Background : Anabolic steroids have become popular drugs among athletes and are known to have a multitude of pathological effect when administered in suprapharmacological doses. The purpose of this study was to determine the effects of 8 weeks testosterone enanthate (TE) injection and resistance training on serum Total triiodothyronine (TT3), total thyroxin (TT4) and Thyroid stimulating hormone (TSH) levels in rat . Materials and methods: In this study, 35 male adult wistar rats were randomly divided into 5 groups; Group I: TE (20 mg/kg), Group II: resistance training + placebo, Group III: TE (20 mg/kg) + resistance training; Group IV: TE (50 mg/kg) + resistance training; GroupV: placebo. The resistance training consisted of climbing (5 reps/3 sets) a ladder carrying a load suspended from the tail. At the end of 8 weeks rats were anaesthetized, and whole blood samples were obtained from the orbital sinus. The samples were centrifuged; sera were separated and TT3, TT4 and TSH were determined by radioimmunoassay using DiaSource kits. Results: TT4 concentration in group IV was decreased significantly (P< 0.05) compared to the groups II, III and V. No statistically significant changes were observed in the concentrations of serum TT3 between different groups. Although serum TSH concentrations in group IV was greater than other groups but it was not significant. Conclusion: The results show that muscle injection of testosterone enanthate in high doses unlike low doses result in severe reduce of serum total T4.

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