Inhibition of the active lymph pump by flow in rat mesenteric lymphatics and thoracic duct

There are only a few reports of the influence of imposed flow on an active lymph pump under conditions of controlled intraluminal pressure. Thus, the mechanisms are not clearly defined. Rat mesenteric lymphatics and thoracic ducts were isolated, cannulated and pressurized. Input and output pressures were adjusted to impose various flows. Lymphatic systolic and diastolic diameters were measured and used to determine contraction frequency and pump flow indices. Imposed flow inhibited the active lymph pump in both mesenteric lymphatics and in the thoracic duct. The active pump of the thoracic duct appeared more sensitive to flow than did the active pump of the mesenteric lymphatics. Imposed flow reduced the frequency and amplitude of the contractions and accordingly the active pump flow. Flow-induced inhibition of the active lymph pump followed two temporal patterns. The first pattern was a rapidly developing inhibition of contraction frequency. Upon imposition of flow, the contraction frequency immediately fell and then partially recovered over time during continued flow. This effect was dependent on the magnitude of imposed flow, but did not depend on the direction of flow. The effect also depended upon the rate of change in the direction of flow. The second pattern was a slowly developing reduction of the amplitude of the lymphatic contractions, which increased over time during continued flow. The inhibition of contraction amplitude was dependent on the direction of the imposed flow, but independent of the magnitude of flow. Nitric oxide was partly but not completely responsible for the influence of flow on the mesenteric lymph pump. Exposure to NO mimicked the effects of flow, and inhibition of the NO synthase by N (G)-monomethyl-L-arginine attenuated but did not completely abolish the effects of flow.

Molecular and functional analyses of the contractile apparatus in lymphatic muscle

Lymphatics are necessary for the generation and regulation of lymph flow. Lymphatics use phasic contractions and extrinsic compressions to generate flow; tonic contractions alter resistance. Lymphatic muscle exhibits important differences from typical vascular smooth muscle. In this study, the thoracic duct exhibited significant functional differences from mesenteric lymphatics. To understand the molecular basis for these differences, we examined the profiles of contractile proteins and their messages in mesenteric lymphatics, thoracic duct, and arterioles. Results demonstrated that mesenteric lymphatics express only SMB smooth muscle myosin heavy chain (SM-MHC), whereas thoracic duct and arterioles expressed both SMA and SMB isoforms. Both SM1 and SM2 isoforms of SM-MHC were detected in arterioles and mesenteric and thoracic lymphatics. In addition, the fetal cardiac/skeletal slow-twitch muscle-specific beta-MHC message was detected only in mesenteric lymphatics. All four actin messages, cardiac alpha-actin, vascular alpha-actin, enteric gamma-actin, and skeletal alpha-actin, were present in both mesenteric lymphatics and arterioles. However, in thoracic duct, predominantly cardiac alpha-actin and vascular alpha-actin were found. Western blot and immunohistochemical analyses corroborated the mRNA studies. However, in arterioles only vascular alpha-actin protein was detected. These data indicate that lymphatics display genotypic and phenotypic characteristics of vascular, cardiac, and visceral myocytes, which are needed to fulfill the unique roles of the lymphatic system.

Lymph and pulmonary response to isobaric reduction in plasma oncotic pressure in baboons

Plasma colloid osmotic pressure was reduced by 76% (from 19.6 +/- 0.6 to 4.7 +/- 1.5 mm Hg) in five baboons while pulmonary capillary hydrostatic pressure was maintained at a normal level. This resulted in fluid retention, weight gain, peripheral edema and ascites, but no pulmonary edema. Thoracic duct lymph flow increased 6-fold and pulmonary lymph flow 7-fold. Thoracic duct lymph had a lower colloid osmotic pressure (2.0 +/- 0.7 mm Hg) than plasma (4.7 +/- 1.5 mm Hg), whereas the colloid osmotic pressure of pulmonary lymph (4.7 +/- 0.7 mm Hg) was the same as that of plasma. The lymph-plasma ratio for albumin fell in thoracic duct lymph but remained unchanged in pulmonary lymph. The difference between plasma colloid osmotic pressure and pulmonary artery wedge pressure decreased from 15.3 +/- 1.9 to -0.7 +/- 2.9 mm Hg. Despite this increase in filtration force, the lungs were protected from edema formation by a decrease of 11 mm Hg in pulmonary interstitial colloid osmotic pressure and a 7-fold increase in lymph flow.

