Measurement of blood flow in the chick egg yolk sac membrane

Blood vessels of the yolk sac membrane are the transport route by which a chick embryo obtains nutrients from the egg yolk. After 4 days of incubation at 37 degrees C a sparse network of blood vessels are visible within the membrane and they become denser over the following days. The preparation has been used to assess angiogenesis. Using visual inspection to assess the growth of new vessels towards pellets of test substances placed on the membrane surface, responses are judged negative or positive. Laser Doppler flowmetry has been used to investigate the potential of this technique to quantify blood flow through the yolk sac membrane. Measurements have been taken from capillary beds and single larger vessels over a range of temperatures and from avascular yolk and egg white using a Perimed PF3 with PF310 bent-tipped probe. Capillary beds exhibited vasomotion (about one cycle per minute) and oscillations of longer duration (about five cycles per hour). Cardiac pulses, strongly present in larger vessels (mean 90 pu, pulse 75 pu), were not easily identified in the capillary bed. Avascular yolk measurements gave flux values (due to Brownian motion of yolk proteins) which were greater than for capillary beds but without oscillations. Angiogenesis was stimulated by pellets containing 2 micrograms of basic fibroblast growth factor. There were significant increases in single vessel blood flow after 24 h compared with blank control pellets placed on the same egg.