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.

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.

Chylothorax associated with substernal goiter treated with transcervical thyroidectomy

BACKGROUND

Substernal goiters are frequently associated with compressive symptoms. Compression of the trachea and esophagus are common, whereas thoracic duct compression is a rare occurrence.

METHODS

We report a rare case of a 72-year-old woman with thoracic duct compression by a large substernal goiter that presented with shortness of breath. After undergoing thoracentesis multiple times, the patient was treated with thyroidectomy.

RESULTS

Transcervical thyroidectomy was performed without sternotomy. This led to resolution of her symptoms. Confirmation of chylothorax resolution was obtained with postoperative computed tomography of the chest.

CONCLUSION

Chylothorax is a rare sequela of substernal goiters. It can be managed with thyroidectomy. Sternotomy was avoided in this case.

[Changes of dynamics of the lymph production after the cannulation of the thoracic duct]

An adequate cannulation of the thoracic duct is always accompanied with appropriate dynamics of the lymph production. As a result, the daily output of lymph increases from 2.0 to 2.2 times during 4-5 days. To find out the reasons of the lymph production changes were examined 57 patients with acute purulent inflammatory diseases of abdominal and thoracic organs. It was determined that the lymph production change is conditioned by 2 factors: the first is the stopping of the flow into venous vessels via lympho-venous anastomosies of the thoracic duct, lymphatic trunks and large lymphatic vessels. It leads to a mobilization of the greater part of lymph in lymphatic vessels. The second is the speeding-up of lymph production.

Automated measurement of diameter and contraction waves of cannulated lymphatic microvessels

BACKGROUND

Studies of lymphatic function often employ collecting lymphatic vessels that exhibit large-amplitude, spontaneous contractions. Data from such preparations have been analyzed using cardiac pump analogies that require accurate determination of vascular dimensions, including external (OD) and internal (ID) diameters. These measurements would be facilitated by an accurate automated measurement system.

METHODS AND RESULTS

A computer-based diameter tracking system was developed specifically for lymphatic vessels, with advantages over previous automated systems. The system also permits continuous diameter tracking at two axial locations, enabling the measurement and analysis of contraction wave conduction. The method was validated using spontaneously contracting segments of rat thoracic duct which sometimes exhibited conducted contraction waves. In such preparations, conduction wave velocity was modulated by the axial flow rate and could be easily measured by the tracking system.

CONCLUSIONS

The method offers improvement and increased convenience over manual diameter measurements in lymphatic vessels, with little or no sacrifice in accuracy. It should be a useful tool for general studies of collecting lymphatic function as well as for the analysis of contraction wave conduction and coordination.

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.

Spontaneous healing of retroperitoneal chylous leakage following anterior lumbar spinal surgery: a case report and literature review

Cisterna chyli is prone to injury in any retroperitoneal surgery. However, retroperitoneal chylous leakage is a rare complication after anterior spinal surgery. To the best of our knowledge, only ten cases have been reported in the English literature. We present a case of a 49-year-old man who had lumbar metastasis and associated radiculopathy. He had transient retroperitoneal chylous leakage after anterior tumor decompression, interbody bony fusion, and instrumental fixation from L2 to L4. The leakage stopped spontaneously after we temporarily clamped the drain tube. Intraperitoneal ascites accumulation developed thereafter due to nutritional loss and impaired hepatic reserves. We gathered ten reported cases of chylous leak after anterior thoracolumbar or lumbar spinal surgery, and categorized all these cases into two groups, depending on the integrity of diaphragm. Six patients received anterior spinal surgery without diaphragm splitting. Postoperative chylous leak stopped after conservative treatment. Another five cases received diaphragm splitting in the interim of anterior spinal surgery. Chylous leakage stopped spontaneously in four patients. The remaining one had a chylothorax secondary to postop chyloretroperitoneum. It was resolved only after surgical intervention. In view of these cases, all the chylous leakage could be spontaneously closed without complications, except for one who had a secondary chylothorax and required thoracic duct ligation and chemopleurodesis. We conclude that intraoperative diaphragm splitting or incision does not increase the risk of secondary chylothorax if it was closed tightly at the end of the surgery and the chest tube drainage properly done.

