The anti-inflammatory agent alpha-trinositol exerts its edema-preventing effects through modulation of beta 1 integrin function

Diuretic-Resistant Ascites Following Laparoscopic Surgery in a Patient With Chronic Myeloid Leukemia on Imatinib Therapy

Imatinib mesylate is a tyrosine kinase inhibitor with high efficacy in the treatment of chronic myeloid leukemia (CML). Although fluid retention is a common adverse effect of imatinib, it rarely necessitates discontinuation of therapy. Isolated ascites has not been reported as a complication of imatinib therapy in patients with CML. Here, we report the case of a 72-year-old male with CML on imatinib (600 mg daily), who developed ascites two weeks after a laparoscopic hernia repair with intraperitoneal placement of a nylon mesh. The ascites was resistant to diuretic therapy and required repeated large-volume paracentesis. Discontinuation of imatinib resulted in arrest of ascites production, but reintroduction of the drug at the same dose two weeks later was rapidly followed by recurrence of ascites requiring further therapeutic paracenteses. It was postulated that peritoneal inflammation had resulted in increased capillary permeability, which was further augmented by imatinib via inhibition of platelet-derived growth factor receptor (PDGFR), a tyrosine kinase known to play a significant physiological role in the regulation of interstitial fluid pressure and capillary permeability. The possibility of developing ascites after abdominal surgery should be considered in patients receiving imatinib or related PDGFR inhibitors. In such cases, perioperative interruption of tyrosine kinase therapy might be indicated.

A Modern View of the Interstitial Space in Health and Disease

Increases in the volume of the interstitial space are readily recognized clinically as interstitial edema formation in the loose connective tissue of skin, mucosa, and lung. However, the contents and the hydrostatic pressure of this interstitial fluid can be very difficult to determine even in experimental settings. These difficulties have long obscured what we are beginning to appreciate is a dynamic milieu that is subject to both intrinsic and extrinsic regulation. This review examines current concepts regarding regulation of interstitial volume, pressure, and flow and utilizes that background to address three major topics of interest that impact IV fluid administration. The first of these started with the discovery that excess dietary salt can be stored non-osmotically in the interstitial space with minimal impact on vascular volume and pressures. This led to the hypothesis that, along with the kidney, the interstitial space plays an active role in the long-term regulation of blood pressure. Second, it now appears that hypovolemic shock leads to systemic inflammatory response syndrome principally through the entry of digestive enzymes into the intestinal interstitial space and the subsequent progression of enzymes and inflammatory agents through the mesenteric lymphatic system to the general circulation. Lastly, current evidence strongly supports the non-intuitive view that the primary factor leading to inflammatory edema formation is a decrease in interstitial hydrostatic pressure that dramatically increases microvascular filtration.

Additional evidence that the rat renal interstitium contracts in vivo

We recently provided highly suggestive preliminary evidence that the renal interstitium contracts reactively in vivo. We demonstrated that renal medullary direct interstitial volume expansion (rmDIVE = 100 μl bolus infusion of 0.9% saline (SS)/30 s) brought about a biphasic renal interstitial hydrostatic pressure (RIHP) response which was abolished when dibutyryl-cAMP was concomitant and interstitially infused. To assess more deeply the feasibility of the concept that the renal interstitium contracts in vivo, two experimental series (S1, S2) were performed in hydropenic rats subjected to acute left renal-denervation, hormonal clamping, and control of renal arterial pressure. In S1, RIHP and renal outer medullary blood flow (RoMBF) were continuously measured before and after a sudden micro-bolus (5μl) injection, into the renal medullary interstitium, of SS containing α-trinositol (α-TNS, anti-inflammatory drug) to either two doses 2 or 4 mM (SS + 2 α-TNS and SS + 4 α-TNS groups). No overall differences between groups in either ΔRIHP or %ΔRoMBF time courses were found; however, in the SS + 2 α-TNS group the data were less scattered and the ΔRIHP time course tended to peak faster and then persisted there, so that, this α-TNS dose was selected for S2. In S2, RIHP and RoMBF were similarly measured in rats randomly assigned to three groups: the CTR group (sham time-control), SS group (SS alone), and SS + α-TNS group. The micro-bolus injection of SS alone (SS group) was unable to increase ΔRIHP. The group with no micro-bolus injection (CTR group) experienced a decrease in ΔRIHP. The micro-bolus injection of SS + 2 α-TNS was accompanied by a differential increase in ΔRIHP (vs. CTR and SS groups). These responses were not associated with differential changes among groups in %ΔRoMBF or hemodilution parameters. These results provide additional evidence that the renal interstitium contracts in vivo.

Highly suggestive preliminary evidence that the renal interstitium contracts in vivo

To learn more about controlling renal interstitial hydrostatic pressure (RIHP), we assessed its response to renal medullary direct interstitial volume expansion (rmDIVE = 100 μL bolus infusion/30 sec). Three experimental series (S) were performed in hydropenic, anesthetized, right‐nephrectomized, acute left renal‐denervated and renal perfusion pressure‐controlled rats randomly assigned to groups in each S. S1: Rats without hormonal clamp were contrasted before and after rmDIVE induced via 0.9% saline solution bolus (SS group) or 2% albumin in SS bolus (2% ALB + SS group). Subcapsular ΔRIHP rose slowly, progressively and similarly in both groups by ~3 mmHg. S2: Rats under hormonal clamp were contrasted before and after sham rmDIVE (time CTR group) and real rmDIVE induced via either SS bolus (SS group) or SS bolus containing the subcutaneous tissue fibroblast relaxant dibutyryl‐cAMP (SS + db‐cAMP group). ΔRIHP showed time, group, and time*group interaction effects with a biphasic response (early: ~1 mmHg; late: ~4 mmHg) in the SS group that was absent in the SS + db‐cAMP group. S3: Two groups of rats (SS and SS + db‐cAMP) under hormonal clamp were contrasted as in S2, producing similar ΔRIHP results to those of S2 but showing a slow, progressive, and indistinct decrease in renal outer medullary blood flow in both groups. These results provide highly suggestive preliminary evidence that the renal interstitium is capable of contracting reactively in vivo in response to rmDIVE with SS and demonstrate that such a response is abolished when db‐cAMP is interstitially and concomitantly infused.

