Intrinsic rhythmic propulsion of lymph in the unanaesthetized sheep

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

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

Substance P and gastrin releasing peptide in bovine mesenteric lymphatic vessels: chemical characterization and action

Alcoholic extracts of bovine mesenteric lymphatic vessels were assayed for the presence of SP, GRP, VIP, PHI, GIP and NT using specific radioimmunoassays. SP and GRP immunoreactivities were detected at concentrations of 190 +/- 20 and 1,000 +/- 130 pg.g-1, respectively. No significant levels of immunoreactivity were detected for any of the other peptides. SP and GRP immunoreactivities coeluted with their synthetic counterparts from both Sephadex G-50 and reversed phase HPLC columns. Synthetic SP (10(-9)-10(-7) M) and the naturally occurring analogue of GRP, bombesin (10(-9)-10(-7) M), increased spontaneous contraction rate in isolated vessel segments. This excitatory effect was not blocked by the alpha-adrenoceptor antagonist phentolamine (3 x 10(-6) M).

Suppression of fluid pumping in isolated bovine mesenteric lymphatics by interleukin-1: interaction with prostaglandin E2

In addition to local physiological forces, the modulation of lymphatic pumping by chemical mediators may play an important role in the regulation of extravascular water in inflammation and shock. Since Interleukin-1 (IL-1) appears to be of major importance in the host's response to infection by mediating many inflammatory events, we thought it important to determine if this cytokine could affect the lymphatic circulation and in particular to ask whether IL-1 was capable of altering lymphatic pumping in response to changes in transmural pressure. Bovine lymphatic segments (6 to 8 cm in length) were cannulated at both ends and suspended in an organ bath preparation. The vessels were provided with Krebs solution from a reservoir. With no net driving pressure, a transmural pressure applied to the ducts elicited contractile activity and fluid pumping with increases in pumping up to 8 cm H2O and reductions in flow above this level of distension. Human recombinant IL-1 alpha (10(-7) to 10(-9) M) administered into the lumina of the vessels depressed pumping activity approximately 5-30% at transmural pressures between 2 and 16 cm H2O. With limited supplies, we could only assess the effects of human recombinant IL-1 beta at 10(-8) M. However, it was more potent than IL-1 alpha, inhibiting pumping at all transmural pressures with maximum suppression in the range of 70% at peak flows. The ability of IL-1 to induce prostaglandin synthesis may be one of its most important biologic functions. It is likely therefore that IL-1 and PGE2 are closely linked and are probably present together in inflammatory lesions. With this in mind, we investigated the effects of PGE2 alone and in combination with IL-1 alpha. PGE2 by itself reduced pumping at concentrations between 10(-6) and 10(-9) M. When mixed with IL-1 alpha (both agents at a final concentration of 10(-9) M), the mixture had a marked inhibitory effect on flow, reducing pumping 50 to 70% at peak flows. The effect of the mixture of IL-1 alpha and PGE2 compared with the two agents administered separately was greater than the predicted additive effect at transmural pressures above 6 cm H2O. At lower transmural pressures, however, the level of real inhibition was less than the predicted additive effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Beta-adrenoceptor-mediated facilitation of [3H]-noradrenaline release from the intramural nerves of bovine mesenteric lymphatic vessels

1. Isolated segments of bovine mesenteric lymphatic vessels were loaded with [3H]-noradrenaline and its efflux in response to field stimulation at 2 Hz (0.3 ms pulses, 1 min train) examined. 2. Isoprenaline (10(-6) M) increased evoked fractional 3H efflux (3H released as a percentage of total tissue 3H at the onset of stimulation) from its control value of 0.67 +/- 0.09 to 1.2 +/- 0.18% (s.e.mean; n = 5). 3. Propranolol (10(-6) M) alone had no effect on evoked fractional 3H efflux but blocked the increase in transmitter overflow induced by isoprenaline (10(-6) M). 4. In the presence of the alpha-adrenoceptor antagonist phentolamine (10(-6) M) the facilitatory effect of isoprenaline (10(-6) M) on transmitter efflux was enhanced. In 5 experiments isoprenaline increased evoked fractional 3H efflux from its control value of 1.07 +/- 0.17 to 2.5 +/- 0.37% when phentolamine was present. 5. Adrenaline (10(-8) M) increased evoked fractional 3H efflux from its control value of 0.76 +/- 0.09 to 1.13 +/- 0.17% (n = 7). 6. These findings are consistent with the presence of presynaptic beta-adrenoceptors in this preparation. There is no evidence that these receptors play any role in feedback regulation of transmitter release.

