Endothelial nitric oxide synthase gene polymorphism and maternal vascular adaptation to pregnancy.

A common polymorphism of the endothelial NO synthase gene that predicts a Glu298Asp amino acid substitution in the mature protein has been associated with cardiovascular disorders in which NO bioactivity is impaired. However, the influence of this polymorphism on endothelial function is unknown. Healthy pregnancy is associated with enhanced endothelium-dependent, flow-mediated dilation (FMD) of the brachial artery, a response mediated by NO. In this study, we investigated the effect of the endothelial NO synthase Glu298Asp polymorphism on endothelium-dependent vasodilation in early pregnancy, making the hypothesis that any genotype-dependent differences in NO generation would be more marked during pregnancy, when the production of NO is upregulated. FMD of the brachial artery was recorded during the first trimester in 139 healthy women with normal singleton pregnancies genotyped for the Glu298Asp variant of endothelial NO synthase. Maternal FMD exhibited a codominant inverse relation with the number of Asp298 alleles (r=-0.21, P=0.01). Among homozygotes for endothelial NO synthase Asp298, FMD (7.99+/-1.46%) was significantly lower than that observed among individuals homozygous for endothelial NO synthase Glu298 (10.12+/-3.44) (P=0.002). In a backward stepwise multiple regression analysis, vessel size (P<0.0001) and Glu298Asp polymorphism (P=0.01) were significantly and independently correlated with FMD. Our findings indicate that the endothelial NO synthase Glu298Asp polymorphism is associated with differences in endothelium-dependent dilation at 12-week gestation and are the first to implicate genetic factors in the normal vascular adaptation to pregnancy. They also provide a potential mechanism linking the endothelial NO synthase polymorphism with the development of cardiovascular disorders and have implications for understanding the genetic basis of preeclampsia.

An endothelium-derived hyperpolarizing factor-like factor moderates myogenic constriction of mesenteric resistance arteries in the absence of endothelial nitric oxide synthase-derived nitric oxide.

Myogenic tone is an important determinant of vascular tone and blood flow in small resistance arteries of certain vascular beds. The role of the endothelium in myogenic responses is unclear. We hypothesized that endothelium-derived NO release modulates myogenic constriction in small resistance arteries and that mesenteric small arteries from mice with targeted disruption of the gene for endothelial NO synthase (eNOS) (knockout mice) demonstrate greater myogenic tone than do wild-type mice. Third-order mesenteric arteries (approximately 200 micrometer) were isolated and mounted in a pressure myograph. Internal diameter was recorded over a pressure range of 10 to 80 mm Hg. Removal of the endothelium significantly (P<0.05) enhanced the magnitude of myogenic constriction in wild-type mice. Similarly, pretreatment of arteries with N(G)-nitro-L-arginine methyl ester (L-NAME; 300 micromol/L) produced a comparable significant (P<0.05) increase in myogenic tone, whereas indomethacin (5 micromol/L) had no effect. eNOS knockout arteries also exhibited myogenic constriction. Neither L-NAME nor indomethacin had any effect on myogenic tone in the arteries of eNOS knockout mice. However, blockade of potential endothelium-derived hyperpolarizing factor-like mechanisms via inhibition of K(+) flux using either apamin (100 nmol/L) with charybdotoxin (100 nmol/L), Ba(2+) (30 micromol/L) with ouabain (1 mmol/L), or 18alpha-glycyrrhetinic acid (100 micromol/L) significantly (P<0.01) enhanced myogenic constriction. This study demonstrates that basal endothelium-derived NO modulates myogenic tone in mesenteric small arteries of wild-type mice. However, eNOS knockout arteries display normal myogenic responsiveness despite the absence of basal NO activity. The data suggest that this compensatory effect is due to the activity of an endothelium-derived hyperpolarizing factor to normalize vascular tone.

Dialysis improves endothelial function in humans.

