Intrinsic rhythmic propulsion of lymph in the unanaesthetized sheep

Lymphatic Clearance and Pump Function

Lymphatic vessels have an active role in draining excess interstitial fluid from organs and serving as conduits for immune cell trafficking to lymph nodes. In the central circulation, the force needed to propel blood forward is generated by the heart. In contrast, lymphatic vessels rely on intrinsic vessel contractions in combination with extrinsic forces for lymph propulsion. The intrinsic pumping features phasic contractions generated by lymphatic smooth muscle. Periodic, bicuspid valves composed of endothelial cells prevent backflow of lymph. This work provides a brief overview of lymph transport, including initial lymph formation along with cellular and molecular mechanisms controlling lymphatic vessel pumping.

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.

Two pathways for venom toxin entry consequent to injection of an Australian elapid snake venom

Here we test and refute the hypothesis that venom toxins from an Australian elapid, the Eastern Brown snake (Pseudonaja textilis, PTx), solely require lymphatic transport to enter the circulation. Studies were made using anaesthetised non-recovery rats in which a marker dye (India ink) or highly potent PTx venom was injected into the hind paw. The studies required a means of inhibiting lymphatic function, as achieved by cooling of the test hind limb to low temperatures (~3 °C). Maintained entry of a non-lethal dose (0.15 mg/kg) and respiratory arrest consequent to injection of a lethal dose (1 mg/kg) of PTx venom at these low temperatures indicate that venom including toxin components enter the circulation directly via the vascular system, a process facilitated by, but not dependent on, lymphatic transport. Notably, the venom had a direct effect on vascular permeability markedly increasing this to allow extravasation of plasma albumin (MWt ~60 kDa).

Rapid lymphatic efflux limits cerebrospinal fluid flow to the brain

The relationships between cerebrospinal fluid (CSF) and brain interstitial fluid are still being elucidated. It has been proposed that CSF within the subarachnoid space will enter paravascular spaces along arteries to flush through the parenchyma of the brain. However, CSF also directly exits the subarachnoid space through the cribriform plate and other perineural routes to reach the lymphatic system. In this study, we aimed to elucidate the functional relationship between CSF efflux through lymphatics and the potential influx into the brain by assessment of the distribution of CSF-infused tracers in awake and anesthetized mice. Using near-infrared fluorescence imaging, we showed that tracers quickly exited the subarachnoid space by transport through the lymphatic system to the systemic circulation in awake mice, significantly limiting their spread to the paravascular spaces of the brain. Magnetic resonance imaging and fluorescence microscopy through the skull under anesthetized conditions indicated that tracers remained confined to paravascular spaces on the surface of the brain. Immediately after death, a substantial influx of tracers occurred along paravascular spaces extending into the brain parenchyma. We conclude that under normal conditions a rapid CSF turnover through lymphatics precludes significant bulk flow into the brain.

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.

Quantitative measurement of lymphatic function in mice by noninvasive near-infrared imaging of a peripheral vein

Optical imaging methods have been developed to measure lymphatic function in skin; however, the lymphatic system of many organs is not accessible to this technology. Since lymphatic transport of macromolecules from any organ proceeds to the blood circulation, we aimed to develop a method that can measure lymphatic function by monitoring the fluorescence in a superficial vein of an interstitially injected tracer. We selected a 40-kDa PEGylated near-infrared dye conjugate, as it showed lymphatic system-specific uptake and extended circulation in blood. Lymphatic transport to blood from subcutaneous tissue required a transit time before signal enhancement was seen in blood followed by a steady rise in signal over time. Increased lymphatic transport was apparent in awake mice compared with those under continuous anesthesia. The methods were validated in K14-VEGFR-3-Fc and K14-VEGF-C transgenic mice with loss and gain of lymphatic function, respectively. Reduced lymphatic transport to blood was also found in aged mice. The technique was also able to measure lymphatic transport from the peritoneal cavity, a location not suitable for optical imaging. The method is a promising, simple approach for assessment of lymphatic function and for monitoring of therapeutic regimens in mouse models of disease and may have potential for clinical translation.

