Racial differences in visceral adipose tissue but not anthropometric markers of health-related variables.

This study sought to determine whether visceral adipose tissue (VAT) and/or its anthropometric surrogates could significantly predict health-related variables (HRV) in overweight Caucasian (CC) (n = 36) and African-American (AA) (n = 30) women. With the use of magnetic resonance imaging, findings showed significantly higher volume and area of VAT (P < 0.0001 for both) as well as higher triacylglycerol (P = 0.009) in CC compared with AA women. Furthermore, VAT volume, race, and VAT volume x race interaction could significantly predict triacylglycerol (P = 0.0094), high-density lipoprotein cholesterol (P = 0.0057), insulin (P = 0.0002), and insulin resistance (P < 0. 0001). Additionally, the VAT volume x race interaction for insulin (P = 0.040) and insulin resistance (P = 0.003) was significant. In a separate analysis, waist circumference and race predicted the identical variables. Our results support the use of volume or area of VAT in predicting HRV in CC women; however, its use in AA women appears limited. In contrast, waist circumference can provide a suitable VAT alternative for both CC and AA women; however, VAT clearly represents the more powerful predictor.     

Escherichia coli peritonitis activates thermogenesis in brown adipose tissue: relationship to fever.

Fever is a complex and important nonspecific, host defense mechanism against infection. The generation of the heat necessary to increase body temperature may involve thermogenesis in brown adipose tissue. To investigate whether the febrile response to Escherichia coli peritonitis involves thermogenesis in brown adipose tissue, we assessed whole rat oxygen consumption and brown adipose tissue mitochondrial guanosine 5'-diphosphate binding. Non-lethal doses of E. coli, 1 x 10(6) to 1 x 10(8) colony forming units, induced a fever for greater than 8 h. In contrast, a dose of 1 x 10(9) colony forming units resulted in a progressive hypothermia culminating in death. A 48% increase in oxygen consumption (p less than 0.05) in E. coli-infected rats occurred almost immediately, preceded the development of the fever, and was sustained throughout the fever. There was a highly significant correlation (r = 0.736, p less than 0.01) between oxygen consumption and body temperature for both control and infected animals. Guanosine 5'-diphosphate binding assessed by multi-point Scatchard analysis of [3H]guanosine 5'-diphosphate binding to isolated mitochondria was increased by 45.4 +/- 7.3% at 1.75 h and by 31.9 +/- 9.0% at 3.5 h (p less than 0.05). The greater increase was during the rising phase of the fever. Unexpectedly, a lethal dose of 5 x 10(9) colony forming units of E. coli also increased guanosine 5'-diphosphate binding sites by 54.4 +/- 14.2% (p less than 0.05) despite a hypothermia of -1.71 +/- 0.29 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epicardial adipose tissue extent: relationship with age, body fat distribution, and coronaropathy

Epicardial fat is a relatively neglected component of the heart and could be an important risk factor of cardiac disease. The objective of our study was to assess the relationship between epicardial adipose tissue (EAT) extent, fat distribution, and coronaropathy in a group of adult victims of accidental or suspicious sudden death. In 56 cadavers, we performed 34 measurements of EAT from five computerized photographs of the heart (anterior and posterior faces, and three ventricle transversal slices) and analyzed their relationship with anthropometric markers of adiposity (BMI, waist and leg circumference, thickness of abdominal and thigh subcutaneous adipose tissue (SAT)), with the presence and staging of coronary artery disease (CAD), and with markers of myocardial hypertrophy. Simple linear regressions showed that EAT measurements are highly intercorrelated (r from 0.4 to 0.6, P < 0.001), and correlate with age, waist circumference, and heart weight, and to a lesser extent, with BMI, abdominal SAT thickness, and leg SAT thickness. Multiple regression showed that age, waist circumference, and heart weight significantly and independently correlate with EAT (P < 0.0001). No other anthropometric measurement was found independently correlated with EAT. The EAT/myocardium ratios correlated positively with age and waist circumference. Anterior and posterior areas of EAT were found significantly increased in patients with CAD and correlated positively with CAD staging (P = 0.0034, r = 0.38). Anterior EAT surface was found positively associated with CAD (P = 0.01), independently of age and other adiposity measurements. Prospective studies are needed to assess the risk of occurrence/progression of CAD that relate to EAT excess.     

Ontogenetical changes in adipose tissue of the cat: Convertible adipose tissue

The ultrastructural characteristics of the inguinal, interscapular, and perirenal adipose tissue in kittens and cats were studied. There were no qualitative differences among adipocytes in the three anatomical areas. The only recorded difference was in the amount of lipids stored in the adipocytes in younger stages. Immediately after birth lipids occupied 25% of the volume in the inguinal area, 15% in interscapular fat tissue, and 10% in perirenal fat tissue. At this stage the adipose tissue morphologically resembled brown adipose tissue (BAT) of rodents. Two weeks after birth, lipids accumulated and adipocytes in the inguinal area became unilocular and appeared similar to white adipose tissue (WAT). A similar transition occurred approx 25 days after birth in interscapular fat and approx 6 weeks after birth in the perirenal area. No morphological signs of any cell degradation or destruction, nor any increased activity of preadipocytes, were seen during this conversion from BAT-like to WAT-like adipose tissue. The conversion of the adipose tissue was correlated with a decrease in vascularization and innervation, a loss of intercellular connections, and a changed mitochondrial population. Mitochondria in multilocular adipocytes resembled those in typical BAT which contain uncoupling protein (“UC-mitochondria”). After conversion to unilocular adipocytes the amount of mitochondria was halved, their cristae even more reduced, and their appearance was of a WAT-type (UCP-lacking mitochondria, which are coupled under physiological conditions; “C-mitochondria”). Since this category of adipose tissue differs from both typical brown and white adipose tissue, the name “convertible adipose tissue” (CAT) is proposed. Apparently adipose tissue from comparatively large mammals is of this convertible type.     

