Spontaneous activity in isolated bovine mesenteric lymphatics

Potentiating glymphatic drainage minimizes post-traumatic cerebral oedema

Cerebral oedema is associated with morbidity and mortality after traumatic brain injury (TBI)1. Noradrenaline levels are increased after TBI2-4, and the amplitude of the increase in noradrenaline predicts both the extent of injury5 and the likelihood of mortality6. Glymphatic impairment is both a feature of and a contributor to brain injury7,8, but its relationship with the injury-associated surge in noradrenaline is unclear. Here we report that acute post-traumatic oedema results from a suppression of glymphatic and lymphatic fluid flow that occurs in response to excessive systemic release of noradrenaline. This post-TBI adrenergic storm was associated with reduced contractility of cervical lymphatic vessels, consistent with diminished return of glymphatic and lymphatic fluid to the systemic circulation. Accordingly, pan-adrenergic receptor inhibition normalized central venous pressure and partly restored glymphatic and cervical lymphatic flow in a mouse model of TBI, and these actions led to substantially reduced brain oedema and improved functional outcomes. Furthermore, post-traumatic inhibition of adrenergic signalling boosted lymphatic export of cellular debris from the traumatic lesion, substantially reducing secondary inflammation and accumulation of phosphorylated tau. These observations suggest that targeting the noradrenergic control of central glymphatic flow may offer a therapeutic approach for treating acute TBI.

Morphological, Mechanical and Hydrodynamic Aspects of Diaphragmatic Lymphatics

The diaphragmatic lymphatic vascular network has unique anatomical characteristics. Studying the morphology and distribution of the lymphatic network in the mouse diaphragm by fluorescence-immunohistochemistry using LYVE-1 (a lymphatic endothelial marker) revealed LYVE1⁺ structures on both sides of the diaphragm-both in its the muscular and tendinous portion, but with different vessel density and configurations. On the pleural side, most LYVE1⁺ configurations are vessel-like with scanty stomata, while the peritoneal side is characterized by abundant LYVE1⁺ flattened lacy-ladder shaped structures with several stomata-like pores, particularly in the muscular portion. Such a complex, three-dimensional organization is enriched, at the peripheral rim of the muscular diaphragm, with spontaneously contracting lymphatic vessel segments able to prompt contractile waves to adjacent collecting lymphatics. This review aims at describing how the external tissue forces developing in the diaphragm, along with cyclic cardiogenic and respiratory swings, interplay with the spontaneous contraction of lymphatic vessel segments at the peripheral diaphragmatic rim to simultaneously set and modulate lymph flow from the pleural and peritoneal cavities. These details may provide useful in understanding the role of diaphragmatic lymphatics not only in physiological but, more so, in pathophysiological circumstances such as in dialysis, metastasis or infection.

Lymphatic Contractile Function: A Comprehensive Review of Drug Effects and Potential Clinical Application

BACKGROUND

The lymphatic system and the cardiovascular system work together to maintain body fluid homeostasis. Despite that, the lymphatic system has been relatively neglected as a potential drug target and a source of adverse effects from cardiovascular drugs. Like the heart, the lymphatic vessels undergo phasic contractions to promote lymph flow against a pressure gradient. Dysfunction or failure of the lymphatic pump results in fluid imbalance and tissue oedema. While this can due to drug effects, it is also a feature of breast cancer-associated lymphoedema, chronic venous insufficiency, congestive heart failure and acute systemic inflammation. There are currently no specific drug treatments for lymphatic pump dysfunction in clinical use despite the wealth of data from pre-clinical studies.

AIM

To identify (1) drugs with direct effects on lymphatic tonic and phasic contractions with potential for clinical application, and (2) drugs in current clinical use that have a positive or negative side effect on lymphatic function.

METHODS

We comprehensively reviewed all studies that tested the direct effect of a drug on the contractile function of lymphatic vessels.

RESULTS

Of the 208 drugs identified from 193 studies, about a quarter had only stimulatory effects on lymphatic tone, contraction frequency and/or contraction amplitude. Of FDA-approved drugs, there were 14 that increased lymphatic phasic contractile function. The most frequently used class of drug with inhibitory effects on lymphatic pump function were the calcium channels blockers.

CONCLUSION

This review highlights the opportunity for specific drug treatments of lymphatic dysfunction in various disease states and for avoiding adverse drug effects on lymphatic contractile function.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Morphological and Molecular Characterization of Human Dermal Lymphatic Collectors

Millions of patients suffer from lymphedema worldwide. Supporting the contractility of lymphatic collectors is an attractive target for pharmacological therapy of lymphedema. However, lymphatics have mostly been studied in animals, while the cellular and molecular characteristics of human lymphatic collectors are largely unknown. We studied epifascial lymphatic collectors of the thigh, which were isolated for autologous transplantations. Our immunohistological studies identify additional markers for LECs (vimentin, CCBE1). We show and confirm differences between initial and collecting lymphatics concerning the markers ESAM1, D2-40 and LYVE-1. Our transmission electron microscopic studies reveal two types of smooth muscle cells (SMCs) in the media of the collectors with dark and light cytoplasm. We observed vasa vasorum in the media of the largest collectors, as well as interstitial Cajal-like cells, which are highly ramified cells with long processes, caveolae, and lacking a basal lamina. They are in close contact with SMCs, which possess multiple caveolae at the contact sites. Immunohistologically we identified such cells with antibodies against vimentin and PDGFRα, but not CD34 and cKIT. With Next Generation Sequencing we searched for highly expressed genes in the media of lymphatic collectors, and found therapeutic targets, suitable for acceleration of lymphatic contractility, such as neuropeptide Y receptors 1, and 5; tachykinin receptors 1, and 2; purinergic receptors P2RX1, and 6, P2RY12, 13, and 14; 5-hydroxytryptamine receptors HTR2B, and 3C; and adrenoceptors α2A,B,C. Our studies represent the first comprehensive characterization of human epifascial lymphatic collectors, as a prerequisite for diagnosis and therapy.

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.

Adaptation of mesenteric lymphatic vessels to prolonged changes in transmural pressure

In vitro studies have revealed that acute increases in transmural pressure increase lymphatic vessel contractile function. However, adaptive responses to prolonged changes in transmural pressure in vivo have not been reported. Therefore, we developed a novel bovine mesenteric lymphatic partial constriction model to test the hypothesis that lymphatic vessels exposed to higher transmural pressures adapt functionally to become stronger pumps than vessels exposed to lower transmural pressures. Postnodal mesenteric lymphatic vessels were partially constricted for 3 days. On postoperative day 3, constricted vessels were isolated, and divided into upstream (UP) and downstream (DN) segment groups, and instrumented in an isolated bath. Although there were no differences between the passive diameters of the two groups, both diastolic diameter and systolic diameter were significantly larger in the UP group than in the DN group. The pump index of the UP group was also higher than that in the DN group. In conclusion, this is the first work to report how lymphatic vessels adapt to prolonged changes in transmural pressure in vivo. Our results suggest that vessel segments upstream of the constriction adapt to become both better fluid conduits and lymphatic pumps than downstream segments.

