Chronotoxicological effect of methyl mercury in rat submandibular gland. Immunohistochemical changes of r-EGF, S-100 protein and keratin.

The effect of toxicity of methyl mercury was investigated in the submandibular gland (SMG) of adult male rats subjected to 12 h light dark cycle (6 a.m. to 6 p.m. light/resting phase; 6 a.m. to 6 p.m. dark/active phase). Two groups of rats received a defined dose of methyl mercury hydroxide at seven different time points during the active (dark) and resting (light) phase over a 24 h period. After 10 d, the rats were killed at 9 a.m. and 9 p.m. in the resting and active phase, respectively. The immunohistochemical distribution pattern of epidermal growth factor (r-EGF), S-100 protein and K8.12 keratin were studied in granular convoluted tubules (GCT). Those rats which received injections during the active phase (6 p.m. to 6 a.m.), showed stronger reactivity for r-EGF; however, the reactivity for S-100 protein was unchanged. On the contrary, in both groups, GCT cells showed intense staining for K8.12 keratin. It is concluded that the detoxification mechanism of mercury appears to be dependent on the chronobiological oscillation pattern of the GCT and their substructures.