Actinomycin D: Effect on induced metamorphosis in the Mexican axolotl

Actinomycin D was used to inhibit the action of T in the induction of metamorphic changes in the Mexican axolotl. Am D was administered before and after (in hours) T injection as follows: (1) ‐48; (2) ‐24; (3) ‐8; (4) 0; (5) +24; (6) +48; (7) +72; (8) +120; (9) +168. Five μg Am D administered alone was not lethal. However the majority of the animals injected with T and Am D died within 30 to 33 days. All experiments were at 20°. Suppression of metamorphic change was greater in group 2 than 1 and greater in groups 4 and 5 than 6. Group 3 showed maximum inhibitory effects of Am D. Very little inhibition was seen in groups 7 through 9. Gill filament resorption and sloughing of skin could not be inhibited completely in any of the groups. Exophthalmia was seen in all except group 3. Least changes occurred in the main gill rachis and the fins. When Am D was administered to hypophysectomized axolotls eight hours prior to T there was complete gill filament resorption before any change was observed in controls. Also skin sloughing and exophthalmia were precocious in Am D and T injected hypophysectomized axolotls. The observations above indicate variable responses in the metamorphosing tissues of the axolotl to Am D. Hence utmost caution is necessary in the interpretation of any of the inhibitory effects of Am D at the cellular level. Copyright © 1967 Wiley‐Liss, Inc., A Wiley Company 3 3 3 3