Behaviour of DNA, protein and acid hydrolases in response to thyroxine in isolated tail tips ofXenopus-larvae.

Analysis of factors influencing survival of tail tips ofXenopus larvae "in vitro" has shown that prevention of infection by antibiotic pretreatment of donor tadpoles and amputated tips is most critical. In tail tips exceeding not more than 1/3 of the body length, maintenance of N-content and regenerative capacity are superior in Niu-Twitty and Steinberg's saline than in Holtfreter's solution, all media being supplemented by 0.04 % sulfathiazole. Addition of nutrient ingredients to saline (glucose, Parker's medium 199, serum protein) does not improve viability of tail explants.In isolated tail tips 2.5×10-7M L-thyroxine (T4) induces involution "in vitro", resulting in losses of about 85% in DNA and 70% of protein respectively after 12 days of treatment. A significant decrease in DNA occurs after three days, and for protein after 6 days of hormone treatment, when tail fins are almost fully resorbed.Statistical analysis of the regression curves for decrease in DNA and protein, produced by different concentrations of T4, indicates the presence of an upper threshold (2.5×10-7M) and a lower threshold (2.5×10-8M) of sensitivity to hormone. Intermediate concentrations affect the latency time required for onset of DNA and protein loss, lengthening it at lower concentration.In tail tips exposed to 2.5×10-7M T4 a concurrent rise in activity of cathepsins, DNase and acid phosphatase has been demonstrated. The specific activities of these acid hydrolases are significantly higher in T4-treated tails after four days of hormone administration, this response proceeding detectable loss in protein by two days. Extent and duration in the rise of activity are characteristic for each enzyme, the increase in both specific and total activities being highest for cathepsins, intermediate for DNase and lowest for acid phosphatase.