L-arginine administration during reperfusion improves pulmonary function

Therapeutic Potential of Citrulline as an Arginine Supplement: A Clinical Pharmacology Review

Supplemental arginine has shown promise as a safe therapeutic option to improve endogenous nitric oxide (NO) regulation in cardiovascular diseases associated with endothelial dysfunction. In clinical studies in adults, L-arginine, an endogenous amino acid, was reported to improve cardiovascular function in hypertension, pulmonary hypertension, preeclampsia, angina, and MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome. L-citrulline, a natural precursor of L-arginine, is more bioavailable than L-arginine because it avoids hepatic first-pass metabolism and has a longer circulation time. Although not yet well-studied, arginine/citrulline has immense therapeutic potential in some life-threatening diseases in children. However, the optimal clinical development of arginine or citrulline in children requires more information about pharmacokinetics and exposure-response relationships at appropriate ages and under relevant disease states. This article summarizes the preclinical and clinical studies of arginine/citrulline in both adults and children, including currently available pharmacokinetic information. The pharmacology of arginine/citrulline is confounded by several patient-specific factors such as variations in baseline arginine/citrulline due to developmental ages and disease states. Currently available pharmacokinetic studies are insufficient to inform the optimal design of clinical studies, especially in children. Successful bench-to-bedside clinical translation of arginine supplementation awaits information from well-designed pharmacokinetic/pharmacodynamic studies, along with pharmacometric approaches.

Increased Arginase Expression and Decreased Nitric Oxide in Pig Donor Lungs after Normothermic Ex Vivo Lung Perfusion

An established pig lung transplantation model was used to study the effects of cold ischemia time, normothermic acellular ex vivo lung perfusion (EVLP) and reperfusion after lung transplantation on l-arginine/NO metabolism in lung tissue. Lung tissue homogenates were analyzed for NO metabolite (NOx) concentrations by chemiluminescent NO-analyzer technique, and l-arginine, l-ornithine, l-citrulline and asymmetric dimethylarginine (ADMA) quantified using liquid chromatography-mass spectrometry (LC-MS/MS). The expression of arginase and nitric oxide synthase (NOS) isoforms in lung was measured by real-time polymerase chain reaction. EVLP preservation resulted in a significant decrease in concentrations of NOx and l-citrulline, both products of NOS, at the end of EVLP and after reperfusion following transplantation, compared to control, respectively. The ratio of l-ornithine over l-citrulline, a marker of the balance between l-arginine metabolizing enzymes, was increased in the EVLP group prior to reperfusion. The expression of both arginase isoforms was increased from baseline 1 h post reperfusion in EVLP but not in the no-EVLP group. These data suggest that EVLP results in a shift of the l-arginine balance towards arginase, leading to NO deficiency in the lung. The arginase/NOS balance may, therefore, represent a therapeutic target to improve lung quality during EVLP and, subsequently, transplant outcomes.

The fibrin-derived peptide Bbeta(15-42) significantly attenuates ischemia-reperfusion injury in a cardiac transplant model

BACKGROUND

The inflammatory response after prolonged ischemia and subsequent reperfusion leads to increased risk of primary organ dysfunction after cardiac transplantation. It has been demonstrated that the fibrin-derived peptide Bbeta(15-42) (also called FX06) reduces infarct size in coronary artery occlusion/reperfusion models by inhibition of leukocyte migration. Further, Bbeta(15-42) preserves endothelial barrier function. The purpose of this study was to investigate whether Bbeta(15-42) has a protective effect in cardiac allografts exposed to prolonged global ischemia and subsequent in vivo reperfusion.

METHODS

Hearts of male Lewis rats were flushed and stored in cold Bretschneider preservation solution for 4 or 8 hr. Bbeta(15-42) was administered before being transplanted into syngeneic recipients. Serum samples were collected for troponin-T measurements. Hemodynamic performance was evaluated after a reperfusion period of 24 hr. Morphologic quantification of myocardial necrosis was performed in hearts exposed to 24 hr or 10 days of reperfusion.

RESULTS

Allografts from Bbeta(15-42) treated animals showed less myocardial necrosis (2.5% +/- 2.5% vs. 18.4% +/- 9.2%, P=0.0019) and decreased values of cardiac troponin-T (1.1 +/- 0.6 ng/mL vs. 2.7+/-2.3 ng/mL, P=0.0045), reduced number of infiltrating leukocytes (7.2 +/- 13.6 vs. 49.2 +/- 34.9 per high powerfield, P=0.0045), and superior cardiac output (78.1 +/- 1.8 mL/min vs. 21.7 +/- 4 mL/min, P = 0.0034). Hearts exposed to 0 and 4 hr of ischemia showed no severe signs of myocardial damage.