Relation of anthropometric and dynamometric variables to serious postoperative complications.

Prediction of serious postoperative complications by using standard anthropometric and biochemical nutritional variables was attempted in 225 patients admitted for major abdominal surgery. In 102 of the patients hand-grip dynamometry was also measured, and this proved the most sensitive test, predicting complications in 48 of the 55 patients (87%) who developed them (p < 0.001). Arm muscle circumference and forearm muscle circumference below 85% of the standard value were also of predictive value (p < 0.02 and p < 0.01 respectively); weight for height and serum albumin concentrations were less satisfactory, while weight loss of more than 10% was not significantly related to complications. Dynamometry is a useful, rapid, and inexpensive screening test for detecting malnutrition that is likely to predispose to serious postoperative morbidity.     

Development of thermogenic adipose tissue.

Besides having a metabolic and insulatory-supporting function, adipose tissue in endotherms also performs a thermogenic function. Thermogenic adipocytes contain specific UC-mitochondria with uncoupling protein (UCP) and produce heat. Thermogenic adipose tissue has two forms: brown adipose tissue (BAT) and convertible adipose tissue (CAT). Brown adipocytes have UC-mitochondria and express UCP throughout the entire life of small rodents, chiropterans, and insectivores. However, in other endotherms and in humans CAT participates as thermogenic tissue only during early postnatal period. Both BAT and CAT start to develop in utero, although in some animals (hamsters, marsupials) or in some particular areas (thoraco-periaortal and medio-perirenal areas in rats) development of thermogenic adipose tissue starts after birth. Postnatal development of BAT in small endotherms is characterized by quantitative changes (the amount of UC-mitochondria, UCP, and lipids). Postnatal development of CAT causes qualitative changes during which UC-mitochondria in convertible adipocytes are replaced by common, nonthermogenic C-mitochondria; vascularization of adipocytes drops to a low level and, with lipid accumulation, convertible adipocytes appear as lipid-store cells. Postnatal development of CAT can be modulated or reversed by the environmental temperature. The duration of postnatal changes varies between species; i.e., cats, rabbits and sheep, change their thermogenic form of CAT into the lipid-store form within the first postnatal month, while in humans the same process takes up to 15-20 years. In maturity all these large endotherms have CAT in lipid-store form. In light of these results, the question of participation of thermogenic adipose tissue in the regulation of human obesity needs to be answered.     

Hormone-sensitive lipase of adipose tissue.

Some physiologic aspects of the mobilization and fate of free fatty acids are reviewed. The molecular mechanism of the activation of hormone-sensitive lipase in adipose tissue is then discussed. Recent evidence established that hormone-sensitive lipase, concerned with fat mobilization, is both functionally and immunochemically distinct from lipoprotein lipase, concerned with uptake of plasma triglycerides. Lipoprotein lipase activity is not altered by cyclic AMP-dependent protein kinase. The latter enzyme enhances not only triglyceride hydrolase but also monoglyceride, diglyceride and cholesterol ester hydrolase activities in chicken adipose tissue. Finally, it is shown that the activation of all four acyl hydrolases is reversible, the deactivation being magnesium-dependent. Protein phosphatase fractions from heart and liver active against phosphorylase a can reversibly deactivate adipose tissue hormone-sensitive lipase, implying a low degree of substrate specificity for lipase phosphatase.     

Intermediary metabolism of adipose tissue.

Metabolism of ruminant adipocytes involves the synthesis and mobilization of lipids. Rates of lipid synthesis from the uptake of preformed fatty acids (via lipoprotein lipase) and de novo synthesis of fatty acids are related to the energy balance. Acetate is the major carbon source for fatty acid synthesis with NADPH originating from the pentose cycle and the isocitrate cycle. Ruminant adipose tissue lacks the ability to utilize for lipogenesis those substrates that generate mitochondrial acetyl CoA because of an absence of ATP citrate-lyase and NADP-malate dehydrogenase. Lipid mobilization in ruminant adipocytes is apparently regulated via cAMP levels and a summary of the compounds investigated for lipolytic responses is presented. The control of lipid synthesis and mobilization is interrelated in ruminant adipose tissue. The coordinated manner in which these two functions are regulated is examined with regard to adipocyte responses to insulin and epinephrine. In both lipid synthesis and lipid mobilization, ruminant adipocytes are uniquely different from nonruminant adipose tissue. The physiological significance and possible basis for these species differences in adipose metabolism are discussed.