Response of Chicken Ductus Arteriosus to Hypercarbic and Normocarbic Acidosis

Abstract

Background: Changes in pH can have profound effects on vascular tone and reactivity, but their influence on the ductus arteriosus (DA) remains unknown. Objective: To analyzethe effects of hypercarbic and normocarbic acidosis in the reactivity of the chicken DA. Methods: DA rings from 19-day chicken fetuses (total incubation time, 21 days) were mounted in a wire myograph for isometric tension recording. Results: In DA rings (pulmonary side) stimulated with O₂, norepinephrine (NE), KCl, or U46619, changes from control conditions (5% CO₂, 24 mM NaHCO₃, pH 7.4) to 7.5% CO₂ (pH 7.25) or 10% CO₂ (pH 7.14) induced a concentration-dependent relaxation that reached 43.0% (SD 21.3) of the O₂-, 28.6% (SD 23.1) of the NE-, 10.4% (SD 18.7) of the KCl-, and 6.8% (SD 12.6) of the U46619-induced contraction. Hypercarbic-acidosis-induced relaxation was impaired by the non-selective K⁺ channel blocker tetraethylammonium or the BK_Ca channel inhibitor iberiotoxin. Normocarbic acidosis (5% CO₂, 12 mM NaHCO₃, pH 7.13) induced transient relaxation of the DA, which was not affected by the presence of tetraethylammonium or iberiotoxin. Euhydric hypercarbia (10% CO₂, 48 mM NaHCO₃, pH 7.46) induced a transient contraction of the DA. Conclusions: Our results indicate that the chicken DA is very sensitive to changes in extracellular pH, and that stimulation of BK_Ca channels may account for the ductal-relaxing effects of hypercarbic acidosis.