Contractile and relaxing reactivity in carotid and femoral arteries of chicken embryos

In the embryo, hypoxemia causes redistribution of cardiac output from the p eriphery toward the heart and the brain. In view of this, we investigated d evelopmental changes in the contractile and relaxing properties of the peri pheral femoral artery (Fem) and the more central carotid artery (Car) at 0. 7, 0.8, and 0.9 of the chicken embryo incubation time. Isolated arteries we re studied in myographs and were exposed to norepinephrine or phenylephrine . High K+ (125 mM) and electrical field stimulation (0.25-16 Hz) were used to induce receptor-independent and neurogenic contractions. Relaxing respon ses to ACh were evaluated in the absence and presence of the nitric oxide ( NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) and before and after endothelium removal. alpha(1)-Adrenergic contractile responses i ncreased in a time-dependent manner and were significantly larger in Fem th an in Car. Neurogenic contractions and adrenergic nerves could only be demo nstrated in Fem at 0.9 incubation. ACh caused relaxation in both Fem and Ca r at 0.7, 0.8, and 0.9 incubation. The NO-independent part of the relaxatio n was more pronounced in Car than in Fem at all developmental stages. We co nclude that the chicken embryo is a useful model to investigate the develop ment of vasomotor control and vascular heterogeneity. The observed regional vascular differences may contribute to cardiac output redistribution durin g hypoxia in the embryo and might result from endothelial and neurogenic in fluences on vascular smooth muscle differentiation.