Lymphatic anatomy and biomechanics

Lymph formation is driven by hydraulic pressure gradients developing between the interstitial tissue and the lumen of initial lymphatics. While in vessels equipped with lymphatic smooth muscle cells these gradients are determined by well-synchronized spontaneous contractions of vessel segments, initial lymphatics devoid of smooth muscles rely on tissue motion to form lymph and propel it along the network. Lymphatics supplying highly moving tissues, such as skeletal muscle, diaphragm or thoracic tissues, undergo cyclic compression and expansion of their lumen imposed by local stresses arising in the tissue as a consequence of cardiac and respiratory activities. Active muscle contraction and not passive tissue displacement is required to support an efficient lymphatic drainage, as suggested by the fact that the respiratory activity promotes lymph formation during spontaneous, but not mechanical ventilation. The mechanical properties of the lymphatic wall and of the surrounding tissue also play an important role in lymphatic function. Modelling of stress distribution in the lymphatic wall suggests that compliant vessels behave as reservoirs accommodating absorbed interstitial fluid, while lymphatics with stiffer walls, taking advantage of a more efficient transmission of tissue stresses to the lymphatic lumen, propel fluid through the lumen of the lymphatic circuit.

Tissue contribution to the mechanical features of diaphragmatic initial lymphatics

The role of the mechanical properties of the initial lymphatic wall and of the surrounding tissue in supporting lymph formation and/or progression was studied in six anaesthetized, neuromuscularly blocked and mechanically ventilated rats. After mid-sternal thoracotomy, submesothelial initial lymphatics were identified on the pleural diaphragmatic surface through stereomicroscopy. An 'in vivo' lymphatic segment was prepared by securing two surgical threads around the vessel at a distance of ∼2.5 mm leaving the vessel in place. Two glass micropipettes were inserted into the lumen, one for intraluminar injections of 4.6 nl saline boluses and one for hydraulic pressure (Plymph) recording. The compliance of the vessel wall (Clymph) was calculated as the slope of the plot describing the change in segment volume as a function of the post-injection Plymph changes. Two superficial lymphatic vessel populations with a significantly different Clymph (6.7 ± 1.6 and 1.5 ± 0.4 nl mmHg−1 (mean ± S.E.M.), P < 0.001) were identified. In seven additional rats, the average elastic modulus of diaphragmatic tissue strips was determined by uniaxial tension tests to be 1.7 ± 0.3 MPa. Clymph calculated for an initial lymphatic completely surrounded by isotropic tissue was 0.068 nl mmHg−1, i.e. two orders of magnitude lower than in submesothelial lymphatics. Modelling of stress distribution in the lymphatic wall suggests that compliant vessels may act as reservoirs accommodating large absorbed fluid volumes, while lymphatics with stiffer walls serve to propel fluid through the lumen of the lymphatic vessel by taking advantage of the more efficient mechanical transmission of tissue stresses to the lymphatic lumen.

Lymphatic pump function in the inflamed gut

The role of the lymphatic circulation to actively remove fluid, cells, proteins, and other particles from the interstitium to prevent mounting edema is well appreciated, but whether and how this function is compromised during inflammation has been scarcely investigated. We discuss here the mechanisms of lymphatic pumping and their modulation in inflammatory conditions or by inflammatory mediators in the context of inflammatory bowel disease (IBD), an ensemble of disorders typically described with abnormal or dysfunctional intestinal or mesenteric lymphatic vessels. We report our findings showing impaired mesenteric lymphatic contractile activity in an animal model of intestinal inflammation that recapitulates some features of IBD and suggests a role for prostanoids in this dysfunction. With the knowledge that prostaglandin E(2) and prostacyclin are implicated in IBD pathogenesis and induce a potent inhibition of lymphatic pumping, we established the pharmacological profile for these prostaglandin receptors in mesenteric lymphatic vessels and their respective role in pumping inhibition. Inhibition of mesenteric lymphatic pumping during inflammation may be a cause of edema, compromised immune response, and granuloma associated with IBD.

Review article: lymphatic system and associated adipose tissue in the development of inflammatory bowel disease

BACKGROUND

The lymphatic system plays critical roles in tissue fluid homoeostasis, immune defence and metabolic maintenance. Lymphatic vessels transport lymph, proteins, immune cells and digested lipids, allowing fluid and proteins to be returned to the blood stream, lipids to be stored and metabolized and antigens to be sampled in lymph nodes. Lymphatic drainage is mainly driven by rhythmic constrictions intrinsic to the vessels and critically modulated by fluid pressure and inflammatory mediators.

AIM

To collect and discuss the compelling available information linking the lymphatic system, adiposity and inflammation.

METHODS

A literature search was performed through PubMed focusing on lymphatic system, inflammation, immune cells and fat transport and function in the context of IBD.

RESULTS

Evidence collected allows us to propose the following working model. Compromised lymph drainage, reported in IBD, leads to oedema, lymphangiogenesis, impaired immune cell trafficking and lymph leakage. Lymph factor(s) stimulate adipose tissue to proliferate and produce cytokines, which affect immune cell functions and exacerbate inflammation.

CONCLUSIONS

Understanding the lymphatic system's role in immune cell trafficking and immune responses, contribution to fat transport, distribution, metabolism and implication in the pathogenesis of chronic intestinal inflammation may provide the basis for new therapeutic strategies and improved quality-of life.

Hydrodynamic regulation of lymphatic transport and the impact of aging

To accomplish its normal roles in body fluid regulation/macromolecular homeostasis, immune function, and lipid absorption; the lymphatic system must transport lymph from the interstitial spaces, into and through the lymphatics, through the lymphatic compartment of the nodes, back into the nodal efferent lymphatics and eventually empty into the great veins. The usual net pressure gradients along this path do not normally favor the passive movement of lymph. Thus, lymph transport requires the input of energy to the lymph to propel it along this path. To do this, the lymphatic system uses a series of pumps to generate lymph flow. Thus to regulate lymph transport, both lymphatic pumping and resistance must be controlled. This review focuses on the regulation of the intrinsic lymph pump by hydrodynamic factors and how these regulatory processes are altered with age. Intrinsic lymph pumping is generated via the rapid/phasic contractions of lymphatic muscle, which are modulated by local physical factors (pressure/stretch and flow/shear). Increased lymph pressure/stretch will generally activate the intrinsic lymph pump up to a point, beyond which the lymph pump will begin to fail. The effect of increased lymph flow/shear is somewhat more complex, in that it can either activate or inhibit the intrinsic lymph pump, depending on the pattern and magnitude of the flow. The pattern and strength of the hydrodynamic regulation of the lymph transport is different in various parts of the lymphatic tree under normal conditions, depending upon the local hydrodynamic conditions. In addition, various pathophysiological processes can affect lymph transport. We have begun to evaluate the influence of the aging process on lymphatic transport characteristics in the rat thoracic duct. The pressure/stretch-dependent activation of intrinsic pumping is significantly impaired in aged rat thoracic duct (TD) and the flow/shear-dependent regulatory mechanisms are essentially completely lacking. The loss of shear-dependent modulation of lymphatic transport appears to be related to a loss of normal eNOS expression and a large rise in iNOS expression in these vessels. Therefore, aging of the lymph transport system significantly impairs its ability to transport lymph. We believe this will alter normal fluid balance as well as negatively impact immune function in the aged animals. Further studies are needed to detail the mechanisms that control and alter lymphatic transport during normal and aged conditions.

