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Introduction: Ghrelin, increases food intake, decreases T3 and T4 concentrations and stimulates insulin release, while leptin reduces food intake and suppresses appetite. Considering the importance of thyroid hormones, ghrelin and leptin in body metabolism, the purpose of this study was to investigate the effect of interactions between ghrelin and leptin (injected via ICV route) and plasma T3 and T4 concentrations in rats. Methods: Fifty-six Wistar male rats (230 to 250 g/BW) were randomly divided into 7 groups. Groups 1, 2 and 3 received 1, 3 and 5 nmol ghrelin, while groups 4, 5 and 6 received 1, 5, 10 nmol leptin (2 μl via lateral cerebral ventricle). Animals in the 7th group received 5 nmol ghrelin with 10 nmol leptin via the same route for 3 days. Blood samples were collected daily starting from one day before until one day after infusions and plasma samples were used to assess T3 and T4 concentrations by RIA. To ensure proper cannulation, perfusion and brain slices were performed. Results: The results indicated that ghrelin significantly decreased T3 and T4 concentrations, whereas leptin increased these concentrations. The simultaneous injection of ghrelin and leptin significantly reduced the inhibitory effect of ghrelin on thyroid hormones concentrations. Conclusion: According to the results and other researchers’ suggestions, the opposite effects of leptin and ghrelin could be emphasized and some hormonal mechanisms for these 2 hormones (transmitters) such as HPA and/or HPT axes or MSH systems could be suggested.

Keywords: Ghrelin, leptin, T3, T4, ICV injection

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