The management of chylothorax

A series of 15 patients was treated for chylothorax over a 20-year period. The anatomy, physiology, and diseases of the thoracic duct are described, and a plan for the management of chylothorax is presented. If conservative therapy (e.g., aspiration or drainage with restriction of oral intake and intravenous replacement) is not successful after two to three weeks, surgical treatment is necessary and efficacious. The thoracic duct is explored by a full thoracotomy on the side of the effusion. It is readily seen if 6 to 8 oz of a mixture of milk and cream is given to the patient a few hours before operation. The milky fluid drips from the open duct, which is easily oversewn.

Anatomy and function of the vertebral column lymphatic network in mice

Cranial lymphatic vessels (LVs) are involved in the transport of fluids, macromolecules and central nervous system (CNS) immune responses. Little information about spinal LVs is available, because these delicate structures are embedded within vertebral tissues and difficult to visualize using traditional histology. Here we show an extended vertebral column LV network using three-dimensional imaging of decalcified iDISCO+-clarified spine segments. Vertebral LVs connect to peripheral sensory and sympathetic ganglia and form metameric vertebral circuits connecting to lymph nodes and the thoracic duct. They drain the epidural space and the dura mater around the spinal cord and associate with leukocytes. Vertebral LVs remodel extensively after spinal cord injury and VEGF-C-induced vertebral lymphangiogenesis exacerbates the inflammatory responses, T cell infiltration and demyelination following focal spinal cord lesion. Therefore, vertebral LVs add to skull meningeal LVs as gatekeepers of CNS immunity and may be potential targets to improve the maintenance and repair of spinal tissues.

Drainage of CSF through lymphatic pathways and arachnoid villi in sheep: measurement of 125I-albumin clearance

We investigated lymphatic drainage pathways of the central nervous system in conscious sheep and quantified the clearance of a cerebrospinal fluid (CSF) tracer into lymph and blood. In the first group of studies, 125I-HSA was injected into the lateral ventricles of the brain or into lumbar CSF and after 6 h, various lymph nodes and tissues were excised and counted for radioactivity. Multiple lymphatic drainage pathways of cranial CSF existed in the head and neck region defined by elevated 125I-HSA in the retropharyngeal/cervical, thymic, pre-auricular and submandibular nodes. Implicated in spinal CSF drainage were mainly the lumbar and intercostal nodes. In a second group of experiments, multiple cervical vessels and the thoracic duct were cannulated and lymph diverted from the animals. Transport of tracer through arachnoid villi was taken from recoveries in venous blood. Following intraventricular administration, the 6 h recoveries of 125I-HSA in the lymph (sum of cervical and thoracic duct) and blood were 8.2% +/- 3.0 and 12.5% +/- 4.5 respectively and at 22 h, 25.1% +/- 6.9 and 20.8% +/- 4.1 respectively. When 125I-HSA was injected into lumbar CSF, the 6 h recoveries of tracer in thoracic duct and blood were 11.6% +/- 2.7 and 16.3% +/- 3.7 respectively. Total lymph and blood recoveries were not significantly different in any experiment. We conclude that the clearance of 125I-HSA from the CSF is almost equally distributed between lymphatic and arachnoid villi pathways.

Lymphatic drainage of the peritoneal space: a pattern dependent on bowel lymphatics

BACKGROUND

Understanding lymph drainage patterns of the peritoneum could assist in staging and treatment of gastrointestinal and ovarian malignancies. Sentinel lymph nodes (SLNs) have been identified for solid organs and the pleural space. Our purpose was to determine whether the peritoneal space has a predictable lymph node drainage pattern.

METHODS

Rats received intraperitoneal injections of near-infrared (NIR) fluorescent tracers: namely, quantum dots (designed for retention in SLNs) or human serum albumin conjugated with IRDye800 (HSA800; designed for lymphatic flow beyond the SLN). A custom imaging system detected NIR fluorescence at 10 and 20 minutes and 1, 4, and 24 hours after injection. To determine the contribution of viscera to peritoneal lymphatic flow, additional cohorts received bowel resection before NIR tracer injection. Associations with appropriate controls were assessed with the chi(2) test.

RESULTS

Quantum dots drained to the celiac, superior mesenteric, and periportal lymph node groups. HSA800 drained to these same groups at early time points but continued flowing to the mediastinal lymph nodes via the thoracic duct. After bowel resection, both tracers were found in the thoracic, not abdominal, lymph node groups. Additionally, HSA800 was no longer found in the thoracic duct but in the anterior chest wall and diaphragmatic lymphatics.

CONCLUSIONS

The peritoneal space drains to the celiac, superior mesenteric, and periportal lymph node groups first. Lymph continues via the thoracic duct to the mediastinal lymph nodes. Bowel lymphatics are a key determinant of peritoneal lymph flow, because bowel resection shifts lymph flow directly to the intrathoracic lymph nodes via chest wall lymphatics.

