Mechanism of the sustained action of histamine and bradykinin on transport of large molecules across capillary walls in the dog paw

Lymph node staging using dedicated magnetic resonance contrast agents--the accumulation mechanism revisited

When diagnosing cancer, assessing the nodal stage is tremendously important in determining the patient's prognosis. Computed tomography (CT) and magnetic resonance (MR) imaging (MRI) assessments of the regional lymph node (LN) size and shape are currently used for the initial nodal staging in clinical settings, although this approach has a rather low sensitivity, and biopsy often leads to restaging of the LNs. Acknowledging the great medical need to accurately stage LNs, scientists and clinicians have been working since the late 1980s on MR contrast agents that provide more reliable staging results. Different types of molecules (i.e., iron oxide nanoparticles and Gd-based contrast agent) have shown promising LN accumulation and imaging results, but no clinically approved, dedicated LN staging contrast agent is currently available. The literature describes a mechanism of contrast agent accumulation in the LNs that considers some but not all published experimental evidence. However, confidence in the mechanism of LN accumulation is a prerequisite for the directed synthesis of compounds for accurate and sensitive LN staging. To improve our understanding of the LN contrast agent accumulation mechanism, we reviewed the published data on the enrichment of colloidal MR contrast agent candidates in LNs, and we suggest an extended mechanism for contrast agent enrichment in LNs. For further clarification, physiology and results from drug targeting studies are considered where applicable.

Barrier enhancing signals in pulmonary edema

Increased endothelial permeability and reduction of alveolar liquid clearance capacity are two leading pathogenic mechanisms of pulmonary edema, which is a major complication of acute lung injury, severe pneumonia, and acute respiratory distress syndrome, the pathologies characterized by unacceptably high rates of morbidity and mortality. Besides the success in protective ventilation strategies, no efficient pharmacological approaches exist to treat this devastating condition. Understanding of fundamental mechanisms involved in regulation of endothelial permeability is essential for development of barrier protective therapeutic strategies. Ongoing studies characterized specific barrier protective mechanisms and identified intracellular targets directly involved in regulation of endothelial permeability. Growing evidence suggests that, although each protective agonist triggers a unique pattern of signaling pathways, selected common mechanisms contributing to endothelial barrier protection may be shared by different barrier protective agents. Therefore, understanding of basic barrier protective mechanisms in pulmonary endothelium is essential for selection of optimal treatment of pulmonary edema of different etiology. This article focuses on mechanisms of lung vascular permeability, reviews major intracellular signaling cascades involved in endothelial monolayer barrier preservation and summarizes a current knowledge regarding recently identified compounds which either reduce pulmonary endothelial barrier disruption and hyperpermeability, or reverse preexisting lung vascular barrier compromise induced by pathologic insults.

Permeability of pulmonary vascular endothelium

Three aspects of transendothelial exchange in the lungs are considered: stretching of interendothelial junctions of pulmonary microvessels by increase in pulmonary capillary pressures; selective stretching of interendothelial junctions of bronchial venules in response to histamine, bradykinin and endotoxin; active transport of peptides across the body of the endothelial cell after enzymic action at or near the luminal surface of the endothelial cell. Stretching of interendothelial junctions between the cells lining the pulmonary capillaries was demonstrated using a variety of macromolecular tracers under controlled haemodynamic conditions. Selective leakage of bronchial venules, the systemic venules of the lungs, was shown using colloidal carbon as a tracer. Transendothelial transport of peptides across the pulmonary capillary lining involved the use of electron microscopic autoradiography after intravenous administration of radioactively-labelled lipoproteins. Different mechanisms appear to provide routes of entry into the perivascular interstitial spaces of the lungs.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

"Bronchial artery delivery of viral vectors for gene delivery in cystic fibrosis; superior to airway delivery?"

BACKGROUND

Attempts at gene therapy for the pulmonary manifestations of Cystic Fibrosis have relied mainly on airway delivery. However the efficiency of gene transfer and expression in the airway epithelia has not reached therapeutic levels. Access to epithelial cells is not homogenous for a number of reasons and the submucosal glands cannot be reached via the airways.

PRESENTATION

We propose to inject gene delivery vectors directly into bronchial arteries combined with pre-delivery of vascular endothelial growth factor to increase vascular endothelial permeability and post-delivery flow reduction by balloon occlusion. Thus it may be possible to reach mucous secreting cells of the bronchial luminal epithelium and the submucosal glands in an increased and homogenous fashion.

