Physiological concentrations of insulin induce endothelin-dependent vasoconstriction of skeletal muscle resistance arteries in the presence of tumor necrosis factor-α dependence on c-jun N-terminal kinase

Objective - Tumor necrosis factor-alpha (TNF-alpha) has been linked to obesity-related insulin resistance and impaired endothelium-dependent vasodilatation, but the mechanisms have not been elucidated. To investigate whether TNF-alpha directly impairs insulin-mediated vasoreactivity in skeletal muscle resistance arteries and the role of c-Jun N-terminal kinase (JNK) in this interference. Methods and Results - Insulin-mediated vasoreactivity of isolated resistance arteries of the rat cremaster muscle to insulin (4 to 3400 mu U/mL) was studied in the absence and presence of TNF-alpha (10 ng/mL). Although insulin or TNF-alpha alone did not affect arterial diameter, insulin induced dose-dependent vasoconstriction of cremaster resistance arteries in the presence of TNF-alpha, (-12 +/- 1% at 272 mu U/mL). Blocking endothelin receptors in the absence of TNF-alpha uncovered insulin-mediated vasodilatation (18 +/- 6% at 272 mu U/mL) but not in the presence of TNF-alpha (2 +/- 2% at 272 mu U/mL), showing that TNF-alpha inhibits vasodilator effects of insulin. Using digital imaging microscopy, we discovered that TNF-alpha activates JNK in arterial endothelium, visible as an increase in phosphorylated JNK. Moreover, inhibition of JNK with the cell-permeable peptide inhibitor L-JNKI abolished insulin-mediated vasoconstriction in the presence of TNF-alpha, showing that JNK is required for interaction between TNF-alpha and insulin. Conclusions - TNF-alpha inhibits vasodilator but not vasoconstrictor effects of insulin in skeletal muscle resistance arteries, resulting in insulin-mediated vasoconstriction in the presence of TNF-alpha. This effect of TNF-alpha is critically dependent on TNF-alpha-mediated activation of JNK.