Vacuolar H+-ATPase is involved in the process of lu-menal acidification in the male reproductive tract of both rats and humans. The acidic lumenal environment is believed to play a role in maintaining and storing sperm in an immotile state prior to ejaculation. We have previously shown that H+-ATPase is expressed in a subpopulation of epididymal epithelial cells, the narrow cells in the initial segments, and clear cells in the remainder of the epididymis, and that these cells are present as early as 2 wk after birth. At this time point, a large number of H+ATPase-rich cells were observed in the vas deferens, whereas only a few positive cells were detected in the epididymis, suggesting that the ability to secrete protons may begin in the vas deferens and progress back toward the epididymis during postnatal development.
The peak time of H+-ATPase expression in the epididymis occurs at around Postnatal Day 25. Therefore, both the onset and peak expression of the H+-ATPase occur at ages when the testicular production of testosterone is relatively low, suggesting that the expression of H+-ATPase might be regulated by factors other than androgens, or in addition to them. Alternatively, the low levels of androgens present in prenatal and prepubertal male rats might be sufficient to trigger the development of H+-ATPase-rich cells. In addition, the epididymis acquires detectable activity of the enzyme A4-5a-reductase, which converts testosterone to the more potent DHT at 21 days after birth, and it remains possible that significant levels of local DHT might be present and contribute to the initiation of the H+ATPase-rich cell phenotype during early postnatal development.