Inorganic mercury binding to fish oocyte plasma membrane induces steroidogenesis and translatable messenger RNA synthesis.

Both in vitro and in vivo HgCl2 treatment demonstrated a remarkably high rate of progesterone synthesis accompanied by a low rate of conversion to 17 beta-estradiol in the oocyte of Channa punctatus. On depuration, however, there was a reversal of the steroidogenic scenario with a low progesterone and high estradiol level. The accumulation of progesterone was positively correlated with the significant increase in 3 beta-hydroxysteroid dehydrogenase activity in the Hg-treated fish. Thus, it was clear that at the early stage of intoxication Hg does play a role in the induction of 3 beta-hydroxysteroid dehydrogenase in the oocyte of fish at the spawning stage. The induction of this enzyme was found to be mediated by specific binding of Hg to the plasma membrane Na(+)-K(+)-ATPase (Bmax: 14 nmoles mg-1 protein; Ka 1.14 x 10(8) moles) and increase in the specific messenger RNA translating 3 beta-hydroxysteroid dehydrogenase. It is concluded that inorganic mercury is able to initiate translatable messenger RNA synthesis in fish oocyte at a low degree of intoxication.