Isolation of rat trachea interstitial fluid and demonstration of local cytokine production in lipopolysaccharide-induced systemic inflammation.

Access to interstitial fluid from trachea is important for understanding tracheal microcirculation and pathophysiology. We tested whether a centrifugation method could be applied to isolate this fluid in rats by exposing excised trachea to G forces up to 609 g. The ratio between the concentration of the equilibrated extracellular tracer 51Cr-labeled EDTA in fluid isolated at 239 g and plasma averaged 0.94 +/- 0.03 (n = 14), suggesting that contamination from the intracellular fluid phase was negligible. The protein pattern of the isolated fluid resembled plasma closely and had a protein concentration 83% of that in plasma. The colloid osmotic pressure in the centrifugate in controls (n = 5) was 18.8 +/- 0.6 mmHg with a corresponding pressure in plasma of 22 +/- 1.5 mmHg, whereas after overhydration (n = 5) these pressures fell to 9.8 +/- 0.4 and 11.9 +/- 0.4 mmHg, respectively. We measured inflammatory cytokine concentration in serum, interstitial fluid, and bronchoalveolar lavage fluid in LPS-induced inflammation. In control animals, low levels of IL-1 beta, IL-6, and TNF-alpha in serum, trachea interstitial fluid, and bronchoalveolar lavage fluid were detected. LPS resulted in a significantly higher concentration in IL-1 beta and IL-6 in interstitial fluid than in serum, showing a local production. To conclude, we have shown that interstitial fluid can be isolated from trachea by centrifugation and that trachea interstitial fluid has a high protein concentration and colloid osmotic pressure relative to plasma. Trachea interstitial fluid may also reflect lower airways and thus be of importance for understanding, e.g., inflammatory-induced airway obstruction.

Lowering of interstitial fluid pressure after neurogenic inflammation in mouse skin is partly dependent on mast cells.

Neurogenic inflammation is known to induce lowering of interstitial fluid pressure (P(if)) in mouse skin. This study examined the possible role of mast cell activation secondary to neuropeptide release in lowering of P(if) by using Kit(W)/Kit(W-v) mice, which are devoid of mast cells, including connective tissue mast cells (CTMCs). P(if) was measured in paw skin of anesthetized (fentanyl-fluanison and midazolam, 1:1) mice with glass capillaries connected to a servo-controlled counterpressure system. In contrast to wild-type mice, intravenous administration of mast cell-activating compound 48/80 induced no lowering of P(if) in Kit(W)/Kit(W-v) mice. Intravenous challenge with substance P (SP), calcitonin gene-related peptide (CGRP), or capsaicin induced a significant (P < 0.05) lowering of P(if) in wild-type mice to -2.16 +/- 0.28, -1.96 +/- 0.11, and -2.22 +/- 0.19 mmHg, respectively, compared with vehicle (-0.49 +/- 0.11 mmHg). In Kit(W)/Kit(W-v) mice the P(if) response to SP was completely abolished (-0.53 +/- 0.32 mmHg) while the response to CGRP and capsaicin was attenuated (-1.33 +/- 0.13 and -1.42 +/- 0.13 mmHg, respectively) although significantly (P < 0.05) lowered compared with vehicle. Immunohistochemical analysis revealed no difference in distribution or density of SP- and CGRP-immunoreactive fibers in paws of Kit(W)/Kit(W-v) compared with wild-type mice. We conclude that lowering of P(if) normally depends on mast cells. However, the sensory nerves can also elicit a lowering of P(if) that is independent of mast cells.

Problems in physiological experimental animal models investigated with factorial design.

In the present study we investigated four variables using factorial design to decide if any of these could explain the variations in the control measurements of interstitial fluid pressure (P if) in rat trachea that were experienced. This approach requires only a fraction of the animals normally needed when studying each factor separately. P if in tracheal tissue was measured with the servocontrolled counterpressure system using sharpened micropipettes. The measurements were performed over a period of 60 min and are presented as mean for every 15 min period. The factors investigated in the study were: three strains of female rats (Strain) two brands of diets (Food); two breeder companies (Source); and finally two batches of the same set of animals to repeat the experiment twice (Week), using a total of 48 animals. There was a highly significant effect within Strain the first week (p=0.007), but this response was not observed the second week. The interaction between Strain×Week was significant (p=0.007) while the main effects Strain or Week alone were not significant. The response pattern for Strain and Food was inconsistent for the two experimental weeks studied. These experiments made it possible for us to simultaneously test several factors and exclude these factors as the reason for the observed changes in our experiments since the experiments did not allow the conclusion that one or several of these factors could explain the variation in P if.

