Autoradiographic distribution and physiological regulation of 2-[125I]iodomelatonin binding in rat epididymis

Autoradiographic study was conducted to localize 2-[I-125]iodomelatonin binding in the rat epididymis. In the peripubertal (6 weeks old), postpubertal (8 weeks old) and adult (3 months old) rats, intense specific 2-[I-125]iodomelatonin labelling of the corpus epididymidis was observed. The intensity of 2-[I-125]iodomelatonin binding in the distal epididymal segment was significantly decreased in orchidectomized rats but the effect could be reversed with testosterone replacement. The intensity of 2-[I-125]iodomelatonin binding in the distal rat epididymal segment did not show any diurnal rhythmicity when mid-light period and mid-dark period levels were compared, and was unaffected by constant lighting. Our data suggest androgen-dependent expression of 2-[I-125]iodomelatonin binding sites, independent of light-induced changes in circulating melatonin, in the rat corpus epididymidis. A novel role of melatonin and its receptor in the regulation of the functions of rat corpus epididymidis is strongly implicated.