Isolation of interstitial fluid in skin during volume expansion: evaluation of a method in pigs.

The ability to isolate interstitial fluid (IF) from skin would make it possible to study the microcirculation and proteins in this environment both during normal and pathophysiological conditions. Traditional IF sampling using implanted wicks suffer from low volumes with risk of contamination by local inflammatory, intracellular, and vascular proteins. To sample larger volumes of true IF, a recently described tissue centrifugation method was compared with dry and wet wicks from porcine skin under normal conditions and following volume expansion. With all three methods, volume expansion caused a significant lowering of interstitial colloid osmotic pressure as expected, and the fluid was similar to plasma when compared using size-exclusion HPLC. The centrifugation method was superior with respect to isolating larger amounts of true IF for further studies. Mass spectrometry of IF sampled with centrifugation showed that most of the proteins reflected the major plasma proteins with some tissue-specific proteins like decorin, gelsolin, and orosomucoid-1. Lumican, pigment epithelium-derived factor, and fatty acid-binding protein 4 were only identified in IF after volume expansion, possibly reflecting a local response to increased fluid filtration. Tissue centrifugation to collect IF from skin should be applicable to both clinical and experimental studies on IF balance during different pathophysiological conditions and interventions.

Edema in oral mucosa after LPS or cytokine exposure.

Lowering of interstitial fluid pressure (P(if)) is an important factor that explains the rapid edema formation in acute inflammation in loose connective tissues. Lipopolysaccharide (LPS) and the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are pathogenetic in gingivitis. To test if these substances induce lowering of P(if) in rat oral mucosa, we measured P(if) with a micropuncture technique. IL-1beta and TNF-alpha caused lowering of P(if), whereas LPS induced an immediate increase in P(if), followed by lowering after 40 min. Measurements of fluid volume distribution showed a significant change in interstitial fluid volume (V(i)) 1.5 hr after LPS exposure as V(i) changed from 0.41 +/- 0.02 to 0.51 +/- 0.03 mL/g wet weight (p < 0.05), confirming edema. These findings show that LPS, IL-1beta, and TNF-alpha induce lowering of P(if) in the rat oral mucosa and contribute to edema formation in LPS-induced gingivitis.

Platelet activating factor (PAF) increases plasma protein extravasation and induces lowering of interstitial fluid pressure (P) in rat skin.

AIM: To investigate the ability of the microdialysis technique to measure capillary selectivity of different sized plasma proteins induced by local administration of platelet activating factor (PAF). METHODS: We used hollow plasmapheresis fibres with 3 cm membrane (cut off 3000 kDa) placed on the back of anaesthetized rats. RESULTS: Platelet activating factor (50 microg mL(-1)) administered locally via the fibre, increased extravasation of radiolabelled 125I-HSA from plasma to the microdialysis fibre by approximately 900% compared both to baseline and the control fibre within 70 min (n = 6, P < 0.05). The extravasation in the control fibre did not change over time. HPLC measurement of plasma proteins in the microdialysis perfusate also demonstrated decreased capillary selectivity for proteins in the diameter range of 73 A, 56 A and 39 A after local administration of PAF (n = 6, P < 0.05). PAF also significantly lowered interstitial fluid (P(if)) pressure after subcutaneous administration (50 microg mL(-1)). Mean arterial pressure (MAP) after intravenous injection of PAF (0.4 microg kg(-1)) fell instantly by about 50 mmHg, and stabilized at 50 mmHg after 15 min (n = 6). MAP was unaltered when PAF was given through the microdialysis fibre (n = 4). Both total tissue water (TTW) and extravasation of albumin, measured as the plasma-to-tissue clearance (E-alb) showed a significant increase after PAF (n = 7, P < 0.05). CONCLUSIONS: The present study demonstrates that PAF induces plasma protein extravasation and decrease capillary selectivity of different sized plasma proteins. It also increases transcapillary fluid flux, and lowers P(if), indicating a role for PAF in the interstitium for generation of transcapillary transport of water and large molecules followed by formation of oedema.

[Subcutaneous emphysema in gastrointestinal tract perforation]. / Subkutant emfysem ved perforasjon i gastrointestinaltractus.

Perforation of the gastrointestinal tract can lead to retroperitoneal abscess formation. Clinical signs and symptoms are often non-characteristic. In undetected cases the first sign of perforation may be subcutaneous emphysema. The place where this first appears correlates with the localization of the perforation. The pathogenetic mechanisms and clinical features are discussed, with reference to a case report.

Effect of tumor necrosis factor-alpha, IL-1beta, and IL-6 on interstitial fluid pressure in rat skin.

Interstitial fluid pressure (P(if)) decreases in several experimental models of acute inflammation, enhancing edema formation. The present study was designed to determine the effect of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, and IL-1beta as well as lipopolysaccharides (LPS) on P(if) in a model of gram-negative sepsis. P(if) was measured in the paw skin of anesthetized rats (pentobarbital sodium, 50 mg/kg ip) using micropipettes (3-7 micrometer) and servo-controlled counterpressure technique. Test substances were injected intra-arterially (ia), intravenously (iv), or subdermally (sd). After intra-arterial or intravenous administration, the test substances were circulated for 1 min before circulatory arrest was induced with an intravenous injection of KCl while the rats were under pentobarbital anesthesia. Circulatory arrest was induced to avoid edema formation, which would raise interstitial fluid volume to cause a more positive P(if). Administration of 0.5 ml of LPS (5 mg/ml ia) lowered P(if) significantly from control values of -0.2 +/- 0.3 to -2.0 +/- 0.3 mmHg (P < 0.05) within 1 h. Corresponding values for TNF-alpha (500 ng/ml iv) were -0.4 +/- 0.2 to -2.3 +/- 0.1 mmHg (P < 0.05). Administration of 5 microliter (5 mg/ml sd) of LPS did not affect P(if) significantly (P > 0.05), but TNF-alpha, IL-1beta, and IL-6 had a significant effect on P(if) when given subdermally. IL-6 (50 ng/ml) caused a decrease in P(if) from control values of -1.2 +/- 0.3 to -2. 8 +/- 0.5 mmHg (P < 0.05) within 1 h. The experiments demonstrate that LPS, TNF-alpha, IL-1beta, and IL-6 induce lowering of P(if) when given intravenously or intra-arterially, whereas only TNF-alpha, IL-1beta, and IL-6 induce lowering of P(if) when given subdermally. We therefore suggest that the lowering of P(if) in this experimental model of sepsis is related to the release of and a local effect in skin of TNF-alpha, IL-1beta, and IL-6.