LYMPHATIC DRAINAGE OF THE PERITONEAL-CAVITY IN SHEEP

Lymphatic drainage of the peritoneal cavity has been investigated in anesthetized sheep. Studies involving intraperitoneal administration of a complex of Evans blue dye and bovine serum albumin demonstrated the existence of three anatomically distinct pathways. In the first pathway, dye is removed from the peritoneal cavity by diaphragmatic lymphatics that pass into caudal sternal lymph nodes. Efferent lymphatics from these nodes transport the material to cranial sternal lymph nodes. Efferent cranial sternal lymphatics then convey the material either directly or indirectly, via tracheal lymphatic trunks, to the right lymph duct. In the second pathway, the complex is transported from the peritoneal cavity by diaphragmatic lymphatics that pass into the caudal mediastinal lymph node. Efferent lymphatic ducts from this node transport the material to the thoracic duct. The third pathway appears to involve transport of the dye across the mesothelial lining of the abdominal viscera and removal from the interstitium by afferent visceral lymphatics. Material taken up in this manner is ultimately transported to the thoracic duct by efferent visceral lymphatics. Experiments involving measurements of lymphatic absorption of I-125-labeled human serum albumin from the peritoneal cavity indicated that, over the 6-h period studied, 4.55 +/- 1.20 and 1.43 +/- 0.56% of the injected tracer could be recovered in thoracic duct lymph and caudal mediastinal efferent lymph, respectively, and the sum of these values represented 26% of the recovered radioactivity. On the other hand, 16.95 +/- 6.93% of the injected radioactivity could be found in the blood over the same period. Therefore, 74% of the recovered peritoneal protein in the sheep may be returned to the blood by the right lymph duct or other unknown lymphatics, although direct entry of albumin into the bloodstream cannot be ruled out.