The role of natriuretic peptide receptor-A signaling in unilateral lung ischemia-reperfusion injury in the intact mouse

Ischemia-reperfusion (IR) causes human lung injury in association with the release of atrial and brain natriuretic peptides (ANP and BNP), but the role of ANP/BNP in IR lung injury is unknown. ANP and BNP bind to natriuretic peptide receptor-A (NPR-A) generating cGMP and to NPR-C, a clearance receptor that can decrease intracellular cAMP. To determine the role of NPR-A signaling in IR lung injury, we administered the NPR-A blocker anantin in an in vivo SWR mouse preparation of unilateral lung IR. With uninterrupted ventilation, the left pulmonary artery was occluded for 30 min and then reperfused for 60 or 150 min. Anantin administration decreased IR-induced Evans blue dye extravasation and wet weight in the reperfused left lung, suggesting an injurious role for NPR-A signaling in lung IR. In isolated mouse lungs, exogenous ANP (2.5 nM) added to the perfusate significantly increased the filtration coefficient sevenfold only if lungs were subjected to IR. This effect of ANP was also blocked by anantin. Unilateral in vivo IR increased endogenous plasma ANP, lung cGMP concentration, and lung protein kinase G (PKG(I)) activation. Anantin enhanced plasma ANP concentrations and attenuated the increase in cGMP and PKG(I) activation but had no effect on lung cAMP. These data suggest that lung IR triggered ANP release and altered endothelial signaling so that NPR-A activation caused increased pulmonary endothelial permeability.     

PAF potentiates protamine-induced lung edema: role of pulmonary venoconstriction

We studied the synergistic interaction between platelet-activating factor (PAF) and protamine sulfate, a cationic protein that causes pulmonary endothelial injury, in isolated rat lungs perfused with a physiological salt solution. A low dose of protamine (50 micrograms/ml) increased pulmonary artery perfusion pressure (Ppa) but did not increase wet lung-to-body weight ratio after 20 min. Pretreatment of the lungs with a noninjurious dose of PAF (1.6 nM) 10 min before protamine markedly potentiated protamine-induced pulmonary vasoconstriction and resulted in severe lung edema and increased lung tissue content of 6-keto-prostaglandin F1 alpha, thromboxane B2, and leukotriene C4. Pulmonary microvascular pressure (Pmv), measured by double occlusion, was markedly increased in lungs given PAF and protamine. These potentiating effects of PAF were blocked by WEB 2086 (10(-5) M), a specific PAF receptor antagonist. Pretreatment of the lungs with a high dose of histamine (10(-4) M) failed to enhance the effect of protamine on Ppa, Pmv, or wet lung-to-body weight ratio. Furthermore, PAF pretreatment enhanced elastase-, but not H2O2-, induced lung edema. To assess the role of hydrostatic pressure in edema formation, we compared lung permeability-surface area products (PS) in papaverine-treated lungs given either protamine alone or PAF + protamine and tested the effect of mechanical elevation of Pmv on protamine-induced lung edema. In the absence of vasoconstriction, PAF did not potentiate protamine-induced increase in lung PS. On the other hand, mechanically raising Pmv in protamine-treated lungs to a level similar to that measured in lungs given PAF + protamine did not result in a comparable degree of lung edema. We conclude that PAF potentiates protamine-induced lung edema predominantly by enhanced pulmonary venoconstriction. However, a pressure-independent effect of PAF on lung vasculature cannot be entirely excluded.     

