Microdialysis for the Assessment of Catecholamine-Induced Lipolysis in Adipose and Skeletal Muscle Tissue

Abstract

Publisher Summary In recent times in situ techniques for studies of regional adipose tissue lipolysis have been developed, such as the arteriovenous-metabolite difference technique over a subcutaneous fat depot and the microdialysis technique. Microdialysis also has been introduced for studies of skeletal muscle tissue as well as several other tissues in the body. The major regulatory hormones for human adipose tissue lipolysis are insulin and catecholamines, which act on hormone-sensitive lipase. Binding sites for all adrenoceptor subtypes have been found in fat cells. It has to be pointed out that, with microdialysis, only one of the end-products of lipolysis, glycerol, can be monitored. Free fatty acids (FFAs) are hydrophobic and not dialyzable with the presently used membranes. As glycerol is not reutilized by adipose tissue, it is considered an index of lipolysis. The evaluation of blood flow variations in conjunction to in situ glycerol measurements is an important aspect. This is because the interstitial concentration of a metabolite can be determined both by its production and uptake in the tissue and by the transportation away or delivery to the tissue by the capillary bloodstream. The content of the dialysis sample reflects the net sum of these events. Tissue blood flow can be estimated either by Xenon-133 washout or by addition of a flow marker (for example, ethanol) to the microdialysis perfusate solvent. The microdialysis technique can be used in various types of lipolysis studies such as mechanistic in situ studies, systemic hormonal challenge, combinations of mechanistic in situ studies and systemic hormonal challenge, hormonal interactions, and in investigations of various tissues.