In vitro studies of the influence of hormones on tail regeneration in adult Diemictylus viridescens.

A total of 260 tail blastemata (13 to 15-day regenerates) of adult newts was cultured, with 170 controls, in medium no. 1760 (modified Parker's Medium, CMRL-1415) for 98 h at 20 ±0-5 °C. Various hormones, related to the regeneration process, were added individually and in combinations. If hormones were not included in the culture medium, blastema growth and differentiation did not ensue. The results of these in vitro experiments further showed that the presence of insulin was essential in the maintenance and promotion of growth and differentiation of the explanted blastemata. In addition, thyroxine also promoted a limited amount of growth and differentiation of the blastema and maintained a normal epidermis in culture. Furthermore, advanced cartilage differentiation and maximum growth of the blastemata were observed in cultures treated with combinations of insulin, growth hormone and hydrocortisone; insulin, growth hormone and thyroxine or all four of these hormones. The evidence presented indicates that the collective influence of the hormones (insulin, growth hormone, hydrocortisone and thyroxine) is greater than the effect of any of them individually. The action of insulin on the tissues and the metabolism of vertebrates is discussed and related to the regeneration process. The possible involvement of a multiple hormone action (insulin, thyroxine, hydrocortisone and growth hormone) in regeneration is discussed.