Heterogeneity in immunohistochemical, genomic, and biological properties of human lymphatic endothelial cells between initial and collecting lymph vessels

The immunohistochemical properties of selective lymph vessel markers, and NO synthase (NOS) and cyclo-oxygenase (COX) activities, were examined in two kinds of human lymphatic endothelial cells isolated from collecting (macro-) and initial (micro-) lymph vessels. The constitutively expressed genes in the two kinds of lymphatic endothelial cells were also evaluated by using oligonucleotide microarray analysis and RT-PCR. We also investigated the effects of oxygen concentration in culture conditions or growth factors such as basic fibroblast growth factor (bFGF), VEGF-A, and VEGF-C on proliferation activities of the two kinds of human lymphatic endothelial cells. Immunoreactivity to LYVE-1 and the RT-PCR expression level of LYVE-1 mRNA in endothelial cells of micro-lymph vessels were stronger than those of macro-lymph vessels. Immunoreactivity to VEGF R1 was also observed as significantly stronger in the micro-lymph vessels. In contrast, the immunoreactivity to Prox-1 and the RT-PCR expression level of Prox-1 mRNA in endothelial cells of macro-lymph vessels were stronger than those of micro-lymph vessels. Similarly, immunoreactivity to ecNOS, iNOS, COX1, and COX2 was also found as significantly higher than in macro-lymph vessels. In contrast, the increase of O(2) concentration ranging from 5% to 21% caused a significant reduction of the proliferation activity of endothelial cells in macro-lymph vessels. In conclusion, these findings suggest marked heterogeneity in the immunohistochemical, genomic, and proliferation activity of human lymphatic endothelial cells between micro-(initial) and macro-(collecting) lymph vessels.

Lymphatic vessels transition to state of summation above a critical contraction frequency

Although behavior of lymphatic vessels is analogous to that of ventricles, which completely relax between contractions, and blood vessels, which maintain a tonic constriction, the mixture of contractile properties can yield behavior unique to lymphatic vessels. In particular, because of their limited refractory period and slow rate of relaxation, lymphatic vessels lack the contractile properties that minimize summation in ventricles. We, therefore, hypothesized that lymphatic vessels transition to a state of summation when lymphatic vessel contraction frequency exceeds a critical value. We used an isovolumic, controlled-flow preparation to compare the time required for full relaxation with the time available to relax during diastole. We measured transmural pressure and diameter on segments of spontaneously contracting bovine mesenteric lymphatic vessels during 10 isovolumic volume steps. We found that beat-to-beat period (frequency−1) decreased with increases in diameter and that total contraction time was constant or slightly increased with diameter. We further found that the convergence of beat-to-beat period and contraction cycle duration predicted a critical transition value, beyond which the vessel does not have time to fully relax. This incomplete relaxation and resulting mechanical summation significantly increase active tension in diastole. Because this transition occurs within a physiological range, contraction summation may represent a fundamental feature of lymphatic vessel function.

Structure function relationships in the lymphatic system and implications for cancer biology

The lymphatic system, composed of lymphatic vessels, lymph, lymph nodes, and lymphocytes, is a distinctive vasculature (discontinuous basement membrane, open endothelial junctions, anchoring filaments, valves, and intrinsic contractility), different yet similar to the blood vasculature; an integral component of the plasma-tissue fluid-lymph circulation (the "blood-lymph loop"); and the center of the immunoregulatory network. Lymphatics are involved in diverse developmental, growth, repair, and pathologic processes both analogous to and distinct from those affecting the blood vasculature. Interference with the blood-lymph loop produces swelling [an imbalance between lymph formation (regulated by Starling's law of transcapillary fluid exchange) and lymph absorption], scarring, nutritional and immunodysregulatory disorders, as well as disturbances in lymph(hem)angiogenesis (lymphedema-angiodysplasia syndromes). The lymphatic system is also the stage on which key events during cancer development and progression are played out, and historically, also forms the basis for current evaluation, prognostication, and/or both operative and non-operative treatment of most cancers. Recent advances in molecular lymphology (e.g., discovery of lymphatic growth factors, endothelial receptors, transcription factors, genes, and highly specific immunohistochemical markers) and growing interest in lymphangiogenesis, combined with fresh insights and refined tools in clinical lymphology, including non-invasive lymphatic imaging, are opening up a window for translation to the clinical arena. Therefore, in cancer biology, attention to the multifaceted structure-function relationships within this vast, relatively unexplored system is long overdue.

Lymphatic muscle: a review of contractile function

A recent surge in lymphangiogenesis research has led to a greater understanding of lymphatic endothelial cell biology. However, a general understanding of lymphatic muscle cell biology lags far behind its endothelial counterpart. Lymphatics at the level of the collecting vessels and higher contain muscular walls capable of both tonic and phasic contractions, which both generate and regulate lymph flow. Because lymphatic contraction is crucial to lymphatic function, a solid understanding of lymphatic muscle development and function is necessary to understand lymphatic biology. This review summarizes the current body of lymphatic muscle research and addresses important questions that are currently unanswered.

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.

Lymphodynamic properties governing sentinel lymph nodes

Biological properties of lymph microvessels include characteristics of spontaneous contractions of lymph vessels, nitric oxide (NO)-mediated modulation of active lymph pump activity, flow-induced production and release of NO from lymphatic endothelial cells, and localization of NO synthase in cultured lymphatic endothelial cells. B16-BL6 melanoma cells release factors that inhibit active pump activity in isolated lymph microvessels. We have found that basic fibroblast growth factor (bFGF) induces significant proliferation and migration of canine cultured lymphatic endothelial cells. This growth factor facilitates the formation of capillary-like tubes by the cultured endothelial cells.

