DISTRIBUTION OF BLOOD-FLOW BETWEEN EMBRYO AND VITELLINE BED IN THE STAGE-18, STAGE-21 AND STAGE-24 CHICK-EMBRYO

Objective: We defined the distribution of blood flow between the embry o and the extraembryonic vascular bed as an initial step in understand ing the control of flow distribution in the early developing heart. Me thods: Dorsal aortic blood flow of stage 18, 21, and 24 chick embryo ( n greater than or equal to 7 at each stage) was measured with a 20 MHz pulsed-Doppler velocity meter. Analog waveforms were digitally sample d at 500 Hz. 1-5 x 10(3) yellow microspheres in saline suspension were injected into the vitelline vein. The embryo and the extraembryonic v ascular bed were harvested and separated from each other. The dye on t he microspheres from each portion was extracted and extrapolated from the standard curve of the absorbance of dye concentrations per number of microspheres quantified by spectrophotometry. Blood flow was calcul ated from the integral of blood velocity and aortic cross-sectional ar ea multiplied by the fraction distribution of microspheres in the embr yo and extraembryonic vascular bed. Data were presented as mean +/- st andard error of the mean. Results: The proportion distribution of micr ospheres between embryo and extraembryonic vascular bed shifted from 1 8.7 +/- 2.5 vs. 81.3 +/- 2.5% at stage 18, 25.1 +/- 3.0 vs, 74.9 +/- 3 .0% at stage 21, and 34.2 +/- 2.4 vs. 65.8 +/- 2.4% at stage 24. Indic es of blood flow normalized to wet weight (mean +/- 95% confidence int erval) were similar between the embryo and the extraembryonic vascular bed, but increased throughout the stages. Conclusion: During embryoge nesis, blood flow per unit mass is evenly distributed between the meta bolically active embryo and the extraembryonic vascular bed.