Spontaneous injury in isolated sheep lungs: role of perfusate leukocytes and platelets

Perfusion of isolated sheep lungs with blood causes spontaneous edema and hypertension preceded by decreases in perfusate concentrations of leukocytes (WBC) and platelets (PLT). To determine whether these decreases were caused by pulmonary sequestration, we continuously measured blood flow and collected pulmonary arterial and left atrial blood for cell concentration measurements in six lungs early in perfusion. Significant sequestration occurred in the lung, but not in the extracorporeal circuit. To determine the contribution of these cells to spontaneous injury in this model, lungs perfused in situ with a constant flow (100 ml.kg-1.min-1) of homologous leukopenic (WBC = 540 mm-3, n = 8) or thrombocytopenic blood (PLT = 10,000 mm-3, n = 6) were compared with control lungs perfused with untreated homologous blood (WBC = 5,320, PLT = 422,000, n = 8). Perfusion of control lungs caused a rapid fall in WBC and PLT followed by transient increases in pulmonary arterial pressure, lung lymph flow, and perfusate concentrations of 6-ketoprostaglandin F1 alpha and thromboxane B2. The negative value of reservoir weight (delta W) was measured as an index of fluid entry into the lung extravascular space during perfusion. delta W increased rapidly for 60 min and then more gradually to 242 g at 180 min. This was accompanied by a rise in the lymph-to-plasma oncotic pressure ratio (pi L/pi P). Relative to control, leukopenic perfusion decreased the ratio of wet weight to dry weight, the intra- plus extravascular blood weight, and the incidence of bloody lymph. Thrombocytopenic perfusion increased lung lymph flow and the rate of delta W, decreased pi L/pi P and perfusate thromboxane B2, and delayed the peak pulmonary arterial pressure. These results suggest that perfusate leukocytes sequestered in the lung and contributed to hemorrhage but were not necessary for hypertension and edema. Platelets were an important source of thromboxane but protected against edema by an unknown mechanism.     

Pulmonary microvascular response to LTB4: effects of perfusate composition

We examined the effects of leukotriene B4 (LTB4) on pulmonary hemodynamics and vascular permeability using isolated perfused guinea pig lungs and cultured monolayers of pulmonary arterial endothelial cells. In lungs perfused with Ringer solution, containing 0.5 g/100 ml albumin (R-alb), LTB4 (4 micrograms) transiently increased pulmonary arterial pressure (Ppa) and capillary pressure (Pcap). Pulmonary edema developed within 70 min after LTB4 injection despite a normal Pcap. The LTB4 metabolite, 20-COOH-LTB4 (4 micrograms), did not induce hemodynamic and lung weight changes. In lungs perfused with autologous blood hematocrit = 12 +/- 1%; protein concentration = 1.5 +/- 0.2 g/100 ml), the increases in Ppa and Pcap were greater, and both pressures remained elevated. The lung weight did not increase in blood-perfused lungs. In lungs perfused with R-alb (1.5 g/100 ml albumin) to match the blood perfusate protein concentration, LTB4 induced similar hemodynamic changes as R-alb (0.5 g/100 ml) perfusate, but the additional albumin prevented the pulmonary edema. LTB4 (10(-11)-10(-6) M) with or without the addition of neutrophils to the monolayer did not increase endothelial 125I-albumin permeability. Therefore LTB4 induces pulmonary edema when the perfusate contains a low albumin concentration, but increasing the albumin concentration or adding blood cells prevents the edema. The edema is not due to increased endothelial permeability to protein and is independent of hemodynamic alterations. Protection at higher protein-concentration may be the result of LTB4 binding to albumin.     

Edema from cyclooxygenase products of endogenous arachidonic acid in isolated lung

We infused A23187, a calcium ionophore, into the pulmonary circulation of dextran-salt-perfused isolated rabbit lungs to release endogenous arachidonic acid. This led to elevations in pulmonary arterial pressure and to pulmonary edema as measured by extravascular wet-to-dry weight ratios. The increase in pressure and edema was prevented by indomethacin, a cyclooxygenase enzyme inhibitor, and by 1-benzylimidazole, a selective inhibitor of thromboxane (Tx) A2 synthesis. Transvascular flux of 125I-albumin from vascular to extravascular spaces of the lung was not elevated by A23187 but was elevated by infusion of oleic acid, an agent known to produce permeability pulmonary edema. We confirmed that A23187 leads to elevations in cyclooxygenase products and that indomethacin and 1-benzylimidazole inhibit synthesis of all cyclooxygenase products and TxA2, respectively, by measuring perfusate levels of prostaglandin (PG) I2 as 6-ketoprostaglandin F1 alpha, PGE2, and PGF2 alpha and TxA2 as TxB2. We conclude that release of endogenous pulmonary arachidonic acid can lead to pulmonary edema from conversion of such arachidonic acid to cyclooxygenase products, most notably TxA2. This edema was most likely from a net hydrostatic accumulation of extravascular lung water with an unchanged permeability of the vascular space, since an index of permeability-surface area product (i.e., transvascular albumin flux) was not increased.     