The effect of anesthetics on lymphatic contractility

Spontaneous contractions and those elicited by electrical stimulation were studied in isolated segments of bovine mesenteric lymphatic vessels. The effects of three general anesthetics, pentobarbitone, halothane, and ether, on these spontaneous and evoked contractions were studied. Pentobarbitone and halothane inhibited spontaneous contractions in a dose-dependent fashion. In doses of 10(-4) M or greater both drugs completely abolished spontaneous contractility but when contractions were elicited by electrical stimulation pentobarbitone inhibited them in a dose-dependent manner whereas halothane did not. In contrast to the above results ether in doses as high as 10(-2) M had little effect on lymphatic contractility. It is concluded that, in doses similar to plasma levels found during general anaesthesia, halothane and pentobarbitone significantly depressed lymphatic contractility while ether did not.

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

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

Release of [3H]-noradrenaline from the sympathetic nerves to bovine mesenteric lymphatic vessels and its modification by alpha-agonists and antagonists

1. Isolated segments of bovine mesenteric lymphatic vessels were loaded with [3H]-noradrenaline and its efflux in response to field stimulation examined. Vessels were attached to an isometric force transducer for the simultaneous recording of mechanical activity. 2. Field stimulation at 1, 4 and 8 Hz (0.3 ms pulses, 1 min train) increased spontaneous contraction rate and evoked 3H release up to a maximum of 4.5% of total tissue 3H at 8 Hz. Output per pulse was maximal at 4 Hz. 3. Tetrodotoxin (3 x 10(-6) M) blocked the release of 3H in response to field stimulation although the drug did not attenuate release evoked by high K+ (65 mM) solution. Field-evoked release of 3H was also absent in Ca2+ -free solution containing EGTA (1 mM). 4. When vessels were preincubated with labelled transmitter plus cocaine (5 x 10(-5) M) evoked release of 3H was absent. After preloading with [3H]-noradrenaline, cocaine (10(-6) M) potentiated both the mechanical response to field stimulation and evoked 3H release. 5. The relatively non selective alpha-adrenoceptor antagonist phentolamine (3 x 10(-6) M) and the alpha 2-antagonists yohimbine (10(-8) M) and rauwolscine (10(-6) M) significantly increased evoked 3H release at both of the frequencies examined (1 and 4 Hz). In contrast, the selective alpha 1-antagonist prazosin (10(-6) M) failed to alter 3H release to 4 Hz stimulation although release at 1 Hz was potentiated in the presence of the drug. 6. The postsynaptic excitatory response to field stimulation remained in the presence of prazosin (10(-6) M), but was converted to an inhibitory effect in the presence of phentolamine (3 x 10(-6) M), yohimbine (10(-6) M) or rauwolscine (10(-6) M). 7. Evoked 3H efflux was significantly reduced by clonidine (10(-6) M), xylazine (10(-6) M) and exogenous noradrenaline (5 x 10(-7) M), although phenylephrine (10(-6) M) reduced release only at the lower of the two frequencies tested (1 Hz). 8. These findings suggest that release of 3H by field stimulation reflects endogenous transmitter release and that this is subject to autoinhibition via feedback onto inhibitory prejunctional alpha 2-adrenoceptors. The postjunctional excitatory response is mediated via postjunctional alpha 2-adrenoceptors.

Decreased density distribution of mesenteric and diaphragmatic microvascular anionic charges during murine abdominal sepsis

Pulmonary edema of sepsis is a consequence of increased transmural conductance for water and proteins at the level of lung microvessels induced by vasoactive endogenous mediators, liberated after activation of complement by bacterial endotoxins. Intermittent opening of interendothelial junctions at the level of post-capillary venules has been implicated as being the pathway for the leaking plasma proteins and water. Microvascular basement membranes and endothelial cell surfaces have fixed anionic charges (AS) which prevent the escape of plasma proteins from the circulation as well as the adhesion of blood cells to the luminal endothelium. The density distribution of these AS was substantially reduced in visceral and systemic microvessels during murine abdominal sepsis. This observation suggest that MOF secondary to sepsis is the consequence of a severe and generalized alteration of the microvascular electronegative charge, induced by liberation of inflammatory mediators.

The effect of electrical stimulation of the sympathetic chain on peripheral lymph flow in the anaesthetized sheep

1. Pressure fluctuations and lymph flow were measured in cannulated popliteal efferent and metatarsal afferent lymphatics in anaesthetized sheep. 2. Stimulation of the lumbar sympathetic chain at 1.4 and 10 Hz increased lymph flow and lymphatic contraction frequency. These effects were most marked during 10 Hz stimulation where, in some efferent preparations, greater than 5-fold increases in lymph flow and contraction frequency were observed. 3. Strain-gauge plethysmograph recordings in the lymphatic's drainage area indicated that during stimulation blood flow was reduced. There was also a slow continuous fall in tissue volume throughout the periods of stimulation, presumably due to a net uptake of fluid by the blood vessels. 4. Intra-arterial infusion of phentolamine at a rate of 10 micrograms kg-1 min-1 blocked the increases in lymph flow and contraction frequency. 5. These results suggest that the observed increases in lymph flow were due to direct neurogenic stimulation of lymphatic pumping.

