Previous studies have suggested that 1 α ,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] has a role in reproductive function. Gonadal insufficiencies were observed as a result of 1,25(OH) 2 D 3 deficiency and in 1,25(OH) 2 D 3 receptor (VDR) null mutant mice. To study human sperm anatomy at the molecular level, we first evaluated the ultrastructural localization of VDR by immunogold electron microscopy using a monoclonal antibody against amino acids 344-424 of human VDR, in normozoospermic samples. Intriguingly, VDR was associated predominantly with the cell nucleus. In fact, it is known that VDR is a transcription factor, and that in vitamin-D-depleted animals, VDR is largely localized in the cell nucleus. To assess the significance of VDR in the male gamete, we investigated the role of 1,25(OH) 2 D 3 /VDR in sperm survival and capacitation. Our results revealed that the action of 1,25(OH) 2 D 3 depended on its concentration because although lower doses induced cholesterol efflux, protein phosphorylation and sperm survival, a higher concentration seemed to be ineffective or did not show an increased effect. These results increase our knowledge of human sperm anatomy at the molecular level and suggest that 1,25(OH) 2 D 3 /VDR may have an important role in sperm survival and the acquisition of fertilizing ability.

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