Cyclical incorporation of 33P into rat incisor enamel in vivo as visualized by whole-mount radioautography.

ABSTRACT

Phosphorus uptake during amelogenesis was investigated in the continuously erupting rat incisor. Five minutes after intravenous injection of 33P-labelled ortho phosphoric acid, whole-mount radioautography of entire incisors revealed heavy labelling in the form of bands and narrow parallel stripes at the surface of the enamel in the maturation zone. There was relatively little labelling over enamel in the secretion zone and over pigmented enamel. Thus 33P is incorporated cyclically into maturing enamel and is visualized as (1) a banded pattern that reflects the modulation of ruffle-ended and smooth-ended maturation ameloblasts and (2) a striped pattern that reflects the distribution of newly-formed protein secreted by maturation ameloblasts. Presumably these P incorporation patterns are closely related to other cyclical events known to occur during enamel maturation.