Acute thymic involution and increased lipoperoxides in thymus of nickel chloride-treated rats

Acute thymic involution occurred in male, Fischer-344 rats following a single injection of nickel chloride (0.5 mmol/kg, sc). In nickel-treated rats, the mean thymic weight became significantly decreased at 24 h, continued to diminish at 48 h, and reached 24% of the control value at 72 h post-injection. The ratio of thymic weight to body weight (mg/g) decreased from 1.24 +/- 0.05 (SD) in control rats to 0.30 +/- 0.05 in nickel-treated rats at 72 h post-injection (p less than 0.01). Concentrations of thymic lipoperoxides were assayed by the thiobarbituric acid reaction, with HPLC separation and spectrophotometric quantitation of the malondialdehyde-thiobarbituric acid complex. The mean concentration of thymic lipoperoxides was unchanged at 24 h, increased 2-fold at 48 h, and reached 8-times the control value at 72 h after nickel chloride injection. On histological examination, sections of thymus from nickel-treated rats showed moderate to profound depletion of cortical lymphocytes at 72 h post-injection. Marked degenerative changes were noted in cortical lymphocytes, with pyknosis and karyorrhexis; swelling and vacuolation were evident in thymic reticular epithelial cells. The time-courses of the biochemical and histopathological responses suggest that the lipid peroxidation may be an end-result, rather than a cause, of thymic involution and injury to thymic lymphocytes in nickel-treated rats.