Effect of lidocaine with and without epinephrine on lymphatic contractile activity in mice in vivo

A local anesthetic, lidocaine, is known to affect cutaneous blood flow when injected into the skin. However, it is unknown if dermal lymphatic function can also be affected. Therefore, we characterized lymphatic function in response to administration of lidocaine with and without epinephrine. Non-invasive near-infrared fluorescence imaging (NIRFI) with intradermal injection of indocyanine green (ICG) was used to characterize the lymphatic "pumping" function in mice after subcutaneous injection of 2 % lidocaine with and without 1:100,000 epinephrine or saline. NIRFI was performed for 10-20 min immediately after and 1, 3, and 5 h after these interventions. Lymphatic contraction frequencies significantly decreased 10 min after subcutaneous injection of lidocaine and remained plateaued for another 5 min, before returning to baseline. However, addition of 1:100,000 epinephrine to 2 % lidocaine rapidly increased lymphatic contraction frequencies at 5 min post-injection, which returned to baseline levels 15 min later. Injection of saline also increased lymphatic contraction frequency 5 min after injection, which returned to baseline 10 min post-injection. Although lidocaine administration showed a decrease in lymphatic function, the combination of epinephrine with lidocaine resulted in a predominant net effect of increased contractile activity.

Control of Lymphatic Pumping: Interest of Daflon 500 mg

Objective:

To determine the effects of Daflon 500 mg on lymph flow, known to be modulated by lymph formation and contractility of the collecting ducts.

Experimental design:

The effect of Daflon 500 mg was investigated in vitro on isolated rings of sheep mesenteric lymphatics, at concentrations of 10-7 M and higher. In vivo, lymph flow was measured in unanaesthetized sheep before and after 5 days of administration of Daflon 500 mg at the oral dose of 10 mg/kg/day.

Results:

Daflon 500 mg significantly increased the frequency of spontaneous contractions in vitro, and in vivo increased the lymph flow when compared with pre-drug levels.

Conclusion:

It is suggested that Daflon 500 mg increases lymph flow under these conditions by stimulating the lymph pump directly, a result that is consistent with previous studies.

Lymphatic disorders after renal transplantation: new insights for an old complication

In renal transplanted patients, lymphoceles and lymphorrhea are well-known lymphatic complications. Surgical damage of the lymphatics of the graft during the procurement and of the lymphatic around the iliac vessels of the recipients has been associated with development of lymphatic complications. However, lymphatic complications may be related to medical factors such as diabetes, obesity, blood coagulation abnormalities, anticoagulation prophylaxis, high dose of diuretics, delay in graft function and immunosuppressive drugs. Consistently, immunosuppression regimens based on the use of mTOR inhibitors, especially in association with steroids and immediately after transplantation, has been associated with a high risk to develop lymphocele or lymphorrhea. In addition, several studies have demonstrated the association between rejection episodes and lymphatic complications. However, before the discovery of reliable markers of lymphatic vessels, the pathogenic mechanisms underlining the development of lymphatic complications during rejection and the influence of mTOR inhibitors remained not fully understood. The recent findings on the lymphatic systems of either native or transplanted kidneys together with the advances achieved on lymphangiogenesis shared some lights on the pathogenesis of lymphatic complications after renal transplantation. In this review, we describe the surgical and medical causes of lymphatic complications focusing on the rejection and immunosuppressive drugs as causes of lymphatic complications.

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.

Mesenteric lymphatic vessels adapt to mesenteric venous hypertension by becoming weaker pumps

