Real-Time Sampling of Rat Femoral Arteriovenous Adventitial Interstitial Fluid by Placement of a Microdialysis Probe

Interstitial fluid (ISF) is a vital element of the extracellular microenvironment, facilitating metabolic exchange and intercellular communication. Nevertheless, the anatomical depth and close proximity to vascular structures make the adventitial ISF (AISF) especially difficult to sample without introducing contamination or causing tissue disruption. In this study, we introduce a real-time, minimally invasive method for AISF collection through the use of microdialysis in anesthetized rats. Dual 20 kDa cut-off probes were surgically implanted in the femoral arteriovenous adventitia and the jugular vein to allow for continuous sampling of ISF and blood, respectively. The perfusion with artificial extracellular fluid enabled the selective diffusion of low-molecular-weight metabolites. Through principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA), a distinct metabolic divergence between AISF and blood was observed, identifying 146 significantly differential metabolites. The enrichment patterns of lactate and serotonin confirmed the anatomical specificity and functional reliability of the method. Importantly, AISF was enriched with locally synthesized metabolites that were absent in plasma, highlighting its unique physiological significance. In comparison to current interstitial fluid (ISF) sampling methodologies, such as microneedles, suction blisters, and reverse iontophoresis, microdialysis provides enhanced molecular resolution, greater sampling stability, and reduced invasiveness. This technique constitutes a reliable platform for in vivo analysis of analytes in interstitial fluid (AISF) and shows significant potential for advancing biomarker discovery and research into vascular pathophysiology.