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The oxygen content in the environment is very important for the normal development as its changes can significantly influence the embryogenesis and the survival of the hatchlings. It is known, that the response of the developing chick embryo to hypoxia is a complex process, depending on developmental stage, but the mechanism remains unknown. Numerous functional systems, including the extra-embryonic membranes, are involved in this response to protect vital organs from the damage.
The present study describes the effect of the extreme (10% O2) and mild (15% O2) acute hypoxia on the frequency of amnion rhythmic contractions (ARC) and heart rate (HR) of chick embryo. The ARC in the developing eggs were recorded using a force transducer, connected with amniotic membrane, HR was recorded simultaneously using the digital video camera. The recordings were performed under normal conditions and under acute hypoxia for periods of 10–20 minutes on 12-14 embryonic days. After the hypoxic exposure the concentration of adrenaline, noradrenaline and dopamine was measured in the amniotic fluid using the HPLC method.
Exposure of eggs to 10% or 15% O2 inhibited or arrested ARC and decreased HR. The effects of these hypoxia treatments were fully reversible after both 10 and 20 minutes of exposure. The significant increase of dopamine and noradrenaline concentration but not adrenaline concentration in amniotic fluid was found after exposure of eggs to 10% O2.
Thus, the decrease of ARC frequency accompany the changes in cardiovascular system during the acute hypoxia. We suppose that there is not only a direct influence of the low oxygen tension on the amnion, but an indirect influence through the increase of the concentration of the inhibitors, such as noradrenaline and dopamine, in the amniotic fluid.