BACKGROUND: Circulating inhibitors of endothelial function have been implicated in the pathogenesis of vascular disease in chronic renal failure. The aim of this study was to determine if lowering the plasma concentration of these and other dialysable toxins improves endothelial function. To do this we compared the acute effects on endothelial function of single episodes of haemodialysis with automated peritoneal dialysis. We hypothesized that endothelial function would improve after dialysis, with a greater effect seen after haemodialysis due to more substantial clearance of endothelial toxins per-treatment. METHODS: Subjects with end-stage renal failure undergoing haemodialysis (n=16) or automated peritoneal dialysis (n=14) were investigated. Endothelial function was determined using vascular ultrasound to measure flow-mediated dilatation of the brachial artery and was compared with the dilatation caused by sublingual glyceryl trinitrate. Endothelial function was assessed before and after a single dialysis treatment. Plasma concentrations of the inhibitors of endothelial function, asymmetric dimethyl-l-arginine and homocysteine were measured. Flow-mediated dilatation was expressed as percentage change from basal diameter and analysed using Student's t test. RESULTS: The plasma concentration of circulating inhibitors of endothelial function was reduced after haemodialysis but not peritoneal dialysis. Haemodialysis increased flow-mediated dilatation from 4.0+/-1.0% to 5.8+/-1.2% (P<0.002). These changes persisted for 5 h but returned to baseline by 24 h. Automated peritoneal dialysis had no acute effect on flow-mediated dilatation (5.9+/-1.1% vs 5.4+/-0.8% after, P>0.5). There were no effects of either dialysis modality on dilatation to glyceryl trinitrate. CONCLUSIONS: Short-term reduction of circulating inhibitors of endothelial function by haemodialysis is associated with increased flow-mediated dilatation. These data suggest that dialysable endothelial toxins have deleterious effects on endothelial function that are rapidly reversible.

Endogenous factors involved in regulation of tone of arterial vasa vasorum: implications for conduit vessel physiology.

The walls of conduit blood vessels are nourished by diffusion of oxygen from luminal blood and from the vasa vasorum. The vasa vasorum, or 'vessels of a vessel', form a network of microvessels that lie in the adventitia and penetrate the outer media of the host vessel wall. Although the importance of the vasa vasorum in providing nutritional support is not well defined, obstruction of blood flow through these vessels has been implicated in the pathogenesis of certain cardiovascular diseases including atherosclerosis. This review focuses on the mechanisms that regulate tone in the vasa vasorum of large arteries and the functional implications of changes in reactivity of vasa vasorum.

Effects of sodium intake on the pressor and renal responses to nitric oxide synthesis inhibition in normotensive individuals with different sodium sensitivity.

OBJECTIVE: The present study evaluated the role of nitric oxide (NO) in the systemic vascular and renal adaptation to changes in dietary sodium intake. DESIGN AND METHODS: Seven healthy normotensive male subjects were randomized to high or low sodium diets in a double blind crossover design (7 days on each diet). The NO synthesis inhibitor, NGmonomethyl-L-arginine (L-NMMA) was infused systemically (1.8 mg/kg over 30 min) at the end of each dietary period and its effects on blood pressure, renal plasma flow, glomerular filtration rate, urinary flow rate and sodium excretion were measured. RESULTS: Blood pressure increased in response to L-NMMA on a high sodium diet only (area under time curve percentage change in mean blood pressure, low sodium = -94.5 +/- 164.3; high sodium = 391.1 +/- 228.6; P < 0.05 low versus high). The increase in blood pressure was directly and significantly associated with the individual salt sensitivity, defined by the difference in systemic mean blood pressure between high and low sodium diets (r = 0.756; P < 0.05). L-NMMA also reduced renal plasma flow and urinary flow rate in subjects on high sodium diet. CONCLUSIONS: The data support a significant influence of endogenous NO in the systemic and renal vascular adaptation to a high sodium diet in normotensive men. In addition, the direct association between the individual sodium-sensitivity and the pressor response to L-NMMA suggests that there is increased dependence of vascular tone on NO in normotensive subjects whose blood pressure is more sodium sensitive.

Nitric oxide-mediated vasodilation in human pregnancy.

