO1) and mitochondrial complex I, but that NQO1 genotype was not a factor in CoQ(1) reduction on passage through the mouse lung. The aim of the present study was to evaluate the complex I contribution to CoQ(1) reduction in the isolated perfused wild-type (NQO1(+/+)) and Nqo1-null (NQO1(-)/(-)) mouse lung. CoQ(1) reduction was measured as the steady-state pulmonary venous CoQ(1) hydroquinone (CoQ(1)H(2)) efflux rate during infusion of CoQ(1) into the pulmonary arterial inflow. CoQ(1)H(2) efflux rates during infusion of 50 μM CoQ(1) were not significantly different for NQO1(+/+) and NQO1(-/-) lungs (0.80 ± 0.03 and 0.68 ± 0.07 μmol·min(-1)·g lung dry wt(-1), respectively, P > 0.05). The mitochondrial complex I inhibitor rotenone depressed CoQ(1)H(2) efflux rates for both genotypes (0.19 ± 0.08 and 0.08 ± 0.04 μmol·min(-1)·g lung dry wt(-1) for NQO1(+/+) and NQO1(-/-), respectively, P < 0.05). Exposure of mice to 100% O(2) for 48 h also depressed CoQ(1)H(2) efflux rates in NQO1(+/+) and NQO1(-/-) lungs (0.43 ± 0.03 and 0.11 ± 0.04 μmol·min(-1)·g lung dry wt(-1), respectively, P < 0.05 by ANOVA). The impact of rotenone or hyperoxia on CoQ(1) redox metabolism could not be attributed to effects on lung wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total venous effluent CoQ(1) recoveries, the latter measured by spectrophotometry or mass spectrometry. Complex I activity in mitochondria-enriched lung fractions was depressed in hyperoxia-exposed lungs for both genotypes. This study provides new evidence for the potential utility of CoQ(1) as a nondestructive indicator of the impact of pharmacological or pathological exposures on complex I activity in the intact perfused mouse lung.