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.