EFFECTS OF THYROXINE AND PROLACTIN ON COLLAGEN BREAKDOWN IN THE THIGH BONE AND TAIL FIN OF THE RANA CATESBEIANA...

Injection of 14 C-proline into the tadpole causes labeling of protein in the collagen fraction of the thigh bone and tail fin. The radioactivity of the 14 C-hydroxyproline residue is about 26% of the total radioactivity in the 14 C-labeled protein of the collagen fraction in the thigh bone as well as in the tail fin. In 14 C-proline-loaded tadpoles into which prolactin has been injected, the radioactivity in the collagen fraction in these tissues is markedly higher than that in control animals. In thyroxine-treated tadpoles, the 14 C-radioactivity of the collagen fraction in the thigh bone is always higher than that of the controls, but it is markedly low in the tail fin. During the incubation of thigh bone and tail fin isolated from 14 C-proline-loaded tadpoles, low molecular weight materials containing 14 C-hydroxyproline are released from the 14 C-labeled protein of these tissues. The rate of 14 C-hydroxyproline release, which represents the rate of collagen breakdown, is higher in thigh bone and tail fin isolated from thyroxine-treated tadpoles and is markedly lower in these tissues isolated from prolactin-treated tadpoles than in those isolated from controls. In these tissues, the high rate of collagen breakdown in thyroxine-treated tadpoles is reduced by prolactin injection.