Quantification of the Whole Lymph Node Vasculature Based on Tomography of the Vessel Corrosion Casts

Lymph nodes (LN) are crucial for immune function, and comprise an important interface between the blood and lymphatic systems. Blood vessels (BV) in LN are highly specialized, featuring high endothelial venules across which most of the resident lymphocytes crossed. Previous measurements of overall lymph and BV flow rates demonstrated that fluid also crosses BV walls, and that this is important for immune function. However, the spatial distribution of the BV in LN has not been quantified to the degree necessary to analyse the distribution of transmural fluid movement. In this study, we seek to quantify the spatial localization of LNBV, and to predict fluid movement across BV walls. MicroCT imaging of murine popliteal LN showed that capillaries were responsible for approximately 75% of the BV wall surface area, and that this was mostly distributed around the periphery of the node. We then modelled blood flow through the BV to obtain spatially resolved hydrostatic pressures, which were then combined with Starling’s law to predict transmural flow. Much of the total 10 nL/min transmural flow (under normal conditions) was concentrated in the periphery, corresponding closely with surface area distribution. These results provide important insights into the inner workings of LN, and provide a basis for further exploration of the role of LN flow patterns in normal and pathological functions.

Acute exposure to space flight results in evidence of reduced lymph Transport, tissue fluid Shifts, and immune alterations in the rat gastrointestinal system

Space flight causes a number of alterations in physiological systems, changes in the immunological status of subjects, and altered interactions of the host to environmental stimuli. We studied the effect of space flight on the lymphatic system of the gastrointestinal tract which is responsible for lipid transport and immune surveillance which includes the host interaction with the gut microbiome. We found that there were signs of tissue damage present in the space flown animals that was lacking in ground controls (epithelial damage, crypt morphological changes, etc.). Additionally, morphology of the lymphatic vessels in the tissue suggested a collapsed state at time of harvest and there was a profound change in the retention of lipid in the villi of the ileum. Contrary to our assumptions there was a reduction in tissue fluid volume likely associated with other fluid shifts described. The reduction of tissue fluid volume in the colon and ileum is a likely contributing factor to the state of the lymphatic vessels and lipid transport issues observed. There were also associated changes in the number of MHC-II⁺ immune cells in the colon tissue, which along with reduced lymphatic competence would favor immune dysfunction in the tissue. These findings help expand our understanding of the effects of space flight on various organ systems. It also points out potential issues that have not been closely examined and have to potential for the need of countermeasure development.

ID: 96: CINOBUFOTALIN AS A NOVEL AGENT TO INHIBIT IN-VITRO EPITHELIAL OVARIAN CANCER CELL PROLIFERATION, MIGRATION AND INVASION

Objective

Cinobufotalin (CINO), a cardiotonic steroid (CTS) or bufadienolide, is extracted from the skin secretions of giant toads and is utilized in traditional Chinese medicine (Chan Su). CINO has been used as a cardiotonic, diuretic and a hemostatic agent. Our lab is familiar with CINO and has shown it to inhibit cytotrophoblast cells function. Recently, it has been shown that CINO also inhibits the lung cancer cell function, and has been further implicated in other disease processes. In the present study, we propose to pursue this potential application of CINO using ovarian tumor cell line SK-OV-3.

Study Design

We evaluated the in-vitro effect of CINO on ovarian cancer cell line SK-OV-3. Cells were treated with 0.1, 1, 5, and 10 µM CINO. Cell proliferation was measured using a CellTiter Assay (Promega), which is a colorimetric method for determining the number of viable cells. Cell migration was measured using a CytoSelect Assay (Cell Biolabs). Cell invasion was measured using a FluoroBlok Assay (BD). Cell viability was measure using a CellTiter Assay (Promega). Cell cycle progression was evaluated by a Cell Cycle Phase Determination Kit (Cayman Chemical) and apoptosis was evaluated by an Apoptotic Blebs Assay Kit (Cayman Chemical). Cell cycle arrest and apoptotic signaling was determined by fluorescence-activated cell sorting (FACS) analysis.

Results

CINO at ≥0.5 µM inhibited SKOV-3 cell proliferation, migration, and invasion (p<0.05). There was a higher (p<0.05) percentage of S phase cells in groups treated with CINO at 0.5 µM. CINO at ≥0.5 µM down regulated expression of PCNA and caused cell death.

Conclusion

This data demonstrates that CINO impairs SK-OV-3 cell function via cell cycle arrest and apoptotic signaling. These findings demonstrate the complex nature of this compound. Not only is CINO directly modulating the actions of the Na/K ATPase through classic mechanism of cardiotonic steroids, but is also directly influencing the nuclear expression of proteins involved in cell cycle progression and DNA repair. Additional investigational studies looking into the molecular pathways involved in altering cell cycle and entry into apoptosis are warranted.

In conclusion, we have shown CINO to impair SK-OV3 cell function via cell cycle arrest and apoptotic signaling and suggest that CINO might be further investigated as a novel anti-ovarian cancer agent.

ID: 71: PRAVASTATIN PROTECTS A SW-71 CYTOTROPHOBLAST CELL LINE FROM A HYPERGLYCEMIA-INDUCED PREECLAMPSIA PHENOTYPE

Objective

An increasing level of evidence supports the utility of pravastatin as prevention against preeclampsia (preE). We previously demonstrated a hyperglycemia induced cytotrophoblast (CTBs) dysfunction characteristic of a preE-like phenotype and sought to demonstrate the utility of pravastatin in rescuing CTBs from this hyperglycemia induced dysfunction.

Methods

Human CTBs were treated with 100, 150, 200, 300, or 400 mg/dL glucose for 48 hrs. Cells were treated with pravastatin (1 ug/mL) either alongside or 2 hrs prior to glucose exposure. Some cells were treated with D-Mannitol as a negative control for glucose exposure. Cell migration was performed by Matrigel migration assay kit according to manufacturer protocol. Cell lysates were utilized to evaluate the mRNA expression of urokinase plasminogen activator (uPA) and plasminogen activator inhibitor 1 (PAI-1), while also assessing proliferating cell nuclear antigen (PCNA) and p38 MAPK phosphorylation by western blot. Levels of vascular endothelial growth factor (VEGF), placental growth factor (PlGF), soluble fms-like tyrosine kinase-1 (sFlt-1), soluble endoglin (sEng) and interleukin 6 (IL-6) were measured in culture media using ELISA kits. Statistical comparisons were performed using analysis of variance with Duncan's post hoc test.

