Fragmentation of the distal portion of Tomes' processes of secretory ameloblasts in the forming enamel of rat incisors

In order to investigate enamel and dentin phospholipid metabolic pathways, two separate experiments were carried out. Firstly, rats were given chloroq uine, a drug which induces a lipidosis-like disease. Extensive accumulation inside lysosomes was seen in all the groups of cells in the forming part o f the rat incisor, except secretory ameloblasts which were unaffected by th e drug. Secondly, the uptake and fate of H-3-choline were studied by radioa utography on rats fed either normally or on an essential fatty acid deficie nt diet (EFAD). Four hours after the injection of the precursor, incorporat ion reached a maximum then decreased gradually. At 4 days the forming ename l displayed higher silver grain density than any other compartment. In EFAD rats H-3-choline incorporation was decreased drastically in each compartme nt except in the forming enamel which was not affected by the deficiency. T he longer retention of the labeling in the forming enamel and the lack of l ysosomal accumulation in chloroquine-treated secretory ameloblasts support the hypothesis that fragments of the distal Tomes' process are released dur ing enamel formation. Disconnected from the cells, membrane remnants are ne ither reinternalized nor subjected to further degradation inside lysosomes.