Importance of vasoconstriction in lipid mediator-induced pulmonary edema

Lipid mediators of inflammation cause pulmonary edema, yet it is unclear to what degree hemodynamic alterations or increased vascular permeability contribute to lung edema formation. The isolated rat lung preparation was used to examine the effect of leukotriene C4 (LTC4) and platelet-activating factor (PAF) on pulmonary arterial pressure (Ppa), lung microvascular pressure (Pmv), lung wet-to-dry weight ratio, and the 125I-albumin escape index. We first defined the response of the isolated rat lung perfused with protein-free salt solution to hydrodynamic stress by raising the lung outflow pressure. Sustained elevation of the lung outflow pressure less than 5.5 cmH2O (4.01 mmHg) caused a negligible increase in Ppa and wet-to-dry lung weight ratio. Elevation of outflow pressures greater than 7.5 cmH2O (5.4 mmHg) increased the vascular albumin escape index more than the lung wet-to-dry weight ratio. Dibutyryl adenosine 3',5'-cyclic monophosphate (db-cAMP) inhibited the increase in albumin escape index because of increased lung outflow pressure, suggesting perhaps a pressure-independent microvascular membrane effect of db-cAMP. Both LTC4 (2-micrograms bolus) and PAF (2-2,000 ng/ml perfusate) increased the albumin escape index in association with increases in Ppa and Pmv. Because the increased albumin escape index after LTC4 or PAF injection was largely accounted for by the increased vascular pressures and because db-cAMP and papaverine inhibited the rise in vascular pressures and in the albumin escape index, we conclude that vasoconstriction is an important contributor to LTC4- and PAF-induced edema formation in rat lungs.     

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.     

Therapeutic actions of alpha-human atrial natriuretic polypeptide in 16 clinical cases

Alpha-human atrial natriuretic polypeptide (alpha-hANP) was applied to 16 clinical patients, 6 patients with essential hypertension, 7 patients with congestive heart failure and 3 patients with cirrhosis. Following intravenous bolus injection of 400 micrograms of synthetic alpha-hANP, a hypotensive effect of very rapid onset was found, which was more potent in the hypertensive patients than in the normotensive cases. Cardiac functions were improved significantly with a similar time course as the depressor response in the cases of heart failure or hypertension. Hemodynamic observations showed a marked increase in cardiac output, cardiac index, stroke volume, ejection fraction and ejection rate, and a concomitant decrease of the pressure in the right side of the heart and pulmonary circulation in these subjects. In addition, the renal response to alpha-hANP induced obvious increases in urine volume, electrolytes and creatinine excretions in all the subjects. Finally, plasma levels of aldosterone, Arg-vasopressin and noradrenaline were also altered by alpha-hANP. No significant side effects were registered. The above result confirms the therapeutic actions of alpha-hANP in human subjects and opens the possibility to research alpha-hANP as a powerful pharmacological tool as well as potential new medicine for human disorders.     

Vasodilatory and diuretic actions of alpha-human atrial natriuretic polypeptide (alpha-hANP)

Vascular and diuretic actions of synthetic alpha-human atrial natriuretic polypeptide (alpha-hANP) were studied using anesthetized dogs and isolated canine arterial strip preparations. alpha-hANP, when given intra-arterially or intravenously, dilated the renal artery more selectively than the vertebral, femoral, common carotid and coronary arteries. alpha-hANP selectively relaxed the high K+-contracted renal artery strip as compared with the basilar, coronary and femoral arterial strips. Intravenous alpha-hANP also increased urine volume and urinary excretion of electrolytes at doses, at which it increased renal blood flow and lowered systemic blood pressure without changing heart rate. It is concluded that alpha-hANP has a vasodilatory property relatively specific for the renal artery, and that it possesses diuretic, natriuretic, kaliuretic, magnesiuretic, calciuretic and chloruretic activities concomitantly with a definite hypotensive activity.     