The integrin needle in the stromal haystack: emerging role in corneal physiology and pathology

Several studies have established the role of activated corneal keratocytes in the fibrosis of the cornea. However, the role of keratocytes in maintaining the structural integrity of a normal cornea is less appreciated. We focus on the probable functions of integrins in the eye and of the importance of integrin-mediated keratocyte interactions with stromal matrix in the maintenance of corneal integrity. We point out that further understanding of how keratocytes interact with their matrix could establish a novel direction in preventing corneal pathology including loss of structural integrity as in keratoconus or as in fibrosis of the corneal stroma.

Corticotropin-releasing factor reduces tumor volume, halts further growth, and enhances the effect of chemotherapy in 4T1 mammary carcinoma in mice

The present study examines the effect of the endogenous neuroendocrine factor, corticotropin-releasing factor (CRF), alone or in combination with 5-fluorouracil (5-FU), on 4T1 mammary tumor cells in vitro and in vivo. CRF has been detected in breast cancer tissues; however, the biological effects reported in the literature are sparse and variable. We found that exogenously administered CRF significantly reduced tumor growth without influencing angiogenesis or cell death. Furthermore, CRF reduced tumor interstitial fluid pressure (Pif) and potentiated the effect of 5-FU. These results show that CRF has antitumor effect on mammary carcinoma in mice.

Transcapillary exchange: role and importance of the interstitial fluid pressure and the extracellular matrix

This review will summarize current knowledge on the role of the extracellular matrix (ECM) in general and on the interstitial fluid pressure (P(if)) in particular with regard to their importance in transcapillary exchange. The fluid volume in the interstitial space is normally regulated within narrow limits by automatic re-adjustment of the interstitial hydrostatic and colloid osmotic pressures in response to perturbations in capillary filtration and by the lymphatics. Contrary to this commonly accepted view, P(if) can become an active force and create a fluid flux across the capillaries in several inflammatory reactions and trauma situations rather than limit the changes occurring. The molecular mechanisms involved in the lowering of P(if) include the release of cellular tension exerted on the collagen and microfibril networks in the connective tissue via the collagen-binding beta(1)-integrins, thereby allowing the glycosaminoglycan ground substance, which is normally underhydrated, to expand and take up fluid. Several growth factors and cytokines, including the platelet-derived growth factor BB, are able to reverse a lowering of P(if) and restore the normal compaction of the ECM. The magnitude of the lowering of P(if) varies with the inflammatory response. In several inflammatory reactions, a lowering of P(if) to -5 to -10 mmHg is seen, which will increase capillary filtration by 10-20 times since the normal capillary filtration pressure is usually 0.5-1 mmHg (skin and skeletal muscle). Unless this lowering of P(if) is taken into account, the enhanced solute flux resulting from an inflammatory response will be ascribed to an increased capillary permeability.

Intraventricular injection of antibodies to β1-integrins generates pressure gradients in the brain favoring hydrocephalus development in rats

In some tissues, the injection of antibodies to the β1-integrins leads to a reduction in interstitial fluid pressure, indicating an active role for the extracellular matrix in tissue pressure regulation. If perturbations of the matrix occur in the periventricular area of the brain, a comparable lowering of interstitial pressures may induce transparenchymal pressure gradients favoring ventricular expansion. To examine this concept, we measured periventricular (parenchymal) and ventricular pressures with a servo-null micropipette system (2-μm tip) in adult Wistar rats before and after anti-integrin antibodies or IgG/IgM isotype controls were injected into a lateral ventricle. In a second group, the animals were kept for 2 wk after similar injections and after euthanization, the brains were removed and assessed for hydrocephalus. In experiments in which antibodies to β1-integrins ( n = 10) but not isotype control IgG/IgM ( n = 7) were injected, we observed a decline in periventricular pressures relative to the preinjection values. Under similar circumstances, ventricular pressures were elevated ( n = 10) and were significantly greater than those in the periventricular interstitium. We estimated ventricular to periventricular pressure gradients of up to 4.3 cmH2O. In the chronic preparations, we observed enlarged ventricles in many of the animals that received injections of anti-integrin antibodies (21 of 29 animals; 72%) but not in any animal receiving the isotype controls. We conclude that modulation/disruption of β1-integrin-matrix interactions in the brain generates pressure gradients favoring ventricular expansion, suggesting a novel mechanism for hydrocephalus development.

A fibronectin-binding protein from Streptococcus equi binds collagen and modulates cell-mediated collagen gel contraction

The N-terminal fragment (FNZN) of the fibronectin-binding protein FNZ from Streptococcus equi subspecies zooepidemicus was investigated as to effects on murine cell interactions with extracellular matrix proteins. FNZN bound to immobilized fibronectin (FN) and native, but not denatured, collagen type I. FNZN had no effect on primary adhesion of cells from the murine myoblastic C2C12 cell line to immobilized fibronectin. C2C12 cells adhered to immobilized FNZN, a process that was not inhibited by anti-human FN IgG or by an inhibitor of integrin alphaVbeta3. C2C12 cells lack collagen-binding beta1 integrins and neither adhere to native collagen nor mediate contraction of three-dimensional collagen gels. FNZN stimulated collagen gel contraction by C2C12 cells but not adhesion of C2C12 cells to collagen. Experiments with an alphaVbeta3-inhibitor suggested that FNZN promoted contraction by a process requiring alphaVbeta3. Our data suggest that FNZN by binding to cells, collagen, and FN modulate complex adhesive processes mediated by the alphaVbeta3 integrin. Since alphaVbeta3-mediated contractile events function to counteract edema formation during inflammation, it is possible that FNZN and its secreted homologue FNE modulate edema responses in infected tissues.

Effect of the cytoskeletal fixation agent phalloidin on transcapillary albumin transport and interstitial fluid pressure following subdermal prostaglandin E1 administration in the rat

AIM

Lowering of interstitial fluid pressure (Pif) facilitates fluid filtration across the capillary membrane and oedema formation in acute inflammation. The cellular mechanism behind this lowering of Pif involves beta1-integrins mediating contact between dermal cells and the extracellular matrix fibres, and also the cell cytoskeleton as disruption of actin filaments using cytochalasin-D induced a lowering of Pif and oedema formation. Fixation of actin with phalloidin attenuates oedema formation and abolishes lowering of Pif in anaphylaxis in the rat. The objective of this study was to determine whether phalloidin modifies lowering of Pif and albumin extravasation in rat skin also after prostaglandin E1 (PGE1).

