Abstract
Summary
The administration of cortisone in young rats resulted in an increase in the number of colchicine arrested cells in the basal (proliferative) loop of the maxillary incisor during certain periods of the day. A single injection of 0.5 or 1 mg in normal rats resulted in an increase in colchicine arrested cells at 7 a.m., 7 p.m., and to some extent at 1 a.m. with no effect at 1 p.m. A cyclic cell division was evident in both experimental and control animals. In rats receiving 0.5 mg more mitoses were observed at 7 p.m. and 1 a.m. Controls revealed the same rhythmicity. Animals injected with 1 mg showed a less pronounced circadian rhythm with more mitotic figures at 7 a.m. and 7 p.m. The controls showed significantly more activity at 1 p.m. and 1 a.m. It is concluded that these results provide additional evidence in support of the theory that cell proliferation in the rat is one of the causative factors in incisor eruption.
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