Lipids in the developing enamel of the rat incisor. Parallel histochemical and biochemical investigations.

Morphologic examination of the developing enamel of rat incisors showed the presence of cell processes and remnants. Histochemical investigation of rapid-frozen freeze-substituted samples, using p-phenylenediamine or a phosphotungstic acid chromic acid mixture, revealed osmiophilic components which were extractable in chloroform-methanol solution and were located inside the tubule-like structures of the extracellular matrix. The presecretory cell-rich and developing enamel zones underwent quantitative and qualitative lipid analysis. Comparison of the biochemical data as well as of the morphological observations, suggests a cellular origin for enamel lipids randomly adsorbed by extracellular matrix components during enamel processing. The nature of the material which appeared as an osmiophilic intra-tubular filling is still unresolved.