Development of an experimental apparatus for investigating lymphatic pumping activity of murine mesentery in vivo

Beta-adrenergic glaucoma drugs reduce lymphatic clearance from the eye: A sequential photoacoustic imaging study

Our study aims to determine whether the beta-adrenergic system is involved in the regulation of lymphatic drainage from the eye. For this purpose, we assessed the effect of 2 topical beta-adrenergic blockers, timolol and betaxolol, commonly used as glaucoma drugs, on lymphatic clearance of albumin from the aqueous humor to neck lymph nodes. Adult mice were treated with either topical timolol, a non-selective β-blocker, 0.5% (n = 8), or topical betaxolol, a selective β₁-adrenergic blocker, 0.5% (n = 6) twice daily for 14 days and compared to respective control groups (n = 5 and n = 7). Changes in lymphatic clearance from the eye were assessed using a quantitative in vivo photoacoustic imaging approach. In all subjects, right eye and neck lymph nodes were longitudinally assessed by sequential photoacoustic imaging just prior to near-infrared dye injection into the anterior chamber of the eye, and 20 min, 2 and 4 h after injection. Repeat measurements of mean pixel intensities (MPIs) of right eyes and nodes were performed at all timepoints. The areas under the curves (AUC) were calculated and the AUC of the treated-group was compared to that of controls using the Mann-Whitney U test. The slopes of MPI of each region of interest over time were compared using the linear mixed model after adjusting for IOP decrease after treatment and other parameters such as sex and body weight. In the timolol-treated group, right neck nodes showed significant decrease in AUC signal intensity compared with controls (P = 0.003), and significant decrease in slope of MPI compared with controls (P = 0.0025). In the betaxolol-treated group, right neck nodes showed significant decrease in AUC signal intensity compared with controls (P = 0.02), and significant decrease in slope of MPI compared with controls (P = 0.0069). Topical treatment with timolol and betaxolol reduced lymphatic clearance of albumin from the aqueous humor to the neck lymph nodes. This finding may be relevant for the management of secondary glaucomas and inflammatory eye disease in which the clearance of accumulated proteins and antigen from the eye is important to disease recovery and sight protection. This study suggests that the beta-adrenergic system plays a role in the regulation of lymphatic clearance from the eye.

A Distinct Role of the Autonomic Nervous System in Modulating the Function of Lymphatic Vessels under Physiological and Tumor-Draining Conditions

Lymphatic vessels (LVs) are important in the regulation of tissue fluid homeostasis and the pathogenesis of tumor progression. We investigated the innervation of LVs and the response to agonists and antagonists of the autonomic nervous system in vivo. While skin-draining collecting LVs express muscarinic, α₁- and β₂-adrenergic receptors on lymphatic endothelial cells and smooth muscle cells, intestinal lacteals express only β-adrenergic receptors and muscarinic receptors on their smooth muscle cells. Quantitative in vivo near-infrared imaging of the exposed flank-collecting LV revealed that muscarinic and α₁-adrenergic agonists increased LV contractility, whereas activation of β₂-adrenergic receptors inhibited contractility and initiated nitric oxide (NO)-dependent vasodilation. Tumor-draining LVs were expanded and showed a higher innervation density and contractility that was reduced by treatment with atropine, phentolamine, and, most potently, isoproterenol. These findings likely have clinical implications given the impact of lymphatic fluid drainage on intratumoral fluid pressure and thus drug delivery.

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Murine lymphatic vessels are innervated in an organ-specific manner

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α₁-adrenergic and muscarinic agents enhance lymphatic contractility in vivo

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β₂-adrenergic agents reduce lymphatic contractility

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Tumor-draining lymphatic vessels have increased innervation and contractility

Differences in L-type Ca2+ channel activity partially underlie the regional dichotomy in pumping behavior by murine peripheral and visceral lymphatic vessels