The maternal circulation vasodilates during pregnancy. We investigated the contribution of nitric oxide to this vasodilatation. Using venous occlusion plethysmography, we measured the effect of nitric oxide synthase inhibition on hand blood flow during human pregnancy. We compared the response to a brachial artery infusion of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) with the response to norepinephrine in three groups of women: nonpregnant, early pregnant (9-15 wk), and late pregnant (36-41 wk). Basal hand blood flow increased significantly during late pregnancy compared with nonpregnant and early pregnant subjects (P = 0.007). L-NMMA produced a greater reduction in hand blood flow in both pregnant groups compared with nonpregnant controls (P = 0.0003). Norepinephrine produced an attenuated response in late pregnancy compared with nonpregnant and early pregnant women (P = 0.0029). If other vascular beds respond in the same way as the hand, the gestational increase in vasoconstrictor response to L-NMMA that we observed implicates increased generation of nitric oxide in the fall of peripheral vascular resistance during healthy human pregnancy.

Local L-NG-monomethyl-arginine attenuates the vasodilator action of bradykinin in the human forearm.

1. Studies in animals indicate that bradykinin relaxes blood vessels directly through an action on smooth muscle and indirectly through the release of endothelium-derived mediators. Its precise mechanism of action in the human arterial circulation is not yet known. 2. In this study the effects of a specific inhibitor of nitric oxide synthase, L-NG-monomethyl-arginine (L-NMMA) and noradrenaline on the vasodilator responses to bradykinin were examined in the forearm arterial bed of healthy volunteers. Noradrenaline was used as a control for vasoconstriction by L-NMMA; glyceryl trinitrate (GTN) as a control vasodilator acting independently of the NO synthase enzyme. 3. L-NMMA (4 mumol min-1; 5 min) alone reduced resting forearm blood flow by 44% (P < 0.01; n = 6) confirming that nitric oxide plays an important role in regulating vascular tone. 4. Bradykinin (10 and 100 pmol min-1; 3 min each dose) and GTN (2 and 5 nmol min-1; 3 min each dose) increased forearm blood flow in a dose-dependent manner (percentage changes 171 +/- 17% and 398 +/- 35%, and 176 +/- 21% and 268 +/- 42%, respectively; n = 6). 5. The response to bradykinin, but not that to GTN, was attenuated by L-NMMA compared with noradrenaline (P < 0.05; n = 6), suggesting that bradykinin-induced vasodilatation in the forearm is mediated, at least in part, by stimulating release of nitric oxide.

Effects of S-nitroso-glutathione in the human forearm circulation: evidence for selective inhibition of platelet activation.

OBJECTIVE: Nitric oxide (NO) is a vasodilator and inhibitor of platelet function. The clinical use of NO donors as inhibitors of platelet activation is limited by their concomitant hypotensive effect. S-nitroso-glutathione (GSNO) has a significant antiplatelet effect at doses that cause only a small decrease in blood pressure in rats. The aim of this study was to examine the antiplatelet and vasodilator properties of this nitrosothiol in the human forearm. METHODS: Forearm blood flow was measured by forearm occlusion plethysmography in five healthy males. Ex vivo platelet aggregation to ADP was performed in a platelet ionised calcium lumi-aggregometer. RESULTS: Intra-arterial infusion of GSNO (0.2, 1, and 5 nmol.min-1) resulted in inhibition of ADP (1-10 microM) induced platelet aggregation. This inhibition was submaximal for 0.2 and maximal for 1 and 5 nmol.min-1. However, the antiaggregatory effect observed at the lowest dose of GSNO was accompanied only by a threshold increase in forearm blood flow. CONCLUSIONS: These results show that GSNO is more effective as an inhibitor of platelet activation than as a vasodilator, suggesting that it is possible to achieve selective antiplatelet and potentially antithrombotic effects with NO donors.

Human saphenous vein contains both endothelin ETA and ETB contractile receptors.