METHODS

Pif was measured using micropipettes connected to a servo-controlled counterpressure system. Microvascular permeability was estimated as the albumin extravasation (Ealb) using radiolabelled human serum albumin.

RESULTS

Subdermal injection of PGE1 (0.85 mg mL-1) lowered Pif from -0.8 +/- 0.8 mmHg (SD) in control to -3.5 +/- 0.9 mmHg (P < 0.05) within 30 min. Pre-treatment with phalloidin (500 microg kg-1) before PGE1 resulted in Pif of -1.7 +/- 1.0 mmHg (P < 0.05 compared with PGE1). Ealb after subdermal saline was 0.07 +/- 0.04 mL g-1 DW and increased to 0.32 +/- 0.32 mL g-1 DW with PGE1 (P < 0.05) but was unaffected by pre-treatment with phalloidin given before PGE1 0.32 +/- 0.35 mL g-1 DW (P > 0.05 compared with PGE1 alone).

CONCLUSION

These results are consistent with the concept that the cytoskeleton actin filaments participate in control of Pif.

Effect of alpha-trinositol on interstitial fluid pressure, edema generation, and albumin extravasation after ischemia-reperfusion injury in rat hind limb

Reperfusion of ischemic tissue often leads to an acute inflammatory response, which acts directly to aggravate the injury in the reperfused zone, characterized by adhesion and subsequent infiltration of inflammatory cells that injure the tissue through the generation of oxygen-derived free radicals and release of various inflammatory mediators. The rapid edema formation associated with reperfusion injury is induced by increased microvascular permeability to plasma proteins and/or increased net filtration pressure across the microvascular wall, and the latter is at least in part induced by lowering of the interstitial fluid pressure (P(if)). We investigated the anti-inflammatory effect of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate) on edema formation, microvascular protein leakage, and P(if) in rat hind limb after ischemia-reperfusion (I/R) injury. There was significant increase of both albumin extravasation from 0.02 +/- 0.02 to 0.41 +/- 0.21 mL g dry weight-1 (P < 0.05) and total tissue water from 1.08 +/- 0.07 to 1.65 +/- 0.55 mL g dry weight(-1) (P < 0.05) in the skin of paws undergoing I/R injury. P(if) was significantly lowered from -0.51 +/- 0.34 to -5.00 +/- 1.53 mmHg (P < 0.05) concomitant with substantial edema formation. The edema formation, and lowering of P(if) during I/R injury was significantly lowered and nearly totally abolished in the animals treated with alpha-trinositol 30 min before reperfusion. We conclude that alpha-trinositol limits the increased vascular permeability and edema formation by preventing the decrease in P(if) as well as acting protective on the microvascular wall.

Cerebral microvessel responses to focal ischemia

Cerebral microvessels have a unique ultrastructure form, which allows for the close relationship of the endothelium and blood elements to the neurons they serve, via intervening astrocytes. To focal ischemia, the cerebral microvasculature rapidly displays multiple dynamic responses. Immediate events include breakdown of the primary endothelial cell permeability barrier, with transudation of plasma, expression of endothelial cell-leukocyte adhesion receptors, loss of endothelial cell and astrocyte integrin receptors, loss of their matrix ligands, expression of members of several matrix-degrading protease families, and the appearance of receptors associated with angiogenesis and neovascularization. These events occur pari passu with neuron injury. Alterations in the microvessel matrix after the onset of ischemia also suggest links to changes in nonvascular cell viability. Microvascular obstruction within the ischemic territory occurs after occlusion and reperfusion of the feeding arteries ("focal no-reflow" phenomenon). This can result from extrinsic compression and intravascular events, including leukocyte(-platelet) adhesion, platelet-fibrin interactions, and activation of coagulation. All of these events occur in microvessels heterogeneously distributed within the ischemic core. The panorama of acute microvessel responses to focal cerebral ischemia provide opportunities to understand interrelationships between neurons and their microvascular supply and changes that underlie a number of central nervous system neurodegenerative disorders.

Lowering of interstitial fluid pressure in rat trachea after substance P alone and in combination with calcitonin gene-related peptide

Neurogenic inflammation is mediated following a release of sensory neuropeptides including calcitonin gene-related peptide (CGRP) and substance P (SP). The release of peptides can be mediated chemically with capsaicin, or electrically by stimulation of the vagal nerve, both inducing vasodilation, plasma protein extravasation and lowering of interstitial fluid pressure (Pif) which will contribute to the enhancement of oedema formation.

AIM

Lowering of Pif has previously been demonstrated following intravenous (i.v.) treatment with CGRP, but it was not possible to demonstrate that SP had this effect under the same condition.

METHODS

Micropuncture measurements of Pif in the submucosa, without opening of the trachea, was conducted on rats anaesthetized with pentobarbital sodium (50 mg kg-1) and cardiac arrest was induced with i.v. KCl.

RESULTS

Pif in vehicle-treated animal averaged -1.7 +/- 0.4 (SD) mmHg (n = 9). Intravenous injection of SP induced significant lowering of Pif compared with control, both at low dose (0.47 nmol kg-1 body weight) with 1 min distribution time (P < 0.007, -4.2 +/- 2.3 mmHg) and at high dose with seconds of distribution time (P < 0.03, -4.2 +/- 1.6 mmHg). The same response was observed after treatment with SP co-injected with CGRP.

CONCLUSIONS

Substance P alone or in combination with CGRP is able to induce a rapid lowering of Pif showing that this peptide is a potent agent in increasing the hydrostatic driving pressure initially transporting fluid into the tissue during an acute inflammatory reaction.

New and active role of the interstitium in control of interstitial fluid pressure: potential therapeutic consequences

Here we present recent data indicating that the present view of the interstitium as a passive fluid reservoir has to be revised. The connective tissue cells and extracellular matrix have a role in the control of P(if) and a fundamental role in the rapid development of edema in burns and in the initial swelling in inflammation by generating a lowering of interstitial fluid pressure. In this process, the beta1-integrin system seems to provide a common pathway by which the cells can lower as well as raise P(if). Inflammatory swelling can be reversed by endo- and exogenous substances, thereby suggesting that the connective tissue can serve as a novel target for pharmacological intervention. Furthermore, the new knowledge in interstitial physiology on means to reduce interstitial fluid pressure may be of importance for drug delivery into solid tumors, where a high P(if) limits the uptake of therapeutic agents.