TESTING

This combination of techniques to the best of our knowledge has not previously been investigated, and may enable us to overcome some of the current limitations to gene therapy for Cystic Fibrosis.

Microvascular permeability

This review addresses classical questions concerning microvascular permeabiltiy in the light of recent experimental work on intact microvascular beds, single perfused microvessels, and endothelial cell cultures. Analyses, based on ultrastructural data from serial sections of the clefts between the endothelial cells of microvessels with continuous walls, conform to the hypothesis that different permeabilities to water and small hydrophilic solutes in microvessels of different tissues can be accounted for by tortuous three-dimensional pathways that pass through breaks in the junctional strands. A fiber matrix ultrafilter at the luminal entrance to the clefts is essential if microvascular walls are to retain their low permeability to macromolecules. Quantitative estimates of exchange through the channels in the endothelial cell membranes suggest that these contribute little to the permeability of most but not all microvessels. The arguments against the convective transport of macromolecules through porous pathways and for the passage of macromolecules by transcytosis via mechanisms linked to the integrity of endothelial vesicles are evaluated. Finally, intracellular signaling mechanisms implicated in transient increases in venular microvessel permeability such as occur in acute inflammation are reviewed in relation to studies of the molecular mechanisms involved in signal transduction in cultured endothelial cells.

Differing effects of histamine and serotonin on microvascular permeability in anaesthetized rats

1. We have investigated simultaneous changes in the hydraulic permeability (Lp) and the retention of perfusate macromolecules in single mesenteric venules of anaesthetized rats during perfusion with either histamine or serotonin. 2. The venules were microperfused in situ. Retention of macromolecules was assessed from the effective oncotic pressure (omega delta pi) exerted by the perfusate across the vessel walls. Lp and omega delta pi were estimated by the red cell microperfusion technique. 3. Perfusion with histamine (at concentrations between 16 microM and 3.26 mM) and serotonin (at concentrations between 26 microM and 1.3 mM) transiently increased Lp and reduced omega delta pi. Maximal changes were seen at 6-9 min with histamine and at 3 min with serotonin. 4. Maximal increases in Lp were greater with histamine (approximately 3-fold) than with serotonin (1.5- to 2-fold). Serotonin, however, decreased omega delta pi from a baseline of 14-15 cmH2O to one of 6-7 cmH2O whereas the fall of omega delta pi with histamine was only from 14-15 cmH2O to 10-11 cmH2O. 5. The data are consistent with the hypothesis that serotonin increases permeability by inducing openings in the venular endothelium which do not retain macromolecules. If histamine also increases permeability by gap formation, these gaps are able to retain macromolecules to a significant extent.

Inhibitory influence of sympathetic nerves on afferent nerve-induced extravasation in the rat incisor pulp upon direct electrical stimulation of the tooth

Previous studies have shown that sympathetic nerve stimulation reduces afferent nerve-induced vasodilation by mechanisms unrelated to vasoconstriction in the rat incisor pulp. The present investigation concerned whether similar modulatory mechanisms might also influence neurogenic plasma extravasation in dental pulp. Rat mandibular incisors were electrically stimulated and blood flow reactions in the pulp were recorded by laser Doppler flowmetry. Plasma extravasation in the incisor pulp, gingiva and lip were indirectly assessed by the Evans-blue method. Stimulation of teeth with 50 microA (5 min) did not cause increased dye accumulation in the stimulated pulps whereas stimulation with 100 microA significantly increased the dye content in ipsilateral pulps by 32% as compared to controls; 100 microA stimulation was without effect in unilaterally denervated animals. Tooth stimulation with 50 microA (5 min), in the presence of either the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), or the alpha 1-adrenergic antagonist prazosin (50 micrograms/kg), as well as in chronically sympathectomized animals, significantly increased the Evans-blue content in the stimulated pulps by 47, 83 and 86%, respectively. Application of short trains of impulses (same number of impulses as for the continuous stimulation but producing minimal vasoconstriction) resulted in some dye accumulation, which was enhanced in the ipsilateral pulps in the presence of prazosin (100 micrograms/kg) or after acute resection of the superior cervical sympathetic ganglion by 70 and 64%, respectively. The Evans-blue content in the lip and gingiva was uninfluenced by the tooth stimulation. The results indicate that activation of sympathetic nerves inhibits the afferent nerve-induced plasma extravasation in rat incisor pulp and this effect is mediated by alpha-adrenoceptors not associated with vasoconstriction.