Results

Hyperglycemia inhibited CTBs migration by down-regulating uPA, PAI-1, PCNA and up-regulating p38 phosphorylation in cells treated with >150 mg/dL glucose compared to basal (100 mg/dL) (*p<0.05 for each). Secretion of sFlt-1, sEng and IL-6 were increased while VEGF and PIGF were decreased in CTBs treated ≥150 mg/dl of glucose (*p<0.05 for each). Both pravastatin pretreatment and co-treatment significantly rescued CTBs migration, up-regulating uPA, PAI-1, PCNA, down-regulating p38 phosphorylation, and correcting the angiogenic profile of CTBs (p<0.05 for each). D-Mannitol showed no osmotic effect on CTBs.

Conclusions

Pravastatin mitigates the hyperglycemia-induced dysfunction of CTBs by attenuating the glucose-induced anti-proliferative, anti-migratory, anti-invasive and anti-angiogenic phenotype similar to that seen in Preeclampsia. This study supports the potential for pravastatin use on CTBs development early in pregnancy and the importance of continuing research of pravastatin in preE prevention.

ID: 69: MARINOBUFAGENIN-INDUCED ANTI-ANGIOGENIC MILIEU IN CYTOTROPHOBLASTS IS ATTENUATED BY NOVEL ANTI-MBG ANTIBODIES

Preeclampsia (PreE) is a hypertensive pregnancy disorder, which occurs in approximately 10% of all gestations. Recently, a digitalis-like factor, marinobufagenin (MBG) has been implicated as a causative factor in preE. We demonstrated that MBG inhibits the proliferation, migration, and invasion of cytotrophoblast (CTB) cells. We have identified a novel human monoclonal antibody with higher specificity than Digibind for MBG. We assessed the attenuation of MBG-induced CTBs dysfunction by three anti-MBG antibodies: 206–208, H1L2, and 3e9.

Methods

A panel of anti-MBG antibodies with potential as human therapeutic agents was developed by Panorama Research, Inc.; Sunnyvale, CA (206–208, H1L2). H1L2 was a humanized version of previously described anti-MBG murine antibody 3e9. 206–208 was identified in a human phage antibody library. Human CTBs were treated with DMSO (vehicle) or 0.1, 1, 10 or 100 nM of MBG for 48 h. Some cells were pretreated with 206–208, H1L2, or 3e9 for 2h, while others were co-treated with these antibodies prior to MBG treatment. Culture media were collected for analysis of pro-angiogenic and anti-angiogenic factors. Cell viability was measured using a CellTiter Assay kit. Cell lysates were utilized to evaluate the expression of proliferating cell nuclear antigen (PCNA) and p38 MAPK phosphorylation by western blot. Levels of vascular endothelial growth factor (VEGF), placental growth factor (PlGF), soluble fms-like tyrosine kinase-1 (sFlt-1), and soluble endoglin (sEng) were measured in culture media using ELISA kits. Statistical comparisons were performed using analysis of variance with Duncan's post hoc test.

Results

MBG down-regulated PCNA and up-regulated p38 phosphorylation in CTBs treated with ≥1 nM MBG compared to basal (DMSO treatment) (*p<0.05 for each). Secretion of sFlt-1 and sEng were increased, while VEGF and PIGF were decreased in CTBs treated with ≥1.0 nM MBG (*p<0.05 for each). Both anti-MBG antibodies pretreatment and co-treatment significantly up-regulated PCNA and down-regulated p38 phosphorylation, and corrected the angiogenic profile of CTBs (p<0.05 for each). The anti-proliferative and anti-angiogenic effects of MBG were not due to a cytotoxic effect, as evaluated by a cell viability assay. MBG at 0.1 nM had no effect.

Conclusions

We found that all 3 anti-MBG antibodies attenuate MBG-induced anti-proliferative and anti-angiogenic milieu in cultured CTBs. Here we describe for the first time two fully human anti-MBG antibodies, which can be targeted as therapeutic agents for the development of innovative treatment strategies for preE and potentially other disorders involving aberrant MBG signaling.

ID: 105: COMPARISON OF PLACENTAL AND PLASMA SOLUBLE (PRO)RENIN RECEPTOR IN NORMAL AND PREECLAMPTIC PREGNANCY

Objective

Preeclampsia (preE), a syndrome of hypertension and proteinuria. Most recently it was demonstrated that high circulating levels of soluble (pro) renin receptor s(P)RR at delivery were associated with preE. In this study the placental expression of (P)RR were evaluated in preE patients and in a rat model of preE as well as in nonhuman primates. We also evaluated the circulatory levels of s(P)RR.

Study Design

(1) Placental samples were collected from 20 NP and 20 preE consenting patients in an IRB approved prospective study. (2) An established rat model of preE and NP rats (n=10 each) were used. (3) The placental samples from squirrel monkey (NP; n=10) and owl monkey (both early and term, NP, n=1) were collected. The (P)RR expression were measured both by western blotting (WB) and Immunohistochemistry (IHC) using anti-ATP6IP2. The levels of serum s(P)RR were measured by ELISA.

Results

The placental expression of (P)RR were higher (p<0.05) in preE compared to NP both in patients and rat model. The s(P)RR levels were higher in preE (preE patients: 29.2±4.5; PDS rats: 16.9±1.9 ng/mL) compared to NP (NP human: 19.3±4.2; NP rats: 10.4±3.7 ng/mL). The early placenta of owl monkey expressed higher (P)RR compared to term and were expressed in squirrel monkey placentas.

Conclusions

These data suggest that increased expression of (P)RR in the placenta are related to the occurrence of preE in both patients and rat models. These data also reconfirmed that the high level of circulatory s(P)RR is associated with preE. The higher expression of (P)RR in early owl monkey in compare to term placenta suggests that the (P)RR is important for normal placental development. The expression of (P)RR in nonhuman primates reveals the approach of future studies on owl monkey and squirrel monkey preE models.

ID: 45: EVALUATION OF CELLULAR MECHANISMS BY WHICH CINOBUFOTALIN INHIBITS OVARIAN CANCER CELL LINES FUNCTION

Objective

Cinobufotalin (CINO), a cardiotonic steroid (CTS) or bufadienolide, is extracted from the skin secretions of the traditional Chinese medicine giant toads (Chan su). CINO has been used as a cardiotonic, diuretic and a hemostatic agent. Previously we have shown that CINO inhibits the cytotrophoblast cell function. Recently other study has shown that CINO inhibits A549, a lung cancer cell function. In this study, we assessed the effect of CINO on three different ovarian cancer cell lines; SK-OV-3, CRL-1978 and CRL-11731 to confirm whether the effect of CINO is cell specific.

