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A Novel Ex Ovo Banding Technique to Alter Intracardiac Hemodynamics in an Embryonic Chicken System
Published on: May 13, 2016
Interruption of cardiac output does not affect short-term growth and metabolic rate in day 3 and 4 chick embryos
W W Burggren1, S J Warburton, M D Slivkoff
1Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA. burggren@unt.edu
Insights
Early chick embryos develop a heartbeat before it is needed for nutrient transport, indicating its role may be in angiogenesis. Growth and oxygen consumption are independent of cardiac output in these early developmental stages.
Area of Science:
- Developmental Biology
- Embryology
- Physiology
Background:
- The onset of the vertebrate embryonic heart beat is traditionally linked to the establishment of convective blood transport.
- This study investigates the necessity of cardiac output for early embryonic development and metabolic function.
Purpose of the Study:
- To determine if cardiac output is essential for embryonic growth and oxygen consumption in early chick embryos.
- To challenge the established hypothesis regarding the timing and function of the embryonic heart beat.
Main Methods:
- Chick embryos (days 3-4) were subjected to outflow tract ligation to inhibit cardiac output.
- Embryonic growth (eye diameter), cervical flexure, and oxygen consumption rates (V(O2)) were measured and compared to control and sham-ligated embryos.
Main Results:
- Embryonic growth rates and cervical flexure progression were not significantly affected by the ligation of the outflow tract.
- Oxygen consumption (V(O2)) remained statistically similar between ligated and control embryos on both day 3 and day 4.
- Regression analysis showed no dependence of V(O2) on cardiac output, with similar slopes across groups.
Conclusions:
- Early embryonic growth and oxygen consumption are independent of cardiac output and convective blood flow.
- The findings suggest that the embryonic heart beat and blood flow develop hours or days before being required for nutrient and oxygen transport.
- Angiogenesis is proposed as the most probable function for the early establishment of the embryonic heart beat.
Abstract:
The heart beat of vertebrate embryos has been assumed to begin when convective bulk transport by blood takes over from transport by simple diffusion. To test this hypothesis, we measured eye growth, cervical flexure and rates of oxygen consumption ( V(O2)) in day 3-4 chick embryos denied cardiac output by ligation of the outflow tract and compared them with those of embryos with an intact cardiovascular system. Eye diameter, used as the index for embryonic growth, increased at a rate of approximately 4.5-5 % h(-)(1) during the observation period. There was no significant difference (P>0.1) in the rate of increase in eye diameter between control (egg opened), sham-ligated (ligature present but not tied) and ligated embryos. Similarly, the normal progression of cervical flexure was not significantly altered by ligation (P>0.1). V(O2) (ml O(2 )g(-)(1 )h(-)(1)) at 38 degrees C, measured by closed respirometry, was not significantly different (P>0.1) on day 3 in sham-ligated (14.5+/-1.9 ml O(2 )g(-)(1 )h(-)(1)) and ligated 17.6+/-1.8 ml O(2 )g(-)(1 )h(-)(1)) embryos. Similarly, on day 4, V(O2) in sham-ligated and ligated embryos was statistically the same (sham-ligated 10. 5+/-2.9 ml O(2 )g(-)(1 )h(-)(1); ligated 9.7+/-2.9 ml O(2 )g(-)(1 )h(-)(1)). Expressed as a linear function of body mass (M), V(O2) in sham-ligated embryos was described by the equation V(O2)=-0.48M+24.06 (r(2)=0.36, N=18, P<0.01), while V(O2) in ligated embryos was described by the equation V(O2)=-0.53M+23.32 (r(2)=0.38, N=16, P<0.01). The regression line describing the relationship between body mass and V(O2) for pooled sham-ligated and ligated embryos (the two populations being statistically identical) was V(O2)=-0.47M+23.24. The slope of this regression line, which was significantly different from zero (r(2)=0.30, N=34, P<0.01), was similar to slopes calculated from previous studies over the same range of body mass.Collectively, these data indicate that growth and V(O2) are not dependent upon cardiac output and the convective blood flow it generates. Thus, early chick embryos join those of the zebrafish, clawed frog and axolotl in developing a heart beat and blood flow hours or days before required for convective oxygen and nutrient transport. We speculate that angiogenesis is the most likely role for the early development of a heart beat in vertebrate embryos.
