HORMONES CONTROLLING COLLAGEN SYNTHESIS DURING METAMORPHOSIS IN THE THIGH BONE OF THE TADPOLE OF RANA CATESBEIANA

The rate of 14 C-proline incorporation into collagen in the thigh bone of the Rana catesbeiana tadpole was determined in vitro. Intraperitoneal injection of bovine prolactin caused an increase in the rate of collagen synthesis during the premetamorphic stages (stages 12-16) and the early metamorphic stage (stage 18), but it exerted no effect on collagen synthesis in the metamorphic stages (stages 20-25). On the other hand, injection of growth hormone stimulated the rate of collagen synthesis in the metamorphic stages and caused a slight increase in the premetamorphic stages. When a tadpole in the early premetamorphic stages (stages 12-14) was kept in 5 × 10-8 M thyroxine solution for several days, the rate of collagen synthesis became higher than that in the bone of the control animal. The rate of collagen synthesis was not enhanced by prolactin in the thyroxine-treated tadpole, but was stimulated by growth hormone, even when the thyroxine-treated animal remained in the premetamorphic stages. With the treatment of the tadpole by thyroxine, prolactin-sensitivity seems to be reduced, and growth hormone-sensitivity becomes apparent.