The role of external compression and movement in lymph propulsion in the sheep hind limb

1. Pressure fluctuations and lymph flow were measured in metatarsal lymphatics in anaesthetized sheep. 2. Intermittent compression significantly increased lymph flow when this was applied over the hoof but did not increase flow significantly when applied over the metatarsal region. 3. In a second preparation a 15 cm length of metatarsal lymphatic was cannulated at both ends and measurements were made of the ability of the duct to pump saline from an inflow reservoir through an outflow at the same height. 4. In the absence of external forces fluid was propelled by the lymphatic's intrinsic contractions but when intermittent compression was applied over the metatarsal region flow increased almost fourfold. 5. When animals with the doubly cannulated duct were allowed to recover, the effect of normal limb movements on fluid propulsion was examined. Under these conditions flow only occurred in response to intrinsic lymphatic contractions and appeared to be unaffected by the animal moving round the cage. 6. These results suggest that the effects of external forces on lymph flow are more dependent on compression of tissues in the lymphatic drainage area than on compression of the main lymphatic ducts. External compression can increase fluid propulsion by these vessels but, since forces of adequate magnitude appear not to be encountered in normal hind-limb movements, lymph propulsion in this region must depend on intrinsic lymphatic pumping.

Thoracic duct lymph and PEEP studies in anaesthetized dogs. II. Effect of a thoracic duct fistula on the development of a hyponcotic-hydrostatic pulmonary oedema

PEEP impedes thoracic duct drainage (LF). This can be counteracted by a thoracic duct fistula. Consequently, lung oedema (LOE) should develop during PEEP more slowly with LF at atmospheric pressure (LFAP) than with LF against jugular venous pressure (LFJVP). In 12 anaesthetized dogs LOE was produced by Ringer's solution i.v. (2.5 ml/min per kg) for 6 h during PEEP (10 mmHg) with either LFAP or LFJVP. Ringer's + PEEP greatly increased aortic, pulmonary artery and wedge pressures, JVP, and cardiac output. Colloid osmotic pressures in plasma and lymph were drastically reduced, pulmonary effective filtration pressure (EFP) rose by about 20 mmHg. LFJVP increased 7-fold, LFAP about 19-fold, the respective loss of plasma proteins was 1.83 and 1.06 g/kg during 6 h. Thermal-dye extravascular lung water showed an increment of 68 with LFJVP versus 43 microliter/h/g per mmHg with LFAP. Final lung water content was at any delta EFP (12.8-31.9 mmHg) lower with LFAP than with LFJVP amounting 512 with LFJVP versus 377 microliters/g/per mmHg with LFAP. LFAP decreased the development of LOE during PEEP by bypassing the PEEP-induced high JVP and thus facilitating the removal of interstitial fluid. It is hypothesized that a thoracic duct fistula might aid the treatment of patients with LOE due to ARDS and therefore requiring high levels of PEEP.

Thoracic duct lymph and PEEP studies in anaesthetized dogs. I. Lymph formation and the effect of a thoracic duct fistula on lymph flow

The effect of positive end-expiratory pressure ventilation (PEEP, 11-12 mmHg, 60-90 min without, 19 h with circulatory support) on fractional escape rate of plasma proteins (FER), and on thoracic duct lymph flow draining against jugular venous (LFJVP) or atmospheric pressure (LFAP) was studied in anaesthetized dogs. FER was 10.8%/h, 15.3%/h, and 8.5%/h before, during, and after PEEP, respectively, indicating augmented lymph formation probably due to the increase in venous pressure from 4.8 to 10.8 mmHg during PEEP. LFJVP was 39 microliter/min per kg before PEEP, decreased transiently during PEEP but the steady state value (up to 19 h) was not different from control, and increased transiently after PEEP. LFAP was 37, 80, and 38 microliter/min per kg before, during, and after PEEP, respectively. Long-term PEEP increased LFAP fourfold. Changing the drainage mode during PEEP yielded an immediate increase from LFJVP = 34 to LFAP = 79 microliter/min per kg and an instantaneous reduction from LFAP = 95 to LFJVP = 35 microliter/min per kg. Lymph protein concentration and protein lymph/plasma ratio increased concomitantly with LFAP during PEEP suggesting augmented hepatic contribution to LFAP, augmented intestinal contribution was revealed by labelling intestinal lymph using olive oil orally, muscular lymph flow was not increased as shown by i.m. Evans blue. In conclusion, the augmentation of venous pressure by PEEP promotes capillary filtration but obstructs lymph drainage from the thoracic duct into the jugular vein. PEEP imbalances formation and return of lymph and affects the development and removal of oedema.

