Evidence for a direct arteriovenous connection (A-V shunt) between the testicular artery and pampiniform plexus in the spermatic cord of the tree shrew (Tupaia glis).

In the tree shrew Tupaia glis, 5 or 6 small ramifying arterioles arose directly from the testicular artery and then gave off numerous small capillaries. The capillaries made a series of anastomoses with neighbouring counterpart capillaries to become a complicated network. Some of the capillaries drained into a small venule, which was connected directly with the testicular vein (pampiniform plexus), to form an arteriovenous connection (A-V shunt) between the testicular artery and the pampiniform plexus. This A-V shunt appears to make the transfer of substances from the pampiniform plexus to the testicular artery more efficient. In addition, the shunt may control the volume of the blood draining into the testis. The capillaries were covered by vesiculated cells which were located adjacent to the pericytes. The vesiculated cells contained abundant mitochondria, rough endoplasmic reticulum, a well developed Golgi complex and cytoplasmic vesicles. Their cellular processes were long and surrounded more than one capillary. The morphological features of the vesiculated cells suggest that they may synthesise substances that are released into the network and which affect the activity of the capillaries. Since the cellular processes contacted each other, the cells could provide support for the capillaries and prevent their collapse when the shunts are closed.