A Thyrotropic Field Surrounding the Immature Pituitary of the Tadpole. ∗

Abstract

It was previously reported that pituitary primordia when grafted are capable of developing thyrotropic activity in the tadpole, though such activity is generally delayed in appearance and much less than that of the normal gland. 1 , 2 In the course of a series of investigations on the development of function in such grafts, it was found that multiple grafts placed under the adhesive discs and into the eye cup of hypophysectomized tailbud embryos of Rana sylvatica induced prococious metamorphosis in the host. Since single grafts similarly placed did not induce precocity, it was considered that the excess pituitary tissue was responsible for the precocity. 3 No precocity was observed by Blount in Amblystoma with excess pituitary grafts. 5

In attempting to confirm these observations in R. pipiens, a series of normal animals with extra pituitary primordia inserted into the eye, near the otocyst and under the adhesive discs was prepared. Only those animals which had extra pituitaries placed under the adhesive discs showed precocity. In another experiment one animal which had its own pituitary primordium placed under the adhesive discs, displayed unmistakable metamorphic precocity.

It was thought that the explanation of these results might lie in some effect of the proximity between the pituitary and thyroid, for when grafts are placed under the adhesive discs, they develop in the neighborhood of the thyroid gland. The high proportion of precocity observed in tadpoles with several grafts in this region as compared to those with one, may be accounted for by the greater depth to which the grafts must be pushed when several are inserted, for embryological considerations indicated that the more deeply placed the grafts are, the closer they approach to the place of origin of the thyroid. The following experiment was conducted to test this hypothesis.