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Role of Rho‐Kinase Activity and Expression in the Ductus Arteriosus in the Chicken Embryo

Incubation O2 levels have significant effects on the O2‐induced contraction of the chicken ductus arteriosus (DA) and its eventual closure. Incubation in hyperoxia speeds up closure while hypoxic incubation delays closure of the chicken ductus arteriosus. We hypothesized that one mechanism for this may be timing differences in the maturation of the Rho‐kinase pathway involved in calcium sensitization and myosin light chain phosphatase inhibition. To examine this, embryos were incubated in hypoxia (15%O2), normoxia (21%O2) and hyperoxia (30%O2) and used on embryonic day 18 and as internally and externally pipped embryos. The role of Rho‐kinase in O2‐induced contraction was measured by pre‐contracting the vessel with O2 and then exposing vessels to step‐wise increase in the Rho‐kinase inhibitor Y‐27632. On day 18 of incubation, Y‐27632 relaxed the O2 −induced DA significantly more in hyperoxia than normoxia or hypoxia suggesting that Rho‐kinase activity increases earlier in the DA from hyperoxic incubated embryos. To examine changes in DA gene expression within the pathway, RhoA mRNA levels from hypoxic, normoxic and hyperoxic embryos was measured using rtPCR. Preliminary data suggest that incubation in chronic hyperoxia increases RhoA mRNA levels. Taken together with the in vitro contractile response to Y‐27632 this suggests that development in high O2 up regulates RhoA gene expression. Development in a hyperoxic environment speeds up the maturation of the Rho kinase pathway in the chicken DA. This work was funded by the American Heart Association South Central Affiliate.