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This study is undertaken to identify the regulatory switch for the activation of superoxide radical generation pathway and repression of superoxide dismutase (SOD) at the time of implantation using estrogen as a control factor and delayed implantation as a model system. The results revealed high SOD activity and negligible oxyradical generation in progesterone-treated animals on day-5 and day-8 (delayed implantation) while an enormous rise in oxyradical generation and an abrupt fall in SOD in animals which received both estrogen and progesterone injections were observed on days 5 and 8 of pregnancy. These results strongly suggest that estrogen regulates superoxide anion radical generation by lowering the SOD activity.Blastocyst implantation in the uterus remains an intriguing field in the area of reproductive biology. The immunologically alien blastocyst graft invades actively into a genetically non-identical tissue, the uterus, thereby yielding points of communication between two important current research domains, those of transplantation immunology and invasity of neoplastic tissue. Thus, a thorough study of implantation remains an area of utmost importance, not only for the understanding of one crucial step of mammalian embryology, but also in a wider contact for elucidation of basic concepts in cell biology.

The primary aim of this study was to evaluate the effect of melatonin on the oxyradical load in avian thyroid. The superoxide free radicals have been spin trapped by EPR spectroscopy in the thyroid gland of Indian rock pigeon Co/umba/ivia following melatonin implantation for two weeks. Melatonin implantation resulted in augmentation in the levels of superoxde radical in the thyroid gland of pigeons with a concomitant decrease in the levels of the total superoxide dismutase activity. This was also associated with increased lipid peroxidation. Melatonin implantation caused a significant increase in plasma levels of glucose. Plasma levels of thyroxine (T4) and triiodothyronine (T3) were lower in the melatonin-treated pigeons. However, the T3/T4 ratio was higher following melatonin implantation. Since iodination of tyrosine is an H2Oz-dependent phenomenon, the inhibition in the activity of SOD could lead to impaired thyroid hormone synthesis.

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