The use of prolonged respiratory support under the form of high-flow nasal cannula (HFNC) or nasal continuous positive airway pressure (nCPAP) is frequent in newborn infants. Introduction of oral feeding under such nasal respiratory support is, however, highly controversial among neonatologists, due to the fear that it could disrupt sucking, swallowing, and breathing coordination and in turn induce cardiorespiratory events. The recent observation of tracheal aspirations during bottle-feeding in preterm infants under nCPAP justifies the use of animal models to perform more comprehensive physiological studies on the subject, in order to gain further insights for clinical studies. The objective of this study was to assess and compare the impact of HFNC and nCPAP on bottle-feeding in newborn lambs, in terms of bottle-feeding efficiency and safety as well as sucking–swallowing–breathing coordination. Eight full-term lambs were instrumented to record sucking, swallowing, and respiration as well as electrocardiogram and oxygenation. Lambs were bottle-fed in a standardized manner during three randomly ordered conditions, namely nCPAP 6 cmH2O, HFNC 7 L/min, and no respiratory support. Results revealed that nCPAP decreased feeding duration [25 vs. 31 s (control) vs. 57 s (HFNC), p = 0.03] and increased the rate of milk transfer [2.4 vs. 1.9 mL/s (control) vs.1.1 mL/s (HFNC), p = 0.03]. No other indices of bottle-feeding safety or sucking–swallowing–breathing coordination were significantly altered by HFNC or nCPAP. In conclusion, our results obtained in full-term newborn lambs suggest that: (i) nCPAP 6 cmH2O, but not HFNC 7 L/min, increases bottle-feeding efficiency; (ii) bottle-feeding is safe under nCPAP 6 cmH2O and HFNC 7 L/min, with no significant alteration in sucking–swallowing–breathing coordination. The present informative and reassuring data in full-term healthy lambs must be complemented by similar studies in preterm lambs, including mild-to-moderate respiratory distress alleviated by respiratory support in order to mimic preterm infants with bronchopulmonary dysplasia and pave the way for clinical studies.

Background Deep vein thrombosis (DVT) is the primary cause of pulmonary embolism and the third most life‐threatening cardiovascular disease in North America. Post‐DVT anticoagulants, such as warfarin, heparin, and direct oral anticoagulants, reduce the incidence of subsequent venous thrombi. However, all currently used anticoagulants affect bleeding time at various degrees, and there is therefore a need for improved therapeutic regimens in DVT. It has recently been shown that mast cells play a crucial role in a DVT murine model. The underlying mechanism involved in the prothrombotic properties of mast cells, however, has yet to be identified. Methods and Results C57BL/6 mice and mouse mast cell protease‐4 (mMCP‐4) genetically depleted mice (mMCP‐4 knockout) were used in 2 mouse models of DVT, partial ligation (stenosis) and ferric chloride–endothelial injury model of the inferior vena cava. Thrombus formation and impact of genetically repressed or pharmacologically (specific inhibitor TY‐51469) inhibited mMCP‐4 were evaluated by morphometric measurements of thrombi immunochemistry (mouse and human DVT), color Doppler ultrasound, bleeding times, and enzymatic activity assays ex vivo . Recombinant chymases, mMCP‐4 (mouse) and CMA‐1 (human), were used to characterize the interaction with murine and human plasmin, respectively, by mass spectrometry and enzymatic activity assays. Inhibiting mast cell–generated mMCP‐4, genetically or pharmacologically, resolves and prevents venous thrombus formation in both DVT models. Inferior vena cava blood flow obstruction was observed in the stenosis model after 6 hours of ligation, in control‐ but not in TY‐51469–treated mice. In addition, chymase inhibition had no impact on bleeding times of healthy or DVT mice. Furthermore, endogenous chymase limits plasmin activity in thrombi ex vivo. Recombinant mouse or human chymase degrades/inactivates purified plasmin in vitro. Finally, mast cell–containing immunoreactive chymase was identified in human DVT. Conclusions This study identified a major role for mMCP‐4, a granule‐localized protease of chymase type, in DVT formation. These findings support a novel pharmacological strategy to resolve or prevent DVT without affecting the coagulation cascade through the inhibition of chymase activity.

Multiple sclerosis is a neurodegenerative disease affecting predominantly female patients between 20 and 45 years of age. We previously reported the significant contribution of mouse mast cell protease 4 (mMCP-4) in the synthesis of endothelin-1 (ET-1) in healthy mice and in a murine model of experimental autoimmune encephalomyelitis (EAE). In the current study, the cardiovascular effects of ET-1 and big endothelin-1 (big-ET-1) administered systemically or intrathecally were assessed in the early preclinical phase of EAE in telemetry instrumented/conscious mice. Chymase-specific enzymatic activity was also measured in the lung, brain, and mast cell extracts in vitro. Finally, the impact of EAE immunization was studied on the pulmonary and brain mRNA expression of different genes of the endothelin pathway, interleukin-33 (IL-33), and monitoring of immunoreactive tumor necrosis factor-a (TNF-a). Systemically or intrathecally administered big-ET-1 triggered increases in blood pressure in conscious mice. One week post-EAE, the pressor responses to big-ET-1 were potentiated in wild-type (WT) mice but not in mMCP-4 knockout (KO) mice. EAE triggered mMCP-4-specific activity in cerebral homogenates and peritoneal mast cells. Enhanced pulmonary, but not cerebral preproendothelin-1 and IL-33 mRNA were found in KO mice and further increased 1 week post-EAE immunization, but not in WT animals. Finally, TNF-a levels were also increased in serum from mMCP-4 KO mice, but not WT, 1 week post-EAE. Our study suggests that mMCP-4 activity is enhanced both centrally and systemically in a mouse model of EAE.

Angiotensin-converting enzyme (ACE), 7-amino-4-methylcoumarin (AMC), Angiotensin I (Ang I), Angiotensin II (Ang II), big endothelin-1 (big ET-1), bovine serum albumin (BSA), Compound 48/80 (C48/80), endothelin-1 (ET-1), endothelin-1 (1-31) (ET-1 (1-31)), endothelin-converting enzyme (ECE), heart rate (HR), intramuscular (IM), intraperitoneal (IP), intravenous (IV), knock out (KO), mean arterial pressure (MAP), mouse mast cell protease 4 (mMCP-4), neprilysin (NEP), nitric oxide (NO), phosphate buffer solution (PBS), recombinant mMCP-4 (rmMCP-4), variations (Δ), wild-type (WT).