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Introduction: Verapamil, a phenylalkylamin –type Ca2+ channel blocker, is widely used in the treatment of cardiovascular disorders especially as an antiaryhthmic and antiangina agent. Theoretically, calcium can influence thyroid function and there are evidences that Ca2+ channel blockers are able to interfere with thyroid function. In this study, the effects of chronic oral administration of verapamil on thyroid function of male Wistar rats were investigated. Methods: Study was performed on 5 groups of animals groups 1 to 3 were treated with verapamil at doses of 10, 20 and 50 mg /kg respectively for two months via oral tube. Sham group received only distilled water, while control group received neither verapamil nor distilled water. At the end of this period animals were anaesthetized, abdomen was opened and blood samples were obtained from abdominal aorta. The samples were centrifuged sera were separated and stored at – 20 ◦C until the time of the assays. Total triiodothyronine (TT3), total thyroxin (TT4), free triiodothyronine (FT3) and free thyroxin (FT4), T3 uptake levels were assayed by ELISA (DRG). Thyroid stimulating hormone (TSH) was determined by radioimmunoassay using DRG kits. Results: Total T4 level was significantly lower in sham (3.49 ± 0.1μg/dl) and verapamil dose 10 mg /kg (3.6±0.14) groups than in control group (4.5±0.34), while it was significantly higher in verapamil 50 mg /kg (4.24±0.2) group as compared to the sham group. Total T3 concentration in verapamil 20 mg /kg group (62±8.9ng/ dl) was decreased significantly compared to the control group (103.3±14). Free T3 and free T4 were significantly lower in sham group (p<0.005) compared to control group, while it was increased in verapamil groups of 20 and 50 mg /kg compared to sham group. Level of T3 up-take was decreased significantly (p<0.005) in sham (20.97±1.49%) and verapamil 20 (20.7±1.4) mg /kg compared to control group (27.6±1), while it was higher in verapamil 10 and 50 mg /kg groups than sham group. Thyroid stimulating hormone levels were similar in all groups. There were no significant differences in the T3/T4 ratio and body weights on first and last day of the groups compared to control group. Conclusion: It can be concluded that long term oral administration of verapamil doesn’t have inhibitory effect on thyroid function, however it can block adverse effect of handling stress on thyroid function. Therefore, from thyroid function point of view, the drug can be used safely for the duration of this study.

Keywords: verapamil, thyroid function, long term, rats.

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