Davis J T, Ong D E
Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232, USA.
Biol Reprod. 1995 Feb;52(2):356-64. doi: 10.1095/biolreprod52.2.356.
The cells that surround and support the seminiferous epithelium of the tubules in the testis, i.e., the peritubular or myoid cells, are known to contain relatively high amounts of cellular retinol-binding protein (CRBP). This suggests that they may play an important role in the movement or metabolism of retinol (vitamin A alcohol), which is required for the maintenance of spermatogenesis. Peritubular cells in culture, isolated from the testes of the 20-day-old rat, maintained high levels of CRBP and had the ability to internalize retinol from retinol-binding protein (RBP), the blood transport protein for retinol, in a manner 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 from the cultured cells. The cells did, however, have the ability to synthesize and release their own RBP to the medium. This suggests that retinol from the blood may actually reach the seminiferous epithelium by passing across the peritubular cell, released on a new molecule of RBP, rather than by entering into the tubule bound to the preexisting RBP present in the interstitial fluid.
睾丸中围绕并支持生精小管生精上皮的细胞，即睾丸周细胞或肌样细胞，已知含有相对大量的细胞视黄醇结合蛋白（CRBP）。这表明它们可能在视黄醇（维生素A醇）的转运或代谢中发挥重要作用，而视黄醇是维持精子发生所必需的。从20日龄大鼠睾丸中分离出来的培养睾丸周细胞，保持高水平的CRBP，并能够以一种提示受体介导过程的方式从视黄醇结合蛋白（RBP，视黄醇的血液转运蛋白）内化视黄醇。与其他含有大量CRBPs的细胞类型中发生的情况相反，内化的视黄醇很少被酯化，并且从培养细胞获得的微粒体中几乎不存在（如果有的话）卵磷脂 - 视黄醇酰基转移酶活性。然而，这些细胞确实有能力合成并向培养基中释放自身的RBP。这表明血液中的视黄醇实际上可能通过穿过睾丸周细胞到达生精上皮，然后释放到一个新的RBP分子上，而不是通过与间质液中预先存在的RBP结合进入小管。
