BARRIER PROPERTIES OF TESTIS MICROVESSELS

The blood-testis barrier is believed to be constituted by tight juncti ons between Sertoli cells in seminiferous tubules and possibly by myoi d cells that encircle these tubules. We now show that testis microvess els are endowed with several markers of barrier properties of brain mi crovessels, such as the glucose transporter, P-glycoprotein, and gamma -glutamyl transpeptidase. Quantitative EM studies show that the endoth elium in testis, as in brain, is continuous and has long junctional pr ofiles and few vesicles. However, a small proportion of testis capilla ries have expansions in their junctional clefts suggestive of patent p aracellular channels, which may explain their higher permeability. Bec ause barrier features are thought to be induced and/or maintained in b rain microvessels by astrocytes, we assessed whether astrocyte-like ce lls exist in the testis. We found that the intertubular Leydig cells, adjacent to microvessels, express the astrocyte markers: glial fibrill ary acidic protein, glutamine synthetase, and S-100 protein. We sugges t that the testis endothelium contributes to the blood-testis barrier and that these endothelial barrier features are influenced by Leydig c ells. We believe that the endothelial and the epithelial (Sertoli) com ponents of the blood-testis barrier are ''in series'' and complement e ach other in achieving a stable milieu for spermatogenesis.