A study of induced metamorphosis in the Axolotl

Metamorphic changes occurred in dark and white Mexican axolotls injected with 3,3′,5‐triiodo‐L‐thyronine (T3) or DL‐thyroxine (T4), when exposed at the following ages (in days) after spawning: 3–8, 45, 62, 117, 521–541, 541‐571, at 20°C. The dosage of the hormone administered as a single injection varied from 10 μg to 100 μg. Optimum conditions in group 1 proved to be 10 μg T3 injected into the perivitelline space of six‐day‐old embryos which were subsequently released from the jelly to fresh water nine days later at 15 days of age. After two days in fresh water tissue changes were observed in this order: gills — ventral, middle, dorsal; tailtip; skin; upper eyelid. T3‐treated animals had a shorter latent period than T4 groups. There was heavy mortality in younger animals. Surviving axolotls completed metamorphosis within 25 to 35 days. Embryonic tissues, therefore, are capable of taking up the hormone and responding after the treatment is terminated, raising doubts as to the obligatory persistence of the hormone. The implications of these observations with regard to the effect of hormone at the molecular level are discussed.