CIRCADIAN-RHYTHMS IN THE INCORPORATION AND SECRETION OF H-3-PROLINE BY ODONTOBLASTS IN RELATION TO INCREMENTAL LINES IN RAT DENTIN

Circadian incremental lines are universally found in the dentin of ani mals. They are believed to be caused by functional changes in odontobl asts over 24 hrs. However, the mechanism of rhythmic dentin formation has not yet been elucidated In the present study, we investigated whet her there is a 24-hour rhythm in the collagen-synthetic and secretory activities of odontoblasts by radioautography with H-3-proline as a tr acer. Six different groups of rats were injected with H-3-proline at 0 000, 0400, 0800, 1200, 1600, or 2000 after the animals had become accl imated to a 12/12-hour light-dark illumination cycle for 2 wks. One ho ur after the injection, the maxillary incisors were removed and proces sed for radioautographic study. The silver grains of H-3-proline were most intense over odontoblasts and predentin during the environmental light period, while the nadir occurred during the dark period. The pea k value was approximately two-fold higher than the minimum value. More over, in the dentin from rats that had been infused with H-3-proline c ontinuously for 10 days by means of osmotic minipumps, silver grains o f H-3-proline were heavily distributed over the dark hematoxylin-stain ed incremental lines. Thus, we demonstrated that odontoblasts show cir cadian rhythm with regard to collagen synthesis and secretion. These r hythms in odontoblastic function may be responsible for circadian incr emental lines in dentin.