Jörg Weimann

Sustained pulmonary hypertension and right ventricular hypertrophy after chronic hypoxia in mice with congenital deficiency of nitric oxide synthase 3.

Chronic hypoxia induces pulmonary hypertension and right ventricular (RV) hypertrophy. Nitric oxide (NO) has been proposed to modulate the pulmonary vascular response to hypoxia. We investigated the effects of congenital deficiency of endothelial NO synthase (NOS3) on the pulmonary vascular responses to breathing 11% oxygen for 3-6 wk. After 3 wk of hypoxia, RV systolic pressure was greater in NOS3-deficient than in wild-type mice (35+/-2 vs 28+/-1 mmHg, x+/-SE, P < 0.001). Pulmonary artery pressure (PPA) and incremental total pulmonary vascular resistance (RPI) were greater in NOS3-deficient than in wild-type mice (PPA 22+/-1 vs 19+/-1 mmHg, P < 0.05 and RPI 92+/-11 vs 55+/-5 mmHg.min.gram.ml-1, P < 0.05). Morphometry revealed that the proportion of muscularized small pulmonary vessels was almost fourfold greater in NOS3-deficient mice than in wild-type mice. After 6 wk of hypoxia, the increase of RV free wall thickness, measured by transesophageal echocardiography, and of RV weight/body weight ratio were more marked in NOS3-deficient mice than in wild-type mice (RV wall thickness 0.67+/-0.05 vs 0.48+/-0.02 mm, P < 0.01 and RV weight/body weight ratio 2.1+/-0.2 vs 1.6+/-0.1 mg. gram-1, P < 0.05). RV hypertrophy produced by chronic hypoxia was prevented by breathing 20 parts per million NO in both genotypes of mice. These results suggest that congenital NOS3 deficiency enhances hypoxic pulmonary vascular remodeling and hypertension, and RV hypertrophy, and that NO production by NOS3 is vital to counterbalance pulmonary vasoconstriction caused by chronic hypoxic stress.

Sildenafil is a pulmonary vasodilator in awake lambs with acute pulmonary hypertension.

Background Phosphodiesterase type 5 (PDE5) hydrolyzes cyclic guanosine monophosphate in the lung, thereby modulating nitric oxide (NO)/cyclic guanosine monophosphate–mediated pulmonary vasodilation. Inhibitors of PDE5 have been proposed for the treatment of pulmonary hypertension. In this study, we examined the pulmonary and systemic vasodilator properties of sildenafil, a novel selective PDE5 inhibitor, which has been approved for the treatment of erectile dysfunction. Methods In an awake lamb model of acute pulmonary hypertension induced by an intravenous infusion of the thromboxane analog U46619, we measured the effects of 12.5, 25, and 50 mg sildenafil administered via a nasogastric tube on pulmonary and systemic hemodynamics (n = 5). We also compared the effects of sildenafil (n = 7) and zaprinast (n = 5), a second PDE5 inhibitor, on the pulmonary vasodilator effects of 2.5, 10, and 40 parts per million inhaled NO. Finally, we examined the effect of infusing intravenous l-NAME (an inhibitor of endogenous NO production) on pulmonary vasodilation induced by 50 mg sildenafil (n = 6). Results Cumulative doses of sildenafil (12.5, 25, and 50 mg) decreased the pulmonary artery pressure 21%, 28%, and 42%, respectively, and the pulmonary vascular resistance 19%, 23%, and 45%, respectively. Systemic arterial pressure decreased 12% only after the maximum cumulative sildenafil dose. Neither sildenafil nor zaprinast augmented the ability of inhaled NO to dilate the pulmonary vasculature. Zaprinast, but not sildenafil, markedly prolonged the duration of pulmonary vasodilation after NO inhalation was discontinued. Infusion of l-NAME abolished sildenafil-induced pulmonary vasodilation. Conclusions Sildenafil is a selective pulmonary vasodilator in an ovine model of acute pulmonary hypertension. Sildenafil induces pulmonary vasodilation via a NO-dependent mechanism. In contrast to zaprinast, sildenafil did not prolong the pulmonary vasodilator action of inhaled NO.

