Effect of age on L-3,5,3'-triiodothyronine-induced ethane exhalation

The effect of age on thyroid hormone-induced lipid peroxidation in rats was determined by measuring ethane exhalation (EE) rate. The mean basal EE rates (in pmol · min^-1 · 100 g^-1) at room air in 25-mo-old aged rats [3.07 ± 0.26 (SE)] and in intermediate age (18-mo-old) rats (3.42 ± 0.18) were significantly lower than that in young (3- to 5-mo-old) rats (4.44 ± 0.27) (P < 0.01). After 8 days of L-3,5,3'-triiodothyronine (T₃) administration, EE rates in aged rats (4.10 ± 0.25) and in intermediate-age rats (4.16 ± 0.35) were significantly lower than that in young rats (5.61 ± 0.36) (P < 0.01). T₃-treated young rats pair-fed with aged rats for 2 wk had EE rates (5.53 ± 0.18) comparable to ad libitum-fed young rats, although the basal rate of EE was significantly reduced with partial food restriction (4.44 ± 0.27 vs. 3.50 ± 0.24) (P < 0.01). These observations indicate that reduced food intake with age cannot account for the age-related changes in T₃-stimulated peroxidation rate of lipids.