Thoracic duct variations may complicate the anterior spine procedures

The aim of this study is to localize and document the anatomic features of the thoracic duct and its tributaries with special emphasis on the spinal surgery point of view. The thoracic ducts were dissected from nine formaldehyde-preserved male cadavers. The drainage patterns, diameter of the thoracic duct in upper, middle and lower thoracic segments, localization of main tributaries and morphologic features of cisterna chyli were determined. The thoracic duct was detected in all cadavers. The main tributaries were concentrated at upper thoracic (between third and fifth thoracic vertebrae) and lower thoracic segments (below the level of ninth thoracic vertebra) at the right side. However, the main lymphatic tributaries were drained into the thoracic duct only in the lower thoracic area (below the level of the tenth thoracic vertebra) at the left side. Two major anatomic variations were detected in the thoracic duct. In the first case, there were two different lymphatic drainage systems. In the second case, the thoracic duct was found as bifid at two different levels. In formaldehyde preservation, the dimensions of the soft tissues may change. For that reason, the dimensions were not discussed and they may not be a guide in surgery. Additionally, our study group is quite small. Larger series may be needed to define the anatomic variations. As a conclusion, anatomic variations of the thoracic duct are numerous and must be considered to avoid complications when doing surgery.

Chylothorax

Chylothorax is a rare complication of pulmonary resection. It requires prompt treatment, which is initially conservative. This treatment consists of drainage, nutritional support, and measures to diminish chyle flow. Surgical intervention is indicated when conservative management is ineffective. Delay in surgical intervention leads not only to serious metabolic, nutritional, and immunologic disturbances from the loss of chyle but also increases the risk for adhesion formation, loculation, organization, and infection of the chylothorax, making subsequent surgical attempts difficult and increasing postoperative morbidity and mortality. VATS provides a minimally invasive approach for the treatment of chylothorax complicating pulmonary resection. Clipping of the thoracic duct or chemical pleurodesis may be performed with minimal morbidity and mortality. Conservative treatment is expensive and fails in most patients who have high-output chylous fistulae. On the other hand, VATS is uniformly effective, is less expensive, and has low morbidity. Indeed, VATS is rapidly becoming the preferred approach for the management of chylothorax complicating pulmonary resection. The need to prevent the occurrence of a chylothorax by careful dissection techniques and liberal clipping of lymphatic vessels particularly in areas of high anatomic risk during the initial operation cannot be overemphasized.

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.

Increased lymphatic flow in the thoracic duct during manipulative intervention

The thoracic pump and the abdominal pump are osteopathic manipulative (OM) lymphatic pump techniques frequently used by osteopathic physicians to treat patients with infections (eg, pneumonia, otitis media). Although there is a widely accepted belief among the osteopathic medical profession that increasing lymphatic flow is beneficial, no measurements of lymph flow during osteopathic manipulative treatment have been reported. The authors surgically instrumented five mongrel dogs to record lymphatic flow in the thoracic duct (TDF) and cardiac variables during three intervention protocols. After recovery from surgery, canine subjects were placed in a standing-support sling, and TDF, cardiac output, mean aortic blood pressure, and heart rate were recorded during two randomized 30-second sessions of manipulative intervention using the osteopathic thoracic pump and abdominal pump techniques on two successive days. Lymph flow in the thoracic duct increased from 1.57+/-0.20 mL x min(-1) to a peak TDF of 4.80+/-1.73 mL x min(-1) during abdominal pump, and from 1.20+/-0.41 mL x min(-1) to 3.45+/-1.61 mL x min(-1) during thoracic pump. Lymph flow in the thoracic duct and cardiac variables were also recorded for canine subjects during physical activity (ie, treadmill exercise at 3 miles per hour at 0% incline). During physical activity, TDF increased from 1.47+/-0.33 mL x min(-1) to 5.81+/-1.30 mL x min(-1). Although cardiac variables did not change significantly during manipulative intervention with lymphatic pump techniques, cardiac output and heart rate did increase during physical activity. The authors conclude that physical activity and manipulative intervention using thoracic pump and abdominal pump techniques produced net increases in TDF (P<.05).

