Abstract 330

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 circulating catecholamines. In the present study we measured the cardiac output distribution during normoxia and after 5 minutes of hypoxia in two groups of chick embryos at day 11, 15 and 19 of incubation. The normal incubation time until hatching is 21 days. To study the contribution of alphareceptor stimulation by catecholamines in the response to hypoxia we treated one group with alphareceptor blocker phentolamine. 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

The control group showed during hypoxia an increase in the cardiac output directed to the heart from 46 to 163% and to the brain from 18 to 62% at the expense of liver, intestine, yolk and carcass. In the phentolamine group the increase in cardiac output directed to the heart decreased (21 to 74%) and the increase to the brain disappeared (8 minus 25%). After alphareceptor blockade the fraction of the cardiac output directed to the carcass increased in response to hypoxia with 6 to 28%.

Conclusion

Hypoxia produces alphareceptor stimulation resulting in peripheral vasoconstriction which causes a redistribution of the cardiac output in favor of heart and brain.