The effect of colchicine on the pigmentation of the enamel surface in rat incisors.

The effect of colchicine and lumicolchicine on the secretion of an iron-containing pigment vesicle onto the enamel surface in the rat maxillary incisors has been studied histologically and by line scan analysis of the iron with an X-ray microanalyzer. Rats were killed at intervals of 12 and 24 hours and 3, 6 and 10 days after the subcutaneous injection of colchicine or lumicolchicine at a dose of 1.3 mg/kg. At 10 days after the colchicine injection, two pigmentation-free bands were observed on the enamel surface in each pair of incisors. By the line scan analysis of the iron with an X-ray microanalyzer, the pigmentation-free bands corresponded to the decrease of the iron concentration profile. By the histological observation at 12 and 24 hours after the injection, no remarkable changes were observed from the late pigmentation stage to the regression stage. However, at 3 and 6 days after the injection, the pigmentation-free bands appeared on the enamel surface. A large number of pigment vesicles was observed in the ameloblasts and in the papillary cells facing the pigmentation-free bands. These phenomena were not observed in the rats injected with lumicolchicine. The present study suggests that the secretion of an iron-containing pigment vesicle in the ameloblasts onto the enamel surface is mediated by the microtubules.