Effects of Insulin on sympethetic tone

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we determined the role of endothelium in insulin-induced vasodilation in young healthy volunteers (n=13). Forearm blood flow (FBF) was measured by strain gauge plethysmography. A cannula was inserted in the brachial artery for direct measurements of arterial pressure and drug infusions. Intra-arterial infusion of insulin for 15 minutes increased plasma insulin level from 15.8 <plus-minus> 1.7 at rest to 141.6 <plus-minus> 12.3muU・mL^<-1> (p<.01). intra-arterial infusion of insulin (n=7) for 15 minutes increased FBF 4.8 <plus-minus> 1.4 at rest to 6.0 <plus-minus> 1.7mL・min^<-1>・100mL^<-1> and increased plasma 6-keto prostaglandin F_1alpha (PGF_1alpha), stable metabolite of prostacyclin, from 14.9 <plus-minus> 3.3 at rest to 29.3 <plus-minus> 5.7 pg/ml. Thus intra-arterial infusion of insulin caused forearm vasodilation with increases in prostacyclin in the venous effluents. Intra-arterial infusion of insulin was repeated after administration of indomethacin 75 mg per os (n=7). Indomethacin abolished insulin-induced vasodilation and increases in PGF_1alpha. In another group of subjects (n=6), intra-arterial infusion of insulin was repeated after intra-brachial artery infusion of N^G-monomethyl-L-arginine (L-NMMA,n=7) at 4.0mumol・min^<-1> for 5 minutes (n=6). Infusion of L-NMMA decreased resting FBF to 3.6 <plus-minus> 1.0mL・min^<-1>・100mL^<-1> (p<.05) without changes in resting blood pressure and heart rate. Infusion of L-NMMA did not affect insulin-induced forearm vasodilation.Our results may suggest that insulin-induced vasodilation is mediated by prostacyclin but not by nitric oxide in the forearm of heathy humans.