Adrenocortical suppression in highland chick embryos is restored during incubation at sea level

By combining the chick embryo model with incubation at high altitude, this study tested the hypothesis that development at high altitude is related to a fetal origin of adrenocortical but not adrenomedullary suppression and that hypoxia is the mechanism underlying the relationship. Fertilized eggs from sea-level or high altitude hens were incubated at sea level or high altitude. Fertilized eggs from sea-level hens were also incubated at altitude with oxygen supplementation. At day 20 of incubation, embryonic blood was taken for measurement of plasma corticotropin, corticosterone, and Po(2). Following biometry, the adrenal glands were collected and frozen for measurement of catecholamine content. Development of chick embryos at high altitude led to pronounced adrenocortical blunting, but an increase in adrenal catecholamine content. These effects were similar whether the fertilized eggs were laid by sea-level or high altitude hens. The effects of high altitude on the stress axes were completely prevented by incubation at high altitude with oxygen supplementation. When chick embryos from high altitude hens were incubated at sea level, plasma hormones and adrenal catecholamine content were partially restored toward levels measured in sea-level chick embryos. There was a significant correlation between adrenocortical blunting and elevated adrenal catecholamine content with both asymmetric growth restriction and fetal hypoxia. The data support the hypothesis tested and provide evidence to isolate the direct contribution of developmental hypoxia to alterations in the stress system.