CAPILLARIES IN THE LAMINA PROPRIA OF HUMAN SEMINIFEROUS TUBULES ARE PARTLY FENESTRATED

The three capillary parts of the microvasculature of the human testis, namely the arterial side inter-Leydig cell capillaries, the intramura l capillaries, and the venous side inter-leydig cell capillaries, were studied in detail by dual detection of alkaline phosphatase enzyme ac tivity and endothelial marker immunoreactivity, and by means of light- and transmission-electron microscopy. Alkaline phosphatase enzyme act ivity was seen in intertubular arterioles, capillaries, and venules, a nd in intramural capillaries of the human testis, whereas the lamina p ropria of human seminiferous tubules showed no staining. Alkaline phos phatase enzyme activity and the endothelial marker detected by the Qbe nd 30 antibody co-existed within the endothelial cells of the microvas culature. Electron-microscopically, the endothelial cells of the arter ial and venous side inter-leydig cell capillaries, and of the intertub ular capillaries free of Leydig cells were of the continuous type with out fenestrations (A-1-alpha type). The intramural capillaries consist ed of non-fenestrated (A-1-alpha type) and fenestrated sections (A-2-a lpha type). The fenestrations faced the germinal epithelium. Capillari es with a continuous non-fenestrated endothelium contained a large num ber of transcytotic vesicles and channels. These were numerous in the endothelial cells of the inter-leydig cell capillaries and the non-fen estrated part of the intramural capillaries. Capillaries partly ran in between the layers of the lamina propria and therefore represented th e capillarization of the seminiferous tubules. Thus the multilayered l amina propria probably requires its own capillary supply to allow rapi d exchange between the microvasculature and the epithelium of the huma n seminiferous tubules.