We identified a regional dichotomy in murine lymphatic contractile function with regard to vessel location within the periphery or visceral cavity. All vessels isolated from peripheral regions [cervical, popliteal, inguinal, axillary, and internodal inguinal axillary (Ing-Ax)] developed robust contractions with maximal ejection fractions (EFs) of 50-80% in our ex vivo isobaric myograph experiments. Conversely, vessels isolated from the visceral cavity (mesenteric, thoracic duct, and iliac) demonstrated maximal EFs of ≤10%. Using pressure myography, sharp electrode membrane potential recordings, and Ca²⁺ imaging, we assessed the role of L-type Ca²⁺ channels in this contractile dichotomy. Ing-Ax membrane potential revealed a ~2-s action potential (AP) cycle (resting -35 mV, spike -5 mV, and plateau -11 mV) with a plateau phase that was significantly lengthened by the L-type Ca²⁺ channel agonist Bay K8644 (BayK; 100 nM). APs recorded from mesenteric vessels, however, displayed a slower upstroke and an elongated time over threshold. BayK (100 nM) increased the mesenteric AP upstroke velocity and plateau duration but also significantly hyperpolarized the vessel. Contractions of vessels from both regions were preceded by Ca²⁺ flashes, detected with a smooth muscle-specific endogenous Ca²⁺ reporter, that typically were coordinated over the length of the vessel. Similar to the membrane potential recordings, Ca²⁺ flashes in mesenteric vessels were weaker and had a slower rise time but were longer lasting than those in Ing-Ax vessels. BayK (100 nM) significantly increased the Ca²⁺ transient amplitude and duration in both vessels and decreased time to peak Ca²⁺ in mesenteric vessels. However, a higher concentration (1 μM) of BayK was required to produce even a modest increase in EF in visceral lymphatics, which remained at <20%. NEW & NOTEWORTHY Lymphatic collecting vessels isolated from murine peripheral tissues, but not from the visceral cavities, display robust contractile behavior similar to lymphatic vessels from other animal models and humans. These differences are partially explained by L-type Ca²⁺ channel activity as revealed by the first measurements of murine lymphatic action potentials and contraction-associated Ca²⁺ transients.

In vivo visualization and quantification of collecting lymphatic vessel contractility using near-infrared imaging

Techniques to image lymphatic vessel function in either animal models or in the clinic are limited. In particular, imaging methods that can provide robust outcome measures for collecting lymphatic vessel function are sorely needed. In this study, we aimed to develop a method to visualize and quantify collecting lymphatic vessel function in mice, and to establish an in vivo system for evaluation of contractile agonists and antagonists using near-infrared fluorescence imaging. The flank collecting lymphatic vessel in mice was exposed using a surgical technique and a near-infrared tracer was infused into the inguinal lymph node. Collecting lymphatic vessel contractility and valve function could be easily visualized after the infusion. A diameter tracking method was established and the diameter of the vessel was found to closely correlate to near-infrared fluorescence signal. Phasic contractility measures of frequency and amplitude were established using an automated algorithm. The methods were validated by tracking the vessel response to topical application of a contractile agonist, prostaglandin F2α, and by demonstrating the potential of the technique for non-invasive evaluation of modifiers of lymphatic function. These new methods will enable high-resolution imaging and quantification of collecting lymphatic vessel function in animal models and may have future clinical applications.

Abdominal Respiration Induces Hemodilution and Related Reduction in ADH Concentration of Blood

To establish effective lymph drainage methods and develop concise and accurate clinical techniques for evaluating lymph drainage in healthy individuals and patients with cancer treatment-related lymph edema, we investigated the numbers of red (RBC) and white (WBC) blood cells, and platelets (PLT) in blood, hematocrit (Ht), and the blood concentrations of total protein (TP), albumin (Alb), and anti-diuretic hormone (ADH) before and after 5 min manual lymph drainage, followed by 30 min rest with or without abdominal respiration in the supine or sitting position in 48 healthy volunteers. The 5 min facial, upper and lower extremities lymph drainage, followed by 30 min rest in the supine position induced significant reductions of the TP and Alb in all subjects, and their RBC and Ht levels in some subjects. The 30 min rest only in the supine position without lymph drainage produced also significant reductions of blood TP and Alb. In addition, abdominal respiration in the supine position without manual lymph drainage caused more significant hemodilution, being significant reductions of TP, Alb, RBC, Ht, and ADH in all volunteers. These findings may be related to effective lymph drainage from the chylocyst. Furthermore, it also resulted in a significantly increased micturition desire. In conclusion, abdominal respiration during 30 min rest in the supine position is effective at inducing lymph drainage, and the associated induction of hemodilution and lowering of the blood ADH concentration (and increased micturition desire in some cases) can be used to accurately assess the extent of lymph drainage.

A High-Salt Diet Differentially Modulates Mechanical Activity of Afferent and Efferent Collecting Lymphatics in Murine Iliac Lymph Nodes

BACKGROUND

The lymphatic system contributes to fluid homeostasis in various tissues. Recent evidence suggests that lymphangiogenesis induced by a high-salt diet (HSD) is associated with blood pressure regulation. Lymph nodes, located along lymphatic pathways, are not only important secondary lymphoid tissues for cancer metastasis, inflammation, and immune responses, but are also important for fluid homeostasis. Afferent lymphatics collect lymph from the pre-nodal area and efferent lymphatics drain lymph out of the lymph nodes. However, the difference in mechanical activity between afferent and efferent lymphatics and the effect of a HSD on these vessels have not been shown.