Lymphangions, the segments of lymphatic vessels between two adjacent lymphatic valves, actively pump lymph. Acute changes in transmural pressure and lymph flow have profound effects on lymphatic pump function in vitro. Chronic changes in pressure and flow in vivo have also been reported to lead to significant changes in lymphangion function. Because changes in pressure and flow are both cause and effect of adaptive processes, characterizing adaptation requires a more fundamental analysis of lymphatic muscle properties. Therefore, the purpose of the present work was to use an intact lymphangion isovolumetric preparation to evaluate changes in mesenteric lymphatic muscle mechanical properties and the intracellular Ca(2+) in response to sustained mesenteric venous hypertension. Bovine mesenteric veins were surgically occluded to create mesenteric venous hypertension. Postnodal mesenteric lymphatic vessels from mesenteric venous hypertension (MVH; n = 6) and sham surgery (Sham; n = 6) animals were isolated and evaluated 3 days after the surgery. Spontaneously contracting MVH vessels generated end-systolic active tension and end-diastolic active tension lower than the Sham vessels. Furthermore, steady-state active tension and intracellular Ca(2+) concentration levels in response to KCl stimulation were also significantly lower in MVH vessels compared with those of the Sham vessels. There was no significant difference in passive tension in lymphatic vessels from the two groups. Taken together, these results suggest that following 3 days of mesenteric venous hypertension, postnodal mesenteric lymphatic vessels adapt to become weaker pumps with decreased cytosolic Ca(2+) concentration.

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.

Modelling the lymphatic system: challenges and opportunities

The lymphatic system is a vital part of the circulatory and immune systems, and plays an important role in homeostasis by controlling extracellular fluid volume and in combating infection. Nevertheless, there is a notable disparity in terms of research effort expended in relation to the treatment of lymphatic diseases in contrast to the cardiovascular system. While similarities to the cardiovascular system exist, there are considerable differences in their anatomy and physiology. This review outlines some of the challenges and opportunities for those engaged in modelling biological systems. The study of the lymphatic system is still in its infancy, the vast majority of the models presented in the literature to date having been developed since 2003. The number of distinct models and their variants are few in number, and only one effort has been made thus far to study the entire lymphatic network; elements of the lymphatic system such as the nodes, which act as pumps and reservoirs, have not been addressed by mathematical models. Clearly, more work will be necessary in combination with experimental verification in order to progress and update the knowledge on the function of the lymphatic system. As our knowledge and understanding of its function increase, new and more effective treatments of lymphatic diseases are bound to emerge.

Current concepts and future directions in the diagnosis and management of lymphatic vascular disease

Despite the central, complex role for the lymphatic system in the maintenance of human health, the biology of this important and complex vasculature has been relatively under-investigated. However, the last decade has witnessed a substantial growth in the elucidation of lymphatic structural biology and the function of this system in health and in disease. These newly gained insights can be used to formulate our evolving concepts about the diagnostic and therapeutic approaches to patients with lymphatic vascular disorders. In lymphedema, there is a spectrum of disease that extends from primary (heritable) to secondary (acquired) causes. Once detected, the presence of lymphatic edema mandates very specific modalities of intervention, predominated by physiotherapeutic techniques. In addition, a physiological basis for adjunctive, intermittent pneumatic compression has been established, and these modalities may be indicated in selected patient populations. The acknowledgement of a unique biology in lymphatic edemas is, increasingly, guiding research efforts within this field. Increasing investigative attention is being directed toward animal models of lymphatic vascular disease. As insight into the complex biology of the lymphatic vasculature continues to expand through focused biomedical investigation, the translation of these mechanistic insights into targeted, rationally conceived therapeutics will become increasingly feasible.

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.

Arnold Heller and the lymph pump

This article reviews studies on lymph propulsion in the lymph vessels by active contraction of the vessels, first described by Arnold Heller in 1869 in German language, and here translated into English. His observations were first confirmed by Beatrice Carrier (1926) and Howard Flory et al. (1927), and several groups were active up to World war II. Few publications appeared in the period 1940--1960, followed by increasing activity and development of new experimental techniques for use both in various experimental animals and in humans. Recently it has been shown that passive lymph flow may add to active propulsion. Both mechanisms depend on lymph formation, i.e. the uptake of interstitial fluid by the initial lymph vessels which is still not well understood.

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.

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.

Molecular control of lymphangiogenesis

The lymphatic vasculature plays a critical role in the regulation of body fluid volume and immune function. Extensive research into the molecular mechanisms that control blood vessel growth has led to identification of molecules that also regulate development and growth of the lymphatic vessels. This is generating a great deal of interest in the molecular control of the lymphatics in the context of embryogenesis, lymphatic disorders and tumor metastasis. Studies in animal models carried out over the past three years have shown that the soluble protein growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. Furthermore, disfunction of VEGFR-3 has recently been shown to cause lymphedema. The capacity to induce lymphangiogenesis by manipulation of the VEGF-C/VEGF-D/VEGFR-3 signaling pathway offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders.

