Heteroplastic Transplantation of the Hypophysis Between Different Species of Ambystoma. ∗

Abstract

The differences in metamorphic activity of the axolotl (Ambystoma mexicanum) and the related species, A. tigrinum, are well known. That the thyroid of A. mexicanum will metamorphose thyroidless frog tadpoles although not able to metamorphose the axolotl itself was shown by Swingle. 1 It is also known through the work of Uhlenhuth and Schwartzbach 2 and others that the axolotl can be metamorphosed by anterior pituitary substances. The establishment of the pituitary's influence upon the thyroid-releasing mechanism makes it probable that the difficulty is in this relationship between these glands. The question arises as to which gland is primarily different. Witschi 3 joined axolotl and tigrinum embryos in parabiosis. These pairs metamorphosed when they were normal but did not when the tigrinum was hypophysectomized, thus showing that the pituitary gland of the tigrinum was responsible for the metamorphosis. The tigrinum thyroid was, however, present and must be considered. Bytinski-Salz 4 interchanged the pituitaries of these 2 species at the orthotopic position. His results showed no effects of the interchange. He concluded that the Ambystoma tigrinum with an A. mexicanum hypophysis will metamorphose and that conversely the axolotl with a tigrinum hypophysis will remain neotenous. This he explained by assuming that the pituitary does not act independently and that the connections between the hypophysis and the thyroid are not quantitatively fixed, but are probably controlled by another factor within the host. It would seem that the simplest explanation of his results would be on the basis of degeneration of the transplant and regeneration of the host's hypophysis. This is made more probable by the rest of his results and he admits that one can not tell the glands of the two species apart histologically.

In the present experiments the differences between the hypophysis of Ambystoma tigrinum and A. mexicanum have been brought out by comparing the results of heteroplastic and homoplastic transplants.