Effect of iron-deficiency anemia on hormone levels and thermoregulation during cold exposure.

When exposed to an ambient temperature of 4 degrees C, iron-deficient anemic rats become hypothermic. This lesion is related more to anemia than to tissue iron deficiency, since exchange transfusion to hematocrits over 25 restored normal thermoregulatory performance. Likewise poor cold responses were induced in control rats by transfusion to low hematocrits. Cold sensitivity in all anemic animals was paralleled by poor thyroid responses: there was a significant positive correlation between hematocrit and percent rise in triiodothyronine (r = 0.63) and thyroxine (r = 0.53) during 6 h at 4 degrees C. Basal levels of thyroid-stimulating hormone (TSH) were similar in control and iron-deficient animals: after cold exposure, TSH rose to higher levels in those animals with hematocrits over 25 than in those with lower hematocrits. Diminished O2 delivery to tissues responsible for heat production is probably a major component of the cold sensitivity of anemic rats. The novel finding that thyroid hormone responses are compromised by anemia implies effects on hormonal regulation that may also contribute to this functional lesion.