Vascular leakage induced by histamine, bradykinin, serotonin and prostaglandin E2 in greyhounds

Vascular leakage induced by intradermal injection of histamine, bradykinin and serotonin alone and co-injected with prostaglandin E2 was measured in Greyhounds using 125iodine-labelled human serum albumin (125I-HSA) as a marker in the blood. Histamine and bradykinin produced dose-dependent vascular leakage. At equimolar concentrations, histamine was more than twice as potent as bradykinin. Serotonin did not induce vascular leakage and was irritant. Prostaglandin E2 did not induce significant vascular leakage (maximum 5 microL) when injected alone, but when co-injected with histamine and bradykinin, the vascular leakage of both histamine and bradykinin was increased. This effect was more pronounced if lower concentrations of histamine and bradykinin were injected. The induced vascular leakage was greatest during the first five minutes of lesion development for histamine, during the second five minutes of lesion development for bradykinin, and the synergistic effect of prostaglandin E2 was maximal during the third five minute period of lesion development.

Kallikrein messenger RNA in rat arteries and veins

Glandular kallikrein (EC 3.4.21.8) belongs to a subgroup of serine proteases coded by a multigene family. A kininogenase resembling glandular kallikrein has been identified in vascular tissue; however, it is not clear whether it is synthesized by vascular tissue or taken up from plasma. To determine the potential for kallikrein synthesis in vascular tissues, we tested whether messenger RNA (mRNA) for glandular kallikrein is present in rat arteries and veins. Poly(A+) RNA was isolated from pools of arteries or veins (n = 3, 30 rats each). Poly(A+) RNA from the kidney and liver was used as a positive and negative control, respectively. As a probe, we used rat pancreatic kallikrein 32P-labeled complementary DNA, which recognizes mRNA of the entire rat kallikrein family. Slot-blot analysis indicated that kallikrein mRNA was present in mRNA from the arteries, veins, and kidney but not from the liver. Poly(A+) RNA from arteries and veins contained approximately 1% as much kallikrein mRNA as that from the kidney. To confirm the slot-blot results and determine whether the mRNA for true glandular kallikrein was present in vascular tissue, we employed a polymerase chain reaction assay, first using primers specific for the entire kallikrein family (which amplify a 430-bp fragment) and then using primers specific for true glandular kallikrein mRNA (which amplify a 370-bp fragment). After the polymerase chain reaction assay, both arteries and veins showed fragments of these sizes when tested with rat kallikrein complementary DNA probe, thus confirming the presence of glandular kallikrein mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hydroxyethyl rutosides upon the permeability of single capillaries in the frog mesentery

1. We have investigated the effects of a standardised mixture of hydroxyethyl rutosides (HR) upon the permeability of the walls of single capillaries and venules of the frog mesentery. 2. In each experiment a single vessel was perfused via a micropipette with frog Ringer solutions containing bovine serum albumin (10 mg ml-1) and Ficoll 70 (40 mg ml-1) first in the absence of HR and then with HR added to the perfusate. The permeability of the vessel walls was assessed during each perfusion by using a development of the Landis micro-occlusion technique to estimate their hydraulic permeability (Lp) and the effective osmotic pressure (sigma delta pi) exerted across them by the perfusate macromolecules. 3. Measurements were made both in vessels which appeared to be healthy and in vessels showing signs of stasis or inflammation before perfusion. 4. HR at concentrations of 1.0, 0.1 and 0.01 mg ml-1 reduced hydraulic permeability to approximately half of its value in the absence of HR. It increased sigma delta pi to macromolecules at concentrations of 10, 1.0, 0.1, 0.01 and 0.001 mg ml-1. The effects of HR upon permeability were not reversed within 10 min of perfusion with an HR-free solution. 5. Ultrastructural examination of a number of vessels in which initial high values of permeability were reduced to values within the normal range of permeabilities by HR, showed clear signs of damage to the endothelium, with large gaps between adjacent endothelial cells. 6. These observations suggest that HR does reduce microvascular permeability both in healthy vessels and vessels showing of inflammation. The reduction in permeability of inflamed vessels does not appear to be the result of closure of the gaps between adjacent endothelial cells.