We have investigated the endothelin receptor subtypes mediating contraction in isolated preparations of human saphenous vein. Endothelin-1 (EC50: 17.8 nM), endothelin-3 (EC50: 82.3 nM) and the endothelin ETB receptor-selective agonists, [Ala1,3,11,15]endothelin-1 (EC50: 63 nM) and sarafotoxin S6c (EC50: 0.75 nM) all produced concentration-dependent contractions of human saphenous vein, although [Ala1,3,11,15]endothelin-1 and sarafotoxin S6c only produced a contraction in approximately 50% of the preparations tested. The endothelin ETA receptor antagonist, BQ123 (D-Val,Leu,D-Trp,D-Asp,Pro; 10 microM), antagonized endothelin-1-induced contractions with an estimated potency (pKB approximately 6.0) which was an order of magnitude lower than reported previously for non-human isolated vascular tissues from other species (pA2 values approximately 7.0). These data suggest that both endothelin ETA and endothelin ETB receptors can mediate vascular smooth muscle contraction in human saphenous vein.

Endothelin receptors mediating functional responses in human small arteries and veins.

1. In the present study, responses of human omental small arteries and veins to endothelin-1 and endothelin-3 were characterized by use of the ETB receptor selective agonist, sarafotoxin S6c, the ETA receptor antagonist, BQ123, the ETB receptor antagonist, IRL1038, the NO-synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 300 microM) and indomethacin (10 microM). 2. Small arteries (internal diameter 413 +/- 22 microns) and parallel running veins (646 +/- 35 microns) were mounted in a myograph under a normalized tension equivalent to 90% of a transmural pressure of 100 mmHg and 19 mmHg in vivo, respectively. 3. In small arteries and veins, endothelin-1 caused a concentration-dependent increase in wall tension (Emax = 3.90 +/- 0.56 mN mm-1 and 1.90 m +/- 0.32 mN mm-1 respectively, P < 0.05) and was equipotent (arteries: pD2 = 8.91 +/- 0.11; veins: pD2 = 8.63 +/- 0.08, NS). In endothelium intact arteries, L-NMMA significantly enhanced the sensitivity to endothelin-1 (pD2 control: 8.92 +/- 0.16; pD2 L-NMMA: 9.37 +/- 0.11; P < 0.05). L-NMMA did not affect the sensitivity of veins to endothelin-1. Indomethacin was without effect in arteries and veins. In veins, endothelin-3 was about a hundred times less potent than endothelin-1 and showed a biphasic response curve. Small arteries did not contract to endothelin-3. Neither small arteries nor veins contracted to sarafotoxin S6c. Furthermore, no relaxation to endothelin-1 or sarafotoxin S6c was seen in any precontracted vessels. 4. BQ123 (0.03-3 MicroM) produced a concentration-dependent rightward parallel displacement of the endothelin-l concentration-response curve in small arteries and veins yielding pA2 values of 7.09 and 7.48 respectively. The slope of the Schild plot in arteries and veins was 1.26 +/- 0.24 (NS from unity) and 0.61 +/- 0.13 (P <0.05 compared to unity) respectively. IRL1038 (3 MicroM) did not affect the potency of endothelin-1 in arteries and veins. In veins, the low sensitivity component (pD2 = 7.16 +/- 0.08) of the biphasic response curve to endothelin-3 was completely blocked by BQ123 (3 MicroM), whereas the high sensitivity component (pD2 = 8.66 +/- 0.08) was resistant to BQ123 (3 MicroM) and IRL1038 (3 MicroM).5. These results indicate that contractions of human small vessels to endothelin-l are predominantly mediated by ETA receptors and that nitric oxide modulates the response to endothelin-l in small arteries but not in veins. The different antagonistic potency of BQ123 against endothelin-l and the differential endothelin-1/endothelin-3 potency ratios in arteries and veins provide evidence for the hypothesis that ETA receptors in human small arteries are different from ETA receptors in human small veins. There is no evidence of contractions mediated by 'classical' ETB receptors in these vessels, but small veins appear to contain a functional non ETA/non ETB receptor with a high affinity for endothelin-3.

Diagnostic features of localised pericardial constriction.

We report a case of localised pericardial constriction leading to right ventricular outflow tract obstruction. Localised pericardial constriction is rare, but the diagnosis should be considered in patients who present with recurrent pericardial constriction following previous partial pericardiectomy. Close attention to physical findings may enable the diagnosis to be made prior to cardiac catheterisation.