Effects of Intrabrachial metacholine infusion on muscle capillary recruitment and forearm glucose uptake during physiological hyperinsulinemia in obese, insulin-resistant individuals.
BACKGROUND
Impairment of insulin-mediated capillary recruitment in skeletal muscle contributes to a hampered glucose uptake in obesity.


OBJECTIVE
The objective of this study was to evaluate whether metacholine (MCh), a nitric oxide vasodilator, potentiates muscle capillary recruitment and forearm glucose uptake (FGU) during physiological hyperinsulinemia.


METHODS
The double-forearm technique [i.e. infused vs. control (Ctrl) forearm] was combined with im microdialysis during an oral glucose tolerance test in 15 nondiabetic, obese subjects divided into a group of insulin-resistant (IR) (n = 7) and insulin-sensitive (n = 8) individuals.


RESULTS
After the oral glucose tolerance test, forearm blood flow in the Ctrl forearm was unchanged, whereas it increased about 3-fold (P < 0.0001 vs. baseline) in response to MCh. Capillary permeability surface area product for glucose (PS(glu)) (capillary recruitment), FGU, and interstitial insulin concentrations increased significantly over time (P < 0.001) in both forearms. Compared with insulin-sensitive, the IR subjects exhibited lower PS(glu) (P < 0.001) and FGU (P < 0.01) in the Ctrl arm, whereas this difference was insignificant in the MCh arm despite the blunted forearm blood flow increase. Moreover, in IR individuals MCh significantly (P < 0.05) ameliorated the delayed onset of insulin action, i.e. the FGU response to hyperinsulinemia. Finally, we found PS(glu) to be a strong and independent predictor of FGU response (adjusted R(2) 0.72; P < 0.0001).


CONCLUSIONS
MCh-induced vasodilation may improve the microvascular and metabolic responses to physiological hyperinsulinemia in obese, IR individuals. Further studies are required to unravel whether stimulation of nitric oxide production in skeletal muscle may represent an attractive therapeutic approach to bypassing cellular resistance to glucose disposal.
Murdolo
Giuseppe
G
Department of Internal Medicine, Section of Internal Medicine, Endocrine and Metabolic Sciences, Perugia University, Via Enrico Dal Pozzo I, Perugia, Italy. tugiuseppe.murdolo@medic.gu.seut
Sjöstrand
Mikaela
M
Strindberg
Lena
L
Gudbjörnsdóttir
Soffia
S
Lind
Lars
L
Lönnroth
Peter
P
Jansson
Per-Anders
PA
D000328:Adult; D001916:Brachial Artery; D002196:Capillaries / Q000187:drug effects / Q000502:physiology; D005542:Forearm / Q000098:blood supply; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D006946:Hyperinsulinism / Q000378:metabolism; D007328:Insulin / Q000502:physiology*; D007333:Insulin Resistance; D019344:Lactic Acid / Q000097:blood; D016210:Methacholine Chloride / Q000494:pharmacology*; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply*; D009569:Nitric Oxide / Q000502:physiology; D009765:Obesity / Q000378:metabolism*; D012039:Regional Blood Flow; D014664:Vasodilation / Q000187:drug effects
D007328:Insulin; D016210:Methacholine Chloride; D009569:Nitric Oxide; D019344:Lactic Acid; D005947:Glucose