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.

Lymphatic function, lymphangiogenesis, and cancer metastasis

The lymphatic system serves as the primary route for the metastasis of many cancers and the extent of lymph node involvement is the most important indicator of tumor aggressiveness. Despite the apparent importance of the lymphatic vessels for tumor dissemination, it has remained unclear whether activation of lymphatic endothelial cells may affect tumor progression and metastasis and the molecular mechanisms of lymphangiogenesis are just beginning to be elucidated. This overview describes the unique structural and functional characteristics of the lymphatic vessels that render them particularly suitable for invasion by tumor cells and for their efficient transport to lymph nodes. Recent evidence indicates occurrence of tumor lymphangiogenesis and its correlation with metastasis. Molecular regulation of tumor lymphangiogenesis, its significance for tumor metastasis, and implications for cancer therapy are discussed.

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.

Lymph flow pattern in the intact thoracic duct in sheep

1. To study the lymph flow dynamics in the intact thoracic duct, we applied an ultrasound transit-time flow probe in seven anaesthetized and four unanaesthetized adult sheep (approximately 60 kg). In unanaesthetized non-fasting animals we found that lymph flow in the thoracic duct was always regular pulsatile (pulsation frequency, 5.2 +/- 0.8 min-1) with no relation to heart or respiratory activity. At baseline the peak level of the thoracic duct pulse flow was 11.6-20.7 ml min-1 with a nadir of 0-3.6 ml min-1. Mean lymph flow was 5.4 +/- 3.1 ml min-1. The flow pattern of lymph in the thoracic duct was essentially the same in the anaesthetized animals. 2. In both the anaesthetized and unanaesthetized animals, the lymph flow response to a stepwise increase in the outflow venous pressure showed interindividual variation. Some were sensitive to any increase in outflow venous pressure, but others were resistant in that lymph flow did not decrease until outflow venous pressure was increased to higher levels. This resistance was also observed in the high lymph flow condition produced by fluid infusion in the anaesthetized animal and mechanical constriction of the caudal vena cava in the unaesthetized animals. Pulsation frequency of the thoracic duct flow initially increased and then decreased with a stepwise increase in the outflow venous pressure. This initial increase might be a compensatory response to maintain lymph flow against elevated outflow venous pressure. 3. To test the effect of long-term outflow venous pressure elevation in unanaesthetized sheep, outflow venous pressure was increased by inflation of a cuff around the cranial vena cava for 1, 5 or 25 h. The cuff was inflated to a level where lymph flow was reduced. Lymph flow remained low or decreased further during the entire cuff-inflation period. We calculated the lymph debt caused by the outflow venous pressure elevation and the amount 'repaid' when venous pressure returned to normal. Lymph debt for 25 h was 6400 ml but only 200 ml was repaid. Since we observed no visible oedema formation in the lower body of the sheep, the non-colloidal components of the lymph must have been reabsorbed into the bloodstream, most likely in the lymph nodes.

Outward currents in smooth muscle cells isolated from sheep mesenteric lymphatics

1. The patch-clamp technique was used to measure membrane currents in isolated smooth muscle cells dispersed from sheep mesenteric lymphatics. Depolarizing steps positive to -30 mV evoked rapid inward currents followed by noisy outward currents. 2. Nifedipine (1 microM) markedly reduced the outward current, while Bay K 8644 (1 microM) enhanced it. Up to 90% of the outward current was also blocked by iberiotoxin (Kd = 36 nM). 3. Large conductance (304 +/- 15 pS, 7 cells), Ca(2+)- and voltage-sensitive channels were observed during single-channel recordings on inside-out patches using symmetrical 140 mM K+ solutions (at 37 degrees C). The voltage required for half-maximal activation of the channels (V1/2) shifted in the hyperpolarizing direction by 146 mV per 10-fold increase in [Ca2+]i. 4. In whole-cell experiments a voltage-dependent outward current remained when the Ca(2+)-activated current was blocked with penitrem A (100 nM). This current activated at potentials positive to -20 mV and demonstrated the phenomenon of voltage-dependent inactivation (V1/2 = -41 +/- 2 mV, slope factor = 18 +/- 2 mV, 5 cells). 6. Tetraethylammonium (TEA; 30 mM) reduced the voltage-dependent current by 75% (Kd = 3.3 mM, 5 cells) while a maximal concentration of 4-aminopyridine (4-AP; 10 mM) blocked only 40% of the current. TEA alone had as much effect as TEA and 4-AP together, suggesting that there are at least two components to the voltage-sensitive K+ current. 7. These results suggest that lymphatic smooth muscle cells generate a Ca(2+)-activated current, largely mediated by large conductance Ca(2+)-activated K+ channels, and several components of voltage-dependent outward current which resemble 'delayed rectifier' currents in other smooth muscle preparations.