Study Design

We evaluated the effect of CINO on three ovarian cancer cells SK-OV-3, CRL-1978, and CRL-11731 function in vitro. Each Cell lines were treated with different concentrations of CINO (0.1, 1, 5 and 10 µM). For each cell line cell proliferation, migration and invasion were measured by using a CellTiter Assay (Promega), Cytoselect Assay (Cell Biolabs) and by using a FluoroBlock Assay (BD) respectively. Proliferating Cell Nuclear Antigen (PCNA) was also evaluated in cell lysates of CINO treated these 3 ovarian cancer cells by western blot analysis. Cell Cycle arrest and Cell viability were determined by fluorescence-activated cell sorting (FACS) analysis. We also performed Annexin V staining on CINO treated these 3 ovarian cancer cell lines by immunofluorescence to evaluate the pro-apoptotic protein expression. In addition mitochondrial membrane potential has also been measured for all these 3 ovarian cell lines after CINO treatment using MMP kit, by FACS analysis.

Results

Concentration of CINO at 0.5 µM inhibit SK-OV-3, CRL-1978, and CRL-11731 ovarian cancer cells proliferation, migration and invasion without cell death and loss of cell viability but cell viability differs for each cell line. Each cell lines differ in response to CINO doses for PCNA expression as well as Annexin V pro-apoptotic protein expression. CINO decreases mitochondrial membrane potential for SK-OV-3 but for CRL-1978 and CRL-11731 increases in response to CINO treatment.

Conclusion

CINO is cell specific, as each cancer cell line responds differently. These data demonstrate that the mode of action of CINO is different on these 3 types of ovarian cancer cells.

ID: 104: CINOBUFOTALIN HINDERS CYTOTROPHOBLASTS FUNCTION VIA CELL CYCLE ARREST

Objective

Preeclampsia (preE) is a hypertensive disorder of pregnancy. Cardiotonic steroids (CTS) are endogenous inhibitors of Na+/K+ ATPase and at least one CTS, marinobufagenin (MBG), is elevated in preE prior to the development of the syndrome in rats with preE. MBG and ouabain impair cytotrophoblast (CTB) function, which is critical for placental development.

Study Design

We evaluated the effect of a CTS, cinobufotalin (CINO), on CTB cell function in vitro.

Results

CINO at ≥1 nM inhibited CTB cell proliferation, migration, and invasion (p<0.05) but had no effect on cell viability. There was a higher (p<0.05) percentage of G0/G1 phase cells in groups treated with CINO at ≥1 nM. CINO caused an increase in stress signaling p38 MAPK and a positive annexin-V staining in CTB cells, indicating the activation of apoptotic signaling. However, the CINO induced apoptotic signaling was prevented by p38 inhibition.

Conclusion

This data demonstrates that CINO impairs CTB cell function via cell cycle arrest and apoptotic signaling.

ID: 18: DIABETES AND PRE-ECLAMPSIA: A RETROSPECTIVE CROSS-SECTIONAL STUDY OF PREGNANCY OUTCOMES

Objective

Despite growing knowledge of the pathophysiology leading to the development of preeclampsia (PreE) and diabetes mellitus (DM), the interaction between the two disease processes needs to be further examined. This study compared normal pregnancies to those complicated with preE, gestational diabetes mellitus (GDM), and/or pre-existing diabetes in order to assess the effects of elevated glucose on placental development and its potential role in the pathogenesis of preE.

Methods

The chart review was performed in an IRB approved retrospective cross-sectional study of live born singleton deliveries. A total 621 subjects were randomly selected from deliveries occurring between 2008 to 2011 at Baylor Scott & White Memorial hospital. Statistical analysis was performed using Duncan's post-hoc test and ANOVA.

Results

Patients who developed preE had higher systolic and diastolic blood pressures than those who did not develop preE (p<0.05). Patients with either pre-existing diabetes or GDM were older. There was no difference among groups for gravidity (p=0.21) with an average gravidity of 2.7 (1.8SD) for 621 subjects and a range of 1 to 14 pregnancies. Patients with preE delivered earlier in pregnancy than those without preE regardless of diabetes status. However, those with preE and pre-existing diabetes delivered significantly earlier at 35.0+/−0.4 than the other two preE groups (*p<0.05 for each), suggesting more severe condition. Additionally, patients with pre-existing diabetes who developed preE delivered smaller babies than those with pre-existing diabetes without preE (1.00±0.03, p<0.05 for each). However, the development of GDM did not result in smaller babies for those pregnancies with preE.

Conclusions

The development of preE in those with pre-existing diabetes led to growth restriction and more severe disease as evidenced by lower birth weights and earlier gestational ages at delivery. These differences were not seen in GDM pregnancies. This supports the concept that elevated glucose levels during placental development in the first trimester may alter the placenta and lead to restriction later in pregnancy when a second stimulus triggers preE.

IL-1β reduces tonic contraction of mesenteric lymphatic muscle cells, with the involvement of cycloxygenase-2 and prostaglandin E2

BACKGROUND AND PURPOSE

The lymphatic system maintains tissue homeostasis by unidirectional lymph flow, maintained by tonic and phasic contractions within subunits, 'lymphangions'. Here we have studied the effects of the inflammatory cytokine IL-1β on tonic contraction of rat mesenteric lymphatic muscle cells (RMLMC).

EXPERIMENTAL APPROACH

We measured IL-1β in colon-conditioned media (CM) from acute (AC-CM, dextran sodium sulfate) and chronic (CC-CM, T-cell transfer) colitis-induced mice and corresponding controls (Con-AC/CC-CM). We examined tonic contractility of RMLMC in response to CM, the cytokines h-IL-1β or h-TNF-α (5, 10, 20 ng·mL(-1) ), with or without COX inhibitors [TFAP (10(-5)  M), diclofenac (0.2 × 10(-5)  M)], PGE2 (10(-5)  M)], IL-1-receptor antagonist, Anakinra (5 μg·mL(-1) ), or a selective prostanoid EP4 receptor antagonist, GW627368X (10(-6) and 10(-7)  M).