Calcium dependence of histamine-induced increases in capillary permeability in isolated perfused rat hindquarters

Experiments were performed on isolated maximally vasodilated perfused rat hindquarters to evaluate the role of calcium and magnesium for the capillary permeability increase(s) elicited by histamine. Changes in capillary permeability were quantified by determinations of capillary filtration coefficient (CFC) with gravimetric technique, and capillary diffusion capacity (PS) for vitamin B12 (MW = 1,355) with a single injection indicator dilution technique. During control, vascular resistance was 2.2 PRU100 at a flow of 9.4 ml min-1 per 100 g, and PS for B12 was 3.7 +/- 0.1 ml min-1 per 100 g, while CFC was 0.0377 +/- 0.0004 ml min-1 mmHg-1 per 100 g. Perfusion with 'Mg-free' solution for 1 h caused a 24% increase in CFC, while neither 'Ca-free' perfusion nor perfusion with verapamil (5 X 10(-5) M) nor felodipine (1 X 10(-6) M) induced any changes in CFC. Histamine (100-200 microM) caused in all preparations a 150-200% increase in CFC with only small changes in PS for B12. This histamine effect was absent after 1 h of 'Ca-free' perfusion and was partially blocked after 1 h of perfusion with 0.1 mM calcium, while the calcium antagonists verapamil and felodipine had no effects on the histamine-induced changes. The results imply that histamine exerts its action on the endothelial cells through a calcium-dependent process, probably involving low affinity calcium sites but this process could not be inhibited by the calcium antagonists used. Thus, endothelial cell contractility, which probably is responsible for the histamine-induced increase in capillary permeability, exhibits unique characteristics, differing from those of vascular smooth muscle.

Bradykinin causes a prolonged increase in skin microvascular permeability

Bradykinin is an endogenous inflammatory mediator, and its mechanism of action is incompletely understood. It is controversial whether bradykinin causes a sustained increase in microvascular permeability, or has only a transient effect. In anesthetized dogs intraarterial infusion of bradykinin (0.14 to 0.54 micrograms/kg/min) produced an immediate increase in flow of protein-rich, hindpaw lymph. After 210 min of bradykinin infusion lymph flow was threefold greater than baseline, lymph protein concentration remained doubled, and in a dose-related fashion bradykinin produced a sustained increase in lymph protein flux. Lymph flow was then further increased with venous hypertension, and after 4 hr lymph protein flux remained greater from the bradykinin paws than from the control paws. This sustained increase in protein flux indicates that bradykinin produces an increase in permeability at the microvascular membrane by a mechanism that is different from how the initial increase in permeability was produced.

Luteinising hormones activate a factor(s) in testicular interstitial fluid which increases testicular vascular permeability

The mechanism by which hCG increases the rat testicular vascular permeability was studied by injecting the testes with hCG (0.1-100 ng) together with testicular interstitial fluid (150 mul) or with the fluid alone (control) and measuring the uptake of i.v. injected [125I]hCG and the interstitial fluid volume in the testes. Both parameters were already increased with 1 ng of hCG and maxima were seen with 2 ng of hCG. The effect of hCG was not inhibited by injection of a 1000-fold excess of deglycosylated hCG together with hCG. No increase was seen after injection of 2 ng of hCG in saline or in rat serum. The response was specific to luteinising hormones since only rLH mimicked the effect of hCG, but deglycosylated hCG, rFSH or rat prolactin did not. Denaturation of the fluid or addition of serine protease inhibitor (p-aminobenzamidine) to the fluid prevented the effect of hCG. Treatment of the hCG-activated fluid with anti-hCG gamma-globulin Sepharose did not abolish the permeability effect of the fluid. This, and the finding that hCG is not catabolised during incubation in the fluid, suggests that hCG itself is not transformed to a vasoactive compound in the fluid. These results strongly suggest that luteinising hormones activate a factor(s) in rat testicular fluid which mediates their permeability effect. The putative factor(s) seems to be heat-sensitive with a molecular weight of over 10 000 Da.

