Melatonin decreases the nitric oxide response in thyrotoxic rats

Purpose: Hyperthyroidism results in free radical production and this free radical production results in cell damage. Melatonin, which is an effective hormone in the management of the metabolism, prevents the harmful effects of free radicals like nitric oxide via its direct antioxidant effect. This study was conducted to investigate the role of nitric oxide in experimental hyperthyroidism and the effect of melatonin on nitric oxide. Materials and Methods: Thirty Wistar Albino female rats were randomized into three groups: Group A [negative control group] underwent saline injection; Group B [positive control group] underwent intraperitoneal L-Thyroxine 0.2 mg/kg/ day and Group C [treatment group] underwent intraperitoneal L-Thyroxine 0.2 mg/kg/day + melatonin 3 mg/ kg/day. After 3 weeks, all rats were decapitated and blood, liver and heart tissue samples were taken. Biochemically, FT3, FT4, TSH and NO levels were investigated. Results: There was a significant change in FT3 levels between Groups A and B, and Groups B and C [p < 0.001 and p= 0.004, respectively]. Concerning FT4 levels, there was a significant change between Groups A and B and Groups A and C [p< 0.001 and p= 0.02 respectively]. Changes in median blood NO levels of Group A, B and C were significantly different [5,93 mu M/L; 48,41 mu M/L and 42,69 mu M/L, respectively] [p< 0.001]. Heart NO level of Group B is similar to Group A [1,74 mu mol/g vs. 1,74 mu mol/g]. There was also no statistically significant difference between Group B and C, although heart levels decreased in Group C [1,25 mu mol/g], [p= 0,05]. Liver NO levels showed a significant difference between Group A and B, while there was no significant difference between Groups B and C [0,30 mu mol/g; 0,46 mu mol/g ve 0,41 mu mol/g, respectively]. Conclusion: Results of this study should be confirmed with future studies conducted with different doses and application time intervals of melatonin. We believe that these future studies will lead melatonin to a major role in the fight against pathologies like hyperthyroidism that affect many systems.