Action of prostaglandins, endoperoxides, and thromboxanes on the lamb ductus arteriosus

Prostaglandin (PG) E2, the PG endoperoxides PGG2 and PGH2, and enzymatically generated PGI2 and thromboxane A2 (TXA2) were tested in vitro on circular strips of ductus arteriosus from mature fetal lambs. Both PGE2 and the PG endoperoxides produced a dose-dependent relaxation of the ductus at low PO2 (7-11 torr), and their action was reduced or abolished at high PO2 (410-660 torr). PGE2, however, was more potent than the endoperoxides. The reaction mixture containing PGI2 relaxed the hypoxic ductus, but this response was not due to PGI2 but to two, more stable and as yet unidentified, compounds, one of which is most certainly PGE2. TXA2 was inactive on the vessel at low and high PO2. These results confirm that PGE2 is the most effective PG acting on the ductus and provide further support to the hypothesis that this PG is responsible for patency of the vessel during fetal life. PGE2 action, however, may be complemented by that of another endoperoxide derivative formed in the PGI2 synthetic reaction which remains to be identified.