Transient effects of histamine on the capillary filtration coefficient

The duration of the effect of histamine to increase the capillary filtration coefficient (CFC) was evaluated in isolated, denervated canine forelimb, hindpaw, and gracilis muscle. CFC was estimated at timed intervals during local intraarterial histamine (12 micrograms base.min-1 per 100 ml.min-1 blood flow). Propranolol (3 mg/kg) was administered to inhibit possible catecholamine-mediated inhibition of histamine-induced increases in CFC. The increase in CFC was greatest after 10 min of drug infusion and returned to control values after 25 min of histamine. These data indicate that the effect of histamine to increase CFC is highly transient. The relative contributions of increases in surface area and/or permeability to increases in CFC were assessed by maximally dilating the vasculatures of the three tissues with nitroprusside (increasing surface area to a maximum). Any further increase in CFC produced by combined nitroprusside-histamine infusion would then be due to increased permeability. Histamine, when infused concomitantly with nitroprusside, produced further increases in CFC relative to CFC obtained during infusion of nitroprusside alone. The time course for the transient increase in CFC during combined histamine-nitroprusside infusion was similar to the time course during histamine alone. These data suggest that the transient increase in CFC induced by histamine is primarily mediated by a transient increase in microvascular permeability to fluid in all three tissues. The transient nature of this increase in permeability was probably not related to a beta-antagonistic action of the catecholamines (which may have been increased reflexly) because these tissues were beta-blocked with propranolol. An equation was derived to estimate the ratio of the number of gaps which form between venular endothelial cells to the number of small pores. It was concluded that less than 3% of small pores need increase in radius to form large pores or gaps with radii ranging from 195 to 1000 A to explain the increases in CFC demonstrated in the hindpaw and gracilis muscle and that structures beyond the microvascular endothelium may provide the principle resistance to fluid efflux during histamine.

The effect of altering the external calcium concentration and a calcium channel blocker, verapamil, on microvascular leaky sites and dextran clearance in the hamster cheek pouch

The role of calcium in contractile mechanisms has been well documented. Since the formation of intraendothelial gaps may be due to a contractile process, these studies were initiated to describe the effects of altering the external calcium concentration and a calcium blocker, verapamil, on the development of leaky sites and clearance of dextran in the hamster cheek pouch under normal and histamine-stimulated conditions. Adult Syrian hamsters were anesthetized and tracheostomized, and the femoral vein was cannulated for injecting the FITC-Dextran-70K. In all hamsters, a removable plastic chamber was placed in the cheek pouch to observe and collect suffusate from the microvasculature. In one series of experiments, suffusion was begun with either "normal" calcium (1.5 mM) or a calcium-free, Ringer's bicarbonate (pH 7.4, 36 degrees) buffer. After a 30-min period, fluorescein-labeled dextran (FITC-Dextran-70K) was given intravenously and the number of leaky sites and dextran clearance determined for 30-45 min. Two 5-min periods of stimulation with histamine (10(-7) and 10(-6) M) followed by a 30-min equilibration were completed while the above measurements were repeated. Then, the suffusate was switched to the opposite calcium buffer and the same sequence repeated. A similar protocol was followed using either the "normal" buffer or a high (4.5 mM)-calcium buffer. In another series of experiments, similar measurements were completed with and without verapamil (10(-4) M) using a "normal" calcium buffer and histamine-stimulated conditions. In the control, nonstimulated state, there was a significant increase in the leaky sites while suffusing with low-calcium buffer; however, there were no changes in leaky sites while suffusing with the high-calcium buffer. In the histamine-stimulated state, the increase in the number of leaky sites and dextran clearance was attenuated with the low-calcium buffer and potentiated with the high-calcium buffer. While suffusing with the verapamil buffer, there was an increase in the control number of leaky sites and in the histamine-stimulated state there was an attenuation of the histamine-stimulated response. These results indicate that external calcium influences and modulates microvascular leaky sites in normal and stimulated states and that the formation of leaky sites and dextran clearance after histamine stimulation require the transmembrane flux of calcium. Also, the formation of leaky sites was coupled directly to the clearance of dextran.

Early cell alterations induced by histamine and epinephrine in rabbit lung

This study was concerned with the early effects on lung cells of infusion of 18 micrograms/kg histamine to the rabbit. For comparison purposes, other rabbits received a bolus of 0.4 micrograms/kg epinephrine. After administration, the lungs were immediately fixed by vascular perfusion of osmium tetroxide. In the group that received histamine, we observed selective alterations in the type I epithelial cells of the alveolar wall, consisting of localized thickening, increased number of cytoplasmic ribosomes, and homogeneity and increased electron density with reduction of the number of plasmalemmal vesicles. These alterations were quantitated; the vesicular load (no. of vesicles/cm2) was computed separately for each cell front of epithelial and endothelial cells. Epinephrine induced only edema in epithelial and endothelial cells, resulting in high electron lucency, thickening, and irregular cell profiles. We interpret the alterations seen in histamine-treated animals as reflecting uptake of histamine by the alveolar epithelium leading to an increased level of metabolic activity. Histamine induced no interstitial edema and no immediate reduction of capillary volume. The cellular edema related to epinephrine, a substance which is not taken up or metabolized by the lung, represented a form of cell injury.

