Maturation of the oxygen‐induced contractile response of the chicken ductus arteriosus during exposure to increased oxygen

Abstract

As with the mammalian DA, the avian ductus arteriosi (DA) are O2‐sensitive vessels that constrict in response to increasing O2 levels. The O2‐induced contraction of the avian DA is strongest during the last stages of hatching on day 20 of incubation. Previously we have shown that on day 19, the chicken DA respond weakly to acute increases in O2. Here we examined the O2‐induced contractile response of the chicken DA during a longer three hour exposure to 25 kPa O2 on day 19 of incubation. The DA initially responded to the increase in O2 with a weak contraction (0.15 ± 0.04 mN/mm) that increased in strength (0.63 ± 0.06 mN/mm) during the three hour exposure to 25 kPa O2. A tonic influence of nitric oxide appeared during the three hour exposure to 25 kPa O2. The contractile response after three hour exposure to O2 was not mimicked by the Kv channel inhibitor 4‐aminopyridine. This O2‐induced contraction is mediated by both L‐type Ca2+ channels and internal Ca2+ stores. The Rho‐kinase pathway inhibitors Y‐27632 and fasudil produced significant relaxation suggesting a role for Ca2+ sensitization in the contractile response to the three hours of elevated O2. While the day 19 DA initially exhibits an immature contractile response to O2, the maturation of the pathways regulating O2‐induced contraction were accelerated by longer exposure to 25 kPa O2 producing contractions similar in magnitude to those found during the last stage of hatching.