RETINOL PROCESSING BY THE PERITUBULAR CELL FROM RAT TESTIS

The cells that surround and support the seminiferous epithelium of the tubules in the testis, i.e., the peritubular or myoid cells, are know n to contain relatively high amounts of cellular retinol-binding prote in (CRBP). This suggests that they may play an important role in the m ovement or metabolism of retinol (vitamin A alcohol), which is require d for the maintenance of spermatogenesis. Peritubular cells in culture , isolated from the testes of the 20-day-old rat, maintained high leve ls of CRBP and had the ability to internalize retinol from retinol-bin ding protein (RBP), the blood transport protein for retinol, in a mann er suggesting a receptor-mediated process. Little of the internalized retinol was esterified, in contrast to what occurs in other cell types that contain high amounts of CRBPs, and very little, if any, lecithin -retinol acyltransferase activity was present in microsomes obtained f rom the cultured cells. The cells did, however, have the ability to sy nthesize and release their own RBP to the medium. This suggests that r etinol from the blood may actually reach the seminiferous epithelium b y passing across the peritubular cell, released on a new molecule of R BP, rather than by entering into the tubule bound to the preexisting R BP present in the interstitial fluid.