INDUCED METAMORPHOSIS - RECTIFICATION OF A GENETIC DISABILITY BY THYROID HORMONE IN MEXICAN AXOLOTL SIREDON MEXICANUM

Evidence is presented to show that the pituitary-thyroid axis functions at an elevated level in axolotls induced to metamorphose by single injections of triiodothyronine. Investigations conducted were: (1) changes in premetamorphic skin grafts in intact and thyroidectomized postmetamorphic axolotls. (2) changes in the histological picture of the thyroid of hypophysectomized pre- and postmetamorphic animals. (3) effect of thyroidectomy on the pituitary of the pre- and postmetamorphic animals. (4) thin-layer chromatography of thyroid hormones in serum and thyroid and 131I uptake by thyroid gland of pre- and postmetamorphic animals. Premetamorphic skin grafts metamorphosed on intact postmetamorphic animals but not on thyroidectomized animals. Hypophysectomy affected the thyroid in both pre- and postmetamorphic animals. The most pronounced change was the loss of granular texture in the colloid of operated animals. The cell height of the follicle epithelium showed a reduction in the animals as follows: Intact postmetamorphic > hypophysectomized postmetamorphic > intact premetamorphic > hypophysectomized premetamorphic. Histological variations in pituitary cytology could not be detected. Monoiodotyrosine was detected in the blood stream of all animals except those that were hypophysectomized or thyroidectomized. 131I uptake by thyroid of premetamorphic axolotl was much lower than that seen in postmetamorphic animals. The implications of the observations mentioned above are discussed. © 1968.