Decrease in the Number of Human Ap and Ad Spermatogonia and in the Ap/Ad Ratio with Advancing Age New Data on the Spermatogonial Stem Cell

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Abstract
The numbers of Ap and Ad spermatogonia per unit section of the testis were calculated in autopsy specimens from young adults and elderly men without testicular pathology. The number of Ap spermatogonia decreased from the 6th decade of life, whereas that of Ad spermatogonia began to decrease in the 8th decade. Although it has been reported that Ad spermatogonia are more sensitive to noxious agents than Ap spermatogonia, the involution of Ap spermatogonia precedes that of Ad spermatogonia. These findings provide new information on concepts relating to the spermatogonial stem cell in man.