Metabolic rate and thyroxine 5′-deiodinase in iron deficiency: Effects of the estrous cycle

Abstract

Thyroid function is severely compromised in male iron-deficient (ID) rats. Similar effects in female rats are undocumented. Therefore, we examined thyroid hormone metabolism in female iron-deficient and control (CN) rats throughout the estrous cycle. Overall, iron-deficient rats had significantly lower plasma concentrations of thyroxine than controls (25.1 ± 8.4 nmol/L in ID; 31.5 ± 9.3 nmol/L in CN, mean ± SD, p≤0.001), while plasma triiodothyronine concentrations were similar to those of controls (0.44 ± 0.19 nmol/L vs. 0.48 ± 0.16 nmol/L, p≥0.05). Oxygen consumption was unaffected by either iron deficiency or the estrous cycle. Control animals had higher liver thyroxine 5′-deiodinase activity at estrus (567 ± 260 pmoles I − produced • mg protein −1 • 20 min −1) while iron-deficient animals had lower activity (310 ± 145 pmoles I − • mg protein −1 • 20 min −1) relative to other stages of the estrous cycle. In contrast, the lower interscapular brown adipose tissue 5′-deiodinase activity in iron-deficiency rats (p≤0.02) was not affected by the estrous cycle (p≥0.05). In conclusion, iron deficiency alters the normal estrous cycle variation in hepatic triiodothyronine production and plasma thyroid hormone concentrations