Temperature and photoperiod effects on thyroid function and metabolism in cotton rats (Sigmodon hispidus)


This study investigates the environmental cue(s) used by cotton rats to mediate seasonal shifts in thyroid function and metabolism. Summer-caught and winter-caught animals were exposed to combinations of five photoperiods and two temperatures for 60 days. Oxygen consumption and several parameters of thyroxine (T4) and triiodothyronine (T3) dynamics were then measured. Photoperiod had a significant effect only on serum T3 concentration: an inverse relationship with length of day. Cold exposure also increased serum T3, as well as the T3 pool and T3 utilization (i.e., disappearance) rate. In addition, cold increased metabolic rate, T4 clearance, and T4 volume of distribution, while it decreased serum T4 concentration. For a few parameters, season of capture also had a significant effect. Because many of the observed changes could result from a seasonal or temperature-induced shift in T4 to T3 deiodination, it is suggested that one important effect of these environmental cues is the regulation of this enzyme(s). Since T3 utilization increases over 12-fold in winter-caught cotton rats maintained at 5°C (over summer-caught animals maintained at 30°C), but metabolic rate only increased about 25% in these same animals, the roles/fates of this additional T3 remains to be determined.



Document Type





hormone turnover, hormone utilization, metabolic rate, photoperiod, Sigmodon hispidus, temperature, thyroxine (T ) 4, triiodothyronine (T ) 3

Publication Date


Journal Title

Comparative Biochemistry and Physiology - A Physiology