Postnatal development of dependence on thyroid hormones for growth and differentiation of rat skeletal structures
Liu, L.; Nicoll, C.S.
Growth 50(4): 472-484
1986
ISSN/ISBN: 0017-4793 PMID: 3297936 Document Number: 285080
We have studied the development of thyroid hormone dependence for growth and differentiation of rat skeletal tissues. The radius, tail tip or xiphoid process from 1-day-old rats was transplanted in its entirety under the kidney capsule of euthyroid or hypothyroid (TX) adult syngeneic virgin rats and grown there for 3, 6, 9, 12 or 15 days. Pieces of the sternum or calvarium were treated similarly. Growth of transplanted radius and sternum in TX hosts showed significant retardation by day 3, and that of transplanted calvarium, tail tip and xiphoid showed significant inhibition by day 6 post transplantation. Tissue differentiation of all of the transplants was inhibited in TX hosts and the appearance of epiphyseal ossification centers was significantly delayed. Injection of Propylthiouracil (PTU) in solvent into the neonatal rats from day 1 to day 15 post partum inhibited tail length increase by day 7, and body weight gain by day 9, as compared to the growth of solvent injected littermate pups. Our results indicate that the growth and differentiation of endochondral bones are more dependent on TH levels than are those of membranous bones and cartilage. Endochondral bones develop TH dependence for growth and differentiation before day 4 post partum, while the membranous bones and cartilage develop this dependence at the end of the first week.