Biologic Effects of Nitrous Oxide : A Mechanistic and Toxicologic Review

Nitrous oxide is the longest serving member of the anesthesiologist’s pharmacologic armamentarium but remains a source of controversy because of fears over its adverse effects. Recently, the Evaluation of Nitrous oxide In a Gas Mixture for Anaesthesia (ENIGMA) trial reported that nitrous oxide use increases postoperative complications; further preclinical reports have suggested that nitrous oxide may contribute to neurocognitive dysfunction in the young and elderly. Therefore, nitrous oxide’s longevity in anesthetic practice is under threat. In this article, the authors discuss the evidence for the putative toxicity of nitrous oxide, from either patient or occupational exposure, within the context of the mechanism of nitrous oxide’s action. Although it would seem prudent to avoid nitrous oxide in certain vulnerable populations, current evidence in support of a more widespread proscription from clinical practice is unconvincing.

Inhaled nitric oxide inhibits platelet aggregation after pulmonary embolism in pigs

Background Inhaled nitric oxide (NO) is reported to prolong bleeding time in animals and humans and to inhibit platelet aggregation in persons with acute respiratory distress syndrome. In pulmonary embolism (PE), inhibition of platelet aggregation appears useful because further thrombus formation may lead to right ventricular dysfunction that results in circulatory failure. In the present study, the effect of inhaled NO on platelet aggregation after acute massive PE was investigated. Methods After acute massive PE was induced in 25 anesthetized pigs by injecting microspheres, 5, 20, 40, and 80 parts per million inhaled NO were administered stepwise for 10 min each in 11 animals (NO group). In the control group (n = 14), NO was not administered. Adenosine diphosphate‐induced initial and maximal platelet aggregation were measured before PE (t0), immediately after induction of PE (PE), at the end of each 10‐min NO inhalation interval (t10‐t40), and 15 min after cessation of NO inhalation (t55) in the NO group, and at corresponding times in the control group, respectively. Results Two animals in the control group and one in the NO group died within 10 min after PE induction and were excluded from analysis. Peaking at t40 and t55, respectively, initial (+13 +/‐ 6%; P < 0.05) and maximal (+44 +/‐ 17%; P < 0.05) platelet aggregation increased significantly after PE in the control group. In contrast, NO administration after PE led to a significant decrease in initial (maximum decrease, ‐9 +/‐ 3% at t40; P < 0.05) and maximal (maximum decrease, ‐15 +/‐ 7% at t30; P < 0.05) platelet aggregation. In the NO group, platelet aggregation had returned to baseline levels again at t55. In addition, NO administration significantly decreased mean pulmonary artery pressure and significantly increased end‐tidal carbon dioxide concentration and mean systemic blood pressure. Conclusions Inhaled NO has a systemic and rapidly reversible inhibitory effect on platelet aggregation after acute massive PE in pigs. This may be beneficial in treating acute massive PE.

Inhalation of the Phosphodiesterase-3 Inhibitor Milrinone Attenuates Pulmonary Hypertension in a Rat Model of Congestive Heart Failure

Background:Most patients with congestive heart failure (CHF) develop pulmonary venous hypertension, but right ventricular afterload is frequently further elevated by increased pulmonary vascular resistance. To investigate whether inhalation of a vasodilatory phosphodiesterase-3 inhibitor may reverse this potentially detrimental process, the authors studied the effects of inhaled or intravenous milrinone on pulmonary and systemic hemodynamics in a rat model of CHF. Methods:In male Sprague-Dawley rats, CHF was induced by supracoronary aortic banding, whereas sham-operated rats served as controls. Milrinone was administered as an intravenous infusion (0.2–1 &mgr;g · kg body weight−1 · min−1) or by inhalation (0.2–5 mg/ml), and effects on pulmonary and systemic hemodynamics and lung water content were measured. Results:In CHF rats, intravenous infusion of milrinone reduced both pulmonary and systemic arterial blood pressure. In contrast, inhalation of milrinone predominantly dilated pulmonary blood vessels, resulting in a reduced pulmonary-to-systemic vascular resistance ratio. Repeated milrinone inhalations in 20-min intervals caused a stable reduction of pulmonary artery pressure. No hemodynamic effects were detected when 0.9% NaCl was administered instead of milrinone or when milrinone was inhaled in sham-operated rats. No indications of potentially adverse effects of milrinone inhalation in CHF, such as left ventricular volume overload, were detected. Moreover, lung edema was significantly reduced by repeated milrinone inhalation. Conclusion:If these results can be confirmed in humans, inhalation of nebulized milrinone may present a novel, effective, safe, and pulmonary selective strategy for the treatment of pulmonary venous hypertension in CHF.

