Signalling pathways determining the shear stress-induced production of NO from endothelial cells in situ were investigated using a bioassay system in which shear stress was increased by inducing vasoconstriction in an endothelium-intact donor segment (rabbit iliac artery) while maintaining a constant luminal perfusion rate. Shear stress-induced NO production, as assessed by changes in the tone of a preconstricted endothelium-denuded detector ring, was biphasic and consisted of an initial transient (20- to 25-minute) Ca(2+)-dependent phase followed by a Ca(2+)-independent plateau phase, which was maintained as long as the donor segment remained constricted. Stretching the donor segments to their in vivo length abolished the initial phase without affecting the plateau phase of NO release. Inhibition of the Na(+)-H+ exchanger using HOE 694 elicited an intracellular acidification which attenuated shear stress-induced NO production. The specific protein kinase C inhibitor, Ro 31-8220, was without effect, whereas the unspecific inhibitors, staurosporine and calphostin C, abolished the shear stress-induced production of NO. Erbstatin A, a tyrosine kinase inhibitor, attenuated the shear stress-induced tyrosine phosphorylation of specific cellular proteins and abrogated the associated NO production. In summary, these data indicate that shear stress activates the NO synthase at basal levels of [Ca2+]i via a mechanotransduction cascade that involves tyrosine phosphorylation and can be modulated by changes in pHi. The apparent fundamental alteration of the endothelial NO synthase under shear stress that renders its maintained activation independent of an increase in [Ca2+]i is probably the consequence of a change in the enzyme microenvironment.

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Abstract-Excess production of superoxide anion in response to angiotensin II plays a central role in the transduction of signal molecules and the regulation of vascular tone. We examined the ability of insulin resistance to stimulate superoxide anion production and investigated the identity of the oxidases responsible for its production. Rats were fed diets containing 60% fructose (fructose-fed rats) or 60% starch (control rats) for 8 weeks. In aortic homogenates from fructose-fed rats, the superoxide anion generated in response to NAD(P)H was more than 2-fold higher than that of control rats. Pretreatment of the aorta from fructose-fed rats with inhibitors of NADPH oxidase significantly reduced superoxide anion production. In the isolated aorta, contraction induced by angiotensin II was more potent in fructose-fed rats compared with control rats. Losartan normalized blood pressure, NAD(P)H oxidase activity, endothelial function, and angiotensin II-induced vasoconstriction in fructose-fed rats. To elucidate the molecular mechanisms of the enhanced constrictor response to angiotensin II, expressions of angiotensin II receptor and subunits of NADPH oxidase were examined with the use of angiotensin II type 1a receptor knockout (AT1a KO) mice. Expression of AT1a receptor mRNA was enhanced in fructose-fed mice, whereas expression of either AT1b or AT2 was unaltered. In addition, protein expression of each subunit of NADPH oxidase was increased in fructose-fed mice, whereas the expression was significantly decreased in fructose-fed AT1a KO mice. The novel observation of insulin resistance-induced upregulation of AT1 receptor expression could explain the association of insulin resistance with endothelial dysfunction and hypertension. Key Words: insulin resistance Ⅲ angiotensin II Ⅲ angiotensin antagonist Ⅲ endothelium Ⅲ free radicals Ⅲ blood pressure T here is a growing body of evidence demonstrating the coexistence of hypertension in the insulin-resistant states, such as obesity and type 2 diabetes. 1-3 Impairment of vasomotor function in hypertension may be caused by an imbalance of vasodilating and vasoconstricting factors. 4 We have recently reported that insulin resistance may be a pathogenic factor for endothelial dysfunction through impaired endothelial NOS (eNOS) activity caused by the enhanced formation of superoxide anion (O 2 Ϫ ), which is caused by relative deficiency of tetrahydrobiopterin (BH 4 ) in vascular endothelial cells. 5 Although BH 4 supplementation results in the restoration of the endothelial function, BH 4 treatment did not normalize blood pressure and vascular oxidative stress in the insulin-resistant state. 6 These findings suggest that an additional element to regulate vascular tone is therefore likely to be present in the insulin-resistant state.Apart from the L-arginine-nitric oxide (NO) pathway, the vascular tone is regulated by a variety of autocrine and paracrine systems localized in the endothelium and smooth muscle cells. Blockade of the renin-angiotensin system with angiotensin-conv...

