Adrenergic regulation of regional fat metabolism

Introduction: An increased gluteofemoral adipose tissue (AT) mass is associated with a protective cardiovascular and metabolic risk profile, and effective fatty acid retention in femoral AT has been proposed as a possible mechanism. Catecholamines are important regulators of AT lipolysis and blood flow (ATBF). The aim of the thesis was to investigate regional differences in the adrenergic regulation of fatty acid release and ATBF between abdominal and femoral AT in vivo. Furthermore, in vivo regional fatty acid trafficking was studied in a physiological setting over 24 h.Methods: Regional fatty acid trafficking, along with the measurement of ATBF, was studied with the arterio-venous difference technique and stable isotope tracers in healthy volunteers. Adrenergic agonists (isoprenaline, adrenaline) were infused either locally by microinfusion, or systemically. Local microinfusion of adrenoreceptor antagonists (propranolol, phentolamine) was used to characterize specific adrenoreceptor subtype effects. The trafficking of dietary fatty acids was studied over a 24 h period involving three meals containing stable isotope-labelled fatty acids along with intravenous infusions of another labelled fatty acid.Results: Femoral ATBF and lipolysis was less responsive to adrenergic stimulation with adrenaline compared to abdominal AT. This was due to increased femoral α-adrenoreceptor responsiveness. When studied over 24 h, femoral AT showed a lower lipolysis rate compared to abdominal AT, while dietary fatty acids were extracted more avidly by abdominal AT. Uptake of non-dietary fatty acids (derived from very-low-density lipoproteins or unbound non-esterified fatty acids) was comparable between abdominal and femoral AT.Conclusion: There are fundamental differences in response to adrenergic stimuli between abdominal and gluteofemoral tissues and the ability of femoral AT to trap non-dietary fatty acids may provide protection of other tissues from ectopic fatty acid deposition.This thesis is not currently available via ORA