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Insulin-mediated microvascular recruitment (IMVR) regulates delivery of insulin and glucose to insulin-sensitive tissues. We have previously proposed that perivascular adipose tissue (PVAT) controls glucose metabolism and vascular function through outside-to-inside communication and through vessel-to-vessel, or “vasocrine” signaling. Here, we studied this hypothesis in mice by examining effects of removal of local intramuscular PVAT on muscle blood flow and glucose metabolism. Using the hyperinsulinemic, euglycemic clamp (HEC) in combination with positron emission tomography, we found that local PVAT removal transiently reduces muscle glucose uptake by ±50 percent. Contrast-enhanced ultrasonography and intravital microscopy of the gracilis artery (GA) during the HEC showed that PVAT removal abolishes insulin-induced increases in GA diameter and abrogated insulin-stimulated muscle blood volume (microvascular recruitment or IMVR). The effect of PVAT on IMVR was mediated by distinct microvessels or anastomoses, which we showed using lightsheet microscopy of mice expressing mCherry in endothelial cells. Proteomics analysis revealed that PVAT removal significantly alters expression of 109 of 1719 detected proteins in muscle. Observed changes in protein expression included reduction of a mitochondrial protein cluster and of vesicle-associated membrane protein 5 (Vamp5), involved in Glut4 trafficking. In conclusion, we have found that PVAT within muscle regulates muscle perfusion, glucose uptake and muscle protein expression, communicating with the distal microcirculation via microvascular anastomoses. These data highlight the importance of PVAT in vascular and metabolic physiology, and are relevant for type 2 diabetes and associated muscle dysfunction. Disclosure A.H. Turaihi: None. E.H. Serne: None. C. Molthoff: None. M.T. Goumans: None. C.J. Jimenez: None. J.S. Yudkin: None. Y.M. Smulders: None. V.W. van Hinsbergh: None. E.C. Eringa: None.

Objective: Cognitive impairments in type 1 diabetes may result from hyperglycemia-associated cerebral microangiopathy. In this study we aimed to identify cerebral microangiopathy and skin microvascular dysfunction - as surrogate marker for generalized microvascular function - as predictors of cognitive decline over time. Research Design and Methods: Twenty-five type 1 diabetes patients and 25 matched healthy controls underwent neurocognitive testing at baseline and after follow-up (mean duration of 3.8±0.8 years). At baseline, 1.5 T cerebral magnetic resonance imaging was used to detect white matter lesions (WML) and cerebral microbleeds. In addition, skin capillary perfusion was assessed by means of capillary microscopy. Multiple linear regression analysis was performed to examine if cerebral microangiopathy and capillary perfusion were associated with changes in cognitive performance. Results: In type 1 diabetes patients, but not in healthy controls, the presence of WML (ß=-0.419;p=0.037) as well as lower skin capillary perfusion (baseline: ß=0.753;p Conclusions: In type 1 diabetes patients, presence of WML and lower skin capillary perfusion predict poorer general cognitive ability over time. The relationship between WML and cognitive decline was significantly reduced when adjusting for capillary perfusion, suggesting that generalized microvascular dysfunction at least partly underlies WML-associated cognitive decline. Disclosure A.L. Emanuel: None. E. van Duinkerken: None. M.P. Wattjes: Consultant; Self; Biogen. Speaker's Bureau; Self; Janssen Pharmaceuticals, Inc.. Consultant; Self; Roche Pharma, Sanofi Genzyme. M. Klein: None. F. Barkhof: None. F.J. Snoek: None. E.C. Eringa: None. R. Ijzerman: Research Support; Self; AstraZeneca. E.H. Serne: None.

To test the hypothesis that free fatty acids (FFAs) modulate microvascular function and that this contributes to obesity-associated insulin resistance, hypertension, and microangiopathy, we examined the effects of both FFA elevation in lean women and FFA lowering in obese women on skin microvascular function. A total of 16 lean and 12 obese women underwent, respectively, Intralipid plus heparin (or saline) infusion and overnight acipimox (or placebo) treatment. We measured capillary recruitment with capillaroscopy and endothelium-(in)dependent vasodilation by iontophoresis of acetylcholine and sodium nitroprusside before and during hyperinsulinemia (40 mU · m−2 · min−1). FFA elevation impaired capillary recruitment and acetylcholine-mediated vasodilation before (44.6 ± 16.8 vs. 56.9 ± 18.9%, P < 0.05; and 338 ± 131 vs. 557 ± 162%, P < 0.01, respectively) and during (54.0 ± 21.3 vs. 72.4 ± 25.4%, P < 0.01; and 264 ± 186 vs. 685 ± 199%, P < 0.01, respectively) hyperinsulinemia. FFA lowering improved capillary recruitment before (50.9 ± 14.6 vs. 37.4 ± 9.3%, P < 0.01) and during (66.8 ± 20.6 vs. 54.8 ± 15.4%, P < 0.05) hyperinsulinemia. Changes in FFA levels were inversely associated with changes in capillary recruitment and insulin sensitivity in lean (r = −0.46, P = 0.08; and r = −0.56, P = 0.03) and in obese (r = −0.70, P = 0.02; and r = −0.62, P = 0.04) women. Regression analyses showed that changes in capillary recruitment statistically explained ∼29% of the association between changes in FFA levels and insulin sensitivity. In conclusion, FFA levels modulate microvascular function and may contribute to obesity-associated insulin resistance, hypertension, and microangiopathy.

