Impaired thyroid hormone status and thermoregulation during cold exposure of zinc-deficient rats.

Forty-five male, weanling Sprague-Dawley rats were matched by weight into three groups (n = 15). One group was fed ad libitum a semipurified diet containing all essential nutrients and 30 ppm of zinc (control). A second group was fed ad libitum a similar diet but with a deficient zinc intake of less than 1 ppm (ZnD). A third group was pair-fed (PF) the control diet in amounts equal to that consumed by the matched ZnD animals. After 42 days, the animals were fasted for 12 hr then five animals from each group were sacrificed and the remainder was exposed to 3 degrees C for 6 hr. Rectal temperatures were lower (p less than 0.05) in ZnD at 23 degrees C and during cold exposure. Plasma thyroxine (T4) and triiodothyronine (T3) concentrations were reduced (p less than 0.05) at room temperature in ZnD rats. During cold exposure, the ZnD animals had depressed (p less than 0.05) plasma thyrotropin, T4 and T3 concentrations. Thus, ZnD adversely affects thermoregulatory performance of rats acutely exposed to cold by influencing thyroid hormone metabolism.