Mercury, a non-essential metal, has been recognized as a nephrotoxic agent. Besides, a recent study has demonstrated that this metal also alters some hepatic parameters in vivo, such as hepatic and seric alanine aminotransferase (ALT). The purpose of this work was to investigate the possible in vitro effects of HgCl₂ on alanine aminotransferase and lactic dehydrogenase (LDH) activities from liver and serum of young rats in order to better understand the mechanism involved in in vivo effect.

Wistar rats 10-13 day-old were sacrificed by decapitation, and livers were dissected and homogenized in 20 volumes of Tris HCl 10 mM plus MgSO₄ 1 mM, pH 7.4. Blood samples were collected, centrifuged and sera and homogenate samples were frozen until analyses.

The results revealed that both enzymes were inhibited by mercury in vitro. The LDH activity was the more sensitive: hepatic enzyme was inhibited in 30% and seric in 40% by 0.01 mM and 0.5 mM, respectively. Seric and hepatic ALT activities presented inhibition of 60% when in presence of 5 and 25 mM, respectively. Thus, these results demonstrate that HgCl₂ in vitro inhibits both enzymatic activities from both sources. However, the sensitivity of enzymes to metal was dependent on the activity (LDH or ALT) and source (liver or serum) analyzed. Moreover, it is possible to observe that the concentrations necessary to inhibit these enzymes in vitro were superior that those achieved in these tissues after in vivo exposure.