[Functional anatomy of lymphangion]

This paper reviews the results of the studies performed mainly by the Russian anatomists on the functional anatomy of lymphangion as a structural and functional unit of lymphatic vessel. One of the peculiar features of functional anatomy of lymphangion is the heterogeneity of its structures (myocytes, endothelium, blood supply and innervation). The functional heterogeneity of different lymphangions, which depends on the local differences in the combination of lymph flow factors, was demonstrated. The role of lymphatic vessels is discussed on the basis of significance of lymphangion in active lymph transport. This is demonstrated by the multiple correlations between lymphangion structure, rate and type of its contractions, length of thoracic duct lymphangions and contraction type (peristaltic, rhythmic), number of lymphangions of thoracic duct and its type (presence of collaterals), form of individual variability of thoracic duct and its myoarchitecture, body mass and lymphangion volume in various animals and at different stages of ontogenesis.

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.

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.

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.

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.

Histochemical analysis of lymphatic endothelial cells in lymphostasis

The ultrastructure of endothelial cells of intestinal lymphatics and the thoracic duct (TD) and the relation to lymphostasis were examined in rats and monkeys. Localization of 5'-nucleotidase (5'-Nase) and endothelial nitric oxide synthase (eNOS) was studied. In normal lymphatic endothelial cells, 5'-Nase reaction product was evenly deposited on the cell surface in vivo and on cultured TD endothelial cells (TDECs), whereas eNOS was evenly distributed throughout the nucleus and cytoplasm. TDECs had a long filamentous process extending towards the subendothelial extracellular matrix but became flat and regular within 30-40 minutes after gastric perfusion with olive oil. According to their electron-density, two types of cells were found in the TD endothelial layer. The cells with low electron-density exhibited stronger 5'-Nase activity. Valves were bicuspid formations and the valvular endothelial surface of the convex side showed weaker 5'-Nase activity than the concave side. During TD blockage-induced lymphostasis in rats, the 5'-Nase product was almost not discernible in the TDECs within 2 weeks. Larger vesicles were found in the endothelial cytoplasm of the ligated TD. Their number decreased after 6-12 weeks. The small intestinal lymphatics in the mucosa and submucosa were dilated, with numerous open intercellular junctions. The endothelial lining appeared to have reduced activities for 5'-Nase and eNOS in 9 of 11 experimental animals. The results indicated that the inability of the open intercellular junctions, normally working as one-way endothelial flap valves, may be a key morphological feature after TD blockage. Reduced eNOS and 5'-Nase may functionally influence contractile activity and transport capability of the lymphatic vessels in the lymphostasis.

Flow in lymphatic networks: interaction between hepatic and intestinal lymph vessels

OBJECTIVE

Lymph from both the liver and intestine flows into the cisterna chyli. We hypothesized that increasing liver lymph flow would increase cisterna chyli pressure and, thereby, decrease intestinal lymph flow, potentiating intestinal edema formation.

METHODS

Anesthetized dogs were instrumented to measure and manipulate portal vein pressure and cisterna chyli pressure. The effects of directly increasing portal pressure with and without directly increasing cisterna chyli pressure on intestinal wet-to-dry ratio and intestinal ascites formation rate were determined. Target values for portal and cisterna chyli pressures were determined following elevation of inferior vena caval pressure to levels seen in patients with obstructive caval disease.

RESULTS

Direct elevation of portal pressure (P(port)) alone to 17.5 mm Hg caused a significant increase in intestinal wet-to-dry ratio (3.98 +/- 0.24 vs. 3.40 +/- 0.43) and the rate of ascites formation (0.36 +/- 0.12 vs. 0.05 +/- 0.03 mL/g dry wt/h). Simultaneous direct elevation of cisterna chyli pressure to 6.0 mm Hg and P(port) to 17.5 mm Hg caused further increases in intestinal wet-to-dry ratio (5.52 +/- 1.20) and ascites formation (0.57 +/- 0.11 mL/g dry wt./h).

CONCLUSIONS

Inferior vena caval hypertension increases liver lymph flow that elevates cisterna chyli pressure, which inhibits intestinal lymph flow and augments intestinal edema formation.

Correction of lymph circulation during immediate hypersensitivity reaction

We measured lymph flow rate in the thoracic lymphatic duct of dogs with anaphylactic shock receiving mono- or combination therapy with norepinephrine and hydrocortisone. Intensification of lymph circulation improved resorption and transport of metabolic products from the interstitial space through lymphatic vessels and stimulated exchange processes in the blood and tissues during allergic alterations.