KEY RESULTS

Tonic contractility of RMLMC was reduced by AC- and CC-CM compared with corresponding control culture media, Con-AC/CC-CM. IL-1β or TNF-α was not found in Con-AC/CC-CM, but detected in AC- and CC-CM. h-IL-1β concentration-dependently decreased RMLMC contractility, whereas h-TNF-α showed no effect. Anakinra blocked h-IL-1β-induced RMLMC relaxation, and with AC-CM, restored contractility to RMLMC. IL-1β increased COX-2 protein and PGE2 production in RMLMC.. PGE2 induced relaxations in RMLMC, comparable to h-IL-1β. Conversely, COX-2 and EP4 receptor inhibition reversed relaxation induced by IL-1β.

CONCLUSIONS AND IMPLICATIONS

The IL-1β-induced decrease in RMLMC tonic contraction was COX-2 dependent, and mediated by PGE2 . In experimental colitis, IL-1β and tonic lymphatic contractility were causally related, as this cytokine was critical for the relaxation induced by AC-CM and pharmacological blockade of IL-1β restored tonic contraction.

Measurement of shear stress-mediated intracellular calcium dynamics in human dermal lymphatic endothelial cells

The shear stress applied to lymphatic endothelial cells (LEC) by lymph flow changes dramatically under normal conditions as well as in response to disease conditions and immune reactions. In general, LEC are known to regulate the contraction frequency and strength of lymphatic pumping in response to shear stress. Intracellular calcium concentration ([Ca(2+)]i) is an important factor that regulates lymphatic contraction characteristics. In this study, we measured changes in the [Ca(2+)]i under different shear stress levels and determined the source of this calcium signal. Briefly, human dermal LEC were cultured in custom-made microchannels for 3 days before loading with 2 µM fura-2 AM, a ratiometric calcium dye to measure [Ca(2+)]i. Step changes in shear stress resulted in a rapid increase in [Ca(2+)]i followed by a gradual return to the basal level and sometimes below the initial baseline (45.2 ± 2.2 nM). The [Ca(2+)]i reached a peak at 126.2 ± 5.6 nM for 10 dyn/cm(2) stimulus, whereas the peak was only 71.8 ± 5.4 nM for 1 dyn/cm(2) stimulus, indicating that the calcium signal depends on the magnitude of shear stress. Removal of the extracellular calcium from the buffer or pharmocological blockade of calcium release-activated calcium (CRAC) channels significantly reduced the peak [Ca(2+)]i, demonstrating a role of extracellular calcium entry. Inhibition of endoplasmic reticulum (ER) calcium pumps showed the importance of intracellular calcium stores in the initiation of this signal. In conclusion, we demonstrated that the shear-mediated calcium signal is dependent on the magnitude of the shear and involves ER store calcium release and extracellular calcium entry.

Increased susceptibility of aging kidney to ischemic injury: identification of candidate genes changed during aging, but corrected by caloric restriction

Aging is associated with an increased incidence and severity of acute renal failure. However, the molecular mechanism underlying the increased susceptibility to injury remains undefined. These experiments were designed to investigate the influence of age on the response of the kidney to ischemic injury and to identify candidate genes that may mediate this response. Renal slices prepared from young (5 mo), aged ad libitum (aged-AL; 24 mo), and aged caloric-restricted (aged-CR; 24 mo) male Fischer 344 rats were subjected to ischemic stress (100% N(2)) for 0-60 min. As assessed by biochemical and histological evaluation, slices from aged-AL rats were more susceptible to injury than young counterparts. Importantly, caloric restriction attenuated the increased susceptibility to injury. In an attempt to identify the molecular pathway(s) underlying this response, microarray analysis was performed on tissue harvested from the same animals used for the viability experiments. RNA was isolated and the corresponding cDNA was hybridized to CodeLink Rat Whole Genome Bioarray slides. Subsequent gene expression analysis was performed using GeneSpring software. Using two-sample t-tests and a twofold cut-off, the expression of 92 genes was changed during aging and attenuated by caloric restriction, including claudin-7, kidney injury molecule-1 (Kim-1), and matrix metalloproteinase-7 (MMP-7). Claudin-7 gene expression peaked at 18 mo; however, increased protein expression in certain tubular epithelial cells was seen at 24 mo. Kim-1 gene expression was not elevated at 8 or 12 mo but was at 18 and 24 mo. However, changes in Kim-1 protein expression were only seen at 24 mo and corresponded to increased urinary levels. Importantly, these changes were attenuated by caloric restriction. MMP-7 gene expression was decreased at 8 mo, but an age-dependent increase was seen at 24 mo. Increased MMP-7 protein expression in tubular epithelial cells at 24 mo was correlated with the gene expression pattern. In summary, we identified genes changed by aging and changes attenuated by caloric restriction. This will facilitate investigation into the molecular mechanism mediating the age-related increase in susceptibility to injury.

Protein transfection of intact microvessels specifically modulates vasoreactivity and permeability

Precise regulation of microvascular tone and barrier function is essential for proper coronary perfusion and performance. Agonist-induced alterations in either or both of these functions ultimately lead to microcirculatory dysfunction and cardiac insufficiency. Two important pathways involved in regulating vasomotor response and barrier function are the activation of nitric oxide synthase (NOS) and upregulation of protein kinase C (PKC). To date, studies of these two signaling proteins have relied mainly on pharmacological approaches. Unfortunately, the specificity of various inhibitors can be cause for concern. In order to address this problem, a protein transfection technique we developed for cultured endothelial cells has been modified and applied to isolated, intact coronary microvessels. Our results from green fluorescent protein transfection in arterioles and venules showed that this procedure could be used to introduce proteins into the microvascular wall. By transfecting inhibitor peptides against NOS and PKC into coronary arterioles and venules, we have been able to determine the specific roles of these two enzymes in vasodilation and hyperpermeability responses.

Physiology of human lymphatic contractility: a historical perspective

The lymphatic system is a transport system that has important roles in fluid/macromolecule homeostasis, lipid absorption, metastasis and immune function. It accomplishes these roles via the generation of a regulated lymph circulation which is dependent upon valves and pumps to overcome the normal fluid pressure gradients. Lymphatic contractility plays crucial roles in the regulation and generation of lymph transport. Whereas our understanding of lymphatic contractility in humans is somewhat limited, a number of studies both in situ and in vitro have provided important insights into the presence and modulation of lymphatic contractility. These studies have clearly demonstrated that lymphatic vessels from a number of different human tissues possess both tonic and phasic changes in contractility. These changes in contractility are presumably involved in the generation and regulation of lymph flow. It has been shown that human lymphatic contractility can be influenced by a number of neural and humoral agents as a means to control lymph transport. However our understanding of the physical and chemical factors which regulate both the spontaneous pumping activity and the vessel tone are more limited. An understanding of thefactors which regulate human lymph transport could provide valuable information on human biology that could be of benefit to the treatment and prevention of diseases.

