Determination of Body Fat Distribution by Dual-Energy X-ray Absorptiometry and Attenuation of Visceral Fat Vasoconstriction by Enalapril

Abstract

Use of dual-energy X-ray absorptiometry (DEXA) data to calculate the percent of body fat in the visceral (%VF) and subcutaneous (%SF) compartments and the mechanism of visceral fat vasoconstriction when intestinal mucosal afferent nerves are stimulated has not been reported. The aim of this study was to compare visceral fat weight determined by DEXA and direct weighing and determine whether enalapril attenuates visceral fat vasoconstriction induced by stimulation of intestinal mucosal afferent nerves. We performed two studies. Study 1: In euthanized mice, DEXA scans were obtained before and after visceral fat dissection. The dissected fat weight was determined by DEXA (VF) and by direct weighing. Study 2: In anesthetized rat preparations, visceral (mesenteric) fat blood flow was monitored by laser Doppler flowmetry (LDF). After baseline, vehicle or 3 mg/kg enalapril (angiotensin-converting enzyme inhibitor) was administered intravenously, followed by 2 ml/kg of 640 microm capsaicin intraduodenally. In study 1, there was agreement between visceral fat weight determined by the DEXA (y) and direct weighing (x): y = 0.98x, r = 0.99, n = 10. In study 2, LDF signals showed an instantaneous decline when capsaicin was administered into the duodenal lumen. After enalapril treatment, the reductions were significantly attenuated compared with those after vehicle treatment. DEXA results combined with visceral fat dissection permit determination of body fat distribution. The instantaneous decline in visceral fat blood flow suggests that the reduction is a neural- rather than a hormone-mediated event, and attenuation by enalapril suggests angiotensin II plays a role.

Capsaicin-sensitive intestinal mucosal afferent mechanism and body fat distribution

“…Compared with the rats given intragastric vehicle treatment, the hyperemic response in the superior mesenteric artery blood flow (7 ± 1%) was significantly attenuated in the rats given repeated intragastric capsaicin treatment; the reduction in mesenteric adipose tissue blood flow (7± 9%) was abolished; and the decrease in inguinal adipose tissue blood flow (−24 ± 6%) was attenuated. The attenuation of vasoconstriction in the subcutaneous adipose tissue occurred to a significantly lesser degree than in the mesenteric adipose tissue (Leung et al, 2008).…”

“…The laser Doppler flow signals showed an instantaneous decline (−33.2 ± 3.3%, n = 5) when capsaicin was administered into the duodenal lumen. After enalapril treatment, the reductions were significantly attenuated (−6.6 ± 7.3%) (p b 0.05, unpaired t test) compared with those after vehicle treatment (Leung et al, 2008).…”

“…None of the tested doses of irbesartan affected these markers in non-obese rats. A link between the intestinal capsaicin-sensitive afferent nerves and angiotensin II function in visceral adipose tissue circulation is suggested by one report (Leung et al, 2008). Enalapril, an angiotensin converting enzyme inhibitor, did not alter baseline mesenteric fat blood flow documented by laser Doppler flowmetry.…”

“…Intact intestinal mucosal afferent nerve function was necessary for normal accumulation of fat at visceral sites (Leung et al, 2008). A reflex-initiated (characterized by rapid onset, laser Doppler flowmetry) and sustained decrease (−33.2 ± 3.3%) in blood flow (vasoconstriction) in visceral fat occurs when intestinal mucosal afferent nerves were stimulated (Leung et al, 2008).…”

“…A reflex-initiated (characterized by rapid onset, laser Doppler flowmetry) and sustained decrease (−33.2 ± 3.3%) in blood flow (vasoconstriction) in visceral fat occurs when intestinal mucosal afferent nerves were stimulated (Leung et al, 2008). When the intestinal mucosal afferent nerves were exposed to repeated (2 weeks) intragastric capsaicin treatment, the intestinal vasodilatation and visceral fat vasoconstriction were attenuated significantly (Leung et al, 2007) suggesting desensitization of the intestinal mucosal capsaicin-sensitive afferent nerves.…”