In vitro effect of mercury on aryl hydrocarbon hydroxylase, quinone reductase, catecholamine-O-methyltransferase and glucose-6-phosphate dehydrogenase activities in term human placenta.

The effect of HgCl2 on human term placental aryl hydrocarbon hydroxylase (AHH), quinone reductase (QR), catecholamine-O-methyltransferase (COMT), and glucose-6-phosphate dehydrogenase (G-6-PD) enzyme activities was studied after incubation of placental explants with the salt for either a 6 or 24 hr period. Mercury (Hg) increased the activities of AHH, QR and COMT, but decreased that of G-6-PD. The increases in enzyme activities, as well as the decrease in G-6-PD activity observed were in all cases time- and dose-dependent. The data suggest that Hg exerts an enhancing effect on the activity of placental phase I enzyme (AHH) and phase II enzymes (QR and COMT). This enhancement may be due to increased de novo synthesis, elimination of some suppressing agent(s), or the decreased breakdown of enzyme protein. Also, the inhibitory effect of Hg on G-6-PD activity appears to indicate that this enzyme is appreciably more sensitive to Hg than the other three enzymes. These findings may imply increased cellular resistance to Hg toxicity. The altered state of activity may also be used as a tool for monitoring exposure to this metal.