Abstract

Endocannabinoids and related N-acylethanolamines (NAEs) are lipid mediators involved in a number of physiological and pathological mechanisms in peripheral tissues. Microdialysis (MD) technique allows continues sampling of endogenous substances in the interstitial fluids of the tissues. The main limitation of MD sampling of lipophilic compounds is low recovery due to adsorption to the MD system and particularly to the catheter membranes. In this in vivo study microdialysate samples were collected from human trapezius muscle and forearm skin. The levels of arachidonoylethanolamide (AEA), 2-arachidonoylglycerol (2-AG), oleoylethanolamide (OEA), palmitoylethanolamide (PEA), and stearoylethanolamide (SEA) were analyzed in both microdialysate and in catheter membrane samples using liquid chromatography tandem mass spectrometry. OEA, PEA and SEA were identified in all microdialysate and catheter membrane samples from trapezius and skin. 2-AG was found in all catheter membrane samples from both tissues but not in the actual microdialysate. In conclusion sampling of OEA, PEA and SEA was achievable from trapezius and skin with the presented MD set-up. 2-AG is present in both trapezius muscle and skin tissue but adsorbs to the membranes in a higher extent than the NAEs. Furthermore, consideration of data conserved in the membrane during an MD experiment could be a relevant and more broadly applicable extension of MD sampling methodology which could fill an “information gap” and enhance an adequate interpretation of microdialysate data outcomes.

Keywords: Microdialysis; Endocannabinoids; 2-arachidonoylglycerol; N-acylethanolamines; Trapezius muscle; Skin tissue; Catheter membrane