Studies on the uptake of ¹²⁵ I‐triiodo‐L‐thyronine and ¹⁴C‐L‐thyroxine by Mexican axolotl tissues

Abstract

Various Mexican axolotl tissues were collected at different times after a single injection of either 1251-triiodothyronine ( T3) or 14C-thyroxine (T4) to: (a) 5 day old embryos, (b) 150-170 day old larvae, (c) 1400-1440 day old neotenic adults.Pattern of total radioactivity was similar in gill, tail and body of embryos injected with T3 or T,. In both the body continued to accumulate the label whereas gill and tail tissues showed a minor peak by three to five hours, a drop by 16 hours and an increase by 96 hours and a reduction by 240 hours. However, a TLC fractionation of butanol extracts of tissues mentioned above indicated that T, concentration reached a maximum at three hours and later continued to drop.A large amount of radioactivity was associated with the solvent front fraction.TLC fractionation of tissues from T4 injected embryos showed that very little of the radioactivity was associated with T4 up to 48 hours after which time there was an increase in T4 fraction. Thus, it is seen that the uptake of labeled T3 and T4 by embryonic tissues showed variations even though the total radioactivity appeared to be similar. Larval and adult axolotls injected with T3 showed that radioactivity reached a peak by 16 hours in the larval gill, skin and tail and continued to decline later. The liver showed a peak at 24 hours and decreased after that time. All of the above mentioned tissues from adult axolotls showed a peak radioactivity at 16 hours and later continued to drop. Thus, it is seen that the pattern of labeled thyroid hormone uptake is different in embryonic and post embryonic axolotl tissues. The implications of these results are discussed.