ASTRACT: Cold stress is an environmental cause of pulmonary hypertension syndrome (PHS) in broiler chickens. This factor could increase the rate of metabolic activity via thyroid hormones (T3 and T4). To evaluate the effect of these hormones on the heart, the plasma concentration of T3, T4, and the gene expression of their receptors (THRα and THRβ) and many contractile proteins (ACTC1, MHCα, MHCβ, RYR2, SERCA2, THRα, THRβ, and troponin I) were measured in the right ventricle in 2 periods of age (21 and 35 d). Plasma T3 concentration was significantly higher in the PHS group of chickens than in the control one at 21 and 35 d while plasma T4 did not change. The relative expression of MHCα, RYR2, SERCA2, and THRα genes in the right ventricle tissues was only higher in PHS group of broilers than control group at 21 d (P < 0.05) whereas the expression of ACTC1, MHCβ, and troponin I did not differ at 2 periods of age. The positive correlations between MHCα, RYR2, SERCA2, and T3, THRα were confirmed. The expression of THRβ gene was only higher in PHS group of broilers than control at 35 d (P < 0.05). The data determined that cold stress could increase thyroid hormones and the gene expression of their receptor (THRα) in the pick of chicken growth (21 d) that they themselves elevates the expression of many genes related to contractile elements (MHCα, RYR2, and SERCA2), leading to adaptive right ventricle hypertrophy.
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