Prostacyclin does not change during an oxygen induced increase in pulmonary blood flow in the fetal lamb

The role of prostacyclin in mediating the increase in pulmonary blood flow caused by an increase in oxygen tension in the fetal lamb was investigated. Plasma concentrations of 6-keto-PGF(1a), the hydrolysis product of prostacyclin, were measured during an increase in pulmonary blood flow caused by a rise in oxygen tension in eight intrauterine fetal lambs. Fetal oxygen tension was increased by placing the pregnant ewes in a hyperbaric chamber and having them breathe 100% oxygen at three atmospheres absolute pressure. This increased fetal PaO₂ from 27 ± 3 to 60 ± 6 torr (mean ± S.E., p ≤ 0.0001) and increased the proportion of right ventricular output distributed to the fetal lungs from 6 ± 2 to 45 ± 7% (mean ± S.E., p ≤ 0.001). However, the fetal plasma concentration of 6-keto-PGF(1a) did not change, 186 ± 26 to 208 ± 40 pg/ml (mean ± S.E.). Indomethacin decreased plasma concentrations of 6-keto-PGF(1a) in each of three fetuses but did not decrease the proportion of right ventricular output distributed to their lungs. The increase in pulmonary blood flow caused by an increase in oxygen tension in the fetal lamb is not associated with an increase in plasma concentrations of 6-keto-PGF(1a). Prostacyclin does not appear to be involved in the increase in pulmonary blood flow caused by the increase in oxygen tension at birth.