Congenital NOS2 Deficiency Protects Mice from LPS-induced Hyporesponsiveness to Inhaled Nitric Oxide

BACKGROUND In animal models, endotoxin (lipopolysaccharide) challenge impairs the pulmonary vasodilator response to inhaled nitric oxide (NO). This impairment is prevented by treatment with inhibitors of NO synthase 2 (NOS2), including glucocorticoids and L-arginine analogs. However, because these inhibitors are not specific for NOS2, the role of this enzyme in the impairment of NO responsiveness by lipopolysaccharide remains incompletely defined. METHODS To investigate the role of NOS2 in the development of lipopolysaccharide-induced impairment of NO responsiveness, the authors measured the vasodilator response to inhalation of 0.4, 4, and 40 ppm NO in isolated, perfused, and ventilated lungs obtained from lipopolysaccharide-pretreated (50 mg/kg intraperitoneally 16 h before lung perfusion) and untreated wild-type and NOS2-deficient mice. The authors also evaluated the effects of breathing NO for 16 h on pulmonary vascular responsiveness during subsequent ventilation with NO. RESULTS In wild-type mice, lipopolysaccharide challenge impaired the pulmonary vasodilator response to 0.4 and 4 ppm NO (reduced 79% and 45%, respectively, P < 0.001), but not to 40 ppm. In contrast, lipopolysaccharide administration did not impair the vasodilator response to inhaled NO in NOS2-deficient mice. Breathing 20 ppm NO for 16 h decreased the vasodilator response to subsequent ventilation with NO in lipopolysaccharide-pretreated NOS2-deficient mice, but not in lipopolysaccharide-pretreated wild-type, untreated NOS2-deficient or untreated wild-type mice. CONCLUSIONS In response to endotoxin challenge, NO, either endogenously produced by NOS2 in wild-type mice or added to the air inhaled by NOS2-deficient mice, is necessary to impair vascular responsiveness to inhaled NO. Prolonged NO breathing, without endotoxin, does not impair vasodilation in response to subsequent NO inhalation. These results suggest that NO, plus other lipopolysaccharide-induced products, are necessary to impair responsiveness to inhaled NO in a murine sepsis model.

4-Aminopyridine Restores Impaired Hypoxic Pulmonary Vasoconstriction in Endotoxemic Mice

Background:Hypoxic pulmonary vasoconstriction (HPV) is impaired during inflammatory lung processes such as pneumonia or the acute respiratory distress syndrome. Voltage-gated potassium channels play a central role in mediating HPV. The aim of this study was to determine whether 4-aminopyridine (4-AP), a known voltage-gated potassium channel inhibitor, may restore HPV in sepsis. Methods:The effects of 0.01, 0.1, and 1.0 mm 4-AP on HPV responsiveness were assessed in isolated lungs of untreated mice and of mice 18 h after lipopolysaccharide injection (20 mg/kg intraperitoneal Escherichia coli 0111:B4 lipopolysaccharide). HPV was quantified as the increase in perfusion pressure in response to hypoxic ventilation in percent of baseline perfusion pressure. Intrinsic pulmonary vascular resistance (R0) and pulmonary vascular distensibility (&agr;) were determined by nonlinear regression analysis of pulmonary vascular pressure–flow curves generated during normoxic and hypoxic ventilation, respectively. Results:HPV was impaired in lungs isolated from lipopolysaccharide-challenged mice. Addition of 4-AP to the perfusate did not alter HPV responsiveness in untreated mice but dose dependently restored HPV in endotoxemic mice. Analysis of pulmonary vascular pressure–flow curves revealed that 4-AP (1) counteracted the observed lipopolysaccharide-induced changes in &agr; and R0 under normoxic conditions and (2) augmented the hypoxia-induced increase in R0 in lungs of endotoxemic mice. Conclusions:This study demonstrates that lipopolysaccharide-induced pulmonary vascular hyporesponsiveness to hypoxia can be restored by 4-AP in murine endotoxemia and, thus, may be a new therapeutic approach to treat patients with hypoxemia due to impaired HPV.

Effects of ketamine on hypoxic pulmonary vasoconstriction in the isolated perfused lungs of endotoxaemic mice.

