Trade-Off Relationship between Melatonin and Gonadal Steroid on Melatonin Receptor (MEL 1A R) Expression in Lymphoid Tissue

Endogenous melatonin is involved in regulation of reproductive function of the photoperiodic species. A circannual rhythmicity of the pineal gland in relation to reproduction has been observed in a tropical seasonally breeding mammal, Funambulus pennanti. A trade-off relation is known to exist between melatonin and the gonadal steroids. In vitro suppression of splenocyte proliferation by testosterone and the reversal of this effect by melatonin supplementation have already been reported. Melatonin receptors have been detected in the lymphoid tissues by binding of 2-[¹²⁵I] iodomelatonin to splenocytes and thymocytes. We analyzed the presence of melatonin receptor adopting Western blot technique. We found that MTl receptor protein, one of the variants of melatonin receptor, is expressed in both the thymus and spleen tissue and the expression is suppressed by testosterone treatment. This substantiates the direct immunomodulatory role of melatonin. To find the significance of steroid toxicity at molecular level, particularly testosterone, it is important to study its effect on the expression pattern of these receptors.