Primo-Vessels as New Flow Paths for Intratesticular Injected Dye in Rats

Primo-vessels (PVs) and nodes forming a network on the surface of an abdominal organ. (A) Semitransparent PV located on the right upper abdominal wall (arrows). (B) Three nodes stained by chromium hematoxylin (Cr-Hx) were located from the abdominal wall to the small intestine (arrows). These were connected by semitransparent PVs, and the structures continued to adjacent intestine and connective tissue (arrowhead). (C) Cr-Hx stained PV floating on the small intestine (arrow). This PV branched out to thinner structures stained by Cr-Hx (arrowhead). (D) Cr-Hx stained PV and a node floating on the liver. (E) Semitransparent PVs (arrow) floating on the colon, with a branch point (arrowhead). A blood clot was attached to the PV. (F) PV and a node on the surface of the urinary bladder. Some blood was centrally located in the node (arrowhead) with no blood vessels in the PV (arrows).

A primo-vessel enters an abdominal organ. (A) A primo-vessel (black arrow) is attached to the small intestine adjacent the mesentery. (B) Cross section of the rectangular area of (A) was analyzed by immunohistochemistry. It shows that red fluorescent nanoparticles (white arrow) flow into the muscularis externa of the intestine through the PV.

Photomicrographs of cross sections of the primo-vessel (PV) of a rat after injection with tracing dye. (A) A toluidine-blue-stained section showing the general morphology of the PV. (B) Electron micrograph showing numerous sinuses in the PV. A magnified image of the rectangular area shows that the boundary of the sinus is linked by a single membrane surrounded by collagenous fibers. (C) Some sinuses of the PV contain cytoplasmic granules and cellular remnants. (D) Nanoparticles (arrows) are located in the phagosomes of the macrophage just near the sinuses of the PV. (E) Nanoparticles (arrows) were engulfed by neutrophils adjacent the sinus of the PV. Ct = connective tissue; Mf = muscle fiber; S = sinus; G = cytoplasmic granules; Cr = cellular remnants; Ma = macrophages; Ne = neutrophils.

(A) Electron micrograph showing the presence of an early reticulocyte in the primo-vessel (PV). (B) Late reticulocyte (LR) and mature erythrocyte (Er) in the PV. These blood cells were in the extracellular matrices of collagenous fibers in the PV. P = pinocytotic vesicle; M = mitochondria; F = ferritin; V = vacuole.