Update on adipose tissue blood flow regulation

Abstract

According to Fick's principle, any metabolic or hormonal exchange through a given tissue depends on the product of the blood flow to that tissue and the arteriovenous difference. The proper function of adipose tissue relies on adequate adipose tissue blood flow (ATBF), which determines the influx and efflux of metabolites as well as regulatory endocrine signals. Adequate functioning of adipose tissue in intermediary metabolism requires finely tuned perfusion. Because metabolic and vascular processes are so tightly interconnected, any disruption in one will necessarily impact the other. Although altered ATBF is one consequence of expanding fat tissue, it may also aggravate the negative impacts of obesity on the body's metabolic milieu. This review attempts to summarize the current state of knowledge on adipose tissue vascular bed behavior under physiological conditions and the various factors that contribute to its regulation as well as the possible participation of altered ATBF in the pathophysiology of metabolic syndrome. obesity; insulin; sympathetic nervous system; nitric oxide; angiotensin II; atrial natriuretic peptide; glucagon-like peptide-1; glucose-dependent insulinotropic polypeptide OVER THE LAST DECADES, THE WORLDWIDE PANDEMIC of obesity, metabolic syndrome, and type 2 diabetes mellitus (T2DM) (188) has attracted ever-increasing attention to the role and significance of adipose tissue (AT). Originally regarded as a mere energy store with insulation and protective cushioning functions, AT is now recognized as a bona fide and highly active metabolic and endocrine organ (102). It has also become evident that the white AT is a heterogeneous tissue. From a metabolic point of view, AT can be subdivided into central (abdominal) and peripheral (hips and buttocks) depots (78). Although extra-abdominal fat accumulation does not bring upon higher metabolic and cardiovascular risk, some reports show a protective influence (124). Conversely, a negative metabolic effect has been associated with central fat (102), which in fact comprises two distinct masses (visceral and subcutaneous) with different metabolic and hormonal activities and impacts on metabolic syndrome pathogenesis (95) and blood flow rates (102).Metabolic processes in fatty tissue require adequate substrate(s) and humoral factor delivery (76). Conversely, adipocytes communicate with other metabolically active tissues through humoral factors (128) as well as through metabolic products (118) serving as energetic substrates. Humoral factors derived from AT arise not only from adipocytes themselves but also from other components of AT such as macrophages and endothelial cells. Moreover, AT is a known conversion site for several hormones or humoral factors, e.g., steroid hormones (156) or components of the renin-angiotensin-aldosterone system (RAAS). All of these functions of AT are tightly linked to the pattern of blood supply and its regulation, which largely differ from other metabolically active organs such as the liver or skeletal muscle (141).In add...

Adrenergically stimulated blood flow in brown adipose tissue is not dependent on thermogenesis

“…Alternatively, it can be speculated that because of the dually innervated nature of iBAT, signals from the brain could trigger specifically the NPY-containing nerves surrounding the vasculature without affecting thermogenesis in the parenchymal cells (5). Nevertheless, our results confirm that, regarding BAT, blood flow responds to glucose similarly to WAT (30). Although a transient increase in iBAT blood flow can be measured, it does not seem to be accompanied by classical activation of thermogenesis, supporting the interpretation that these phenomena are physiologically dissociated from each other.…”

“…In WAT, postprandial elevation of blood flow is considered to be regulated mostly by central sympathetic drive acting on local adrenoceptors, causing the production and release of nitric oxide (NO) from both parenchymal and vascular cells (1,30). This effect seems to be dependent on the glucose present in meals but not on the lipid content of the meals (8,30). In accord with this, in BAT blood flow also increases postprandially following a high-carbohydrate meal compared with a high-fat meal (13).…”

“…NO is one of the main molecules involved in smooth muscle relaxation and modulation of tissue blood flow (1,30). Indeed, inhibition of NO synthesis totally abolishes adrenergically stimulated blood flow (21) in BAT, demonstrating that alternative mediators of vasodilation would not be involved.…”

Adipose Tissue in Sleep Apnea

“…Goossens and coworkers continuously monitored adipose tissue blood flow and PO 2 in lean and obese humans (Goossens et al, 2011). Obese subjects showed a blunted increase in blood flow and PO 2 in adipose tissue in response to ingestion of glucose, confirming previous findings ( Sotornik et al, 2012). However, PO 2 in adipose tissue of obese subjects was high despite decreased blood flow, suggesting that a low metabolic rate in fat was associated with insufficient capillarization, insulin resistance, and inflammation (Goossens et al, 2011).…”

Perioperative management of the severely obese patient: a selective pathophysiological review

“…15 This reduction is already evident at baseline flow, but there is also significant blunting of the usual post-prandial ATBF increase. This is important because the post-prandial rise in blood flow is essential for uptake and storage of FFA (i.e., the protective functions of adipose in lowering plasma FFA concentrations).…”