5-HT decreases contractile and electrical activities in lymphatic vessels of the guinea-pig mesentery: role of 5-HT 7-receptors

1 Constriction measurements and intracellular microelectrode recordings were performed in vitro on lymphatic vessels isolated from the guinea-pig mesentery to investigate whether 5-hydroxytryptamine (5-HT) affected lymphatic pumping and smooth muscle membrane potential. 2 5-HT decreased in a concentration-dependent manner the frequency of constrictions induced by intraluminal vessel perfusion. In nonperfused vessels, 5-HT hyperpolarized the lymphatic smooth muscle membrane potential and decreased the frequency and amplitude of spontaneous transient depolarizations (STDs). 3 The actions of 5-HT were significantly reversed by the 5-HT(7) receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine (SB269970, 0.5 micro M) and by the 5-HT(1/2/5/7) receptor antagonists methysergide (0.5 micro M), and were mimicked by the 5-HT(1/7)-receptor agonist, 5-CT. 4 The 5-HT(4)-receptor antagonists 1-methyl-1H-indole-3-carboxylic acid [1-2-[(methyl sulfonyl) amino] ethyl-4-piperidinyl] methyl ester (GR113808, 1 micro M) and (1-piperidinyl) ethyl 1H-indole 3-carboxylate (SB203186, 1 micro M) did not significantly affect the 5-HT-induced responses. The 5-HT(4)-receptor agonist 1-(4-amino-5-chloro-2-methoxy-phenyl)-3-[1-(2-methylsulfonylamino) ethyl-4-piperidinyl]-1-propanone hydrochloride (RS67506) decreased the constriction frequency, albeit only at 50 micro M and without affecting the smooth muscle membrane potential. 5 Responses to 5-HT were attenuated by the nitric oxide synthase inhibitor N(G)-nitro L-arginine (100 micro M), whereas indomethacin (10 micro M) and tetrodotoxin (1 micro M) were without effects. 6 5-HT-induced responses were inhibited by the ATP-sensitive K(+) channel blocker, glibenclamide (10 micro M) and the cAMP-dependent protein kinase inhibitor N-[2-(p-bromociannamylamino)-ethyl]-5-isoquinolinesulfonamide-dichloride (H89, 10 micro M) blocked the hyperpolarization. 7 These results suggest that 5-HT modulates the rate of lymphatic vessel pumping by eliciting K(ATP) channel-mediated smooth muscle hyperpolarization and decrease in STD activity, which appear to be mediated by activation of 5-HT(7) receptors coupled to cAMP production.

Physiologic aspects of lymphatic contractile function: current perspectives

The lymphatic system plays an important role in fluid/macromolecular balance, lipid absorption, and immune functions, and is involved in many different pathologic conditions, like inflammation, spread of cancer cells, and lymphedema. There are several forces that drive lymph centripetally. Extrinsic driving forces, or the passive lymph pump, include lymph formation, arterial pulsations, skeletal muscles contractions, fluctuations of central venous pressure, gastrointestinal peristalsis, and respiration. Intrinsic forces, or the active lymph pump, are the result of coordinated contractions of lymphangions, the morpho-functional units of the lymphatic vessels, which include the valve and portion of the vessel extending to the next valve. The contractions of the lymphangions are initiated by the pacemaker activity of the smooth muscle cells of lymphangion wall. Transmural pressure is an important hydrodynamic factor that modulates pacemaking. Under conditions of low filling, lymphangions might produce negative intraluminal pressures and a suction effect. Because of the complicated hydrodynamic conditions in lymphatic beds, the passive and active lymph pumps sometimes work together to propel lymph centripetally. In other cases (i.e., under conditions of enhanced lymph flow), flow-mediated inhibition of the active lymph pump could serve to decrease lymphatic outflow resistance and save metabolic energy when the driving force of the passive lymph pump is enough to propel lymph. We have recently found that there are profound differences in the pressure and flow sensitivities of lymphatic vessels derived from different tissues, such as the thoracic duct and mesenteric lymphatics. Such results, when considered in light of the controversy surrounding some studies performed in different animals, lead to the idea that the active lymph pumps in humans may have greater regional differences in contractile function than has been seen in animals, because of the upright posture in bipedal humans. This posture creates an additional outflow resistance for lymphatics of the lower part of the body. Thus, despite the ongoing attempts to determine the mechanisms of lymphatic diseases and useful therapies to treat them, there are many disputable or unknown issues regarding the physiology of lymph transport in humans.

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.

Review article: lymphatic vessel pumping and inflammation--the role of spontaneous constrictions and underlying electrical pacemaker potentials

The lymphatic circulation is important in maintaining tissue fluid homeostasis. It removes fluid, proteins and other particles from tissue spaces and returns them to the blood stream. This function is achieved by rhythmical contractions of the collecting lymphatic vessels. The contractile mechanism is intrinsic to the smooth muscles present in the vessel wall and consequent to action potentials. The underlying electrical mechanism has been proposed to be due to rhythmic synchronization of Ca2+-dependent spontaneous transient depolarizations. The lymphatic pumping activity adapts to changes in fluid load and has been observed to augment during inflammatory reactions to help resolve the associated oedema. This beneficial action has been generally attributed to the increase in interstitial pressure consequent to the oedema. However, little attention has been paid to the possible role inflammatory mediators that are present in the lymphatic vessel environment, could play in directly affecting the lymphatic contractile mechanism. This review article discusses our current knowledge on the mechanism and initiation of lymphatic pumping and how these events are modulated during inflammatory conditions.

Physiological roles of endogenous nitric oxide in lymphatic pump activity of rat mesentery in vivo

Physiological roles of endogenous nitric oxide (NO) in the lymphatic pump activity of rat mesenteries in vivo were evaluated using an intravital video microscope system. Changes in the pumping frequency (F), the end diastolic diameter (EDD), and the end systolic diameter (ESD) of the mesenteric lymph microvessels were measured with the microscope system and then the pump flow index (PFI) was calculated. A 15-min superfusion of 30 microM N(omega)-nitro-L-arginine methyl ester (L-NAME) in the mesenteries caused significant increases of F and PFI and a significant decrease of the EDD and ESD. Simultaneous superfusion of 1 mM L-arginine with 30 microM L-NAME produced a significant reversal of the L-NAME-mediated increase of F and decrease of ESD. A 15-min superfusion of 100 microM aminoguanidine caused no significant effects on F, EDD, and ESD of the mesenteric lymph vessels in vivo. These findings suggest that endogenous NO has physiologically modulated the lymphatic pump activity in rat mesentery in vivo and that the production and release of NO may be mediated by constitutive NO synthase but not by inducible NO synthase.

Effects of endothelin on spontaneous contractions in lymph vessels

A mode of action of endothelin (ET) on spontaneous contractions was investigated in ring preparations of isolated bovine mesenteric lymphatics. ET-1 at concentrations between 10(-10) and 10(-9) M caused a dose-dependent increase in the frequency of spontaneous contractions. The specific ET(A)-receptor antagonist BQ-123 (5 x 10(-7) M) caused a significant inhibition of the ET-1-induced positive chronotropic effect in the ring preparations with and without the endothelium. Mechanical denudation of the lymphatic endothelial cells produced a significant potentiation of the ET-induced positive chronotropic effect. BQ-3020 (10(-8)-10(-7) M), a selective ET(B)-receptor agonist, induced dose dependently negative chronotropic and inotropic effects on the spontaneous contractions in the ring preparations with intact endothelium. Mechanical removal of the endothelium caused a significant reduction of the BQ-3020-induced negative chronotropic and inotropic effects. The ET-1-induced positive chronotropic effect was potentiated by pretreatment with N(omega)-nitro-L-arginine methyl ester (L-NAME) (10(-5) M) but unaffected by aspirin (10(-5) M). Additional treatment with L-arginine (10(-4) M) completely reversed the L-NAME-mediated potentiation of the ET-induced chronotropic effect. These results suggest that stimulation of ET(A) receptors on the lymphatic smooth muscles causes a positive chronotropic effect on the spontaneous contractions, and stimulation of ET(B) receptors on the lymphatic endothelial cells induces a release of nitric oxide, which results in the chronotropic and inotropic effects on spontaneous contractions in isolated bovine mesenteric lymphatics.

