The effect of temperature on the action of thyroid hormone and prolactin in larvae of the salamander Hynobius retardatus.

To elucidate the environmental factors and endocrine mechanisms which are responsible for inducing neoteny in the salamander Hynobius retardatus, the effect of temperature on the growth and metamorphosis of this amphibian, as well as the actions of thyroid hormone and prolactin at low temperature, were studied. (1) The metamorphosis of larvae cultivated at 10 degrees was significantly delayed compared with that of larvae cultivated at 22 degrees, but the metamorphosis was eventually completed. At 4 degrees, metamorphosis never occurred, even after 2 years. (2) Exogenously administered thyroid hormone accelerated metamorphosis at 10 degrees or 22 degrees, but was ineffective in larvae kept at 4 degrees, whether administered by injection or immersion. (3) If a higher concentration of thyroid hormone was given by a single injection to larvae cultured at 4 degrees, an appreciable acceleration of metamorphosis was observed after transferring the larvae to 22 degrees. (4) Unlike thyroid hormone, prolactin promoted growth at 4 degrees.