METHODS AND RESULTS

Changes in mechanical activity of isolated afferent and efferent lymphatics in normal salt diet (NSD) and 4-week HSD mice in response to increases in intraluminal pressures from 3 to 7 cmH2O were measured using video-microscopy. The higher intramural pressure equivalently decreased pumping activity of afferent and efferent lymphatics in NSD mice. A HSD suppressed the amplitude, ejection fraction, and stroke volume of afferent lymphatics, leading to marked reductions in pumping activity. In contrast, the pumping activities of efferent lymphatics were resistant to a HSD and were preserved by enhancing the contraction frequency.

CONCLUSIONS

A HSD differentially modulated the mechanical activity of afferent and efferent collecting lymphatics in murine iliac lymph nodes.

Proposed new lymphology combined with lymphatic physiology, innate immunology, and oncology

As one of the lymphatic functions, it is well known that the transport and drainage of hydrophilic substances including plasma protein through the lymphatic system play pivotal roles in maintaining the homeostasis of the internal environment between the cells in tissues in collaboration with the exchange of the substances through the blood capillaries and venules. The physiological functions of the lymphatic system have been studied by many investigations of microcirculation, i.e., Yoffey and Courtice, Ruszunyak et al., Földie and Casley-Smigh et al., Roddie, Schmid-Schönbein et al., and Ohhashi et al. On the other hand, it is also well known that the initial clinical signs of primary diseases such as inflammation, tumors, and circulatory disorders including infarction and thrombosis appear as functional abnormalities of the internal environment in tissues. These abnormalities of the functions are strongly related to immunological defense reactions around the internal environment and abnormal actions of the transport and drainage of the lymphatic system. Taking into consideration the current inspired findings in lymphatic physiology, innate immunology, and oncology, we have proposed a new lymphology combined with new knowledge of the three above-mentioned academic fields from a defense mechanism points of view. In this review, we would like to demonstrate comprehensively our latest studies related to the possibility of establishing a new lymphology, hoping the readers will evaluate this possibility.

Sphingosine 1-phosphate (S1P) induces S1P2 receptor-dependent tonic contraction in murine iliac lymph vessels

OBJECTIVE

We studied the effects of S1P on the diameter and spontaneous contraction of murine iliac collecting lymph vessels.

METHODS

The isolated lymph vessel was cannulated with two glass micropipettes and then pressurized to 4 cmH(2) O at the intraluminal pressure. The changes in lymph vessel diameter were measured using a custom-made diameter-detection device. Immunohistochemical studies were also performed to confirm S1P receptors on the lymph vessels.

RESULTS

S1P (10(-7) M) had no significant effect on the frequency or amplitude of the lymph vessels' spontaneous contractions. In contrast, S1P (10(-8) -10(-6) M) produced a concentration-related reduction in lymph vessel diameter (tonic contraction). Pretreatment with 10(-4) M l-NAME or 10(-5) M aspirin had no significant effect on the S1P-induced tonic contraction of the lymph vessels. To evaluate the intracellular signal transduction pathway responsible for the S1P-induced tonic contractions and their Ca(2+) -dependence, we investigated the effects of JTE013, VPC23019, U-73122, xestospongin C, and nifedipine on the S1P-induced tonic contractions. All of these inhibitors except VPC23019 and nifedipine significantly reduced the S1P-induced tonic contractions. S1P (5x10(-7) M) also induced significant tonic contractions in the lymph vessels that had been superfused with high K(+) Krebs-bicarbonate solution or Ca(2+) -free high K(+) Krebs solution containing 1 mM EGTA. S1P2 receptors were immunohistochemically detected in the lymph vessels.

CONCLUSION

These findings suggest that neither endogenous NO nor prostaglandins are involved in the S1P-induced tonic contraction of lymph vessels, which is mainly caused by Ca(2+) release from intracellular Ca(2+) stores through the activation of S1P2 and 1,4,5 IP(3) receptors.

