17-BETA-HYDROXYSTEROID OXIDOREDUCTASE ACTIVITY IN HUMAN MATERNAL AND UMBILICAL-CORD SERA

The specific activity of 17β-hydroxysteroid oxidoreductase (17β-HSOR) in human umbilical cord arterial serum has been reported to be similar to that of maternal serum and 5- to 15-times higher than that of cord venous serum. Based on these findings, it was proposed that 17β-HSOR in cord arterial serum arises from fetal tissue sources other than placenta. In the course of studies of the role of 17β-HSOR in the modulation of bioactive estrogen levels in the human fetus, we determined that: (i) the specific activity of 17β-HSOR in maternal serum is 2.1- to 55-times higher than that in either umbilical cord venous serum or cord arterial serum; (ii) the specific activity of 17β-HSOR in umbilical cord venous and cord arterial sera are similar; (iii) anti-human placental cytosolic 17β-HSOR antibody inactivates the 17β-HSOR in maternal, umbilical cord arterial, and cord venous sera but not in maternal or fetal erythrocytes; (iv) the specific activity of 17β-HSOR in maternal serum (expressed per mg protein) is higher than that in umbilical cord serum and maternal and fetal erythrocytes, and is approximately 700-times lower than that of the placental microsomal enzyme; (v) the preferred cofactor for maternal serum 17β-HSOR is NADP+; (vi) 17β-HSOR is associated with the high speed supernatant fraction of maternal serum rather than with the particulate fraction; and, (vii) the patterns of binding of [3H]estradiol-17β to proteins in maternal and umbilical cord arterial sera and those of 17β-HSOR activity, determined in corresponding fractions obtained after sucrose density gradient centrifugation, are approxi-mately coincidental at S20,ω, 4.6-5. The findings of higher 17β-HSOR levels in maternal serum compared with umbilical cord arterial serum and the inactivation of the cord arterial serum enzyme by an antibody that recognizes human placental cytosolic 17β-HSOR is suggestive that 17β-HSOR in cord arterial serum is of placental origin. © 1990.