Epigenetic role of epidermal growth factor expression and signalling in embryonic mouse lung morphogenesis.

A major unsolved problem in developmental biology is to determine when and how time- and position-restricted instructions are signaled and received during secondary embryonic inductions such as branching morphogenesis. The mouse embryonic lung rudiment was used to test the hypothesis that endogenous peptide growth factors, specifically epidermal growth factor (EGF), serve as instructive epigenetic signals for morphogenesis. The presence of EGF precursor mRNA transcripts was detected using the reverse-transcriptase-coupled polymerase chain reaction both in E11-E17-day mouse embryo lung tissues in vivo and in E11-day lung cultured for up to 7 days in vitro under chemically defined, serum-free conditions. Immunolocalization identified a position-restricted distribution of EGF in and around the primitive airways both during in vivo lung morphogenesis and in culture. EGF receptors (EGFR) coimmunolocalized with EGF in the primitive airways. Addition of exogenous EGF to lungs in culture resulted in significant concentration-dependent stimulation of branching morphogenesis, DNA, RNA, and protein content, and in [3H]thymidine incorporation into DNA. Conversely, the addition of tyrphostin (specific EGF receptor kinase antagonist) to lungs in culture resulted in concentration-dependent inhibition of branching morphogenesis, DNA, RNA, and protein content, and in [3H]thymidine incorporation into DNA without apparent cytotoxicity. The inhibition of the EGF signal by tyrphostin was confirmed by immunoprecipitation of tyrosine phosphoproteins. We conclude that early mouse embryo lungs express EGF transcripts and corresponding EGF peptides in a specific position-restricted distribution which coimmunolocalizes with EGFR in the primitive airways, while stimulatory and inhibitory studies indicate a functional role for the transduced EGF signal in the epigenetic regulation of lung branching morphogenesis. We speculate that the peptide growth factor EGF serves a function in secondary embryonic morphogenetic inductions, which may be modulated by interaction with other growth factors.

Effect of fasting on the lung glutathione redox cycle in air- and oxygen-exposed mice: beneficial effects of sugar.

Fasting increases susceptibility to hyperoxic lung damage in mice, at least in part, by decreasing lung glutathione level. To determine whether fasting alters other components of the glutathione redox cycle, and whether a diet of sugar alone reverses fasting's effects, normally fed, sugar-fed, and fasted mice were exposed to room air or 100% oxygen for up to 4 days. In air-exposed mice, fasting decreased glutathione peroxidase (GP) and glutathione reductase (GR) activities 15% to 20% on days 3 and 4 (p less than 0.01) and glutathione level 25% to 30% on days 2 to 4 (p less than 0.05). When corrected for protein concentration, GP and GR values were similar to those in the fed mice, but glutathione levels remained lower on days 2 and 3 (p less than 0.05). Oxidized glutathione (GSSG) was unchanged, but the ratio of GSSG to total glutathione (reduced glutathione plus GSSG) increased on day 2 (p less than 0.05). In oxygen-exposed fed mice, GP increased 62% and GR increased 39% on day 4 (p less than 0.05), the time when the lung injury was most severe; glutathione increased 30% on days 3 and 4 (p less than 0.05); and GSSG increased threefold and eightfold on days 3 and 4 (p less than 0.01). Oxygen-exposed fasted mice were all dead by day 3 (versus no deaths in the fed mice), failed to increase GR and total glutathione in response to the oxidant stress, and increased GP and GSSG on day 3 to the same extent as the fed mice did on day 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of high-frequency oscillatory ventilation and high-frequency jet ventilation in cats with normal lungs.

Four adult cats received alternating high-frequency oscillatory ventilation (HFOV) and high-frequency jet ventilation (HFJV) at equivalent proximal airway pressures. Physiologic measurements were made before and after each ventilator change. Proximal airway pressures were then adjusted as necessary to reestablish normal pH and PaCO2 values. Aortic, pulmonary artery, and central venous pressures were monitored. Cardiac outputs were measured. Pulmonary and systemic vascular resistance, intrapulmonary shunt, and alveolar-arterial oxygen gradient were determined. Following the change from HFOV to HFJV at similar proximal airway pressures, HFJV always produced higher pH values (P less than 0.0001), higher PaO2 values (P less than 0.05), lower PaCO2 values (P less than 0.0001), as well as higher cardiac outputs (P less than 0.01), lower pulmonary artery pressures (P less than 0.001), and lower pulmonary vascular resistances (P less than 0.001). Following the reciprocal crossover, from HFJV to HFOV, HFJV pH values were again higher (P less than 0.001), and PaCO2 values were again lower (P less than 0.001). A comparison of HFOV and HFJV at similar pH and PaCO2 values showed that HFOV consistently required higher peak inspiratory pressures (P less than 0.001), higher mean airway pressure (P less than 0.001), and higher pressure wave amplitudes (P less than 0.001). Under the circumstances of this study, HFJV produced better gas exchange at lower proximal airway pressures.