Adenohypophysial-thyroid activity of the XXXX salamander, Ambystoma tigrinum, as a function of metamorphosis and captivity.

@entity1955 @entity7287 @entity6145 @entity7928 @entity1954
The aim of this study was to determine the timing of adenohypophysial activation during metamorphosis of the @entity7928 salamander, Ambystoma tigrinum. It consisted of two parts: 1) determination of plasma @entity6145 concentrations and analysis of thyroid gland histology as a function of metamorphic stage and 2) analysis of the time-course of uptake of 125I by the thyroids during metamorphosis as an indicator of endogenous @entity7287 (TSH) levels. Significant increases in both @entity1954 (T3) and @entity1955 (T4) first were evident at the onset of metamorphic climax (stage II). Maximum levels of both hormones were not observed, however, until the completion of gill resorption (stage VII). No changes in thyroid histology were observed that could be unambiguously related to metamorphic transformation. The thyroids accumulated 125I in a slow but linear fashion in premetamorphic larvae (stage I). However, uptake exhibited a rapid peak during early climax (stage II), before maximum concentrations of thyroid hormones were observed. In addition, uptake was maintained above premetamorphic levels at stage VII, in conjunction with maximum levels of T4 and T3. Captivity alone produced a small but significant increase in plasma concentrations of T3. It produced no significant effect on either thyroid histology or uptake of 125I. These results indicate that adenohypophysial activation occurs rapidly and is maximal at the onset of metamorphic climax.