Absorption of water-miscible forms of vitamin E in a patient with cholestasis and in thoracic duct-cannulated rats

Oral administration of vitamin E (100 mg tocopherol X kg-1 X day-1) as tocopheryl polyethylene glycol 1000 succinate (TPGS) to a child with congenital hepatic cholestasis (unresponsive to oral administration of dl-alpha-tocopheryl acetate) promoted an increase of tocopherol in plasma and adipose tissue while tocopheryl acetate emulsified with medium chain triglycerides and polysorbate 80 (MCT-E) did not. alpha-Tocopherol absorption, quantitated in thoracic duct-cannulated rats receiving intraduodenal infusions of soybean oil and saline, was similar for TPGS, MCT-E, and dl-alpha-tocopheryl acetate; gamma-tocopherol absorption from soybean oil was not affected by the presence of the supplemental alpha-tocopherol. Following bile duct ligation in one rat, TPGS promoted the absorption of alpha-tocopherol while absorption of gamma-tocopherol from soybean oil was decreased 30 fold, demonstrating that TPGS, which forms a micellar solution, delivers alpha-tocopherol through the unstirred water layer to enterocytes, while free tocopherol (alpha or gamma) absorption requires the presence of bile salts.

Gut intraepithelial lymphocyte development

CD8alphabeta(+) and CD4(+) intraepithelial lymphocytes, the progeny of double-positive thymocytes, are oligoclonal T-cell populations that have accumulated in the gut wall as the result of repeated antigenic stimulations, which lead to rounds of traffic through the lymph/blood circuit ending in an alpha4beta7-integrin-driven homing all along the gut mucosa. In contrast, CD8alphaalpha(+) intraepithelial lymphocytes, which may be TCRgammadelta(+) or alphabeta(+), result in part from local differentiation in the gut, but studies comparing euthymic and athymic mice suggest a thymic double-negative origin for many of them.

Effect of somatostatin on the flow rate and triglyceride levels of thoracic duct lymph in normal and vagotomized dogs

The role of circulating somatostatin (SRIF) in triglyceride (TG) homeostasis was evaluated in fasting and postprandial lymph of the canine thoracic duct. Cyclic SRIF at a very low, near physiologic (50 ng/min), and pharmacologic (5 μg/min) doses was infused into the portal or the femoral vein, and lymph was collected every 10 min through a cannula inserted into the duct under neuroleptanalgesia. The intraportal (IP) and intrafemoral (IF) SRIF infusion, but not saline infusions, significantly and almost identically reduced the rates of fasting lymph flow to levels of 87% and 91% of the preinfusion values, respectively, at a dose of 50 ng/min, and to 78% and 80%, respectively, at both rates at a dose of 5 μg/min. The attenuating effect of the IP and IF SRIF infusions at both rates upon lymph flow was completely abolished by vagotomy at the diaphragmatic level. The flow rate, TG concentration, and TG content (flow × concentration) of lymph obtained 3 h after a fat- and protein-rich meal ingestion were significantly and almost identically reduced during the IP and IF SRIF infusions at 50 ng/min, but not during saline infusions. Greater attenuation of these parameters was observed with 5 μg/min infusions, regardless of the route of administration. These results indicate that SRIF in near physiologic as well as pharmacologic doses can inhibit lymph flow after traversing the liver in the presence of the vagus nerve. They suggest the the other splanchnic organs may have a physiologic influence upon TG entry from the gut through alterations of dynamics of the splanchnic lymph system.

Effects of outflow pressure on fetal lymph flow

The purpose of this study was to determine to what extent fetal thoracic duct lymph flow may be reduced by increases in fetal venous pressure. In pregnant sheep the fetal left thoracic lymph duct was catheterized at the base of the neck and this catheter was connected to a jugular-vein catheter so the lymph could spontaneously return to the fetal circulation. At 5 days after catheter implantation in nine unanesthetized fetuses at 133 +/- 1 (SE) days' gestation, lymph flow was measured by disconnecting the lymphatic catheter from that in the jugular vein and varying outflow pressure of the lymphatic catheter independent of venous pressure. Whenever outflow pressure was negative, lymph flow was independent of outflow pressure and averaged 0.66 +/- 0.05 ml/min. When outflow pressure of the left thoracic duct was increased above zero, lymph flow decreased linearly with outflow pressure and flow stopped at an outflow pressure of 11.5 +/- 0.6 mm Hg. At a normal venous pressure of 3 mm Hg, the lymph-flow sensitivity to venous pressure was such that a 1 mm Hg rise in venous pressure reduced lymph flow by 12.7% +/- 1.2%. Thus it appears that fetal lymph flow is very sensitive to outflow pressure and only moderate elevations in venous pressure potentially may lead to fetal edema.

