William Hunter and lymphatics

William Hunter along with his brother, John, and their colleagues William Hewson, William Cruikshank and John Sheldon made a large contribution to understanding of lymphatic vessels. Hewson, Cruikshank and Sheldon all carried out mercury injections and made much progress in mapping the distribution of lymphatics in the human body. William Hunter appreciated that lymphatics absorbed fluid from the tissues of the body and that lacteals of the intestine and lymphatics are similar structures. John Hunter carried out an elegant series of experiments that proved that lacteals absorb products of digestion. The Hunters, however, were wrong in dismissing absorption by blood vessels and missed the importance of blood capillaries. William Hewson showed that lymphatics were not confined to mammals but that they are present in reptiles, birds and fish. Hewson also demonstrated that tracheobronchial glands are lymph nodes and not mucus-secreting glands as previously thought. Although William Hunter appreciated that tuberculosis and venereal diseases might involve the regional lymph nodes, he does not seem to have fully grasped that malignant disease might involve the local nodes or the concept that knowledge of lymph drainage could be used to define the likely site of a primary malignancy.

Pharmacokinetics of pegylated liposomal doxorubicin administered by intraoperative hyperthermic intraperitoneal chemotherapy to patients with advanced ovarian cancer and peritoneal carcinomatosis

The pharmacokinetics of pegylated liposomal doxorubicin (PLD) were investigated in 17 women undergoing intraoperative hyperthermic intraperitoneal chemotherapy (HIPEC) for advanced ovarian cancer and peritoneal carcinomatosis. HIPEC was performed immediately after completing debulking surgery, which included a number of peritonectomy procedures. PLD was injected and allowed to equilibrate in peritoneal cavity filled with 4 liters of physiological solution and stabilized at 42°C; next, the outflow line was opened and perfusion proceeded for 1 h. PLD was stable in peritoneal perfusate and plasma. During HIPEC, PLD peritoneal perfusate/plasma gradients averaged ∼600 or ≥1000 for peak concentration or area under the curve. After HIPEC, PLD plasma levels remained stable or decreased. Biopsy samples of residual normal peritoneum or ovarian carcinomatosis were collected at the end of HIPEC and were shown to contain free doxorubicin. Correlating PLD decrements in peritoneal perfusate with plasma exposure to PLD or peritoneal deposition of free doxorubicin showed that the former occurred during preperfusional equilibration of PLD in peritoneal cavity, whereas the latter occurred during 1 h of perfusion. Plasma exposure to PLD correlated negatively with the number of peritonectomy procedures performed during surgery, whereas peritoneal deposition of free doxorubicin correlated positively. Taken together, these results show that PLD administered by intraoperative HIPEC undergoes limited systemic diffusion and releases active free doxorubicin in peritoneum exposed to ovarian carcinomatosis. PLD pharmacokinetics seem to be influenced by peritonectomy procedures.

Development of the peritoneal lymphatic stomata and lymphatic vessels of the diaphragm in mice

The generation and development of the peritoneal lymphatic stomata (PLS) and lymphatic vessels of the diaphragm were studied in mice at gestational ages from the embryonic to the postnatal period with TEM, SEM and enzyme histochemistry and the PLS data were quantitatively analyzed with computer-assisted image processing technology (Elescope image analysis software). The results showed that the diaphragmatic mesothelium was covered only by flattened mesothelial cells (FMC) at the 13th embryonic day (ED 13). At ED 15, some cuboidal mesothelial cells (CMC) and immature lymphatic stomata (NLS) were found scattered on the diaphragmatic mesothelium. The sub-peritoneal lymphatic capillaries did not appear until ED 18. However, no absorptive function was observed in NLS when trypan blue granules were injected into the peritoneal cavity. At postnatal day 1 (PND 1), the endothelial cytoplasm processes of the diaphragm lymphatic capillaries span the connective tissue fibers and the basal membrane of CMC to form the subperitoneal channels. These channels were connected with NLS and serve as the absorptive route between the peritoneal cavity and the sub-peritoneal lymphatic vessels. The trypan blue absorption test demonstrated that postnatal PLS possessed an absorptive function and had transformed to mature lymphatic stomata (MLS) by PND 1. Thus, NLS were renamed of MLS. At PND 5, the cuboidal mesothelial cell ridge (CMCR) appeared with increased CMC areas. At PND 10, CMCR were fused to form the band-like CMC area with much more MLS distributed in the muscular portion of the diaphragm. With distribution area and density of PLS increasing and growth of lymphatic vessels, an increased absorptive function from the peritoneal cavity was observed in the experiment.