[Contractions of the lymphangion under low filling conditions and the absence of stretching stimuli. The possibility of the sucking effect]

Regulation of the function of the lymphatic pump is tightly connected to the degree of filling of the lymphangion. This mechanism is one of the principle ways that the lymphatics self-regulate lymph transport. But interpretation of the causes and consequences of this regulation is still far from perfect. The issue of whether automatism of electrical activity of the lymphatic smooth muscle cells or the distension of the cell membranes first causes depolarization, is a principal question which needs answering in order to understand the control of lymph transport. In our experiments with perfused isolated bovine mesenteric lymphangions, different values of lymph pressure were simulated. For this purpose, lowfrequency sinusoidal fluctuations of the input pressure were applied to lymphangions under conditions of regulated filling. A poor correlation was seen between lymph pressure fluctuations and lymphangion contractions, as well as between the rate of lymphangion filling and contractions. We observed stable spontaneous contractions of both bovine and rat mesenteric lymphangions at 0 cm of water intralymphatic pressure, and in the absence of distension stimuli (both radial and axial stretch). Under conditions of low filling, contractions of bovine lymphangions produced negative intralymphatic pressure and a suction effect. The automatism is an inherent feature of the lymphatic smooth muscle cells. Distension of the lymphangion modulates the electrical characteristics of the membranes and thus the contractile mechanisms in lymphangions.

Role of phospholipase C, protein kinase C, and calcium in VEGF-induced venular hyperpermeability

We previously demonstrated that vascular endothelial growth factor (VEGF)-elicited increase in the permeability of coronary venules was blocked by the nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). The aim of this study was to delineate in more detail the signaling pathways upstream from NO production in VEGF-induced venular hyperpermeability. The apparent permeability coefficient of albumin (Pa) and endothelial cytosolic Ca2+ concentration ([Ca2+]i) were measured in intact perfused porcine coronary venules using fluorescence microscopy. VEGF (10(-10) M) induced a two- to threefold increase in Pa, which was blocked by a monoclonal antibody directed against the VEGF receptor Flk-1/KDR, the phospholipase C (PLC) antagonist U-73122, or the protein kinase C (PKC) antagonist bisindolylmaleimide (BIM). In 12 venules that displayed the [Ca2+]i response to bradykinin (10(-6) M) and ionomycin (10(-6) M), only 4 vessels responded to VEGF with a transient increase in [Ca2+]i. Furthermore, Western blot analysis of cultured human umbilical vein endothelial cells showed that VEGF increased tyrosine phosphorylation of PLC-gamma and serine phosphorylation of endothelial constitutive NO synthase (ecNOS). The hyperphosphorylation of PLC-gamma was greatly attenuated by the KDR receptor antibody and U-73122, but not by BIM or L-NMMA. In contrast, U-73122 and BIM were able to inhibit VEGF-elicited serine phosphorylation of ecNOS. The results suggest that VEGF induces venular hyperpermeability through a KDR receptor-mediated activation of PLC. In turn, ecNOS is activated by PLC-mediated PKC and/or cytosolic Ca2+ elevation stimulation.

Lymphatic microcirculation

OBJECTIVE

The importance of the lymphatic system during inflammatory response is underscored by the discovery that numerous inflammatory mediators alter the lymph pump. Inhibition of the lymph pump will reduce the lymphatic outflow from the interstitial space and thus initiate the lymphatic generation of edema. We evaluated the effect that reactive oxygen metabolites have on the contractile activity of lymphatic vessels.

METHODS

Reactive oxygen metabolites are produced during inflammation and have been implicated in a number of pathologies. Exposure to reactive oxygen metabolites inhibited the lymph pump flow in a time- and concentration-dependent fashion by decreasing contraction frequency, strength, and propagation.

RESULTS

Substance P (SP) (1.0 microM) produced the following changes (% control): reductions in diastolic diameter (56%), systolic diameter (47%), and stroke volume of the lymph pump (62%); a large increase in lymphatic contraction frequency (640%); and a modest increase in lymph pump flow (43%). SP also stimulated quiescent vessels to develop typical contraction-relaxation patterns. These effects may serve to minimize the formation of edema in the face of inflammatory edemagenic conditions that are produced by SP.

CONCLUSIONS

We concluded that reactive oxygen metabolites significantly inhibit the active lymph pump and that this inhibition could be an important contributing factor in the formation of interstitial edema during inflammation We have also determined the effects of a putative mediator of inflammation (SP) on the lymphatic pumping function.

Interaction of neutrophils and endothelium in isolated coronary venules and arterioles

This study reports measurements of porcine neutrophil dynamics in isolated microvessels. Porcine coronary venules and arterioles were isolated, cannulated, and perfused with fluorescently labeled neutrophils at a series of flow velocities. In venules (62.50 +/- 5.41 microns diam) under control conditions, rolling neutrophils were often observed at intraluminal flow velocities ranging from 600 to 6,000 microns/s, and the rolling fraction varied inversely as a function of flow velocity. There was no significant adherence under the control conditions at any of the various flow velocities. Pretreatment of the neutrophils with human recombinant complement 5a (C5a, 10(-8) M) increased adherence at low flow velocities but did not alter the rolling fraction. In contrast to venules, rolling neutrophils were not observed in arterioles (58.80 +/- 5.6 microns diam). Furthermore, neutrophils that were pretreated with C5a did not adhere to the arteriolar endothelium even at low flow velocities. We suggest that 1) isolated microvessels perfused with fluorescently labeled neutrophils are suitable models for the study of the interaction between neutrophils and the microvascular endothelium, 2) shear force plays an important role in neutrophil rolling in coronary venules but is not the major factor that prevents neutrophil rolling and adherence in arterioles, and 3) C5a causes neutrophil adherence in venules but not in arterioles, indicating that different mechanisms underlie the interaction between neutrophils and endothelium in venules and arterioles.

