Respiratory function of catecholamines during the late period of avian development

To study the function of catecholamines in the late period of avian embryogenesis, the time course of plasma catecholamines, the release of catecholamines by hypoxia and finally the effect of adrenergic agents on blood parameters and on circulation were recorded. The experiments reveal a temporary increase in plasma adrenaline and noradrenaline shortly before internal pipping occurs. On the other hand a premature increase of plasma catecholamines is induced by hypoxia. Furthermore, treating the embryo with adrenergic agents such as adrenaline, noradrenaline and phenylephrine resulted in changes of blood gas parameters: increase of PO2, O2-saturation and negative base excess, decrease of PCO2 and HCO3-. In addition, exogenous adrenaline and noradrenaline released an increase in the blood flow and an enhanced hemoglobin content in the chorioallantoic membrane, but not in the kidneys. Finally, adrenaline caused a decrease of 2,3 DPG and an increase of lactate in the plasma. The data indicate that hypoxia, which is formed normally towards the end of embryogenesis, induces an increased secretion of catecholamines which in turn improves the blood gas status. In this way the embryo is protected from deleterious hypoxic damages. This conclusion has been derived from experiments, in which the release of catecholamines was blocked under hypoxia. Under these conditions a significant increase in the mortality rate was observed.