Mechanical characteristics of the canine thoracic duct: what are the driving forces of the lymph flow?

This study is designed to better understand the mode of lymph transport, particularly through the extrinsic pumping by external compression of the lymph vessel. The pressure-diameter relationship of lymphatic segments isolated from the canine thoracic duct was examined using a laser optical micrometer measurement system. Results revealed that the thoracic duct displayed a high extensibility or compliance in the physiological pressure range, yet became progressively less so with increasing internal pressure. The calculated incremental circumferential modulus of the thoracic duct under physiological pressure (range of 2 to 6 cm H2O) showed values ranging from 1.2 x 10(4) to 3.61 x 10(5) dyn/cm2. At a pressure of 35 cm H2O, the modulus reached a limiting value of approximately 6.0 x 10(6) dyn/cm2. In the physiological pressure range, the relative wall thickness (h/R0) of the canine thoracic duct was approximately 3.5%, which was much lower than that reported for canine arterial segments and similar in value to that of the canine jugular vein. In conclusion, the pressure-diameter curve of the canine thoracic duct was shown to resemble that of venous vessels. However, the circumferential elastic modulus of the thoracic duct wall was lower than the moduli of veins, proving that lymphatics are more compliant than veins. This suggests lymph flow in the thoracic duct may be better promoted by external compression of the lymphatic vessel.

Effects of VEGF on Ca(2+)-transient in cultured lymphatic endothelial cells and mechanical activity of isolated lymph vessels

We investigated the effects of vascular endothelial growth factor (VEGF(165)) on [Ca(2+)](i)-transient in cultured lymphatic endothelial cells (LEC) and mechanical activity of isolated dog thoracic ducts. VEGF (0.1-10 ng/ml) caused a dose-dependent increase of the [Ca(2+)](i) in LEC. Pretreatment with 10(-5) M genistein or 5x10(-6) M herbimycin A produced a significant reduction of the VEGF-induced [Ca(2+)](i)-transient. In the presence of 10(-6) M thapsigargin, VEGF caused no significant effect on the [Ca(2+)](i)-transient. Pretreatment with Ca(2+)-free solution containing 0.1 mM EGTA produced no significant effect on the peak increase of [Ca(2+)](i) induced by 0.1 or 10 ng/ml VEGF, but significantly depressed the sustained part of [Ca(2+)](i) observed at the higher concentration of VEGF. The VEGF (0.1-10 ng/ml) caused a significant dilation of the isolated lymph vessels with intact endothelium, which were precontracted with U46,619. The 10 ng/ml VEGF-induced dilation was significantly reduced by 3 x 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME). The action of L-NAME was inhibited by the simultaneous application of 10(-3) M L-arginine. Mechanical rubbing of the endothelium also caused significant inhibition of the VEGF-induced dilation. The findings suggest that VEGF(165) may activate the receptor-related tyrosine kinase and cause the release of Ca(2+) from the inositol 1,4, 5-triphosphate-sensitive intracellular Ca(2+) stores in LEC. VEGF(165) also produces endothelium-dependent nitric oxide-mediated dilation of the precontracted isolated lymph vessels.

Thoracic duct lymph flow and its driving pressure in anesthetized sheep

We examined the relationship between thoracic duct lymph flow (TDF) and its driving pressure (DP) in six anesthetized sheep. DP was determined as the thoracic duct pressure (TDP) minus the innominate vein pressure (VP). TDF was measured using an ultrasound transit-time flow meter, placing a flow probe beside the caudal mediastinal lymph node. TDP was measured with a fine needle inserted near the flow probe. TDP increased linearly together with an increase in VP after balloon inflation in the cranial vena cava with a TDP/VP ratio of 0.79. DP decreased, therefore, with an increase in VP and this decrease in DP correlated directly with a fall in TDF. After rapid i.v. fluid infusion, TDF increased but DP varied among the six sheep. Nonetheless, after balloon inflation with expanded volume (i.e., i.v. fluid infusion), DP and TDF were positively correlated. We conclude that DP is the main factor determining TDF when VP rises in conjunction with increased lymph production.