Mechanical coupling and liquid exchanges in the pleural space

The pleural space provides the mechanical coupling between lung and chest wall: two views about this coupling are reported and discussed. Information on volume, composition, thickness, and pressure of the pleural liquid under physiologic conditions in a few species is provided. The Starling pressures of the parietal pleura filtering liquid into pleural space, and those of the visceral pleura absorbing liquid from the space are considered along with the permeability of the mesothelium. Information on the lymphatic drainage through the parietal pleura and on the solute-coupled liquid absorption from the pleural space under physiologic conditions and with various kinds of hydrothorax are provided.

Evidence that the substance P-induced enhancement of pacemaking in lymphatics of the guinea-pig mesentery occurs through endothelial release of thromboxane A2

1. In vitro studies were performed to examine the mechanisms underlying substance P-induced enhancement of constriction rate in guinea-pig mesenteric lymphatic vessels. 2. Substance P caused an endothelium-dependent increase in lymphatic constriction frequency which was first significant at a concentration of 1 nM (115 +/- 3% of control, n = 11) with 1 microM, the highest concentration tested, increasing the rate to 153 +/- 4% of control (n = 9). 3. Repetitive 5 min applications of substance P (1 microM) caused tachyphylaxis with tissue responsiveness tending to decrease (by an average of 23%) and significantly decreasing (by 72%) for application at intervals of 30 and 10 min, respectively. 4. The competitive antagonist of tachykinin receptors, spantide (5 microM) and the specific NK1 receptor antagonist, WIN51708 (10 microM) both prevented the enhancement of constriction rate induced by 1 microM substance P. 5. Endothelial cells loaded with the Ca2+ sensing fluophore, fluo 3/AM did not display a detectable change in [Ca2+]i upon application of 1 microM substance P. 6. Inhibition of nitric oxide synthase by NG nitro-L-arginine (L-NOARG; 100 microM) had no significant effect on the response induced by 1 microM substance P. 7. The enhancement of constriction rate induced by 1 microM substance P was prevented by the cyclooxygenase inhibitor, indomethacin (3 microM), the thromboxane A2 synthase inhibitor, imidazole (50 microM), and the thromboxane A2 receptor antagonist, SQ29548 (0.3 microM). 8. The stable analogue of thromboxane A2, U46619 (0.1 microM) significantly increased the constriction rate of lymphangions with or without endothelium, an effect which was prevented by SQ29548 (0.3 microM). 9. Treatment with pertussis toxin (PTx; 100 ng ml-1) completely abolished the response to 1 microM substance P without inhibiting either the perfusion-induced constriction or the U46619-induced enhancement of constriction rate. 10. Application of the phospholipase A2 inhibitor, antiflammin-1 (1 nM) prevented the enhancement of lymphatic pumping induced by substance P (1 microM), without inhibiting the response to either U46619 (0.1 microM) or acetylcholine (10 microM). 11. The data support the hypothesis that the substance P-induced increase in pumping rate is mediated via the endothelium through NK1 receptors coupled by a PTx sensitive G-protein to phospholipase A2 and resulting in generation of the arachidonic acid metabolite, thromboxane A2 this serving as the diffusible activator.

Co-ordination of contractile activity in guinea-pig mesenteric lymphatics

1. Intraluminally perfused lymphatic vessels from the mesentery of the guinea-pig were examined in vitro to investigate their contractile activity and the co-ordination of this activity between adjacent lymphangions. 2. Lymphangions constricted at fairly regular intervals and exhibited 'refractory' periods of up to 3 s during which constrictions did not occur. 3. The contractile activity of adjacent lymphangions was highly co-ordinated. 4. The smooth muscle was found to be continuous between the adjacent lymphangions for the majority of valve regions examined morphologically (52 of 63 preparations). 5. Mechanical and electrical coupling between adjacent lymphangions was indicated, as some lymphangions underwent transient dilatations just prior to constriction, whereas direct electrophysiological measurements showed that the smooth muscle of most adjacent lymphangions was electrically coupled across the valve (15 out of 20 pairs of lymphangions). 6. It is concluded that perfused lymphangions of guinea-pig mesenteric lymphatic vessels rhythmically constrict, with the contractile activity of adjacent lymphangions highly co-ordinated. The findings also indicate that transmission of both mechanical and electrical signals between the adjacent lymphangions contribute to the co-ordination of their contractile activity.

Beta-agonist activation of an amiloride-insensitive transport mechanism in rabbit pleura

The beta-agonist terbutaline increases the net rate of liquid absorption from hydrothoraces with albumin-Ringer solution: since beta-agonists decrease lymphatic drainage, the effect of terbutaline seems due to an increase in solute-coupled liquid absorption, (Zocchi et al. 1994 Respir. Physiol. 97:347-356). In this research we determined in anesthetized rabbits the rate of volume change in albumin-Ringer hydrothoraces of different size with amiloride plus terbutaline, and compared it with that previously obtained in hydrothoraces with amiloride alone. The net rate of liquid absorption was 0.09 ml/h greater (P < 0.01) with amiloride plus terbutaline than with amiloride alone. This indicates that terbutaline activates an amiloride-insensitive mechanism of Na+ transport. The increase in net rate of liquid absorption produced by terbutaline persisted with bumetanide 10(-6) M and SITS 10(-4) M, disappeared almost completely with bumetanide 10(-5) M, and completely with furosemide 10(-3) M. These findings suggest that the mechanism activated by terbutaline, when the amiloride-sensitive mechanisms of the pleura have been blocked, is a Na(+)-K(+)-2 Cl- or Na(+)-Cl- symport little sensitive to bumetanide.