Lymphography of the Thoracic Duct by Percutaneous Injection of Iohexol into the Popliteal Lymph Node of Dogs: Experimental Study and Clinical Application

OBJECTIVE

To evaluate the efficacy of percutaneous administration of iohexol into the popliteal lymph node as a non-invasive technique for thoracic duct lymphangiography in dogs.

STUDY DESIGN

Experimental study and clinical report.

ANIMALS

Normal adult dogs (n=4) and 1 dog with recurrent chylothorax.

METHODS

For the experimental study, 4 dogs (weight, 8.4-12.3 kg) had 5-10 mL iohexol injected percutaneously into 1 popliteal lymph node and then thoracic radiographs were taken. Popliteal lymph nodes were examined by histopathology 8 days later. One 25-kg dog with recurrent chylothorax had 25 mL iohexol injected into the right popliteal lymph node followed by thoracic radiography.

RESULTS

In experimental dogs, the thoracic duct was best visualized on thoracic radiographs after administration of 10 mL iohexol. Clinically, no abnormalities were identified in the injected limb and except for 1 dog that had large numbers of siderocytes and erythrophagocytic macrophages in the injected lymph node, the histopathologic findings in the other injected popliteal lymph nodes were not different from contralateral nodes. In the clinical case, the thoracic duct was visualized, but there was leakage of iohexol around the node.

CONCLUSION

The thoracic duct in dogs can be visualized by lymphography after percutaneous injection of iohexol (1 mL/kg at 2 mL/min) into the popliteal lymph node.

CLINICAL RELEVANCE

Percutaneous popliteal lymph node administration of iohexol should be considered as an alternative to mesenteric lymph node injection for radiographic identification of the thoracic duct in dogs.

Evaluation of the Efficacy of the Electrosurgical Bipolar Vessel Sealer (LigaSure) Devices in Sealing Lymphatic Vessels

Various sources of ultrasonic and thermal energy have been developed to facilitate blood vessel ligation. However, their efficacy in sealing lymphatics has not been clearly established to date. We hypothesized that the electrosurgical bipolar vessel sealer (EBVS) produces reliable and durable sealing of large lymphatic vessels in a porcine model. Thoracic ducts from 4 adult pigs were explanted and sealed at multiple levels by using 3 different EBVS devices: LigaSure Atlas, XTD, and V. Fifteen seals (5 per group) were analyzed for sealing time and visual quality. Seal burst strength was measured by using a graduated pressure saline injection system. Twelve intact seals also underwent a histologic analysis. The mean overall burst strength of the seals was 271 78 mm Hg (127 to 360 mm Hg). The burst pressures in the 3 groups were not statistically different. The overall mean time to achieve a seal was 5.12.2 seconds (3 to 10 seconds). Seals were achieved significantly faster in the V group (4.10.6 seconds) compared with the Atlas (6.32.3 seconds) and XTD (6.4 2.6 seconds) groups. Qualitative seal assessment revealed minimal sticking and charring, a favorable degree of seal tissue clarity, and desiccation in the 3 groups. Histologic analysis demonstrated a fusion of lymphovascular channels with a complete obliteration of the lumens. We demonstrated that the use of EBVS results in a fast and effective sealing of large porcine lymphatic vessels. The seals created by all 3 devices burst at markedly supraphysiologic intraluminal pressures. Ongoing randomized human trials may prove the clinical benefits of the routine use of EBVS devices for various tissue dissections.

One technique, two approaches, and results: thoracic duct cannulation in small laboratory animals

Experimental studies in immunology, pharmacology, or hematology require the sampling of the total thoracic duct lymph in awake and unrestrained rats or mice. Several approaches have been described for cannulation of the thoracic duct, but they are characterized by a modest reproducibility and a low lymph flow rate. An improved technique for obtaining thoracic duct lymph is described here, emphasizing the similarities and differences concerning both rats and mice (average weights of 305 and 15 g, respectively). Rats yielded a mean of 55.6 ml/day thoracic duct lymph, while lymph output in mice reached unexpected volumes of 29.3 ml/day. The use of an operating microscope and silicone cannula, and maintenance of mobility of the animals during lymph collection, offer a reliable method for a high and constant output of thoracic duct lymph. Relevant aspects of the murine thoracic duct anatomy are also identified.