Conversion of PGE2 to PGF2alpha by fetal sheep blood

In an attempt to explain the differences in the concentration of primary prostaglandins in the circulation of adult and fetal sheep, we have examined the ability of whole blood from adult and fetal sheep to reduce PGE2 to PGF2alpha in vitro. PGF2alpha was the principal radioactive product formed from 3H PGE2 by both adult and fetal blood. The enzyme initial reaction velocity was significantly higher (P = 0.02) per ml of fetal than adult blood. The optimum enzyme pH (7.0 - 7.5) was similar for both adult and fetal blood. The Km of the enzyme in fetal and adult blood were 3.59 x 10(-7) M and 5.02 x 10(-7) M respectively (P greater than 0.05). There was no detectable metabolism of PGF2alpha by either adult or fetal sheep blood. The results indicate that prostaglandin 9-ketoreductase is present in both adult and fetal sheep blood. Differences in the activity of this enzyme are unlikely to explain the higher concentrations of PGE reported in the plasma of fetal lambs.