Phosphoinositide 3-Kinase Mediates Enhanced Spontaneous and Agonist-Induced Contraction in Aorta of Deoxycorticosterone Acetate-Salt Hypertensive Rats

Abstract— Arteries from deoxycorticosterone acetate (DOCA)-salt and N&ohgr;-nitro-l-arginine (L-NNA) hypertensive but not normotensive rats develop spontaneous tone. LY294002 and wortmannin, phosphoinositide 3-kinase (PI3-kinase) inhibitors, eliminate spontaneous tone. We hypothesized that PI3-kinase protein and/or activity was increased in hypertension and contributed to the observed enhanced contractility. PI3-kinase activity assays revealed 2-fold higher activity in thoracic aorta from DOCA-salt [systolic blood pressure (SBP)=184±5 mm Hg] compared with sham rats (SBP=111±2 mm Hg). Western analyses of aortic homogenates revealed the presence of p85&agr;, p110&agr;, p110&bgr;, and p110&dgr; but not p110&ggr; PI3-kinase subunits; p110&dgr; protein was elevated in aorta of hypertensive rats as compared with sham. Aortic homogenates from L-NNA rats also had elevated p110&bgr; protein density, but neither L-NNA nor DOCA-salt had differences in p85&agr; and p110&agr;. Total Akt density was unaltered, but pAkt was significantly lower in homogenates from DOCA-salt rats. LY294002 (20 &mgr;mol/L) and nifedipine (50 nmol/L) abolished Ca2+-induced spontaneous tone in aorta from DOCA-salt rats. However, LY294002 did not alter BayK8644-induced contraction, indicating that LY294002 does not inhibit L-type Ca2+ channels directly. PTEN (phosphatase and tensin homolog) and pPTEN were expressed but not different in aorta from DOCA-salt and sham rats. LY294002 corrected the enhanced contraction to KCl and norepinephrine in aorta from DOCA-salt rats. These data support an increase in PI3-kinase activity and p110&dgr; density in aorta from L-NNA and DOCA-salt rats. Importantly, this increase contributes to the enhanced contractility observed in two models of hypertension.