title: Vasoconstrictor effects of insulin in skeletal muscle arterioles are mediated by ERK1/2 activation in endothelium.
abstract: Insulin exerts both NO-dependent vasodilator and endothelin-dependent vasoconstrictor effects on skeletal muscle arterioles. The intracellular enzymes 1-phosphatidylinositol 3-kinase (PI3-kinase) and Akt have been shown to mediate the vasodilator effects of insulin, but the signaling molecules involved in the vasoconstrictor effects of insulin in these arterioles are unknown. Our objective was to identify intracellular mediators of acute vasoconstrictor effects of insulin on skeletal muscle arterioles. Rat cremaster first-order arterioles (n=40) were isolated, and vasoreactivity to insulin was studied using a pressure myograph. Insulin induced dose-dependent vasoconstriction of skeletal muscle arterioles (up to -22 +/- 3% of basal diameter; P <0.05) during PI3-kinase inhibition with wortmannin (50 nmol/l). Insulin-induced vasoconstriction was abolished by inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) with PD-98059 (40 micromol/l). In addition, inhibition of ERK1/2 without PI3-kinase inhibition uncovered insulin-mediated vasodilatation in skeletal muscle arterioles (up to 37 +/- 10% of baseline diameter; P <0.05). Effects of insulin on ERK1/2 activation in arterioles were then investigated by Western blot analysis. Insulin induced a transient 2.4-fold increase in ERK1/2 phosphorylation (maximal at approximately 15 min) in skeletal muscle arterioles (P <0.05). Removal of the arteriolar endothelium abolished insulin-induced vasoconstriction, which suggests that activation of ERK1/2 in endothelial cells is involved in acute insulin-mediated vasoconstriction. To investigate this, acute effects of insulin on ERK1/2 phosphorylation were studied in human microvascular endothelial cells. In support of the findings in skeletal muscle arterioles, insulin induced a 1.9-fold increase in ERK1/2 phosphorylation (maximal at approximately 15 min) in microvascular endothelial cells (P <0.05). We conclude that acute vasoconstrictor effects of insulin in skeletal muscle arterioles are mediated by activation of ERK1/2 in endothelium. This ERK1/2-mediated vasoconstrictor effect antagonizes insulin-induced, PI3-kinase-dependent vasodilatation in skeletal muscle arterioles. These findings provide a novel mechanism by which insulin may determine blood flow and glucose disposal in skeletal muscle.
authors.affiliation: Laboratory for Physiology, Vrije Universiteit Medical Centre, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands. e.eringa@vumc.nl
authors.forename: Etto C
authors.initials: EC
authors.lastname: Eringa
authors.forename: Coen D A
authors.initials: CD
authors.lastname: Stehouwer
authors.forename: Geerten P
authors.initials: GP
authors.lastname: van Nieuw Amerongen
authors.forename: Lenneke
authors.initials: L
authors.lastname: Ouwehand
authors.forename: Nico
authors.initials: N
authors.lastname: Westerhof
authors.forename: Pieter
authors.initials: P
authors.lastname: Sipkema
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000201:enzymology; D004730:Endothelium, Vascular / Q000201:enzymology*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D008833:Microcirculation; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D018482:Muscle, Skeletal / Q000098:blood supply*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014661:Vasoconstriction; D014662:Vasoconstrictor Agents / Q000008:administration & dosage / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D007328:Insulin; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D014662:Vasoconstrictor Agents; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000077191:Wortmannin