Dynamics of renal histamine in normal rat kidney and in nephrosis induced by aminonucleoside of puromycin

Histamine is known to have a profound effect on capillary permeability in nonrenal tissues and this effect is presumably mediated by cyclic (c)AMP. Because in our previous experiments we found that histamine stimulates cAMP accumulation in glomeruli (Torres, V. E., T. E. Northryn, R. M. Edwards, S. V. Shah, and T. P. Dousa. 1978. Modulation of cyclic nucleotides in isolated rat glomeruli. J. Clin. Invest.62: 1334.), we now explored whether this amine is formed in renal tissue, namely in glomeruli, and whether its renal metabolism is altered in experimental nephrosis induced by puromycin aminonucleoside (PA) in rats. In normal rats, histamine content was higher (Delta + 240%) in cortex than in medulla. In glomeruli isolated from renal cortex, histamine content was significantly higher (Delta + 260%) than in tubules. Incubation of isolated glomeruli with l-histidine resulted in a time-dependent increase of histamine content in glomeruli, but no change was found in tubules. The increase in glomerular histamine was blocked by the histidine decarboxylase inhibitor bromocresine. In rats with PA nephrosis induced by a single intraperitoneal injection of PA (15 mg/100 g body wt) urinary excretion of histamine was markedly increased (>Delta + 200%), but control rats did not differ from rats with PA nephrosis in urinary excretions of l-histidine and of creatinine. At the peak of proteinuria (day 9 after injection of PA) the plasma level of histamine was slightly elevated, and plasma histidine slightly decreased in animals that developed PA nephrosis. The content of histamine was markedly higher and the level of histidine was significantly lower in the renal cortex of PA-nephrotic rats as compared with controls; PA-nephrotic and control rats did not differ in the content of histidine and histamine in the liver. In addition, the content of histamine was higher in glomeruli isolated from PA-nephrotic rats; lesser difference was found in cortical tubules. The results further indicate that PA-nephrotic rats have higher content of histamine in the renal cortex, predominently in glomeruli with increased urinary histamine excretion. The elevated renal cortical histamine is not due to higher availability of histamine precursor l-histidine. Results thus show that glomeruli are a major site of intrarenal histamine synthesis and accumulation, and also suggest that abnormal renal metabolism of this amine in PA nephrosis may be related, as a cause or as a consequence, to the pathogenesis of this disease.

Local aortic histamine metabolism and albumin accumulation. Differences between blue and white areas

Relationships between histamine metabolism, histamine content, and albumin accumulation were examined in Evans blue dye stained areas (blue) and unstained (white) areas of normal canine aortas. Results indicated that, while no differences existed in histamine methyltransferase-mediated catabolism, both histidine decarboxylase-mediated histamine synthesis and the histamine content of blue regions were significantly greater (p less than 0.005) than in contiguous white areas. Blue areas also showed significantly higher fluorescein-labeled albumin accumulation than white areas. By multiple regression analysis, a significant relationship (r = 0.81) was obtained between local aortic albumin accumulation and combined influences of local histidine decarboxylase activity and histamine content. The best predictor in this case was the local histidine decarboxylase activity. These data indicate that blue areas, believed to represent areas of spontaneous hemodynamic-induced vascular injury, have a larger nascent histamine pool than do contiguous white areas and that the distribution of histamine and histamine synthesis in the aorta is highly variable depending on the region examined. The data also suggest that local aortic histamine synthesis in blue areas may play a significantly role in mediation of the increased albumin accumulation observed in these regions.

An assessment of the potential use of anionic dextrans as a plasma substitute

Several problems exist when dextrans are used as plasma substitutes. High molecular weight dextrans can cause red cell aggregation and increased blood viscosity. Low molecular weight dextrans, although shown to improve circulation and promote flow, are removed rather rapidly from the circulation due to high premeation rates across capillary walls. In the present study, a small anionic charge is introduced onto the dextran to make it electrostatically negative. Since capillary walls have been shown to retain negatively charged solutes in preference to neutral solutes, the anionic dextran should retain its effectiveness for longer periods of time compared to similar sized neutral dextran. Studies were done on eight unanaesthetized dogs to compare the relative disappearance rates of dextran and anionic dextran (carboxymethyl dextran) from the circulation. It was shown that anionic dextrans do remain in the circulation over a longer period of time compared to neutral dextrans.

