Kinetics of labelled precursors incorporated in the enamel matrix during amelogenesis as shown by radioautography

The kinetics of (3)H-tymidine and (3)H-proline incorporated by ameloblasts and enamel, were studied in undecalcified mouse incisors from birth to 6 days of age. Serial cross sections of unfixed right incisors were cut with a cryotome. The left incisors were fixed in paraformaldehyde, embedded in polybed as to get sagital 1 mum-thick sections. (3)H-thymidine was used to determine the apparent daily migration rate of ameloblasts, which was 513 mum in the unfixed sections and 610 mum/p.d. in the fixed ones. The semi-thin epon-embedded sections were also used to measure the lengths of the regions of the secretory and post-secretory zone of amelogenesis and to determine their growth during the experimental period. (3)H-proline was used to show the fate of the enamel proteins by correlating the radiactivity, determined by silver grain counts, with the migration rate of the ameloblasts. The results showed that the (3)H-proline labeled protein reached a peak of radiactivity at 4 h over ameloblasts and between 24 and 48 h after injection over enamel. In the unfixed section of the righ incisor a second peak of reaction was shown at48 h over ameloblasts and at72 h over enamel matrix. All these peaks were related to ameloblasts and enamel of the secretory zone. These results were interpreted as the evidence of reabsorption and reutilization of labeled proteins broken down in the young enamel, but may also be explained as secretion of low molecular weight proteins which are not kept by fixation. Another evidence of reutilization of labeled compounts for the biosynthesis of enamel proteins were given by the labeling of ameloblasts and enamel formed after birth at a considerable time after the pulse of (3)H-proline.

Efeito da sialoadenectomia sobre a incorporaçäo de 3H-prolina nas células e matriz do esmalte jovem e dentina de incisivos de camundongos, estudados através de radioautografia / Sialoadenectomy effect on 3H-proline incorporation in cells and matrix of young enamel and incisors dentin of mice, studied by radioautography

Estudaram-se os efeitos da remoçäo das glândulas salivares maiores sobre a incorporaçäo de 3H-prolina pelos ameloblastos secretores e odontoblastos de incisivos de camundongos. Animais sialoadenectomizados e controles foram injetados com 3H-prolina, sendo sacrificados e perfundidos 30 min, 2h, 12h e 24h após. Cortes de 1*m obtidos de incisivos inferiores incluídos em Polybed foram radioautografados. A distribuiçäo percentual de gräos de prata reduzida/100*m* sobre as referidas células, assim como em suas respectivas matrizes, foi sempre maior nos animais sialoadenectomizadas, nos diferentes intervalos de tempo. Duas hipóteses poderiam explicar esses resultados: 1. um aumento na biossíntese protéica provavelmente devida à falta do fator submandibular inibidor da insulina (SII) associada a um relativo aumento do pool de 3H-prolina devido à remoçäo das glândulas salivares; 2. um decrécimo na degradaçäo protéica devido ao hipotireoidismo que eventualmente ocorre nos animais sialoadenectomizados