Disorders of lymph flow

Disturbances in blood capillary exchange of fluid, macromolecules, and cells across intact and abnormal microvessels and deranged lymphatic transport are integral, interacting components in disorders of tissue swelling. Lymphedema or low-output failure of the lymph circulation is often indolent for many years before lymphatic insufficiency (failure) and tissue swelling emerge and persist. Superimposed occult or overt infection (lymphangitis) are probably major contributors to progressive limb deformity (elephantiasis). Long-standing lymphedema is characterized by trapping in the skin and subcutaneous tissue of fluid, extravasated plasma proteins, and other macromolecules: impaired immune cell trafficking; abnormal processing of autologous and foreign antigens; heightened susceptibility to superimposed infection; local immunodysregulation; defective lymphatic (lymphangion) propulsion from an imbalance of mediators regulating vasomotion; soft-tissue overgrowth; scarring and hypertrophy; and exuberant angiogenesis occasionally culminating in vascular tumors (Fig. 8). In contrast to the blood circulation, where flow depends primarily on the propulsive force of the myocardium, lymph propulsion depends predominately on intrinsic truncal contraction, a phylogenetic vestige of amphibian lymph hearts. Whereas venous "plasma" flows rapidly (2-3 l/min) against low vascular resistance, lymph flows slowly (1-2 ml/min) against high vascular resistance. On occasion, impaired transport of intestinal lymph may be associated with reflux and accumulation and leakage of intestinal chyle in a swollen leg. Although the term "lymphedema" is usually reserved for extremity swelling, the pathogenesis of a wide variety of visceral disorders also may be traceable to defective tissue fluid and macromolecular circulation and impaired cell trafficking of lymphocytes and macrophages. Thus, lymph stasis, with impaired tissue fluid flow, underlies or complicates an indolent subclinical course with a long latent period and sporadic episodes of lymphangitis, which culminates in intense scarring. Examples are pulmonary fibrosis (e.g., pneumoconiosis), regional enteritis, retroperitoneal fibrosis, and perhaps chronic pancreatitis and cirrhosis of the liver. Transdifferentiation and ultimately transformation of endothelial and other vascular accessory cells during lymph stasis also may be pivotal to a wide range of dysplastic and neoplastic vascular disorders, including Stewart-Treves angiosarcoma, AIDS-associated Kaposi's sarcoma, and lymphangitic metastatic carcinomatosis. Lymphscintigraphy has now replaced conventional lymphography as the procedure of choice to corroborate the diagnosis of peripheral lymphedema, whereas MR imaging using paramagnetic and superparamagnetic contrast agents has the potential to yield huge dividends in furthering understanding of a variety of enigmatic edematous states, including lymphedema. Not only are better explanations and insights into swelling disorders likely to be forthcoming, but, equally important, these new, safe, noninvasive imaging techniques can and should be used to monitor the evolution and document the efficacy of commonly advocated operations and nonoperative remedies for defective lymph transport and function.

Effects of beta-adrenergic blockade or stimulation on net rate of hydrothorax absorption

We determined in anesthetised rabbits the net rate of liquid absorption (NRLA) from Ringer or 1% albumin-Ringer hydrothoraces with the beta-blocker propranolol (or nadolol) or the beta-agonist terbutaline. The beta-blocker reduced NRLA by 38% in 2 ml Ringer hydrothoraces, and did not change it in 2 ml albumin-Ringer hydrothoraces; hence, with beta-blocker NRLA became similar in both kinds of hydrothorax (0.31 +/- 0.02 ml/h). Terbutaline decreased NRLA by 25% in 2 ml Ringer hydrothoraces, and increased it by 29% in 2 ml albumin-Ringer hydrothoraces; hence, with terbutaline NRLA became similar in both kinds of hydrothorax (0.40 +/- 0.02 ml/h), and 25% higher than with beta-blocker. Because beta-adrenoreceptor activity inhibits lymphatic smooth muscles and may increase Na+ transport in epithelia, these results suggest that: (1) pleural mesothelium is provided with beta-receptors, which increase Na+ transport and seem activated by protein dilution, (2) beta-receptors of the pleural lymphatics are essentially silent with and without protein dilution, (3) the lymphatic drainage produced by smooth muscle activity is smaller than the increase in solute-coupled liquid absorption caused by mesothelium beta-receptors.

Pacemaker potentials in lymphatic smooth muscle of the guinea-pig mesentery

1. Intracellular microelectrode recordings have been made from lymphatic smooth muscle (SM) to investigate pacemaker mechanisms underlying lymphatic pumping. 2. The SM of small lymphangions or that of short segments, cut from lymphangions of any length, behaved similarly. Both preparations exhibited spontaneous transient depolarizations (STDs) and exhibited simplified electrical characteristics approximating those of a spherical cell. 3. STDs were found to underlie activation of action potentials and hence constrictions. 4. The level of STD activity correlated to the pumping activity of lymphangions, the SM from more active chambers exhibiting increased STD activity. 5. Lymphatic SM exhibited STDs with properties similar to the STDs of mesenteric veins. STDs appeared to be of myogenic origin as they were present despite denervation or substantial destruction of the endothelium. 6. Noradrenaline enhanced the size and frequency of STDs. 7. STD activity was abolished by chelation of cytosolic Ca2+. 8. It is proposed that STDs provide a mechanism for pacemaking in the lymphatic SM studied here. Furthermore, it is postulated that STDs are the consequence of Ca(2+)-dependent pulsatile release of an intracellular messenger, probably Ca2+ itself. This mechanism provides a novel means for pacemaking.

Lymphatic drainage from the distal small intestine in sheep

Lymphatic drainage from the wall of the distal small intestine, important especially in young sheep as a major site of gut-associated lymphoid tissue, begins with a series of longitudinally oriented subserosal vessels. These vessels convey lymph to the mesenteric border of the intestinal wall and unite to form larger vessels which course through the mesentery to the mesenteric lymph nodes. These nodes lie towards the periphery of a broad, fan-shaped mesentery, adjacent to major arteries and veins. Mesenteric vessels convey lymph from the jejunum and part of the proximal ileum to the jejunal nodes. Lymph from most of the ileum is conveyed to caecal nodes. The larger mesenteric lymphatics have well formed smooth muscle and connective tissue layers surrounding the endothelium. They are often adjacent to, but rarely within, the connective tissue band anchoring the major arteries and veins to one or both lamellae of mesentery. Few anastomoses occur between vessels from opposing sides of the gut wall or the mesentery. Afferent lymphatics enter the subcapsular and trabecular sinuses of the nodes over most surfaces apart from the hilar region. Lymph flows through cortical tissue to the medulla, which occupies most of the node. In the medulla, sinuses occur within medullary cords as well as between them. Initial efferent lymphatics occur throughout medullary tissue. Efferent vessels emerge at a hilus then coalesce and drain into the jejunal or ileal trunk. The hilus of the node varies from a flat, poorly defined area on the lesser curvature, to a depression or groove. The latter commonly occurs in elongated jejunal nodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-ordination of pumping in isolated bovine lymphatic vessels

1. Segments of bovine mesenteric lymphatic of varying diameter taken from different parts of the lymphatic tree were cut to 20 mm in length and set up so that measurements could be made of spontaneous isometric contractions. 2. There was considerable variability in frequency of spontaneous contractions but this was independent of resting tension. There was no significant correlation between lymphatic diameter and inherent frequency of contraction. 3. Isolated segments of bovine mesenteric lymphatic 70-80 mm in length were cannulated and set up in a three-compartment organ bath which allowed independent temperature control in each compartment. Pressure was recorded at inflow and outflow ends and experiments were video recorded. 4. Contractile activity was normally initiated at the end of the lymphatic maintained at the higher temperature and the contractile wave was propagated along the length of the vessel. 5. Propagation could occur either in the direction of valve orientation (orthograde) or retrogradely. The volume of fluid pumped was not significantly affected by the direction of propagation. 6. Perfusion of the central compartment with Krebs solution at 0-2 degrees C disrupted normal propagation and allowed the two parts of the lymphatic to contract at different frequencies although the two parts maintained an approximately 2:1 ratio. 7. Perfusion of the central compartment with 10 mM-heptanol also disrupted normal propagation but the rates on either side of the partition bore no harmonic relationship to one another. 8. These results suggest that relatively short segments of lymph duct have the ability to contract spontaneously and that their inherent frequencies are not determined by their position in the lymphatic tree. The results are consistent with the existence of electrical coupling along the lymphatic's length and they suggest that over distances of at least 80 mm independent pacemakers are capable of mutual entrainment at a frequency representing a compromise between the fastest and slowest components.

