Operative deliveries induce a significant activation of indoleamine 2,3-dioxygenase in human placenta: existence of a new mechanism for activating the enzyme.

The physiological activating mechanism for human placental indoleamine 2,3-dioxygenase was investigated. No cell fractions of the placental homogenate were found to replace the electron-mediation activity of methylene blue from a reductant to the enzyme in the exogenous enzyme-activating system with L-ascorbic acid, B-NADPH, or B-NADH as a reductant. However, the preincubation at 37 degrees C of the supernatant fraction (10,000 x g, 30 min) prior to starting the indoleamine 2,3-dioxygenase reaction drastically caused the activation of the enzyme without added reductants and methylene blue, which suggests the existence of an endogenous indoleamine 2,3-dioxygenase-activating system. The endogenous enzyme activation was induced in the placentas delivered operatively by vacuum extraction or cesarean section much more significant degree than in those delivered normally.