Spontaneous injury in isolated sheep lungs: role of resident polymorphonuclear leukocytes.

Perfusion of isolated sheep lungs with homologous blood caused pulmonary hypertension and edema that was not altered by depletion of perfusate polymorphonuclear (PMN) leukocytes (D. B. Pearse et al., J. Appl. Physiol. 66: 1287-1296, 1989). The purpose of this study was to evaluate the role of resident PMN leukocytes in this injury. First, we quantified the content and activation of lung PMN leukocytes before and during perfusion of eight isolated sheep lungs with a constant flow (100 ml.kg-1.min-1) of homologous blood. From measurements of myeloperoxidase (MPO) activity, we estimated that the lungs contained 1.2 x 10(10) PMN leukocytes, which explained why the lung PMN leukocyte content, measured by MPO activity and histological techniques, did not increase significantly with perfusion, despite complete sequestration of 2.0 x 10(9) PMN leukocytes from the perfusate. MPO activities in perfusate and lymph supernatants did not increase during perfusion, suggesting that lung PMN leukocytes were not activated. Second, we perfused lungs from 6 mechlorethamine-treated and 6 hydroxyurea-treated sheep with homologous leukopenic blood and compared them with 11 normal lungs perfused similarly. Despite marked reductions in lung PMN leukocyte concentration, there were no differences in pulmonary arterial pressure, lymph flow, or reservoir weight between groups. Extravascular lung water was greater in both groups of leukopenic lungs. These results suggest that resident PMN leukocytes did not contribute to lung injury in this model.     

Simultaneous measurement of fluid and protein permeability in isolated rabbit lungs during edema.

Fluid conductance and protein permeability have been studied in isolated perfused lung models of pulmonary edema. However, previous studies have not investigated changes of both fluid conductance and protein permeability in the same isolated lung preparation after injury. Arachidonic acid (AA) metabolites are involved in the inflammatory processes that lead to the development of pulmonary edema. The hemodynamic effects of AA have been well established; however, controversy exists concerning the ability of AA to alter the permeability of the pulmonary microvasculature to fluid and protein. The purpose of this study was to simultaneously determine whether transvascular fluid conductance and protein permeability are increased in isolated perfused rabbit lungs with pulmonary edema induced by AA. Indomethacin (80 microM) was added to the perfusate to inhibit the hemodynamic effects of AA and produce a pressure-independent model of pulmonary edema. Fluid conductance was assessed by determination of the capillary filtration coefficient (Kf), and protein permeability was evaluated by measurement of 125I-albumin clearance. The injection of AA (3 mg/200 ml of perfusate) into the pulmonary arterial catheter resulted in an increase in lung weight over the remaining 30-min experimental period. Kf (microliter.s-1 x cmH2O-1 x g dry lung-1) was increased (P < 0.05) in AA-treated lungs at 10 and 30 min post-AA injection when compared with control lungs and baseline values (determined 10 min before AA injection). Albumin clearance was also greater (P < 0.05) in lungs that received AA. 125I-albumin clearance was measured at different rates of fluid flux produced by elevation of venous pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous lung chemiluminescence upon paraquat administration

In vivo rat lung chemiluminescence was measured at different times after a single injection of either 30 or 60 mg paraquat/kg b.w. The lungs were isolated to determine myeloperoxidase (index of polymorphonuclear leukocytes), lung wet weight (lung edema) and malondialdehyde (lipid peroxidation). The highest chemiluminescence was reached 30 hours after injection of 30 mg/kg or 6 hours after a 60 mg/kg dose. The peak chemiluminescence was coincident with the maximum concentration of myeloperoxidase and lung wet weight suggesting that most chemiluminescence was the consequence of polymorphonuclear activation after migration to the injured areas.     