Use of a PEG-conjugated bright near-infrared dye for functional imaging of rerouting of tumor lymphatic drainage after sentinel lymph node metastasis

Tumor lymphangiogenesis promotes metastatic cancer spread to lymph nodes and beyond. However, the potential remodeling and functionality of tumor-draining lymphatic vessels has remained unclear. Thus, we aimed to develop non-invasive imaging methods for repeated quantitative imaging of lymphatic drainage and of contractile collecting lymphatic vessel function in mice, with colloidal near-infrared (NIR) tracers and a custom fluorescence stereomicroscope specially adapted for NIR sensitive imaging. Using these tools, we quantitatively determined pulse rates and valvular function of collecting lymphatic vessels with high resolution. Unexpectedly, we found that tumor-draining lymphatic vessels in a melanoma footpad model initially were dilated but remained functional, despite lower pulse rates. In two independent tumor models, impaired lymphatic function was detected once metastases were present in draining lymph nodes. Importantly, we found that lymphatic dysfunction, induced by metastatic tumor spread to sentinel lymph nodes, can lead to a rerouting of lymphatic flow away from the metastatic lymph node, via collateral lymphatic vessels, to alternate lymph nodes. These findings might have important clinical implications for the procedure of sentinel lymph node mapping that represents the standard of care for determining prognosis and treatment of melanoma and breast cancer patients.

Genetic removal of basal nitric oxide enhances contractile activity in isolated murine collecting lymphatic vessels

The role of nitric oxide (NO) in regulating lymphatic contractile function and, consequently, lymph flow has been the subject of intense study. Despite this, the precise effects of NO on lymphatic contractile activity remain unclear. Recent hypotheses posit that basal levels of endogenous NO increase lymphatic contraction strength as a consequence of lowering frequency (i.e. positive lusitropy), whereas higher agonist-evoked concentrations of NO exert purely inhibitory effects on contractile function. We tested both hypotheses directly by isolating and cannulating collecting lymphatic vessels from genetically modified mice for ex vivo study. The effects of basal NO and agonist-evoked NO were evaluated, respectively, by exposing wild-type (WT), endothelial NO synthase (eNOS)(-/-) and inducible NO synthase (iNOS)(-/-) lymphatic vessels to controlled pressure steps followed by ACh doses. To compare with pharmacological inhibition of eNOS, we repeated both tests in the presence of l-NAME. Surprisingly, genetic removal of basal NO enhanced contraction amplitude significantly without increasing contraction frequency. Higher levels of NO production stimulated by ACh evoked dilation, decreased tone, slowed contraction frequency and reduced fractional pump flow. We conclude that basal NO specifically depresses contraction amplitude, and that greater NO production then inhibits all other aspects of contractile function. Further, this work demonstrates definitively that mouse collecting lymphatic vessels exhibit autonomous, large-amplitude contractions that respond to pressure similarly to collecting lymphatics of other mammalian species. At least in the peripheral lymphatic vasculature, NO production depresses contractile function, which influences lymph flow needed for fluid regulation, humoral immunity and cancer metastasis.

Platelet-derived growth factor (PDGF)-BB produces NO-mediated relaxation and PDGF receptor β-dependent tonic contraction in murine iliac lymph vessels

We studied the effects of PDGF-BB on changes in the diameters of murine lymph vessels with or without intact endothelium. PDGF-BB induced dilation of the lymph vessels with endothelium. Pretreatment with l-NAME or removal of the endothelium caused a significant attenuation in the PDGF-BB-induced dilation. PDGF-BB also produced dose-related reduction of the diameters of the lymph vessels without endothelium. To evaluate intracellular signal transduction and Ca(2+) -dependence of the PDGF-BB-induced tonic contraction, we investigated the effects of imatinib, GW5074 (an inhibitor of Raf-1 kinase), U-73122 (an inhibitor of phospholipase C), and xestospongin C on the PDGF-BB-induced reduction responses. All of these inhibitors caused a significant attenuation in the PDGF-BB-induced reduction response that was significantly decreased by treatment with Ca(2+) -free Krebs-bicarbonate solution or nifedipine. Higher concentrations of PDGF-BB produced a marked reduction of lymph vessel diameter within both high K(+) Krebs-bicarbonate solution and Ca(2+) -free high K(+) Krebs solution containing 1mM EGTA. These findings suggest that PDGF-BB induced endothelium-dependent NO-mediated relaxation of lymphatic smooth muscles in murine lymph vessels. PDGF receptor β-mediated tonic contraction of the muscles through increased Ca(2+) influx through the membrane and the release of membrane-bound and intracellular Ca(2+) .

Methods for lymphatic vessel culture and gene transfection

OBJECTIVE

To develop the techniques needed for the specific gene/protein targeting transfection experiments in isolated lymphatic vessels, we completed two major tasks: 1) optimize the experimental conditions to maintain the viability of isolated rat lymphatic vessels in culture for sufficiently long periods of time to permit knockdown or overexpression of selected proteins/genes and 2) develop effective transfection protocols for lymphatic muscle and endothelial cells in intact lymphatic vessels without nonspecific impairment of lymphatic contractile function due to the transfection protocol itself.

