Sympathoadrenal system activity at birth: integration of postnatal adaptation

In this article we have reviewed available information characterizing an increase in SAS activity at birth, in the so-called "catecholamine surge." Also, we have described the sources of circulating CA in the sheep fetus at birth and reviewed recent data on the significance of the CA surge at birth with regard to vital events of postnatal metabolic and cardiovascular adaptations. The results available to date suggest a unique, early neonatal dependence on circulating catecholamines for maintenance of physiologic homeostasis. The duration of this dependence and the ability of newborn animals or humans to sustain such high circulating catecholamine levels is not known. Further studies will clarify the relative importance of circulating and neuronally released CA in these adaptive events in various organ systems and test the applicability of a wide variety of adrenergic agents for therapeutic intervention.