Characterization of beta-adrenoceptor subtypes and indications for two cell populations in isolated bovine mesenteric lymphatic vessels

The pharmacological characterization of beta-adrenoceptor subtypes and the identification of two cell populations were investigated in isolated bovine mesenteric lymphatic vessels. The beta-adrenoceptor agonists isoprenaline, dobutamine and salbutamol concentration dependently decreased the amplitude and the frequency of spontaneous contractions and the amplitude of electrically induced contractions. The order of potency was isoprenaline greater than salbutamol greater than dobutamine. These effects were competitively antagonized by atenolol with pA2 values close to 7 with isoprenaline and dobutamine as agonists, and near 5.5 with salbutamol as the agonist. Noradrenaline concentration dependently reduced electrically induced contractions, an effect which was reversed to a slight enhancement after blockade of beta-adrenoceptors with propranolol (10(-6) M). These results confirmed the presence of postjunctional beta 1- and beta 2-adrenoceptor subtypes in lymphatic vessels and provide the first indication of the existence of two pharmacologically and functionally distinct cell populations, one of which exhibits pacemaker activity.

The effects of field stimulation on bovine mesenteric lymph node contractility

In these studies isometric tension was recorded from isolated strips of bovine mesenteric lymph node capsule. The possible influence of intrinsic nerves on their contractile activity was examined using field stimulation and the pharmacology of the response was investigated. Over 75% of the tissues studied demonstrated regular spontaneous activity at a frequency of 3.9 +/- 0.2 contractions/5 min under control conditions. Field stimulation at 2.8 and 32 Hz (pulse width = 0.3 ms, nominal voltage 60 V) produced frequency-dependent increases in the rate of this spontaneous activity associated with a raised baseline tension. These responses were not diminished on repeat stimulation under control conditions. The contraction frequency response to stimulation at 8 Hz was blocked completely in the presence of 1 microM tetrodotoxin, while the increase in baseline tension was reduced by over 80%, suggesting that field stimulation was activating intrinsic nerves. The responses to stimulation (8 Hz) were also greatly reduced by 10 microM phentolamine but were unaffected by 10 microM propranolol. These experiments suggest that intrinsic nerves can modulate the contractile activity of lymph node capsule acting, at least in part, through excitatory alpha-adrenoceptors. The possible functional significance of this is discussed.

Lymphatics and lymphoid tissue of the fallopian tube: immunoelectronmicroscopic study

Lymphoid tissue of the human fallopian tube consists of follicles, lymphoepithelium, and lymphatic and blood capillaries and is located consistently in the interstitial part of the human fallopian tube. Using an immunoelectronmicroscopic technique, we have elucidated the ultrastructure of the lymphoid tissue of the human fallopian tube and the fine distribution and ultrastructure of the lymphatics associated with the rabbit fallopian tube. Lymphatic capillaries arise in the lamina propria mucosa and the periphery of follicles, where they are sparsely distributed, run through the muscular layer, and form a dense network in the subserosa. Characteristic features of the ultrastructure are aggregations of smooth muscle cells, alternating areas of densely and sparsely distributed collagen fibers, and unmyelinated nerve fibers beneath the lymphatic endothelium. Immunoelectronmicroscopic analysis has demonstrated an obvious difference in the distribution of T- and B-lymphocytes in the lymphoid tissue of the human fallopian tube. Many T-lymphocytes are present in the follicles and epithelium, but B-lymphocytes are either absent or rarely found. T-lymphocytes sometimes infiltrate into the basal lamina of the epithelium lying in close contact with the follicles. We conclude that the lymphoid tissue is constantly located in the interstitial part of the human fallopian tube and that intraepithelial lymphocytes, mainly T-lymphocytes, migrate via the basal lamina of the epithelium from follicles. Lymphatic capillaries in the fallopian tube may be the main migratory route of intraepithelial lymphocytes. The intraepithelial lymphocytes and epithelial cells of the fallopian tube have attracted considerable interest as a result of immunological studies of the recognition of spermatozoal antigens and the fertilized ovum.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of alpha- and beta-adrenoceptors in the response to noradrenaline of lymphatic vessels isolated from the bovine mesentery

The role of postsynaptic adrenoceptors in the spontaneous activity of isolated bovine mesenteric lymphatic vessels was characterized. Low concentrations of noradrenaline (less than 10(-6) M) increased the amplitude and the frequency of the spontaneous contractions whereas high concentrations (less than 10(-6) M) depressed the activity. beta-Adrenoceptor blockade with propranolol enhanced the stimulation by noradrenaline and suppressed the inhibition. alpha 1-Blockade by prazosin or alpha 2-blockade by idazoxan antagonized the stimulation by noradrenaline and potentiated the inhibition. Activation of alpha 1-adrenoceptors by methoxamine, or of alpha 2-adrenoceptors by clonidine, stimulated lymphatic activity. The increases in the amplitude and frequency of the spontaneous contractions produced by each agonist were competitively antagonized by prazosin and idazoxan, respectively. Our results confirm the presence of postjunctional beta-, alpha 1-and alpha 2-adrenoceptors in lymphatic vessels and show that each of these receptors plays an important role in the adrenergic regulation of the spontaneous activity, with beta-adrenoceptors mediating inhibition, and alpha 1- and alpha 2-adrenoceptors mediating stimulation.

The use of crystalloidal and colloidal solutions for volume replacement in hypovolemic shock

A wide variety of colloidal and crystalloidal fluids, as well as blood and blood products, are available to the clinician for treatment of the hypovolemic patient. These fluids vary with respect to the size, shape, and concentrations of electrolytes, colloidal molecules, and/or cellular components, duration of volume-expanding effects, incidence of allergic reactions, and effect on the coagulation system. When these fluids are administered intravenously, their distribution in the vascular, interstitial, and cellular compartments can be predicted from fundamental physiological principles as well as from the results of laboratory and clinical research. It is thus recognized that colloidal fluids and blood provide more rapid expansion of the intravascular space when compared with crystalloidal fluids. Similar volumes of crystalloidal fluids more rapidly expand the interstitial and intracellular spaces. These principles guide therapy in hypovolemic shock. A logical decision regarding intravenous fluid therapy may be based on the nature of the volume deficit (blood, plasma, or selective protein loss, loss of free water and/or electrolytes) and the predicted changes in cellular and extracellular compartments.