METHODS

Experimental protocols were developed for the maintenance of isolated lymphatic vessels under nonpressurized and pressurized conditions for 3-12 days in culture and for adenoviral gene transfection of the lymphatic muscle and endothelial cells.

RESULTS

The data demonstrate the effectiveness of the newly developed experimental protocols for the maintenance of isolated rat mesenteric lymphatic vessels and thoracic duct in culture up to 3-12 days without significant impairment of the parameters of their pumping and effective adenoviral/GFP transfection of lymphatic endothelial and muscle cells in isolated rat mesenteric lymphatic vessels.

CONCLUSIONS

These experimental techniques will extend the set of the modern experimental tools available to researchers investigating the physiology of lymphatic function.

Glucose and glucose transporters regulate lymphatic pump activity through activation of the mitochondrial ATP-sensitive K+ channel

We investigated the pivotal roles of glucose and its transporter in the regulation of mechanical activity of isolated rat thoracic ducts and then examined whether mitochondrial ATP-sensitive K(+) channels (mitoK(ATP)) are involved in those responses. In the absence of extracellular glucose, the thoracic ducts showed pump activity during 120 min. Extracellular glucose caused a dose-dependent increase in the frequency of pump activity and a constriction in the thoracic ducts. Pump activity of the thoracic ducts in 0 mm glucose was completely inhibited in the presence of chlorogenic acid (an inhibitor of glucose-6-phosphatase). Cytochalasin B, an inhibitor of facilitative glucose transporter (GLUT), or phlorizin, an inhibitor of sodium-dependent glucose cotransporter (SGLT), significantly reduced the frequency of pump activity and dilated the thoracic ducts. A decrease in the frequency of pump activity induced by 5-hydroxydecanoate (5-HD, a selective blocker of mitoK(ATP)) was completely reversed by ruthenium red (an inhibitor of Ca(2+) uniporter in mitochondria). Diazoxide (a selective opener of mitoK(ATP)) significantly increased the frequency of pump activity. Carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP, a protonophore of mitochondrial proton pump action) significantly reduced the frequency of pump activity and dilated the thoracic ducts. Collectively, these findings suggest that glucose derived from intracellular glycogen and/or through GLUT/SGLT in lymphatic smooth muscles contributes to the regulation of the pump activity of isolated rat thoracic ducts, and that mitoK(ATP) in the cells may partially serve as a modulator of the mechanical functions associated with mitochondrial Ca(2+) uptake.

NT-702, a selective phosphodiesterase 3 inhibitor, dilates rabbit spinal arterioles via endothelium-dependent and endothelium-independent mechanisms

We investigated the effects of NT-702, a selective phosphodiesterase (PDE) 3 inhibitor, on arterioles isolated from rabbit lumbar spinal cords. NT-702 caused a dose-dependent dilation of the isolated spinal arterioles. The disruption of endothelium produced a significant reduction of higher concentrations (10(-7) and 10(-6) M), but not lower concentrations (less than 10(-8) M), of NT-702-induced vasodilation. The NT-702-induced vasodilation of the arterioles with endothelium was not affected by pretreatment with an inhibitor of nitric oxide, cyclooxygenase, or cytochrome P-450 monooxygenase. In contrast, catalase reduced significantly the higher concentrations of NT-702-induced vasodilation only. Tetraethylammonium (TEA) completely reduced the lower concentrations of NT-702-induced vasodilation, but decreased only partially the higher concentrations of NT-702-induced vasodilation of the arterioles with endothelium. Hydrogen peroxide dilated significantly the isolated arterioles with endothelium, the response of which was reduced significantly by TEA. KT5720 (a selective protein kinase inhibitor) significantly decreased both the lower and higher concentrations of NT-702-induced vasodilation of the arterioles with endothelium. The findings suggest that NT-702 dose-dependently dilated the isolated spinal arterioles of rabbits via endothelium-dependent and endothelium-independent mechanisms. Protein kinase A (PKA)- and TEA-sensitive K(+) channels may be involved in the NT-702-induced vasodilation. Moreover, hydrogen peroxide may contribute in part to the endothelium-dependent higher concentrations of NT-702-induced vasodilation.