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.

The formation of lymph in the ovary

The lymphatics of the ovaries of pregnant and non-pregnant ewes were outlined either by direct or retrograde injection of indian ink or Berlin blue and the distribution of these vessels within the ovary was determined. In active ovaries the mature follicles and corpora lutea contained a profuse network of lymphatics. In inactive ovaries the lymphatics were very small and poorly developed. Lymph was collected from the ovaries of conscious ewes for periods of several days. The flow of lymph from ovaries with corpora lutea averaged 4.15 ml./h; a maximum rate of flow of 14.9 ml./h was recorded in one ewe. The protein concentration of ovarian lymph was 73 % of the plasma concentration. When 131 I labelled albumin was injected intravenously into ewes it entered the ovarian lymph very rapidly and the specific activities of albumin in the plasma and lymph equilibrated within 10 to 20 min of injection. The structure of the ovarian blood capillaries provided an explanation for the very high rate of lymph flow and protein leakage in the ovary. The endothelium of the blood capillaries was discontinuous with gaps up to 1 to 2 μm in diameter through which red cells, indian ink particles and ferritin passed into the interstitial spaces. Where the basement membrane of the capillaries was deficient over gaps the surfaces of the luteal cells came into direct contact with the circulating plasma, and occasionally cytoplasmic extensions from the luteal cells projected into the lumen of the blood capillaries. The lymphatics which were associated with many of the blood capillaries had open intercellular junctions and material could enter these vessels readily from the interstitial spaces. The blood capillaries in the ovarian stroma and those around immature follicles appeared less permeable than the capillaries of the corpus luteum. The association between the development of the corpus and an increase in lymph production in the ovary suggests the possibility that the changes in capillary permeability may be related to the synthesis and secretion of steroid hormones.

Effect of postural changes on human lymphatic capillary pressure of the skin

1. The influence of postural changes on cutaneous lymphatic capillary pressure and venous pressure was measured at the dorsum of the foot in twelve healthy volunteers. Measurements were performed in the supine and sitting positions. 2. Lymphatic skin capillaries were visualized by fluorescence microlymphography with fluorescein isothiocyanate (FITC)-Dextran 150000. Subsequently a lymphatic capillary was punctured with a glass micropipette and pressure was measured using the servo-nulling technique. Lymphatic capillary pressure, venous pressure, heart and respiration rates were recorded simultaneously. 3. Mean lymphatic capillary pressure was significantly higher (P = 0.0096) in the sitting (9.9 +/- 3.0 mmHg) than in the supine (3.9 +/- 4.2 mmHg) position. There was no significant difference (P = 0.09) between lymphatic capillary pressure and venous pressure (6.8 +/- 3.4 mmHg) in the supine position. During sitting mean lymphatic capillary pressure was significantly lower (P = 0.0022) than mean venous pressure (53.3 +/- 4.1 mmHg). The smaller increase in lymphatic capillary pressure may be caused by the discontinuous fluid column in the lymphatic system and enhanced orthostatic contractile activity of lymphatic collectors and precollectors. Spontaneous low frequency pressure fluctuations occurred in 89% of recordings during sitting, which was significantly (P = 0.02) higher than in the supine position (54%). 4. The present results support the suggestion of enhanced intrinsic contractile activity of lymph precollectors and collectors in the dependent position. This mechanism is primarily responsible for the propulsion of lymph from the periphery to the thoracic duct during quiet sitting, when extrinsic pumping by the calf muscles is not active.

