[Quantitative evaluation of human placental aromatase during pregnancy by ELISA]

To examine the relationship between the modulation of estrogen synthesis and placental maturation during pregnancy, we measured enzyme quantities and catalytic activities of aromatase in 78 normal human placentas (7-41 weeks gestation). The quantity was determined by ELISA with monoclonal antibodies specific to aromatase cytochrome P-450 (P-450arom). The activity was assessed by radioassay with [1 beta-3H] androstenedione. Intracellularly, the P-450arom concentration was twice as great in the microsomal fraction of term placentas (0.18 +/- 0.07%) as in the homogenate and mitochondrial fractions. Aromatase activity was also twice as great in the microsomal fraction as in the other fractions. The P-450arom concentration in microsomes increased linearly as pregnancy progressed (r = 0.759, p less than 0.001). The total P-450arom quantity in the placenta increased quadratically as pregnancy progressed (r = 0.891). Similar results were observed for aromatase activity. These results indicated that the increase in P-450arom was responsible for the increase in aromatase activity in normal human placenta. Therefore, in addition to the increase in placental weight and substrate derived from fetal adrenal during pregnancy, a further increase in P-450arom contributes to the marked increase in maternal estrogen production.