High oxygen tension constricts epineurial arterioles of the rat sciatic nerve via reactive oxygen species

Microcirculation of the sheath of the rat sciatic nerve fiber was investigated by using an intravital microscope, and changes in the diameter of the epineurial arterioles in response to highly oxygenated Krebs-bicarbonate solution were evaluated. Superfusion of low-oxygen (0%) Krebs-bicarbonate solution (LKS) onto rat sciatic nerves did not affect changes in the diameter of the arterioles. Nifedipine, a Ca(2+)-channel blocker, caused a dose-dependent dilation of the epineurial arterioles in LKS. In contrast, superfusion of high-oxygen (21%) Krebs-bicarbonate solution (HKS) onto rat sciatic nerves significantly constricted the epineurial arterioles in a time-dependent manner. The HKS-induced constriction of the epineurial arterioles was significantly reduced by treatment with 120 U/ml superoxide dismutase (SOD) alone or 5,000 U/ml catalase alone. In the presence of 120 U/ml SOD plus 5,000 U/ml catalase, 10(-4) M tempol, 10(-6) M diphenyleneiodium, 2 x 10(-4) M apocynin, or 10(-6) M allopurinol, the HKS-induced constriction of the epineurial arterioles completely disappeared. These results suggest that superfusion of highly oxygenated solution onto rat sciatic nerves constricts the epineurial arterioles through reactive oxygen species (ROS), including superoxide and hydrogen peroxide, and that production of superoxide involves a NADPH oxidase- or xanthine oxidase-dependent pathway. In conclusion, ROS play significant roles in the regulation of microcirculation of rat sciatic nerves in vivo.

Arachidonic Acid-Induced COX-1 and COX-2-Mediated Vasodilation in Rat Gingival Arterioles In Vivo

The roles of cyclooxygenase (COX) and prostaglandins (PGs) in the regulation of vasoreactivity of rat gingival arterioles in vivo were evaluated by sing an intravital microscope. The superfusion of indomethacin (a nonselective COX inhibitor) or SC-560 (a selective COX-1 inhibitor) onto the gingiva significantly constricted the arterioles, though NS-398 (a selective COX-2 inhibitor) did not affect the diameter of the arterioles. The SC-560-mediated constriction of the arterioles was completely reversed by an additional treatment with arachidonic acid (AA). The superfusion of AA, beraprost-Na (an analogue of PGI2) or PGE2 onto the gingival significantly dilated the arterioles dose-dependently. The AA-induced dilation of the arterioles was significantly reduced by the treatment with SC-560 or NS-398. The expression of COX-1 and COX-2 were positive in the endothelium, but not the smooth muscles, of the arterioles. The expression of PGE synthase (PGES) was found only in the smooth muscles, but not the endothelium, of the arterioles. Neither the endothelium nor the smooth muscles of the arterioles expressed PGI synthase (PGIS). These findings suggest that the COX-2-mediated PG cascade may collaborate with the COX-1 pathway in the regulation of arteriolar myogenic activity in rat gingiva in the case of the supply of a large amount of AA.

Effective permeability of hydrophilic substances through walls of lymph vessels: roles of endothelial barrier

The wall effective permeability of hydrophilic substances labeled with fluorescent dyes was evaluated in an isolated cannulated rat single lymph vessel through a videomicroscope system. Sodium fluorescein (NaFl; 332 mol wt) and FITC-dextrans (4,400, 12,000, and 71,200 mol wt) were administered into the intraluminal space of the lymph vessels and then excited by a Xenon lamp. Changes in the fluorescence intensity of the dyes were continuously measured by a silicon-intensified target camera through appropriate filters. The net flux of each dye in the wall of the lymph vessels was calculated by the relationship between the fluorescence intensity and the concentration of the dyes. NaFl and FITC-dextran 4,400 in the intraluminal space of isolated rat lymph vessels significantly penetrated the wall of the lymph vessels. FITC-dextran 12,000 in the intraluminal space of isolated rat lymph vessels slightly passed through the lymphatic wall, whereas FITC-dextran 71,200 did not penetrate the wall. Intraluminal pressures ranging from 4 to 8 cmH2O did not significantly affect the net flux of dyes used in the present study. After administration of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate into the lymph vessels, the net flux of FITC-dextran 4,400 and 12,000 but not 71,200 was augmented significantly. These results suggest that small molecular hydrophilic substances (≤4,400) are permeable from the intraluminal to extraluminal space of isolated lymph vessels and that the endothelial cell surface structure may play a barrier role in the effective permeability of large molecular hydrophilic substances (4,400 to 12,000) through the wall of the lymph vessels.

