Abstract
Summary
A single injection of cortisone in adrenalectomized rats resulted in a significant increase in number of 3H-thymidine labeled cells in the cervical loop of maxillary incisors at 7 am, 1 pm, 7 pm, and 1 am when compared to untreated adrenalectomized animals. The increase was most pronounced at 1 pm and least significant at 7 pm. Controls showed consistently and significantly fewer labeled nuclei than cortisone-treated adrenalectomized rats at all periods except 7 pm. Again, the most significant increase occurred at 1 pm. In addition, control values were consistently and significantly higher than those of untreated adrenalectomized rats for all periods except those of the 1 pm period. A circadian rhythm in uptake of 3H-thymidine was noted in all groups. Both treated and untreated adrenalectomized animals revealed significantly more labeled cells at 7 am and 1 pm. Control rats showed a cyclic activity which varied between individual cell layers and was less pronounced than in adrenalectomized rats. The results provide further evidence to support the concept that the manner in which cortisone accelerates rate of eruption is by stimulation of proliferative activity in the tissues of incisor. It is suggested that the chief effect of the adrenals on growth of these tissues is stimulatory in nature but that inhibitory influences also exist which may result in fluctuations in rate of DNA synthesis over a 24-hr period.
The authors express their sincere thanks to Mrs. Irene Stone and Miss Carla Constanza for their skillful technical assistance.
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