The neurotensin fragment AcNT(8-13) inhibits lowering of interstitial fluid pressure in rat trachea

Injury to soft tissue results in the lowering of interstitial fluid pressure (P(if)), plasma protein extravasation, and increased total tissue volume. In this study, the effects of N-acetyl neurotensin(8-13) [AcNT(8-13)] on P(if) in rat trachea were examined after electrical stimulation (ES) of the vagus nerve. P(if) was measured with glass capillaries connected to a servocontrolled counterpressure system. In pentobarbital-anesthetized female Wistar rats, the P(if) after intravenous saline was -1.8 +/- 0.3 mmHg (means +/- SD) and decreased to -5.0 +/- 0.6 mmHg (P < 0.01, n = 9) after ES. AcNT(8-13) (10 microg/kg) blocked the fall in P(if) after ES (-2.5 +/- 2.3 mmHg, P < 0.01, n = 8). In tracheal tissue from animals pretreated with AcNT(8-13) at the same dose and immersed in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation in excised tissues was significantly reduced after 2 h. The ability of AcNT(8-13) to modulate the fluid mechanics of tracheal interstitium after inflammation suggests that it may be a useful tool for studying cell adhesion and related factors that maintain structural integrity of connective tissue after injury.

Cytochalasin D induces edema formation and lowering of interstitial fluid pressure in rat dermis

The increased capillary fluid filtration required to create a rapid edema formation in acute inflammation can be generated by lowering the interstitial fluid pressure (P(IF)). The lowering of P(IF) appears to involve dynamic beta(1)-integrin-mediated interactions between dermal cells and extracellular matrix fibers. The present study specifically investigates the role of the cell cytoskeleton, i.e., the contractile apparatus of cells, in controlling P(IF) in rat skin as the integrins are linked to both the cytoskeleton and the extracellular matrix. P(IF) was measured using a micropuncture technique in the dorsal skin of the hind paw at a depth of 0.2--0.5 mm and following the induction of circulatory arrest with the intravenous injection of KCl in pentobarbital anesthesia. This procedure prevented the transcapillary flux of fluid and protein leading to edema formation in acute inflammation, which in turn can increase the P(IF) and therefore potentially mask a decrease of P(IF). Control P(IF) (n = 42) averaged -0.8 +/- 0.5 (means +/- SD) mmHg. In the first group of experiments, subdermal injection of 2 microl cytochalasin D, a microfilament-disrupting drug, lowered P(IF) to an average of -2.8 +/- 0.7 mmHg within 40 min postinjection (P < 0.05 compared with control). Subdermal injection of vehicle (10% DMSO in PBS or PBS alone) did not change the P(IF) (P > 0.05). Lowering of the P(IF) was not observed after the injection of colchicine or nocodazole, which specifically disrupts microtubuli in cultured cells. In the second group of experiments, 2 microl of cytochalasin D injected subdermally into rats with intact circulation increased the total tissue water (TTW) and albumin extravasation rate (E(ALB)) by 0.7 +/- 0.2 and 0.4 +/- 0.3 ml/g dry wt, respectively (P < 0.05 compared with vehicle). Nocodazole and colchicine did not significantly alter the TTW or E(ALB) compared with the vehicle (P > 0.05). Taken together, these findings strongly suggest that the connective tissue cells can participate in control of P(IF) via the actin filament system. In addition, the observation that subdermal injection of cytochalasin D lowered P(IF) indicates that a dynamic assembly and disassembly of actin filaments also occurs in the cells of dermal tissues in vivo.

Rapid loss of microvascular integrin expression during focal brain ischemia reflects neuron injury

The integrity of cerebral microvessels requires the close apposition of the endothelium to the astrocyte endfeet. Integrins alpha1beta1 and alpha6beta4 are cellular matrix receptors that may contribute to cerebral microvascular integrity. It has been hypothesized that focal ischemia alters integrin expression in a characteristic time-dependent manner consistent with neuron injury. The effects of middle cerebral artery occlusion (MCAO) and various periods of reperfusion on microvasclar integrin alpha1beta1 and alpha6beta4 expression were examined in the basal ganglia of 17 primates. Integrin subunits alpha1 and beta1 colocalized with the endothelial cell antigen CD31 in nonischemic microvessels and with glial fibrillary acidic protein on astrocyte fibers. Rapid, simultaneous, and significant disappearance of both integrin alpha1 and beta1 subunits and integrin alpha6beta4 occurred by 2 hours MCAO, which was greatest in the region of neuron injury (ischemic core, Ic), and progressively less in the peripheral (Ip) and nonischemic regions (N). Transcription of subunit beta1 mRNA on microvessels increased significantly in the Ic/Ip border and in multiple circular subregions within Ic. Microvascular integrin alpha1beta1 and integrin alpha6beta4 expression are rapidly and coordinately lost in Ic after MCAO. With loss of integrin alpha1beta1, multiple regions of microvascular beta1 mRNA up-regulation within Ic suggest that microvessel responses to focal ischemia are dynamic, and that multiple cores, not a single core, are generated. These changes imply that microvascular integrity is modified in a heterogeneous, but ordered pattern.

Effects of lactoferrin on rat dermal interstitial fluid pressure (Pif) and in vitro endothelial barrier function

We recently demonstrated that intravenous (i.v.) injection of the iron-binding protein lactoferrin (Lf) followed by antilactoferrin (aLf) antibodies or iron-saturated Lf alone increased albumin extravasation in vivo in several tissues including skin. Increased driving pressure for blood-tissue exchange or direct effects of Lf on the endothelial barrier are possible mechanisms. We therefore, firstly, measured interstitial fluid pressure (Pif) in dermis of rats given 1 mg Lf i.v. followed 30 min later by aLf or saline and circulatory arrest 1 or 5 min thereafter and compared with controls. Secondly, transmonolayer passage of Evans blue labelled albumin (EB-albumin) was evaluated in porcine pulmonary artery endothelial cells exposed to iron-free or iron-saturated Lf (both 100 microg mL-1) in the absence and presence of 0.5 mM hydrogen peroxide. Pif increased significantly at 11-30 min following Lf to +2.1 +/- 0.3 and +1.7 +/- 0.2 mmHg at 11-20 and 21-30 min, respectively, compared with +0.1 +/- 0.2 mmHg before Lf (P < 0.05, n=25). Endothelial transmonolayer passage of EB-albumin during 3 h was not affected by iron-free or iron-saturated Lf neither in the absence nor presence of hydrogen peroxide that increased passage 3.5 times compared with controls. In conclusion, Lf-induced increase in albumin extravasation in rat skin is not explained by changes in Pif (because Lf raised Pif significantly) or direct effects of Lf on the endothelial barrier.

