Melatonin affects proopiomelanocortin gene expression in the immune organs of the rat.

The induction of opioid peptides derived from cells of the immune system is postulated to be the main mechanism involved in the immunomodulatory role of melatonin. In this study, it has been demonstrated for the first time that melatonin can act on the level of proopiomelanocortin (POMC) gene expression. The effect of the pineal hormone, administered in late-afternoon subcutaneous injections, was studied in the immune organs of adult male Wistar rats by means of a highly sensitive reverse transcription polymerase chain reaction method (RT-PCR), followed by polyacrylamide gel electrophoresis and densitometric analysis of the bands. It was demonstrated that melatonin stimulates the expression of the 3rd exon of the POMC gene in the lymph nodes and in bone marrow. No significant effects of the pineal hormone were observed in the spleen and thymus. The study establishes that the formation of short POMC transcripts in the bone marrow and lymph nodes may be upregulated by melatonin. Moreover, the pineal hormone exerts its effect without antigenic stimulation.