Distribution of vitamin D3 receptor in the epididymal region of roosters (Gallus domesticus) is cell and segment specific.

Vitamin D3 is a steroid hormone well known by its role in maintaining calcium homeostasis, however this hormone may also participate in other biological functions, including control of reproductive processes. The vitamin D3 action is mediated by the vitamin D3 receptor (VDR). VDR is widely distributed in the rodent reproductive tract, however the occurrence of VDR and the role of the vitamin D3 in the avian reproductive tract remain unknown. The aim of the present study was to investigate the expression and cellular distribution of VDR in the epididymal region of roosters. VDR expression was investigated by Western blotting analysis and the tissue distribution of the receptor was determined by immunohistochemistry. The Western blotting assay revealed a major VDR protein band of 61kDa in the epididymal region of rooster. Nuclear VDR expression was found in all segments of the epididymal region, namely rete testis, efferent ductules, connecting ducts and epididymal ducts. Nonciliated cells of the distal efferent ductules showed the highest levels of VDR expression, followed by the proximal efferent ductules and rete testis. The connecting and epididymal ducts showed less intense VDR immunostaining. The differential VDR expression in the epididymal region segments reveals that several extratesticular ducts may be target for vitamin D3 action and suggests that vitamin D3 may have a regional-specific function, such as calcium transport, that is modulated through VDR activity.