Inhibition of the active lymph pump in rat mesenteric lymphatics by hydrogen peroxide

The lymphatic system plays an important role in the regulation of fluid and macromolecular exchange. It is a key "safety factor" against the formation of gross edema. Spontaneous contractions in collecting lymphatics of the rat intestine are necessary for the normal transportation of lymph. Hydrogen peroxide is one of the compounds released in inflammation. Therefore, the effects of H2O2 on the pumping activity of spontaneously contracting lymphatics were evaluated in the anesthetized rat (n = 16). Diameter oscillations of the mesenteric collecting lymphatics were monitored before and after the application of H2O2 (4 and 37 microM). The activity of the lymph pump was evaluated using: contraction frequency (F), stroke volume (SV), ejection fraction (EF), and lymph pump flow (LPF). These parameters were determined from the lymphatic diameter tracings. The following changes in lymphatic activity were seen after a 20 minute exposure to 37 microM H2O2: 1) F declined 85%, from 11.6 +/- 1.5 to 1.9 +/- 1.9 cpm. 2) SV fell over 93%. 3) EF decreased 93%, from 0.57 +/- .07 to 0.05 +/- .04. 4) LPF fell dramatically (> 95%) from 41.5 +/- 10.5 to 2.6 +/- 2.5 nl/min. In conclusion, H2O2 produced an intense inhibition of the active lymph pump and it is possible that the inhibition of the active pump contributes to the edema which occurs during inflammation.

Permeability to albumin in isolated coronary venules

This study reports measurements of albumin permeability in isolated coronary venules. The isolated microvessel technique allows the quantification of transmural exchange of macromolecules under tightly controlled physical and chemical conditions. Transvenular exchange of albumin was studied in isolated coronary venules during alterations in filtration rate caused by changes in intravascular pressure. The apparent permeability coefficient of albumin (Pa) at an intraluminal pressure of 11 cmH2O was 3.92 +/- 0.43 x 10(-6) cm/s. Elevating intraluminal pressure to 16 and 21 cmH2O increased Pa to 5.13 +/- 0.57 x 10(-6) and 6.78 +/- 0.66 x 10(-6) cm/s, respectively. Calculation of the true diffusive permeability coefficient of albumin (Pd) at zero filtration rate was 1.54 x 10(-6) cm/s. The product of hydraulic conductance (Lp) and (1 - sigma), where sigma is the solute reflection coefficient, was 3.25 x 10(-7) cm.s-1 x cmH2O-1. At a net filtration pressure of 4-5 cmH2O, diffusion accounts for > 60% of total albumin transport across the venular wall. Transmural albumin flux is very sensitive to filtration rate, rising 6.7% for each cmH2O elevation of net filtration pressure. At 11 cmH2O net filtration pressure, convection accounts for nearly 70% of net albumin extravasation from the venular lumen. We suggest that the isolated coronary venule is a suitable preparation for the study of solute exchange in the heart.

Histamine increases venular permeability via a phospholipase C-NO synthase-guanylate cyclase cascade

In this study, we hypothesized that histaminergic increases in venular permeability result from a cascade triggered by activation of phospholipase C (PLC), inducing the synthesis of nitric oxide (NO) and activating guanylate cyclase. The apparent permeability coefficient to albumin (Pa) was measured in isolated porcine coronary venules subjected to constant flow and hydrostatic and oncotic pressures. Histamine (2.5, 5, and 10 microM) transiently and progressively increased Pa. The PLC inhibitor 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate (NCDC; 100 microM) decreased baseline permeability and abolished the effect of histamine. The NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 10 microM) and the guanylate cyclase inhibitor 6-anilinoquinoline-5,8-quinone (LY 83583; 10 microM) also blocked the histamine-induced hyperpermeability. L-Arginine (3 mM) reversed the inhibition by L-NMMA. NG-monomethyl-D-arginine did not influence the effect of histamine. Furthermore, sodium nitroprusside (10 microM) augmented Pa by two- to threefold; this effect was blocked in the presence of LY 83583 but not altered in the presence of NCDC. The results suggest that histamine increases coronary venular permeability by a direct action on the venular endothelial cells through a PLC-NO synthase-guanylate cyclase-signaling cascade.

Distribution, propagation, and coordination of contractile activity in lymphatics

The propagation and coordination of lymphatic contractions were studied in the mesentery of the rat small intestine using in situ microscopic observation. Indexes of lymphatic diameter were simultaneously measured at two adjacent lymphangions in spontaneously contracting lymphatics (n = 51). Diameter index, contraction frequency, and the percentage of the intersegmental contractions that were propagated and coordinated (PP) were determined at both sites. The conduction velocity of the contractile activity and the percentage of the coordinated contractions that were propagated both antegrade to the direction of lymph flow and retrograde to the flow stream were determined. The results indicate that 1) 80-90% of the lymphatic contractions in the vessels we evaluated were propagated, 2) the wave of contractile activity propagated both centrally and peripherally, and 3) the conduction velocity of the contractile activity was approximately 4-8 mm/s. We tested the hypothesis that gap junctional communication is responsible for the coordination of the contractile event. To accomplish this, we used the gap junction blockers n-heptanol and oleic acid. PP was 90 +/- 4% under normal conditions and fell to a minimum value of 55 +/- 7% during the gap junction blockade. These results indicate that gap junctional communication played an important role in the propagation and coordination of contractions that occurred in spontaneously active lymphatics.

Stretch-induced increases in intracellular calcium of isolated vascular smooth muscle cells

Vascular smooth muscle responds to stretch with an increase in active force development. To investigate the role of Ca2+ in this response, we used the fluorescent dye fura-2 to quantitate changes in cytosolic Ca2+ in single, vascular smooth muscle cells during rapid stretch. Cells were enzymatically dispersed from pig coronary arteries, loaded with fura-2/AM, and studied using a digital-imaging microscope. Stretch of individual cells was accomplished by attachment with suction to two patch-type micropipettes to apply force to the ends of the cell. Stretch induced the release of Ca2+ from intracellular stores as well Ca2+ influx across the plasma membrane. In physiological saline solution containing 1.5 mM Ca2+, intracellular calcium increased with cell stretch in a sigmoidal fashion. This relationship was shifted upward in 10 mM Ca2+ bath solution and abolished after several minutes in Ca(2+)-free solution. The dihydropyridine Ca2+ channel blocker nifedipine, in doses sufficient to completely block inward Ca2+ current, produced only a partial block of the sustained stretch-induced intracellular Ca2+ response. It is concluded that in isolated pig coronary arterial smooth muscle cells, stretch-induced Ca2+ influx occurs in part via a nifedipine-resistant pathway, which may be a stretch-activated cation channel.

