Acute modulation of endothelial Akt/PKB activity alters nitric oxide-dependent vasomotor activity in vivo

The serine/threonine protein kinase Akt (protein kinase B) phosphorylates e ndothelial cell nitric oxide synthase (eNOS) and enhances its ability to ge nerate nitric oxide (NO). Because NO is an important regulator of vasomotor tone, we investigated whether Akt can regulate endothelium-dependent vasom otion in vivo using a rabbit femoral artery model of gene transfer. The end o thelium of isolated femoral arteries was infected with replication-defect ive adenoviral constructs expressing beta-galactosidase, constitutively-act ive Akt (myr-Akt), or dominant-negative Akt (dn-Akt). Femoral arteries tran sduced with myr-Akt showed a significant increase in resting diameter and b lood flow, as assessed by angiography and Doppler flow measurements, respec tively. L-NAME, an eNOS inhibitor, blocked myr-Akt-mediated vasodilatation, In contrast, endothelium-dependent vasodilatation in response to acetylcho line was attenuated in vessels transduced with dn-Akt, although these vesse ls showed normal responses to nitroglycerin, an endothelium-independent vas odilator. Similarly, relaxation of murine aorta ex vivo in response to acet ylcholine, but not nitroglycerin, was inhibited by transduction of dn-Akt t o the endothelium. These data provide evidence that Akt functions as key re gulator of vasomotor tone in vivo.