Isolation of interstitial fluid from skeletal muscle and subcutis in mice using a wick method

Abstract

Markhus, Carl Erik, and Helge Wiig. Isolation of interstitial fluid from skeletal muscle and subcutis in mice using a wick method. Am J Physiol Heart Circ Physiol 287: H2085-H2090, 2004. First published June 24, 2004 doi:10.1152/ajpheart.00379.2004.-Until recent years, mice were sparsely used in physiological experiments, and therefore, data on the basic cardiovascular parameters of mice are lacking. Our aim was to gain access to interstitial fluid and thereby study transcapillary fluid dynamics in this species. Using a modified wick method, we were able to isolate interstitial fluid from subcutis and skeletal muscle in mice. Three-stranded, dry, nylon wicks were inserted post mortem in an attempt to avoid local inflammation and thus eliminate protein extravasation and wick contamination. Colloid osmotic pressure (COP) was measured with a colloid osmometer for submicroliter samples and averaged (means Ϯ SE) 18.7 Ϯ 0.4 in plasma, 9.1 Ϯ 0.4 in subcutis, and 12.3 Ϯ 0.5 mmHg in muscle. HPLC of plasma and wick fluid showed similar patterns except for some minor peaks eluting in the Ͻ40-kDa region. Plasma protein extravasation as determined by 125 I-labeled human serum albumin showed that contamination of wick fluid by plasma proteins was negligible (Ͻ2%). Capillary hyperfiltration induced by intravenous infusion of saline (10% of body wt) was reflected in tissue fluid isolated by wicks as shown by the average postinfusion COP values of 14.5 Ϯ 0.6, 6.8 Ϯ 0.3, and 7.7 Ϯ 0.4 mmHg in plasma, subcutis, and muscle, respectively. We conclude that the wick technique can be easily adapted for use in mice and may represent a reliable method to isolate interstitial fluid and study transcapillary fluid flux in this species. plasma proteins; transcapillary exchange; Starling forces; colloid osmotic pressure RECENT ADVANCES IN GENETIC manipulations in mice have opened nearly unlimited possibilities for studying the physiological and pathophysiological roles of almost any functional or regulatory protein in the intact animals. These developments have made the mouse an increasingly popular model animal for physiological research. Because mice have been relatively sparsely used in physiological experiments, data regarding their basic parameters are still limited (9,15,18). This also applies to the factors that determine transcapillary fluid flux.One of these factors is the colloid osmotic pressure of the interstitial fluid (COP i ). To determine this pressure, it is necessary to isolate fluid that is representative for interstitial fluid. Such fluid is not readily available; therefore, various methods have been developed for fluid sampling. One of these is the wick method, which was first described by Aukland and Fadnes (2). In the original version of the wick method, fluid was isolated after implantation of saline-soaked wicks in rat subcutis in vivo. Owing to problems related to inflammation induced by wick insertion in subcutis (5) and cell damage during implantation in muscle (26), the method was modified. Later studies show tha...

Increased Interstitial Protein Because of Impaired Lymph Drainage Does Not Induce Fibrosis and Inflammation in Lymphedema

“…Interstitial fluid pressure was measured by micropipettes, 7 and interstitial fluid was sampled with implanted wicks 8 or by tissue centrifugation. 9 Tissue fluid volumes were measured with radioactive tracers or by weighing, 4 and COPs on a colloid osmometer designed for submicroliter samples.…”

Transcapillary fluid balance consequences of missing initial lymphatics studied in a mouse model of primary lymphoedema

“…Access to native interstitial fluid was crucial here. Since the major changes in transcapillary fluid parameters were found in body areas where use of other methods like wicks would have been difficult (Markhus & Wiig, 2004), we used a newly developed centrifugation method (Wiig et al 2003) to isolate skin interstitial fluid. In our method evaluation study we found that less than 2% of the fluid isolated by centrifugation of skin at g < 424 derived from plasma, showing that the contamination from plasma is negligible.…”

Interstitial Fluid and Lymph Formation and Transport: Physiological Regulation and Roles in Inflammation and Cancer

“…These authors also showed that the insertion resulted in an inflammatory reaction that was later avoided by performing experiments in rats after arresting the circulation (249,499) in skin and combined with catheters for muscle im-plantation (284,511). In peritoneum, where pressures determining fluid flux are of special interest due to the importance for determining fluid exchange in peritoneal dialysis, COP if was 60% of that in plasma in the control situation, falling to 28% after a 4-h peritoneal dialysis dwell (394).…”

“…Although the in vitro data suggest that the protein recovery is high and severalfold that of microdialysis (415), the protein concentration in the fluid sampled fluid is, however, 1/300 or less of the interstitial fluid concentration as estimated from COP if in mouse subcutaneous wick fluid (284,439) and the Landis-Pappenheimer equation for relationship between plasma protein concentration and COP (255). A likely explanation for this finding is that the negative pressure used during the ultrafiltration induces an increased capillary filtration, resulting in sieving of proteins at the capillary membrane, in the tissue, or at the tissue-membrane interface.…”