There is limited reliable evidence on the extent and consequences of adiposity in UK South Asian and black African-Caribbean children. Most available evidence is based on body mass index (BMI), potentially unreliable for ethnic comparisons; bioelectrical impedance (bioimpcdance) is promising but its validity for ethnic comparisons remains uncertain. The primary aims of this thesis were to describe adiposity patterns in UK South Asian, black African-Caribbean and white European children, to examine ethnic differences in the associations between adiposity and type 2 diabetes risk and to compare adiposity patterns in Indian children living in India and the UK. The main data source was the Child Heart and Health Study in England, a cross-sectional study of adiposity (including bioimpedance, skinfolds and BMI) and type 2 diabetes risk markers in 5759 South Asian, black African-Caribbean and white European children. This was supplemented by a study validating bioimpedance against deuterium dilution in 864 children from these ethnic groups and a study of adiposity and cardiometabolic risk in 483 Indian children. Compared with white European children, South Asians had higher adiposity levels based on bioimpedance and skinfolds; black African-Caribbeans had either similar (bioimpedance) or lower (skinfolds) adiposity levels. In contrast, BMI was lower among South Asians and higher among black African-Caribbeans. The associations between adiposity (all markers), insulin resistance and HbAle were stronger in South Asians than white Europeans; patterns in black African-Caribbeans were inconsistent. The use of newly validated ethnic-specific equations to derive body fat from bioimpedance further emphasized the higher adiposity levels in South Asians and lower levels in black African-Caribbeans, but had little effect on adiposity-insulin, adiposity-HbA 1 c associations. UK Indian children had markedly greater adiposity than Indian children. These results have important implications for adiposity measurement in children of different ethnic origin, and for adiposity prevention, especially in UK South Asian children

This thesis has investigated adipocytes development and adipokine signalling with a view to enhance the understanding of tissue functionality and to identify possible targets or pathways for therapeutic intervention. Adipocyte isolation from human tissue samples was undertaken for these investigative studies, and the methodology was optimised. The resulting isolates of pre-adipocytes and mature adipocytes were characterised and evaluated. Major findings from these studies indicate that mature adipocytes undergo cell division post terminal differentiation. Gene studies indicated that subcutaneous adipose tissue exuded greater concentrations and fluctuations of adipokine levels than visceral adipose tissue, indicating an important adiposensing role of subcutaneous adipose tissue. It was subsequently postulated that the subcutaneous depot may provide the major focus for control of overall energy balance and by extension weight control. One potential therapeutic target, 11β-hydrosteroid dehydrogenase (11β-HSD1) was investigated, and prospective inhibitors of its action were considered (BVT1, BVT2 and AZ121). Selective reduction of adiposity of the visceral depot was desired due to its correlation with the detrimental effects of obesity. However, studies indicated that although the visceral depot tissue was not unaffected, the subcutaneous depot was more susceptible to therapeutic inhibition by these compounds. This was determined to be a potentially valuable therapeutic intervention in light of previous postulations regarding long-term energy control via the subcutaneous tissue depot.

Ca2+ is a ubiquitous intracellular signalling molecule that is involved in the regulation of numerous cellular functions. To date Ca2+ influx pathways present in white fat adipocytes have not been characterised. Additionally impaired [Ca2+]i management is implicated in the induction of the insulin resistant state in adipocytes. As adipocytes have a prominent role in the management of energy homeostasis, the presence of Ca2+ influx pathways was examined. Initial [Ca2+]i measurements confirmed the presence of functional Ca2+ influx and efflux pathways in adipocytes. Further [Ca2+]i measurements identified the Cav1.3 Voltage-gated Ca2+ channel (VGCC). The presence of the α1 subunit of Cav1.3 channel protein in adipocytes was confirmed by Western blotting, the expression of which was reduced in adipocyte samples sourced from Zucker obese rats. Initial [Ca2+]i imaging experiments utilising conditions of elevated extracellular K+ (50mM) did not stimulate Ca2+ influx. The plasma membrane potential (Vm) regulates many physiological processes, including cellular Ca2+ influx by VGCCs, with dysregulations in Vm underlying functional pathologies. K+ is widely believed to be the predominant ion that controls Vm for many cell types, however, whether K+ regulates adipocyte Vm is also unknown, prompting, investigation into the ionic species involved in the regulation of Vm in primary and differentiated 3T3-L1 adipocytes. As insulin and β-adrenoceptors regulate adipocyte function, their effect on Vm was also explored. The Vm of primary and 3T3-L1 adipocytes were -34.14mV (n=68) and -28.5mV (n=88) respectively. Elevation of extracellular K+ from 5.6mM to 50mM had no significant effect on the Vm of either type of adipocyte. The role of Cl- on adipocyte Vm was then investigated. Reduction of extracellular Cl- from 138 to 5mM, by equimolar substitution with Gluconate significantly depolarised the Vm of both primary and 3T3-L1 adipocytes. Patch clamp investigations also revealed a role of Na+ in adipocyte Vm. Neither insulin (100nM) or the β-adrenocpetor agonist isoprenaline (10µM) significantly changed adipocyte Vm. The role of Cl- in adipocyte Vm is indicative of the presence of Cl- channels, however electrophysiological studies failed to characterise the Cl- currents underlying adipocyte Vm. Overall, further investigations are required to characterise not only the Ca2+ influx pathways in adipocytes, and the roles thereof, but also the means by which they are regulated.

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.