Integrated photothermal flow cytometry in vivo

The capability of integrated flow cytometry to detect, in real time, moving cells in their natural states in vivo is demonstrated in a study of circulating red and white blood cells in lymph and blood flow of rat mesentery. This system combines dual pump-probe photothermal (PT) techniques, such as PT imaging, the PT thermolens method, and PT velocimetry, with high-resolution (up to 0.3 microm), high-speed (up to 1000 fps) transmission digital microscopy (TDM) and fluorescence imaging. All PT techniques are based on irradiation of cells in rat mesenteric microvessels with a spectrally tunable laser pulse (420 to 570 nm, 8 ns, 0.1 to 300 microJ) and on detection of temperature-dependent variations of the refractive index with a second continuous probe laser beam (633 nm, 1.4 mW). We focus on intravital monitoring of the integral PT response from single, moving, unlabeled cells (from 100 to 500 cells in one measurement). Potential in vivo applications of this new optical tool, called PT flow cytometry (PTFC), are discussed, including identification of selected cells with differences in natural absorptive properties and sizes, determination of laser-induced cell damage, estimation of flow velocity, and monitoring of circulating cells labeled with PT probes.

In vivo integrated flow image cytometry and lymph/blood vessels dynamic microscopy

The high spatial resolution (approximately 350 nm) transmission digital microscopy (TDM) was developed for real time in vivo imaging of microlymphatics of rat mesentery at a single cell level without any contrast agent. The main mesenteric microstructures (lymph-vessel diameter, valve geometry, cells, etc.) and their dynamics (wall motion, valve function, cell velocity, etc.) were monitored with TDM. Depending on structure size, different magnifications were used to image relatively large whole lymphangion (x4 to x10) as well as to image single cells (x40 to x100) in lymph and blood flow including estimation of their shape, size, and aggregation state. Various potential applications of the TDM for in vivo studies are discussed, including visualization of circulating cells in lymph and blood flows, studying the kinetics of platelets, leukocyte rolling, as well as imaging absorbing nonfluorescent mesentery structures and leukocytes with a high optical resolution.

Current topics of physiology and pharmacology in the lymphatic system

We have reviewed physiological significance of rhythmical spontaneous contractions of collecting lymph vessels, which play a pivotal role in lymph transport and seem to control lymph formation through changing the pacemaker sites of the rhythmic contractions and contractile patterns of the lymphangions. A characteristic feature that the rhythmic pump activity works in vivo physiologically under the specific environment of lower oxygen tension in lymph (25-40 mm Hg) has been evaluated. With the characteristic feature, generation of endogenous nitric oxide (NO) from lymphatic endothelial cells and/or activation of ATP-sensitive potassium channels (K(ATP)) are reviewed to play crucial roles in the regulation of lymph transport at physiological or pathophysiological conditions. Chemical substances released from malignant tumor cells and tumor-derived parathyroid hormone-related peptide (PTHr-P) are also shown to cause a significant reduction of lymphatic pump activity through generation of endogenous NO and activation of K(ATP) channels. Finally, we have discussed physiological significance and roles of the lower oxygen tension in lymph, generation of endogenous NO, and activation of K(ATP) in lymph formation, lymph transport, and the functions of lymph nodes.

ATP inhibits pump activity of lymph vessels via adenosine A1 receptor-mediated involvement of NO- and ATP-sensitive K+ channels

We examined the effects of ATP on intrinsic pump activity in lymph vessels isolated from the rat. ATP caused significant dilation with a cessation of lymphatic pump activity. Removal of the endothelium or pretreatment with Nomega-nitro-L-arginine methyl ester (L-NAME) significantly reduced ATP-induced inhibitory responses of lymphatic pump activity, whereas reduction was not suppressed completely by 10(-6) M ATP. L-arginine significantly restored ATP-induced inhibitory responses in the presence of L-NAME. ATP-induced inhibitory responses in lymph vessels with endothelium were also significantly, but not completely, suppressed by pretreatment with glibenclamide. 8-Cyclopentyl-1,3-dipropylxanthine (a selective adenosine A1 receptor antagonist), but not suramine (a P2X and P2Y receptor antagonist) or 3,7-dimethyl-1-proparglyxanthine (a selective adenosine A2 receptor antagonist), significantly decreased ATP-induced inhibitory responses. alpha,beta-methylene ATP (a selective P2X and P2Y receptor agonist) had no significant effect on lymphatic pump activity. In some lymph vessels with endothelium (24 of 30 preparations), adenosine also caused dose-dependent dilation with a cessation of lymphatic pump activity. L-NAME significantly reduced the inhibitory responses induced by the lower (3 x 10(-8)-3 x 10(-7) M) concentrations of adenosine. Glibenclamide or 8-cyclopentyl-1,3-dipropylxanthine also significantly suppressed adenosine-induced inhibitory responses. These findings suggest that ATP-induced dilation and inhibition of pump activity of isolated rat lymph vessels are endothelium-dependent and -independent responses. ATP-mediated inhibitory responses may be, in part, related to production of endogenous nitric oxide, involvement of ATP-sensitive K+ channels, or activation of adenosine A1 receptors in lymphatic smooth muscle and endothelium.