Scanning and transmission electron microscopic study of visceral and parietal peritoneal regions in the rat

The visceral peritoneum of intraabdominal organs (spleen, stomach, liver, small intestine), omentum majus and the parietal peritoneum of the anterior abdominal wall and the diaphragm were studied in adult Wistar rats by combined scanning and transmission electron microscopy (SEM, TEM). In general, the peritoneal surface consisted of a mesothelium composed of cubic, flat or intermediate cell types delimited by a basal lamina. Cubic mesothelial cells predominated in parenchymal organs (spleen, liver) and were characterized by prominent and indentated nuclei, a cytoplasm richly supplied with organelles, a dense microvillous coat, basal invaginations and elaborate intercellular contacts. Flat mesothelial cells were observed in the intestinal, omental and parietal peritoneum (tendinous diaphragm, abdominal wall) and showed elongated nuclei, scant cytoplasm, a poorly developed organelle apparatus and sparsely distributed microvilli. An intermediate mesothelial cell type was described within the gastric peritoneum characterized by a central cytoplasmic protrusion at the nuclear region containing most of the cytoplasmic organelles and by thin finger-like cytoplasmic processes. The submesothelial connective tissue layer was composed of collagen fiber bundles, fibroblasts and free cells (macrophages, granulocytes, mast cells) and contained blood and lymphatic vessels. In the spleen, elastic fibers formed a membranous structure with intercalated smooth muscle cells. Mesothelial openings were observed as tunnel-like invaginations within the hepatic peritoneum and as clusters of peritoneal stomata within the parietal peritoneum of the anterior abdominal wall and the muscular diaphragm. The round or oval openings of the peritoneal stomata were frequently occluded by overlapping adjacent mesothelial cells and their microvillous coat or obstructed by cellular material. At the side of the peritoneal stomata the mesothelial cell layer was interrupted to allow a direct access to the underlying submesothelial lymphatic system. The mesothelium and lymphatic endothelium shared a common basal lamina. The endothelial cells were discontinuous and displayed valve-like plasmalemmatic interdigitations facilitating an intercellular transport of fluids and corpuscular elements from the peritoneal cavity to the submesothelial lymphatic lacunae. The findings underline the morphological heterogeneity of the peritoneum in visceral and parietal regions, suggesting different functional implications, and further support the presence of extra-diaphragmatic peritoneal stomata.

A scanning electron microscopy study of peritoneal stomata in different peritoneal regions

Peritoneal stomata constitute the principal pathways for the drainage of intraperitoneal contents from the peritoneal cavity to the lymphatic system and have been claimed to be exclusively restricted to the peritoneal surface of the diaphragm. This concept has been revised by the demonstration of peritoneal stomata in the omental, mesenteric, ovaric and pelvic peritoneum. Therefore, the aim of this study was to further assess peritoneal surfaces of several other abdominal organs and of the abdominal wall with special reference to the occurrence of peritoneal stomata. The peritoneum covering the spleen, stomach, intestine, liver, diaphragm and anterior abdominal wall obtained from rats was examined by scanning electron microscopy. Whereas the splenic and hepatic peritoneal surfaces were composed of uniformly distributed cuboidal mesothelial cells, the gastric and intestinal peritoneal surfaces were arranged in parallel folds composed of prominent mesothelial cells with elongated finger-like cytoplasmic processes. In addition to diaphragmatic peritoneal stomata, mesothelial openings were also found on the peritoneal surfaces covering the anterior abdominal wall and the liver. The parietal peritoneal stomata were arranged in clusters, oval in shape and delimited by flattened mesothelial cells exposing the underlying submesothelial connective tissue. The hepatic mesothelial openings formed by deep channel-like gaps of adjacent cuboidal mesothelial cells were almost completely occluded by a dense microvillous coat. As the submesothelial connective tissue was not identifiable with certainty, the mesothelial openings were regarded as corresponding to stoma-like structures. These findings yield further evidence that peritoneal stomata are obviously not confined to the diaphragmatic area but extend to other peritoneal regions. It is therefore suggested that these extra-diaphragmatic parietal and visceral peritoneal surfaces contribute to the absorption capacity of the entire peritoneum and are subsequently involved in either therapeutic procedures or pathological processes affecting the peritoneal cavity.

