Persistent responsiveness of the neonatal ductus arteriosus in immature lambs: a possible cause for reopening of patent ductus arteriosus after indomethacin-induced closure.

Reopening of the ductus arteriosus after successful indomethacin-induced closure has become a major problem with indomethacin treatment. In full-term human newborns and lambs, the ductus behaves like ischemic tissue after its initial constriction. Its ability to continue to relax or contract depends on the amount of left-to-right shunt through the ductus lumen. To see if ductus constriction in preterm lambs would produce the same loss of ductus responsiveness, we delivered 42 lambs by cesarean section and ventilated them for 6.6 +/- 0.5 (+/- SE) hr. We measured ductus arteriosus resistance and left-to-right shunt with the use of radionuclide-labeled microspheres. After the hemodynamic measurements were obtained, the ductus was studied in vitro. Immature lambs were more likely to have reactive ductus (after their initial ductus constriction) than were more mature lambs. This was due to a diminished degree of ductus constriction as well as persistence of ductus responsiveness in immature lambs when compared with more mature lambs. This persistence of ductus responsiveness in immature lambs after ductus constriction may account for the high reopening rate in preterm infants after successful indomethacin-induced closure.