Physiological and biochemical markers of alveolar epithelial barrier dysfunction in perfused human lungs

To study air space fluid clearance (AFC) under conditions that resemble the clinical setting of pulmonary edema in patients, we developed a new perfused human lung preparation. We measured AFC in 20 human lungs rejected for transplantation and determined the contribution of AFC to lung fluid balance. AFC was then compared with air space and perfusate levels of a biological marker of epithelial injury. The majority of human lungs rejected for transplant had intact basal (75%) and beta(2)-adrenergic agonist-stimulated (70%) AFC. For lungs with both basal and stimulated AFC, the basal AFC rate was 19 +/- 10%/h, and the beta(2)-adrenergic-stimulated AFC rate was 43 +/- 13%/h. Higher rates of AFC were associated with less lung weight gain (Pearson coefficient -0.90, P < 0.0001). Air space and perfusate levels of the type I pneumocyte marker receptor for advanced glycation end products (RAGE) were threefold and sixfold higher, respectively, in lungs without basal AFC compared with lungs with AFC (P < 0.05). These data show that preserved AFC is a critical determinant of favorable lung fluid balance in the perfused human lung, raising the possibility that beta(2)-agonist therapy to increase edema fluid clearance may be of value for patients with acute lung injury and pulmonary edema. Also, although additional studies are needed, a biological marker of alveolar epithelial injury may be useful clinically in predicting preserved AFC.     

Pulmonary vascular reactivity: effect of PAF and PAF antagonists.

We investigated the effects of two different platelet-activating factor (PAF) antagonists, SRI 63-441 and WEB 2086, on PAF-, angiotensin II-, and hypoxia-induced vasoconstrictions in isolated rat lungs perfused with a physiological salt solution. Bolus injection of PAF (0.5 micrograms) increased pulmonary arterial and microvascular pressures and caused lung edema. Both SRI 63-441, a PAF-analogue antagonist, and WEB 2086, a thienotriazolodiazepine structurally unrelated to PAF, completely blocked PAF-induced vasoconstriction and lung edema at 10(-5) M. At a lower concentration (10(-6) M), WEB 2086 was more effective than SRI 63-441. WEB 2086 also blocked the pulmonary vasodilation induced by low-dose PAF (15 ng) in blood-perfused lungs preconstricted with hypoxia. SRI 63-441 and CV 3988 (another PAF analogue antagonist), but not WEB 2086, caused acute pulmonary vasoconstriction at 10(-5) M and severe lung edema at a higher concentration (10(-4) M). PAF-induced but not SRI- or CV-induced pulmonary vasoconstriction and edema were inhibited by WEB 2086. In addition, SRI 63-441 potentiated angiotensin II- and hypoxia-induced vasoconstrictions. This effect of SRI 63-441 is not due to PAF receptor blockade because 1) addition of PAF (1.6 nM) to the perfusate likewise potentiated angiotensin II-induced vasoconstriction and 2) WEB 2086 did not cause a similar response. We conclude that both SRI 63-441 and WEB 2086 are effective inhibitors of PAF actions in the rat pulmonary circulation. However, antagonists with structures analogous to PAF (SRI 63-441 and CV 3988) can have significant pulmonary vasoactive side effects.     

The PDE inhibitor zaprinast enhances NO-mediated protection against vascular leakage in reperfused lungs