Increased intrinsic pumping of intestinal lymphatics following hemorrhage in anesthetized sheep

The return of fluid and protein to the bloodstream by the lymphatic circulation may play an important role in reconstituting intravascular volume following hemorrhage. In this study, we have defined the lymph-flow changes that occur in cannulated mesenteric lymphatics following a 25% blood loss in anesthetized sheep and investigated the effects of hemorrhage on the intrinsic contractile activity (lymph pumping) of these vessels in vivo using a new model system. The removal of 25% of the calculated blood volume resulted in increases in lymph flow over a 6-hour period, with peak changes to 3.5 times the prebleed levels. Systemic arterial pressures dropped to roughly 50% of control values immediately following the bleed and returned to control in 3 hours. To directly assess the effects of hemorrhage on lymphatic pumping, a segment of intestinal lymphatic was isolated from all lymph input and supplied with fluid from a reservoir. While there was no net pressure driving fluid through the duct, a transmural distending pressure was applied to the vessel, which stimulated resting lymphatic contractions and fluid pumping. A 25% blood loss resulted in increased activity of the lymph pump; up to 6 times more fluid was propelled through this "isolated" vessel in vivo than in similar preparations in sheep that were not bled (p less than 0.01). Measurements of fluid pulse pressures in this preparation indicated increased pumping frequency and/or force after hemorrhage compared with prebleed levels. We conclude that lymphatic contractile activity is stimulated after a blood loss independent of changes in lymph formation and speculate that this mechanism may play an important role in the reexpansion of the vascular space.

The functioning in unanaesthetized sheep of the popliteal lymph node after the surgical removal of its blood supply

Operations were performed to cannulate the efferent duct of the popliteal node of sheep and, at the same time, the blood vascular system was removed surgically from the popliteal fossa so that the node was deprived of it blood supply. Twelve preparations were technically successful in that lymph flowed spontaneously from the unanaesthetised sheep for from 3 to 30 days after the operation. Eight control preparations were established in which the blood supply of the node with the cannulated efferent duct was left intact. In only four of the test preparations was the function of the node decisively impaired so that dendritic macrophages appeared in the lymph, the output of lymphocytes remained very low, and later histological examination showed the nodes to be grossly depleted of lymphocytes. In two of these four preparations the surgical devascularization of the node was aided by arterial embolization. In the remaining eight test preparations the outputs of lymphocytes in the lymph gradually regained normal values, and the nodes then responded normally to antigenic stimuli.

Peripheral lymphatic responses to outflow pressure in anaesthetized sheep

1. Lymph flow and pressure fluctuations were measured by cannulating popliteal efferent and distal hind-limb afferent lymphatic vessels in anaesthetized sheep. The cannula outflow height was raised above the vessels to increase lymphatic outflow pressure. 2. Lymph flow decreased non-linearly as the outflow was raised. The rate of decrease increased with increasing outflow height. 3. Lymphatic contraction frequency rose and stroke volume fell with increasing outflow height. 4. The calculated power necessary to move lymph along the cannula initially increased with outflow height but it reached a peak and was reduced again by raising the outflow further. Calculated lymphatic stroke work followed a very similar pattern. 5. Lymph flow was maintained up to a greater outflow height in afferent than in efferent vessels. Curves relating frequency, power and stroke work to outflow height were shifted to the right in the afferent lymphatics. 6. These results are consistent with an intrinsic lymphatic pump which can be stimulated by increasing pressure. At high pressures, however, the pump fails.

Outflow pressure reduces lymph flow rate from various tissues

We previously reported that the very act of cannulating a lung lymph vessel could alter the unique flow characteristics that existed within the lymphatic before cannulation. We postulated that this phenomenon could hold true for lymphatics draining any organ within the body. Since it is frequently important to know the relationship between the transmicrovascular fluid flux and true lymph flow rate, it would be critical that a cannulated lymphatic vessel have the same flow characteristics as those uncannulated vessels draining the same organ. In order to test our hypothesis we cannulated lymph vessels draining the heart, liver, small intestine, kidney, and skeletal muscle. By altering the lymphatic outflow pressure (normally related to systemic venous pressure) and by using lymphatic cannulas of various resistance, we were able to demonstrate that lymph flow varied linearly with lymphatic outflow pressure in every organ. By increasing transmicrovascular fluid flux and lymph flow rate in each organ we were also able to demonstrate that effective resistance of the lymphatic vessels and the effective pressure driving lymph flow varied as a function of the physical characteristics of the organ under investigation. Characteristic effective resistances of the heart, liver, skeletal muscle, kidney, and small intestine lymphatics decreased by 83, 40, 61, 36, and 50%, respectively. Along with these changes in effective resistance, the effective lymph driving pressure in the same organs varied by 49, 0, 257, 0, and 63%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent pathways of lymph flow within the popliteal node in sheep