CONCLUSION

Bbeta(15-42) ameliorates the ischemia-reperfusion injury in transplanted hearts during extended cold ischemia by reduction of infiltrating leukocytes. This experimental protocol provides evidence that Bbeta(15-42) may play a useful role in organ preservation, but clinical evaluation is warranted.

Post-ischemic infusion of atrial natriuretic peptide attenuates warm ischemia-reperfusion injury in rat lung

BACKGROUND

The serious shortage of organs for transplantation, especially lungs, has drawn increasing attention to donation after cardiac death and protection of organs against warm ischemic injury. Atrial natriuretic peptide (ANP) activates guanylate cyclase receptors and increases cyclic guanosine monophosphate (cGMP) levels, which decrease in the lung during ischemia. In this study we investigated the effect on lung ischemia-reperfusion injury of administering synthetic ANP (carperitide) at the onset of reperfusion after warm ischemia.

METHODS

An isolated rat lung perfusion model was used. The rats were allocated into three groups: the control group; the ANP group; and the sham group. In the control and ANP groups, the heart-lung block was exposed to 60 minutes of ischemia at 37 degrees C, and subsequently reperfused for 60 minutes. At the onset of reperfusion, either saline or ANP was added to the perfusate. In the sham group, lungs were continuously perfused without ischemia and only saline was added to the perfusate.

RESULTS

ANP significantly reduced pulmonary vascular resistance and pulmonary edema, and improved oxygenation. It also significantly increased cGMP levels in reperfused lungs. Histologically, lungs in the ANP group showed significantly fewer signs of injury and fewer cells demonstrated apoptotic changes or single-stranded DNA than lungs in the control group.

CONCLUSIONS

Our results indicate that ANP administered at the onset of reperfusion increases cGMP in lung tissue and attenuates warm ischemia-reperfusion injury in isolated perfused rat lung.

Continuous pulmonary infusion of L-arginine during deep hypothermia and circulatory arrest improves pulmonary surfactant integrity in piglets

BACKGROUND

The integrity of pulmonary surfactant (PS) is impaired during deep hypothermia and circulatory arrest (DHCA), a preferred bypass strategy for infants undergoing complex cardiac operations, due mainly to bypass-induced systemic inflammation. The requirement of L-arginine, a precursor of nitric oxide, is elevated during acute pulmonary inflammation. We hypothesized that continuous intrapulmonary supplementation of L-arginine during DHCA can maintain the integrity of PS metabolism and thus protect the pulmonary function.

METHODS

Sixteen piglets underwent 90-minute circulatory arrest at 18 degrees C before rewarming. During circulatory arrest, antegrade infusion of Ringer's lactate solution alone (n = 8) or containing L-arginine (1 mg/kg/min, n = 8) was initiated into the pulmonary circulation. Disaturated phosphatidylcholine, total phospholipids, and total proteins from tracheal aspirates were measured serially until the experiment ended (4 hours after rewarming). Various variables of pulmonary function were also monitored.

RESULTS

L-arginine led to less decrement of disaturated phosphatidylcholine/total phospholipids and disaturated phosphatidylcholine/total proteins after DHCA. At 4 hours after rewarming, L-arginine had significantly mitigated the deterioration of pulmonary static compliance (3.6 +/- 0.5 vs 3.3 +/- 0.3 mL/cm H2O) and partial pressure of arterial oxygen/fraction of inspired oxygen (330 +/- 48 vs 296 +/- 32 mm Hg). Pulmonary retention of water (6.2 +/- 1.0 vs 5.5 +/- 1.2) was significantly reduced. The L-arginine-treated group showed an increase in NO metabolites (NO2-/NO3-) from the pulmonary circulation, the extent of which is correlated to PS content.

CONCLUSIONS

Continuous L-arginine supplementation during DHCA attenuated PS depletion and, therefore, ameliorated postoperative pulmonary dysfunction.

L-arginine protects the mesenteric vascular circulation against cardiopulmonary bypass-induced vascular dysfunction

BACKGROUND

The aim of our study was to determine whether addition of the nitric oxide donor l-arginine at reperfusion may prevent the cardiopulmonary bypass (CPB)-induced vascular alterations in the intestine.

