GREYNER, H*; COPELAND, J; PALENSKE, N; WARBURTON, S; BURGGREN, WW; DZIALOWSKI, EM; Univ. of North Texas, Denton; Univ. of North Texas, Denton; Univ. of North Texas, Denton; Northern Arizona Univ., Flagstaff; Univ. of North Texas, Denton; Univ. of North Texas, Denton: Cardiovascular changes during hatching in emus (Dromaius novaehollandiae)

In developing avian embryos, the right and left ductus arteriosi (DA) allow for a shunt of systemic venous return away from the lungs to the body and chorioallantoic membrane (CAM). Here we examined the physiological and morphological changes in the emu (Dromaius novaehollandiae) DA that occur during hatching. By examining the distribution of microspheres injected into a CAM vein, we found that there was no change in DA blood flow between the pre-pipped to internally pipped stages. Two hours after external pipping, a significant (p<0.05) decrease in DA blood flow was observed as a decrease in systemic blood flow and a subsequent increase in lung blood flow. Upon hatching, the right-to-left shunt disappeared, suggesting complete, quick closure of the DA. These physiological changes in DA blood flow at hatching correspond to a large decrease in the DA lumen diameter from the pre-pipped stage to Day 1 hatchlings. It is expected that increased arterial oxygen tensions during hatching stimulate the closure of the DA. To examine this, we measured in vitro contraction of the right DA and aorta in pre-pipped embryos in response to increased oxygen. The oxygen-induced contraction of the DA was significantly larger than the response to 120 mM KCl and produced double the contractile tension of the aorta. Between the initiation of external pipping and hatching the DA closes rapidly, resulting in circulatory patterns similar to the adult. This response is most likely produced by increased DA constriction in response to increased arterial oxygen levels and the initiation of vessel remodeling. This study was funded by NSF grant IOB0417205 to EMD.