3 Developmental Contractile Response in the Chicken Embryo Ductus Arteriosus in Vitro

Abstract

Background and aim: During prenatal life the chicken embryo presents a pattern of circulation similar to mammalians. Despite the abundant information about ontogeny of vascular reactivity in mammalian ductus arteriosus (DA), this has not been characterized in the chicken embryo. The aim of the present work was to study the response to vasoconstrictors of the chicken embryo DA between 0.7 and 0.9 incubation. Methods: Isolated right DA segments from chick embryos at day 15 and day 19 of the 21-d incubation were mounted in a myograph for isometric tension recording, bubbled with 0%, 5% or 95% O2/5% CO2. The contractile responses induced by KCl (31.25 mM-125 mM), the thromboxane A2 mimetic U46619 (10 nM-0.1 microM), endothelin-1 (ET-1, 10 nM- 10 microM), and the adrenergic agonist noradrenaline (NA, 0.3 nM- 10 mM) were tested. Response to oxygen was tested in a separate protocol. Sympathetic neuroeffector mechanisms were studied using electrical field stimulation (EFS, 0.25 16 Hz, 2 ms, 85 mA). Density of sympathetic innervation was evaluated using glyoxylic acid staining. Results: Chicken embryo DA responded to depolarizing high-K+ solution with a tonic contraction that increased with age. Also the contractile responses to NA, U46619 and ET-1 augmented. Depletion of calcium abolished the contractile response to K+ and NA, whereas the response to ET-1 decreased 77% and to U46619 decreased 20%. EFS did not evoke any response and catecholamine-containing perivascular nerves were not observed at any age. No clear response to oxygen in either 15 or 19 days embryos was observed. A contractile response to oxygen was only observed in 21 days externally pipped embryos. Conclusions: The DA of the chicken embryo responded, in vitro, to receptor-dependent and -independent contraction. The responses to contractile agonists augmented with age. The response to oxygen was only present at a very late stage of incubation.