Intravital and electron microscopic study of bradykinin-induced vascular permeability changes using FITC-dextran as a tracer

Fluorescein-labelled dextran (FITC-dextran) of molecular weight 145,000 was used to study vascular permeability to macromolecules by intravital and electron microscopy. Anaesthetised hamsters prepared for intravital observation of the cheek pouch microvasculature were given an intravenous injection of FITC-dextran. Leakage of macromolecules was induced by topical application of bradykinin to the cheek pouch microvasculature and observed in fluorescent light. Leakages occurred only from postcapillary venules of a diameter well below 50 micrometer. The cheek pouch preparation was rapidly fixed by immersion and samples of tissue with intravitally identified leakages of FITC-dextran were studied by electron microscopy. FITC-dextran appeared as black precipitates in the vascular lumen and also outside the lumen in bradykinin-treated animals. In most animal; gaps were found between endothelial cells and these gaps contained dextran precipitates. The results support much other evidence that bradykinin induces macromolecular leakage by opening gaps between endothelial cells in postcapillary venules.

The morphologic effects of histamine on the lateral cochlear wall

The chinchilla lateral cochlear wall (stria vascularis, spiral ligament, and spiral prominence) was examined by morphologic and histochemical techniques following various doses of intravenous histamine. The three main findings were as follows: (1) the basic ultrastructure was not altered by histamine; (2) there is a time- and dose-dependent change in the rate of stria vascularis vessel permeability to a small protein tracer (horseradish peroxidase), but the mode of transport (large pore system) is unchanged; and (3) glycogen depletion in stria marginal cells occurs with its apparent mobilization into stria intercellular spaces.

On the heterogeneity of capillaries of pigeon pectoralis muscle: a histoenzymatic and ultrastructural study

Earlier studies had failed to show the presence of capillaries between the white fibres of pigeon pectoralis muscle. In this paper, data are reported for the first time documenting that these capillaries occur in both intra- and inter-fasicular areas of the muscle. Fresh frozen sections of pigeon pectoralis major muscle were incubated for alkaline ATPase reaction following pretreatment with different EDTA solutions (4.3 mM, pH 4.3). The results showed the existence of an inherent heterogeneity of capillaries. The capillaries of white fibres stained intensely for K+/Mg2+-EDTA or Mg2+-EDTA pre-incubated ATPase; the capillaries of red fibres stained poorly. Both white fibre and red fibre capillaries were examined ultrastructurally in the non-perfused pigeon pectoralis muscle. It is suggested that a possible correlation exists between the distinctive metabolic and mechanical characteristics of the Type II white, glycolytic, fast-twitch fast-fatigue muscle fibres and the high ATPase activity of their capillaries.

Transcapillary passage of albumin, effects of tissue cooling and of increases in filtration and plasma colloid osmotic pressure

'Initial' clearance of radiolabelled serum albumin was measured in the perfused, maximally vasodilated muscle vascular bed of rat hindquarters during tissue cooling, during increases in filtration and during changes in serum colloid osmotic pressure. Albumin clearance during ordinary serum perfusion at isogravimetry amounted to 0.03 ml/min times 100 g, increasing linearly with filtration rate to some 0.07 ml/min times 100 g at 0.5 ml/min times 100 g of filtration. During cooling from 36 degrees C to 14 degrees C both CFC and initial albumin clearance at isogravimetry decreased some 40%, in due proportion to the increased viscosity of the fluid. Increases of the colloid osmotic pressure of the perfusate correspondingly increased both the isogravimetric capillary pressure and 'initial' albumin clearance during isogravimetry.--It is concluded that even during isogravimetry the transmicrovascular albumin passage is to about 70 per cent due to filtration, and only some 30 per cent of transport at ordinary serum colloid osmotic pressure takes place by diffusion, both events presumably via 'large pores'. There was no evidence that transendothelial vesicular transport should to any significant extent contribute to the passage of albumin from vessels to tissue.