There has been a rapid increase in the amount of information on the physiological and pathophysiological roles of nitric oxide (NO) in the brain. This molecule, which is formed by the constitutive isoforms of NO synthase, endothelial (eNOS) and neuronal (nNOS), plays an obligatory role in the regulation of cerebral blood flow and cell viability and in the protection of nerve cells or fibres against pathogenic factors associated with Alzheimer's disease, Huntington's disease, seizures, and migraine. Cerebral blood flow is impaired by decreased formation of NO from endothelial cells, autonomic nitrergic nerves, or brain neurons and also by increased production of reactive oxygen species (ROS). The NO-ROS interaction is an important topic in discussing blood flow and cell viability in the brain. Excessive production of NO by inducible NOS (iNOS) and nNOS in the brain participates in neurotoxicity. Recent studies on brain circulation have provided useful information about the involvement of impaired NO availability or uncontrolled NO production in cerebral pathogenesis, including Alzheimer's disease, seizures, vascular headaches, and inflammatory disorders. Insight into the role of NO in the brain will contribute to our better understanding of cerebral hemodynamic dysfunction and will aid in developing novel therapeutic measures in diseases of the central nervous system.

The authors performed investigations to functionally determine the route of efferent innervation in vivo responsible for cerebral vasodilation mediated by nitric oxide (NO). In anesthetized beagles, electrical stimulation of the pterygopalatine ganglion vasodilated ipsilateral cerebral arteries such as the middle cerebral and posterior communicating arteries. Intravenous injections of NG-nitro-L-arginine (L-NA) markedly inhibited the response to nerve stimulation, and the effect was reversed by L-arginine. Stimulation of the proximal portion of the greater superficial petrosal nerve, upstream of the pterygopalatine ganglion, also produced cerebral vasodilation, which was abolished by L-NA and restored by L-arginine. Treatment with hexamethonium abolished the response to stimulation of the petrosal nerve but did not affect the response to pterygopalatine ganglion stimulation. Destruction of the pterygopalatine ganglion by cauterization constricted the cerebral arteries. Postganglionic denervation abolished the vasodilation, lacrimation, and nasal secretion induced on the ipsilateral side by stimulation of the pterygopalatine ganglion and petrosal nerve. The vasodilator response was suppressed by L-NA but unaffected by atropine, whereas lacrimation and nasal secretion were abolished solely by atropine. It is concluded that postganglionic neurons from the pterygopalatine ganglion play crucial roles in cerebral vasodilation mediated by NO from the nerve, and preganglionic neurons, possibly from the superior salivatory nucleus through the greater superficial petrosal nerve, innervate the pterygopalatine ganglion. Tonic discharges from the vasomotor center participate significantly in the maintenance of cerebral vasodilation.

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Vasodilator substances liberated from endothelial cells, mainly nitric oxide (NO), play important roles in physiologically regulating blood flow and blood pressure and preventing pathological vascular damage. Impairment of these actions promotes the genesis of cardiovascular diseases such as hypertension, cerebral and cardiac hypoperfusion, impaired vasodilatation and atherosclerosis. Low concentrations of alcohol induce increased release of NO from the endothelium due to activation and expression of NO synthase (NOS). In contrast, administration of high concentrations of alcohol or its chronic ingestion impairs endothelial functions in association with reduced NO bioavailability. The endogenous NOS inhibitor asymmetric dimethylarginine may participate in decreased synthesis of NO. Chronic alcohol intake also impairs penile erectile function possibly by interfering with endothelial, but not nitrergic nerve, function. This review article summarizes the vascular actions of NO derived from endothelial and neuronal NOS as affected by alcohol, other than wine, and acetaldehyde in healthy individuals, human materials and various experimental animals.