Dual effects of histamine on spontaneous activity in isolated bovine mesenteric lymphatics

The mode of action of histamine on spontaneous contractions is isolated bovine mesenteric lymphatics was investigated by recording isometric tensions. Histamine at lower concentrations between about 5 x 10(-8) and 10(-6) M caused a dose-dependent deceleration of the rhythm of spontaneous contractions. Higher concentrations of histamine (more than about 5 x 10(-6) M) produced a dose-related acceleration of the rhythm in association with a slight elevation of basal tone in 115 of 173 preparations. In 58 of 173 lymphatic preparations, histamine at concentrations ranging from about 5 x 10(-8) to 10(-5) M caused only the positive chronotropic effect. The histamine-induced positive and negative chronotropic effects were unaltered by pretreatment with alpha- and beta-adrenergic antagonists but were dose-dependently antagonized by pretreatment with H1- or H2-blockers (diphenhydramine or cimetidine). The specific H1- and H2-agonists, 2-pyridylethylamine (2PEA) and dimaprit caused dose-related positive and negative chronotropic effects, respectively, on spontaneous contractions of isolated bovine mesenteric lymphatics. The effect of 2PEA was significantly blocked by pretreatment with 10(-6) M diphenhydramine, whereas the effect of dimaprit was suppressed by 10(-6) M cimetidine. These results suggest that both H1- and H2-receptors are located on the plasma membrane of smooth muscle cells in bovine mesenteric lymphatics, and that the excitations of H1- and H2-receptors respectively produce an acceleration and a deceleration of the rhythm of spontaneous contractions in lymphatic smooth muscles.

Beta-adrenergic inhibition of bovine mesenteric lymphatics

The beta-action of catecholamines on lymphatic smooth muscle was studied by observing the effect of isoprenaline on electrical and mechanical activity in the double sucrose-gap. Action potentials and phasic contractions evoked by depolarizing pulses were abolished within 2 min of drug addition. Isoprenaline hyperpolarized the membrane and increased membrane conductance. Tetraethylammonium (10 mM) did not itself affect membrane resistance but reduced the hyperpolarization and the increase in conductance caused by isoprenaline. Removal of K+ from the external solution reduced membrane conductance and increased the hyperpolarization due to isoprenaline. When the NaCl content of Krebs solution was replaced with LiCl or choline chloride, isoprenaline no longer blocked action potential firing and its effects on phasic contractions and membrane conductance were reduced. In contrast, ouabain (10(-5) M) did not block the effect of isoprenaline on membrane potential and membrane conductance. These results suggest that beta-adrenergic inhibition of lymphatic smooth muscle involves an increase in an outward K+ current, though an additional metabolic effect cannot be ruled out.

Lymphatic endothelial and smooth-muscle cells in tissue culture

Endothelial and smooth-muscle cells from bovine mesenteric lymphatic vessels have been collected and cultured in vitro. The endothelial cells grew as a monolayer exhibiting a "cobblestone" appearance with individual cells tending to be more flattened at confluence than their blood vascular counterparts. Approximately 30% of these cells expressed Factor VIII antigen compared with bovine mesenteric artery or human umbilical-vein endothelium in which the majority of cells were positive. The lymphatic smooth-muscle cells exhibited focal areas of multilayering and were Factor VIII negative. The availability of lymphatic endothelial and smooth-muscle cells in culture will provide a new tool for the investigation of the biological properties of the lymphatic vessels and their role in homeostasis.

The inhibitory effect of aspirin on lymphatic contractility

Spontaneous contractions and those elicited by two different methods of electrical stimulation were studied in isolated segments of bovine mesenteric lymphatic vessels. The effect of aspirin (a cyclo-oxygenase inhibitor) on spontaneous and evoked contractions of isolated lymphatic vessels was investigated. Aspirin at doses of 10(-6) M or greater depressed both spontaneous and action potential-dependent evoked contractions, but failed to inhibit contractions evoked by high current field stimulation. These latter contractions were rapidly depressed by the application of D600. When aspirin was applied for five minute periods, inhibition never occurred within the period of drug administration but was delayed, with maximum inhibition occurring approximately 10 min after washout of the drug. It is concluded that the inhibitory action of aspirin is unlikely to be a non-specific depression of the contractile mechanism, but rather a reduction in excitability probably as a result of cyclo-oxygenase inhibition.

Relationship between intestinal motility, tone, water absorption and lymph flow in the rat

The relations between motility, tone, water absorption rate (Jv) and lymph flow (J1), were studied in an exteriorized upper jejunal preparation in vivo, with its serosal side bathed in Krebs-Ringer or other solutions. Neither Jv nor J1 was correlated with motility. When the luminal fluid consisted of an isotonic solution of MgSO4, glucose or LiCl, motility was greatly increased with no increase in J1. When the serosal fluid consisted of an isotonic solution of mannitol, glucose or MgSO4, motility was depressed with a large decrease in tone, and Jv was increased by 51-83% with a decrease in J1. When the serosal fluid consisted of an isotonic solution of NaCl, Na2SO4, LiCl or KCl, motility was decreased with either no change or an increase in tone, and both Jv and J1 were much decreased. When isotonic choline Cl solution was employed as the serosal fluid, motility increased with an increase in tone, Jv became negative (fluid secretion), and J1 decreased to 0. Acetylcholine depressed motility but increased tone with a decrease in Jv and J1. Eserine increased both tone and motility with a decrease in Jv and J1. Serotonin caused no change in motility but increased tone with a decrease in Jv and J1. Noradrenaline and adrenaline depressed motility and reduced tone with an increase in Jv and J1. Isoprenaline abolished motility and reduced tone with a large increase in Jv but no change in J1. Pentobarbitone depressed motility and reduced tone with an increase in Jv but a decrease in J1. It is concluded that the intestine responds to various stimuli with a change in motility, or tone, or both. Intestinal motility per se does not produce lymph. Since an increase or decrease in tone always results in a decrease or increase in Jv, respectively, regardless of the nature of the conditions, a relaxation of the intestinal musculature appears to be associated with an increase in water absorption.

The effects of catecholamines on pumping activity in isolated bovine mesenteric lymphatics

Bovine mesenteric lymphatics of 8 cm length were cannulated and arranged so that pressure changes produced by spontaneous contractions and accompanying flow could be measured. The mean frequency of spontaneous contractions, although constant for any one vessel, varied between vessels from 0.5 to 5.2 beats/min (mean 2.6, S.D. 1.6, n = 33). Noradrenaline (100 ng/ml.) invariably increased frequency of contractions but flow was increased only in those vessels which had a low resting frequency. In those vessels which had a higher resting frequency, flow was decreased despite the increase in frequency because stroke volume decreased. This may have been due to increased pace-maker activity causing desynchronization of the contractile activity in the vessel wall and thus decreased effectiveness of pumping. High doses (greater than 1 microgram/ml.) of noradrenaline invariably depressed flow. Isoprenaline slowed the frequency of spontaneous contractions and this either had little effect on flow (due to an increased filling time and thus stroke volume) or depressed it, finally abolishing it entirely at higher doses. It is concluded that in suitable dosage (which varies for different vessels) noradrenaline is capable of enhancing flow and this might, at least in part, explain the increase in lymph flow resulting from noradrenaline infusion in living animals.