Submitted to: Poultry Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/30/2008
Publication Date: 7/21/2008
Citation: Rosebrough, R.W., Russell, B.A., Richards, M.P. 2008. Short-term effects of triiodothyronine on hypothyroid chickens. Poultry Science 87:88.
Technical Abstract: These experiments determined relationships among certain indices of lipid metabolism and gene expression in chickens fed methimazole. Male, broiler chickens were fed diets containing 18% crude protein and either 0 or 1 g methimazole per kg of diet. At 28 days, these two groups were further subdivided into groups receiving 18% crude protein diets containing either 0 or 1 mg triiodothyronine (T3) per kg. In the first experiment, birds were sampled at 0, 1, 2 & 4 days post relief from a diet containing methimazole. In the second experiment, birds were sampled at 0, 3, 6, 9, 24 & 48 hr post relief from the methimazole diet. Measurements taken in the first experiment included in vitro lipogenesis (IVL), malic enzyme (ME), isocitrate dehydrogenase (ICD-NADP), aspartate aminotransferase (AST) enzyme activities and the expression of the genes for ME, fatty acid synthase (FAS) and acetyl coenzyme carboxylase (ACC), ICD-NADP and AST. The same enzyme activities and gene expressions were assayed over the intervals mentioned above. Gene expression was approximated with real time RT-PCR assays. Gene specific primers were designed with Primer 3. Expression rates were noted as Ct’s or cycles to significant deviation from baselines. Hypothyroidism (dietary methimazole) decreased IVL and ME at 28 d of age. T3 supplementation for 1 d restored both IVL and ME. Paradoxically, continuing T3 replenishment for a longer period decreased IVL without affecting ME activity. There was only a transitory relationship between enzyme activity and gene expression when plasma T3 was replenished with exogenous T3. Most metabolic changes in response to feeding T3 occurred within a short period of time, suggesting that changes in intermediary metabolism preceded morphological changes although it should be noted that the thyroid state of the animal determines responses to exogenous T3.