METHODS

Twelve dogs underwent 90-minute hypothermic CPB. After 60 minutes, the cardiac arrest-treated group (n = 6) received 40 mg/kg intravenous bolus l-arginine, followed by 3 mg/kg/min infusion for 20 minutes. Hemodynamic parameters, blood gases, lactate, and glucose were monitored. Reactive hyperemia (RH) in response to superior mesenteric artery ischemia and vasorelaxation to systemically administered vasoactive drugs (acetylcholine [ACH] and sodium nitroprusside) were assessed before and after CPB and defined as percent change of vascular resistance.

RESULTS

In the control group, CPB reduced reactive hyperemia (RH) (-26 +/- 15% vs -53 +/- 5%), and the response to ACH (-30 +/- 3% vs -42 +/- 7%). In the treated group, the post-CPB endothelial dysfunction was reversed (-37 +/- 1%, P <.05 vs control group) and RH partially recovered (-34 +/- 4%, P <.05). Administration of l-arginine resulted in a higher mesenteric oxygen delivery, increased nitrite/nitrate production, and lower lactate release from the mesenteric vascular circulation after reperfusion.

CONCLUSIONS

CPB disrupts some of the regulatory functions of the endothelial cell in the mesenterium and these are mostly related to nitric oxide unavailability. Systemic supplementation of l-arginine at reperfusion prevents the CPB-induced mesenteric endothelial dysfunction in association with an increased blood distribution and a reduced metabolic impairment.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

Survival and graft function in a large animal lung transplant model after 30 h preservation and substitution of the nitric oxide pathway

OBJECTIVE

Substitution of the nitric oxide- (NO-) pathway improves early graft function following lung transplantation. We previously demonstrated that 8-Br-cGMP (second messenger of NO) to the flush solution and tetrahydrobiopterin (BH4, coenzyme of NO synthase) given as additive during reperfusion improve post-transplant graft function. In the present study, the combined treatment with 8-Br-cGMP and BH4 was evaluated.

METHODS

Unilateral left lung transplantation was performed in weight matched outbred pigs (24-31 kg). In group I, grafts were preserved for 30 h (n=5). 8-Br-cGMP (1mg/kg) was added to the flush solution (Perfadex, 1.5l, 1 degrees C) and BH4 (10mg/kg/h) was given to the recipient for 5h after reperfusion. In group II, lungs were transplanted after a preservation time of 30 h (n=3) and prostaglandin E(1) (250 g) was given into the pulmonary artery (PA) prior to flush. In all recipients 1h after reperfusion the contralateral right PA and bronchus were ligated to assess graft function only. Survival time after reperfusion, extravascular lung water index (EVLWI), hemodynamic variables, and gas exchange (PaO(2)) were assessed during a 12h observation period.

RESULTS

All recipients in group I survived the 12h assessment, whereas none of the group II animals survived more than 4h after reperfusion with a rapid increase of EVLWI up to 24.8+/-6.7 ml/kg. In contrast, in group I EVLWI reached up to 8.9+/-1.5 ml/kg and returned to nearly normal levels at 12h (6.1+/-0.8 ml/kg). In two animals of group I the gas exchange deteriorated slightly. The other three animals showed normal arterial oxygenation over the entire observation time.

CONCLUSION

Our data indicate that the combined substitution of the NO pathway during preservation and reperfusion reduces ischemia/reperfusion injury substantially and that this treatment even allows lung transplantation after 30 h preservation in this model.

L-Arginine in lung graft preservation and reperfusion

BACKGROUND

Inhaled nitric oxide has been shown to ameliorate early lung graft dysfunction. It improves oxygenation by inducing pulmonary vasodilatation in well-ventilated lung areas, and it also modulates leukocyte-endothelium interactions. We used a porcine, single lung transplantation model to evaluate whether the benefits of exogenously administered gas could be achieved easier by adding L-arginine, the substrate of endogenous nitric oxide synthesis, as an additive to the flush solution and intravenously during reperfusion.

METHODS

Six pig lungs were flushed with modified Euro-Collins solutions containing L-arginine (2 g/liter). After cold (4 degrees C) storage, the left lung was transplanted. Ischemic time was 260 minutes. The recipients received intravenous boluses of L-arginine (30 mg/kg), followed by infusion (20 mg/kg/min) during the first 30 minutes of reperfusion. Six control animals received saline as placebo. We measured the blood flow and pulmonary vascular resistance (PVR) in the transplanted and in the native lung using a right heart bypass model. We measured blood gases, leukocyte counts, plasma free-radical trapping capacity, and diene conjugates in pulmonary venous blood and myeloperoxidase activity of the lung tissue.