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.

Managing lymphoedema

Lymphoedema is perceived by clinicians in the UK as a rare condition for which there is no effective treatment. I would like to argue that lymphoedema is in fact a common condition which is misunderstood and often poorly managed. To explain further the basic physiology of oedema has to be considered.

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 endothelium isolation, characterization and long-term culture

Using a collagenase trypsin-EDTA treatment, we have been able to successfully isolate and grow primary cultures of the lymphatic endothelium (LEC) that were subcultured, frozen for storage, subsequently thawed with good recovery and growth, and serially subcultured. The morphological features of cultured LEC were consistent with that observed for the endothelium of intact lymphatic vessels. A prominent feature of growing cultures was the appearance of large vacuoles in the perinuclear region of the cytoplasm, which became filled with fluid and cell debris engulfed from the culture medium. The basal cell surface lacked a well defined basal lamina and anchoring filaments were observed extending from the basal plasmalemmal surface into the underlying substratum. LEC in cultures were also positive for Factor VIII-related antigen. However, specific granules, characteristic of Weibel-Palade bodies were not observed in ultrathin sections of confluent cultures. F-actin was identified in LEC cultures using fluorescein phalloidin, and in confluent cultures actin filaments were located at the periphery of the cell as a continuous circumferential thin band and short filamentous bundles in the central part of the cell. By using heparin and endothelial cell growth supplement in the culture medium we have been able to grow stable cultures of lymphatic endothelial cells that could be maintained when serially subcultured for over two years. These LEC cultures provide an in vitro model for investigating the function and biochemical properties of the lymphatic endothelium.

Flow and composition of afferent mammary gland lymph

Afferent mammary lymphatic flow was characterized in conscious lactating cows during milking and prior to, during, and after intramammary infusion of endotoxins. Lymph flow (13 to 45 ml/h) was pulsatile with monophasic and multiphasic episodes. Flow resulted from 62 to 67 episodes per h. Episodes varied from 1 to 53 s in duration. Maximum instantaneous flow ranged from 163 to 245 microliters/s. Flow did not increase consistently during milking. Lymph flow increased (5.5- to 8-fold) during endotoxin-induced mastitis. Flow rates were elevated for up to 48 h after infusion of endotoxin. Compositional comparisons between afferent mammary lymph and blood plasma showed distinct differences. Lymph contained 7, 6, and 10 times less protein, albumin, and globulin, respectively, than did plasma. Glucose concentrations were equivalent. Lymph had 17 times less cholesterol and about one-half as much triglyceride and calcium as did plasma. gamma-Glutamyl-transaminase and aspartate transaminase were substantially higher in plasma than in lymph. Afferent mammary lymph has unique compositional characteristics. The lymph ducts contained an intrinsic mechanism for lymph movement. Moreover, this mechanism was altered by inflammation. The techniques herein provide a better understanding of the mammary lymphatic system.

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.

Initial treatment of pulmonary edema: a physiological approach

An understanding of the physiological principles involved in lung fluid balance is useful in the initial treatment of pulmonary edema. Normally, a very small volume of fluid is filtered from the pulmonary vasculature into the interstitial space. This interstitial fluid enters the pulmonary lymphatics and is transferred to mediastinal lymphatics at an estimated rate of 20 ml/hr. Under abnormal circumstances, fluid filtration may occur at such a rapid rate that it overwhelms the lymphatics and interstitial space and results in alveolar flooding. This may occur as a result of increased pulmonary vascular pressure or increased vascular permeability. The two general goals of initial therapy are (1) to relieve hypoxemia and (2) to reduce pulmonary capillary pressure. Relieving hypoxemia may require the use of supplemental oxygen by nasal prongs or mask, continuous positive airway pressure (CPAP) mask, or even endotracheal intubation and mechanical ventilation. Measures to decrease preload and thereby reduce pulmonary capillary pressure include sitting the patient up, administering a loop diuretic or morphine intravenously, and in some circumstances using sublingual nitroglycerin. After initial treatment is underway, a search for and specific management of the underlying cause of pulmonary edema can proceed.

