Developmental changes in plasma catecholamine concentrations during normoxia and acute hypoxia in the chick embryo

1. In the mammalian fetus, the cardiovascular responses to acute hypoxaemia include a redistribution of the cardiac output away from the periphery tow ards the adrenal, myocardial and cerebral circulations. A component of the peripheral vasoconstriction is mediated by increased release of catecholami nes into the fetal circulation during acute hypoxaemia. Previously, we have shown that the chick embryo also shows an increase in peripheral vascular resistance during acute hypoxaemia and that this response becomes progressi vely larger towards the end of the incubation period. However, the ontogeny of the catecholaminergic response to acute hypoxaemia has not been investi gated in this species. 2. Fertilised chicken eggs were studied on days 10, 13, 16 and 19 of incuba tion (hatching is at 21 days). At each stage of incubation, Mood samples we re obtained from the chorioallantoic artery of the chick embryos during nor moxia and after 5 min of hypoxaemia for measurement of plasma concentration s of adrenaline and noradrenaline by HPLC. 3. Basal plasma adrenaline and noradrenaline concentrations by the end of t he incubation period were much higher in the chick embryo than values repor ted for mammalian fetuses during late gestation. During normoxia, basal pla sma noradrenaline concentration remained unchanged during development but p lasma adrenaline concentration showed developmental increase from < 25.1 pm ol l(-1) at day 10 to 3 nmol l(-1) at day 19 of incubation. Acute hypoxaemi a caused an increase in plasma noradrenaline and adrenaline from day 13 and day 16 of incubation, respectively. In addition, the increase in plasma ad renaline and noradrenaline and in the ratio of plasma adrenaline to noradre naline during acute hypoxaemia became progressively larger by the end of th e incubation period. 4. These data show an ontogenic increase in basal plasma catecholamines and in the catecholaminergic response to acute hypoxaemia in the chick embryo during the last third of the incubation period.