Neurogenic inflammation in mice deficient in heparin-synthesizing enzyme.

Mast cell activation, or neurogenic inflammation, is known to induce lowering of interstitial fluid pressure (P(if)) and plasma protein extravasation (PPE) in several tissues from both rats and mice. To examine a possible role of connective tissue mast cells (CTMCs) in these inflammatory responses, we used mice with dysfunctional CTMCs due to lack of the N-deacetylase/N-sulfotransferase-2 enzyme (NDST-2(-/-)). P(if) and PPE were measured after challenge with compound 48/80 (C48/80), and P(if) alone was measured after treatment either with capsaicin, substance P (SP), or calcitonin gene-related peptide (CGRP). Measurements of P(if) in anesthetized (fentanyl/fluanison and midazolam, 1:1) mice were performed in paw skin with glass capillaries connected to a servo-controlled counterpressure system. PPE was measured with microdialysis by using hollow plasmapheresis fibers (cutoff at 3,000 kDa) placed subcutaneously on the back. Intravenous administration of C48/80 lowered P(if) significantly (P < 0.05) in NDST-2(-/-) mice (-1.67 +/- 0.42 mmHg) compared with vehicle (-0.57 +/- 0.17 mmHg) but the lowering was significantly (P < 0.05) less compared with that of the NDST-2(+/+) mice (-2.31 +/- 0.47 mmHg). PPE was increased 300% after treatment with C48/80 in NDST-2(+/+) mice, whereas there was no increase in PPE in NDST-2(-/-) mice. Capsaicin, SP, and CGRP lowered P(if) significantly (P < 0.05) compared with vehicle and to the same extent in both NDST-2(+/+) and NDST-2(-/-) mice. We can conclude that although NDST-2(-/-) mice demonstrate an altered response in P(if) after mast cell activation, there was no similar alteration after neurogenic inflammation. Therefore, we suggest that neurogenic inflammation in mouse skin is not exclusively dependent on intact CTMCs.

Role of EETs in regulation of endothelial permeability in rat lung.

This study tested the hypothesis that epoxyeicosatrienoic acids (EETs) derived from arachidonic acid via P-450 epoxygenases are soluble factors linking depletion of endoplasmic reticulum Ca(2+) stores and store-dependent regulation of endothelial cell (EC) permeability in rat lung. EC permeability was measured via the capillary filtration coefficient (K(f,c)) in isolated, perfused rat lungs. 14,15-EET and 5,6-EET increased EC permeability, a response that was significantly different from that of 8,9-EET, 11,12-EET, and vehicle control. The permeability response to 14,15-EET was not significantly attenuated by the nonspecific Ca(2+) channel blocker Gd(3+) (P = 0.068). In lungs perfused with low [Ca(2+)], 14,15-EET tended to increase EC permeability, although a significant increase in K(f,c) was observed only following Ca(2+) add-back. As positive control, we showed that the 3.7-fold increase in K(f,c) evoked by thapsigargin (TG), a known activator of store depletion-induced Ca(2+) entry, was blocked by both Gd(3+) and low [Ca(2+)] buffer. Nonetheless, the permeability response to TG could not be blocked by the phospholipase A(2) inhibitors mepacrine or methyl arachidonyl fluorophosphonate or the P-450 epoxygenase inhibitors 17-octadecynoic acid or propargyloxyphenyl hexanoic acid. Similarly, combined pretreatment with ibuprofen and dicyclohexylurea to block EET metabolism had no effect on the permeability response to TG. We conclude that EETs have a heterogeneous impact on EC permeability. Despite a requirement for Ca(2+) entry with both TG and 14,15-EET, our data suggest that distinct signaling pathways or heterogeneity in EC responsiveness is responsible for the observed EC injury evoked by EETs and store depletion in the isolated rat lung.

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.