Oxidative Damage and Apoptosis Induction by L-thyroxine in the Spleen of a Tropical Bird Perdicula asiatica : Rescue by Melatonin

Avian thyroid gland is known to influence the immunity and reproduction in an opposite manner. In this study, we evaluated the immunostimulatory, anti-oxidative and anti-apoptotic roles of melatonin in a tropical bird, Indian jungle bush quail, Perdicula asiatica , having L-thyroxine (thyrotoxicity)-induced oxidative stress. Administration of L-thyroxine (100 I¼g/kg body weight) enhanced the thyroidal lipid peroxidase (LPO), with a parallel decrease in the levels of antioxidant enzyme (SOD, GPx, CAT, MDA & NO) activities. Cellular immune response (%SR) and humoral immune response (anti-KLH-IgG level) of splenocytes along with general hematological parameters (TLC, LC & HF/L ratio) decreased significantly upon L-thyroxine treatment. Further, decrease in circulatory anti-inflammatory cytokines IL-2 and TNFI± suggested drastic effects of induced thyrotoxicity (elevated levels of T3 & T4) on immunity. Melatonin pre-treatment (25 I¼g/100g BW) during evening hours (prior to L-thyroxine treatment in the afternoon) for 30 days circumvented the deleterious effects of L-thyroxine-induced oxidative stress (level of Corticosterone) and apoptosis index of the avian spleen. Our results clearly indicate the potential of melatonin in rescuing/reducing the thyrotoxicity-induced oxidative damage to avian immunity.