RESULTS

Pulmonary vascular resistance was 4 to 5-fold higher in the transplanted lung than in the native lung, which received 80% of the total blood flow. L-arginine reduced PVR by 30% in the native lung (p < 0.001), but not in the transplanted lung. L-arginine had no effect on oxygenation or carbon dioxide exchange of the transplanted lung. Nor did L-arginine treatment have any effect on leukocyte sequestration or myeloperoxidase activity in the transplanted lung. The plasma antioxidant capacity in venous blood of the transplanted lung almost doubled shortly during early reperfusion without influence of L-arginine.

CONCLUSIONS

L-arginine reduced PVR in the native lung but did not improve pulmonary hemodynamics, gas exchange, or reduce leukocyte sequestration of the transplanted lung.

No effect of L-arginine supplementation on pulmonary endothelial dysfunction after cardiopulmonary bypass

BACKGROUND

Acetylcholine is an endothelium-dependent vasodilator through the L-arginine-nitric oxide pathway. After ischemia-reperfusion this effect is attenuated, also demonstrated in the pulmonary circulation after cardiopulmonary bypass. Administration of L-arginine has been shown to have a protective effect on endothelial function in reperfusion injury. The aim of the current study was to test the possible effect of L-arginine on the acetylcholine reactivity in the pulmonary circulation after cardiopulmonary bypass.

METHODS

Thirty-five patients with ischemic and/or valvular heart disease were investigated in a randomized, double-blinded, placebo-controlled study. The patients were divided into three groups. Group 1: high dose L-arginine (n=10), group 2: low dose L-arginine (n=10), group 3: placebo, no L-arginine, (n=15). The acetylcholine reactivity was tested with measurements of pulmonary vascular resistance before surgery and 1, 2 and 3-4 h after cardiopulmonary bypass.

RESULTS

After cardiopulmonary bypass an attenuation of the acetylcholine reactivity over time was observed in all groups, with no differences between groups.

CONCLUSION

In the current study L-arginine had no protective effect on the pulmonary endothelium after cardiopulmonary bypass, measured as reactivity to an infusion of acetylcholine.

Overview and future practice patterns in cardiac and pulmonary preservation

Heart and lung transplantation have become standard therapy for many patients with end-stage heart and lung disease. Successful transplantation requires preservation of allografts until they can be implanted and reperfused. In the decades since the transplantation of thoracic organs became a clinical reality, many advances have been made in preoperative donor management, procurement, and preservation techniques. This article summarizes the state of the art in heart and lung preservation and review some of the areas of current research that may lead to improvements in preservation techniques in the future.

Modulation of lung reperfusion injury by nitric oxide: impact of inspired oxygen fraction

BACKGROUND

Attempts to attenuate lung reperfusion injury by administration of inhaled nitric oxide have yielded conflicting results. We hypothesized that the inspired oxygen fraction may play an important role in determining the outcome of nitric oxide therapy.

METHODS

Rat lungs were reperfused in a circuit incorporating a support animal either immediately after flushing (group A) or after 24-hr hypothermic storage (groups B-D). During the first 10 min of reperfusion, grafts were ventilated with 95% oxygen in groups A and B, 95% oxygen and 20 ppm nitric oxide in group C, and 20% oxygen and 20 ppm nitric oxide in group D. Ventilation during the subsequent 50 min of reperfusion was with 100% oxygen only, in all groups.

RESULTS

Graft function in group B was poor compared to group A in terms of blood flow and pulmonary artery and peak airway pressures. In group C, although 5 out of 10 grafts functioned at control levels, the remainder performed poorly. Function in group D, on the other hand, was uniformly good.

CONCLUSIONS

Inhaled nitric oxide can prevent lung reperfusion injury, but this effect may be compromised by concurrent ventilation with high oxygen concentrations.

The nitric oxide synthase cofactor tetrahydrobiopterin reduces allograft ischemia-reperfusion injury after lung transplantation

OBJECTIVE

Exogenous nitric oxide reduces ischemia-reperfusion injury after solid organ transplantation. Tetrahydrobiopterin, an essential cofactor for nitric oxide synthases, may restore impaired endothelium-dependent nitric oxide synthesis. We evaluated whether tetrahydrobiopterin administration to the recipient attenuates lung reperfusion injury after transplantation in swine.

