Abstract
Summary
We have shown an increase in TCT in the blood and thyroid gland with increased age in two different strains of rats.
Fischer (F344) rats, 6 to 18-months old, have a higher level of circulating TCT (-1.5 ng/ml) than young 10-week-old Fischer rats (<0.2 ng/ml). Thyroid TCT concentrations in old Fischer rats also were significantly higher than in young Fischer rats, and this was associated with a significantly higher area ratio of C-cells to follicular cells in the older rats. In Holtzman rats a similar increase in blood and thyroid TCT with age was also observed. Comparing the two strains, both thyroid and serum TCT in old Fischer rats were significantly higher than in old Holtzman rats.
The authors wish to thank Drs. Paul L. Munson and Philip F. Hirsch for valuable suggestions during the course of this study. The authors also thank Dr. H. Stanley Bennett and Mr. Yukio Tanaka of the Laboratories for Reproductive Biology at the University of North Carolina for advice, criticism, and permission to use their equipment for the morphological study. The fine technical assistance of Mr. Johnny F. Obie and Mrs. Deloris B. Alston also is appreciated.
Get full access to this article
View all access options for this article.