Lowering of interstitial fluid pressure after neurogenic inflammation is inhibited by mystixin-7 peptide

Soft tissue injury is accompanied by lowering of interstitial fluid pressure (P(if)), plasma protein extravasation, and edema. Inflammation was produced by electrical stimulation (ES) of the vagus and the effects of the synthetic peptide mystixin-7 (p-anisoyl-Arg-Lys-Leu-Leu-D-Thi-Ile-D-Leu-NH(2)) on P(if) were examined. Micropuncture measurement of P(if) in submucosa, without opening the trachea, was conducted on rats anesthetized with pentobarbital sodium (50 mg/kg) and euthanized with intravenous KCl. P(if) in control (intravenous saline) was -1.2 +/- 0.7 mmHg before ES and decreased to -4.7 +/- 1.0 mmHg (P < 0.01, n = 8) after ES. Mystixin-7 (10 and 20 microg/kg iv) blocked the fall in P(if) after ES (-1.1 +/- 0.3 and -0.8 +/- 0.2 mmHg, P < 0.01, n = 8 and n = 4). The 1 microg/kg dose was without effect. When trachea from animals pretreated with mystixin-7 (20 microg/kg iv) were soaked in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation was significantly reduced. This study suggests that mystixin peptides, which have structural similarity to a fragment from laminin-alpha1 chain, may be useful tools for studying cell adhesion and factors that maintain the structural integrity of connective tissue after injury.

Stimulation of integrin-mediated cell contractility by fibronectin polymerization

Ligation of integrins with extracellular matrix molecules induces the clustering of actin and actin-binding proteins to focal adhesions, which serves to mechanically couple the matrix with the cytoskeleton. During wound healing and development, matrix deposition and remodeling may impart additional tensile forces that modulate integrin-mediated cell functions, including cell migration and proliferation. We have utilized the ability of cells to contract floating collagen gels to determine the effect of fibronectin polymerization on mechanical tension generation by cells. Our data indicate that fibronectin polymerization promotes cell spreading in collagen gels and stimulates cell contractility by a Rho-dependent mechanism. Fibronectin-stimulated contractility was dependent on integrin ligation; however, integrin ligation by fibronectin fragments was not sufficient to induce either tension generation or cell spreading. Furthermore, treatment of cells with polyvalent RGD peptides or pre-polymerized fibronectin did not stimulate cell contractility. Fibronectin-induced contractility was blocked by agents that inhibit fibronectin polymerization, suggesting that the process of fibronectin polymerization is critical in triggering cytoskeletal tension generation. These data indicate that Rho-mediated cell contractility is regulated by the process of fibronectin polymerization and suggest a novel mechanism by which extracellular matrix fibronectin regulates cytoskeletal organization and cell function.

Effect of alpha-trinositol on carrageenan-induced rat paw edema and lowering of interstitial fluid pressure

Alpha-trinositol attenuates edema formation and capillary albumin extravasation and lowering of interstitial fluid pressure (Pif) in several acute inflammatory reactions in rat skin or trachea. The lowering of Pif is an important driving force required to explain the rapid edema formation in acute inflammatory reactions. The lowering of Pif and edema formation are attenuated by alpha-trinositol, which is suggested to act on the cellular adhesion receptor for extracellular matrix components. This would represent a novel therapeutic strategy for acute inflammation. To further clarify the mechanisms behind the anti-inflammatory effects of alpha-trinositol, the effects of pre- and post-treatment with alpha-trinositol on edema formation and lowering of Pif were studied after subdermal injection of carrageenan in the rat. The experiments measuring Pif showed that the lowering of Pif induced by carrageenan was abolished by 10 mg alpha-trinositol when administered either prior to or after injection of 5 microl 1% (w/v) lambda carrageenan in the dorsum of the paw. Edema formation after injection of lambda carrageenan (100 microl, 1.5% w/v) into the foot pad was studied in a separate series. In control animals receiving saline vehicle, the volume of the paw injected with carrageenan increased by approximately 30% after 3-4 h. The only significant effect of infusion of 20 mg kg(-1) h(-1) alpha-trinositol was a reduction of edema to approximately 20% when treatment was started 1 h before carrageenan injection. Therefore, the plasma concentration of alpha-trinositol must already be high when carrageenan is injected in order to prevent edema in the late phase. In conclusion, the present results indicate that the mechanisms involved in the lowering of Pif in the early phase of edema development are different from those responsible for the manifest edema measured 3-4 h after carrageenan.

Effect of alpha-trinositol on interstitial fluid pressure, oedema generation and albumin extravasation in experimental frostbite in the rat

1. The anti-inflammatory effect of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate) on oedema formation, microvascular protein leakage and interstitial fluid pressure (Pif) in rat skin after frostbite injury, was investigated. Alpha-trinositol (40 mg kg body weight(-1)) was administered intravenously as a bolus both before and/or in the interval between freezing and thawing of the tissue. 2. Pif was measured in rat paw skin with micropipettes connected to a servo-controlled counterpressure system. Oedema formation was estimated by measuring the increase in total tissue water content (wet weight minus dry weight divided by dry weight). Albumin extravasation (i.e., the difference between the plasma equivalent space for 125I- and 131I-human serum albumin (HSA) circulating for different time intervals) was used to estimate the microvascular leakage. 3. Compared to untreated animals, alpha-trinositol given pre- and/or post-freeze reduced total tissue water and albumin extravasation as well as the fall in Pif in injured tissue significantly (P<0.05). Alpha-trinositol given only post-freeze reduced total tissue water and albumin extravasation from 4.46+/-0.93 and 2.37+/-1.12 to 2.51+/-0.29 and 0.36+/-0.18 ml g dry weight(-1), respectively (P<0.05). 4. Pif fell from -0.8+/-0.2 mmHg pre-freeze to -3.4+/-1.0 mmHg (P<0.05) at 20 min after tissue injury (circulatory arrest) and was attenuated by treatment with alpha-trinositol. 5. We conclude that alpha-trinositol exerts its anti-oedematous effect by acting on the extracellular matrix, attenuating the lowering of Pif as well as on the microvascular wall, thereby decreasing the protein extravasation.

