Re-evaluation of apparent hypometabolism in iron-deficient rats

Abstract

Experiments were performed to characterize body temperature, metabolic rate, plasma thyroid hormone concentrations, and nonshivering thermogenesis in iron-deficiency anemia at several environmental temperatures (32°, 25°, 20°, 15°, 10°, 8° C). Iron-deficient anemic rats (hemoglobin <60 g/L) were significantly colder than controls after 48-hr exposure to the lowest three temperatures despite having similar metabolic rates per kg 0.75 body weight (BW). These anemic rats were also able to increase metabolic rate 28% above control rats in response to a pharmacologic dose (75μg/100 gm BW) of norepinephrine. Brown adipose tissue mitochondrial 3H-GDP binding was significantly higher in iron-deficient animals than control animals at 25° C, but was significantly lower in iron-deficient animals at lower temperatures due to smaller fat pads and slightly lower mitochondrial protein contents. Thyroid hormone status varied with severity of iron deficiency such that less severely anemic iron-deficient rats with improved thyroid status had an improved thermoregulatory performance. The insufficient metabolic response to cold in iron deficiency is seemingly related to both a thyroid hormone limitation for nonshivering thermogenesis as well as a sympathetic nervous system defect because the pharmacologic dose of norepinephrine was able to increase metabolic rate.