Effect of Thyroid Hormones on the Redox Balance of Broiler Chickens

H. Lin,J. Buyse,E. Decuypere

doi:10.5713/ajas.2008.70305

Abstract

In the present study, two trials were conducted to evaluate the effects of hyper- and hypothyroid status on the redox balance of broiler chickens. In Trial 1, 3 groups of broiler chickens were randomly subjected to one of the three treatments: subcutaneous administration of triiodothyronine (T 3 , 150 μg/kg BW), methimazole (MMI, 150 mg/kg BW), or saline. The blood, liver and heart were sampled at 3 h after injection. In Trial 2, three groups of 20 broiler chickens were randomly fed with one of the three diets: control, dietary supplementation of T 3 (1.5 mg/kg diet) or MMI (1 g/kg diet) for 7 days. In trial 1, the plasma concentrations of T 3 and T 3 to thyronine ratio (T 3 /T 4 ) were significantly increased by T 3 injection. Plasma levels of thiobarbituric acid reacting substances (TBARS) tended to be increased (p = 0.067) by both T 3 and MMI treatments while the ferric reduced/antioxidant capacity (FRAP) was increased only by MMI treatment. Acute T 3 treatment had no significant effect on the activities of superoxide dismutase (SOD) and the concentrations of FRAP and TBARS in either liver or heart tissue. In contrast, the hepatic activities of SOD were decreased (p<0.05) while the cardiac levels of FRAP were significantly increased (p<0.0001) by MMI treatment. In chronic treatments, the rectal temperature of chickens was significantly decreased (p<0.05) by MMI treatment. The circulating T 3 levels were significantly increased (p<0.05) by long-term T 3 treatment, and showed a trend to decrease in MMI treatment. The plasma concentrations of TBARS were significantly (p<0.05) increased by MMI treatment. All the redox parameters measured in either liver or heart were not significantly altered by either long-term T 3 or MMI treatment except that the hepatic SOD activities were significantly augmented by T 3 treatment. The result showed that neither acute nor long-term elevation of circulating T 3 levels induced lipid peroxidation in broiler chickens. The enhanced enzymatic antioxidant system (SOD in cardiac tissue) may be involved in the protection of the bird to increased oxidative challenge. The responses of redox balance to changed thyroid state seem to be tissue specific.

Highlights

Thyroid hormones are known to regulate the energy metabolism of most tissues including liver, kidney, heart, and skeletal muscles
In trial 1, at 3 h after treatment, the body weight (BW) and RT of experimental chickens were all decreased in all treatments but there was no significant difference in BW loss (T3, 17.2±3.0 g; MMI, 8.3±13.1 g; Control, 20.2±5.1 g) and RT reduction (T3, -0.4±0.1°C; MMI, -0.4±0.1°C; Control, -0.3±0.1°C) between treatments (p>0.05)
The plasma concentrations of T3 and T3/T4 ratio were significantly increased by T3 treatment but were not affected by MMI treatment

Summary

Introduction

Thyroid hormones are known to regulate the energy metabolism of most tissues including liver, kidney, heart, and skeletal muscles. It is well established that thyroid hormones accelerate the basal metabolic rate and oxidative metabolism by causing an increase in the mitochondria mass, mitochondrial cytochrome content and respiratory rate. The plasma levels of thyroid hormones are changed with ambient temperature, age, feeding status and pathophysiologic status (Decuypere and Kühn, 1984, 1988; Lin et al, 2000; Stojevic et al, 2000; Luger et al, 2002). The reactive oxygen species (ROS) are generated as by-products of oxidative metabolism in. The enzymatic and not-enzymatic antioxidant systems are involving in the enhanced oxidative stress in hypothyroid patients (Adali et al, 1999; Resch et al, 2002)

Methods

Results

Conclusion