The chicken extraembryonic arterial system comprises the allantoic arteries, which irrigate the gas exchange organ (the chorioallantoic membrane, CAM) and the yolk sac (YS) artery, which irrigates the nutritional organ (the YS membrane). We compared, using wire myography, the reactivity of allantoic and YS arteries from 19-day chicken embryos (total incubation 21 days). The contractions induced by KCl, the adrenergic agonists norepinephrine (NE, nonselective), phenylephrine (α1), and oxymetazoline (α2), electric field stimulation (EFS), serotonin, U46619 (TP receptor agonist), and endothelin (ET)-1 and the relaxations induced by acetylcholine (ACh), sodium nitroprusside (SNP, NO donor), forskolin (adenylate cyclase activator), and isoproterenol (β-adrenergic agonist) were investigated. Extraembryonic allantoic arteries did not show α-adrenergic-mediated contraction (either elicited by exogenous agonists or EFS) or ACh-induced (endothelium-dependent) relaxation, whereas these responses were present in YS arteries. Interestingly, the intraembryonic segment of the allantoic artery showed EFS- and α-adrenergic-induced contraction and ACh-mediated relaxation. Moreover, glyoxylic acid staining showed the presence of catecholamine-containing nerves in the YS and the intraembryonic allantoic artery, but not in the extraembryonic allantoic artery. Isoproterenol- and forskolin-induced relaxation and ET-1-induced contraction were higher in YS than in allantoic arteries, whereas serotonin- and U46619-induced contraction and SNP-induced relaxation did not significantly differ between the two arteries. In conclusion, our study demonstrates a different pattern of reactivity in the arteries perfusing the gas exchange and the nutritional membranes of the chicken embryo.

Arch Dis Child 2012;97(Suppl 2):A1-A539 A325Abstracts and the PAR2-activating peptide SLIGRL-NH 2 (0.1 to 10 µmol/L) in DA rings from 15-, 19-, and 21-d chicken embryos. Results Thrombin, trypsin, and TFLLR-NH 2 , all caused concentration-dependent contraction of the pulmonary side of chicken DA. These contractions were not observed in the aortic side of the DA, in the femoral artery or in the pulmonary artery. Thrombin-, trypsin-and TFLLR-NH 2 -induced contractions were endotheliumindependent but markedly impaired by the elimination of calcium from the external medium. The contraction evoked by thrombin and trypsin increased between day 15 and 19 of incubation and was not affected by oxygen tension. SLIGRL-NH 2 (≥10 µmol/L), evoked endothelium-dependent relaxation of the DA. Conclusions PARs are functionally present in the chicken DA but not in other vascular tissues. Recent studies demonstrate that loss of platelet number or function leads to defective DA closure. We speculate that the role of platelets in DA closure might be partially mediated through the PAR-mediated vasoactive effects of thrombin.

The chicken embryo is an ideal model for the study of new hypotheses on the developmental biology of ductus arteriosus (DA). A unique characteristic of chicken DA is that it is the result of the fusion of two vessels with different embryological origins, morphologies, and functionalities. The pulmonary side (PulmDA) consists almost exclusively of neural crest-derived cells, shows the structure of a muscular artery, and responds to O 2 with contraction whereas the aortic part is of mesodermal origin, shows the morphology of an elastic artery and relaxes in response to O 2. In addition the two parts of the DA show marked differences in responsiveness to other contractile and relaxant agents. In mammals, the most accepted model of O 2-induced DA constriction involves a rise in O 2 modulating the function of the mitochondrial electron transport chain (the sensor), leading to an increased production of H 2 O 2 (the mediator) that causes the inhibition of K V channels (the effector) with Rho kinase acting as another downstream effector of the O 2-sensing system in the DA. In the chicken embryo, we verified the very same pathway, proving a conserved mechanism for O 2 sensing/signaling in mammalian and nonmammalian DA. Moreover, we demonstrated a developmentally regulated response to O 2 , which is restricted to the mature PulmDA and involves parallel maturation of the three components: sensor, mediator, and effectors. Besides O 2 , we used the chicken embryo model to investigate the possible ductal effects of vasoactive mediators such as ceramide, H 2 S, isoprostanes, or platelet-derived vasoactive mediators.