INTERACTIONS OF IRON-DEFICIENCY AND EXERCISE TRAINING RELATIVE TO TISSUE NOREPINEPHRINE TURNOVER, TRIIODOTHYRONINE PRODUCTION AND METABOLIC-RATE IN RATS

The interactions of iron deficiency and exercise training relative to resting metabolic rate (RMR), tissue norepinephrine (NE) turnover and triiodothyronine (T3) production were examined in male Sprague-Dawley rats. Animals were assigned to iron-deficient (ID) or control (CN) diets and to sedentary (SD) or treadmill-exercised (EX) groups 6 or 12 wk. Iron-deficient animals (hemoglobin 7.2 ± 0.2 g·100 mL-1) had a 17% higher RMR and had slower growth rates than CN animals. Exercise training affected growth but not RMR in iron deficiency. Oxygen consumption (V̇O2) following pharmacologic injection of norepinephrine was similar in both iron-deficient and exercised groups despite a 35% lower maximal exercise V̇O2 in trained iron-deficient rats. NE turnover was lower in heart (55%) and liver (88%) of iron-deficient animals relative to controls. Trained iron-deficient animals had lower NE turnover in interscapular brown adipose tissue (IBAT) than sedentary iron-deficient animals; however, training did not alter NE turnover in control animals. In vitro liver and IBAT T3 production was similar in all groups except for lower activities (40%) in 6-wk iron-deficient, exercised animals. The significant effect of exercise on the growth attenuation of iron-deficient, exercised animals is thus not explained by increased IBAT metabolic activity or a generalized sympathetic nervous system activation. Decreased T3 production during periods of rapid growth and lean body mass development, however, may be important in exercised, iron-deficient animals.