Morphological analysis of transportation pathways of microspheres after their introduction into the uterine horn cavity in cyclic pigs.

Abstract

Countercurrent transfer is thought to be one of the most important mechanisms involved in the transfer of substances between the uterus and oviduct. The present study was aimed at recognizing other putative transportation pathways from the uterine cavity through the oviduct onto the surface of and into internal ovarian structures. Microspheres (latex beads, 0.8 microm in diameter) were introduced into the uterine horn cavity of pigs, for 30 min, at various days of the estrous cycle. The transportation pathways of the beads were then analyzed by light and electron microscopy. The transport of microspheres through the oviduct canal into ovarian tissues took place on each day of the estrous cycle. The largest numbers of microspheres passed through the tunica albuginea to the corpora lutea. Some of microspheres also reached the surface of the uterine ligament through the oviduct canal, where they attained the lumen of blood and lymphatic vessels, mainly of the vascular subovarian (VSP) and paraovarian lymphatic plexus (PLP), via the lymphatic stomata pathway. Transport of microspheres also took place simultaneously through the uterine and oviduct walls and from particular organs through blood and lymphatic vessels. Although the present results do not exclude the participation of countercurrent transfer between venous, lymphatic, and arterial vessels, they provide morphological evidence for the presence of direct transportation pathways of substances, released into the uterine lumen, into ovarian tissues through the oviduct canal.