Lymph enters the popliteal node in sheep either at the subcapsular sinus, or through terminal afferent lymphatics which pass within trabeculae to medullary sinuses. Lymph from the subcapsular sinus traverses trabecular sinuses and/or a network of tubular sinuses in the cortex before entering the medullary sinuses, which are very extensive. Carbon particles, injected either into an afferent lymphatic or subcutaneously into the leg, were initially found mainly in a circumscribed area of the subcapsular sinus. Within a few hours they were present within macrophages in and around medullary sinuses in a band which extended around virtually the whole medulla. It was concluded that the pathways taken by lymph constituents in the sheep node may differ from those described for mice, rats and rabbits.

A method for studying lymphatic pumping activity in conscious and anaesthetized sheep

A 20 cm length of the main mesenteric lymph duct in the sheep was cannulated at both ends and measurements were made in both conscious and anaesthetized animals of the ability of the duct to pump saline from an inflow reservoir to an outflow at the same height. Fluid was propelled only when the lymphatic contracted and this was unaffected by movements of the animal round the cage or by fluctuations in abdominal pressure or by respiratory movements. It was confirmed that the mesenteric duct was 'isolated' from the rest of the lymphatic system by closing the inflow tap whereupon fluid propulsion ceased. Raising transmural pressure by varying inflow and outflow by the same amount had the effect of increasing fluid output; this was achieved by an increase in both the frequency and force of lymphatic contractions. Lymphatic frequency of contraction and fluid output increased when the animals were frightened. Intravenous infusions of noradrenaline increased the frequency of lymphatic contraction and increased fluid propulsion, while isoprenaline infusions depressed flow. This preparation demonstrates that it is possible to study the control of lymphatic pumping in conscious sheep without the complication of changing rates of lymph formation.

Lymphatic endothelial and smooth-muscle cells in tissue culture

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

Variegated effects of prostaglandins on spontaneous activity in bovine mesenteric lymphatics

The effects of PGs (PGA2, PGB2, PGE2, PGF2 alpha, PGI2, and 6-keto PGF1 alpha) were investigated quantitatively in insolated bovine mesenteric lymphatics for elucidating the possible significance of PGs in lymph propulsion. 10(-8) M PGF2 alpha, PGA2, and PGB2 produced recognizable increases of frequency and amplitude of spontaneous contractions. The positive chrono- and inotropic responses were enhanced with increasing concentration of the PGs from 10(-8) to 10(-6) M. Both PGE2 and PGI2 in a concentration range from 10(-8) to 10(-6) M caused dose-related reductions in the amplitude of spontaneous contractions. No decrease in contraction rhythm was observed by the administration of PGI2 and PGE2 at concentrations lower than 5 X 10(-7)M. All of the above-mentioned responses induced by PGF2 alpha, PGA2, PGB2, PGI2, and PGE2 were not inhibited by pretreatment with alpha- and beta-adrenergic blocking agents, muscarinic antagonist, antihistamics, and serotonic antagonist. These findings suggest that PGF2 alpha, PGA2, and PGB2 in a low concentration may facilitate lymph flow of bovine mesenteric lymphatics in the living body, since the spontaneous contractions of lymphatic smooth muscle may drive lymph centripetally in the presence of direction valves. On the other hand, PGI2 and PGE2 may cause an inhibition of lymph transport.

The effect of intravenous adrenaline and noradrenaline infusion of peripheral lymph flow in the sheep

Pressure fluctuations and lymph flow were measured in popliteal, prefemoral and mesenteric efferent lymphatic vessels in conscious sheep. Intravenous adrenaline infusion increased frequency of lymphatic contraction and lymph flow in all three vessels. In the case of the prefemoral vessels flow remained high after the infusion had stopped. Intravenous noradrenaline infusion also increased frequency of contraction and lymph flow in all three vessels but prefemoral flow was depressed after the infusion had stopped. Lymphatic frequency of contraction and lymph flow increased when the animals were started. Anaesthetizing the animals with pentobarbitone did not abolish lymphatic contractions, nor did it prevent the response to adrenaline and noradrenaline infusion. The most obvious interpretation of these results is that adrenaline and noradrenaline act by increasing frequency and force of pumping of lymphatic vessels.

