The blood vascular bed of the rat testis was studied by scanning electron microscopy (SEM) of corrosion casts and by light microscopy of tissue sections. The testicular artery penetrates the pampiniform plexus and gives rise to the intertubular arterioles. Each of these arterioles courses in the intertubular connective tissue column, and gives off intertubular and peritubular capillaries. The intertubular capillaries pass the intertubular connective tissue column, whereas the peritubular capillaries reach the peritubular connective tissue sheet. The intertubular and peritubular capillaries anastomose with each other and converge into the intertubular venules in the intertubular connective tissue columns. Thus, the blood vascular bed of the rat testis consists of hexago- or pentago-columnar capillary networks which commonly surround the seminiferous tubules. The Leidig's cells are preferentially observed in the intertubular connective tissue columns. One of the intertubular capillaries is consistently thick, and directly continues into the intertubular venules (arteriolo-venular capillary channels), which finally drain into the pampiniform plexus. These findings suggest that the male sex hormone, testosterone, as secreted by the Leidig's cells, is discharged into the intertubular capillaries and then mainly carried by the arteriolovenular capillary channels and intertubular venules into the pampiniform plexus. This specialized drainage may ensure the presence of highly concentrated testosterone in the pampiniform plexus and allow the testosterone-exchange from the pamipiniform plexus to the testicular artery. The arteriolo-venular capillary channels may also eliminate blood congestion in the testis to enhance the efficiency of the heat-exchange mechanism between the testicular artery and pampiniform plexus. Many arterio-arterial and arterio-venous anastomoses occur, which may regulate the blood flow within the testis.
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