Alkaline phosphatase histochemistry discriminates peritubular cells in primary rat testicular cell culture

Histochemical demonstration of alkaline phosphatase activity appears to be useful in identifying rat peritubular cells in primary testicular cell culture. In both frozen sections of rat testis and Mirsky's fixed, methacrylateembedded rat testis, the reaction product localized primarily in peritubular cells, vascular endothelium and occasionally in interstitial cells, with much smaller amounts of reaction product associated with elongating spermatids in the germinal epithelium. Occasional late‐stage tubules (X‐XIV) showed weak reactivity in the epithelium, associated with spermatocytes or Sertoli cells. Ultrastructurally, Gomori‐method reaction product was localized to peritubular cells, lymphatics, and spermatogonia in stage VII; no staining was found consistently in Sertoli cells. In isolated cell preparations enriched for Sertoli and germ cells, 1 to 8% of the cells demonstrated alkaline phosphatase activity, while greater than 50% of the cells stained positive for alkaline phosphatase activity in peritubular‐enriched fractions. The histochemical demonstration of alkaline phosphatase activity can be useful for identifying peritubular cells in primary cultures of testicular cells.