METHODS

Unilateral left lung transplantation was performed in 15 weight-matched pigs (24-31 kg). Donor lungs were flushed with 1.5 L cold (1 degrees C) low-potassium-dextran solution and preserved for 20 hours. Group I animals served as controls. Group II and III animals were treated with a bolus of tetrahydrobiopterin (20 mg/kg). In addition, in group III a continuous infusion of tetrahydrobiopterin (10 mg/kg per hour over 5 hours) was given. One hour after reperfusion, the recipient right lung was occluded. Cyclic guanosine monophosphate levels were measured in the pulmonary venous and central venous blood. Extravascular lung water index, hemodynamic variables, lipid peroxidation, and neutrophil migration to the allograft were assessed.

RESULTS

In group III a significant reduction of extravascular lung water was noted in comparison with the controls (P =.0047). Lipid peroxidation in lung allograft tissue was significantly reduced in group II (P =.0021) and group III ( P =. 0077) in comparison with group I. Pulmonary venous levels of cyclic guanosine monophosphate increased up to 23 +/- 1 pmol/mL at 5 hours in group II and up to 40 +/- 1 pmol/mL in group III (group I, 4.1 +/- 0.5 pmol/mL [I vs III]; P <.001), whereas central venous levels of cyclic guanosine monophosphate were unchanged in all groups.

CONCLUSION

Tetrahydrobiopterin administration during lung allograft reperfusion may reduce posttransplantation lung edema and oxygen-derived free radical injury in the graft. This effect is mediated by local enhancement of the nitric oxide/cyclic guanosine monophosphate pathway.

8-Br-cGMP is superior to prostaglandin E1 for lung preservation

BACKGROUND

Substitution of the nitric oxide (NO) pathway reduces ischemia/reperfusion injury after lung transplantation. 8-Br-cGMP is a membrane-permeable analogue of cGMP, the second messenger of NO. In this study, we evaluated the effect of administration of 8-Br-cGMP in the flush solution on early graft function.

METHODS

Unilateral left lung transplantation was performed in 10 weight-matched pairs of outbred pigs (24 to 31 kg). Donor lungs were flushed with 1.5 L cold (1 degree C) low potassium dextrane (LPD) solution and preserved for 20 hours. In group I (n = 5), 8-Br-cGMP (1 mg/kg) was added to the flush solution. In group II (n = 5), 8 microg/kg prostaglandin E1 (PGE1) was injected into the pulmonary artery (PA) before flush. One hour after reperfusion, the recipients' contralateral right PA and bronchus were ligated to assess graft function only. cGMP levels in the PA and pulmonary vein were measured. Extravascular lung water index (EVLWI), pulmonary vascular resistance, mean PA pressure, and gas exchange (PaO2) were assessed during a 5-hour observation period. Lipid peroxidation (thiobarbituric acid-reactive substance) and neutrophil migration to the allograft (myeloperoxidase activity) were measured at the end of the assessment.

RESULTS

In group I, a significant reduction of EVLWI (group I, 6.7 +/- 1.0 mL/kg vs group II, 10.1 +/- 0.6 ml/kg after 2 hours of reperfusion; p = 0.022), TBARS (group I, 65.6 +/- 10.0 pmol/g vs group II, 120.8 +/- 7.2 pmol/g, p = 0.0039), and MPO activity (group I, 0.8 +/- 0.1 change in optical density, (deltaOD)/mg/min vs group II, 1.7 +/- 0.3 deltaOD/mg/min, p = 0.036) was noted in comparison with group II. PaO2 levels tended to be higher in cGMP-treated animals, but the changes were not significant. Hemodynamic parameters did not differ between groups.

CONCLUSIONS

In this large animal model of lung allograft ischemia/reperfusion injury, 8-Br-cGMP as additive to the flush solution improves posttransplant lung edema, lipid peroxidation, and neutrophil migration to the allograft. This effect is not attributable to improved flush by vasodilation, as we compared 8-Br-cGMP with PGE1 given before flush in control animals.