Disruption of endothelial barrier properties with development of noncardiogenic pulmonary edema is a major threat in lung ischemia-reperfusion (I/R) injury that occurs under conditions of lung transplantation. Inhaled nitric oxide (NO) reduced vascular leakage in lung I/R models, but the efficacy of this agent may be limited. We coadministered NO and zaprinast, a cGMP-specific phosphodiesterase inhibitor, to further augment the NO-cGMP axis. Isolated, buffer-perfused rabbit lungs were exposed to 4.5 h of warm ischemia. Reperfusion provoked a transient elevation in pulmonary arterial pressure and a negligible rise in microvascular pressure followed by a massive increase in the capillary filtration coefficient and severe lung edema formation. Inhalation of 10 parts/million of NO or intravascular application of 100 microM zaprinast on reperfusion both reduced pressor response and moderately attenuated vascular leakage. Combined administration of both agents induced no additional vasodilation at constant microvascular pressures, but additively protected against capillary leakage paralleled by a severalfold increase in perfusate cGMP levels. In conclusion, combining low-dose NO inhalation and phosphodiesterase inhibition may be suitable for the maintenance of graft function in lung transplantation by amplifying the beneficial effect of the NO-cGMP axis and avoiding toxic effects of high NO doses.     

Alpha-human atrial natriuretic peptide is a coronary vasodilator in the Langendorff-perfused guinea pig heart

The circulating form of atrial natriuretic peptide is now believed to be composed of 28 amino acids (1). Therefore, we studied the coronary vasoactivity of the 28 amino acid, alpha-human atrial natriuretic peptide (alpha-hANP) in five isolated guinea pig hearts Langendorff-perfused at constant pressure (46 mmHg) with Krebs-Henseleit solution. The reactivity of the coronary bed was assured in each heart with bolus injections of norepinephrine, adenosine, and the vasoconstrictor atrial natriuretic peptide, atriopeptin II (APII). APII was a coronary constrictor in each of these five hearts. Nineteen boluses of alpha-hANP were administered to the five hearts, spanning the range 1.6 to 64 nmol/g wet heart weight. alpha-hANP was vasodilator in all five hearts. The equation for the regression of y = flow, % increase, on x = dose, nmol/g, is y = 17.98 logx - 4.11. The correlation coefficient, r, is 0.83, and the coefficient of determination, r2, is 0.69. Analysis of variance of the regression of y on x yields an F statistic of 36.9, P less than 0.00001. These results indicate that coronary vasodilation is correlated with dose of alpha-hANP over much of the range 1.6-64 nmol/g.     

Lymphokine-activated killer cells with interleukin-2: dose toxicity and localization in isolated perfused rat lungs

Lymphokine-activated killer (LAK) cells combined with recombinant interleukin-2 (rIL-2) can produce tumor regression in murine models and in patients with pulmonary metastatic disease. However, the dose escalations of rIL-2 required for optimal therapeutic effect often result in increased vascular permeability ("vascular leak syndrome") and other toxic systemic consequences. To avoid systemic distribution, lung perfusion was used to administer LAK and rIL-2 locally. Preliminary to using these agents to treat tumor-bearing lungs, we used a nonblood-perfused isolated rat lung model to study the localization of radiolabeled rIL-2 and LAK and to characterize effects on normal lung tissue of increasing dosages and exposure times of rIL-2 and LAK cells, individually and combined. Lung function or permeability was assessed by measuring lung weight gain and pulmonary arterial pressure during the perfusion, extravascular lung water by double indicator dilution techniques, and wet weight to dry weight ratio. After perfusion for 1 hour using 200,000 U (1,300 U/ml) rIL-2, injury was detected as visible pulmonary edema, weight gain and increases in wet to dry weight ratio, and extravascular lung water; no injury was detected at lower, clinically appropriate dosages. When 1 X 10(8) LAK cells combined with 100,000 U rIL-2 (666 U/ml) were perfused for up to 2 hours, no injury was ascertained. Uptake and distribution of the radiolabeled rIL-2 or LAK was uniform to all lung lobes and corresponded to the decrease of 12% of the rIL-2 or 50% of the LAK from the perfusate after 1-hour perfusion.     

