We hypothesized that aging is characterized by a reduced release of nitric oxide (NO) in response to shear stress in resistance vessels. Mesenteric arterioles and arteries of young (6 mo) and aged (24 mo) male Fischer 344 rats were isolated and cannulated. Shear stress (15 dyn/cm 2 )-induced dilation was significantly reduced and shear stress (1, 5, 10, and 15 dyn/cm 2 )-induced increases in perfusate nitrite were significantly smaller at all shear stress levels in vessels of aged rats. Inhibition of NO synthesis abolished shear stress-induced release of nitrite. Furthermore, shear stress (15 dyn/cm 2 )-induced release of nitrate was significantly higher and total nitrite (nitrite plus nitrate) was significantly lower in vessels of aged rats. Tiron or SOD significantly increased nitrite released from vessels of aged rats, but this was still significantly less than that in young rats. Superoxide production was increased and the activity of SOD was decreased in vessels of aged rats. There were no differences in endothelial NO synthase (eNOS) protein and basal activity or in Cu/Zn-SOD and Mn-SOD proteins in vessels of the two groups, but extracellular SOD was significantly reduced in vessels of aged rats. Maximal release of NO induced by shear stress plus ACh (10 −5 M) was comparable in the two groups, but phospho-eNOS in response to shear stress (15 dyn/cm 2 ) was significantly reduced in vessels of aged rats. These data suggest that an increased production of superoxide, a reduced activity of SOD, and an impaired shear stressinduced activation of eNOS are the causes of the decreased shear stress-induced release of NO in vessels of aged rats. Keywords endothelium; superoxide; superoxide dismutase Age-related endothelial dysfunction has been characterized by reduced agonist-induced vasodilatation (33). In addition, several studies showed that flow-induced dilation, the most physiologically relevant measure of endothelium-dependent regulation of vascular tone, was reduced in healthy elderly humans and aged animals (4,7,25,36) and that the sensitivity of arteriolar endothelium to fluid shear stress is decreased with advancing age (31). The

No abstract

Abstract-This study investigated the mechanisms responsible for the estrogen-dependent, cytochrome P450 (CYP)-mediated dilator responses to shear stress in arterioles of NO-deficient female rats and mice. Flow-induced dilation (FID) was assessed in isolated arterioles from N G -nitro-L-arginine methyl ester (L-NAME)-treated male and ovariectomized female rats before and after overnight incubation with 17␤-estradiol (17␤-E 2 , 10 Ϫ9 mol/L). In control conditions, prostaglandins (PGs) mediated FID, because indomethacin (INDO) abolished the responses. After incubation of the vessels with 17␤-E 2 , the basal tone of arterioles was significantly reduced and FID was augmented. INDO did not affect the dilation of the vessels incubated with 17␤-E 2 . Dilations of these vessels, however, were eliminated by PPOH and miconazole, inhibitors of CYP/epoxygenase. Simultaneous incubation of the vessels with 17␤-E 2 plus ICI, 182,780, an estrogen receptor antagonist, or wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K) phosphorylation or the transcriptional inhibitor DRB, prevented the reduced arteriolar tone and the enhanced CYP-mediated FID caused by incubation of vessels with17␤-E 2 . Western blot analysis indicated a significantly increased phospho-Akt level in arterioles incubated with 17␤-E 2 compared with those without 17␤-E 2 . The enhanced phospho-Akt in response to 17␤-E 2 was localized, by immunohistochemistry, to arteriolar endothelial cells. Moreover, GC-MS analysis indicated a significantly increased production of epoxyeicosatrienoic acids, vasodilator metabolites of CYP/epoxygenase, in arterioles incubated with 17␤-E 2 , a response that was prevented by ICI 182780 and wortmannin, respectively. Thus, estrogen, via a receptor-dependent, PI3K/Akt-mediated pathway, transcriptionally upregulates CYP activity, leading to an enhanced arteriolar response to shear stress. Key Words: estradiol Ⅲ flow-induced dilation Ⅲ cytochrome P450 Ⅲ Akt Ⅲ transcription S ince the first demonstration of the cardiovascular protective effects of female hormones in endothelial nitric oxide synthase knockout (eNOS-KO) mice in 1998, 1 evaluation of the role of estrogen in the regulation of cardiovascular function in pathological states in which the bioavailability of NO is impaired, such as hypertension and heart failure, has become important. This would answer the question whether alternative mechanisms, independent of NO, could also be activated by estrogen. Our previous studies, conducted on skeletal muscle arterioles of female eNOS-KO mice 2 and female rats treated chronically with a NOS inhibitor, 3 demonstrated that estrogen-related protective mechanisms involving endothelial regulation of shear stress were well preserved, as indicated by the maintenance of augmented flow-induced dilation in vessels of females compared with those of males. Interestingly, the enhanced flow-induced dilation in the vessels of females was mediated by epoxyeicosatrienoic acids (EETs), cytochrome P-450 (CYP)/epoxygenase metabolites of arachidon...

Preterm birth is the leading cause of newborn mortality in the United States and about one third of cases are caused by preterm premature rupture of fetal membranes, a complication that is frequently observed in patients with Ehlers-Danlos Syndrome. Notably, a subtype of Ehlers-Danlos Syndrome is caused by expression of abnormal biglycan and decorin proteoglycans. As compound deficiency of these two small leucine-rich proteoglycans is a model of preterm birth, we investigated the fetal membranes of Bgn−/−;Dcn−/− double-null and single-null mice. Our results showed that biglycan signaling supported fetal membrane remodeling during early gestation in the absence of concomitant changes in TGFβ levels. In late gestation, biglycan signaling acted in a TGFβ–dependent manner to aid in membrane stabilization. In contrast, decorin signaling supported fetal membrane remodeling at early stages of gestation in a TGFβ–dependent manner, and fetal membrane stabilization at later stages of gestation without changes in TGFβ levels. Furthermore, exogenous soluble decorin was capable of rescuing the TGFβ signaling pathway in fetal membrane mesenchymal cells. Collectively, these findings provide novel targets for manipulation of fetal membrane extracellular matrix stability and could represent novel targets for research on preventive strategies for preterm premature rupture of fetal membranes.