EFFECTS OF THYROXINE AND PROPYL-THIOURACIL ON HINDLIMB REGENERATION OF LARVAL XENOPUS-LAEVIS

Xenopus laevis larvae at stage 53 and 55 (according to Nieuwkoop and F aber 1956) were subjected to amputation of one or both hindlimbs and r eared either in thyroxine (T4) 2.5 to 10 mu g/l or in propyl-thiouraci l (PTU) 0.01%. Results have shown that when the limb was amputated thr ough a nearly undifferentiated region (tarsalia level, at stage 53) or through a differentiating region (tarsalia level, at stage 55), T4 ac celerated the regenerative process and enhanced the mitotic and labell ing indices of blastemal cells, when compared with controls. However, PTU delayed the regenerative process and lowered the mitotic and label ling indices. When the limb was amputated through an almost differenti ated region (mid-thigh level, at stage 55), T4 inhibited the conic bla stema formation, while PTU did not significatively influence limb rege neration. T4 did not modify the morphogenetic properties of the regene rative blastemata, which are characteristic of the developmental stage and the degree of differentiation of the limb tissues at the amputati on level. On the whole, the data show that T4, besides being indirectl y responsible for the decline of the limb regenerative capacity in a p roximodistal direction by promoting limb differentiation, also exerts a direct effect on the regenerative process.