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

Abstract

In the mammalian fetus, the cardiovascular responses to acute hypoxaemia include a redistribution of the cardiac output away from the periphery towards the adrenal, myocardial and cerebral circulations. A component of the peripheral vasoconstriction is mediated by increased release of catecholamines 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 progressively larger towards the end of the incubation period. However, the ontogeny of the catecholaminergic response to acute hypoxaemia has not been investigated in this species. Fertilised chicken eggs were studied on days 10, 13, 16 and 19 of incubation (hatching is at 21 days). At each stage of incubation, blood samples were obtained from the chorioallantoic artery of the chick embryos during normoxia and after 5 min of hypoxaemia for measurement of plasma concentrations of adrenaline and noradrenaline by HPLC. Basal plasma adrenaline and noradrenaline concentrations by the end of the incubation period were much higher in the chick embryo than values reported for mammalian fetuses during late gestation. During normoxia, basal plasma noradrenaline concentration remained unchanged during development but plasma adrenaline concentration showed a developmental increase from < 25.1 pmol l−1 at day 10 to 3 nmol l−1 at day 19 of incubation. Acute hypoxaemia caused an increase in plasma noradrenaline and adrenaline from day 13 and day 16 of incubation, respectively. In addition, the increase in plasma adrenaline and noradrenaline and in the ratio of plasma adrenaline to noradrenaline during acute hypoxaemia became progressively larger by the end of the incubation period. 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.

Sympathetic control of the cardiovascular response to acute hypoxemia in the chick embryo

“…Catecholamine concentrations were not measured on day 11, inasmuch as previous studies showed that acute hypoxemia does not increase plasma catecholamine concentrations until day 13 of incubation (21). Arterial blood samples for determination of plasma catecholamine concentrations required Ն0.3 ml of blood.…”

“…Previous studies from our laboratory have demonstrated the importance of catecholamine release in the cardiovascular response to an episode of acute hypoxemia in the chick embryo. At the end of the incubation period, plasma concentrations of catecholamines increase markedly in response to acute hypoxemia (21), and treatment of the chick embryo with the ␣-adrenergic receptor antagonist phentolamine prevented the redistribution of the cardiac output away from the peripheral circulations (22).…”

Effect of Acute Hypoxia on the Motor Activity and Heart Rate of the 10- and 14-Day Chick Embryo

“…It was demonstrated that it induced a rapid, integrated response, numerous functional systems being involved in the prevention of damage to the embryo. This response includes a decrease in the PO 2 of the blood; an increase in the blood catecholamine level; hypotensive bradycardia; redistribution of blood flow to vital organs, such as the brain, adrenals, and heart; and a decrease in the frequency of the amniotic contraction [29][30][31][32][33][34][35]. At the same time, changes in embryonic motility during acute hypoxia have been poorly studied.…”

Developmental changes in the effects of prostaglandin E2 in the chicken ductus arteriosus

“…Previously, we demonstrated that the nonselective adrenergic receptor agonist norepinephrine and the 1 -adrenegic receptor agonist phenylephrine induced a developmentally increased contraction of the chicken DA. Secretion of catecholamines plays an important role in several of the adaptations that characterize the transition of the chicken to ex ovo life (Mulder et al 2000;Wittmann and Prechtl 1991). The augmentation of the -adrenergic-mediated contraction and the concomitant reduction of the -adrenergic-mediated relaxation suggest an active participation of catecholamines in the closure of the chicken DA.…”