Environmental Temperature and Thyroid Activity in the Lizard, Sceloporus occidentalis

The relationship between temperature and the hypophyseal-thyroidal axis in Sceloporus occidentalis has been investigated by a study of radioiodine incorporation by the thyroid in intact animals, and animals with the pars distalis removed, kept at temperatures of 15°, 21°, 30° and 38° C. Over the range of 21 to 38° C there was no evidence of any significant temperature-related change in the normal and experimental animals, although the thyroid activity was reduced after the operation. At 15° C the thyroid functioning was significantly inhibited and there was no difference between the normal and experimental animals. It is suggested that the role of temperature in thyroid activation is a permissive one. Data for I131 incorporation in hypophysectomized animals receiving TSH therapy offers a possible explanation for the different patterns of thyroidal I131 accumulation observed in different forms of lizards.