Temporal and spatial distribution of alkaline phosphatase activity in male hypogonadic rat (hgn/hgn) testis during postnatal development.

In male hypogonadic mutant rat (hgn/hgn), gonocytes degenerate and peritubular cells form multiple layers around seminiferous tubules during early postnatal testicular development. Alkaline phosphatase (AP) activity has been used as not only a tracer for the primordial germ cells (PGCs) but also a histochemical marker for the peritubular myoid cells. In the present study, we examined the localization of AP activity during the postnatal testicular development in the hgn/hgn and phenotypically normal (+/+ or +/hgn) rat. In the normal testis, high AP activity was located in the surface of the PGCs on 3 days of age. As the PGCs differentiated into spermatogonia, the AP activity drastically decreased in intensity on 7 days and was completely lost by 12 days. In the hgn/hgn, the PGCs showing high AP activity occupied the inside of dilated seminiferous tubules on 3 and 7 days of age. The luminal AP activity declined gradually by 18 days and disappeared on 21 days, when the germ cells completely degenerated in the hgn/hgn testis. In the normal, high AP activity emerged in a layer of the peritubular cells surrounding the tubules on 7 days and afterwards, indicating that the peritubular cells were differentiating into myoid cells. In the hgn/hgn, the peritubular cells formed multiple layers around the tubules and showed weak AP activity on 3 to 18 days of age. On 21 days of age, high AP activity emerged in a single layer of the peritubular cells directly attached to the basement membrane in the hgn/hgn. These results indicate that the PGCs showing AP activity kept remained at later stage in the hgn/ hgn and that the single layer of mature myoid cells showing high AP activity appeared much later in the hgn/hgn testis than in normal.