BackgroundEarlier, nothing was known on the thyroid-regulatory potential of caffeic acid (CA). We investigated its role in 6-propyl-thiouracil (PTU)-induced hypothyroid rats and also worked out the possible involvement of 5’-deiodinase I (5’-DI) and thyrotropin receptor (TSHR) in its mode of action. MethodsA pre-standardized dose (100 mg/kg) of CA was orally administered to PTU-induced rats for 30 days and its effects were evaluated on the alterations in the levels of serum triiodothyronine (T3), thyroxine (T4), thyrotropin (TSH) and hepatic 5’-D1activity; expression of thyroid TSHR, aspartate transaminase (AST), alanine transaminase (ALT), tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), total cholesterol (CHOL), triglycerides (TG) and hepatic lipid peroxidation (LPO). For the first time an interaction of CA with TSHR was studied in silico. ResultsPTU significantly reduced serum levels of thyroid hormones (TH), hepatic 5’-D1 and antioxidant activities as well as TSHR expression, but increased the serum TSH, AST, ALT, TNF-α, IL-6, CHOL, TG and hepatic LPO. However, CA treatment ameliorated all these PTU-induced alterations near to normal levels. Further, the distorted histo-architecture of thyroid gland by PTU was corrected by this compound. The molecular docking study indicated that CA possesses a high binding free energy with target TSHR. These results were comparable to that of a standard pro-thyroid drug, thyroxine. ConclusionCA potentially stimulated thyroid function by increasing TH levels, hepatic 5’-D1 activity and upregulation of TSHR protein expression. In addition, it attenuated the increase in oxidative stress markers, liver markers, lipids and improved the thyroid histo-architecture, thus protected from PTU-induced adverse effects. In silico studies suggested the interaction of CA with TSHR that yielded the binding energy (-6.51 kcal/mol) as compared to thyroxine (-6.10 kcal/mol) suggesting it as a highly potent thyro-stimulatory drug.