For Peer Review Only 1 Nitric Oxide Directly Promotes Vascular Endothelial Insulin Transport

Insulin resistance strongly associates with decreased nitric oxide (NO) bioavailability and endothelial dysfunction. In the vasculature NO mediates multiple processes affecting insulin delivery, including dilating both resistance and terminal arterioles in skeletal muscle in vivo. However, whether NO directly regulates vascular endothelial cell (EC) insulin uptake and its trans-endothelial transport (TET) is unknown. Here we report that L-NAME pre-treatment blocked while L-arginine or sodium nitroprusside (SNP), each enhanced EC uptake of fluoroisothiocyanate (FITC)-labeled insulin. SNP also partly or fully reversed the inhibition of EC insulin uptake caused by L-NAME, wortmannin, the Src inhibitor PP1 or TNFα. In addition, SNP promoted