Hypoxic incubation remodeling parabronchial morphology in chicks

Hypoxia during incubation is known to induce many morphophysiological changes that facilitate O₂ exchange, like increased mass and angiogenesis of chorioalantoic membrane. After hatch the chicks also have physiological alterations to hypoxic incubation, including alterations in metabolic rate and ventilatory responses to hypoxia. The phase of incubation that the embryo is exposed to hypoxia is relevant for system plasticity occurs; these are critical windows of development. Lung maturity occurs late during incubation, which may constitute a critical window for the effect of hypoxia in parabronchi (which contains functional structures to gas exchange) development. Thus, we aimed at investigating the effect of hypoxia (15% O₂) from day 12 to 18 of incubation on the parabronchial structure of 1- and 10-day-old chicks. Lungs of chicks from hypoxic and normoxic incubation were fixed into body, extracted from the celomatic cavity, prepared for light microscopy. Stereological techniques were used for measuring lung volume and the density that each structure represents in parabronchi (%). The quantified structures were air capillaries, blood capillaries, atria, infundibula, parabronchial lumen, interparabronchial tissue and blood vessels larger than capillaries. Normoxic 1- and 10-day-old chicks had 22.90%?0.02 and 20.80%?0.02, respectively, of parabronchi occupied by blood capillaries. Hypoxic incubation increased 20.08% of blood capillaries in 1- and 13.30% in 10-day-old chicks (p <0.001). Not only blood but air cappilaries were also favoured by hypoxia. Normoxic group had 14.50%?0.02 of parabronchi occupied by air capillaries in 1 day old and 15.70%?0.02 in 10 days old animals; hypoxia-induced increase in density was 23.44% and 42.03%, respectively (p <0.001). In contrast, air-conducting areas, such as atria and parabronchial lumen had a decrease in density in hypoxic incubated chicks, while no change was observed in total lung volume. Our results indicate that reducing concentration of oxygen during a critical phase of lungs development seems to favour regions for gas exchange in expense of non-exchange areas, at least up to 10 days post hatching.