Uryash A, Wu H, Bassuk J, Kurlansky P, Sackner MA, Adams JA. Low-amplitude pulses to the circulation through periodic acceleration induces endothelial-dependent vasodilatation. J Appl Physiol 106: 1840 -1847, 2009. First published March 26, 2009 doi:10.1152/japplphysiol.91612.2008.-Low-amplitude pulses to the vasculature increase pulsatile shear stress to the endothelium. This activates endothelial nitric oxide (NO) synthase (eNOS) to promote NO release and endothelial-dependent vasodilatation. Descent of the dicrotic notch on the arterial pulse waveform and a-to-b ratio (a/b; where a is the height of the pulse amplitude and b is the height of the dicrotic notch above the end-diastolic level) reflects vasodilator (increased a/b) and vasoconstrictor effects (decreased a/b) due to NO level change. Periodic acceleration (pG z) (motion of the supine body head to foot on a platform) provides systemic additional pulsatile shear stress. The purpose of this study was to determine whether or not pG z applied to rats produced endothelial-dependent vasodilatation and increased NO production, and whether the latter was regulated by the Akt/phosphatidylinositol 3-kinase (PI3K) pathway. Male rats were anesthetized and instrumented, and pG z was applied. Sodium nitroprusside, N G -nitro-L-arginine methyl ester (L-NAME), and wortmannin (WM; to block Akt/PI3K pathway) were administered to compare changes in a/b and mean aortic pressure. Descent of the dicrotic notch occurred within 2 s of initiating pG z. Dose-dependent increase of a/b and decrease of mean aortic pressure took place with SNP. L-NAME produced a dose-dependent rise in mean aortic pressure and decrease of a/b, which was blunted with pG z. In the presence of WM, pGz did not decrease aortic pressure or increase a/b. WM also abolished the pG z blunting effect on blood pressure and a/b of L-NAME-treated animals. eNOS expression was increased in aortic tissue after pG z. This study indicates that addition of low-amplitude pulses to circulation through pG z produces endothelial-dependent vasodilatation due to increased NO in rats, which is mediated via activation of eNOS, in part, by the Akt/PI3K pathway. vascular resistance; N G -nitro-L-arginine methyl ester, wortmannin; nitric oxide ADDED LOW-AMPLITUDE PULSES to the vasculature were generated with periodic acceleration (pG z ). pG z is produced by a motorized platform that repetitively moves the horizontally oriented body sinusoidally in a head to foot direction. Inertia of fluid as the body accelerates and decelerates adds a small-amplitude pulse to the circulation that is superimposed on the natural pulse, increasing pulsatile shear stress to the endothelium (3, 6, 7). In large-animal models, increased pulsatile shear stress activates endothelial nitric oxide (NO) synthase (eNOS) to release NO into the circulation, which, in turn, induces endothelial-dependent pulmonary and systemic vasodilatation, as well as increasing organ blood flows (3,5,6). pG z applied to anesthetized swine increases serum nitrite, which is ...