Apical localization of pulmonary tuberculosis, chronic pulmonary histoplasmosis, and progressive massive fibrosis of the lung

We have reviewed the accumulated evidence for the explanation of the apical localization of pulmonary tuberculosis, chronic pulmonary histoplasmosis, and massive fibrosis of the lung due to silicosis and coal-workers pneumoconiosis. The effect of gravity on the erect human lung results in greatly diminished pulmonary artery blood flow in the apical and subapical areas. This in turn results in higher oxygen tensions but also impairment of tissue clearance mechanisms in these areas. Analysis of the accumulated evidence better supports the theory of lymph stasis and impaired clearance of antigenic substances as the major determinant of the apical localization of pulmonary tuberculosis rather than the presently favored oxygen tension theory. The impaired clearance theory also best explains the apical localization of chronic pulmonary histoplasmosis and progressive massive fibrosis of the lung.

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

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

Spontaneous contractions and stretch-evoked responses of isolated lymph nodes

In this study the spontaneous activities of prescapular lymph nodes, which were isolated from calves, goats and sheep and mesenteric lymph nodes of guinea-pigs were recorded and analysed in the frequency domain. Stretch-evoked contractions of the mesenteric lymph nodes were also recorded and their frequency characteristics analysed. The preparations were placed in a Krebs solution which was kept at 37 degrees C and bubbled continuously with a mixture of 95% O2 and 5% CO2. The tension changes occurring in the lymph nodes were recorded. The patterns obtained were initially transformed into numerical values which were then used to obtain autocorrelation functions and power spectra, according to the time series analysis method. A passive stretch of 100 s duration was applied to the mesenteric lymph nodes and the responses were examined using the transient response-frequency characteristics method. It was observed that prescapular and mesenteric lymph nodes had spontaneous activities due to the contractions of the smooth muscles within the nodes. A frequency analysis of these contractions indicated that at least three contractile components were responsible for the contractions; these components contract within the frequency bands of 0.01-0.04 Hz, 0.05-0.07 Hz and 0.09-0.14 Hz respectively. It was also observed that the spontaneous activities could be regulated and synchronized by stretch. It is suggested that these contractions of the lymph nodes play an essential role in lymph propulsion within the nodes.

Effects of arachidonic acid and its cyclo-oxygenase and lipoxygenase products on lymphatic vessel contractility in vitro

Lymphatic vessels exhibit rhythmical contractility in vivo and in vitro and this activity appears to regulate lymph flow. A technique for measuring the circular muscle contractions of isolated bovine mesenteric lymphatic vessel segments has been devised and utilized to study the pharmacological properties of these vessels. Non-contracting lymphatic vessels can be induced to contract rhythmically with a variety of mediators, the most potent being a stable PGH2 analogue (compound U46619), and the leukotrienes B4, C4 and D4 (threshold concentrations in the nanomolar range). Prostaglandin F2 alpha, noradrenaline, serotonin and histamine also elicited rhythmical activity but much higher concentrations were required. PGE2 and PGE1 were potent inhibitors of spontaneous contractions or those induced with U46619. In keeping with the diverse pharmacological effects of the metabolites of arachidonic acid, the addition of arachidonate to an isolated lymphatic vessel generated both stimulatory and inhibitory activities. It is concluded that arachidonic acid products (produced in the lymphatic vessel or entering the vessel in lymph draining the tissues) regulate lymph flow through their effects on lymphatic smooth muscle.

Effect of outflow pressure upon lymph flow from dog lungs

The pulmonary lymph flow rate (QL) should be a function of the lymph vessels' resistance and the pressure gradient along the vessels. We attempted to study how these factors affect lymph flow. We assumed that the lymph system could be represented by a single pressure generated within the lung (PL) and a single resistance (RL). Thus, QL should be a function of the lymph vessel outflow pressure (Po): QL = (PL - Po)/RL. We cannulated tracheobronchial lymph vessels in eight anesthetized dogs and varied Po by raising the outflow end of the cannula. QL decreased linearly when we increased Po. We estimated RL as - delta Po/ delta QL and PL as the extrapolated Po at which QL = 0. At baseline PL = 7.7 +/- 2.7 (SD) cm H2O and RL = 0.36 +/- 0.25 cm H2O. min/microliters. After we increased capillary pressure to produce edema, PL and RL averaged 22.8 +/- 8.8 and 0.14 +/- 0.12, respectively. After we reduced the capillary pressure to baseline in the edematous lungs, PL and RL averaged 11.6 +/- 2.8 and 0.08 +/- 0.09, respectively. All changes in PL and RL were significant (P less than 0.05). These results show that (1) lymph flow rate depends upon lymph vessel outflow pressure, and (2) the QL vs. Po relationship is changed by edema. PL may be equal to the pressure causing lymph to flow and RL may equal the lymph vessel resistance.

