EFFECT OF XENOBIOTICS ON QUINONE REDUCTASE-ACTIVITY IN 1ST TRIMESTER EXPLANTS

The placental protective enzyme quinone reductase (QR) has recently been reported to be induced by exposure to mercury, which is a toxic metal in vitro at term. In the present study we have examined the effect of three groups of xenobiotics-carcinogens, chemoprotectors and a natural antioxidant, ascorbic acid (vitamin C) on this enzyme activity in the first trimester placenta in vitro. Incubations with the carcinogen benzo[a]pyrene (BP) at 10-50 muM doses increased the enzyme activity at 6 h. At 24 h the effect of 10 muM BP was significant while that of 50 muM BP was not consistent. On the other hand the effect of 50 muM 3-methylcholanthrene at both time points was not significant. Ascorbic acid (5 - 25 muM) added for 24 h caused a 2- and 4-fold increase in the enzyme activity, respectively (P < 0.005). Exposure to a 25 muM concentration of different classes of chemoprotectors 2(3)-tert-butyl-4-hydroxyl-anisole (BHA), dicoumarol and Sudan I caused a 2.5- to 3.6-fold significant increase in the enzyme activity after 24 h (P < 0.01). Present data suggest that QR activity in the early placenta is responsive to a wide variety of xenobiotics in vitro. Vitamin C in concentrations usually consumed, exerted a potent effect on local QR activity in vitro which may protect pregnant women and their conceptus in an adverse environment.