Retinyl esters were quantitatively the most significant product formed in short term incubations of isolated rat germinal cells administered³H-retinol.³H-retinyl palmitate was found to be the single most abundant metabolite accounting for approximately 80 % of the total label 2,h after administration of³Hretinol bound to bovine serum albumin. Differences were found in the relative activity of retinol uptake and metabolism between the various subpopulations of germinal cells separated by the staput sedimentation technique. The strongest correlation was between the magnitude of³H-retinyl palmitate synthesis and the distribution of round spermatids. Large pachytene spermatocyte.s also appealed to correlate with³H-:etinyl palmitate synthesis although this correlation was ambiguous due to the presence of a small population of Sertoli cells and spermatogonia in these fractions.

The concentration of cellular³H-retinol was more than 10fold greater in germinal cells administered³H-retinol bound to bovine serum albumin than when³H-retinol bound to serum retinol -binding protein was administered, and likewise the concentration of cellular³H-retinyl palmitate was approximately 30fold higher. In comparison to germinal cells, Sertoli cells administered³H-retinol bound to serum retinol-binding protein incorporated 20fold more³H-retinol and synthesized more³H-retinyl palmitate. However, both germinal cells and Sertcli cells were found to have incorporated similar concentrations of total label when administered³H-retinol bound to bovine serum albumin. These findings are consistent with that found in a model for retinol transport in the germinal epithelium in vivo where Sertoli cells take up retinol from serum retinol-binding protein in blood and subsequently supply germinal cells with retinol through a transport mechanism independent of serum retinol-binding protein.