ENVIRONMENTAL TEMPERATURE AND THYROID ACTIVITY IN THE LIZARD, SCELOPORUS OCCIDENTALIS.

Area of Science:

• Endocrinology
• Herpetology
• Physiology

Background:

• The hypophyseal-thyroidal axis regulates metabolism and is influenced by environmental factors.
• Understanding temperature's role is crucial for reptile physiology and adaptation.

Purpose of the Study:

• To investigate the relationship between ambient temperature and thyroid activity in Sceloporus occidentalis.
• To determine the influence of the pars distalis on temperature-dependent thyroid function.

Main Methods:

• Radioiodine (I-131) incorporation was measured in the thyroid glands of intact and hypophysectomized lizards.
• Animals were exposed to various temperatures: 15°C, 21°C, 30°C, and 38°C.
• Thyroid activity was assessed by comparing I-131 uptake across different temperature conditions and experimental groups.

Main Results:

• Thyroid activity was significantly inhibited at 15°C in both intact and hypophysectomized lizards.
• Between 21°C and 38°C, no significant temperature-related changes in thyroid activity were observed.
• Thyroid activity was reduced in experimental animals (pars distalis removed) compared to intact controls, irrespective of temperature.

Conclusions:

• Temperature appears to play a permissive role in activating the hypophyseal-thyroidal axis.
• Cold temperatures (15°C) significantly inhibit thyroid function, overriding pituitary influence.
• TSH therapy in hypophysectomized lizards may explain varied I-131 accumulation patterns in different lizard species.