Beneficial effects of leukocyte-depleted blood and low-potassium dextran solutions on microvascular permeability in preserved porcine lung

Modified Euro-Collins (EC) solution, a crystalloid intracellular-type solution, has been commonly used for pulmonary preservation. Several experimental studies have shown the advantages of using extracellular colloid-based solutions. The aim of this study was to compare the quality of preservation of two extracellular colloid solutions, leukocyte-depleted blood (BL) and low-potassium dextran (LPD) solutions, with that of EC solution. Lungs of 22 domestic pigs were flushed and preserved with EC (n = 8), BL (n = 7), or LPD (n = 7) solution. After harvesting, one of the lungs was reperfused immediately in an ex vivo circuit (control lungs), whereas the contralateral lung was reperfused after 8 h of cold (4 degrees C) storage (preserved lungs). Besides the lung function parameters (gas exchange, pulmonary hemodynamics and mechanics), the permeability of the endothelial-epithelial barrier was assessed by determining the transferrin leak index (TLI) using a double radioisotopic method, by measuring the alveolar/arterial protein concentration ratio, and by analyzing histopathologic changes. The functional quality (oxygenation, airway resistance, dynamic compliance [CL, dyn]) of both BL and LPD lungs was slightly but significantly superior to that of EC lungs. However, pulmonary vascular resistance was lower in BL-preserved than in EC- or LPD-preserved lungs. The TLI was increased in EC control and preserved lungs, whereas it was low in BL and LPD control lungs and did not increase after preservation. The alveolar/arterial protein concentration ratio was not different between control groups, but was increased fourfold in EC-preserved compared with BL- or LPD-preserved lungs. Finally, EC-preserved lungs presented a weight gain about twice that of BL- and LPD-preserved lungs. Morphologic analysis confirmed these results, because in the EC-preserved lungs, rupture of alveolar septa and severe alveolar edema and hemorrhage were observed, whereas BL- and LPD-preserved lungs showed a relatively well-preserved structure. The results demonstrate that both BL and LPD flush solutions preserve the endothelial-epithelial barrier better than does EC solution. Although the quality of preservation is similar, pulmonary vascular resistance is higher in LPD-preserved than in BL-preserved lungs.

L-arginine inhibits ischemia-reperfusion lung injury in rabbits

BACKGROUND

Recent studies have reported that nitric oxide (NO) acts as a cytoprotective mediator in ischemia-reperfusion (IR) lung injury. We hypothesized that the addition of L-arginine to the perfusate would attenuate the increases in microvascular permeability and pulmonary vascular resistance.

MATERIALS AND METHODS

Isolated rabbit lungs were reperfused for 60 min after 120 min warm ischemia. Lung injury was assessed using the fluid filtration coefficient (Kf), pulmonary vasucular resistance (PVR) before ischemia and after reperfusion, and a wet-to-dry lung weight ratio (W/D).

RESULTS

The Kf of the control group (without L-arginine) was significantly increased after reperfusion. Lungs perfused with L-arginine showed attenuation of the IR-induced increases in Kf and PVR. Addition of Nomega-nitro-L-arginine (L-NA), a NO synthase inhibitor, to the perfusate reduced the beneficial effects of L-arginine. The lungs perfused with dibutyryl-cyclic GMP (dbcGMP) showed attenuation of IR-induced increases in Kf and PVR. There were no significant differences in the W/D ratio between these groups.

CONCLUSIONS

These results demonstrate that L-arginine has beneficial effects on IR lung injury, perhaps due to enhancement of endothelial cGMP levels.

Relationship between flushing pressure and nitric oxide production in preserved lungs

BACKGROUND

Nitric oxide (NO) is considered to be one of the endogenous inhibitory factors of ischemic reperfusion injury. In this study, the NO-producing ability of the preserved lung, flushed at various pulmonary artery pressures (flushing pressure), was studied during reperfusion using an ex vivo rabbit lung perfusion model.

METHODS

The lungs were flushed with 200 ml of preservation solution with flushing pressures adjusted to 15, 15, 20, and 25 mmHg for groups 1, 2, 3, and 4, respectively (n=5 in each group). In the control group (group 1), the heart-lung block was harvested after flushing and the lungs were assessed without preservation. In the other groups, the harvested blocks were preserved at 8 degrees C for 24 hr and reperfused with homologous blood for pulmonary functional assessment. Pulmonary function was assessed by measuring mean airway pressure, mean pulmonary arterial pressure, partial oxygen tension of pulmonary venous effluent blood, and pulmonary wet-dry weight ratio. The sequential changes in the concentration of NO-related substances (NO-RS) in the serum of reperfused blood were also measured by chemiluminescence.

RESULTS

During reperfusion, biphasic increases in NO-RS were observed in all groups. In groups 3 and 4, the increases in NO-RS were significantly lower than those of groups 1 and 2, and pulmonary function deteriorated.

CONCLUSION

These data suggest that in order to maintain the endogenous NO-producing ability of preserved lung, the flushing pressure must be less than 20 mmHg.