Background : Studies show that smoking can influence endocrinological functions of thyroid gland. The main aim of this study was to determine the effects of cigarette and waterpipe smoke on serum level of TSH, T3 and T4 in male rats.

  Methods: In this laboratory experimental study, male Wistar rats were randomly divided into control, cigarette, and waterpipe smoking animals of 5 in each group. After 6 weeks, blood samples were collected using cardiac puncture method. Following serum collection, levels of TSH, T3 and T4 were measured by radioimmunoassay method. Data were statistically analyzed and compared between groups using ANOVA.

  Results: The results indicated that serum T3 and T4 levels were significantly increased in cigarette smoking rats compared with control animals (p<0.001 and p<0.01, respectively). Serum levels of T3 and T4 were also increased in waterpipe smoking rats compared with control animals (p<0.01). Serum level of TSH was insignificantly decreased in cigarette and increased in waterpipe smoking rats, respectively.

  Conclusion: Our findings show that cigarette or waterpipe smoking enhances endocrinilogical function of thyroid gland appeared in increased serum level of T3 and T4 therefore, the effects of cigarette and waterpipe smoke on hyperthyroidism induction is important.