Forelimb regeneration in thyroidectomized adult newts following organ culture and autografting of the thyroid glands.

Thyroidectomy and organ culture of adult newt thyroid glands three days prior to forelimb amputation was followed by autografting the glands subcutaneously into the animal's lower jaw region 9, 18 or 25 days postamputation (GC9, 18, 25 day series). This was an attempt, utilizing 515 animals, to elucidate further the role of the thyroids in regeneration. Amputated limbs of the thyroidectomized (Thx) and autografted muscle explant (MC = sham) cases underwent stumping or were significantly delayed in their regeneration rate and displayed abnormal morphogenesis compared with control regenerates. In the GC9 series newts, regenerates were identical to controls 45 days postamputation. However, regenerates of the GC18 series cases exhibited delayed and abnormal development at 45 days; but they were not as delayed and had fewer abnormalities than those cases in the Thx and MC groups. Results of the GC25 series newts were similar to those of the Thx group. Within 5 days of autografting the thyroids, epidermal moulting resumed and long-term survival ensued. We conclude that normal limb regeneration in the adult newt is thyroid hormone(s) dependent, specifically the later stages of growth, differentiation and morphogenesis.