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 hi gh rate of progesterone synthesis accompanied by a low rate of convers ion to 17 beta-estradiol in the oocyte of Channa punctatus. On depurat ion, however, there was a reversal of the steroidogenic scenario with a low progesterone and high estradiol level, The accumulation of proge sterone was positively correlated with the significant increase in 3 b eta-hydroxysteroid dehydrogenase activity in the Hg-treated fish, Thus , it was clear that at the early stage of intoxication tig does play a role in the induction of 3 beta-hydroxysteroid dehydrogenase in the o ocyte 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 (B-max:14 nmoles mg(-1) protein; K-a 1.14 x 10(8) moles) and increase in the specific messenger RNA translating 3 beta-hydroxy steroid dehydrogenase. It is concluded that inorganic mercury is able to initiate translatable messenger RNA synthesis in fish oocyte at a l ow degree of intoxication.