Hypoxic pulmonary vasoconstriction (HPV) is a physiological mechanism by which pulmonary arteries constrict in hypoxic lung areas in order to redirect blood flow to areas with greater oxygen supply. Both oxygen sensing and the contractile response are thought to be intrinsic to pulmonary arterial smooth muscle cells. Here we speculated that the ideal site for oxygen sensing might instead be at the alveolocapillary level, with subsequent retrograde propagation to upstream arterioles via connexin 40 (Cx40) endothelial gap junctions. HPV was largely attenuated by Cx40-specific and nonspecific gap junction uncouplers in the lungs of wildtype mice and in lungs from mice lacking Cx40 (Cx40 -/-). In vivo, hypoxemia was more severe in Cx40 -/-mice than in wild-type mice. Real-time fluorescence imaging revealed that hypoxia caused endothelial membrane depolarization in alveolar capillaries that propagated to upstream arterioles in wild-type, but not Cx40 -/-, mice. Transformation of endothelial depolarization into vasoconstriction involved endothelial voltage-dependent α 1G subtype Ca 2+ channels, cytosolic phospholipase A 2 , and epoxyeicosatrienoic acids. Based on these data, we propose that HPV originates at the alveolocapillary level, from which the hypoxic signal is propagated as endothelial membrane depolarization to upstream arterioles in a Cx40-dependent manner. IntroductionHypoxic pulmonary vasoconstriction (HPV) is a fundamental physiological mechanism by which the lung optimizes ventilation/ perfusion (V/Q) matching, redirecting blood flow from poorly to better ventilated areas (1). Yet in cases of global hypoxia, HPV may unfavorably increase total pulmonary vascular resistance and right ventricular afterload, thus contributing to the clinical pathology of pulmonary hypertension and cor pulmonale in chronic hypoxic lung diseases or to pulmonary edema at high altitude (1, 2). While the relevance of HPV has been recognized for over 60 years, the underlying oxygen sensing and signal transduction processes remain a topic of intense research and controversy. Current concepts of HPV are largely based on the notion that pulmonary arterial smooth muscle cells (PASMCs) constitute both the sensor and the transducer of the hypoxic signal as well as its contractile effector (1), while the role of the vascular endothelium is at best considered that of a modulating bystander.From a conceptual standpoint, the ideal site for an oxygen sensor in HPV is within the actual area of pulmonary gas exchange,

Angiotensin-(1-7) or its analogs attenuate the key features of acute lung injury and may present a promising therapeutic strategy for the treatment of this disease.

We describe for the first time in detail the different forms and temporal sequence of impaired alveolar dynamics in the acutely injured lung and report the first direct visualization of alveolar pendelluft. Moreover, we identify individual sighs as an effective strategy to restore intact alveolar ventilation by a mechanism independent of alveolar collapse and reopening.

The pathogenesis of ventilator-induced lung injury has predominantly been attributed to overdistension or mechanical opening and collapse of alveoli, whereas mechanical strain on the airways is rarely taken into consideration. Here, we hypothesized that mechanical ventilation may cause significant airway distension, which may contribute to the pathological features of ventilator-induced lung injury. C57BL/6J mice were anesthetized and mechanically ventilated at tidal volumes of 6, 10, or 15 ml/kg body wt. Mice were imaged by flat-panel volume computer tomography, and central airways were segmented and rendered in 3D for quantitative assessment of airway distension. Alveolar distension was imaged by intravital microscopy. Functional dead space was analyzed in vivo, and proinflammatory cytokine release was analyzed in isolated, ventilated tracheae. CT scans revealed a reversible, up to 2.5-fold increase in upper airway volume during mechanical ventilation compared with spontaneous breathing. Airway distension was most pronounced in main bronchi, which showed the largest volumes at tidal volumes of 10 ml/kg body wt. Conversely, airway distension in segmental bronchi and functional dead space increased almost linearly, and alveolar distension increased even disproportionately with higher tidal volumes. In isolated tracheae, mechanical ventilation stimulated the release of the early-response cytokines TNF-α and IL-1β. Mechanical ventilation causes a rapid, pronounced, and reversible distension of upper airways in mice that is associated with an increase in functional dead space. Upper airway distension is most pronounced at moderate tidal volumes, whereas higher tidal volumes redistribute preferentially to the alveolar compartment. Airway distension triggers proinflammatory responses and may thus contribute relevantly to ventilator-induced pathologies.

Genetic alterations can unpredictably compromise the wellbeing of animals. Thus, more or less harmful phenotypes might appear in the animals used in research projects even when they are not subjected to experimental treatments. The severity classification of suffering has become an important issue since the implementation of Directive 2010/63/EU on the protection of animals used for scientific purposes. Accordingly, the breeding and maintenance of genetically altered (GA) animals which are likely to develop a harmful phenotype has to be authorized. However, a determination of the degree of severity is rather challenging due to the large variety of phenotypes. Here, the Working Group of Berlin Animal Welfare Officers (WG Berlin AWO) provides field-tested guidelines on severity assessment and classification of GA rodents. With a focus on basic welfare assessment and severity classification we provide a list of symptoms that have been classified as non-harmful, mild, moderate or severe burdens. Corresponding monitoring and refinement strategies as well as specific housing requirements have been compiled and are strongly recommended to improve hitherto applied breeding procedures and conditions. The document serves as a guide to determine the degree of severity for an observed phenotype. The aim is to support scientists, animal care takers, animal welfare bodies and competent authorities with this task, and thereby make an important contribution to a European harmonization of severity assessments for the continually increasing number of GA rodents.