Effect of decreased umbilical blood flow and hemorrhage, and decreased prostaglandins on the ductus venosus diameter in the rat.

BACKGROUND

The closing mechanisms of the ductus venosus (DV) have not yet been revealed.

OBJECTIVES

The aims of this study were to document the perinatal closing process of the DV, to study the suppression of prostaglandins by indomethacin, and to determine the effects of umbilical blood flow to the fetal DV.

METHODS

The proximal and distal DV diameters were studied in near-term fetal and neonatal rats with the rapid whole-body freezing method.

RESULTS

The DV diameter changed sensitively at birth, and decreased by 10% immediately after the cessation of the umbilical circulation. Umbilical hemorrhage caused an additional decrease in the DV diameter compared with neonate without the hemorrhage. The neonates showed a DV diameter decreased by 20% at 30 min and 30% at 60 min after birth. The fetal DV was tubular, and the neonatal DV was horn-shaped with a smaller inlet than outlet. A small dose (0.1 mg/kg) of indomethacin administered to the pregnant rats induced a reduction in prostaglandins and decreased the fetal DV diameter to 80% of the control. Indomethacin at a large dose (10 mg/kg), administered to the dams, induced a reduction in prostaglandins, severe constriction of the ductus arteriosus, and decreased blood flow through the descending aorta umbilicus, and caused a further reduction in the DV diameter to 70-80% of the control. A large dose of nifedipine (10 mg/kg), which causes cardiac suppression and heart failure in the fetus, was administered to near-term rats to study the effect of decreased fetal cardiac output and blood flow passing through the DV. Nifedipine induced a 20% decrease in the DV diameter for 2-8 h. In all 1-hour-old neonates with or without pretreatment, the inlet diameter of the DV was reduced more than the outlet diameter, and the DV showed a horn-shaped morphology.

CONCLUSION

In conclusion, perinatal cessation of the umbilical circulation and umbilical hemorrhage are associated with an immediate decrease in DV diameter. The DV diameter is also reduced in other conditions associated with decreased umbilical blood flow, such as induced by nifedipine which leads to heart failure and constricting of the ductus arteriosus induced by indomethacin. The constricting effect of a small dose of indomethacin suggests that prostaglandins dilate the DV physiologically.