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Changes in mean chorioallantoic artery blood flow and heart rate produced by hypoxia in the developing chick embryo
J van Golde1, T Mulder, C E Blanco
1Department of Neonatology, Academic Hospital Maastricht, The Netherlands.
Insights
Hypoxia in chick embryos causes cardiovascular changes like decreased heart rate and blood flow, similar to mammalian fetuses. This response intensifies with embryo development, suggesting maturing cardiovascular control.
Area of Science:
- Developmental Biology
- Cardiovascular Physiology
- Comparative Physiology
Background:
- Fetal hypoxia in mammals induces significant cardiovascular alterations, including bradycardia and hypertension.
- Understanding avian embryonic cardiovascular responses to hypoxia provides insights into conserved physiological mechanisms.
Purpose of the Study:
- To investigate the cardiovascular response of chick embryos to hypoxic conditions.
- To compare the hypoxia-induced cardiovascular changes in chick embryos with those observed in mammalian fetuses.
Main Methods:
- Chick embryos (stages 34-42) were exposed to two levels of hypoxia (100% N2 or 5% O2) for 5 minutes.
- Chorioallantoic artery blood flow (CABF) and heart rate were measured using a flow probe.
- Measurements included mean CABF, heart rate, peak flow, and blood flow acceleration.
Main Results:
- Both mean CABF and heart rate significantly decreased under hypoxia (p < 0.05), with a more pronounced effect in later developmental stages.
- Hypoxia led to decreased chorioallantoic artery peak flow and CABF acceleration.
- Heart rate recovered to baseline, while mean CABF exhibited an overshoot post-hypoxia.
Conclusions:
- The cardiovascular response to hypoxia in chick embryos mirrors that of mammalian fetuses.
- The heightened response in more developed embryos suggests a maturation of cardiovascular control mechanisms during incubation.
Abstract:
Hypoxia in the mammalian fetus produces cardiovascular changes, such as bradycardia, systemic hypertension, and changes in heart rate variability. This response was studied in 140 chick embryos ranging from stage 34 to stage 42 (d 9-16 of the 21-d incubation), by measuring the changes in mean chorioallantoic artery blood flow (CABF) and heart rate for 5 min in two levels of hypoxia (group 1; n = 90; 100% N2) or (group 2; n = 50; 5% O2). Eggs were opened at the air cell and placed in a small plexiglass holder, which had a continuous gas flow of an O2/N2 mixture (5 L/min), at 38 degrees C and 60% humidity. The chorioallantoic artery was placed in the lumen of a flow probe to measure mean CABF, heart rate, peak flow, and blood flow acceleration. After baseline measurements, the gas mixture was changed to 100% N2 or 5% O2 in N2 for 5 min. Mean CABF and heart rate decreased significantly in both groups (Wilcoxon paired sample test, p < 0.05). This response was more pronounced with the development of the chick embryo. Chorioallantoic artery peak flow (mL/min) and CABF acceleration (mL/s2) increased with incubation time and decreased during periods of hypoxia. During recovery, heart rate returned to baseline levels, whereas mean CABF showed an overshoot. The initial decrease in mean CABF and heart rate was similar in both groups. The cardiovascular response to hypoxia in the chick embryo is similar to the response in the mammalian fetus. The more pronounced response in the more developed chick embryo may represent a maturation of cardiovascular control.