Rho-Rho kinase pathway is involved in the regulation of myogenic tone and pump activity in isolated lymph vessels

To evaluate whether or not Rho-Rho kinase pathway is involved in the regulation of mechanical activity of lymph vessels, effects of Y-27632 and okadaic acid on lymph pump activity and myogenic, pressure- and agonist-induced tone were examined in isolated rat lymph vessels. Y-27632 caused a significant dilation with a cessation of the lymph pump activity. Y-27632 also produced a dose-related dilation of the lymph vessels precontracted by norepinephrine (NE)-, U-46619- or 80 mM KCl. Okadaic acid significantly constricted the lymph vessels and reduced the frequency of the lymph pump activity. Okadaic acid also produced a dose-related constriction of the lymph vessels precontracted by NE or U-46619. The Y-27632-induced decrease of the frequency of lymph pump activity was significantly reversed by the pretreatment with okadaic acid. In the presence of Y-27632, the pressure-mediated tone of the lymph vessel was significantly decreased. On the other hand, okadaic acid significantly increased the pressure-mediated tone. These findings suggest that Rho kinase and myosin phosphatase activity in lymphatic smooth muscles may contribute to the regulation of lymph pump activity and may be also involved in the control of myogenic pressure- and agonist-induced tone.

B16-BL6 melanoma cells release inhibitory factor(s) of active pump activity in isolated lymph vessels

We investigated whether supernatant cultured with melanoma cell lines B16-BL6 and K1735 or the Lewis lung carcinoma cell line (LLC) can regulate lymphatic pump activity with bioassay preparations isolated from murine iliac lymph vessels. B16-BL6 and LLC supernatants caused significant dilation of lymph microvessels with cessation of pump activity. B16-BL6 supernatant produced dose-related cessation of lymphatic pump activity. There was no significant tachyphylaxis in the supernatant-mediated inhibitory response of lymphatic pump activity. Pretreatment with 3 x 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME) or 10(-7) M or 10(-6) M glibenclamide and 5 x 10(-4) M 5-hydroxydecanoic acid caused significant reduction of supernatant-mediated inhibitory responses. Simultaneous treatment with 10(-3) M L-arginine and 3 x 10(-5) M L-NAME significantly lessened L-NAME-induced inhibition of the supernatant-mediated response, suggesting that endogenous nitric oxide (NO) plays important roles in supernatant-mediated inhibitory responses. Chemical treatment dialyzed substances of <1,000 molecular weight (MW), producing complete reduction of the supernatant-mediated response. In contrast, pretreatment with heating or digestion with protease had no significant effect on supernatant-mediated response. These findings suggest that B16-BL6 cells may release nonpeptide substance(s) of <1,000 MW, resulting in significant cessation of lymphatic pump activity via production and release of endogenous NO and activation of mitochondrial ATP-sensitive K(+) channels.

Parathyroid hormone-related protein-(1-34) inhibits intrinsic pump activity of isolated murine lymph vessels

Parathyroid hormone-related protein (PTHrP) was originally found as a tumor-derived vasoactive factor and has also been known to produce significant relaxation of vascular smooth muscles. Thus effects of PTHrP-(1-34), a PTH receptor-binding domain, on spontaneous lymphatic pump activity was investigated in isolated pressurized lymph vessels of mice. Low concentrations (1 x 10(-10) and 3 x 10(-10) M) of PTHrP-(1-34) dilated lymph vessels and reduced the frequency of pump activity, whereas high concentrations (1 x 10(-9) to 1 x 10(-8) M) of PTHrP-(1-34) caused dilation with cessation of the lymphatic pump activity. N(omega)-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) M) but not indomethacin (1 x 10(-5) M) significantly reduced the PTHrP-(1-34)-induced inhibitory responses of the lymphatic pump activity. In the presence of L-NAME (3 x 10(-5) M) and L-arginine (1 x 10(-3) M), the L-NAME-induced inhibition in the PTHrP-(1-34)-mediated responses was significantly reduced. Glibenclamide (1 x 10(-6) M) significantly suppressed the inhibitory responses of the lymphatic pump activity induced by PTHrP-(1-34) and S-nitroso-N-acetyl-penicillamine. The PTHrP-(1-34)-mediated inhibitory responses were significantly reduced by treatment with PTHrP-(7-34) (1 x 10(-7) M). These results suggest that PTHrP-(1-34) inhibits spontaneous pump activity of the isolated lymph vessels via PTH receptors and that production and release of endogenous nitric oxide and activation of ATP-sensitive K(+) channels in the lymph vessels contribute to the PTHrP-(1-34)-mediated inhibitory responses of the lymphatic pump activity.

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.