D-myo inositol 1,2,6, triphosphate (alpha-trinositol, pp56): selective antagonist at neuropeptide Y (NPY) Y-receptors or selective inhibitor of phosphatidylinositol cell signaling?

1. D-myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, D-myo inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes anti-inflammatory and analgesic effects and antagonism of neuropeptide Y (NPY)-mediated cellular responses. 2. However, not all responses elicited by this neuropeptide are sensitive to antagonism by pp56. Evidence is emerging, at least in certain tissues, that other receptor populations, in addition to those for NPY, are also sensitive to inhibition by pp56. 3. A direct or allosteric interaction of pp56 at receptors for NPY is now considered unlikely and it is more probable that pp56 might interfere at some point in the phosphatidylinositol signaling pathway, possibly at the level of the plasmalemmal inositol 1,3,4,5, tetrakisphosphate receptor. 4. Full realization of the therapeutic potential of this novel compound, however, must await a thorough characterization of the cellular mechanism(s) associated with the various pharmacological effects of pp56.

Cell interactions with collagen matrices in vivo and in vitro depend on phosphatidylinositol 3-kinase and free cytoplasmic calcium

We have investigated the role of phosphatidylinositol 3-kinase (PI3-kinase) in cellular interactions with collagenous matrices. Platelet-derived growth factor-BB (PDGF-BB) elicited a mobilization of intracellular Ca2+ in pig aortic endothelial (PAE) cells transfected with wild type PDGF beta-receptor. This response was greatly reduced in PAE cells transfected with PDGF beta-receptors mutated at positions Y740 and Y751 to prevent PI3-kinase binding. The experimental drug 1D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol) induced a rapid increase and subsequent oscillations of the cytoplasmic Ca2+ concentration in cultured fibroblasts. This response was not due to an effect of alpha-trinositol on inositol 1,4,5-trisphosphate (IP3) receptors. alpha-Trinositol did not influence PDGF-BB elicited chemotaxis through collagen-coated membranes of PAE cells transfected with the wild-type PDGF beta-receptor, but restored PDGF-BB elicited chemotaxis of PAE cells transfected with the PI3-kinase binding-site mutated PDGF beta-receptor. Collagen gel contraction has been suggested to serve as a model for cellular control of interstitial fluid pressure (PIF) in dermis. The PI3-kinase inhibitors wortmannin (50 nM) and LY294002 (5 microM) inhibited the stimulation of fibroblast-mediated collagen gel contraction by 0.4 nM PDGF-BB. Injection of wortmannin in rat paw skin induced a lowering of PIF, and this effect was abolished in animals pre-treated with alpha-trinositol. Pretreatment of rats with alpha-trinositol abolished the decrease in PIF induced by injecting monoclonal anti-rat alpha 2 beta 1 integrin IgG in rat paw skin. Taken together our data indicate that cell-collagen interactions in vivo and in vitro depend on PI3-kinase, and that this dependence can be bypassed by a drug eliciting intracellular Ca2+ mobilization.

Topical D-myo-inositol-1,2,6-trisphosphate and hexylbetaine treatment reduces albumin extravasation in experimental rat skin burn injury

The anti-inflammatory agent D-myo-inositol-1,2,6-trisphosphate (1,2,6-IP3) has shown beneficial effects in experimental burns following systemic administration. The purpose of this study was to investigate the effect of topical 1,2,6-IP3 cream on a standardised full-thickness 1 cm2 burn injury in rats. The experimental cream contained a transcutaneous absorption enhancer, hexylbetaine. Five different treatment groups were used. Two experimental groups of burned rats received either 1,2,6-IP3 cream with hexylbetaine (n = 10) or without hexylbetaine (n = 10). Two burned control groups were treated either with hexylbetaine cream (n = 10) or placebo cream (n = 10), while a third control group was untreated (n = 14). The various creams (0.5 g) were administered to the experimental burn area and allowed to remain for 3 h covered with an occlusive dressing. Spectrophotometrical quantification of Evans blue albumin extravasation was used to evaluate the effect of the experimental creams on vascular permeability following the burn trauma. Results showed a significant reduction of albumin extravasation both by 1,2,6-IP3 (p<0.05) and by hexylbetaine alone (p<0.01), as compared to placebo cream-treated animals. The transcutaneous absorption enhancer hexylbetaine did not further improve the effect of 1,2,6-IP3 on burn oedema. In conclusion, both topical 1,2,6-IP3 and hexylbetaine induced a significant reduction of albumin extravasation in burned skin. The effect of 1,2,6-IP3 could be related to previously shown anti-inflammatory actions of the agent, while the mechanisms of actions of hexylbetaine remain to be investigated.

Corticotropin-releasing hormone inhibits lowering of interstitial pressure in rat trachea after neurogenic inflammation

Increased negativity of interstitial fluid pressure (Pif) is a key determinant of edema formation after tissue injury. In this study, we addressed the question of whether the anti-inflammatory effects of corticotropin-releasing hormone (CRH) shown by others are mediated by changes in interstitial fluid pressure. CRH, 25 to 50, but not 5 and 11 microg/kg s.c., administered 45 min before antidromic stimulation of the vagal nerve inhibited the lowering of interstitial fluid pressure in rat trachea produced by nerve stimulation. This inhibitory effect of CRH was blocked by pretreatment with the CRH receptor antagonist, alpha-helical CRH-(9-41), 0.15 mg/kg i.v., administered 5 min before CRH. These results suggest that CRH receptors modulate the structural integrity of the extracellular matrix in rat trachea for its response to inflammatory stimuli.

