Submitted to: Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 1998
Publication Date: N/A
Technical Abstract: There are conflicting results concerning the role of the thyroid hormones on lipid metabolism. The purpose of this experiment was to study the effects of T3on metabolic adaptations in hypothyroid or euthyroid birds. Seven-day-old chickens were fed diets containing 18% crude protein + 0 or 1 g methimazole/ kg to produce either euthyroid or hypothyroid groups of birds at 28 d of age. These two groups were then offered diets containing either 0 or 1 mg T3/kg diets. Birds were sampled at 0, 2, 5 & 8 d following the onset of the T3 treatment. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities and plasma thyroid hormones and metabolites. Iodothyronine 5'-monodeiodinase (5'D; EC 18.104.22.168) activity was measured to determine if the native thyroid state would affect this regulatory enzyme's response to thyroid hormone repletion. Hypothyroidism decreased IVL at 28 d of age; however, T3 supplementation for 2 d restored IVL. Paradoxically, continuing T3 replenishment for an additional 3 to 6 d decreased IVL. Supplemental T3 decreased IVL in euthyroid birds. Hypothyroidism increased 5'D activity. Although T3replenishment for 8 d decreased 5'D activity, this activity was still greater than that of the controls. In conclusion, the thyroid state of the animal will determine responses to exogenous thyroid hormones. Most metabolic changes in response to feeding T3occurred within 2 to 5 d, suggesting that changes in intermediary metabolism preceded morphological changes.