Superoxide radical and toxicity of environmental nickel exposure. 
Three nickel compounds were tested for pancreatic, hepatic and osteogenic damage in rats by a single i.m.  injection Ni++ (7 mg kg-1).  The nickel induced biochemical alterations included significantly increased levels of serum alkaline phosphatase in rats with NiS (75%) and NiO (50%).  Amylase and aspartate transaminase were also increased, and lipoperoxide was increased in rats with NiO (5.6-fold) and NiS (3.4-fold).  No serum changes were observed with NiCl2.  Daily injection of Cu-Zn superoxide dismutase (SOD) conjugated with polyethylene glycol prevented the serum level changes, indicating that superoxide radical is an important intermediate in toxicity of nickel insoluble compounds.