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Title: EFFECTS OF SHORT-TERM EFFECTS OF TRIIODOTHYRONINE GIVEN TO EUTHYROID BROILER CHICKENS

Author
item Rosebrough, Robert
item Russell, Beverly
item Poch, Stephen
item Richards, Mark

Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/30/2005
Publication Date: 4/2/2005
Citation: Rosebrough, R.W., Russell, B.A., Poch, S.M., Richards, M.P. 2005. Short-term effects of triiodothyronine given to euthyroid broiler chickens [abstract]. FASEB Journal. 19:335.

Interpretive Summary:

Technical Abstract: The purpose of this experiment was to determine the possible relationship between certain indices of lipid metabolism and specific gene expression in chickens fed methimazole to produce a kind of artificial hypothyroidism. Male, broiler chickens growing from 7 to 28 days of age 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. Birds were sampled at 28, 29, 30, 31, 32 and 33 days. Measurements taken included in vitro lipogenesis (IVL), malic enzyme (ME) activity the expression of the genes for ME, fatty acid synthase (FAS) and acetyl coenzyme carboxylase (ACC). 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. Although methimazole decreased ME gene expression, there was only a transitory relationship between enzyme activity and gene expression when plasma T3 was replenished with exogenous T3. These data may help to explain some of the apparent reported dichotomies in lipid metabolism elicited by changes in the thyroid state of animals. In addition, most metabolic changes in response to feeding T3 occurred within a short period of time, suggesting that changes in intermediary metabolism preceded morphological changes. In conclusion, the thyroid state of the animal will determine responses to exogenous T3.