Response of chicken ductus arteriosus to hypercarbic and normocarbic acidosis.

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 O(2), norepinephrine (NE), KCl, or U46619, changes from control conditions (5% CO(2), 24 mM NaHCO(3), pH 7.4) to 7.5% CO(2) (pH 7.25) or 10% CO(2) (pH 7.14) induced a concentration-dependent relaxation that reached 43.0% (SD 21.3) of the O(2)-, 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% CO(2), 12 mM NaHCO(3), pH 7.13) induced transient relaxation of the DA, which was not affected by the presence of tetraethylammonium or iberiotoxin. Euhydric hypercarbia (10% CO(2), 48 mM NaHCO(3), 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.