Hormonal and nutritional requirements for limb regeneration and survival of adult newts.

Abstract

AbstractNewts which were fed daily for two weeks prior to hypophysectomy survived significantly longer and regenerated limbs better than newts fasted for two weeks prior to hypophysectomy. Since limbs were amputated five days after hypophysectomy, regeneration was initiated in the complete absence of pituitary hormones.Newts which were hypophysectomized 14 days after limb amputation were found to possess blastemas significantly smaller at eight and also at 16 days after the operation than the blastemas of sham‐operated newts. Thus, hypophysectomy, performed after limb regeneration had progressed through the wound healing and dedifferentiation phases, resulted in a significant retardation in the growth of the blastema.To determine which hormones are essential to normal limb regeneration and survival, newts were hypophysectomized and treated with various combinations of hormones, or grafted with pituitaries from newts or from axolotls (Ambystoma mexicanum). A prolactin‐thyroxine combination, growth hormone, and ectopic pituitary grafts from newts or axolotls, significantly prolonged the life of hypophysectomized newts. These newts also regenerated limbs in a normal fashion. Thyroxine alone, prolactin alone, thyroxine + ACTH, ACTH, or saline were not effective in restoring the health of hypophysectomized newts and were not effective in restoring normal limb regeneration ability.