Flow modulates coronary venular permeability by a nitric oxide-related mechanism

This study demonstrates that flow velocity modulates coronary venular permeability to albumin. Apparent permeability coefficients of albumin (Pa) were measured in isolated cannulated coronary venules ranging from 30 to 70 microns in diameter. Hydrostatic and oncotic pressures were controlled while the intraluminal flow velocity was varied. Pa at an intraluminal hydrostatic pressure of 12 cmH2O and a flow velocity of 7 mm/s was 4.01 +/- 0.53 x 10(-6) cm/s. Increasing flow velocity to 10 and 13 mm/s augmented the permeability by 33 +/- 14 and 48 +/- 14%, respectively. The nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA) (10(-5) M), decreased baseline Pa and abolished the flow-induced permeability changes. Administration of L-arginine (3 x 10(-3) M), a physiological precursor of nitric oxide which reverses the effect of L-NMMA, restored the relationship between flow and permeability. From these results we conclude that 1) flow velocity should be considered as a physical force that potentially modulates permeability of venular exchange vessels in the heart and 2) flow modulates coronary venular permeability via the production of nitric oxide.

Effects of f-Met-Leu-Phe-induced inflammation on intestinal lymph flow and lymphatic pump behavior

Previous studies in the literature indicate that intraenteric placement of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe) evokes an intestinal inflammatory response characterized by an accumulation of interstitial fluid and increased lymph flow. Furthermore, it is known that movement of lymph away from the intestine is dependent on the rhythmic pumping of lymph by collecting lymphatics in the mesentery. The purpose of the present study was to determine whether the f-Met-Leu-Phe-induced increase in lymph formation is countered by an increase in lymphatic pump efficiency. Male Sprague-Dawley rats were anesthetized, and a segment of ileum with adjacent mesentery was exteriorized. The mesentery was positioned over an optical window, and a 100-microns collecting lymphatic was selected for study. The preparation was transferred to a video microscope, and the activity of the lymphatic pump was monitored under control conditions and during intraluminal infusion of 1 microM f-Met-Leu-Phe. Lymph propulsion by the lymphatic pump was calculated from the product of stroke volume and contraction frequency. In one group of animals, total lymph flow was determined by cannulating the lymphatic draining the ileal segment. Total lymph flow increased following f-Met-Leu-Phe placement in the intestine. The increased lymph flow was paralleled by a rise in lymphatic pumping. The rise in lymph propulsion by the lymphatic pump resulted exclusively from an increased stroke volume, inasmuch as contraction frequency did not change. The results of the present study suggest that activation of the lymphatic pump during acute inflammation may be important in preventing interstitial edema.

Oxygen radicals, enzymes, and fluid transport through pericardial interstitium

The interstitium is the final link in the transportation of nutrients from the bloodstream to the individual cells of an organism. To assess interstitial fluid transport in normal and inflamed tissue, the hydration (H, ml H2O/g dry wt) and hydraulic conductivity (Kp, 10(-8) cm2.s-1.cmH2O-1) of bovine pericardial stroma were determined. The effect of enzymes and neutrophil-derived products of inflammation on the properties of the interstitial model were determined. Samples of the pericardium were exposed separately to trypsin, elastase, hyaluronidase, collagenase, superoxide radicals, and hydrogen peroxide. After exposure, the tissues were washed repeatedly in physiological saline and equilibrated in transport chambers heated to 37 degrees C and pressurized to 50 cmH2O. Fluid flow across the tissues was monitored. A section of tissue was removed and weighed. The tissue section was subsequently dried and reweighed. Tissue thickness, H, and Kp were calculated. H and Kp of the control tissues were 2.82 +/- 0.04 and 1.71 +/- 0.07, respectively. Hydration was significantly increased (22-38%) by exposure to trypsin, elastase, collagenase, and superoxide radicals. Kp increased significantly (30-1055%) in the groups treated with trypsin, hyaluronidase, collagenase, and superoxide radicals. The inflammatory mediators generally increased the hydration and/or the hydraulic conductivity of the model. These results indicate that neutrophil-derived products could be involved in the development of interstitial edema during the inflammatory process.

Calcium measurement in isolated arterioles during myogenic and agonist stimulation

Vascular smooth muscle calcium was measured during agonist treatment or pressure-induced stimulation of the myogenic response in isolated first-order skeletal muscle arterioles. Arterioles (40-180 microns) with spontaneous tone were isolated from rat cremaster muscle and cannulated. Arterioles were loaded with the calcium-sensitive dye fura-2 and excited at 340 and 380 nm. Images of vessel fluorescence were formed with a fluorescence microscope and digitized using an image processor coupled to a low light level camera. The fluorescent images allowed individual vascular smooth muscle cells to be seen within the arteriolar wall. Fluorescent intensity of the vessel wall, expressed as the ratio of fluorescence at 340 nm/380 nm, was used to estimate changes in vessel wall calcium. Topical application of norepinephrine (10 microM) to the arterioles caused a rapid and sustained constriction of the arterioles (64% of basal diam). The calcium response was biphasic consisting of a transient spike to 271% of basal followed by a decrease to a new steady state at 143% of basal. In comparison, steady-state indolactam (1 microM) produced a similar degree of constriction without an increase in calcium. Adenosine significantly dilated (35%) the arterioles and produced a decrease (24%) in vessel wall calcium. To investigate the myogenic response, intravascular pressure was step increased from 90 to 130 cmH2O. Increasing intravascular pressure caused an initial increase in vessel diameter of approximately 5% followed by active constriction that returned diameter to basal diameter. In association with this diameter change, estimated vessel wall calcium increased rapidly 8 +/- 2% and then continued to increase more slowly and remained elevated at 10-15% above basal levels. This study demonstrates the successful application of calcium-imaging technology in isolated arterioles for study of the role of calcium in arteriolar function. Results indicate that the calcium-contraction relationship differs for different agonists and are further consistent with a role for pressure-induced increases in vascular smooth muscle calcium during the myogenic response.

Reactive oxygen metabolites inhibit spontaneous lymphatic contractions

The effects of oxygen-derived free radicals on the contractile activity of the mesenteric collecting lymphatics were evaluated in the anesthetized rat. Lymphatic contractions were monitored before, during and after the application of oxyradicals. Contraction frequency (F), stroke volume (SV), ejection fraction (EF), contraction propagation (PC), and lymph pump flow (LPF) were determined from the lymphatic diameter tracings. Oxyradicals were generated using hypoxanthine and xanthine oxidase. Exposure to oxyradicals inhibited the lymphatic pumping mechanism: 1) F fell from 15.5 +/- 0.8 to 0.8 +/- 0.7 beats/min; 2) EF went from 0.44 +/- 0.02 to 0.08 +/- 0.04; 3) PC dropped from 92 +/- 2 to 56 +/- 8%; and 4) LPF fell precipitously from 41.0 +/- 5.2 to 0.7 +/- 0.4 nl/min. The effects of the oxyradicals were attenuated by superoxide dismutase, implicating superoxide anion as one of the predominant causative agents. We conclude that oxyradicals significantly inhibit the lymph pump and that this inhibition could be a factor contributing to the formation of interstitial edema during inflammation.