Soluble guanylyl cyclase contributes to ventilator-induced lung injury in mice

High tidal volume (HV(T)) ventilation causes pulmonary endothelial barrier dysfunction. HV(T) ventilation also increases lung nitric oxide (NO) and cGMP. NO contributes to HV(T) lung injury, but the role of cGMP is unknown. In the current study, ventilation of isolated C57BL/6 mouse lungs increased perfusate cGMP as a function of V(T). Ventilation with 20 ml/kg V(T) for 80 min increased the filtration coefficient (K(f)), an index of vascular permeability. The increased cGMP and K(f) caused by HV(T) were attenuated by nitric oxide synthase (NOS) inhibition and in lungs from endothelial NOS knockout mice. Inhibition of soluble guanylyl cyclase (sGC) in wild-type lungs (10 muM ODQ) also blocked cGMP generation and inhibited the increase in K(f), suggesting an injurious role for sGC-derived cGMP. sGC inhibition also attenuated lung Evans blue dye albumin extravasation and wet-to-dry weight ratio in an anesthetized mouse model of HV(T) injury. Additional activation of sGC (1.5 muM BAY 41-2272) in isolated lungs at 40 min increased cGMP production and K(f) in lungs ventilated with 15 ml/kg V(T). HV(T) endothelial barrier dysfunction was attenuated with a nonspecific phosphodiesterase (PDE) inhibitor (100 muM IBMX) as well as an inhibitor (10 muM BAY 60-7550) specific for the cGMP-stimulated PDE2A. Concordantly, we found a V(T)-dependent increase in lung cAMP hydrolytic activity and PDE2A protein expression with a decrease in lung cAMP concentration that was blocked by BAY 60-7550. We conclude that HV(T)-induced endothelial barrier dysfunction resulted from a simultaneous increase in NO/sGC-derived cGMP and PDE2A expression causing decreased cAMP.     

Role of the nitric oxide pathway in ischemia-reperfusion injury in isolated perfused guinea pig lungs

We examined the role of the nitric oxide (NO) pathway on ischemia-reperfusion injury via the use of isolated perfused guinea pig lungs. We administered both L-Arginine and N-nitro-L-arginine methyl ester (L-NAME) to the lungs in or after 3 h of ischemia. We observed pulmonary artery pressures as well as tissue and perfusate malondialdehyde (MDA) and glutathione (GSH) levels. We observed that L-NAME significantly increased both tissue and perfusate GSH levels and pulmonary artery pressures, but it decreased both tissue and perfusate MDA levels. On the other hand, L-arginine significantly decreased pulmonary artery pressure and both tissue and perfusate glutathione levels, but it increased both tissue and perfusate MDA levels. Electron microscopic evaluation supported our findings by indicating the preservation of lamellar bodies of type II pneumocytes. We concluded that L-NAME administration during reperfusion improves lung recovery from ischemic injury.     

Alpha-human atrial natriuretic polypeptide is released from the heart and circulates in the body

In order to clarify whether or not atrial natriuretic polypeptides are hormones in man, we have measured plasma alpha-human atrial natriuretic polypeptide (alpha-hANP)-like immunoreactivity (alpha-hANP-LI) with or without extraction procedure. alpha-hANP-LI was detected in plasma extracts from all 5 normal subjects and 7 patients with heart diseases. The alpha-hANP-LI concentration in normal peripheral plasma was 37.7 +/- 7.0 pg/ml (mean +/- SE). Plasma concentrations of alpha-hANP-LI in the coronary sinus obtained by cardiac catheterization were 3 to 10 times higher than those in the peripheral vein, inferior vena cava, right atrium, pulmonary artery and aorta. High performance gel permeation chromatography coupled with a radioimmunoassay (RIA) for alpha-hANP revealed that alpha-hANP-LI in normal peripheral plasma eluted at the position corresponding to that of authentic alpha-hANP without detectable amounts of high molecular weight forms. alpha-hANP-LI extracted from plasma taken from the coronary sinus of two patients also showed a single peak of alpha-hANP-LI co-eluting with alpha-hANP. In contrast, not only alpha-hANP but gamma-hANP and beta-hANP, high molecular weight forms, were present in the human atrial tissue. These results indicate that alpha-hANP is the predominant form of alpha-hANP-LI in human plasma and that this form generated in the atrial cardiocytes is preferentially released from these cells and circulates in the body.