Effect of PGE1, PGI2, and PGF2 alpha analogs on collagen gel compaction in vitro and interstitial pressure in vivo

Acute inflammation in skin is accompanied by increased negativity of interstitial fluid pressure (PIF), which will increase capillary fluid filtration and thereby potentiate edema formation. A series of studies indicates that the connective tissue cells in rat dermis are involved in the control of PIF and mediate this response. The present study describes a novel effect of prostaglandin (PG) E1 isopropyl ester, carbaprostacyclin (PGI2 analog), and latanoprost (PGF2 alpha analog) on edema formation and PIF in parallel with their action on the fibroblast-populated collagen gel contraction assay. The prostaglandins were injected subdermally in pentobarbital-anesthetized rats. PIF was measured with a servo-controlled counterpressure system after circulatory arrest had been induced with saturated potassium chloride. Circulatory arrest was induced to limit edema formation that would raise interstitial fluid volume and thereby attenuate a possible increased negativity of PIF. PGE1 (0.91 mM) and carbaprostacyclin (1.28 mM) lowered PIF from a control value of -0.8 +/- 0.4 mmHg to -3.0 +/- 0.4 (P < 0.01) and -3.7 +/- 0.9 (P < 0.01) mmHg, respectively, within 45 min in a dose-dependent manner. Edema formation was measured in separate experiments. PGE1 and carbaprostacyclin significantly increased interstitial fluid volume (extravascular 51Cr-EDTA space) at concentrations as low as 0.1 and 1.1 microM, respectively. Latanoprost had no effect on PIF or edema formation. However, latanoprost reversed, in a dose-dependent manner, an increased negativity of PIF accompanying the anaphylactic reaction to dextran. In the gel contraction assay with human diploid fibroblasts (AG 1518), a corresponding specificity was observed where PGE1 and carbaprostacyclin effectively inhibited gel contraction although latanoprost had no effect. Thus the present data demonstrate a novel effect of prostaglandins and provide further evidence for active modulation of PIF via loose connective tissue cells.

Postoperative analgesia by D-myo-inositol-1,2,6-trisphosphate in patients undergoing cholecystectomy

D-myo-inositol-1,2,6-trisphosphate (1,2,6-IP3) possesses antiinflammatory properties, such as reduced eicosanoid synthesis and inhibition of inflammation-induced edema. These properties suggest possible analgesic effects. The analgesic effect of 1,2,6-IP3 was evaluated in a double-blind, randomized study in 24 patients undergoing cholecystectomy. Ten patients received 1,2,6-IP3 as an intravenous (i.v.) bolus dose of 240 mg, followed by a continuous i.v. infusion at 90 mg/h for 24 h. The placebo group (n = 14) received corresponding volumes of isotonic saline. Postoperative pain (visual analog pain scale; VAS) and opiate analgesic requirements (ketobemidon) were evaluated during five postoperative days. Results showed significantly reduced pain during the first five postoperative days in patients treated with 1,2,6-IP3, as measured by using a VAS (P < 0.05). The requirements of opioid analgesics were significantly reduced during the first three postoperative days (P < 0.05). No drug-related side effects were observed. Results of the present study demonstrate a potent and long-lasting analgesic effect of 1,2,6-IP3, possibly related to its antiinflammatory properties.

IMPLICATIONS

A new antiinflammatory drug under investigation, inositol-1,2,6-trisphosphate, was evaluated as a possible analgesic in a pilot study during the postoperative period in cholecystectomized patients. Results showed significantly lower pain assessment and opioid consumption, which should encourage further studies.

Swelling and damage of glial cells by lactacidosis and glutamate: effect of alpha-trinositol

The therapeutical efficacy of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), an isomer of the intracellular messenger IP3, was analyzed on cytotoxic swelling and damage of glial cells in vitro from lactacidosis or glutamate. C6 glioma cells suspended in a physiological medium were either exposed to pH 5.0 by administration of lactic acid, or to 1 mM glutamate. Cell swelling and viability were quantified by flow cytometry. Lactacidosis of pH 5.0 led to an increase in cell volume to 139.7 +/- 1.3% within 20 min whereas alpha-trinositol was reducing the swelling response by approximately 25% (P < 0.01). In addition, at pH 5.0 the fraction of viable cells was lowered from 94.3 +/- 0.2% (control) to only 53.8 +/- 3.1% after 60 min. Alpha-trinositol was found to protect also cell viability; at 60 min of lactacidosis 70.2 +/- 1.6% of the cells still were viable (P < 0.01). The addition of glutamate (1 mM) to the cell suspension led to a steady increase in cell size, reaching 110% of control at 120 min, irrespectively of whether alpha-trinositol was added or not.

alpha-Trinositol prevents increased negativity of interstitial fluid pressure in rat skin and trachea induced by dextran anaphylaxis

The new anti-inflammatory agent alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), is suggested to act on the cellular adhesion receptor towards extracellular matrix components, the beta1-integrins, and may therefore represent a novel principle for therapy of the phenomena associated with acute inflammation. Increased negativity of interstitial fluid pressure (p(if)) is a major driving force for the rapid edema formation in trachea and skin associated with dextran anaphylaxis in the rat. We therefore used this experimental model to study the effect of alpha-trinositol in skin and trachea of pentobarbital anesthetized rats. p(if) was measured with sharpened glass capillaries (3-7 microm) connected to a servocontrolled counterpressure system. alpha-Trinositol (10 mg) was given before or after dextran. Circulatory arrest was induced 2 min after i.v. dextran to limit the increased capillary fluid filtration associated with the anaphylactic reaction. This increased filtration will otherwise raise interstitial volume and thereby p(if) and cause an underestimation of a potential increased negativity of p(if). In the trachea, p(if) was 0.0 +/- 1.0 mmHg (S.D.) and -1.4 +/- 0.5 mmHg in controls given saline vehicle and alpha-trinositol (P > 0.05), respectively, and fell to -8.5 +/- 2.7 mmHg after dextran (P < 0.01). alpha-Trinositol given 2 min prior to or after dextran resulted in p(if) of -1.7 +/- 1.2 mmHg (P > 0.05 versus control, P < 0.01 versus dextran) and -4.7 +/- 3.0 mmHg (P < 0.01 versus control and dextran), respectively. In skin, i.v. dextran caused p(if) to fall from -0.6 +/- 0.5 to -4.6 +/- 1.9 mmHg (P < 0.001). When alpha-trinositol was given prior to dextran the corresponding figures were -0.4 +/- 0.8 and -0.9 +/- 1.1 mmHg, respectively (P > 0.05). Subdermal administration of alpha-trinositol after i.v. dextran and circulatory arrest normalized p(if) in concentration of 100, 10 and partly at 1 mg/ml. Thus, alpha-trinositol prevented the increased negativity of p(if) induced by dextran anaphylaxis when administered prior to as well as after dextran showing that the alpha-trinositol also could influence an already started inflammatory reaction.