Nervous modulation of spontaneous contractions in bovine mesenteric lymphatics

1. Spontaneous isometric contractions were measured in 2 cm segments of bovine mesenteric lymphatics. 2. Field stimulation at 0.25, 1 anf 4 Hz increased the frequency of contraction. 3. Tetrodotoxin 3 x 10(-6) M blocked the response to electrical stimulation. 4. Phenoxybenzamine 3 x 10(-7) M converted the excitatory effect of stimulation to an inhibitory one. 5. Propranolol 3 x 10(-7) M potentiated the excitatory response to stimulation at 1 and 4 Hz. 6. Field stimulation was without effect in the presence of propranolol and phenoxybenzamine together. 7. Cocaine potentiated the response to stimulation at 0.25 and 1 Hz. 8. Atropine 3 x 10(-7) M failed to block the excitatory effect. 9. Field stimulation at 0.5 and 1 Hz increased the frequency of spontaneous contractions and propulsion of fluid by 8 cm cannulated segments of lymphatic. 10. The results suggest that bovine lymphatic vessels have a noradrenergic innervation which is capable of controlling lymph flow.

Congenital chylothorax: report of unique case associated with 'H' -type tracheo-oesophageal fistula

A case of congenital chylothorax associated with a congenital 'H'-type tracheo-oesophageal fistula is reported. The development of the thoracic duct is described and the possible embryological association with tracheo-oesophageal fistula is discussed. The management of the case is reviewed.

Current views on the mechanisms of pulmonary oedema

Understanding of the causes of pulmonary oedema must be based on knowledge of the mechanism responsible for fluid exchange between the several compartments of the normal lung. Recent physiological studies have clarified the main features of these mechanisms. However in three areas knowledge is still incomplete--the magnitude of the hydrostatic and oncotic forces responsible for fluid movement within the lung, the means by which protein leaks across the wall of small pulmonary vessels and the routes by which fluid and protein pass between the interstitial tissues of the lung and the alveolar space. Further work is needed in these areas. On the basis of this physiological knowledge the mode of development of hydrostatic oedema, the role of lymphatics in pulmonary oedema, and the several stages of pulmonary oedema development that may culminate in alveolar flooding are now clearly understood. Knowledge is less complete about oedema due to increased vascular permeability. In some experimental models, such as alloxan, leakage is due to irreversible injury to the alveolar wall; in other models, including ANTU, oedema formation has been shown to depend upon minor and reversible changes in pulmonary vascular endothelium similar to those that cause exudate formation in areas of acute inflammation. In no instance is detailed information available of both the rate and magnitude of protein leakage and of the morphological basis of increased vascular permeability. Further work is required in this area. Present knowledge allows an adequate explanation of the changes that occur in many clinically important types of pulmonary oedema, including cardiac failure and neurogenic pulmonary oedema. Other types of oedema, notably that which may complicate traumatic shock or extrapulmonary sepsis and high altitude pulmonary oedema, are more complex and the details of their pathogenesis are still obscure.

Mechanisms of decubitus ulcer formation--an hypothesis

Understanding of the etiology of decubitus ulcer formation is fragmentary and the existing literature contains much experimental data that are inconsistent with the idea that pressure sore formation is due extensively to depriving a tissue region of blood. In fact, there is substantial data that illustrate that tissue can remain viable for very extended lengths of time, up to 13 hours, when subjected to externally applied pressures that collapse the blood microvasculature in a region. Based on these observations and on studies done in this laboratory on lymph propulsion and pressure sore prevention, an hypothesis has been formulated that is consistent with the published data and with clinical observations. The hypothesis states that a major contributing factor to pressure sores is the tissue necrosis that is caused by the accumulation of anaerobic metabolic waste products due to occlusion of the lymph vessels.

Colloid osmotic pressure as a prognostic indicator of pulmonary edema and mortality in the critically ill

The relationship of colloid osmotic pressure (COP) to pulmonary edema and mortality in 128 critically ill patients was investigated in our critical care unit, and confirms previously reported observations. The COP in the 86 survivors was 22.0 (+/- 0.4 SEM) mm Hg versus 17.2 (+/- 0.6 SEM) mm Hg in the 42 who died (P less than 0.001). The patients were divided into three groups: 71 with no pulmonary edema, COP of 21.5 (+/- 0.5 SEM) mm Hg; 40 with cardiogenic pulmonary edema, COP of 21.4 (+/- 0.4 SEM) mm Hg; and 17 with noncardiogenic pulmonary edema, COP OF 13.6 (+/- 0.8 SEM) mm Hg. Colloid osmotic pressure was significantly lower in patients with noncardiogenic pulmonary edema (P less than 0.001). In 36 patients in whom pulmonary artery wedge pressures (PWP) were available, a COP-PWP gradient of 4.0 mm Hg or less was always associated with pulmonary edema, while a COP-PWP gradient greater than 4.0 mm Hg was never associated with pulmonary edema. Colloid osmotic pressure is a useful prognostic indicator of pulmonary edema and mortality in the critically ill.

