The histology of inhibition of limb regeneration in the newt, Triturus, by actinomycin D

Abstract Adult newts, Triturus viridescens, were treated with from 1.0–10.0 μg/g body weight of actinomycin D one day before amputation of both forelimbs. Mean survival times ranged from over 50 days in newts treated with 1.0 μg/g to 13.2 days in animals given 10.0 μg/g body weight of actinomycin. Low doses little altered the course of regeneration, but animals treated with over 2.0 μg/g never formed blastemas. In another series, animals were given doses of 2.5 μg/g body weight of actinomycin D at intervals from 14 days before to 30 days after amputation. It was found that certain signs of toxicity (loss of equilibrium) are related to the time of administration of the drug whereas others (hemorrhage into the limb stumps) are restricted to a definite phase of the regenerative process. Early administration of actinomycin completely inhibits regeneration whereas later treatment results in a considerably lessened effect. The postamputational stages which are basically destructive in nature are not noticeably affected by actinomycin D, but the phases of dedifferentiation, blastema formation and redifferentiation are strongly inhibited.