Abstract 331 Poster Session IV, Tuesday, 5/4 (poster 222)

Introduction

The chick embryo develops a protective response to acute hypoxia during the second half of incubation. One part of this response is a redistribution of the cardiac output in favor of heart and brain. This redistribution seems to be the result of activation of the autonomous nerve system by chemoreceptor response and by circulating catecholamines. In the present study we measured the cardiac output distribution during normoxia and after 5 minutes of hypoxia (100% N2) in two groups of chick embryos at day 11, 15, and 19 of incubation. The normal incubation time until hatching is 21 days. To investigate the role of the autonomous nerve system one group received ganglion blocker hexamethonium, the other group served as control.

Methods

Fertilized eggs were placed in a Plexi Glass box in which oxygen concentration could be changed. The eggs were opened at the air cell. A chorioallantoic vein was catheterized and cardiac output distribution was determined in normoxia and after 5 minutes of hypoxia using injections of fluorescent microspheres.

Results

Hypoxia caused a similar cardiac output redistribution in favor of heart and brain in both hexamethonium group and controls.

Conclusion

The chick embryo shows during hypoxia a redistribution of the cardiac output in favor of heart and brain. After blockade of the autonomous nerve system with hexamethonium this redistribution is not changed, suggesting no important role for the autonomous nerve system in the hypoxia response.