A novel physiological function for platelet-derived growth factor-BB in rat dermis

1. The present experiments describe a role for platelet-derived growth factor-BB and cellular adhesion receptors towards extracellular matrix molecules (beta 1-integrins) in control of interstitial fluid pressure (Pif). 2. Pif was measured in rat skin with sharpened glass capillaries (3-7 microns) connected to a servocontrolled counter-pressure system. 3. The collagen and laminin-binding alpha 2 beta 1-integrin is involved in the control of Pif since subdermal injection (5 microliters) of monoclonal hamster anti-rat alpha 2 beta 1-integrin IgG (anti-alpha 2 beta 1) resulted in increased negativity of Pif. Control Pif averaged -0.88 +/- 0.23 mmHg (+/- S.D.) and decreased to -2.50 +/- 0.35 mmHg (P < 0.05) and -3.88 +/- 1.45 mmHg (P < 0.05) at anti-alpha 2 beta 1 concentrations of 0.56 and 1.12 mg ml-1, respectively. 4. The effect of anti-alpha 2 beta 1 was abolished when platelet-derived growth factor-BB (PDGF-BB) (200 ng ml-1) was injected together with anti-alpha 2 beta 1. 5. The time- and dose-responses of PDGF-BB to counteract increased negativity of Pif were studied further using dextran anaphylaxis as an experimental model inducing increased negativity of Pif in skin. Control Pif averaged -0.33 +/- 0.43 mmHg and fell to -4.10 +/- 1.47 mmHg within 10 min after dextran (P < 0.01). Subsequent subdermal injection of PDGF-BB at 200 ng ml-1 normalized Pif in 10-20 min which became -1.37 +/- 1.23 mmHg (P < 0.01 versus dextran, P > 0.05 versus control). PDGF-BB had little or no effect at 50 ng ml-1. PDGF-AA and basic fibroblast growth factor had no effect on Pif. 6. The in vivo function reported for PDGF-BB has not been described previously and provides further evidence for active participation of connective tissue cells in control of Pif by altering tension on extracellular matrix structures.

Effects of glibenclamide on the regional haemodynamic actions of alpha-trinositol and its influence on responses to vasodilators in conscious rats

1. In conscious rats, alpha-trinositol (D-myo-inositol-1, 2, 6 triphosphate; 5-80 mg kg-1 h-1 infusion) caused dose-dependent hypotension, tachycardia and hyperaemic dilatation in renal, mesenteric and hindquarters vascular beds. These effects were accompanied by inhibition of the renal vasodilator effects of acetylcholine (ACh), and of the mesenteric vasodilator effects of sodium nitroprusside (SNP) and, particularly, of levcromakalim (LCK). 2. In the light of the latter finding, in a second experiment, we assessed the influence of the KATP channel inhibitor, glibenclamide (20 mg kg-1), on resting haemodynamics, on responses to ACh, bradykinin (BK), SNP and LCK, on the haemodynamic action of alpha-trinositol, and on the effects of the latter on responses to the vasodilators, over a period of 3 days. 3. In the presence of saline, glibenclamide caused a reproducible pressor effect, accompanied by renal, mesenteric, and hindquarters vasoconstrictions on all 3 experimental days; these effects were unrelated to changes in blood glucose. In the presence of glibenclamide, only the hindquarters vasodilator response to BK, and all the cardiovascular actions of LCK were inhibited. 4. On the first experimental day, the hindquarters vasodilator effect of alpha-trinositol was substantially inhibited by glibenclamide, the renal vasodilatation less so, and the mesenteric vasodilatation not at all. However, over the subsequent two days, the mesenteric vasodilator effect of alpha-trinositol became increasingly sensitive to glibenclamide. 5. In the presence of alpha-trinositol and glibenclamide, on the first experimental day, the inhibition of the renal vasodilator effect of ACh was no greater than with alpha-trinositol alone in the first experiment. Moreover, on the third experimental day, both before and after glibenclamide, the inhibition by alpha-trinositol of the renal vasodilator response to ACh was less than on the first experimental day. Similarly, the alpha-trinositol-induced inhibition of the mesenteric vasodilator effect of SNP, and of the hindquarters vasodilator action of BK, waned over the 3 experimental days. The inhibition of the cardiovascular effects of LCK were similar on all 3 experimental days, but no greater in the presence of alpha-trinositol and glibenclamide than with glibenclamide alone. 6. These results indicate that KATP channels are involved in the maintenance of resting vasodilator tone in renal, mesenteric and hindquarters vascular beds. However, although additional activation of KATP channels is responsible for all the haemodynamic effects of LCK, it contributes only to the hindquarters vasodilator action of BK and is not involved in any of the responses to ACh or SNP. The hindquarters, renal and mesenteric vasodilator effects of alpha-trinositol may involve (in the same rank order) activation of KATP channels, probably through an indirect mechanism. However, it is unlikely that direct or indirect interaction of alpha-trinositol with KATP channels explains the ability of the drug to inhibit the renal vasodilator action of ACh, or the mesenteric vasodilator effects of SNP or LCK.

Antinociceptive effect of alpha-trinositol, a novel D-myo-inositol phosphate derivative, in the formalin test in rats

The antinociceptive effect of alpha-trinositol was examined in rats using the formalin test following systemic, spinal and local subcutaneous administration. Injection of formalin into the paw evoked two phases (phase 1: 0-9 min; phase 2: 10-60 min) of flinching behavior of the injected paw. Intrathecal administration of alpha-trinositol resulted in a dose-dependent suppression of the first (ED50: 8 microg) and second (ED50: 9 microg) phase of formalin-evoked behavioral response. Similarly, intraperitoneal delivery showed a dose-dependent reduction of the first (ED50: 83 mg/kg) and second (ED50: 56 mg/kg) phase of the formalin test. Subcutaneous injection of 100 microg, but not 10 mu g, alpha-trinositol into the rat paw together with the formalin solution, had no effect on the first phase, but reduced by 20% the second phase of behavior. These data show that alpha-trinositol produces a suppression of acute and prolonged nociceptive behaviors with a central mechanism of action, although some peripheral component may contribute to the reduction of the late phase following systemic administration.