It has been proposed that insulin-mediated changes in muscle perfusion modulate insulin-mediated glucose uptake. However, the putative effects of insulin on the microcirculation that permit such modulation have not been studied in humans. We examined the effects of systemic hyperinsulinemia on skin microvascular function in eight healthy nondiabetic subjects. In addition, the effects of locally administered insulin on skin blood flow were assessed in 10 healthy subjects. During a hyperinsulinemic clamp, we measured leg blood flow with venous occlusion plethysmography, skin capillary density with capillaroscopy, endothelium-(in)dependent vasodilatation of skin microcirculation with iontophoresis of acetylcholine and sodium nitroprusside combined with laser Doppler fluxmetry, and skin vasomotion by Fourier analysis of microcirculatory blood flow. To exclude nonspecific changes in the hemodynamic variables, a time-volume control study was performed. Insulin iontophoresis was used to study the local effects of insulin on skin blood flow. Compared to the control study, systemic hyperinsulinemia caused an increase in leg blood flow (-0.54 ± 0.93 vs. 1.97 ± 1.1 ml · min-1 · dl-1; P < 0.01), an increase in the number of perfused capillaries in the resting state (-3.7 ± 3.0 vs. 3.4 ± 1.4 per mm2; P < 0.001) and during postocclusive reactive hyperemia (-0.8 ± 2.2 vs. 5.1 ± 3.7 per mm2; P < 0.001), an augmentation of the vasodilatation caused by acetylcholine (722 ± 206 vs. 989 ± 495%; P < 0.05) and sodium nitroprusside (618 ± 159 vs. 788 ± 276%; P < 0.05), and a change in vasomotion by increasing the relative contribution of the 0.01- to 0.02-Hz and 0.4- to 1.6-Hz spectral components (P < 0.05). Compared to the control substance, locally administered insulin caused a rapid increase (∼13.5 min) in skin microcirculatory blood flow (34.4 ± 42.5 vs. 82.8 ± 85.7%; P < 0.05). In conclusion, systemic hyperinsulinemia in skin 1) induces recruitment of capillaries, 2) augments nitric oxide-mediated vasodilatation, and 3) influences vasomotion. In addition, locally administered insulin 4) induces a rapid increase in total skin blood flow, independent of systemic effects.

To test the hypothesis that free fatty acids (FFAs) modulate microvascular function and that this contributes to obesity-associated insulin resistance, hypertension, and microangiopathy, we examined the effects of both FFA elevation in lean women and FFA lowering in obese women on skin microvascular function. A total of 16 lean and 12 obese women underwent, respectively, Intralipid plus heparin (or saline) infusion and overnight acipimox (or placebo) treatment. We measured capillary recruitment with capillaroscopy and endothelium-(in)dependent vasodilation by iontophoresis of acetylcholine and sodium nitroprusside before and during hyperinsulinemia (40 mU . m(-2) . min(-1)). FFA elevation impaired capillary recruitment and acetylcholine-mediated vasodilation before (44.6 +/- 16.8 vs. 56.9 +/- 18.9%, P0.05; and 338 +/- 131 vs. 557 +/- 162%, P0.01, respectively) and during (54.0 +/- 21.3 vs. 72.4 +/- 25.4%, P0.01; and 264 +/- 186 vs. 685 +/- 199%, P0.01, respectively) hyperinsulinemia. FFA lowering improved capillary recruitment before (50.9 +/- 14.6 vs. 37.4 +/- 9.3%, P0.01) and during (66.8 +/- 20.6 vs. 54.8 +/- 15.4%, P0.05) hyperinsulinemia. Changes in FFA levels were inversely associated with changes in capillary recruitment and insulin sensitivity in lean (r = -0.46, P = 0.08; and r = -0.56, P = 0.03) and in obese (r = -0.70, P = 0.02; and r = -0.62, P = 0.04) women. Regression analyses showed that changes in capillary recruitment statistically explained approximately 29% of the association between changes in FFA levels and insulin sensitivity. In conclusion, FFA levels modulate microvascular function and may contribute to obesity-associated insulin resistance, hypertension, and microangiopathy.