Increased capillary permeability to albumin and diabetic neuropathy

An increase in the capillary permeability to albumin (CPA) has been reported in diabetic patients. We observed this frequently with a non-invasive isotopic test derived from the Landis method, using 99mTc-albumin and measuring residual radioactivity externally after removal of forearm venous compression. Evidence of the independent effects of hypertension and microangiopathy on CPA has already been found. The present work was designed to investigate CPA using the same test on diabetic patients without retinopathy and clinical proteinuria. Some of these patients had objective clinical distal and symmetrical polyneuropathy. Neuropathy was clearly present in 10 of the 11 patients with an abnormal test unexplained by causes other than diabetes and in only one of the 17 patients with a normal test. The most frequent abnormality affected the late radioactivity disappearance curve, which probably reflects an impaired lymphatic wash-out of interstitial albumin. These results strongly suggest a link between peripheral neuropathy and diabetic functional microangiopathy. An elevated blood flow secondary to sympathetic nerve failure may induce an increase in CPA and a saturation of lymphatic pumping which could also be deficient due to impaired lymphatic innervation.

The measurement of skin lymph flow by isotope clearance--reliability, reproducibility, injection dynamics, and the effect of massage

The measurement of skin lymph flow was investigated using an isotope clearance technique (ICT). Multiple lymph flow determinations were undertaken in the skin of anaesthetized large white pigs to test for reproducibility, ascertain the most suitable tracer, study the influence of injection dynamics, and observe the effect of massage as a stimulus to lymph flow. Blood clearance of tracer was also investigated. Results demonstrated that lymphatic clearance is a monoexponential function with good reproducibility under controlled laboratory conditions. 99mTc-colloid (TCK17 Cis) compared favorably with 131I-human serum albumin as a tracer and both performed better than colloid gold (198Au). Lymph flow was significantly faster in one pig than in the other. No difference existed between left and right sides or between caudal and rostral sites on each flank, but clearance was significantly slower in thigh than flank skin. Sub-epidermal injections cleared faster and more consistently than either deep or subcutaneous injections. Neither injection volume nor needle tract backflow of tracer influenced results, but local massage significantly enhanced clearance. Escape of 99mTc-colloid by the blood was negligible. These results indicate that skin lymph flow can be reliably measured when conditions are controlled. Extrinsic factors such as massage strongly influence lymph flow. Greater sensitivity in detecting degrees of lymphatic insufficiency may be achieved if a standardized stimulus to lymph flow is administered during isotope clearance measurement.

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.

Demonstration of both beta 1- and beta 2-adrenoceptors mediating negative chronotropic effects on spontaneous activity in isolated bovine mesenteric lymphatics

The pharmacological classification of beta-adrenoceptor subtypes in isolated bovine mesenteric lymphatics was studied by using various beta-adrenoceptor agonists and antagonists. Isoproterenol (ISP) (10(-10)-10(-8) M) produced dose-dependent negative chronotropic effects on the rhythm of spontaneous contractions in the lymphatic preparation. The ISP-induced effects were dose-dependently blocked by pretreatment with 10(-8)-10(-7) M metoprolol (a selective beta 1 antagonist) as well as 10(-8)-10(-7) M propranolol (a beta 1 and beta 2 antagonist). Dobutamine (a selective beta 1 agonist) caused a dose-dependent negative chronotropic effect, which was significantly blocked by pretreatment with 10(-8) M metoprolol. Salbutamol and procaterol (selective beta 2 agonists) also produced dose-dependent negative chronotropic effects, which were dose-dependently inhibited by pretreatment with 10(-8)-10(-7) M propranolol, but not by 10(-7) M metoprolol. The decreasing order of the relative potency was as follows: ISP greater than procaterol greater than salbutamol greater than dobutamine. These results suggest that bovine mesenteric lymphatics contain both beta 1- and beta 2-adrenoceptors and that both subtypes can produce a negative chronotropic effect on the rhythm of spontaneous contractions, when stimulated.

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)