Thermal effects of MR imaging: worst-case studies on sheep

The objective of this study was to provide a worst-case estimate of thermal effects of MR imaging by subjecting anesthetized unshorn sheep to power deposition at specific absorption rates (SARs) well above approved standards for periods of time in excess of normal clinical imaging protocols. A control period with no RF power was followed by 20-105 min of RF power application. Afterward, there was a 20-min or longer recovery period with no RF power. Eight sheep were given whole-body RF exposure (1.5- to 4-W/kg SAR) while rectal and skin temperatures were monitored. Four sheep were subjected to 4-W/kg head scans for an average of 75 min while temperatures of the cornea, vitreous humor, head skin, jugular vein, and rectum were measured. In head scanning experiments, skin and eye temperatures increased about 1.5 degrees C. Jugular vein temperature rose a maximum of 0.4 degrees C after an average exposure of 75 min. In whole-body exposures, elevation of rectal temperature was correlated with energy input. Deep-body temperature rises in excess of 2.0 degrees C were attained for 4-W/kg whole-body exposure periods greater than 82 min. Animals exposed for 40 min to 4 W/kg in either body coil (three sheep) or head coil (two sheep) were recovered and observed to be in good health for 10 weeks; no cataracts were found. MR power deposition at SAR levels well above typical clinical imaging protocols caused body temperature to increase. For exposure periods in excess of standard clinical imaging protocols the temperature increase was insufficient to cause adverse thermal effects. Studies in healthy humans are needed to determine whether enhanced heat-loss effector mechanisms are likely to cause deep-body temperatures to plateau at an acceptable level, and to elucidate mechanisms that determine subcutaneous temperature.

Characterization of intact mesenteric lymphatic pump and its responsiveness to acute edemagenic stress

The contractile properties of the mesenteric collecting lymphatics of the rat were analyzed under control conditions and during periods of enhanced lymph formation using in vivo microscopic techniques. Pressure and diameter were simultaneously monitored in microscopic collecting lymphatics, and lymphatic pump function was analyzed in accordance with basic principles of cardiac mechanics. The lymphatic contractile cycle was divided into two phases of systole and four phases of diastole. Under control conditions, lymphatics contracted with a frequency of 6.4 +/- 0.61 beats/min and ejected approximately 67% of their end-diastolic volume. Ten minutes after the rate of lymph formation was elevated by plasma dilution, end-diastolic diameter, contraction frequency, ejection fraction, and stroke volume increased. Pressure in the lymphatic network became less pulsatile in high lymph flow states. Contractility, an index of inotropic changes in lymphatic pump, was unaltered when lymph flow was increased by plasma dilution. Furthermore, the maximal shortening velocity of lymphatic smooth muscle did not change during periods of enhanced lymph flow. Thus it appears that passive increases in the rate of lymph formation exert few, if any, inotropic effects on the lymphatic pump. The augmented stroke volume and contraction frequency appear to result mainly from intrinsic stretch-dependent mechanisms set in motion by elevated preload. These data represent the first comprehensive characterization of both the flow-generating and muscle characteristics of intact collecting lymphatics and provide a basis for future studies on the physiological regulation of lymphatic contraction.

Physiology and pathobiology of the microcirculation

The delivery of nutrients to the tissues and the removal of waste products from the tissues is made possible by forcing a stream of blood through an arborizing network of microscopic blood vessels that comprise the microcirculation. The rapidity of the flow stream and, therefore, the rate of nutrient delivery to the tissue, is regulated by the automatic adjustment of the caliber of the precapillary arterioles that serve as the primary loci of vascular resistance. Exchange between the blood stream and the parenchymal cells occurs in capillaries and pericytic venules. Pathologic processes such as inflammation, diabetes, ischemia, and hypertension are characterized by abnormalities in microvascular structure and function.

Variations in rat mesenteric tissue thickness due to microvasculature

Studies of microvascular, tissue and lymphatic transport using microphotometric and microfluorometric techniques are potentially subject to artifact due to variations in tissue specimen thickness. Absorbance techniques utilize the Lambert-Beer law in which A = log I0/I = act, where A is absorbance, I0 is incident light intensity, I is transmitted intensity, a is an absorbance coefficient, c is concentration of substance, and t is path length. If differences in t are known to be present, then inferences of changes in c from changes in A become suspect. In microfluorometry the amount of light gathered is proportional to the number of fluorochromes in the effective cuvette, which is determined by the microscope's numerical aperture and the sample thickness. If variations in thickness are known to occur, the effective cuvette volume may be changing; therefore, inferences of changes in fluorochrome concentration from changes in intensity become suspect. Existing data suggest that rat mesentery is 15-30 microns thick, but variation over a tissue region is unknown. Our goals are to determine thickness variation in avascular, fat-free mesenteric tissue regions; thickness variation near blood vessels; and average tissue thickness. Sprague-Dawley rats were anesthetized with Inactin. Mesenteric tissue from a loop of small intestine was draped over a platform for observation; thickness was measured with an oblique microscope and a microgravimetric technique. The average variation in avascular fat-free tissue was 1.1 micron/100-microns distance, and average thickness was 17.4 microns. There was a significant increase in thickness over the microvasculature.

Lymph protein concentration in initial and collecting lymphatics of the rat

Lymph samples were obtained from villus initial and mesenteric prenodal collecting lymphatics of the anesthetized rat using standard micropuncture techniques. The protein concentrations of the lymph samples were determined using a fluorometric microassay. These procedures were performed on preparations either superfused with a modified Krebs solution or covered with paraffin oil. The protein-concentrating ability of the intestinal lymphatics was evaluated to test the osmotic theory of lymph formation. The mean initial lymph protein concentration in superfused preparations was 2.08 g/dl (SE = 0.20). The lymph protein concentration in collecting vessels in superfused preparations was 2.20 g/dl (SE = 0.19). The protein concentration from initial lymphatics in oil-covered preparation was 2.48 g/dl (SE = 0.17). The lymph protein concentration in collecting vessels in oil-covered preparations was 2.32 g/dl (SE = 0.15). The difference between initial and collecting lymph protein concentration found was an order of magnitude lower than that predicted by the osmotic theory. These results cast serious doubts on the effectiveness of the osmotic mechanism of lymph formation as it is presently defined.