The effect of transmural pressure on pumping activity in isolated bovine lymphatic vessels

1. Isolated preparations of bovine mesenteric lymphatics containing about seven valved segments were cannulated and set up in a perfusion system so that, when the preparation was not contracting, the inflow and outflow pressures were exactly equal and there was no flow through the preparation. 2. Transmural pressure was varied by raising or lowering the inflow and outflow pressures simultaneously by the same amount. 3. The isolated vessels showed rhythmic spontaneous activity; it consisted of quick contractions which spread rapidly over the entire preparation, each followed by a rapid relaxation and a diastolic pause. 4. With each contraction, the preparation decreased in both length and diameter and generated an outflow pressure which pumped fluid in the direction determined by the orientation of the values. 5. Raising the transmural pressure in the preparation increased the output of the preparation; this was achieved by an increase in both the frequency and force of the individual contractions. 6. It was concluded that bovine lymphatics could propel fluid by their intrinsic activity at a rate which was related to the degree of distension of their walls.

Interaction of capillary, interstitial, and lymphatic forces in the canine hindpaw

We used plethysmograph techniques to measure or calculate the tissue and capillary forces and flows (capillary pressure, tissue and plasma oncotic pressure, transcapillary pressure drop, lymph flow, and interstitial pressure) in a dog hindpaw preparation in situ at three different venous pressures (PV). Since lymph was flowing from the preparation, an isovolumetric state represented an isofiltration state rather than the conventional isovolumetric or isogravimetric state. At an isofiltration capillary pressure of 12.8 mm Hg, lymph oncotic pressure averaged 3.8 mm Hg, plasma oncotic pressure averaged 20.9 mm Hg, and tissue pressure averaged -4.7 mm Hg (PV normal). The imbalance in transcapillary forces averaged 0.5 mm Hg and represented the lymph flow contribution (lymph flow/filtration coefficient) to maintainance of the normal isofiltration state. As isofiltration capillary pressure increased to 24.9 mm Hg, interstitial fluid volume increased by 1.7 ml/100g of tissue, tissue pressure rose by 4.6 mm Hg, lymph oncotic pressure fell by 2.2 mm Hg, and the transcapillary pressure drop increased to 5.6 mm Hg (PV = 20 mm Hg). At an isofiltration capillary pressure of 38.0 mm Hg, interstitial fluid volume increased by 17.5 ml/100g, interstitial pressure rose to +10 mm Hg, lymph oncotic pressure fell to 0.5 mm Hg, and the transcapillary pressure drop increased to 6.3 mm Hg (PV = 30 mm Hg). At moderate levels of PV elevation, the transcapillary pressure drop and increased tissue pressure provided 80% of the counterbalancing tissue force, each contributing approximately 40%. At higher venous pressures, the only tissue force that opposed filtration was an increase in tissue pressure.

The functioning and interrelationships of blood capillaries and lymphatics

The structure and function of blood capillaries, as related to permeability, depends on tight, close and (in injured vessels) open junctional regions, small vesicles, vacuoles (in injured vessels) and fenestrae. The basement membrane presents a hindrance to the larger macromolecules, at high flow rates, but not to small molecules. The connective tissue channels are probably the paths by which macromolecules, and most of the small ones, pass from the arterial-limbs to the venous ones, and to the lymphatics. In some regions these channels are grouped in special systems: the prelymphatics. The initial lymphatics take up material via open junctions, which close during tissue-compression. The collecting lymphatics retain the lymph because they do not have open junctions. In the close junctional regions the motive force for water flow is the result of Starling's forces; diffusion is very important for other small molecules. The small vesicles transport macromolecules slowly by Brownian motion, as may the vacuoles, but possibly these latter are moved actively. There is much evidence that colloids can develop high effective osmotic pressures even across pores much larger than their molecules, and that proteins can be dragged up a concentration gradient by the resultant fluid flow. On the basis of this, hypotheses have been developed about the functioning of venous-limb fenestrae and the initial lymphatics, for which there is much theoretical, in vitro, and in vivo evidence. Thus, in fenestrated regions there is held to be a large local circulation through the tissues, of which a quantitatively small, but qualitatively vital, part goes to the lymphatics. Material is considered usually to enter these latter because of the relative concentration of the lymph. It is becoming increasingly evident that in the study of the microvasculature, as with other systems, there is much to be gained by quantifying fine structural observations and by combining and contrasting this data, via physical laws, with that obtained by other methods where the characteristics of whole organs and regions are studied. Thus one can obtain interrelated information, which is not possible by either method alone, and which gives us a vital, comprehensive, perspective of the ways in which whole systems function, and how different systems interact. In this paper I shall show how this approach has yielded much that is new about the functioning of different kinds of blood capillaries, of the tissue channels, of the whole lymphatic system, and of the ways they affect each other.