Background and objective During sepsis and endotoxaemia, hypoxic pulmonary vasoconstriction (HPV) is impaired. Sedation of septic patients in ICUs is performed with various anaesthetics, most of which have pulmonary dilatory properties. Ketamine is a sympathetic nervous system-activating anaesthetic that preserves cardiovascular stability. The effects of ketamine on the pulmonary vasculature and HPV during sepsis have not been characterized yet. Methods Therefore, isolated lungs of mice were perfused with ketamine (0, 0.1, 1.0, and 10 mg kg−1 body weight min−1) 18 h following intraperitoneal injection of lipopolysaccharide (LPS); untreated mouse groups served as controls (n = 7 per group, respectively). Pulmonary artery pressure (PAP) and pressure–flow curves during normoxic (FiO2 = 0.21) and hypoxic (FiO2 = 0.01) ventilation were obtained. Results HPV was reduced in endotoxaemic animals when compared with controls (means ± SD; ΔPAP control 103 ± 28% vs. LPS 23 ± 25%, P < 0.05). Ketamine caused a dose-dependent reduction of HPV in the lungs of control (ΔPAP 0 mg kg−1 min−1 ketamine 103 ± 28% vs. 10 mg kg−1 min−1 ketamine 28 ± 21%, P < 0.05) and septic animals (ΔPAP 0 mg kg−1 min−1 ketamine 23 ± 25% vs. 10 mg kg−1 min−1 ketamine 0 ± 4%, P < 0.05). Analysis of pressure–flow curves revealed that ketamine partly reversed the endotoxin-induced changes in basal pulmonary vascular wall properties rather than interfering with the HPV response itself. Conclusion Ketamine modified baseline pulmonary vascular properties, resulting in a reduced HPV responsiveness in untreated mice. Further, ketamine counteracted the LPS-induced changes in pulmonary vascular pressure–flow relationships, but did not affect impaired HPV in this murine endotoxaemia model.

Inhibition of Kv channels by 4-aminopyridine restores impaired hypoxic pulmonary vasoconstriction (HPV) in endotoxemic mice: 5AP2-2

in PAP ([mean SD] LPS: 7 5% vs. control: 55 5%; p 0.05). There was no effect of iCO exposure on PAP in untreated control animals. Exposure of LPS-pretreated mice to 50 ppm iCO completely prevented the development of impaired HPV ( PAP 49 21%; p 0.05 vs. LPS). However, this effect vanished with increasing iCO doses and was absent at 500 ppm iCO ( PAP 12 8%). This was associated with increasing CO-Hb blood levels, but could be overcome by reducing these by exposure with 500 ppm iCO in 50% O2 ( PAP 60 18%). Conclusions: Here we showed that low dose CO inhalation may prevent LPS-induced impairment of HPV in mice. Of interest, this effect vanished with increasing doses of iCO. Our data further suggest, that high CO-Hb levels associated with CO exposure may counteract the beneficial effects of iCO during sepsis. Reference: 1 Spöhr F, Cornelissen AJM, Busch C, et al. Am J Physiol Heart Circ Physiol 2005; 289: 823-831.

Nitric oxide inhalation decreases pulmonary artery remodelling in the injured lungs of rat pups

Vascular injury causes the muscularization of peripheral pulmonary arteries, which is more pronounced in the infant than in the adult lung. Although inhaled NO gas attenuates pulmonary artery remodeling in hypoxic rats, whether or not it protects the lung by mitigating vasoconstriction is unknown. This investigation tested whether inhaled NO decreases the muscularization of injured pulmonary arteries in rat pups by modulating vascular tone. One week after monocrotaline administration, the percentage of muscularized rat pup lung arteries was increased by >3-fold. Nevertheless, monocrotaline exposure did not cause right ventricular hypertrophy, pulmonary hypertension, or vasoconstriction. In addition, it did not increase the expression of markers of inflammation (interleukin-1beta, intercellular adhesion molecule-1, and E-selectin) or of platelet-mediated thrombosis (GPIbalpha). Continuous inhalation of 20 ppm NO gas prevented the neomuscularization of the pulmonary arteries in pups with lung injury. Moreover, a 3-fold increase in cell proliferation and 30% decrease in cell numbers in pulmonary arteries caused by monocrotaline exposure was prevented by NO inhalation. These data indicate that inhaled NO protects infants against pulmonary remodeling induced by lung injury by mechanisms that are independent of pulmonary tone, inflammation, or thrombosis.