Transcapillary transport after thermal injury

The pathophysiology of the burn wound is characterized by an inflammatory reaction leading to rapid edema formation due to (1) dilatation of resistance vessels with increased effective transcapillary filtration pressure, (2) increased extravascular osmotic activity created in damaged tissue, and (3) increased microvascular permeability to macromolecules. In extensive burns increased microvascular permeability was found also in tissues remote from the thermal injury. These reactions are due to direct heat effect on the microvasculature and to chemical mediators of inflammation. Important is the increased biosynthesis of prostaglandins at the site of tissue injury which may partly explain vasodilatation, increased microvascular permeability and accumulation of polymorphonuclear leucocytes observed following thermal injury. The morphological interpretations of the changes in the functional ultrastructure of the blood-lymph barrier following thermal injury seem to be a remarkable and persistant increase in the numbers of vacuoles and many open endothelial intercellular junctions. Further less explored changes of the interstitial tissue after severe burn trauma seem to be of great importance.

Simultaneous measurements of capillary diffusion and filtration exchange during shifts in filtration-absorption and at graded alterations in the capillary permeability surface area products (PS)

The diffusion exchange of Cr-EDTA, using the single injection indicator diffusion method, was followed simultaneously with estimations of the capillary filtration capacity (CFC) in an "isogravimetric" rat hindquarter preparation during artificial perfusion and maximal dilatation. Measurements were performed at constant flow and during 1) shifts in filtration-absorbtion, 2) alterations of perfused capillary wall area (graded rarification of capillary network by microsphere injection) and 3) during alterations of permeability (i.a. infusion of histamine). At maximal vasodilatation CFC was 0.037 +/- 0.001 ml/min X mmHg X 100 g and PS for Cr-EDTA 5.67 +/- 0.13 ml/min X 100 g. During filtration or absorbtion, Cr-EDTA transfer from vessels to interstitium changed only slightly but the situation may well be different for solute transfer from interstitium to vessels. Alterations in capillary wall area resulted in proportional changes in PS for Cr-EDTA while the CFC changes were always relatively smaller. Histamine increased CFC some threefold with a marked increase in protein transfer, while PS for Cr-EDTA increased only marginally. This histamine effect could be ascribed mainly to an increase in the number of large pores which, because of their relative paucity, are of little importance for small molecular diffusion exchange but highly important for convective and macromolecular exchange.

Effects of isoprenaline and cooling on histamine induced changes of capillary permeability in the rat hindquarter vascular bed

Histamine infused intra-arterially into artificially perfused, maximally dilated rat hindquarters markedly increased fluid filtration and CFC but had essentially no effect on the diffusion capacity to small molecules. Isoprenaline largely prevented the increase in fluid filtration and CFC if infused prior to the start of the histamine infusion and, if infused after the start of the histamine infusion, promptly reduced fluid filtration and CFC to near control levels. Additionally, it was noted that severe cooling of the perfusate also largely prevented the marked increase in fluid filtration and CFC by histamine. This antagonism of histamine induced increases in macromolecular permeability represents a direct action of isoprenaline on the microvascular membrane which effectively counteracts that of histamine. The data also suggest that the large pores created by histamine are different from the large pore through which macromolecules normally transverse the microvascular membrane, and that catecholamines may exert a regulatory function in the control of microvascular permeability to macromolecules in pathophysiological states associated with massive histamine release.

[Idiopathic edema, capillaropathy, pericardial and pleural effusions with high protein content (author's transl)]

Clinical and electron microscopic studies of two female patients are reported who, in addition to the symptoms and signs of idiopathic edema, had pericardial (and pleural) effusions. In one patient pericardiectomy had to be performed, in the other patient pharmacotherapy with spironolactone was effective. In these patients the protein-concentrations of edema fluid (25 and 12 g/l) and pericardial fluid (55-61 and 48 g/l) were relatively high; the distribution space of labelled protein was increased; blood volumes were low-normal or decreased. Electronmicroscopy of the microvasculature showed identical alterations in both cases. In the cutaneous vessels the endothelium developed numerous abnormal cytoplasmic processes and intercellular "gaps". In the capillaries of skeletal muscle our findings indicate an increase in vesicular transport. We suggest the electron microscopic alterations to be the morphologic correlate for the increased transport and extravascular accumulation of protein. Changes as they are described here in humans with idiopathic edema have been documented before in animals with experimental edema.

An electrophoretic investigation of the binding of 3-14C coumarin to rat serum proteins

The binding of coumarin to serum proteins of the rat has been demonstrated. Of the total bound coumarin (37% of injected dose), 36% was bound to slow and fast oc1 globulins, 11% to the post albumins, 10% to globulin and 9% to albumin.