The ultrastructure and computer imaging of the lymphatic stomata in the human pelvic peritoneum

The lymphatic stomata in the pelvic peritoneum of human fetuses and mature mice were initially observed and studied quantitatively by using computer image processing (C.I.P.) attached to a scanning electron microscope (SEM). Two types of mesothelial cells were found in the pelvic peritoneum of human fetuses and mature mice, i.e. flattened and cuboidal cells. The lymphatic stomata, arranged in clusters, were only found irregularly distributed among the cuboidal cells. The divergence of stoma area in the pelvic peritoneum of human fetuses varied greatly, ranging from 0.8 micron2 to 43.4 microns2. The average area of the lymphatic stomata in human fetuses was 10.00 +/- 9.44 microns2. The variation coefficient was 94.40. The standard deviations and standard errors were 9.44 and 0.98 respectively. Most of the lymphatic stomata in human fetuses were between 1.34 microns2 and 32.11 microns2 in size (accounting for 90%), with maximum and minimum values of 43.4 microns2 and 0.8 micron2. The average distribution density of the lymphatic stomata in human fetuses was 7.2% and the maximum density was 11.6%, which means that the average and the maximum absorption rates of the human pelvic peritoneum from the peritoneal cavity were 7.2% and 11.6% respectively. Therefore, it is suggested that the lymphatic stomata in pelvic peritoneum play an important role in draining materials from the peritoneal cavity, and that the absorption effect of the pelvic peritoneum is similar to that of the diaphragmatic peritoneum.

A study of the three-dimensional organization of the human diaphragmatic lymphatic lacunae and lymphatic drainage units

The peritoneal stomata, lymphatic drainage units and subperitoneal terminal lymphatics, called lymphatic lacunae, form a specialized drainage system in the diaphragm, by which absorption of fluid in bulk, particles and cells is carried out in the peritoneal cavity. The aim of this study is to elucidate the three-dimensional organization and function of the subperitoneal lymphatic lacunae and lymphatic drainage units by using lymphatic casts in the scanning electron microscope (SEM), ODO (OsO4-DMSO-OsO4) freeze fracture, conventional SEM and the transmission electron microscope (TEM). The subperitoneal lymphatic lacuna is unique for its large size and its multiple morphology and can be recognized by its broad, flattened enlargement and the blind-ends of lymphatic vessels, from which extend numerous main lymphatic vessels and side branches. These lymphatic vessels communicate with each other and form a rich lymphatic plexus under the diaphragmatic peritoneum. Two layers of lymphatic networks, i.e. the subperitoneal plexus and the deeper plexus are found in the muscular portion. Only one layer is present in the tendinous portion of the human diaphragm. The lymphatic plexus is denser in the tendinous portion than that in the muscular portion. The lymphatic lacunae occur exclusively in the muscular portion of the human diaphragm. The lumina of lymphatic lacunae are separated from the peritoneal cavity by a barrier consisting of cuboidal mesothelial cells, endothelial cells of the lymphatic lacunae and intervening connective tissue forming a lymphatic drainage unit. All these three components of the lymphatic drainage unit abut upon each other, but are not linked by specialized junctions. The cuboidal mesothelial cells frequently extend valve-like cytoplasmic processes that bridge the subperitoneal channel and make give it a tortuous course. The fibrous layer of the connective tissue is arranged in fiber bundles and gives a three-dimensional network forming the floor of the peritoneal stomata and the roof of the lymphatic lacunae. Via the fibrous network, the cuboidal mesothelial cells and the endothelial cells of the lacunae come into close contact with each other and form short subperitoneal channels which connect the peritoneal cavity with the subperitoneal lymphatic lacunae. The lymphatic drainage units may regulate the material absorption of the peritoneal stomata from the peritoneal cavity. It is suggested that the peritoneal stomata together with the subperitoneal channels, lymphatic drainage units and lymphatic lacunae comprise an important diaphragmatic lymphatic drainage system which plays an important role in the absorption of materials from the peritoneal cavity.

A scanning electron microscopy and computer image processing morphometric study of the pharmacological regulation of patency of the peritoneal stomata

The experiment on mice was carried out by injecting intraperitoneally Chinese materia medica for treating hepatocirrhosis with ascites. Observations and a quantitative analysis were carried out on the pharmacological regulation of the peritoneal stomata by using a scanning electron microscope (SEM) and a computer image processing system attached to the SEM. There was a significant increase in both the diameter (P < 0.05) and distribution density (P < 0.01) of the peritoneal stomata in the red sage root and alismatis rhizome groups, whereas the effect of poria and poria peel was not significant compared with the control group (P > 0.05). Our findings confirm the effect of red sage root and alismatis rhizome on the regulation of the peritoneal stomata, which can enhance the absorption of ascitic fluid, taking into consideration the absorbent function of these stomata. They indicate that the patency of peritoneal stomata can vary in response to the effect of some Chinese materia. They also suggest that the ascites is drained mainly by means of enhancing the patency of the stomata and lymphatic absorption of the stomata during the process of treatment by traditional Chinese medicine.